Respiratory I
Wendy Phelps RN, MSN, CCRN
Nursing 487 – Spring 2017
Chapter 10 – Determinants and Assessment of Pulmonary
Gas Exchange
Objectives
1. Describe the function and role of the pulmonary
system;
2. Explain pulmonary perfusion and determine
abnormalities of perfusion;
3. Identify normal values for and interpret arterial
blood gases differentiating between respiratory
acidosis and alkalosis and metabolic acidosis and
alkalosis;
4. Describe a focused respiratory nursing history and
assessment;
5. Describe tests and procedures used to evaluate
pulmonary function and oxygenation and list
normal values.
Functions

Protect and defend

Exchange of gases
◦
◦
◦
◦
Intact neuro system
Compliant lungs
Adequate WOB
Adequate hemodynamic/cardiovascular
function
Respiratory Tract -REVIEW

Protective functions

Conducting airway contains a mucociliary
system
◦ in high-acuity patients, initial conducting
airway is bypassed if intubated
Respiratory Process

1. Ventilation

2. Respiration

3. Perfusion
Ventilation
Actual work of breathing
 Air exchanged with the atmosphere
 Changing size of thorax

◦ inspiration/expiration
Air moves from area of higher pressure
to one of lower pressure
 Inside lungs – lower pressure – inspire
until pressure slightly higher – then
expiration

Lung Compliance & Ventilation
Ability of lungs to expand and recoil
 As alveoli approach filling capacity, they
lose compliance and can eventually burst

Can use PEEP (positive end-expiratory
pressure) to increase compliance – but
too much PEEP can cause damage
Lung Compliance

Compliance sensitive to conditions that
affect lung's tissues
◦ deficiency of surfactant leads to decreased
compliance
◦ “stiff lungs"
◦ increases work of breathing, decreases tidal
volume
◦ restrictive pulmonary disorders
Respiration
The body's cells are supplied with oxygen,
and carbon dioxide is eliminated
 Internal respiration – movement of gas
across systemic-capillary cell membranes
in the tissue
 External respiration – movement of gas
across the alveolar-capillary membranes

◦ both use diffusion to exchange gases
Diffusion

Factors that affect diffusion
◦
◦
◦
◦
Gradient
Surface Area
Thickness
Length of exposure
Figure 10-5: Oxyhemoglobin dissociation curve. The percent O2 saturation of hemoglobin and total blood oxygen volume
are shown for different oxygen partial pressures (PO2). Arterial blood in the lungs is almost completely saturated. During
one pass through the body, about 25% of hemoglobin-bound oxygen is unloaded to the tissues. Thus, venous blood is still
about 75% saturated with oxygen. The steep portion of the curve shows that hemoglobin readily off-loads and on-loads
oxygen at PO2 levels below the 50mmHg.
Figure 10-6: Oxyhemoglobin dissociation curve right and left shifts. Normally, when hemoglobin is 50 percent saturated
with oxygen (P50) the PaO2 will be 27 mm Hg. The P50 changes when physiologic factors are altered, shifting the curve.
A shift to the left increases the affinity of oxygen to hemoglobin, inhibiting its release to tissues. A shift to the right
decreases the affinity of oxygen to hemoglobin, making it release to tissues more readily. LeMone & Burke. (2008).
Shifts in OxyHgb curve

Left Shift:
◦ Hgb and oxygen have increased affinity
◦ Alkalosis
◦ Low metabolism

Right Shift:
◦
◦
◦
◦
Hgb and oxygen have decreased affinity
More oxygen released
Acidosis
High metabolism
Perfusion
Third component of respiratory process
 Pumping or flow of blood into tissues and
organs
 Two circulatory systems

◦ systemic system
◦ pulmonary system
 depends on systemic system
Perfusion
Cardiac output
 Gravity
 Pulmonary Vascular Resistance

Cardiac Output
CO = SV x HR
 Normal cardiac output 4-8 liters per
minute
 Stroke volume a function of ventricular
preload, afterload, and contractility
 MAP = Mean arterial pressure

◦ MAP < 60 mmHg is inadequate
◦ clinical goal to maintain MAP at 65 or above
Gravity
Effects of gravity on blood are important
 Blood has weight
 Naturally flows toward dependent areas
of body

Pulmonary Vascular Resistance PVR
Resistance to blood flow in pulmonary
vascular system
 Affected by:

 Length of vessels
 Radius of vessels
 Viscosity of blood
Vessel Radius Determinants

