APPLIED PHYSIOLOGY | The Lungs and Anesthesia

Question 1

TRUE or FALSE

Removal of carbon dioxide (CO2) is determined by alveolar ventilation, not by total (minute) ventilation

Answer 1

TRUE

Question 2

Which of the following statement is INACCURATE regarding the physiologic changes of respiratory physiology during general anesthesia:

A. General anesthesia causes ventilation-perfusion mismatch (airway closure) and shunts (atelectasis)

B. Venous admixture is due to ˙VA/˙Q mismatch (response to increased FiO2) and shunts (unresponsive to increased FiO2)

C. Hypoxic pulmonary vasoconstriction is blunted by most anesthetics, and this results in increased ventilation-perfusion mismatching.

D. Respiratory work is decreased as a consequence of increased respiratory compliance and increased airway resistance.

Answer 2

D. Respiratory work is decreased as a consequence of increased respiratory compliance and increased airway resistance.

Remember that during GENERAL ANESTHESIA, the respiratory work increased as a consequence of reduced respiratory compliance and increased airway resistance.

Compliance relates changes in pressure to changes in volume. For example, highly compliant lungs require less pressure to take in large volumes of air. A stiff lung (ARDS, high extravascular lung water, interstitial lung disease) will require much more pressure to drive in the same volume.

During tidal breathing, inspiratory work equals the area under the pressure-volume (P-V) loop between the functional residual capacity (FRC - air left in the lung after normal expiration) and the tidal volume (VT - air inspired during normal breathing). For the mathematically inclined, it’s the integral of PdV from VT to FRC.

Question 3

What is the normal resting TIDAD VOLUME

A. 5-7 ml/kg

B. 2-3 ml/kg

C. 2,000 - 2,500 ml

Answer 3

5-7 ml/kg

Question 4

What is the Bohr effect?

A. Shift of the oxyhemoglobin dissociation curve to the RIGHT in the presence of 2,3-DPG to facilitate oxygen unloading

B. Shift of the oxyhemoglobin dissociation curve to the LEFT in the presence of 2,3-DPG to facilitate oxygen unloading

Answer 4

Shift of the oxyhemoglobin dissociation curve to the right in the presence of 2,3-DPG to facilitate oxygen unloading

Question 5

Anatomic dead space begins at the mouth and/or nose and ends at the:

A. Lobar bronchi
B. Respiratory bronchioles
C. Terminal bronchioles
D. Alveolar ducts
E. Alveolar sacs

Answer 5

C. Terminal bronchioles

Conducting airways do not participate in gas exchange because they contain no alveoli. The conducting airways begin at the mouth and/or nose and end at the end of the terminal bronchioles. Respiratory bronchioles do participate in gas exchange.

Question 6

What is the normal FRC?

A. 30 mL/kg
B. 20 mL/kg
C. 45 mL/kg
D. 100mL/kg

Answer 6

A. 30 mL/kg or approximately 2.5L

Question 7

TRUE or FALSE

During apnea, PaCO2 increases ∼10 mmHg in the first minute and 3.5 mmHg per minute
afterward.

Answer 7

TRUE

Question 8

Vital capacity is decreased by 25% to 50% within 1 to 2 days after surgery. Generally, when does vital capacity return to its normal state post-operatively?

A. 1 to 2 weeks after surgery

B. 24 hours after surgery

C. 48 hours after surgery

D. 1 month after surgery

Answer 8

A. 1 to 2 weeks after surgery

Vital capacity is decreased by 25% to 50% within 1 to 2 days after surgery and generally returns to normal after 1 to 2 weeks

Question 9

When will TV (tidal volume) return to normal after surgery?

A. after 2 weeks

B. after 48 hours

C. after 1 week

D. after 2 days

Answer 9

A. after 2 weeks

Tidal volume (VT) decreases by 20% within 24 hours after surgery and gradually returns to normal after 2 weeks.

Question 10

What is the FEV1/FVC ratio of a patient with OBSTRUCTIVE pulmonary disease?

A. Increased

B. Decreased

Answer 10

DECREASED or LOW

The ratio FEV1/FVC is useful in differentiating between restrictive and obstructive pulmonary diseases. This ratio is normal in restrictive disease because both FEV1 and FVC decrease, whereas in obstructive disease the ratio is usually low because the FEV1 is markedly decreased compared to the FVC.

Question 11

TRUE or FALSE

The supine position reduces the FRC by 0.8 to 1.0 L

Answer 11

TRUE

Question 12

For the average adult at rest, minute ventilation is about:

Answer 12

5L/min

For the average adult at rest, minute ventilation is about 5 L/min

Question 13

In the upright position, the normal DEAD space is:

A. 150mL

B. 100mL

C. 250mL

D. 45mL

Answer 13

A. 150mL

Dead space is actually composed of gases in nonrespiratory airways (anatomic dead space) and alveoli that are not perfused (alveolar dead space).
The sum of the two components is referred to as physiological dead space.

In the upright position, dead space is normally about 150 mL for most adults (approximately 2 mL/kg) and is nearly all anatomic.

