Download Ventilation and ED Monitoring

Ventilation and ED
Monitoring
for Dummies…
Todd Ring
July 24/03
Objectives
Invasive (IPPV) vs. Non Invasive Positive
(NPPV) Pressure Ventilation
The different modes of IPPV and typical
ventilator settings
CPAP vs. BPAP
Clinical scenarios requiring mechanical
ventilation
Pulse oximetry, non-invasive BP monitoring
and capnography
Case 1: “Dumb” MotorBiker
28 yo male, riding in Calgary, no helmet,
crashes, unconscious, EMS scoop and
run, in ED no spontaneous respirations,
bag and mask ventilation.
What to do?
Indications for Mechanical Ventilation?
Indications for
Mechanical Ventilation
Apnea
Acute ventilatory failure (2/4)
1.
2.
•
•
•
•
3.
4.
5.
Acute dyspnea
RA PO2 < 50
PaCO2 > 50
Significant respiratory acidemia
Impending acute ventilatory failure
Acute hypoxemic respiratory failure
+/- Airway compromise
Case 1: Cont’d
The patient was successfully intubated.
The RT is now “bagging” the patient
manually and asks you to give orders
for mechanical ventilation.
What mode to choose?
Where do you set your ventilator
parameters?
Invasive Mechanical
Ventilation
Volume vs. Pressure control
Spontaneous, controlled or combined
ventilation
Invasive Mechanical
Ventilation
Modes used in the ED:
Assist Control (A/C)
Pressure Support (PSV)
Simulated Intermittent Mechanical
Ventilation (SIMV)
+/- Pressure Control (PCV)
Assist Control Ventilation
(Volume Control)
In volume control ventilation (VCV) the
mechanically ventilated patient receives a
preset volume of gas with every breath.
VCV is frequently administered in an assist
control (A/C) environment


If the patient is apneic the ventilator will deliver a
preset rate
If the patient is breathing they are able to initiate
or trigger a greater then the preset number of
breaths.
A/C Ventilation
Parameters for A/C
TV
Freq
FiO2
PEEP
6 – 8 mls/kg IBW
10 – 18 bpm
.4 – .6
5 cm H2O
Other parameters set in A/C are:
Flow
Trigger Sensitivity
Disadvantages of A/C
Patients receive a mandatory breath every
time they trigger the ventilator therefore
hypocapnia with respiratory alkalemia may
occur
Uncomfortable for patient


Receive mandatory breath every time patient
triggers ventilator
Patient unable to vary volume and flow
Results in patient-ventilator asynchrony
Heavy sedation required which delays
weaning
Observations to make when
using A/C
Is the patient triggering the ventilator?


If the objective of ventilation is to rest the patient,
frequent triggering may require significant work by
the patient
patient component of the inspiratory work in the
A/C mode can be significant (30 to 50%)
When delivering a preset volume of gas, the
pressure in the lungs varies with changes in
lung stiffness (compliance) and airway
resistance

airway pressures should be closely monitored and
when they consistently exceed 35 cm H2O a
change in ventilating strategy should generally
Case 2: Mrs. Seizure
35 yo female, former EtOH abuse,
known EtOH seizure x’s 2, seizure free
for 5 years, no meds, presents to Olds
seizes in EDstatus epilepticus x’s 1h,
STARS RSI intubation. Arrives @ FMC
ED, GCS (E=1, M=5), spontaneous
respirations.
What mode of MV would you choose?
Pressure Support
Ventilation
In pressure support ventilation (PSV) the
patient receives a preset pressure of gas with
every breath
The patient initiates every breath
The preset pressure is rapidly achieved and
maintained throughout inspiration
Volume, flow and duration of inspiration are
variable and change according to patient
demand.
Pressure Support
Ventilation
PSV was originally introduced as a
spontaneous mode that gave a small
amount of pressure support designed to
overcome the work of breathing
imposed by endotracheal tube
resistance.

