Download Oxygen is life

Editorial
Dr. Sundeep Salvi
MD, DNB, PhD, FCCP, Hon FRCP (Lon)
Director, Chest Research Foundation, Pune
O
xygen contributes to around 65% of the
adult body weight. Although most of this is
due to oxygen present in water molecules, oxygen
is also an important structural molecule present
in proteins, carbohydrates, fats, bones and even
teeth. Moreover, the free oxygen circulating in the
blood provides 90% of the human body’s energy
needs, with only 10% coming from the food that
we eat or the water that we drink.
Oxygen has the ability to release the energy
stored in the carbon atoms of glucose and fats
through oxidative metabolism that occurs in the
mitochondria. Glucose produces energy both
in the presence (oxidative glycolysis) as well as
absence (anerobic glycolysis) of oxygen, while free
fatty acids can produce energy only in the presence
of oxygen. In the absence of oxygen, one molecule
of glucose produces 2 ATP molecules, whereas in
the presence of oxygen the same glucose molecule
produces 36 ATP molecules. In the presence of
oxygen, one molecule of free fatty acid produces
around 132 ATP molecules. The oxygen molecule
therefore has a unique ability to amplify energy
production.
What is so special about the oxygen molecule
that helps in efficiently releasing the trapped
energy present in sugars and fats? The outer ring
of the oxygen molecule which should contain 8
electrons, has only 6 electrons, which means that
one molecule of oxygen can accept two electrons.
It is this ability to accept electrons in the electron
transport chain in the mitochondria that makes
oxygen so special in producing large amounts of
ATP molecules.
Oxygen is available in plentiful in the air that
we breathe and is free for all. At the ground level,
air contains 20.95% oxygen, 78.09% nitrogen,
Oxygen
is life
0.93% argon, 0.04% carbon dioxide and variable
amounts of water vapor. Despite the fact that
almost all living organisms on this planet consume
oxygen, the proportion of oxygen in the air is
always kept constant by oxygen producers. Most
of us would believe that all oxygen on this planet is
produced by terrestrial plants through the process
of photosynthesis. However, terrestrial plants
produce only 30% of the earth’s oxygen. 70% of
the earth’s oxygen is produced in the oceans, seas
and lakes by the two microorganisms called green
algae and cyanobacteria. Together, they produce
around 330 billion tonnes of oxygen every year
that is released into the air.
At rest, the human body burns around 500
liters of oxygen every 24 hours. Up to an additional
1000 liters of oxygen is utilized during intense
physical exercise as well as mental exercise. A
total of up to 1500 liters of oxygen is what the
human body can consume every day. This very
important responsibility has been entrusted upon
the respiratory and the circulatory systems. The
respiratory system extracts the oxygen from the
air and delivers it to the circulatory system from
where it is carried to all organs in the body.
The 600 million alveoli or air sacs present
in the lungs offer a vast surface area of around
100m2, through which large amounts of oxygen
diffuse passively via the thin alveolar capillary
membrane (0.2 microns) into the haemoglobin
molecules present inside of the red blood cells
circulating in the pulmonary capillaries. Every
breath that we take, brings in 500 ml of fresh air
into the alveoli that contains 100 ml oxygen. A
total of 10,000 liters of air enters into the lungs
every 24 hours which contains over 2000 liters
of oxygen. Depending on the need, a maximum
of 1500 liters is extracted by the lungs every 24
hours. This suggests that the lung is an extremely
efficient organ in ensuring oxygen uptake and
delivering it to the haemoglobin molecules present
in the red blood cells.
Transporting oxygen from the lungs to
different parts of the body is undertaken by the
haemoglobin molecule present in the red blood
cells. Each haemoglobin molecule contains four
heme groups with iron cores to which oxygen
binds. One molecule of hemoglobin therefore
binds 4 molecules of oxygen. Each red blood
cell contains 280 million hemoglobin molecules;
therefore, a single red blood cell carries over 1
billion molecules of oxygen. An estimated 26
billion red blood cells are required to transport
1 liter of oxygen in the blood. The human body
contains 25 trillion red blood cells circulating
in the blood at any given point of time, which
accounts for around 67% of the total number of
cells present in the human body. Every second 2
million red blood cells are produced and 2 million
red blood cells get destroyed. Each red blood cell
completes one cycle of oxygen delivery from the
lungs to the tissues and back to the lungs in 60
seconds and does so for around 1,70,000 times
before its life ends.
Oxygen is vital for sustaining life. Nature
ensures that there is adequate presence of oxygen
in the atmosphere all the time, and the respiratory
and circulatory systems ensure that sufficient
amount of oxygen is extracted and delivered to
different tissues in the body. The human body
invests a huge amount of resources to ensure a
steady supply of oxygen to all parts of the body
and for this the respiratory and circulatory systems
have to work in perfect harmony. nn
|Volume VII, Issue I, January-February 2017|RespiMirror 1
An Overview of
Medical Gas Therapy
Manjush K., PhD Scholar, Symbiosis International University
Dr. P. Arjun, Sr. Consultant & Coordinator,
Dept. of Resp. Med., KIMS, Trivandrum
Introduction
Oxygen and other medical gases are considered
as inevitable for any practice in respiratory care.
Though other medical gases need an expertise for
administration, oxygen can be provided by any
healthcare professionals based upon the signs and
symptoms of hypoxia or hypoxemia in patients.
On the other hand, unwanted oxygen therapy
worsens the clinical scenario of the patient. Hence
it is to be stressed that, healthcare professionals
who are involved in medical gas administration
should have a proper understanding of clinical
status of patient and other aspects of medical gas
therapy, right from production, regulation, mode
of administration and monitoring. Currently in
India, it is observed that many hospitals do have
standard operational policies, protocols, guidelines
and care plans for the usage of medical gases.
Medical gases are mainly categorized into three
types according to the fire risk i.e. gases that are
non-flammable, gases that support combustion,
and gases that are flammable. Non-flammable
gases include carbon dioxide, nitrogen and helium
whereas gases that support combustion includes
oxygen, air, nitrous oxide, oxygen–carbon dioxide
mixture, helium–oxygen mixture, oxygen–nitrogen
mixture and nitric oxide. Most anesthetic gases
belong to the flammable category.
Air
Atmospheric air consists of a mixture of
naturally occurring gases like nitrogen, oxygen,
carbon dioxide, argon, and other trace gases. Air
has a density of 1.29 g/L and a specific gravity
of 1.0. Nitrogen is the major constituent with a
fraction of 78.08%, whereas Oxygen constitutes
20.95% of atmospheric air. Carbon dioxide
(CO2) is 0.03% and Argon and other trace gases
constitute only 0.93% of atmospheric air. For most
medical purposes, air is prepared in compressed
form. This compressed air is used in most of the
pneumatically powered medical equipment and
is also used as a carrier gas when oxygen is not
indicated.
Oxygen (O2)
O2 is a colorless, odourless, tasteless, transparent
gas that constitutes 20.95% of the atmospheric
air. The partial pressure of O2 is 159 mm Hg at
the sea level. The density is slightly more than air
with 1.429 g/L and with a specific gravity of 1.108.
In the clinical setting, the primary indication for
O2 therapy is documented hypoxemia. In clinical
settings, a partial pressure of arterial O2(PaO2) less
than 60 mm Hg or arterial O2 saturation (SaO2)
less than 90% are considered as the primary
indication for O2 supplementation. Some of the
other indications include medical conditions like
acute myocardial infarction, trauma, postoperative
phases and all conditions where hypoxemia is
suspected. Some of the major complications of O2
therapy include O2 toxicity, absorption atelectasis,
retinopathy of prematurity and depression of
ventilatory drive. It is clearly understood that
2
delivery of a high fraction of inspired O2(FiO2)
for a prolonged time, resulting in a high PaO2 is the
causative factor for those aforementioned events.
A variant form of O2 therapy is hyperbaric oxygen
therapy (HBOT), where O2 is supplemented to
the patient in a pressurized closed chamber or
environment, at a level higher than atmospheric
pressure i.e. more than 1 atmospheric absolute
(1 ATA = 760 mmHg). This increased pressure
allows O2 to dissolve and saturate the blood to have
an improved positive physiological, biochemical
and cellular effects. HBOT is considered as the
reliable method to increase the oxygenation level
in human body. Usually the treatment will last for
60-90 minutes, during which the patient lies down
and breathes normally. Some of the commonest
indications for HBOT include carbon monoxide
or cyanide poisoning, decompression sickness, air
embolism, acute thermal burn injury, gas gangrene,
radiation injury, infection, non-healing ulcers, skin
grafts and wound healing. HBOT is generally well
tolerated and adverse effects are rare. Some of them
include middle ear barotrama, claustrophobia,
reversible myopia, pulmonary barotrauma, and
O2 toxicity and very rarely seizures.
