Mechanical Ventilation Cheat Book for Internal Medicine Residents

This short cheat book talks about basic concepts and physiology of artificial ventilation and also elaborates on point guided approach in maneuvering different modes of mechanical ventilation. Consider this as a basic overview and is intended for all internal medicine residents.

1. MECHANICAL
VENTILATION
INTERNAL MEDICINE
RESIDENTS
FOR
Jaskeerat Singh, MD
Jonathan Henesch, MD
cheat book

2. Mechanical Ventilation Cheat Book for IM-Residents 1
Content

I. The very basics
a. Ventilation and Oxygenation
b. Basic Parameters
c. Negative and Positive pressure ventilation
d. Impact of positive pressure ventilation in cardiac output
e. What is minute ventilation

II. Pressures and monitoring
a. Peak inspiratory pressures PIP
b. Plateau pressures
c. Common causes and complications of high airway pressures
d. Positive end-expiratory pressure PEEP
e. AutoPEEP, intrinsic PEEP or inadvertent PEEP

f. Flow time waveforms

III. Non invasive mechanical ventilation – BiPAP
a. Common parameters and settings
b. Clinical indications and contraindications

IV. Modes of invasive ventilation
V. Airway vs Alveolar disease

a. Ventilation strategy in COPD patients
b. Ventilation strategy in ARDS patients

VI. Ventilation in patients with severe metabolic acidosis

VII. Ventilation in patients with neuromuscular disease

VIII. Screening for weaning
a. Parameters
b. Weaning predictors
c. Upper airway swelling

IX. Spontaneous breathing trials

X. Common clinical scenarios
a. Patient with asthma exacerbation
b. Adjusting vent settings – 1
c. Adjusting vent settings – 2
d. Troubleshooting in COPD patients - diagnosis
e. Troubleshooting in COPD patients - management

3. Mechanical Ventilation Cheat Book for IM-Residents 2
The very basics



Mechanical ventilation has two major
components to it, Ventilation and Oxygenation.

Ventilation
It is the ability to remove CO2.
Mostly controlled by Tidal Volume and
Respiratory rate.


Oxygenation
Ability to allow alveolar oxygen gas exchange
with the blood.
Mostly controlled by oxygen concentration
(FiO2) and PEEP.


Parameters with common initial
values

1. Tidal Volume – 6-8 m/kg
Always use ideal body weight based on gender
and height. Not actual weight.

Think about it, what would be the tidal
volume for a patient weighing 400 lbs?

2. Respiratory Rate
Commonly set at 10 – 20 breaths/min.
Would often change based on indication for
mechanical ventilation.

3. PEEP
Set usually between 0-5 cm H20.

4. Fraction of inspired Oxygen
Common practice is to set it at 100 % and then
titrate accordingly.

5. Flow Rate
By default set at 40-60 Liters/min but would
change based on underlying treating pathology.

4. Mechanical Ventilation Cheat Book for IM-Residents 3
How do we normally breath?
We use our diaphragm to create a low pressure within their lungs (negative pressure
breathing). A pressure gradient is created (where the lungs are at a lower pressure) and air
flows into the lungs.



Positive pressure ventilation
When we put a patient on mechanical ventilation either invasive or non-invasive we change
their way of breathing and make them breath with a positive pressure ventilation.

Positive pressure ventilation essentially affects preload, afterload and ventricular compliance.
The net effect in most situations is a decrease in cardiac output.

Here is a brief summary of what happens when you put someone on a ventilator –
1. With negative pressure ventilation, Right atrial pressure in a normal individual is around
0-5 cm of water.
2. On adding PEEP, you add positive pressure in the intra thoracic cavity which is
transmitted to the Right atrium.
3. As a result of that the venous flow/ preload reduced there by decreasing the cardiac
output and the blood pressure. Hence unless contraindicated, be ready to give your
patient IV fluids when you put them on positive pressure ventilation.