The amount of pressure required to
overcome the resistance of an 8mmID
endotracheal tube is between 5 and 10
cmH2O.
Pressure Support
Ventilation
Parameters in PSV
PS:
FI02:
PEEP:
5 – 35 cm H20
0.40 – 0.60
5 cm H20
Other parameters set in PSV are:
Trigger Sensitivity (pressure or flow)
Ramp – PSV has no flow control and typically
delivers high initial flows.
PSV
PSV is usually used during the recovery
phase of respiratory failure as a weaning
mode.
Levels are set at values < 15 cmH20 and
titrated down as tolerated
Patients are typically extubated at PSV levels
of between 5 and 10 cmH20
The lack of mandatory breaths when using
PSV can result in lower mean airway
pressures which can result in a decrease in a
patient’s PaO2
Disadvantages of PSV
Potential for increased work of
breathing at lower levels of PSV
Reduction in mean airway pressure with
decreased patient oxygenation
Observations
Patient tidal volume should be above 250 –
350 mls (5 mls/kg) as a minimum.

When the level of PSV is inadequate the VT will
drop below this range.
Patient rate (f)

When low-level PSV is not being tolerated the VT
falls and the f rises. Rates greater than 35 bpm
are generally undesirable and signal the need for
higher levels of PSV or a switch to a mandatory
mode (VCV, A/C or PCV).
Case 1: The sequale…
The RT from case one comes up to you
annoyed and states “we need more
sedation/paralysis for the motor-biker
who hit his head. He is starting to fight
the ventilator.”
Do you tell the nurse to give more
sedation/paralytic or is there something
else you can do?
SIMV
The patient gets a preset number of
mandatory breaths (A/C) volume-controlled
and they are synchronized with the patient’s
breathing

Synchronization means that the mandatory breath
will be delivered when triggered by the patient.
The patient will only get the set number of
mandatory breaths per minute.
If the patient’s rate exceeds the set rate the
additional breaths will be spontaneous
breaths

Usually pressure supported
SIMV
TODD’S RULE: SIMV = A/C + PS
Parameters in SIMV
Freq:
8 to 12 bpm
VT: 6 – 8 mls/kg IBW
PS:
5 – 20 cmH20
FIO2:
0.40 to 0.60
PEEP: 5 cm H20
Additional Parameters in SIMV:
Flow
Sensitivity
Disadvantages of SIMV
Mandatory support can be set
inappropriately low when SIMV is used
as the vehicle for VCV or PCV.
Observations in SIMV
Patients total rate
Tidal volume during spontaneous
breaths
Airway pressures during VCV
mandatory breaths
Careful assessment of adequate
mandatory support
Pressure Control
Ventilation (PCV)
A mode in which the patient receives a preset
system pressure, which is rapidly achieved by
high flow and this pressure is maintained
throughout inspiration
Administered in an assist control (A/C)
environment


In the apneic patient a preset rate is delivered
Patients who are breathing are able to initiate or
trigger at greater than the preset number of
breaths
With pressure set instead of volume, the
volume the patient receives will vary as a
PCV
Parameters in PCV
Level of pressure control: 20 to 35 cmH20
Freq:
10 – 18 bpm
I:E ratio: 1:2 to 1:3
FIO2:
0.40 to 0.60
PEEP: 5 cmH20
Additional parameters in PCV:
Trigger Sensitivity (pressure or flow)
Inspiratory time - determined by the rate and
I:E ratio control settings
Ramp adjustment
PCV
PCV is the ideal mandatory mode to use
when ventilating patients who have high
airway pressures using VCV

Because the pressure is preset, a safe upper limit
can be adjusted
PCV is often considered for a lung protective
strategy centered on regulation of peak,
mean and end expiratory pressures
It is often considered as the mode of choice
for patients with acute lung injury or ARDS
Disadvantages of PCV
Inability to maintain a constant tidal volume
and PaCO2
When compliance decreases and resistance
increases, tidal volume falls and PaCO2 may
rise (hypercapnia)
The set I: E ratios are not maintained when
the patient rate exceeds set rate (when in A/C
mode) resulting in shortening expiratory time
which leads to increasing Auto PEEP,
decreasing tidal volumes and increasing
asynchrony.
Observations in PCV
Careful monitoring of tidal volume
Actual patient rate