Carbon dioxide (CO2)
CO2 is a colorless and odourless gas, which
constitutes a very minimal percentage (0.03%) of
atmospheric air with a partial pressure of only 0.2
mm Hg. The specific gravity of CO2 is 1.53, and is
1.5 times as heavy as air. Since CO2 has a solubility
coefficient of 0.592, it is more soluble in water
than O2 and is 20 times more diffusible in water
than O2 on the basis of both Henry’s and Graham’s
laws. CO2 is widely used for laboratory purposes
in medical field, specifically in diagnostics and
equipment calibration. In our normal physiology,
a rise in CO2 acts as the stimulus for breathing and
a concentration of less than 10% of CO2 acts as a
respiratory stimulant. Hence, carbogen, a mixture
of CO2 & O2 was used in situations such as the
investigation and assessment of chronic respiratory
disease, to stimulate breathing after a period
of apnea or hypoventilation. Therapeutically
carbogen is administered as 5% CO2 and 95%
O2 for 10–15 minutes. It has to be cautiously
dealt as, CO2 concentrations above 10% may
result in respiratory depression. Some of the other
indications of carbogen include early treatment of
central retinal artery occlusion, cerebral perfusion
by cerebral vasodilation and in research related
to in vivo O2 and CO2 flow. Adverse effects of
carbogen include headache, palpitations, dizziness,
hypertension, tremors, and mental depression.
Helium (He)
He is also an odourless, tasteless, nonflammable
gas. Helium’s density is only 0.1785 g/L and is
one of the second lightest of all gases. Because of
its low density, Heliox, a combination of He and
O2 is therapeutically used for the transport of O2
in small airway obstructions. The density of an
80:20 He-O2 mixture is only 0.429 g/L, when
RespiMirror|Volume VII, Issue I, January-February 2017|
compared with the density of air i.e. 1.29 g/L.
This lower density of heliox results in a lower
Reynolds number (<2000) and a higher possibility
of laminar flow for any given airway. Thus heliox
helps to significantly improve the patient’s work
of breathing and hypoxia. A mixture of 70% He
and 30% O2 are also recommended for patients
with hypoxemia. The risks and adverse effects of
heliox include anoxia, volutrauma or hypocarbia
due to increased tidal volume, impaired cough,
hypothermia and reduced aerosol carrying capacity.
Nitrous Oxide (N2O)
N2O is a colorless gas and is slightly sweet
in odor and taste. Though it is nonflammable,
it supports combustion like O2. It is used as an
anesthetic agent in clinical practice because of its
depressant effect on the central nervous system.
N2O must always be mixed with at least 20% O2,
during inhalational purposes. True anesthesia is
attained only with dangerously high doses of N2O;
hence, it is usually used in combination with other
anesthetic gases.
Nitric Oxide (NO)
Like N2O, Nitric oxide (NO) is also a
nonflammable gas that supports combustion. NO
is a colorless and toxic gas, that becomes a strong
irritant, when mixed with air. Inhalation of toxic
amounts of NO can result in strong chemical
inflammation, pulmonary edema and even death.
Therapeutically, nitric oxide is potentially useful
in the treatment of pulmonary hypertension due
to its vasodilating properties. The physiological
effect of NO is capillary smooth muscle relaxation
and thereby improving the blood flow to ventilated
alveoli. This improved perfusion results in
improved V̇/Q̇ mismatch, reduced pulmonary
vascular resistance and pulmonary pressures and
finally in improved arterial oxygenation. Some of
the indications for inhaled NO include persistent
pulmonary hypertension of the newborn,
pulmonary hypertension in adults, acute respiratory
distress syndrome (ARDS), right heart failure
(e.g. post-cardiac surgery, post-ventricular assist
device insertion and heart transplant), primary
graft failure, post-lung transplant and to improve
oxygenation and pulmonary hemodynamics in
chronic obstructive pulmonary disease patients.
Though transient improvement of oxygenation in
ARDS is supported by some previous studies, a
recent systemic review concluded that NO has no
mortality benefit in ARDS. It was also observed
that ARDS patients who receive NO are at a risk of
developing renal dysfunction syndromes. Effective
dosage of NO in adults have been reported in the
range of 2–20 ppm (parts per million), with an
optimal dose of 10 to 20 ppm. Doses less than
20 ppm were shown to have minimum adverse
effects. The toxic effect of NO therapy is either
due to its direct action or by its chemical byproducts. Nitrogen dioxide (NO2) is produced
when NO reacts with O2 and has toxic effects at
... Contd. on page 3
... Contd. from page 2
higher concentrations. It was proven in pediatric
population too that high doses of inhaled NO
can worsen surfactant function, whereas low
doses can improve it and even alleviate oxidative
stress, resulting in a reduced risk of developing
chronic lung disease in neonatal population.
Methemoglobinemia, rebound pulmonary
Did you
Know
Dr. Sundeep Salvi
hypertension, increased left ventricular filling
pressures and hypotension are the other common
adverse effects seen with NO therapy.
Medical gas therapy is an integral part of
diagnostic and therapeutic areas of respiratory
therapy. The respiratory care professional who
deals with medical gases must be well versed
with the indications, physiological effects,
hazards and adverse effects of medical gases that
are used in their daily practice. With a sound
clinical knowledge, outcome assessments and
knowledge sharing, a respiratory care practitioner
can contribute significantly to the diagnostic and
prognostic aspects of patient care, resulting in the
better outcome of mankind. nn
?
MD, DNB, PhD, FCCP, Hon FRCP (Lon)
Director, Chest Research Foundation, Pune
Crocodile ice fish that lives in the Antarctic waters.
The crocodile icefish is the only known
vertebrate that does not have red blood cells. They live in very oxygen-rich cold water and transport oxygen freely
dissolved in the blood. They do not synthesize hemoglobin. Oxygen dissolves more easily in water than in air and
this is what supports aquatic life. Cold water has the ability to hold more dissolved oxygen than warm water. As a
result, there is a greater variety of aquatic life in the cold waters of Arctic and Antarctic than the warm tropical waters.
Substantia Nigra
Alveolar Macrophage
kidney mesangial cells
Type II alveolar epithelial cells
endometrial cells
DID YOU ALSO KNOW?
Hemoglobin is produced not only by erythrocytes, but also a whole host of other non-red blood cells. These include, alveolar
macrophages, type II alveolar epithelial cells, kidney mesangial cells, human endometrial cells and specific parts of the
brain, such as dopaminergic neurons in substantia nigra, astrocytes in cerebral cortex, hippocampus and oligodendrocytes.
The reason for why these cells synthesize hemoglobin is not known, but it is widely speculated that the hemoglobin in
non-erythroid cells can help store oxygen in the cells which can be used during periods of increased need.
The human body has 25 trillion red blood cells circulating in the blood, which comprises
67% of the total number of cells in the body. 2 million RBCs are produced every second.
Each red blood cell has 280 million hemoglobin molecules, which together carry 1
billion molecules of oxygen. Each red blood cell carries oxygen from the lungs and
delivers it to the tissues, which it does 1,72,000 times before its life ends.
|Volume VII, Issue I, January-February 2017|RespiMirror 3
OXYGEN DELIVERY DEVICES
Mr Aakash Soni, Respiratory Therapist
Philips Home Care Services India Private Limited
Oxygen Therapy
Normal cellular function depends on the
delivery of an adequate supply of oxygen to the
cells to meet their metabolic needs. The main
objective and goal of oxygen therapy is to deliver
a sufficient concentration of inspired oxygen to
allow full use of the oxygen-carrying capacity of
the arterial blood; this secures adequate cellular
oxygenation, provided the cardiac output and
hemoglobin concentration are adequate.
Principles of Therapy
Oxygen is a gas that must also be considered
a drug, because—like most other drugs—it has
harmful and beneficial effects. Oxygen is one of
the most commonly used and misused drugs. As a
drug, it must be administered for good reason and
in a proper, safe manner. Oxygen is usually ordered
in liters per minute (L/min), as a concentration of
oxygen expressed as a percentage, such as 40%, or
as a fraction of inspired oxygen (FiO2).
The primary indication for oxygen therapy is
hypoxemia. The amount of oxygen administered
depends on the pathophysiological mechanisms
affecting the patient’s oxygenation (Saturation)
status. In most scenarios, the amount required
should provide an arterial partial pressure of
oxygen (PaO2) of greater than 60 mm Hg or
an arterial hemoglobin saturation (SaO2) of
greater than 90% during rest and exercise. The
concentration of oxygen given to an individual
patient is a clinical judgment based on the many
factors that influence oxygen transport, such as
hemoglobin concentration, cardiac output, and
arterial oxygen level.
After oxygen therapy begins, the patient is
constantly and continuously assessed for the
level of oxygenation and the factors affecting it.
The patient’s oxygenation and saturation status
is evaluated several times daily until the desired
oxygen level has been reached and has stabilized.