5. Mechanical Ventilation Cheat Book for IM-Residents 4
What is minute ventilation?
MV = Tidal volume in Liters x Respiratory rate

How do you assess if you patient is ventilating
appropriately? PaCO2

35-45 mmHg Acceptable
range
Maintain settings
<35 mmHg Hyperventilating Decrease minute
ventilation (Vt or RR)
>45 mmHg Hypoventilating Increase minute
ventilation (Vt or RR)

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Pressures and monitoring

Pressures depicted on the ventilator are produced by
resistance in the airway and or compliance of the
lungs.

PIP – Peak Inspiratory Pressure - Resistance
PIP is the highest level of pressure applied
to the lungs during inhalation.
Resistance anywhere along the path from the
ventilator to the lungs can cause an increase in PIP.
PIP should be kept below 35 cmH2O.

Plateau Pressure/Alveolar pressure - Compliance
Plateau pressure is the pressure in the lungs during
peak inspiratory hold.
Plateau pressure should be kept below 30 cmH2O.



Peak pressures in the lungs increases if the resistance
in the airways increases or if lungs become stiff.
Whereas the plateau pressures are only affected by
the lung compliance.



Examples of Elevated Peak
Pressures (Airway issues)

- Bronchospasm
- Retained secretions
- Mucous plug
- Blocked / kinked ETT

Examples of Elevated Plateau
Pressures (Lung compliance issues)

- Pulmonary edema
- Pneumothorax
- ARDS
- Consolidation
- Collapse


Complications of higher pressures

Airway pressure itself is not
particularly deleterious unless it
reflects excessive alveolar pressure.
Excessive alveolar pressure can have
a number of adverse effects:

- barotrauma may result in acute
lung injury (leading to ARDS) or
air leaks (e.g. pneumothorax,
pneumomediastinum).
- Excessive intrathoracic pressure
may also result, with potential
hemodynamic consequences

Pearl: So if the pressure alarm is
going off you need to know whether
it is a high peak pressure causing the
problem or a high plateau pressure.

7. Mechanical Ventilation Cheat Book for IM-Residents 6

PEEP
Positive end-expiratory pressure (PEEP) is the positive pressure that will remain in the airways
at the end of the respiratory cycle (end of exhalation).

To understand better divide PEEP in two categories,

Extrinsic PEEP is the pressure you set on the ventilator and is usually set at 5 cm of water.

Intrinsic PEEP, also called inadvertent PEEP or auto PEEP
It is iatrogenic. Occurs when the expiratory time is shorter than the time needed to fully deflate
the lungs, preventing the lung and chest wall from reaching an elastic equilibrium point.
Also called Air trapping.

How do you measure auto PEEP?

Expiratory hold maneuver
Depressing the expiratory hold or expiratory pause
button on the ventilator keeps the lungs at maximal
exhalation for about 1 second and allows you to
measure the total PEEP.

Next step
You can then calculate the intrinsic PEEP:
Total PEEP - set PEEP = intrinsic PEEP
Intrinsic PEEP > 0 air trapping


Identifying air trapping on a Flow time waveform



As long as the expiratory limb reaches zero,
the lung is fully deflated and the patient is not
air trapping.

A shift in the waveform, such that the
expiratory limb does not return to zero,
indicates air trapping.

8. Mechanical Ventilation Cheat Book for IM-Residents 7

Measures to treat air trapping in patients with COPD
1. Decrease VT
Reducing volume, in reduces volume needed to get out.
2. Decrease RR
Reducing RR allows more time to exhale.
3. Increase flow
Increasing flow shortens inspiration time and therefore increases expiration time.
4. Bronchodilators
5. Steroids

What to Do?
You are the MICU Intern, your nurse calls you to check a patient for alarming ventilator
pressures!
1. Check the circuit – look for any
disconnections!
2. Check the HME – the connector
between the ventilator and ET tube
3. Is the patient sedated enough? Watch
for patient ventilator dysynchrony.
4. Consider continuous bronchodilators
if the patient is wheezing.

In the meanwhile,
• Get a chest Xray
• Call for help! (Never be afraid of
asking for help) – reach out to the
Intensivist/ RT
Low Volume Alarm – watch for
• a disconnected circuit
• dislodged ET tube, cuff leak
• measure cuff pressure
• low set tidal voluime

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8
8
Non Invasive Mechanical Ventilation – BIPAP


Parameters and Common Settings
1. Inspiratory positive airway pressure IPAP
Usually set between 10-20 mmHg
2. Expiratory positive airway pressure EPAP
Usually set between 5-10 mmHg
Analogous to PEEP
3. FiO2
Usually started at 100 % and then titrated
accordingly

Difference of pressures IPAP – EPAP
It is the difference between these two
pressures that drives the tidal volume.

