Pulmonary Physiology,
Oxygen Delivery, and
Mechanical Ventilation
James Barnett, RN, MSN
Clinical Educator – Neuroscience PCC
Vanderbilt University Medical Center
May 2007
Physiology Review
Pulmonary Perfusion
Recruitment—this mechanism decreases
pulmonary vascular resistance (PVR) to
accommodate increased blood flow
Capillary dilation—this mechanism directly
increases capillary size via stimulation of the
autonomic nervous system
Lung Compliance

Compliance
A term used to describe resistance in relation to
elasticity
 Low Compliance

Lungs become stiffer and less elastic
 Stiff lungs (ARDS, pulmonary edema, fibrosis,
pneumonia, atelectasis


High Compliance

More easily distended
Physiology of Gas Exchange
(Respiration)

Respiration: The interchange of gases between an organism
and the environment in which it lives
3 Step Process
1. Ventilation
2. Diffusion
3. Transport
Physiology Review
Ventilation
…movement of air between the body and the
environment…and distribution of air within the
tracheobronchial tree to the alveoli

effected by: respiratory pressures, surface tension
(surfactant), and lung compliance
Physiology Review
Alveolar Diffusion
…gas exchange across the alveolar-capillary
membrane from the air sac (higher
concentration) into the pulmonary blood supply
(lower concentration)
…CO2 is 20 times more diffusable than O2 across
the alveolar-capillary membrane
…effected by five variables
Physiology Review
Five variables determine alveolar diffusion
1. Surface Area
2. Membrane Thickness
3. Amount of Hemoglobin
4. Partial Pressures
5. Diffusion Coefficients
Pathologic Alterations
V/Q Mismatching

Normal pulmonary function

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V=Q
Physiologic shunting


V<Q
Atelectasis or pneumonia
Remember: V = Ventilation and Q = Perfusion
Pathologic Alterations
V/Q Mismatching

Alveolar dead space

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V>Q
Pulmonary emboli
Silent units

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No V nor Q
ARDS secondary to Pulmonary Embolus
Total Lung Ventilation

The Sum of:

Deadspace ventilation

Deadspace Ventilation
+
Alveolar Ventilation
Volume of inspired air that does not participate in
gas exchange (upper airways, trachea, ET tubing)
Total Lung Ventilation

Alveolar Ventilation
That portion of total ventilation that takes part in
gas exchange
 Best indicator is PaCO2

Normal – adequate alveolar ventilation
 High – alveolar ventilation is low and hypoventilation is
present
 Low – alveolar ventilation is high and hyperventilation is
present

Description of Ventilatory Failure

Clinical state produced when PaCO2 rises
quickly enough to produce an immediate, lifethreatening situation

PaCO2 > 50 mmHg
Signs and Symptoms of Acute
Hypoxia

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Tachycardia
Tachypnea
Dyspnea
Euphoria
Stupor
Tremors
Hyperreactive reflexes

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Anxiety
Arrhythmias
Decreased PaO2
HTN
Impaired judgment
Blurred Vision
Coma/Death
Clinical Conditions With
Increased Risk of Hypoxia
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Myocardial infarction
Acute pulmonary
disorders
Sepsis
Drug overdose
Liver failure
Head trauma
CHF

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Hypovolemic shock
Blunt chest trauma
Acute neuromuscular
disease
Acute abdomen
(splinting)
Acute pancreatitis
Spinal cord injury
Indications for Oxygen Therapy
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Tachypnea
Cyanosis
Restlessness
Disorientation
Cardiac arrhythmias
Slow bounding pulse
Tachycardia
Hypertension

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Dyspnea
Coma
Labored breathing (use
of accessory muscles,
nasal flaring)
Lethargy
Tremors/seizure activity
Methods of Oxygen Delivery

Most common methods of oxygen delivery
include
Nasal Cannula
 Venturi Mask
 100% Non-Rebreather Mask
 Mechanical Ventilation

Oxygen Delivery Methods
Nasal Cannula


Comfortable, convenient,
mouth breathing will not
effect % of O2 delivered
Liters/min = %

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2 l/m = 24-28%
3 l/m = 28-30%
4 l/m = 32-36%
5 l/m = 36-40%
6 l/m = 40-44%
Cannot administer > 6
liters/minute (44%)

Nursing Care


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
Clean equipment daily
Evaluate for pressure
sores over ears and
cheeks
Lubricate prongs before
inserting into nares
Liter flow > 6 L/min will
not increase FiO2
Oxygen Delivery Methods
Venturi Masks

FiO2 Delivery (55688)

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Blue 24% Yellow 28%
White 31% Green 35%
Pink 40%

Nursing Care
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Concerns

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Tight seal is a must
Interferes with
eating/drinking
Condensation collection