If in case the desired response to the amount
of oxygen delivered is not achieved, the oxygen
concentration and supplementation is adjusted,
and the patient’s condition is re-evaluated. It is
important to use this dose-response method so that
the lowest possible level of oxygen is administered
that will still achieve a satisfactory PaO2 or SaO2.
Methods of Delivery
Oxygen therapy can be delivered by many
different ways via many different devices (Table).
Common problems with these devices include
system leaks and obstructions, device displacement,
and skin irritation. These devices are classified as
low-flow, reservoir, or high-flow systems.
Low-Flow Systems
A low-flow oxygen delivery system delivers
supplemental oxygen directly into the patient’s
airway at a flow of 8 L/min or less. Because this
flow is not enough to meet the patient’s inspiratory
volume requirements, it results in a variable FiO2
as the supplemental oxygen is mixed with room air.
The patient’s ventilatory pattern affects the FiO2
4
of a low-flow system: as the ventilatory pattern
changes, differing amounts of room air gas are
mixed with the constant flow of oxygen. Low-flow
oxygen delivery systems consist of nasal cannula,
nasal catheters, and transtracheal catheters.
NASAL CANNULA
The standard nasal cannula delivers an
inspiratory oxygen fraction (FiO2) of 24-44% at
supply flows ranging from 1-8 liters per minute. The
formula is FiO2 = 20% + (4 × oxygen liter flow). The
FiO2 is influenced by breath rate, tidal volume and
pathophysiology. The slower the inspiratory flow,
the higher the FiO2 and the faster the inspiratory
flow, the lower the FiO2. Since the delivered oxygen
percentage is very inconsistent during respiratory
distress, a nasal cannula is not recommended for
acute severe hypoxemia or patients that breathe
on a hypoxic drive where to high of an oxygen
concretion may led to respiratory depression.
A nasal cannula utilizes no external reservoir of
oxygen and relies on the patient’s upper airway
as an oxygen reservoir. A humidification device is
recommend for flows greater than four liters to
insure humidification of the dry inspired gas. Even
with humidity added flows 6-8 liters per minute can
cause nasal dryness and bleeding. The best clinical
indications for the nasal cannula is for patients who
have a relative stable respiratory pattern, required
low oxygen percentage, need supplement oxygen
during a operative or diagnostic procedure or for
chronic home care.
NASAL CANNULA
Nasal Catheter
A nasal catheter is a soft paste tube with several
holes at the tip. It is inserted into a nare, which
needs to be changed every eight hours. This device
has been replaced by the nasal cannula but can
be used for a patient that is undergoing an oral
or nasal procedure.
NASAL CATHETHER
Transtracheal Catheter
Transtracheal catheters deliver oxygen directly
into the trachea. There are washout and storage
effects that promote gas exchange, as well as
RespiMirror|Volume VII, Issue I, January-February 2017|
provide high-flow oxygen. High-flow transtracheal
catheters may reduce the work of breathing and
augment CO2 removal in the chronic oxygen
user. Transtracheal oxygen therapy improves the
efficiency of oxygen delivery by creating an oxygen
reservoir in the trachea and larynx. Consequently,
mean oxygen savings amount to 50% at rest
and 30% during exercise. Transtracheal oxygen
reduces dead space ventilation and inspired minute
ventilation, while increasing alveolar ventilation
slightly, which may result in a reduction of the
oxygen cost of breathing. As a result, patients
using this device may experience improved exercise
tolerance and reduced dyspnea. This delivery
device is best used for home care and ambulatory
patients who required long periods of mobility and
do not feel comfortable wearing a nasal cannula.
TRANSTRACHEAL CATHETHER
Reservoir Systems
A reservoir system incorporates some type of
device to collect and store oxygen between breaths.
When the patient’s inspiratory flow exceeds the
oxygen flow of the oxygen delivery system, the
patient is able to draw from the reservoir of oxygen
to meet his or her inspiratory volume needs. There
is less mixing of the inspired oxygen with room
air than in a low-flow system. A reservoir oxygen
delivery system can deliver a higher FiO2 than a
low-flow system. Examples of reservoir systems
are simple face masks, partial rebreathing masks,
and non-rebreathing masks.
Simple Mask
To increase the oxygen concretion delivered,
often a mask reservoir is utilized. The volume of the
facemask is approximately 100-300 cm3 depending
on size. It can deliver a FiO2 of 40-60% at 5-10
liters. The FiO2 is influenced by breath rate, tidal
volume and pathology. A flow rate of greater than 5
liters must be set to insure the washout of exhaled
gas and carbon dioxide retention. The mask is
also indicated in patients with nasal irritation
or epistaxis. It is also useful for patients who are
strictly mouth breathers. However, the mask can
be obtrusive, uncomfortable, and confining. It
muffles communication, obstructs coughing and
impedes eating. It can also mask aspiration in the
semi-conscious patient.
A simple mask should be administered for more
than a few hours because of the low humidity
delivered and the drying effects of the oxygen gas.
This device is best used for short-term emergencies,
operative procedures, or for those patients where
a nasal cannula is not appropriate.
Non Rebreathing Mask
The non-rebreathing facemask is indicated
when an FiO2 >40% is desired and for acute
... Contd. on page 5
... Contd. from page 4
Low Flow Devices
Flow
Fio2
Range
(%)
Advantages
Disadvantages
Best use
Maintenance, Care
and Re-placement
Category
Device
Low-flow
Nasal
cannula
0.25-8 L/min 22-45
(adults)≤2 L/
min (infants)
Use on adults, children,
infants; easy to apply;
disposable, low cost;
well tolerated
Unstable, easily dislodged;
high flows uncomfortable;
can cause dryness/
bleeding; polyps, deviated
septum may block flow
Stable patient needing
low FiO2; home care
patient requiring
long-term therapy
Keep it clean,
Cover when not
in Use & Change
after one month
Nasal
catheter
0.25-8 L/min 45
Use on adults, children,
infants; good stability;
disposable, low cost
Difficult to insert; high flows
increase back pressure;
needs regular changing;
polyps, deviated septum
may block insertion; may
provoke gagging, air
swallowing, aspiration
Procedures where
cannula is difficult to use
(bronchoscopy); longterm care for infants
Keep the external
surface clean, change
after every 20 days
Trans
tracheal
catheter
0.25-4 L/min 35
Lower O2 usage/cost;
eliminates nasal/skin
irritation; improved
compliance; increased
exercise tolerance;
increased mobility;
enhanced image
High cost; surgical
complications; infection;
mucus plugging; lost tract
Home care or
ambulatory patients
who need increased
mobility or who do not
accept nasal oxygen
Cleaning and
care
must be taken for the
catheter externally, Can
be changed after every
10 – 15 days
Reservoir Devices
Category
Device
Reservoir Reservoir
cannula
Flow
0.25-4 L/min
Fio2
Range
(%)
Advantages
Disadvantages
Best use
Maintenance, Care
and Re-placement
22-35
Lower O2 usage/
cost; increased
mobility; less
discomfort because
of lower flows
Unattractive, cumbersome;
poor compliance; must
be regularly replaced;
breathing pattern
affects performance
Home care or
ambulatory patients who
need increased mobility
Keep it clean with
disinfectants,
Cover when not
in Use & Change
after one month
Simple mask 12 L/min
50
Use on adults,
children, infants;
quick, easy to
apply; disposable,
inexpensive
Uncomfortable; must
be removed for eating;
prevents radiant heat
loss; blocks vomitus in
unconscious patients
Emergencies, shortterm therapy requiring
moderate FiO2
Keep it clean with
disinfectants, Cover it
when not in use and
change in every one
month
Partial
rebreathing
mask
6-10 L/min
(prevent bag
collapse on
inspiration)
60
Same as simple
mask; moderate
to high FiO2
Same as simple
mask; potential
suffocation hazard
Emergencies, shortterm therapy requiring
moderate to high FiO2
Keep it clean with
disinfectants, Cover
it when not in use
and change in every
three month
Nonrebreathing
mask
6-10 L/min
(prevent bag
collapse on
inspiration)
70
Same as simple
mask; high FiO2
Same as simple
mask; potential
suffocation hazard
Emergencies, shortterm therapy requiring
moderate to high FiO2
Keep it clean with
disinfectants, Cover
it when not in use
and change in every
three month
Nonrebreathing
circuit
(closed)
Ve(prevent
bag
collapse on
inspiration)
100
Full range of FiO2
Potential suffocation
Patients requiring
hazard; requires 50 psi air/ precise FiO2 at any
O2; blender failure common level (21%-100%)
desaturation. It may deliver a FiO2 up to 90% at
flow settings greater than 10 liters. Oxygen flows
into the reservoir at 8-15 liters, washing the patient
with a high concentration of oxygen. Its major
drawback is that the mask must be tightly sealed
on the face, which is uncomfortable and drying.
emergencies where a high FiO2 is necessary. Its
duration should be less than four hours, secondary
to inadequate humidity delivery and to variable
of an FiO2 for patients who require a precise high
oxygen percentage.