Let’s see some sample settings and understand
how they differ,
a. IPAP/EPAP of 10/5, Delta is 5
b. IPAP/EPAP of 15/5, Delta is 10
c. IAPA/EPAP of 15/10, Delta is 5

Patient with settings b would produce
maximum tidal volume.
Patient with settings c would generate
maximum PEEP.

What is a strategy for the treatment of systolic
CHF?
Answer: BiPAP with high EPAP
Remember EPAP works like PEEP, it increases
the intrathoracic pressure and reduce
afterload, preload, and pushes out the fluid in
the lungs.

Which of the following will reduce the pCO2
and increase ventilation?
Answer: Increase IPAP and keep EPAP the same.

Common indications
§ Respiratory failure not requiring immediate
intubation with:
acute respiratory acidosis
unacceptable hypoxemia despite
supplemental oxygen
§ Intubation contraindicated or refused
§ Post extubation respiratory difficulty in
which re-intubation may be avoided with a
trial of BiPAP

Must requirements for BiPAP
§ Patient should be awake, alert and
cooperative
§ Patent upper airway and with intact reflexes
§ Ideally not much respiratory secretions

Common contraindications
§ Markedly depressed mental status
§ Excessive amount of secretions
§ Upper GI bleeding
§ Proper mask fit cannot be achieved

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Different Modes of Mechanical Ventilation

Which initial mode of ventilation should I use?
Assist Control is the most widely used mode of mechanical ventilation by most providers.

VOLUME MODES

Assist Control

- Also known as continuous
mandatory ventilation (CMV).
- Patient gets the set tidal volume
with each breath (even with
partial breaths triggered by the
patient).
- More tendency to
hyperventilate.



SIMV

- Guarantees a certain number of
breaths, but unlike ACV, patient
breaths are partially their own.
- More tendency to hypoventilate.



ACV vs. SIMV
Personal preference prevails, except in the following scenarios: 1. Patients who breathe rapidly
on ACV should switch to SIMV 2. Patients who have respiratory muscle weakness and/or left-
ventricular dysfunction should be switched to ACV.

PRESSURE Assist Control
In this mode, you set the pressure and the ventilator would generate a tidal volume based on
lung compliance.
Majority of the time is spent at the higher (inspiratory) pressure.
Higher risks of auto PEEP and hemodynamic deterioration due to the decreased expiratory time
and increased mean airway pressure generally outweight the small potential for improved
oxygenation.

11. Mechanical Ventilation Cheat Book for IM-Residents 10
PRESSURE Support Mode
It is used to augment spontaneous breathing.
Can be used to overcome the resistance of ventilator tubing in another cycle (5 – 10 cm H20 are
generally used, especially during weaning).

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Airway disease versus Alveolar disease

Airway Disease
A problem with ventilation
Obstructive disease

Signs:
Increased paCO2
Enlarged lungs on chest xray
Alveolar Disease
A problem with oxygenation
Restrictive disease

Signs:
Decreased PaO2
Lung size appears smaller on chest xray


Ventilation strategies in COPD Exacerbations

Often you will encounter elevated peak inspiratory pressures in a patient with COPD, as you
know they tend to have air trapping. You may apply following maneuvers to treat/prevent this;

a. Setting a low respiratory rate, allowing more time for expiration phase of breathing. But
remember you have to do it within reason or else you will hypoventilate the patient.
b. Increasing Inspiratory Flow Rate (IFR) to decrease Tinspiration and increase Texpiration. This
helps to avoid breath stacking.
Typically set at 80-100 for patients with COPD.
c. Providing an optimal PEEP: The external PEEP should be set at 70 % of the auto PEEP to help
with ventilation synchrony.

Pearl 1: Always ventilate to a target Ph of 7.35-7.40
Do not try reaching to a normal paCO2. Chronic COPD patient would have baseline elevations.