Monitor ABG’s
Check for leaks in system
Do NOT operate at <5
L/min (will not flush out
accumulated CO2)
Clean equipment several
times daily
Oxygen Delivery Methods
100% Non-Rebreather

Delivery percentages

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6 l/min = 55 – 60 %
8 l/min = 60 – 80 %
10 l/min = 80 – 90 %
>12 l/min = 90 + %

Concern
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Nursing Care

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Benefit: Has a one way
expiratory valve that prevents rebreathing expired gases
May lead to O2 toxicity


Monitor ABG’s
Check for leaks
See Venturi mask care
Oxygen Delivery Methods
Mechanical Ventilation

Allows administration of 100% oxygen

Controls breathing pattern for patients who are unable
to maintain adequate ventilation

Is a temporary support that “buys time” for correcting
the primary pathologic process
Indications for Mechanical
Ventilation

Mechanical Failure

Ventilatory Failure

Oxygenation Failure

General Anesthesia

Post-Cardiac Arrest
Mechanical Ventilation
Two categories of ventilators

Negative pressure ventilators
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Iron lung
Cuirass ventilator
Positive pressure ventilators

Two categories
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Volume-cycled (volumepreset)
Pressure-cycled (pressurepreset)
Iron Lung
Positive Pressure Ventilators

Volume-cycled

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terminate inspiration
after delivering a preset
volume of gas
delivered regardless of
required pressure to do
so
volume remains the
same unless high peak
pressures reached

Pressure-cycled
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terminate inspiration when
a preset pressure is reached
varying degrees of
resistance will interfere
with gas flow
best used with drug
overdose patients
not good for postoperative or severe
respiratory infections
Modes of Ventilation
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Volume preset modes
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Volume variable modes
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Control mode ventilation (CMV)
Assist - Control mode ventilation (A/C)
Intermittent mandatory ventilation (IMV/SIMV)
Pressure support ventilation (PSV)
Pressure controlled ventilation (PCV)
Pressure regulated volume control ventilation (PRVC)
Positive Airway Pressure


Positive End Expiratory Pressure (PEEP)
Continuous positive airway pressure (CPAP)
Controlled Mandatory
Ventilation


Allows total control of the patient’s rate and
tidal volume
Used for patient’s needing short term ventilation
When no inspiratory effort is desired
 Multiply injured patients without spontaneous
ventilatory effort

Neurologic injury
 Drug overdose

Assist – Control
Ventilation

Allows patient to “initiate” inspiration and
control “frequency”

Patient initiated breaths are delivered at preset
tidal volumes

Can allow an inappropriately high minute
ventilation and increase work of breathing
Mechanical Ventilation
IMV

Patient receives a baseline minute volume

Breathes spontaneously at a fast or slow rate

Variable tidal volume
Mechanical Ventilation
SIMV

Provides the additional advantage that the IMV
mandatory breaths are triggered when the ventilator
senses inspiratory effort by the patient

Generally well tolerated

Diminished risk of barotrauma (less stacking)
Mechanical Ventilation
SIMV

Key Advantages of IMV/SIMV

Patient’s respiratory efforts are utilized

Weaning begins at the outset of ventilation
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Mean intrathoracic pressure is decreased
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Increased venous return
Increased cardiac filling
IMV versus ACV

In patients who are breathing rapidly during
ACV and have evidence of over-ventilation
(respiratory alkalosis) or hyperinflation (autoPEEP), a switch to IMV should prove beneficial

In patients with evidence of respiratory muscle
weakness or with a history of LV dysfunction,
ACV should be favored over IMV
Mechanical Ventilation
Pressure Support Ventilation (PSV)

Descriptions

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For patients with spontaneous breathing pattern
Ventilator does not deliver a set volume, rather a preset
positive pressure
Pt determines own inspiratory flow rate and time, and
respiratory rate
Indications
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Long-term mechanical ventilation
Often used with SIMV to reduce work of breathing
Useful method for weaning
Mechanical Ventilation
Pressure Support Ventilation (PSV)

Advantages
Reduces work of breathing while maintaining muscle
tone
 Pt determines timing and rate

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Disadvantages
Dangerous if pt’s respiratory rate slows or stops
 Can be used with PEEP or CPAP but increases the
risk of barotrauma or decreased cardiac output

Mechanical Ventilation
Pressure Controlled Ventilation (PCV)



Pressure cycled breathing that is completely
controlled by the ventilator, with no
participation by the patient
The inspiratory flow rate decreases exponentially
during lung inflation reducing peak airway
pressures and improving gas exchange
Disadvantage: inflation volumes vary based on
mechanical properties of the lungs
Mechanical Ventilation
PEEP

Description
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Maintains a preset positive airway pressure at the end of
expiration
Increases PaO2 so that FiO2 can be decreased
Increases DO2 (amt of delivered O2 to tissue)
Maximizes pulmonary compliance
Minimized pulmonary shunting
Indications