Keep it clean with
disinfectants, Cover
it when not in use.
Long term time validity
can be autoclaved
after the use.
High-Flow Systems
With a high-flow system, the oxygen flows out
of the device and into the patient’s airways in an
amount adequate to meet all inspiratory volume
requirements. This type of system is not affected
SIMPLE FACEMASK
There is also a risk of CO2 retention if the
mask reservoir bag is allowed to collapse on
inspiration. Humidification is difficult with this
device, because of the high-flow required and the
possibility of the humidifier popping off. This
device is best utilized in acute cardiopulmonary
VENTURI MASK
NON REBREATHING MASK
... Contd. on page 6
|Volume VII, Issue I, January-February 2017|RespiMirror 5
... Contd. from page 5
High-Flow Devices
Category
High-flow
Device
Flow
Fio2
Range
(%)
Advantages
Disadvantages
24-50
Easy to apply;
disposable,
inexpensive; stable,
precise Fio2
Limited to adult use;
uncomfortable, noisy;
must be removed for
eating; FiO2>0.40 not
ensured; FiO2 varies
with back-pressure
Unstable patients
requiring precise
low FiO2
Keep it clean with
disinfectants, Cover it when
not in use and change
in every three month
Airentrainment
nebulizer
100
Provides temperature
control and extra
humidification
FiO2 <28% or >0.40 not
ensured; FiO2 varies
with back-pressure;
high infection risk
Patients with
artificial airways
requiring low to
moderate FiO
Maintenance can be done
by clean external and the
internal opening areas by
disinfectant and can be
changed in 6 months.
10-15 L/min
input; should
provide output
flow ≥60 L/min
insure the delivered exact FiO2. The Venturi mask
is often utilized in the COPD patient population
where the risk of knocking out the patient’s hypoxic
drive is of concern.
Conclusion
In conclusion, oxygen administration is
the most common clinical intervention for
patients with respiratory distress. Optimizing
outcomes often depends on selecting the correct
oxygen delivery device. In selecting an oxygen
administration device, the Physician, Respiratory
therapist and the Nurses should include the
following in their recommendation:
How does oxygen save
patients of COPD?
amage from hypoxia to multiple organs
was long recognized for over a century, in
the words of J.S. Haldane: ‘Hypoxia not
only stops the machine, but wrecks the machinery’.
While acute hypoxia frequently poses a serious threat
to life hypoxia in a chronic condition like COPD is
responsible for a number of complications ultimately
resulting in significant morbidity and premature
mortality. Amelioration of hypoxia therefore, is the
cornerstone of management of COPD.
Hypoxia in COPD results primarily from
ventilation-perfusion (V̇/Q̇) mismatch because of
low V̇/Q̇ relationship (i.e. shunt physiology). Some
of the factors responsible for V̇/Q̇ mismatch include
infection, bronchospasm and airway inflammation
which are partially reversible. Hypoxemia leads
to reflex pulmonary vasoconstriction and thus
worsens pulmonary hypertension and cor
pulmonale.
Role of Oxygen in COPD
The use of oxygen therapy in COPD can be
divided into two main categories:
I. Oxygen therapy during acute
exacerbations of COPD
Acute exacerbation of COPD can be clinically
defined as worsening of cough, expectoration
and dyspnea along with worsening ventilationperfusion relationship and variable degrees of fluid
retention. It occurs due to either an inadequate
6
Maintenance, Care
and Re-placement
AirVaries; should
entrainment provide output
mask (AEM) flow >60 L/min
by the patient’s pattern of ventilation. An example
of a high-flow system is an air-entrainment mask.
A Venturi mask mixes oxygen with room air,
creating high-flow enriched oxygen of a desired
concentration. It provides an accurate and constant
FiO2 despite varied respiratory rates and tidal
volumes. FiO2 delivery settings are typically set at
24, 28, 31, 35 and 40% oxygen. The Venturi mask
is often employed when the clinician has a concern
about carbon dioxide retention or when respiratory
drive is inconsistent. The addition of humidification
is not necessary with this device, secondary to the
large amount of ambient entrainment that occurs to
D
Best use
and inappropriate maintenance- treatment or
an antecedent complication such as respiratory
tract infection which is most commonly bacterial
in origin. Other conditions like pneumonia,
pulmonary embolism, cardiac dysrhythmias,
pneumothorax, congestive heart failure and use
of sedatives can also exacerbate the clinical and
functional status of a patient with COPD. All the
conditions listed above precipitate hypoxemia and
hypoxia in these patients, essentially implying that
oxygen therapy becomes one of the most essential
components of management.
Oxygen therapy is started immediately at
admission after an arterial blood gas is obtained
for assessment of blood gas tensions. The goal
of supplemental oxygen is to maintain a PaO2
of 55 to 60 mm Hg corresponding to SpO2 of
89-92%. Administration of excess amounts of
oxygen can blunt the ventilator drive with resultant
hypoventilation, hypercapnia and acute respiratory
acidosis superimposed on type II respiratory failure.
Such a situation is potentially life threatening.
Another reason why PaO2 is not increased more
than 60 mm Hg is because it corresponds to an
oxygen saturation of around 90%; there is no
benefit of increasing PaO2 above 60 mm as can
be seen from the oxygen delivery equation.
Oxygen delivery = [1.34 X hemoglobin (gm/
dL) X oxygen saturation] + [0.000031 X PaO2]
In acute situations, it is always better to use
RespiMirror|Volume VII, Issue I, January-February 2017|
• The goal of oxygen delivery,
• The patient’s condition and etiology, and the
performance of the device being selected.
• There are a plethora of oxygen delivery devices
for the clinical practitioner to choose from to
meet the desired clinical endpoint. Selection
depends on the clinical pathophysiology and
the patient’s physiological response. Clinical
assessment and monitoring are essential to
ensure patient safety and to achieve desired
clinical outcomes when administering oxygen.
nn
Dr. S.K. Jindal
Emeritus Professor, Pulmonary Medicine,
Postgraduate Institute of Medical
Education & Research, Chandigarh
Medical Director, Jindal
Clinics, Chandigarh
high-flow devices as one can, to a reasonable
extent, guarantee the oxygen delivered since
the oxygen delivery would not be dependent on
patient’s minute ventilation. Once the patient has
been stabilized, one can shift to nasal prongs, as it
proves more comfortable for the patient.
II. Oxygen therapy for stable COPD
There is evidence in literature to support the
role of domiciliary long-term oxygen therapy
(LTOT) in stable COPD with hypoxaemia;
however, the role of oxygen therapy in patients
who have only nocturnal hypoxemia or hypoxemia
during exercise only, is logical but not well
supported by evidence from the literature.
Long-term oxygen therapy in patients who
have daytime resting hypoxemia
Data from the Medical Research Council
(MRC) trial and the nocturnal oxygen therapy trial
(NOTT) had shown that continuous long-term
oxygen therapy can improve survival in patients
with COPD and resting daytime hypoxemia.
Other studies have also shown that LTOT can
decrease hospitalization in patients with COPD.
Importantly, oxygen should be taken for as long as
possible as hypoxemia related pulmonary vascular
changes could occur rapidly. In fact there is some
data to show that these changes can occur in less
than three hours.
... Contd. on page 7
... Contd. from page 6
Initiation and reassessment of LTOT: Patients
with COPD who have FEV1 less than 40% and/
or pulmonary hypertension should be routinely
screened for LTOT. Before prescribing LTOT, the
indication should be confirmed on at least two
occasions two to three weeks apart with a resting
arterial blood gas analysis performed on room air.
Patient should be stable on maximal and optimal
medical therapy including a complete pulmonary
rehabilitation program. Smoking cessation should
be strictly enforced.
The oxygen flow rate should be set to maintain
a PaO2 > 60 mm Hg during waking and at rest;
usually 1-2 LPM through nasal prongs would
generally suffice. Also the oxygen flow rate should
be increased by 1 LPM during sleep, exertion and
air travel.
The goal of LTOT should be confirmed by
performing an arterial blood gas analysis after
one to two months of initiating oxygen therapy,
and documenting a PaO2 > 60 mm Hg; a repeat
blood gas analysis also helps in assessment of the
hypercapnic response to oxygen therapy. Patients
with significant hypercapnia with oxygen therapy
may also require domiciliary noninvasive pressure
support ventilation.