Question 14

What is the normal V/Q ratio?

A. 0.8 to 1.0
B. 0.5
C. 1.5

Answer 14

A. 0.8 to 1.0

For efficient and effective gas exchange, two systems must co-exist—(1) ventilation (V)—the
inflow and outflow of gas transport in the alveolar space, and (2) perfusion (Q)—the inflow and outflow of gas transport in the capillary.

Overall, the V/Q ratio is 0.8 where normal ventilation in the alveoli is 4 L/min and normal
cardiac output is 5 L/min.

Question 15

TRUE or FALSE

When standing or in an upright position, the alveolar pressure is higher than the pulmonary artery and venous pressure hence the alveoli in the apex receive little blood flow.

Answer 15

TRUE

In Zone 1, alveolar pressure (PA) exceeds pulmonary artery pressure (Ppa), and no flow occurs because the vessels are collapsed.

Question 16

Which of the following disease states causes an increase in V/Q ratio?

A. Pulmonary embolism

B. Hepatopulmonary syndrome

C. Pulmonary edema

D. Chronic bronchitis

Answer 16

A. Pulmonary embolism

States that increase the V/Q ratio (known as dead-space ventilation) cause the opposite. These most
prominently include pulmonary embolism for which a V/Q scan is an often used diagnostic modality, as well as systemic hypotension. Both of these pathologic states decrease blood flow to an area of normally ventilated lung.

Pathologic states that lower the V/Q ratio (also known as a shunt) either increase the blood flow to non-ventilated areas of the lung or decrease ventilation in normally perfused portions of the lung. Examples of the former include hepatopulmonary syndrome, while examples of the latter include small airway obstructive diseases such as chronic bronchitis or asthma as well as
acute pulmonary edema.

This pathologic states DECREASE blood flow to an area of normally ventilated lung.

Question 17

TRUE or FALSE

Elevated ICP causes a left shift in the CO2/ventilation response curve.

Answer 17

TRUE

Question 18

Emphysema causes an __ in alveolar and anatomic dead space:

A. Increased
B. Decreased
C. Unchanged

Answer 18

A. Increased

In emphysema, an obliteration of pulmonary capillaries can lead to increased anatomic dead space (no more V/Q) and increases alveolar dead space because alveoli become non-functional.

Question 19

How does static compliance differ from dynamic compliance measurements?

A) Static compliance measures the lung at a fixed volume

B) Static compliance measures the lung during rhythmic breathing

C) Static compliance is obtained by the change in pressure over the change in volume

D) Static compliance is decreased by pulmonary fibrosis while dynamic compliance is not

Answer 19

A) Static compliance measures the lung at a fixed volume

Static compliance measures the lung at a fixed volume unlike dynamic compliance, which measures the lung during normal rhythmic breathing.

STATIC - Fixed volume
DYNAMIC - Rhythmic breathing

Pulmonary compliance measurements reflect the elastic properties of the lungs and thorax. The equation to determine lung compliance is the change in lung volume over the change in airway pressure.

Compliance is usually expressed in liters (or
millimeters) per kilopascal (or centimeters of water) with a normal value around 150 mL/cmH2O. There are two ways compliance can be described – static or dynamic.

Static compliance is measured after the lung has been held at a fixed volume for as long as possible. Dynamic compliance is measured during the course of normal rhythmic breathing. Compliance is the reciprocal of elastance.

Question 20

Which of the following hormones is LEAST likely to be metabolized by the lungs or within the pulmonary circulation?

A) Bradykinin
B) Epinephrine
C) Norepinephrine
D) Serotonin

Answer 20

B) Epinephrine

The lungs and components of the pulmonary circulation play a significant role in the metabolism of multiple hormones, many of which have vasoactive properties.

Angiotensin-converting enzyme (ACE) is found in great quantities on pulmonary endothelium. The enzyme cleaves almost 70% of the angiotensin I that passes through the pulmonary circulation into angiotensin II. Bradykinin (A) is also cleaved by ACE, but
this results in the former’s inactivation.

Pulmonary endothelium selectively takes up norepinephrine (C) and serotonin (D) from the pulmonary circulation and degrades
the hormones intracellularly. Up to 30% of norepinephrine and >95% of serotonin is removed from the blood with a single pass
through the pulmonary circulation.

Intracellular monoamine oxidase (MAO) breaks down both hormones while catechol omethyltransferase also degrades norepinephrine.

Dopamine, epinephrine (B), and histamine are not metabolized or removed from the pulmonary circulation since the pulmonary endothelium lacks an active transport mechanism for these hormones.

Question 21

Which of the following is evident when considering pulmonary function in the neonate?

A) A pliable rib cage causes retractions with less efficient gas exchange

B) Chest wall compliance is low with an increased lung compliance

C) The intercostal muscles are very important for gas exchange in the neonate

D) There are a greater number of type 1 muscle fibers in the neonate

Answer 21

A) A pliable rib cage causes retractions with less efficient gas exchange

Pulmonary function in the neonate is quite different from that in an adult. Neonates have a more pliable rib cage with more retractions. This leads to less efficient gas exchange and functional airway closure, which causes an increased work of
breathing.