When patient rate significantly exceeds set
rate I: E ratios will inverse.
Potential Adverse
Effects of IPPV
Increased mean intrathoracic pressure
Decreased venous return and cardiac output
Increased ventilation/perfusion ratio
Decreased renal blood flow and glomerular filtration
rate with fluid retention
Air trapping and intrinsic positive end-expiratory
pressure (iPEEP, auto-PEEP)
Barotrauma
Nosocomial infections of the lungs and sinuses
Respiratory alkalosis
Agitation and increased respiratory distress
Increased work of breathing
Ventilator Settings
Rule of 10’s
VT
10ml/kg IBW
 Freq 10 bpm
 FiO2 100%

FiO2: start high and wean down
VT: Between 5 – 10 ml/kg; be aware of
lung compliance
More Ventilator
Settings…
Respiratory Rate: wide range; increase or
decrease according to ventilatory parameters
Inspiratory Pressure: < 35 cm H2O;
generally 10 – 30
Pressure Support: 5 – 30 cm H2O; when
weaning pressures should be < 10 cm
Trigger Sensitivity: amount of negative
pressure that the patient must establish for
the machine to sense patient effort and thus
deliver a breath; generally −1 to −2 cm H2O
Even More Ventilator
Settings…
PEEP: the level of positive pressure that
is maintained in the airways at the end
of expiration; range from 5–20 mm H2O
I:E ratio: generally set at 1:2; may
increase to facilitate complete expiration
in obstructive lung disease
PEEP
Preprogrammed level of positive pressure
maintained at the end of exhalation
Improvement in oxygenation with increased
PEEP
The advantages of PEEP are balanced by its
potential detrimental effects

A worsening of gas exchange is possible if an
increase in dead space ventilation occurs
Auto-PEEP
A phenomenon that is seen most often
in patients with airflow limitation or with
high respiratory rates combined with a
shortened expiratory time. In this
situation, expiration to functional
residual capacity is not accomplished
before the next inspiratory cycle begins,
resulting in dynamic hyperinflation.
Case 3: Mrs. Failure
80 yo female, CAD, MI, CHF, CRF on dialysis
(missed today’s run). Presents to PLC ED via
EMS acutely SOB (“wants to die breathing so
bad”). SaO2 88 % 5L O295% 15 L NRB.
Clinically no failure. CXR bilateral effusions,
CHF. ABG 7.30/65/60/28.
What to do?
CPAP vs. BPAP?
Non-Invasive Positive
Pressure Ventilation
(NPPV)
Positive pressure is delivered by way of a
tightly fitting mask
In 1938 continuous positive airway pressure
(CPAP) shown to be effective for the
treatment of acute pulmonary edema
Nasal CPAP mask for the treatment of
obstructive sleep apnea in the 1980s
In the 1990’s an alternative to endotracheal
intubation in acute respiratory failure
Advantages of NPPV
Avoids complications that are related to
endotracheal intubation and mechanical
ventilation and the loss of airway defenses
caused by endotracheal intubation
NPPV is not as invasive as endotracheal
intubation; it offers a means of temporarily
supporting some patients who do not wish to
have aggressive or prolonged ventilatory
means used in their care.
Evidence?
A case-controlled study by Girou et al found
the use of NPPV in critically ill patients with
acute COPD and CHF exacerbations was
associated with a lower risk for pulmonary
infections, lower antibiotic use, shorter length
of stay, and lower mortality
Girou E, Schortgen F, Delclaux C, et al. Association of noninvasive
ventilation with nosocomial infections and survival in critically ill patients.
JAMA 2000;284:2361
CPAP
Delivers a constant level of positive pressure
throughout the respiratory cycle
Main use is for hypoxemic respiratory failure
Improve oxygenation by:

increasing the mean airway pressure, increasing
functional residual capacity, and opening
underventilated and collapsed alveoli, enhancing
gas exchange and oxygenation
CPAP
Initiated between 0 – 15 cm H2O
Level is set low initially and slowly
increased to allow adequate
oxygenation with as low an FIO2 as
possible
Important to check the mask for leaks
BPAP
Two different pressure levels are cycled
between inspiration and expiration
Inspiratory pressure (IPAP) > expiratory
pressure (EPAP)
The primary benefit of this mode over CPAP
is in patients with ventilatory fatigue or
failure