PaO2 < 60 on FiO2 > 60% by recruiting dysfunctional
alveoli
Increases intrapulmonary pressure after cardiac surgery to
decrease intrathoracic bleeding (research does not
support this idea)
Mechanical Ventilation
PEEP

Advantages

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Improves PaO2 and SaO2 while allowing FiO2 to be
decreased
Decreases the work of breathing
Keeps airways from closing at end expiration (esp. in pts
with surfactant deficiency)
Disadvantages

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Increased functional residual capacity (increases risk for
barotrauma)
Can cause increased dead space and increased ICP
In pts with increased ICP, must assure CO2 elimination
Contraindicated: hypovolemia, drug induced low cardiac
output, unilateral lung disease, COPD
Mechanical Ventilation
CPAP

Description


Constant positive pressure is applied throughout the
respiratory cycle to keep alveoli open
Indications

To wean without having to remove the ventilator and having
to connect to additional equipment
Mechanical Ventilation
CPAP

Advantages

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Takes advantage of the ventilator alarm systems providing
psychological security of the ventilator being there
Disadvantages

Patient may sense resistance as he breathes through the
ventilator tubing
Nursing Care of the Ventilator

Record and document the
following settings per unit
standards
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Rate (mech and spont)
FiO2
Tidal volume (mech & spont)
PS/PEEP/CPAP
Peak pressure (PIP)
SpO2
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NEVER use the top of
the ventilator as a desk
NEVER sit liquids on or
near the ventilator
NEVER make changes
to ventilator settings
Refer to RT, MD, NP, or
Charge Nurse as needed
Care of the Ventilator Patient
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Observe and document
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Airway type, size, and
position
Character of insertion site
Date airway inserted
Pulmonary assessment
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Inspection
Palpation
Percussion
Auscultation
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Provide oral care prn
Reapply ETT tape q24h
and prn
Provide trach care and
replace inner cannula
q12h and prn
Monitor for
complications
Suction as needed
Wean and extubate
Mechanical Ventilation
Complications

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Respiratory arrest from
disconnection
Respiratory infection
(VAP)
Acid-base imbalances
Oxygen toxicity

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Pneumothorax
GI bleeding
Barotrauma
Decreased cardiac output
Troubleshooting Ventilator Alarms

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High Pressure Alarm – something is blocking airflow
(kinked tubing, secretions)
Low Pressure Alarm – not enough pressure (tubing
disconnected)
High Minute Volume Alarm – minute volume is the
respiratory rate times the tidal volume – anything that
increases RR or Vt will increase Minute volume
Low Minute Volume Alarm
FiO2 Alarm – usually due to leaving FiO2 at 100% after
hyper-oxygenation before suction technique
Hazards of Oxygen Therapy

Oxygen induced hypoventilation with the following risk
criteria:
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Pts baseline PaCO2 > 50 mmHg
Baseline O2 saturation < 90%
With supplemental O2, PaO2 doesn’t exceed 60 mmHg
Absorption atelectasis with the following risk criteria:
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FiO2 > 50%
Decreasing alveolar volumes
Airway obstruction
Signs of Oxygen Toxicity
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Substernal pain
Cough
Dyspnea
Anxiety
Paresthesia
Fatigue
Pulmonary infiltrates
Decreased PaO2

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Decreased compliance
Pulmonary edema
Atelectasis
Decreased vital capacity
Increased shunting (V/Q
mismatching)
Potentiators of Oxygen Toxicity

CO2 inhalation or
retention

Adrenocortical
hormones

Epinephrine

Thyroid hormones

Insulin

Amphetamines

Norepinephrine

Vitamin D deficiency
Inhibitors of Oxygen Toxicity

Intermittent O2 therapy

Acclimation to hypoxia

Vitamin E

Adrenergic blockers

Hypothermia

Ganglionic blockers

Hypothyroidism

Anesthesia
Ventilator Weaning

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Vital Capacity at least 10 – 15 ml/kg
Tidal Volume > 5 ml/kg
Resting minute volume > 10 L per minute
ABG’s adequate on < 40% FiO2
Stable vital signs
Intact airway protective reflexes (strong cough)
Absence of dyspnea, neuromuscular fatigue, pain,
diaphoresis, restlessness, use of accessory muscles
Extubation Procedure
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Explain procedure to patient
RT must be at bedside
Wash your hands and don PPE
Suction airway and oropharynx for pooled
secretions (prevents aspiration of secretions atop
balloon)
Place a towel on patient’s chest
Assure new oxygen setup is ready to use
Deflate cuff and remove tube instructing patient to
cough as tube is removed
Apply supplemental oxygen
Monitor pt for distress (stridor, coughing, anxiety)
Finished


You have completed this in-service
Please complete the post test, titled:


Pulmonary physiology, O2 delivery, and
Mechanical Ventilation
At the following website