Pearl 2: Distinguishing between acute and chronic respiratory failure

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Ventilation strategies in ARDS



In ARDS the affected part of the lungs is not
the airways, rather the pathology is at the
alveolar level.

Fluids fill the air sacs which often leads to
collapse and affects the gas exchange. This
causes refractory hypoxemia which does not
respond to high levels of FiO2.


Severity of ARDS = Oxygenation status
Below is the severity classification







How does your ventilation settings differ if you suspect ARDS?

1. Low tidal volume strategy
Increasing volume in does not help because the extra volume just
enters the normal alveoli and overextends them, further increasing
the plateau pressure above the acceptable 30 cm of water which can
often cause lung damage.
6-8 ml/kg à 4-6 ml/kg

14. Mechanical Ventilation Cheat Book for IM-Residents 13
2. High respiratory rate strategy
Increasing the respiratory rate would decrease paCO2 and cause Air
trapping. Air trapping is usually bad but it might help your ARDS
patient!!
It acts like PEEP and help recruit and stabilize the collapsed alveoli.


3. Optimal PEEP strategy

In this strategy, you adjust PEEP up and down
to find the PEEP at which the lung is the most
compliant. To determine when the lung is
most compliant you can monitor PaO2

or
calculate the static compliance.
PEEP that produces the highest PaO2 =
Optimal PEEP
PEEP that produces the highest static
compliance = Optimal PEEP



4. Using a different mode of ventilation

When treating patients with ARDS it is
common to switch from AC volume control
to a mode that is more lung protective.
When using AC volume control you need to
constantly adjust and readjust tidal volume
and PEEP to keep the lungs in the sweet
spot.


APRV Airway Pressure Release Ventilation Mode
It is a pressure controlled, intermittent mandatory ventilation with unrestricted spontaneous
breathing.
First described by Stock et al 1987. This mode of ventilation is often used as a rescue therapy
for severe ARDS.
Respiratory rate is not entered.

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Description
- Two levels of PEEP: high (P-high) and low (P-low)
- Patient breaths spontaneously during P-high and P-low
- Time in P-high (T-high) is longer than P-low (T-low) to
maintain recruitment (85-95%)
- Results in a degree of autoPEEP due to the short release
time (T-low)

16. Mechanical Ventilation Cheat Book for IM-Residents 15
Use of prone positioning
In supine patients, the dorsal regions of the lung are susceptible to profound lung derecruitment
due to increases in parenchymal edema. Recognition that the heterogeneous atelectasis and
consolidation seen in ARDS is often dorsally distributed led investigators to question whether
care for patients with ARDS in the prone – as opposed to the supine – position may lead to
improved mortality outcomes.

An alveolus will remain open
when the intra-alveolar
pressure exceeds PPL. When a
patient with ARDS is placed
prone, the dorsal lung is no
longer subjected to high PPL
and dorsal lung atelectasis
decreases. Conversely, the
ventral lung units are exposed
to a higher PPL and are more
likely to collapse.

Absolute Contraindication
Shock
Acute bleeding
Multiple fractures or trauma (eg, unstable
fractures of femur, pelvis, face)
Spinal instability
Pregnancy
Raised intracranial pressure
Tracheal surgery or sternotomy within two
weeks
Selection Criteria
Patients with severe ARDS who fail to
improve despite use of above mentioned
ventilatory strategies, it is recommended to
try a trial of prone ventilation, provided
there is no contraindication.
Severe ARDS – PROSEVA trial defined
severe ARDS as those having a partial
pressure of arterial oxygen: fraction of
inspired oxygen (PaO2:FiO2) ratio <150
mmHg with a FiO2 ≥0.6 and PEEP ≥5 cm
H2O

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Ventilation strategy in patients with severe
metabolic acidosis

Let’s understand this by using a common scenario,
You have a patient with severe DKA, ABG on admission is 7.21/21/70/8.
You were asked to see the patient for worsening dyspnea and was breathing at a rate of 30
breaths per min. Decision was made to intubate the patient and was started on positive
pressure ventilation.