increases airway pressure in expiration and
decreases WOB by aiding inspiration
Inspiratory pressure set at 8 – 20 cm H2O and
expiratory pressure is set at 0 – 15 cm H2O
Complications of NPPV
Often minor:

nasal congestion, eye irritation, discomfort, and
pressure necrosis caused by the tight mask fit
Airway protection must be addressed in
patients with altered sensorium

especially with tight fitting mouth mask
Gastric distension is uncommon unless
pressures exceed 20–25 cm H2O
NPPV
The most common reason for failure of NPPV
is patient intolerance
Key to success is adequate patient
preparation and acclimatization to the device
Choice of mask depends on familiarity and
availability


Nasal masks allow patients to communicate
verbally, but they suffer from air leaks unless the
patient keeps his or her mouth closed.
Full-face masks offer the tightest seal but can be
hazardous in patients who cannot completely
protect their airway or who are at risk for vomiting
CPAP vs. BPAP
In patients with hypoventilatory respiratory
failure, BPAP should be the preferred mode
because of its theoretic advantage in
providing ventilatory assistance and therefore
decreasing the work of breathing.
With hypoxemic ventilatory failure, CPAP and
BPAP should be similarly efficacious given
that both improve oxygenation

Though BPAP has theoretic advantages over
CPAP, the choice of modes should be based on
familiarity with and patient tolerance of a given
mode
Case 4: Mr. Puff
76 yo male, known COPD, seen at PLC
ED 3 times in prior week for SOB. Dx:
COPD exacerbation. Presents SOB
SaO2 90 % RA, 95 % 10 L O2. Working
++ hard to breath. Initial ABG
7.30/65/70/30
What ventilation strategy would you
employ?
COPD
1st line = consideration of NPPV
Good evidence that NPPV decreases
incidence of the need for intubation and
invasive ventilation


Bott J, Carroll MP, Conway JH, et al. Randomised controlled trial of nasal
ventilation in acute ventilatory failure due to chronic obstructive airways
disease. Lancet 1993;341:1555
Celikel T, Sungur M, Ceyhan B, et al. Comparison of noninvasive positive
pressure ventilation with standard medical therapy in hypercapnic acute
respiratory failure. Chest 1998;114:1636
Case 4: Mr. Puff Breath’s
on…
You initiate BPAP. One hour later Mr.
Puff is beginning to tire despite
continuous ventolin and atrovent, and 4
mg IV MgSO4. You repeat the ABG:
7.15/60/138/30
What is your next step?
COPD: Goals of IPPV
Gradually correct respiratory acidosis (over
hours)
Normalization of lung volume
Decrease auto-PEEP by:





higher flow rates (eg, 100 L/min) during
inspiration
increasing I:E ratio (1:3 to 1:4)
occasionally disconnecting the patient from the
ventilator to allowing complete exhalation
use of bronchodilators and steroids
adding extrinsic PEEP (no more than auto-PEEP)
to decrease work required to maintain auto-PEEP
Asthma
Asthmatics with impending respiratory
failure demonstrate some of the most
difficult management issues with regard
to mechanical ventilation
Asthma is predominantly a problem with
expiration with increased airway
resistance resulting in pulmonary
hyperinflation
Asthma
Mechanical ventilation can help decrease the
work of breathing BUT intubation exaggerates
expiratory obstruction by the fixed diameter of
the endotracheal tube
Potential for significant auto-PEEP and
decreased venous return
Therefore, all attempts should be made to
avoid the initiation of mechanical
ventilation in asthmatic patients except as
a last resort
NPPV in Asthmatics
NPPV has not been studied prospectively
Meduri described the use of BPAP in 17
patients with severe asthma and impending
respiratory failure. Intubation was averted in
all but two patients and no complications
were observed.
Meduri G, Cook T, Turner R, et al. Noninvasive positive pressure
ventilation in status asthmaticus. Chest 1996;110:767
Mechanical Ventilation
and Asthma
Limit the negative effects of positive pressure
Allow maximal expiratory time to minimize the
chances of auto-PEEP and resultant dynamic
pulmonary hyperinflation
When pulmonary pressures remain elevated,
deep sedation and neuromuscular blockade
should be considered in an effort to minimize
ventilator asynchrony
In severe cases controlled hypoventilation
with permissive hypercapnea should be
considered
Case 3: Mrs. Failure
continues to fail…
Despite BPAP for 45 min Mrs. Failure
shows no signs of improvement. Her O2
sat has slowly been decreasing (now
85%) on 15 L and she is starting to
become obtunded. You repeat her ABG
7.25/55/65/30
What is your next step?
Cardiogenic Pulmonary
Edema
A systematic review of CPAP in CHF revealed
a pooled decrease in need for intubation of
26% and a trend toward decreased mortality
Pang D, Keenan SP, Cook DJ, et al. The effect of positive pressure airway support on
mortality and the need for intubation in cardiogenic pulmonary edema: a systematic
review. Chest 1998;114:1185
One randomized trial compared CPAP with
BPAP in a total of 27 patients and found a
more rapid improvement in ventilatory
parameters (PaCO2, pH) and vital signs with
BPAP than CPAP in acute pulmonary edema
Mehta S, Jay GD, Woolard RH, et al. Randomized, prospective trial of bilevel versus
continuous positive airway pressure in acute pulmonary edema. Crit Care Med
1997;25:620
Mechanical Ventilation
in CHF
In mechanically ventilated patients PEEP can
help to reduce extravascular lung water and
thus can result in improved oxygenation
However, PEEP can have an adverse effect
in patients with CHF who are in cardiogenic
shock by decreasing pulmonary venous
return
Compromise is to use only enough PEEP to
decrease FiO2 to less than 60 %
Acute Lung Injury (ALI)
and Acute Respiratory
Distress Syndrome (ARDS)
One small study looked at the use of
NPPV in 10 hemodynamically stable
patients with ALI/ARDS and averted
intubation in 6 of the 10 patients
Rocker GM, Mackenzie MG, Williams B, et al. Noninvasive positive
pressure ventilation: successful outcome in patients with acute lung
injury/ARDS. Chest 1999;115:173
Most cases of ALI and ARDS require
invasive mechanical ventilation
ALI/ARDS
Indication for PCV
Use small tidal volumes (6 mL/kg)
Keep plateau pressure ≤30 cm H2O.
Increase PEEP and RR to help
decrease tidal volumes
Watch for significant amounts of autoPEEP with the increase in respiratory
rate
Physiologic Changes in
Pregnancy
Mother has reduced oxygen reserve
(decreased FRC) and increased oxygen
consumption (15 – 20 %)
The fetus is very vulnerable to any reduction
in oxygen delivery

30% decrease in uterine blood flow with maternal
hypoxia
Higher risk of aspiration in pregnancy
Pregnant patient = difficult airway
Physiologic respiratory alkalosis (PaCO2 of
30 mm Hg) in the last stage of pregnancy
Mechanical Ventilation
in Pregnancy
Rapid sequence induction is
recommended for intubation
Increase tidal volumes when ventilating
Hyperventilate to maintain physiologic
respiratory alkalosis
ED Monitoring
Clinical observation
Routine vital sign measurement
Electrocardiographic monitoring
Pulse oximetry
End-tidal carbon dioxide (CO2 )
measurement
Noninvasive blood pressure (BP)
measurement
Non-Invasive Blood
Pressure Monitoring
Use a detection system based on auscultatory,
oscillometric, or Doppler principles
Automatic oscillometric devices determine BP by
electronically determining the pulse amplitude




Cuff inflated at predetermined intervals to a preset level
Cuff deflated sensing the amplitude of oscillations
Abrupt increase in the magnitude of the oscillation is
the systolic pressure.
The point where there is no longer an alteration in the
magnitude of the oscillation is the diastolic pressure.
The mean arterial pressure (MAP) is the cuff pressure
at the point of largest oscillation
Noninvasive BP
Monitoring
More accurate, precise, and reliable than
auscultation in patients with very low or high
BP
Limitations common to regular BP
measurement

obese arms, uncooperative moving patients, and
those with very high or very low BP
Cycle length of the inflation-deflation
sequence in the older machines was
exceedingly long and led to frequent failure;
resolved in newer machines
Indications for Invasive
Monitoring
1.
2.
Exceedingly high (>250 mm Hg systolic) or
low (<80 mm Hg systolic) pressures
Patients who are rapidly going into shock