Pulmonary vasoconstriction occurs in
response to hypoxia, hypercapnia, and
acidosis
◦ vasoconstriction is a major cause of increased
pulmonary vascular resistance (PVR)
◦ hypoxia is strongest stimulant for pulmonary
vasoconstriction
◦ when an area of the lung becomes hypoxic,
vasoconstriction is triggered
Ventilation-Perfusion
Relationship
V/Q ratio – measurement of alveolar
ventilation and pulmonary perfusion
 Balance of ventilation to perfusion
affected by PaO2 and PaCO2
 Balance depends on adequate diffusion of
oxygen and carbon dioxide
 Should significant imbalance develop,
normal gas exchange cannot take place in
affected areas

Figure 10-8 The relationship of ventilation to perfusion.
Ventilation-Perfusion
Relationship
Clinical significance of ventilationperfusion balance apparent in prolonged
bedrest
 Because blood is gravity dependent, it will
shift from lung bases to lung area in
dependent position while air continues to
be drawn toward diaphragm

Figure 10-9: Positioning and ventilation-to-perfusion relationship. (A) Upright position—Air moves towards diaphragm and
blood gravitates to bases. Best V/Q match (B) Side lying position—Air moves towards diaphragm while blood gravitates to
lateral dependent lung fields. (C) Supine postion—Air moves towards diaphragm while blood gravitates to posterior
dependent lung fields. (D) Prone position—Air moves towards diaphragm while blood gravitates to the anterior dependent
lung fields.
Ventilation/Perfusion mismatching

Can occur due to not enough BLOOD or
not enough AIR
If V is greater than Q ratio >1
 If Q is greater than V, ratio <1

Shunting - Blood flows through pulmonary cap system without
undergoing gas exchange
Anatomic
 Capillary
 “Shuntlike” effect
 Percentage of cardiac output that flows
from right heart and back into left heart
without undergoing pulmonary gas
exchange
 Pulmonary shunting is major cause of
hypoxemia in high-acuity patients

Anatomic Shunt
Not all blood that flows through lungs
participates in gas exchange
 Blood that moves from right heart back
into left heart without contact with
alveoli;
 Normal AS is approximately 2-5% of
blood flow

Anatomic Shunt
Normal anatomic shunting occurs as
result of emptying bronchial and other
veins into lung's own venous system
 Abnormal anatomic shunting can occur
because of heart or lung problems

◦ Congenital heart problems
◦ Lung abnormalities
Capillary Shunt
Normal flow of blood past completely
unventilated alveoli
 Blood flowing by affected units will not
take part in diffusion
 Results from consolidation or collapse of
alveoli, atelectasis, or fluid in alveoli

Absolute shunt
◦ Combo of capillary shunt and anatomic shunt
◦ lung tissue affected by absolute shunt
unaffected by oxygen therapy
◦ shunting of > 15% of cardiac output can result
in severe respiratory failure
◦ patients with acute respiratory distress
syndrome (ARDS)
◦ hallmark of ARDS is refractory hypoxemia
Shuntlike Effect
Not a “true shunt”, because the shunting
is not complete
 Exists when there is an excess of
perfusion in relation to alveolar
ventilation
 Common causes:

◦ Bronchospasm, excess secretions,
hypoventilation

Hypoxemia secondary to shuntlike effect
is very responsive to oxygen therapy
Figure 10-10 Types of physiologic shunt. (a) Anatomic shunt; (b) Capillary shunt; (c) Shuntlike effects—
Alveoli with decreased ventilation may respond well to oxygen therapy.
Estimating Intrapulmonary Shunt
PaO2/FiO2 ratio
ph = 7.3
ph = 7.22
PaO2 70
PaO2 102
PCO2 55
PCO2 34
SIMV, Rate 14
SIMV, Rate 8
TV 750
TV 650
FiO2 40%
FiO2 50%
MWafer
Ischemia-Hypoxemia-Hypoxia

Ischemia - decreased blood flow to tissues

Hypoxemia - reduced transfer of oxygen
from alveolar air to blood; ,measured by
Pa02 – normal 80-100mmHg
 MILD 60-70 mmHg
 MODERATE 45-59 mmHg
 SEVERE <45 mm Hg

Hypoxia - decreased ability to obtain or use
oxygen
Hypoxia vs. Hypoxemia

Can’t “see” hypoxemia - so MUST consider
relationship of SaO2 to PaO2

S/S of hypoxia:
pallor
 dyspnea, tachypnea
 use of accessory muscles
 Tachycardic, dysrhythmias, CP, hypotension w/
bradycardia
 anxiety, restlessness, confusion
 Late signs: cyanosis, diaphoresis, resp arrest