Following initial parameters were set on the ventilator;
Mode AC-Volume, RR: 12, Tidal volume: 450, PEEP: 5 cm of water and FiO2 of 100 %

What do you think would happen to this patient?
Answer: It would not be surprising if the patient’s academia got worse soon after starting
mechanical ventilation.
Explanation: As mentioned in the clinical vignette, patient was noted to breath at 30 breaths
per min in the setting of severe academia. But as you sedate the patient and start mechanical
ventilation at 12 breaths a minute, you also happen to take away the patient’s capability to
compensative!

Pearl: Always watch and try to match for patient’s minute ventilation before you start
mechanical ventilation. Simulate patient’s existing ventilation requirements to keep up with
their demands.


Ventilation strategy in patients with
Neuromuscular weakness

Patient presents with progressive bilateral leg weakness and has high suspicion of Gulian barre
syndrome. How do you decide patient’s need for mechanical ventilation?

Calculate Negative inspiratory force (NIF) or Maximum inspiratory pressure (MIP)
It should be more negative than -20 cm of water. Remember a lower pressure (more negative)
is better!
Eg, if patient’s NIF is measured at -16 cm of water à Intubate the patient or do not extubate if
already on mechanical ventilation.

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Screening for Weaning

Before weaning you need to screen your patient to make sure they meet the following criteria.
1. Cause of respiratory failure 2. Oxygenation status
Probably the most important.
The cause of respiratory failure should
have resolved or improved
SpO2 > 90% on FiO2 < 40%
PEEP < 5cm of water


3. Ventilation status 4. Hemodynamic status
Patient comfortable on the current vent
setting
Often breathing less than 35 breaths/min
Ph > 7.25

Low or no vasopressor requirements
5. Sedation status
No ongoing neuromuscular blocking
agents
Minimal or no sedation
Often patients would follow simple
commands

Weaning Predictors
Numerous weaning predictors have been studied, but none appear to be superior to objective
clinical criteria in predicting a patient's readiness to wean. The rapid shallow breathing index
(RSBI) is the most extensively studied and popular weaning predictor. It is discussed in detail
separately.
RSBI = RR/Tidal Volume in liters
RSBI ideally should be less than 105. RSBI < 80 predicts successful weaning in more than 95%
cases!

Upper Airway Swelling

When should you be concerned for upper airway swelling?
Answer: Cases of prolonged ventilation, traumatic
intubation and patients with smoke injuries.

How do we know when the swelling has decreased enough
in order to extubate the patient?
Answer: Deflate the cuff à Listen for air leak!

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Spontaneous Breathing Trials

SBT refers to a patient breathing through the endotracheal tube either without any ventilator
support (eg, through a T-piece) or with minimal ventilator support.
Two widely used methods are;
CPAP and T-piece

CPAP T-piece

1. Switch patient from AC à CPAP mode
2. CPAP of 5 cm of water helps to distend
alveoli
3. Add pressure support of 6-8 cm of water
to help overcome equipment resistance

1. Switch patient from AC à T-piece
2. Remove all pressure support (but leave
connected to ventilator).
3. Keeping patient connected to ventilator
allows you to monitor spontaneous
breaths and VT.


If patient does well and appears comfortable for up-til 2 hours of the spontaneous breathing
trial à Proceed towards extubation

20. Mechanical Ventilation Cheat Book for IM-Residents 17
Screening for Weaning

Before weaning you need to screen your patient to make sure they meet the following criteria.
1. Cause of respiratory failure 2. Oxygenation status
Probably the most important.
The cause of respiratory failure should
have resolved or improved
SpO2 > 90% on FiO2 < 40%
PEEP < 5cm of water


3. Ventilation status 4. Hemodynamic status
Patient comfortable on the current vent
setting
Often breathing less than 35 breaths/min
Ph > 7.25

Low or no vasopressor requirements
5. Sedation status
No ongoing neuromuscular blocking
agents
Minimal or no sedation
Often patients would follow simple
commands

Weaning Predictors
Numerous weaning predictors have been studied, but none appear to be superior to objective
clinical criteria in predicting a patient's readiness to wean. The rapid shallow breathing index
(RSBI) is the most extensively studied and popular weaning predictor. It is discussed in detail
separately.
RSBI = RR/Tidal Volume in liters
RSBI ideally should be less than 105. RSBI < 80 predicts successful weaning in more than 95%
cases!