Oxygen therapy in patients with hypoxemia
only during sleep at night
Patients with COPD can experience prolonged
episodes of oxygen desaturation during rapid eye
movement sleep, and studies have shown that
nocturnal hypoxemia can exacerbate pulmonary
hypertension in patients with COPD. Current
practice advocates to rule out concomitant
obstructive sleep apnea in patients in patients
who have nocturnal symptoms, and intensify
medical management if the patient is found
to have nocturnal hypoxemia without daytime
hypoxemia. Oxygen therapy in this subgroup
of patients may be indicated if the patients have
evidence of chronic hypoxia-related sequalae like
polycythemia or pulmonary hypertension. Patients
whose oxygen saturation repeatedly falls below
88% for more than one-third of the night may
also benefit from nocturnal oxygen therapy.
Oxygen therapy in patients who have no
daytime resting hypoxemia but hypoxemia during
exercise
The benefits of pulmonary rehabilitation on
exercise capacity and quality of life in COPD
patients support the use of ambulatory oxygen
for all patients on LTOT to allow them to achieve
their full potential in terms the reduced mortality
from continuous oxygen therapy.
There are studies that show improved exercise
tolerance and improved quality of life in patients
who use intermittent oxygen therapy prior to
exercise. However some studies do not show
significant benefit.
In the absence of any definite data, intermittent
oxygen therapy may be prescribed in individual
patients in whom the benefits (dyspnea, exercise
capacity) have been definitely proven by an
exercise test especially in those patients awaiting
lung transplantation or lung volume reduction
surgery, to maintain an increased level of fitness
prior to surgery.
Benefits of long term O2 therapy
i. Duration of survival
ii.Intellectual function: There is significant
improvement in memory, motor coordination,
mood and other hypochondrial symptoms on
long term O2 therapy.
iii.Pulmonary hypertension: There is a decrease
in pulmonary vasoconstriction and vascular
resistance. This improves the severity of right
heart failure.
iv. Red Cell mass: Long term O2 decreases red cell
mass and haematocrit level. Complications of
polycythaemia are therefore diminished.
Potential benefits
These include the following:
i. Increased exercise ability
ii. Improved quality of life – patients resuming
gainful employment and participating in their
own care more actively.
iii.Decrease in dyspnoea
iv. Decrease in hospitalization and exacerbations
of respiratory failure
v. Delayed development of cor pulmonale
Selection of patients
All patients with chronic hypoxaemic lung
disease are potential candidates for long term
oxygen therapy. Following guidelines are used
to select patients for instituting the treatment.
i. A definitive documented diagnosis responsible
for chronic hypoxaemia
ii. An optimal medical treatment should be in
effect
iii.Patient in a stable condition
iv.Oxygen administration should have been
shown to improve hypoxaemia and provide
clinical benefit.
It is important to ensure that the patient is
compliant with the general medical regimen and
follows instructions, such as to quit smoking.
Continued smoking not only aggravates the disease
process but also reduces the full physiological
benefits of oxygen and poses inherent safety risk
of accidental fires.
Following specific indices are used while
prescribing long term oxygen:
i. At rest, in non-recumbent position the PaO2
of 55 mmHg or less.
ii. Patients with PaO2 of more than 55 mmHg
are considered in the following conditions:
a. Patient on optimal medical treatment, with
demonstrable hypoxic organ dysfunction,
such as secondary pulmonary hypertension,
cor pulmonale, polycythaemia or CNS
dysfunction.
b. When there is a demonstrable fall in PaO2
below 55 mmHg during sleep, associated
with disturbed sleep pattern, cardiac
arrhythmias or pulmonary hypertension.
These patients may be benefited by
nocturnal oxygen therapy.
c. When there is demonstrable PaO2 fall
during exercise and oxygen administration
is shown to improve exercise performance,
duration or capacity. These patients may
benefit by oxygen during exercise. They
may also be administered supplemental
oxygen before and after the exercise.
Oxygen dosage
Most of the COPD patients are prescribed
low flow concentrations at 1-2 L/min. Higher
flow rates are required for some of the patients,
especially those with other chronic respiratory
diseases. The treatment is guided by PaO2 which
should be maintained at 60 mmHg or so (SaO2 of
85-90%). During the period of exercise, sleep or
other activities, the flow rate may be increased by
another 1-2 L/min. While continuous therapy is
required for patients who show hypoxaemia at rest,
intermittent treatment during specific periods may
be used for patients who demonstrate intermittent
hypoxaemia.
Supply Sources
There are three main types of systems
commercially available for supply of oxygen at
home: compressed gas cylinders, liquid oxygen
and oxygen concentrators. While cylinders are
commonly used by patients at home as well as in
hospitals, a concentrator is ideal for use at home.
It obviates the need of regular filling of the tank.
Its initial cost is high but the running cost is
negligible. Proper maintenance of equipment
and replacement of filters is required. A back up
source of oxygen supply (e.g. compressed oxygen
cylinder) is necessary in case of a power failure.
Oxygen Delivery devices
Devices used to deliver oxygen include
cannulae, prongs and masks. Those are essentially
the same as used in the hospitals. Nasal cannulae
and prongs are preferred because of the cosmetic
reasons. It is easy to conceal oxygen tubing by
applying it to ordinary thick rimmed frames of eyeglasses (“Oxyspecs”). Different kinds of “oxyspecs”
and other devices are now commercially available
for this purpose.
Humidification is not essential at flow rates
of less than 4 L/min unless the patient complains
of dryness of the nose or mouth, nasal irritation
or crusting. Humidifier is a potential source
of infection and needs regular cleaning and
disinfection. Disposable humidifiers significantly
increase the costs.
Oxygen therapy on long term basis is a costly
proposition. Many patients tend to conserve
oxygen by reducing the flow as well as the duration
of administration. The standard oxygen supply
devices allow the flow of oxygen both during
inspiration and expiration. A lot of oxygen
delivered to the patient is therefore, wasted in
the surroundings. Several methods have been
devised to conserve oxygen in the recent years.
It is possible to save up to 50% oxygen with some
of these methods.
Risks of long term oxygen therapy
There are three types of risks associated with
long term use of oxygen:
i. Physical risks
Oxygen tanks pose potential risks of fire hazard
and tank explosion which are rather small. It is
highly desirable that smoking is stopped with its
use. The other minor risks of oxygen therapy
include the injury to the nose and face from
catheters and masks. Dryness and crusting may
occur from dry, non-humidified gas.
... Contd. on page 8
|Volume VII, Issue I, January-February 2017|RespiMirror 7
... Contd. from page 7
i. Functional risks
Oxygen therapy may accentuate hypoventilation
in patients with COPD. This may induce
hypercapnia and carbon dioxide narcosis.
ii. Cytotoxic damage
Long term oxygen can cause structural damage
to the lungs. But there is no significant effect of
these changes on clinical course or survival of these
patients.
In India, some of the important problems
stated by most of the patients relate to difficulties
of procurement and costs. There are limited
sources of supply. Moreover, the medical expertise
Oxygen Therapy in ILD and ARDS
T
he respiratory system functions to ensure the
delivery of an adequate amount of oxygen
to and elimination of carbon dioxide from the
cells of the body and maintenance of normal
acid-base balance in the body. This gas exchange
depends on the optimal functioning of various
parts of the respiratory system. A disorder in
any of these components can lead to respiratory
failure. Respiratory failure may be acute or
chronic. Inadequate gas exchange is associated
with hypoxemia with or without hypercarbia
(Type-1 respiratory failure or lung failure), while
inadequate ventilation leads to hypoxemia with
hypercarbia (Type-2 or ventilatory failure).
Hypoxia and hypoxemia:
Hypoxia is lack of oxygen at the tissue level
while hypoxemia implies a low arterial oxygen
tension below the normal expected value (85-100
mmHg).
The aims of therapy in respiratory failure are
to achieve and maintain adequate gas exchange
and reversal of the precipitating process that led
to the failure.
Oxygen therapy is required for respiratory
failure of diverse etiology.
Goals of oxygen therapy:
The goal is to relieve hypoxemia by increasing
alveolar tension, to reduce the work of breathing,
and to decrease the work of myocardium.
Many biochemical reactions in the body
depend on oxygen utilization. Supply of oxygen
to the tissues depends on many factors like
ventilation, diffusion across alveolar-capillary
membrane, hemoglobin, cardiac output, and
tissue perfusion.
It is important to determine whether the
hypoxemia can be relieved by oxygen therapy alone
or it needs oxygen and ventilator intervention.
The decision is made on the presence or absence
of hypercapnia and of lung disease.
When decided to use, oxygen should be used
like a drug and its dose should be individualized
and carefully titrated. Arterial blood gases should be
measured repeatedly on oxygen therapy. The goal
is to maintain PaO2 above 60 mmHg. The hazards
of oxygen toxicity must be kept in mind and riskbenefits of oxygen therapy should be determined on
each occasion. Different clinical conditions demand
different ways of using oxygen therapy.
