Download oxygen - Dent-Ed

A Review of the Cardiovascular and R i
Respiratory Systems
S
The Heart
The Heart
• ..is a four chambered pump that circulates blood h i l
bl d
throughout the body
• At rest the heart beats about 72 beats per minute (BPM) (men), 80 BPM (women)
Our pulse increases when we
• Our pulse increases when we are nervous, fearful (tachycardia)
• A pulse greater than 100 BPM A pulse greater than 100 BPM
is considered rapid
Pulse Baseline
• The pulse is the only vital sign to change (tachycardia) when a patient experiences an p
p
adverse reaction to nitrous oxide,
• Unless you have a baseline, Unless you have a baseline,
you will not know if they have tachycardia, so ...
• A patient
A patient’ss normal pulse normal pulse
should be part of your examination. Practice Taking a Pulse
• Place the patient’s left palm face up
• Firmly but gently place two fingers on wrist b l
below the thumb
h h b
• Count the pulse for 15 seconds
d
• Multiply by 4
hemoglobin
• Our
Our body uses oxygen as fuel body uses oxygen as fuel
and gives off carbon dioxide (co2) as a biproduct
• Hemoglobin, a component of H
l bi
t f
red blood cells, carries oxygen to the cells
• Oxygen rich hemoglobin is called “oxyhemoglobin” and is “red”.
red .
• Oxygen depleted hemoglobin or “reduced hemoglobin” is slightly blue.
blue
Blood Flow
Blood Flow
• Reduced hemoglobin returns to the right side of the heart via the
the right side of the heart via the superior vena cava
• It is pumped to the lungs via the pulmonary artery where it is oxygenated (converted to oxyhemoglobin)
• Oxyhemoglobin returns to the left side of the heart via the pulmonary vein and is pumped to the body via the aorta
Measuring Oxygen
• A pulse oximeter measures blood oxygenation by analyzing the blood color
• If the amount of oxyhemoglobin falls too low, (ie, the blood is too blue) an alarm can go off.
• Breathing inadequate levels of oxygen, a condition called hypoxia will decrease oxyhemoglobin,
• Under certain circumstances, high levels of nitrous oxide can cause hypoxia
ASA recommendation
• The American Society of Anesthesiologists recommends that dentists who routinely give nitrous oxide in concentrations 50% or higher use a pulse oximeter!
• It’s not the law but if you don’t follow the ’
h l b f
d ’ f ll
h
recommendation and you have a legal problem, chances of winning decrease!
chances of winning decrease!
The Air We Breathe
• Room air contains 21% oxygen, 78% nitrogen, .03% carbon
78% nitrogen, .03% carbon dioxide.
• Cells use oxygen for fuel, give off Cells use oxygen for fuel give off
carbon dioxide as a biproduct. Plants use carbon dioxide as fuel
Plants use carbon dioxide as fuel source and give off oxygen as a biproduct.
biproduct
• Nitrogen is inert – has no known f ti
function
•
What Makes Us Breath?
What Makes Us Breath? • In healthy individuals, carbon dioxide (CO2) sensors i h b i di i l
in the brain drive involuntary breathing, so b
hi
normally we breathe to reduce CO2 in our bodies,
• A backup system, the carotid body, measures the A backup system the carotid body measures the
amount of oxygen in the blood.
y
y p
• The carotid body drives involuntary respiration in patients with COPD, emphysema,
• Why is this important?..
• A healthy runner breathes f
faster to give off more CO2,
i
ff
CO2
• ..But a person with emphysema breathes faster
emphysema breathes faster to take in more oxygen!
• Remember this when treating emphysema patients, because..
• You are giving them lots of You are giving them lots of
oxygen so their carotid body is happy and may say “you can stop breathing now.” Not b
h
”
a good thing!!
Respiration Anatomy
Respiration Anatomy
• A breath occurs when the di h
diaphragm contracts and t t
d
relaxes,
g
g
• The lungs enlarge when the diaphragm contracts, pulling air into lungs,
• When the diaphragm relaxes, When the diaphragm relaxes
the lungs relax, forcing air out of the lungs.
• At rest, an adult takes 14 –
At rest an adult takes 14 20 20
breaths per minute (BPM) at rest, a child breathes a little faster
• Air
Air moves from trachea, moves from trachea
to the bronchus, to the bronchioles and finally to
bronchioles, and finally to the alveolar sacs where diffusion takes place
diffusion takes place. Alveolar sacs
• Alveolar sacs resemble a cluster of grapes
cluster of grapes,
• There are 300 million alveolar sacs in human lungs
• Alveolar sacs are surrounded by blood y
vessels.
• Components of air pass through the walls of the
through the walls of the alveolar sacs into blood by the process of “diffusion”
diffusion and are and are
carried throughout body. What is Diffusion?
What is Diffusion?
• “Diffusion” is the movement of gas across a membrane.
• Movement occurs from an area of high pressure to an area of fh h
f
low pressure until the pressure is OXYGEN
equal on both sides.
equal on both sides. • With respiration, the wall of the alveolar sac is the membrane that oxygen (and nitrous oxide ) crosses.
OXYGEN
Alveolar Sacs Under A Microscope
Red Blood Cells
Alveolar sacs
Gases we breathe diffuses through the wall of the alveolar sacs.
Remember, there are 300 million of these!