Upper Airway Swelling

When should you be concerned for upper airway swelling?
Answer: Cases of prolonged ventilation, traumatic
intubation and patients with smoke injuries.

How do we know when the swelling has decreased enough
in order to extubate the patient?
Answer: Deflate the cuff à Listen for air leak!

21. Mechanical Ventilation Cheat Book for IM-Residents 18

Spontaneous Breathing Trials

SBT refers to a patient breathing through the endotracheal tube either without any ventilator
support (eg, through a T-piece) or with minimal ventilator support.
Two widely used methods are;
CPAP and T-piece

CPAP T-piece

1. Switch patient from AC à CPAP mode
2. CPAP of 5 cm of water helps to distend
alveoli
3. Add pressure support of 6-8 cm of water
to help overcome equipment resistance

1. Switch patient from AC à T-piece
2. Remove all pressure support (but leave
connected to ventilator).
3. Keeping patient connected to ventilator
allows you to monitor spontaneous
breaths and VT.


If patient does well and appears comfortable for up-til 2 hours of the spontaneous breathing
trial à Proceed towards extubation

22. Mechanical Ventilation Cheat Book for IM-Residents 19
Common Clinical Scenarios

Question 1
A 23-year-old woman with a long history of asthma and previous exacerbations requiring
intubation is evaluated in the emergency department for a 2-day history of increasing wheezing
and dyspnea after the onset of a sore throat. She has used her albuterol inhaler many times in
the past day.

On physical examination, she is alert and cooperative but in severe respiratory distress; the
blood pressure is 160/80 mm Hg, heart rate is 120/min, and respiration rate is 30/min. She is
using accessory muscles of breathing. She has nasal flaring, and chest examination reveals
diffuse inspiratory and expiratory wheezes.

Peak expiratory flow rate is 110 L/min. Measurement of arterial blood gases shows a pH of
7.32, PCO2 of 44 mm Hg, and PO2 of 76 mm Hg with the patient breathing oxygen, 5 L/min by
nasal cannula. Chest radiograph shows hyperinflation but is otherwise normal.
Intravenous corticosteroid therapy is begun.

Which of the following is the most appropriate next step in this patient's management?
A An anticholinergic agent and a short-acting β-agonist
B Helium combined with oxygen (Heliox)
C Intravenous or inhaled magnesium sulfate
D Prompt intubation

Question 2


As you monitor the patient, you
obtain an ABG and check their
oxygen saturation and pressures on
the ventilator. You note these
values. What should you do next?
A. Decrease the PEEP
B. Increase the Tidal Volume
C. Decrease the Flow
D. Increase the FiO2

23. Mechanical Ventilation Cheat Book for IM-Residents 20
Question 3

Several hours after you increase
the FiO2, you note the values
shown. Based on your findings,
what should you do next?
A. Decrease the PEEP
B. Increase the Tidal Volume
C. Decrease the Flow
D. Increase the FiO2


Question 4

As you look at the ventilator
screen of your COPD patient, you
see this flow-time waveform. The
patient most likely has which of
the following?
A. Lung cancer
B. Pneumonia
C. Air trapping
D. Alveolar collapse

Question 5
As following the patient in Question 4, Which of the following should you NOT consider when
trying to reduce air trapping?
A. Decreasing the respiratory rate
B. Increasing the flow
C. Decreasing the inspiratory time
D. Increasing the tidal volume


Question 6
You suspect that your mechanically ventilated patient may have
developed ARDS. The PIP is 55 cmH2O and the plateau pressure
is 36 cmH2O. They are currently on AC volume control mode
with the following settings: tidal volume (VT) is 400 mL,
respiratory rate is 20 breaths/min, FiO2 is 60%, and PEEP is 5
cmH2O. The SpO2 on these settings is 94%.
Based on this information, what should you do?
A. Switch to SIMV
mode
B. Increase tidal
volume to 550 ml
C. Increase the FiO2
to 70 %
D. Switch to pressure
control mode