Let us see the two common conditions one
encounters in practice: Interstitial Lung Disease
8
(ILD) and Acute Respiratory Distress Syndrome
(ARDS)
ILD:
Pathologically, ILDs are characterized by
varying amounts of inflammation and fibrosis
of the lung parenchyma leading to restrictive
physiology and impaired gas exchange. The lungs
are stiff and compliance is low.
Examples are Idiopathic Pulmonary Fibrosis
(IPF), acute and chronic interstitial pneumonias,
ILD due to connective tissues diseases (CTD) and
granulomatous diseases etc.
Disease progression or intercurrent
complications lead disabilities and impairments
in their health-related quality of life. Treatment
options are often limited, without proven effect
on survival and HRQL, and associated with
significant risks and side effects.
Chronic hypoxemia can occur in patients
with severe ILD and may lead to poor tissue
oxygenation and the development of complications
such as pulmonary hypertension. This in turn can
worsen the prognosis.
Patients with fibrosing lung conditions such
as IPF may have acute exacerbations commonly
due to intercurrent chest infections. Others may
develop acute breathlessness due to extrinsic
allergic alveolitis, sarcoidosis or other types of
parenchymal lung disorders. They often need
high oxygen concentrations to achieve satisfactory
blood gases due to a high degree of V̇/Q̇ mismatch.
The oxygen level should be adjusted to maintain
oxygen saturation in the range of 94–98%. It
may be challenging to reach these levels without
a reservoir mask. Mechanical ventilation is usually
not favored because of the progressive nature of
the condition and likely poor outcomes.
Oxygen Therapy:
1. Nocturnal oxygen therapy (NOT) is oxygen
supplemented during the night alone without
additional oxygen therapy during the daytime.
Before daytime resting hypoxemia develops,
many patients develop nocturnal desaturation due
to worsening V̇/Q̇ mismatch in a supine posture
and hypo ventilation during sleep.
NOT should not be given to patients with
ILD with nocturnal hypoxemia alone, who do not
fulfill LTOT criteria. NOT improves nocturnal
oxygenation, but not sleep quality. There is no
evidence of long-term benefit on survival.
RespiMirror|Volume VII, Issue I, January-February 2017|
and advice to supervise domiciliary treatment is
lacking. Patients’ resources to afford the treatment
are also scanty. There are no clear guidelines
available regarding reimbursement of costs on
oxygen and the apparatus. One does expect that
most of the difficulties shall resolve in due course
of time. nn
Dr. Prasad Akole
DNB (Anaesthesiology),
DCCM (Critical Care)
Consultant Intensivist,
Deenanath Mangeshkar Hospital,
Pune, India
2. Long term oxygen therapy (LTOT) can be
defined as oxygen used for at least 15 hours per
day in chronically hypoxemic patients. Chronic
hypoxemia is defined as a PaO2 ≤7.3 kPa (55
mmHg) or, in certain clinical situations, PaO2
≤8.0 kPa (60 mmHg).
LTOT is delivered via an oxygen concentrator.
LTOT should be ordered for patients with
interstitial lung disease (ILD) with a resting
PaO2 ≤7.3 kPa or with a resting PaO2 ≤8 kPa in
the presence of peripheral edema, polycythemia
(hematocrit ≥55%) or evidence of pulmonary
hypertension.
Patients eligible for LTOT should be initiated
on a flow rate of 1 L/min and titrated up in 1 L/
min increments until SpO2>90%. An ABG should
then be performed to confirm that a target PaO2
≥8 kPa (60 mmHg) at rest has been achieved.
LTOT should be ordered for a minimum of 15
hours per day.
3. Short burst oxygen therapy (SBOT) is used
in patients for the relief of breathlessness not
relieved by any other treatments. It is used
intermittently at home for short periods like
10–20 minutes at a time. It may be ordered
for non-hypoxemic patients and used for
subjective relief of dyspnea prior to exercise
for oxygenation or after exercise for relief of
dyspnea and recovery from exertion.
4. Ambulatory oxygen therapy (AOT) is defined
as the use of supplemental oxygen during
exercise and activities of daily living.
AOT may be offered to LTOT patients who are
severely hypoxemic and are too symptomatic to
leave their house without supplemental oxygen.
5. Palliative oxygen therapy (POT) is used to
relieve the sensation of refractory persistent
breathlessness (dyspnea) in advanced disease or
life-limiting illness irrespective of the optimal
treatment of the underlying pathology and
reversible factors.
A palliative care specialist may optimize its use
with judicious use of narcotics to alleviate dyspnea.
Oxygen delivery systems
Oxygen can be administered conveniently by
oro-nasal devices like nasal catheters, cannulae,
and different types of masks. These are simple,
less expensive, and comfortable.
... Contd. on page 9
... Contd. from page 8
Nasal catheter
The light rubber nasal catheter is inserted after
lubricating its tip with liquid paraffin until the
tip is visible behind the uvula in the oropharynx.
Nasal cannulae
In hospitalized patients, these cannulae with
two soft pronged plastic tubes are inserted about
1 cm in each naris. These are comfortable and
well tolerated. These are used in patients without
hypercapnia who require supplementary oxygen up
to 40%. These can be easily used for domiciliary
oxygen therapy. Oxygen has to be humidified
while using these.
Venturi mask
It fits lightly over the nose and mouth. Oxygen
flowing at a high velocity in the form of a jet
through a narrow orifice to the base of the mask
creates negative pressure, entraining atmospheric
air through the perforations in the face piece (the
Bernoulli principle).
By using oxygen at flow rate of 1,2,3 L/min,
we can achieve roughly 24%, 28%, and 35% with
mask, catheter, or cannulae.
These are somewhat uncomfortable and have
to be removed while eating or drinking.
Home oxygen therapy:
Oxygen therapy at home aims to make the
patient active and encourage exercise and other
activities outside the home.
2 types:
a)Stationary (Compressed high pressure gas
cylinders or O2 concentrators) :
These are useful for bedridden patients. They
are of low cost. They need backup of tank
system if there is electricity failure.
b) Portable system (Trans filling gaseous or liquid
system):
They are useful for ambulatory patients
including those who have to remain away from
house for work. They are light weight but costly.
Oxygen is filled from a stationary source.
Monitoring oxygen therapy
Oxygen therapy should be administered
according to guidelines. Proper monitoring
of oxygen therapy is recommended to ensure
adequate oxygenation and to save precious oxygen
from wastage.
Oxygen therapy should be given continuously
and should not be stopped abruptly to avoid a fall
of alveolar oxygen tension. The dose of oxygen
should be calculated and titrated carefully.
Partial pressure of oxygen can be measured in
the arterial blood. But repeatedly doing arterial
blood gases is usually difficult. A simple and
non-invasive technique like pulse oximeter may
instead be used to assess oxygen therapy. Complete
saturation of hemoglobin in arterial blood should
not be attempted.
An increase of 1% oxygen concentration
elevates oxygen tension by 7 mmHg. It is necessary
to maintain normal hemoglobin level in the
presence of respiratory disease as proper oxygen
transport to the tissues is to be maintained.
Dangers of oxygen therapy
1. Physical risks
Oxygen being combustible, fire and explosion
is a great risk. This is more with high concentration
of oxygen, use of pressure chambers and in
smokers. Catheters and masks can cause injury
to the nose and mouth. Dry and non-humidified
gas can cause dryness and crusting.
2. Functional risks
Patients who are dependent upon the hypoxic
drive are in danger of ventilator depression as seen
in patients of COPD. Hypoventilation can lead
to hypercapnia and CO2 narcosis although the
risk is small with low flow oxygen therapy. As
long as pH does not suggest acidosis, long term
oxygen therapy can benefit the patients with CO2
retention.
3. Cytotoxic damage
Patients on long term oxygen therapy show
proliferative and fibrotic changes in their lungs.
In acute conditions, most of the structural damage
occurs from high FiO2 as the oxygen can lead to
the release of various reactive species.
Benefits
Long term oxygen therapy benefits patients
with chronic pulmonary diseases with hypoxemia.
They become more comfortable and there occurs
improvement in pulmonary hypertension and
right heart failure. It increases their survival and
quality of life.
ARDS:
According to the Berlin definition, patients
are considered as having ARDS if they have: (1)
acute respiratory failure not fully explained by
cardiac failure or fluid overload, as judged by the
treating physician; (2) bilateral opacities consistent
with pulmonary edema on the chest radiograph
or the computed tomography scan; and (3) onset
within 1 week after a known clinical insult or
new/worsening respiratory symptoms. Severity
is defined according to oxygenation, and ARDS
is considered as mild if PaO2/FiO2 is between
201 and 300 mm Hg, moderate if PaO2/FiO2 is
between 101 and 200 mm Hg, and severe if PaO2/
FiO2 is less than or equal to 100 mm Hg, in all
cases using a PEEP level at least of 5 cm H2O.
In the beginning, very mild forms of ARDS
may initially be managed with oxygen therapy
which often progressively fails and mechanical
ventilation is needed.