Respiratory Assessment
ABGS
 Nursing History- REVIEW
 Physical Assessment - REVIEW
 Pulmonary Function Tests
 Other tools for resp assessment

Arterial Blood Gas Interpretation
A single ABG measurement represents
only a single point in time
 ABGs most valuable when trends are
evaluated over time
 Interpretation of ABGs includes
determination of acid-base state, level of
compensation, and oxygenation status

ABGs
Acidosis
PH < 7.35
(R) CO2 > 45
(M) HCO3< 22
PH = 7.35 - 7.45
CO2 = 35 - 45
HCO3 = 24-28
Alkalosis
PH > 7.45
(R) CO2< 35
(M) HCO3> 26
Resp = CO2 disturbances
Metabolic = HCO3 disturbances
1. Acidosis or Alkalosis?
2. Respiratory or Metabolic?
3. Compensated disturbances
PaO2 80-100mmHG
SaO2 Greater than 95%
Hgb 13.5-18g/dL(males)
12-15 g/dL (females)
Adapted
fromMWafer
ABG Interpretation








1. Evaluate pH
Consider all values > 7.4 to be alkaline & all values < 7.4 to be acidic
2. Evaluate PaCO2
Consider PaCO2 < 35mmHg to be alkaline & > 45 mmHg to be acidic
3. Evaluate HCO3
If HCO3 < 22 mEq/L, consider it acid. If it is > 26 mEq/L, consider it alkaline
4. Determine Acid-Base Status
Ask: Which individual component matches the pH acid-base state? The
MATCH will determine the PRIMARY acid-base disturbance: respiratory vs.
metabolic
ABGs

Example:
pH: 7.58 (alkalotic)
 PaCO2: 38 (normal)
 HCO3: 32 (alkaline)


pH matches HCO3, so we have metabolic
alkalosis
ABG Interpretation

5. Next step is to determine compensation.

Look at : pH, Pa CO2 & HCO3

pH indicates degree of compensation

Normal pH - indicates normal value or full compensation

Abnormal pH indicates an uncompensated or partially
compensated acid-base state.
Determine Compensation

Uncompensated (Acute) - abnormal pH plus
one abnormal value plus a normal value:

Example: ph - 7.20, PaCO2 - 65mmHg, HCO3 24 mEq/L

INTERPRETATION: pH & PaCO2 match (acid).
HCO3 is normal. NO COMPENSATION is
occurring = state of uncompensated (acute)
respiratory acidosis exists.
Determine Compensation

Partially compensated - abnormal pH plus two abnormal
values (PaCO2 & HCO3 are moving in opposite directions).

Body has initiated neutralizing imbalance but not there yet.

Example: pH - 7.25, PaCO2 60mmHg, HCO3 - 34 mEq/L

INTERPRETATION: pH and PaCO2 match (acid). HCO3 is
alkaline or moving in opposite direction from PaCO2. pH still
abnormal = state of PARTIALLY COMPENSATED
respiratory acidosis exists.
Determine Compensation

Compensated - normal pH plus two abnormal values
(PaCO2 & HCO3 are moving in opposite directions).

Example: pH - 7.39, PaCO2 - 50mmHg, HCO3 31mEq/L
INTERPRETATION - pH & PaCO2 match (acid).
HCO3 is alkaline (opposite of PaCO2). pH is normal =
State of COMPENSATED respiratory acidosis exists.
 You will not be responsible for interpreting mixed acid-base
disorders

Causes of Acid – Base
Disturbances
Resp. Acidosis
Metabolic Acidosis
CNS Disorders, Drug
Renal failure, DKA, drug
overdose, pneumonia,
overdose (ASA, methanol),
pulmonary edema, restrictive diarrhea
lung diseases
Resp. Alkalosis
Hyperventilation, anxiety,
fear, fever, asthma, ARDS,
CHF, PE, CNS disorders
Met. Alkalosis
Too many antacids, vomiting,
NGT suctioning, low
potassium, steroids, diuretics
Lactic Acidosis
Acid metabolites like lactic acid result
from cellular breakdown and anaerobic
metabolism
 Normal range for serum lactate is 0.5-2.0
mEq/L
 High-acuity patients are at risk for
developing elevated levels of lactate
 During shock, cellular hypoxia drives
serum lactate up rapidly

The pH-to-HCO3 Relationship

If a metabolic disturbance is present, the
pH and HCO3 should maintain a stable
relationship
The pH-to-PaCO2 Relationship
pH decreases as PaCO2 increases
 pH increases as PaCO2 decreases