• During inspiration, air g p
,
(oxygen and nitrogen) enters the alveolar sacs.
• Oxygen diffuses into blood and attaches to hemoglobin • Nitrogen diffuses into blood Nit
diff
i t bl d
but combines with nothing.
• During expiration, carbon During expiration carbon
dioxide enters the alveolar sacs and is exhaled.
CO2
O2
N
So, what happens to the nitrogen?
So, what happens to the nitrogen?
• After
After entering the bloodstream, entering the bloodstream,
nitrogen leaves the bloodstream quickly because it is fairly insoluble in blood.
• It diffuses into body cavities like sinuses, the middle ear, the intestines, the cranium, etc.
intestines, the cranium, etc.
• It does so until the pressure of nitrogen in the cavity is the same as in blood
in blood.
• If I looked in your middle ear right now, I’d find a lot of nitrogen!
What happens when we administer N2O ?
• Nitrogen is replaced with N2O, so the nitrogen gas pressure in the lungs decreases, causing..
• Nitrogen to diffuse from g
the blood into the lungs to be exhaled, causing..
• A drop of nitrogen A drop of nitrogen
pressure in the blood, causing..
• Nitrogen in the body Nitrogen in the body
cavities to diffuse back into the blood.
N
O2
N2O
• Nitrous
Nitrous oxide is even less oxide is even less
soluble in blood than nitrogen, therefore..
g ,
• N2O enters body spaces faster than nitrogen leaves,
g
,
• The net result is an increased pressure in the body space!
pressure in the body space!
• Patients may feel ear, sinus head pressure so warn them!
head pressure, so warn them! It’s only temporary.
Respiration Terms To Know
Respiration Terms To Know
•
•
•
•
•
Tidal volume
Tidal
volume
Inspiratory reserve volume
Expiratory reserve volume
i
l
Residual volume Total lung capacity
Tidal Volume
• ..is the amount of air inhaled and exhaled during normal
respirations
• For adults, tidal volume is d l
d l l
normally 6 – 8 liters per minute
• For children, tidal volume is 4‐6 For children tidal volume is 4 6
liters per minute
q p
(
• Nitrous oxide equipment (the flowmeter) can measure tidal volume in liters per minute. Flowmeter measures liters per minute of gas flow
Inspiratory Reserve Volume
..is the additional amount of air i h l dd i
inhaled during maximum i
inhalation (like smelling a flower)
• The effect of a maximum Th ff t f
i
inhalation is to increase the concentration of any substance
concentration of any substance inhaled.
• However, a maximum inhalation However, a maximum inhalation
interrupts normal respiration, and breathing pauses.
Take a Deep Breath
Take a Deep Breath
• Take a deep breath and see if you don’t pause normal breathing for a few seconds
• Patients receiving nitrous oxide may take deep breaths to experience more euphoria.
• However, after a deep breath, they pause , and nitrous However after a deep breath they pause and nitrous
oxide concentrations drop,
• The result is an “up and down” effect, like a roller coaster.
coaster
Roller Coaster Effect
• Patients
Patients sometimes say nitrous sometimes say nitrous
oxide makes them nauseated,
• Abnormal breathing patterns may Abnormal breathing patterns may
be the problem, • tell your patients to breath normally tell your patients to breath normally
to avoid the “roller coaster” effect and the resulting consequences! Other Respiratory Terms
Other Respiratory Terms
Expiratory reserve p
y
volume: The additional air exhaled during maximum exhalation
maximum exhalation
Residual Volume: air remaining after
remaining after maximum exhalation
Total lung capacity: total amount of air lungs can hold Total Lung Capacity
Total Lung Capacity
• Individuals with a large total g
lung capacity (Athletes, exercise enthusiasts, etc,) receive a higher dose of nitrous oxide per body weight,
• Consider a lower percentage of C id
l
t
f
nitrous oxide for such patients.
Establishing Equilibrium
Establishing Equilibrium
• When administering nitrous oxide, the gas passes from g
g p
the lungs to the blood and then to body cavities including the cranium where it produces its effects,
• This process continues until the partial pressures of N2O in the lungs, blood and body cavity are the same.
• Equal pressure in all three is called “equilibrium” and occurs within one to two minutes.
Establishing CORRECT equilibrium
Establishing CORRECT equilibrium
• When
When administering nitrous oxide, allow administering nitrous oxide, allow
equilibrium to be reached before titrating (increasing or decreasing) more nitrous oxide
• If you do not allow equilibrium to be reached with each increase in dose, you may exceed the comfort level of the patient.
What happens when N2O is terminated?
What happens when N
O is terminated?
• When nitrous oxide is terminated, the partial pressure in the lungs drops and i l
i h l
d
d
N2O rapidly diffuses out of blood, filling the lungs with N2O
the lungs with N2O.
• Oxygen content in lungs may be decreased because so much nitrous
decreased because so much nitrous oxide fills the lungs,
• This condition is called This condition is called “diffusion
diffusion hypoxia”
• The symptoms of diffusion hypoxia can y p
yp
be headache, hallucinations, nausea.
Diffusion Hypoxia
yp
• Research disputes whether diffusion hypoxia can occur with N2O/O2 analgesia, nonetheless..
• To avoid the possibility of diffusion hypoxia, y
p
yg
terminate N20 slowly, then post oxygenate for 3 – 5 minutes