In such cases to correct hypoxemia, ventilator
controlled administration of oxygen often with
PEEP (positive end expiratory pressure) is
required. Patients are usually ventilated using
the ARDS net protocol consisting of the variable
PEEP/FiO2 tables. (low PEEP/ high FiO2 or High
PEEP/ low FiO2)
The PEEP is the more important parameter
helping to recruit the diseased alveoli and cause
improvement in oxygenation. Initiation of
ventilation often is done on high FiO2 values and
then titrated to response using PEEP/ FiO2 tables.
After the initial 24 hours, FiO2 should not
exceed 60% (to reduce the risk of O2 toxicity).
Noninvasive Ventilation and High-Flow
Nasal Cannula
Because intubation and mechanical ventilation
may be associated with an increased incidence
of complications, such as ventilator induced
lung injury (VILI) and nosocomial pneumonia,
alternatives to mechanical ventilation such as a
high-flow nasal cannula or noninvasive positivepressure ventilation (NIPPV) may be beneficial
in some patients with ARDS.
High-flow nasal cannula (HFNC) uses a
system of heated humidification and large-bore
nasal prongs to deliver oxygen at flows of up to 50
L/min. This is usually used in conjunction with
an oxygen blender, allowing delivery of precise
inspired oxygen concentrations. High-flow nasal
cannula is usually well tolerated and allows the
patient to talk, eat, and move around.
NIPPV is usually given by full facemask.
Sometimes, continuous positive airway pressure
(CPAP) alone may be sufficient to improve
oxygenation.
In a 2015 study on hypoxemic, non-hypercapnic
patients comparing standard oxygen, high-flow
nasal cannula and NIPPV, all three modes had the
same incidence of need for intubation/mechanical
ventilation, but high-flow nasal cannula resulted
in improved 90-day mortality. It role of HFNC
remains to be reaffirmed in further stronger studies.
Patients who have a diminished level of
consciousness, vomiting, upper GI bleeding,
or other conditions that increase aspiration risk
are not candidates for NIPPV. Other relative
contraindications
include
hemodynamic
instability, agitation, and inability to obtain
good mask fit. Such patients should be intubated
and mechanically ventilated if failing on oxygen
therapy alone.
Oxygen therapy may again help patients of
ARDS in the recovery phase when they improve
and get weaned off ventilator and extubated.
Various means of controlled oxygen therapy
may be given to these recovering patients till they
recover fully and do not need oxygen. It may be
in the form of spontaneous breathing trial on
T piece O2, O2 mask, venturi mask, cannulae etc.
Oxygen therapy thus if used judiciously as
per guidelines, with due precautions, as a drug
with correct dosage, route and duration can prove
life-saving in difficult conditions such as ILD and
ARDS. nn
|Volume VII, Issue I, January-February 2017|RespiMirror 9
Oxygen Therapy at home
for respiratory issues
Dr. B. V. Murali Mohan, MRCP(UK), SCE (Resp. Med.)(UK), FRCP
Dr. Priyadarshini Raykar, DTCD, Post-graduate in DNB (Resp. Med.)
T
he medical uses of oxygen were reported early,
with the French physician Caillens who in
1783 used oxygen for a patient with tuberculosis
who he reported was “very much benefited” by the
newly discovered gas. The discoverer of oxygen,
Joseph Priestley had presciently suggested the
medical application of this new gas: “From the
greater strength and vivacity of the flame of a
candle, in this pure air, it may be conjectured,
that it might be peculiarly salutary to the lungs
in certain morbid cases……..”. He also warned
that too much of this gas may not be good for a
healthy person for its use may cause one to: “ …
live out too fast, and the animal powers be too
soon exhausted in this pure kind of air.”
These early observations encapsulate the two
main concerns about oxygen, its life saving use
and the need for caution when using it.
“Oxygen Therapy is usually defined as the
administration of oxygen at concentrations greater
than those found in ambient air”.
Probably the most widely used therapeutic
agent, oxygen is a drug, with clearly defined
biochemical and physiologic actions, a clear dose
response relationship and clearly recognised adverse
effects. Hence, it should be prescribed like any
other drug with a six-step approach as suggested
by the WHO (1) Define the patient's problem
(2) Specify the therapeutic objective (3) Verify
the suitability of your drug choice (4) Write a
prescription (5) Give information, instructions and
warnings (6) Monitor (and stop?) the treatment.
When oxygen is prescribed for home use, these
steps become even more important, and initial
oxygen administration should supervised.
1. Define the patient's problem and
assess if it can be helped by the
prescription of oxygen.
Indications of long term oxygen therapy
• Arterial oxygen tension (PaO2) ≤ 55 mmHg
(7.3 kPa) or a pulse oxygen saturation (SpO2)
≤ 88%.
• PaO2 ≤ 59 mmHg (7.8kPa) or SpO2 l ≤ 89%,
if there is evidence of cor pulmonale, right
heart failure or erythrocytosis (hematocrit
>55 mmHg).
• Specific situations
A.PaO2 >60 mmHg (7.98 kPa) or SpO2
>90% with lung disease and other clinical
needs such as sleep apnea with nocturnal
desaturation not corrected by CPAP.
B. If the patient is normoxemic at rest but
desaturates during exercise (PaO2 <55
mmHg), oxygen is generally prescribed
during exercise.
2. Specify the therapeutic objective
What is the target SpO2? In COPD this may
be 90-92%, especially if the patient is in
Type 2 respiratory failure, while higher SpO2
targets may be acceptable for patients with
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severe asthma or interstitial lung disease who
rapidly desaturate with mild exertion.
3. Verify the suitability of your drug choice. Ensure
that the administration of oxygen does not lead
to hypercarbiaor otherwise cause harm. Ensure
that the person understands that he/she cannot
smoke or be exposed to a naked flame while
being administered oxygen. Oxygen supports
combustion, rendering it important that care
is exerted around open fires.
4. Write a prescription
As oxygen is a drug, it should be formally
prescribed, including the patient’s name, ID
number, oxygen dose (litres/minute), route
(nasal prongs, mask, partial rebreathing or
non-rebreathing mask etc), and duration. It
should also include the name of the prescriber
including registration number.
5. Give information, instructions and warnings
Ideally, the precautions to be followed should
also be listed or otherwise documented.
6. Monitor (and stop?) the treatment
After starting oxygen, it is important to
monitor the patient to assess if the pre-determined
therapeutic targets have been met, and if there
is emergence of fresh problems, either from the
oxygen itself (e.g. CO2 retention) or from the route
of administration (nasal dryness or crusting). Also
if the condition has improved and oxygen can
be stopped, as oxygen is expensive, inconvenient
and restricts patient mobility and independence.
Responsibilities of the clinician prescribing
Long term oxygen therapy (LTOT) include :Determining the need for LTOT and goal
for therapy: LTOT should be prescribed only
when there is evidence of persistent hypoxemia
in a clinically stable patient on optimal medical
management. Patients who are clinically unstable
or whose medical management is not optimised
should be prescribed oxygen therapy and reassessed
later for their long term oxygen needs.
Patients being assessed for LTOT should
undergo initial arterial blood gas (ABG) sampling
and not be assessed by pulse oximetry alone. This
formal assessment is made after a period of stability
of at least 8 weeks from the last exacerbation, with
two ABG measurements at least 3 weeks apart.
LTOT should be ordered for a minimum period
of 15 hours a day;using it for upto 24 hours may
provide additional benefit.
Flow Rate selection to achieve the target PaO2 /
SpO2 during rest, exercise and sleep. Most patients
are prescribed low flow oxygen at 1-2 L/min. PaO2
should be maintained at 60 mmHg, SpO2 at 8892%. During activity flow rate can be increased
by 1-2 L/min. Ideally, this is done a minute or so
before anticipated exertion, and continued for a
few minutes after exertion, preferably monitoring
with a pulse oximeter.
RespiMirror|Volume VII, Issue I, January-February 2017|
Equipment selection: LTOT can be delivered
via either cylinders or oxygen concentrators, and
can be delivered through a variety of interfaces.
BENEFITS:
Of four RCTs on LTOT in COPD patients,
the NOTT and MRC trial demonstrated improved
survival from LTOT in COPD patients with PaO2
< 60 mmHg, while two other trials that showed
no survival benefit targeted patients with PaO2
< 69 mmHg.
Benefits of LTOT include:
1. Increased survival
2. Improvement in memory, motor coordination,
mood and other somatic symptoms.
3.Reduced pulmonary vascular resistance,
delaying the onset or progression of pulmonary
hypertension and cor pulmonale.
4. Decrease in red cell mass, thereby reducing
complications of polycythemia
5. Increase in exercise capability and endurance,
improved quality of life and decrease in dyspnea
5.