3.
4.
best chance to insert an arterial line may be in
the ED while the arterial pulse is still palpable
Anatomic indications in critically ill patients
with either has no limb or no suitable limb
(e.g., too obese) to undertake conventional
measurement
Frequent arterial sampling is required
Pulse Oximetry
Noninvasive and continuous means of rapidly
determining arterial oxygen saturation and its
changes
Based on differences in the optical
transmission spectrum of oxygenated and
deoxygenated hemoglobin
Uses Beer Lambert Law = relates the
concentration of a solute to the intensity of
light transmitted through a solution
Light absorption is divided into a pulsatile
(AC) component (arterial blood) and a nonpulsatile (venous and capillary)
Limitations of Pulse
Oximetry
Severe vasoconstriction (e.g., shock,
hypothermia)
Excessive movement
Synthetic fingernails and nail polish
Severe anemia
Presence of abnormal hemoglobins

Carboxy and Methemoglobin
COHgb and MetHgb
Pulse oximeter senses COHgb as
oxyhemoglobin and therefore gives an
erroneously high SaO2
MetHgb absorbs light at both red and IR
wavelengths therefore the net effect is a
reading of 85 %
Caution with Pulse
Oximetry
Does not give any information with
regards to adequate ventilation
Capnography/
Capnogram
The measurement and display of CO2
concentrations on a visual display
A. Normal tracing
A-B: inspiratory
phase; B-C:
transnition of
inspiration to
expiration; C-D:
alveloar plateua; DA: inspiratory
downstroke; D: end
tidal point
C. Pt.-vent
asynchrony
-curare cleft =
spontaneous
breath
Capnogram
B. Obstructive
lung disease
D. Endotracheal
cuff leak
Capnometers
Either sidestream (ED) or mainstream in
design
Sidestream capnometers aspire a sample of
gas through a small catheter into a measuring
chamber


lightweight and can be used in intubated and nonintubated patients
disadvantages include plugging by secretions, 2or 3-second delays in response time, and air
leaks, which can dilute the sample
Capnometers
Colorimetric capnometers use pH-sensitive
filter paper impregnated with metacresol
purple, which changes color from purple (<4
mm Hg CO2 ) to tan (4 to 15 mm Hg CO2 ) to
yellow (>20 mm Hg CO2 ) depending on the
concentration of CO2


Yellow = yes (in the right place)
Purple = poor (wrong tube)
The indicator is inserted between the
endotracheal tube and the ventilator bag

detects changes on a breath-by-breath basis
Uses of Capnography
Confirm endotracheal tube placement

in non-arrest settings the ETCO2 approaches
100% sensitivity and specificity in confirming
correct tube placement; it is also useful to monitor
for accidental extubation
Estimate PaCO2
Monitor effectiveness of cardiopulmonary
resuscitation (CPR), mechanical ventilation,
and conscious sedation
Limitations of
Capnography
ETCO2 falsely elevated after
esophageal intubation following
bag/mask ventilation in the following:
ingestion of carbonated beverages or
antacids: these tracings usually resolve
after six breaths and look abnormal
 injection of bicarbonate: falsely elevated for
about 5 minutes after

ETCO2 as Surrogate for
PaCO2
Can estimate PaCO2 in
hemodynamically stable patients who
do not have rapidly progressive lung
pathology
Pa-ETCO2 gradient is usually 2 to 5 mm
Hg, but this may increase to 15 mm Hg
in patients with hemodynamic instability
and pulmonary complications
Review…
Three main ventilation strategies

A/C, PSV, SIMV
Rule of 10’s
Consider NPPV in respiratory failure


Hypoxemic = CPAP or BPAP
Hypoventilatory = BPAP
NIBP, pulse oximetry and capnography are
important monitoring tools in the ED but have
limitations