The PaCO2-to-HCO3
Relationship

Under normal conditions, the PaCO2 and
HCO3 maintain a stable relationship
Nursing History
Assess ABC
 Social History
 Nutritional History
 Cardiopulmonary History
 Sleep-Rest History
 Dyspnea /PND
 Cough

Vital Signs and Hemodynamic
Values
Give crucial baseline data
 Include arterial blood pressure, pulse rate
and rhythm, respiration rate and rhythm,
and temperature
 Obtain pulse oximeter reading
 If pulmonary artery catheter in place,
assess

Focused Respiratory Physical
Assessment
Cyanosis is a late sign of respiratory
distress, not a reliable indicator of hypoxia
 Inspect shape of chest, and observe
movement
 Chest percussion can help detect
presence of air, fluid, or consolidation

Breath Sounds
Type
Location
Associated Problems
Characteristics
Crackles
Peripheral
airways, alveoli
Atelectasis, excess fluid,
mucous, inflammation
Discontinuous
popping sounds,
usually inspiratory
Rhonchi
Large Airways
Inflammation
Excess fluid, mucous
Continuous coarse,
usually expiratory
Wheeze
Large &/or small
airways
Bronchoconstriction (always
narrowing) from
bronchospasm, fluid,
mucous, inflammatory
byproducts, obstructive lesion
Continuous musical
sound usually
expiratory, doesn’t
clear with cough
Pleural
Friction
Rub
Pleural surfaces
Inflamed surfaces
Grating sound
w/cont &
discontinuous
qualities
PThomas
Pulmonary Function Tests (PFTs)
Ventilation is measured using pulmonary
function tests
 Differentiate a restrictive pulmonary
problem from an obstructive one
 PFTs are useful for monitoring
effectiveness of therapeutic interventions
 Diagnostic PFT is usually conducted in a
pulmonary laboratory
 A spirometer can be used at bedside

Work of Breathing
 How

does one assess the WOB?
Dependent on COMPLIANCE & RESISTANCE
PFT
 disease of ventilation
 measure of respiratory muscle strength
 useful in weaning
Total lung capacity

Volume of gas present in the lungs after maximal
inspiration ~ Normal 6000ml in adults

composed of four separate volumes:
◦ Inspiratory Reserve Volume (IRV) – amount of air
inhaled above normal inhalation ~ 3100ml
◦ Tidal Volume (TV) – amount if air in and out with
normal inspiration (details next slide)
◦ Expiratory Reserve Volume (ERV) – amount of air
exhaled after normal expiration ~1200ml
◦ Residual volume (RV) – amount of air remaining
after maximal expiration (dead air space) ~1200ml
Pulmonary Function Tests

Tidal Volume
◦ 7-9ml/kg
◦ 500ml avg adult

Vital Capacity
◦ 4800 ml
◦ Maximum amount of air exhaled after maximal
inspiration
Measure WOB
Pulmonary Function Tests

Minute Ventilation (VE = VT X f)
◦ 5 – 10 L/min
◦ 500ml x 18 = 9000ml or 9L

Forced Expiratory Volume- FEVs – Peak
Flow
Figure 9–17: Pulmonary function tests. The relationship of lung volumes and capacities.Volumes (mL) shown are for an
average adult male.
Pulse Oximetry
Noninvasive technique
 Uses light wavelengths
 Detects pulsatile flow
 Uses a sensor
 Fingers are most commonly used for
placement

Causes of Inaccurate Readings
Many factors can alter the accuracy of
pulse oximetry in high-acuity patients
 Technical problems
 Physiologic factors

Capnography
Monitor C02 levels
 PETCO
 Usefulness for patients on PCA pump
 Use during ACLS

Capnography
Nasal cannula
capnography
Endotracheal
Tube
Capnography
Invasive Blood Gas Monitoring
Arterial catheter is an invasive means to
monitor hemodynamic status and
pulmonary gas exchange status
 Arterial catheters are most commonly
inserted into a radial artery
 May be inserted into a femoral or other
artery
 Major advantage is that frequent samples
can be obtained without causing
additional trauma and pain to the patient

References
Carlson, K. (2013). Advanced Critical Care Nursing. St. Louis, MO: Saunders, Elsevier.
Chulay, M. & Burns, S. (2011). AACN Essentials of Critical Care Nursing. New York, New York:
McGraw-Hill.
Wagner, K., Johnson, K., Hardin-Pierce, M. (2014). High Acuity in Nursing, (6th ed.) Upper Saddle
River, NJ: Pearson.