Possibly, reduced exacerbations and
hospitalisations
ADVERSE EFFECTS:
LTOT is not without potential complications:
1)Facial and upper airway burns, though
infrequent, can be serious and life threatening.
Exposure to open flames like gas stoves,
candle, matches while using oxygen is the
most common cause. Presence of facial hair
and use of hair products containing alcohol
or oils are risk factors for burns.
Oxygen related toxicities:
2) Absorptive atelectasis
3) Loss of hypoxic drive resulting in worsening
hypercapnia
4) Oxidative stress and inflammation
5) Peripheral vasoconstriction limiting oxygen
delivery secondary to hyperoxia.
Equipment for home oxygen therapy
The equipment for home oxygen therapy
comprises of three categories of devices• Oxygen source (concentrators ,cylinders and
liquid oxygen)
• Oxygen delivery (cannulae, masks, conservers
and liquid oxygen) and Supplementary
equipment (humidifiers and equipment to
carry oxygen)
Oxygen sources
Home oxygen can be delivered from cylinders,
concentrators or as liquid oxygen. Each of these can
be stationary or portable and the choice depends
upon the activity, patient’s circumstances and cost.
Oxygen concentrators:
An oxygen concentrator is an electrically
driven device which captures room air and passes
it through a zeolite filtering system, removing
... Contd. on page 11
... Contd. from page 10
nitrogen, to supply an oxygen enriched gas mixture
(usually 85%-95%). Oxygen concentrators may
be home based or portable.
Oxygen concentrators deliver flow rates upto
5 L/min, rarely up to 8 L/min, adjustable in 0.5
L/min increments. Flow meters that regulate the
flow can be added to the standard concentrator.
A stationary or home concentrator is powered
by AC current. It can operate continuously
producing higher liter-per-minute flows of oxygen
than portable concentrators. However, it is large,
weighing upto 15 Kg, with built-in wheels so it
can be moved around.
A portable concentrator is smaller, lighter and
has a DC battery power source. It can be charged
from an AC or DC source e.g., car battery, so that
it can be used while travelling in a car, conserving
battery power.
Portable concentrators may be of continuous
or pulse flow types, with the more sophisticated
machines offering both choices.
Continuous Flow vs Pulse Flow
A continuous flow concentrator delivers a
continual flow of oxygen. All home concentrators
provide continuous flow oxygen. A few portable
concentrators can provide continuous flow;
these are usually larger and are placed in a
lightweight wheeled cart for easy transport.
Lighter concentrators (1.5 - 2.5 kg) that can be
carried around in a handbag or backpack usually
offer pulsed mode of oxygen delivery. They
deliver pulses of concentrated oxygen with each
inhalation. This limits permits a smaller battery
and longer battery use after a single charge. They
deliver 3 L/min of continuous oxygen and upto 6
L/min. of pulsed oxygen. As the pulse is triggered
by inspiratory flow, pulsed concentrators cannot
be used with NIV machines.
Concentrators are recommended for patients
using oxygen for more than 15 hours a day i.e., the
typical LTOT patient. Patients should be advised
about the need of changing filters weekly, and
regular servicing of the machine.
• Advantage : Lower costs than oxygen cylinders
when used long term with no need for regular
refilling.
• Disadvantages: High initial cost, need
for proper maintenance, noise, heat and
requirement of a backup source of oxygen
in case of prolonged electricity failure.
Cylinder oxygen
An oxygen cylinder is a metal container(steel or
other alloys of aluminium or titanium, containing)
with oxygen under high pressure. The higher the
pressure,the greater is the amount of oxygen that
can be compressed into the space of the cylinder.
Oxygen cylinders come in different capacities
ranging from a small portable to a large static
cylinder. The pressure varies between 12,000 –
17,000 kPa between cylinders. The pressure is also
displayed in pounds per square inch(PSI). Oxygen
cylinders have a black body with white top.
The cylinder is connected to a flow and
pressure regulator pin index system which
ensures appropriate connections and safety. A
safety outlet is fitted between the block and the
cylinder neck which melts at
low temperatures, allowing the
escape of gas in case of a fire. The
large cylinder weighs around 150
pounds, contains over 6500 liters
of oxygen. Used continuously
at a flow rate of 2L/min, it lasts
for over 2 days. Small portable
cylinders weigh1.6 -9 kg.
• Advantages : Low cost,
widely available and good
back up facility. The gas
can be stored for a long
time. Portable cylinders can
be refilled at home from a
liquid oxygen source using a special valve.
• Disadvantages : Bulky, heavy and need regular
refilling.
COMPLICATIONS
• Explosion
• Oxygen toxicity
• Barotrauma
Liquid oxygen is generally not available in
India for home use but is available in hospitals.
Conventional liquid oxygen vessels do not require
a power source and hence are particularly useful
in areas with frequent power outages. When a
conventional liquid oxygen base unit is used as
primary oxygen source it usually needs to be filled
every 2 weeks.
BTS guidelines state:
• Portable oxygen should be delivered by
whatever mode is best suited to the individual
needs of the patient to increase the daily
amount of oxygen used and activity levels in
mobile patients (Grade C).
• The type of portable device selected should
balance patient factors with cost effectiveness,
resources and safety.
OXYGEN DELIVERY
Interfaces used for home oxygen delivery include
nasal cannulae and face masks or Venturi masks.
Trans-tracheal delivery is used rarely in home oxygen
delivery. In addition, oxygen conserving devices
may be used to facilitate oxygen delivery.
Nasal cannulae are the most common interface
for oxygen delivery at home. They are made of
silicone/plastic striped tubing, light weight
comfortable and well-tolerated.
Oxygen masks
Oxygen masks are made of soft plastic and fit
over mouth and nose with elasticated straps. Venturi
masks deliver controlled oxygen concentration and
are particularly useful in patients with hypercapnic
respiratory failure.
BTS Recommendations
• Nasal cannulae should be considered as the
first choice of delivery device for patient
requiring home oxygen therapy. Some patients
benefit from Venturi mask. (Grade D)
Oxygen conserving devices
Oxygen conserving devices deliver oxygen
during inspiration only, and reducing oxygen
wasted during expiration, thus enabling cylinders
to last longer compared to constant flow. Oxygen
conserving devices are not easily available in India.
Reservoir cannulae and transtracheal catheters
are oxygen conserving devices.
Reservoir cannulas function by storing oxygen
during exhalation in the reservoir space, thus
making oxygen available as a bolus upon the
onset of the next inhalation. They increase the
percent of oxygen without increasing the flow
from oxygen source.
Reservoir cannulas are available in three
configurations: mustache ( reservoir beneath the
nose), pendant (resting on the chest), and fluidic
mustache reservoir which operates at flow rates
from 1-16 L/min thus acting as both a conserving
and high flow device.
Trans tracheal catheters
Trans tracheal catheters deliver oxygen
directly into the trachea via a catheter inserted
percutaneously between the second and third
tracheal ring. Continuously flowing oxygen is
stored in the upper airways and trachea at endexhalation and is delivered during early inhalation,
thus bypassing some of the upper airways’ dead
space. In the home setting, for selected individualist
can be a valuable method of oxygen delivery but
is rarely used as it requires training, dedicated
support and can be associated with complications
like infection, catheter displacement, and blockage
of the catheter by secretions.
BTS recommendations state:
• Oxygen conserving devices can be used in
home oxygen patients requiring high flow
rates to increase the time the cylinder will last.
(Grade B)
• Oxygen-conserving devices should be considered
in patients who are active outside the home,
following an ambulatory oxygen assessment.
The doctor prescribing home oxygen should be
aware of the capacity of various devices to deliver
oxygen to the patient.
Modified from: Guide to Prescribing Home
Oxygen by Thomas L. Petty, National Lung Health
Education Program.
Conclusions
In the present day scenario a variety of oxygen
delivery sources and delivery devices are available.
It is important to emphasize that oxygen is not
merely a gas, it is a drug, and like any drug should be
prescribed with abundant caution. The physician
prescribing oxygen therapy should be familiar with
the oxygen delivery devices and sources available
and individualise each prescription. nn
|Volume VII, Issue I, January-February 2017|RespiMirror 11
- To read the previous issues of Respimirror visit www.crfindia.com -
Chest Research Foundation
Marigold Premises, Survey No 15,
Kalyaninagar, Pune 411014, Maharashtra, INDIA.
Phone: +91 20 27035361/66208053
Fax: : +91 20 27035371. Website: www.crfindia.com
NOTE : FOR PRIVATE CIRCULATION ONLY.
For your feedback / queries write to [email protected]
Do you want to conduct a training programme in your city?
Please write to Dr. Monica Barne at [email protected]
Edited by : Ms. Madhuragauri Shevade
Published by : Chest Research Foundation, Pune
Disclaimer: The images are taken from google images / provided by authors.
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RespiMirror|Volume VII, Issue I, January-February 2017|