Given the poorly developed intercostal muscles in the neonate, the diaphragm takes on the role of providing most of the gas exchange.

Question 22

The most important muscle of respiration in the neonate is:

A. diaphragm

B. intercostals

Answer 22

DIAPHRAGM

Neonates have a pliable rib cage. This causes retractions, making gas exchange less efficient. Neonates also have a lower lung compliance but an increased chest wall compliance, as only 25% of type 1 muscle fibers are in the diaphragm.

The diaphragm is the most important muscle of respiration in the neonate, as the intercostal muscles are not fully developed.

The diaphragm is made of both type 1 and type 2 muscle fibers. Type 1, high-oxidative fibers with less fatigue, make up only 25% of the neonate’s
diaphragm, whereas the mature diaphragm has approximately 55%.

This can subsequently lead to respiratory fatigue in the neonate when faced with an increased airway resistance.

Question 23

The maturity of alveoli and airways continue to develop in newborn until:

A. 8 years of age

B. 2 years of age

C. 5 years of age

Answer 23

A. 8 years of age

Question 24

The diaphragm as a muscle of respiration is fully developed at what age?

A. 2 years of age

B. 5 years of age

C. 12 months of age

Answer 24

A. 2 years of age

The diaphragm in the neonate has two types of fibers, the type 1, slow twitch, high-oxidative fibers that give sustained contraction with very little fatigue, and the type 2, fast twitch, low-oxidative fibers that give quick contractions but fatigue easily.

The distribution of these fibers in the newborn shows only about 25% type 1 fibers, whereas 55% of the fibers are type 1 in the mature diaphragm at about 2 years of age.

Neonates have approximately 25% of type 1 fibers (slow twitch), while the mature diaphragm has approximately 55% of these fibers. Type 2 fibers, or fast twitch fibers, fatigue faster but are more useful for short powerful bursts of movement.

TYPE 1 - slow
TYPER 2 - fast>fatigue>power

Question 25

TRUE or FALSE

Will a decreased functional residual capacity results in a more rapid or slower uptake of inhalational agents in pregnant patients?

What is the cause of this change in in uptake?

Answer 25

A decrease in FRC results to a RAPID uptake of inhaled anesthetics.

The decreased functional residual capacity (FRC) that is seen during pregnancy is caused primarily by the cephalad displacement of the diaphragm as well as by the general increase in body mass. This decrease in FRC will have two major effects. First, a decreased FRC will result in more rapid desaturation during periods of apnea.

This is doubly true in pregnant patients who have an increased oxygen consumption at baseline. Second, this decreased FRC will result in the more rapid uptake of inhalational anesthetic agents as the alveoli are more rapidly saturated with inspired anesthetic gas.

Question 26

What is the normal A-a gradient?

A. 3 - 15 mmHg

B. 10 - 15 mmHg

C. 15 - 25 mmHg

Answer 26

A. 3 - 15 mmHg

A normal A-a gradient ranges from 3 - 15 mmHg.

A difference > 15 mmHg indicates that there is a problem with gas exchange, suggesting lung pathology.

Question 27

Which of the following contributes the MOST to rapid oxygen desaturation during periods of apnea in the obese patient?

A) Decreased inspiratory capacity

B) Diagnosis of obstructive sleep apnea

C) Increased functional residual capacity

D) Increased respiratory system compliance

E) Tidal volume overlapping with closing capacity

Answer 27

E) Tidal volume overlapping with closing capacity

Closing capacity represents the volume at which the respiratory bronchioles begin to collapse and is calculated by the sum of the residual volume and closing volume. Due to the reduction in FRC, the obese patient’s closing capacity may be very near to, or even overlap with the tidal volume.

This may result in airway collapse with normal tidal ventilation and predisposes the patient to atelectasis and rapid oxygen desaturation with even brief periods of apnea.

Question 28

Cyanide toxicity causes which type of acid-base disorder?

A. Elevated anion gap metabolic acidosis

B. Normal anion gap metabolic acidosis

C. Mixed type of acidosis

Answer 28

A. Elevated anion gap metabolic acidosis

Question 29

TRUE or FALSE

Unlike FRC, closing capacity is unaffected by posture.

Answer 29

TRUE

Closing capacity is normally well below FRC but rises steadily with age. This increase is probably responsible for the normal age-related decline in arterial O2 tension.

At an average age of 44 years, closing capacity equals FRC in the supine position; by age 66, closing capacity equals or exceeds FRC in the upright position in most individuals.

Unlike FRC, closing capacity is unaffected by posture.

Question 30

The volume at which these airways begin to close in dependent areas of the lung is called:

A. closing capacity

B. dynamic compliance

C. static compliance

D. Inspiratory capacity

Answer 30

A. closing capacity

At an average age of 44 years, closing capacity equals FRC in the supine position; by age 66, closing capacity equals or exceeds FRC in the upright position in most individuals.

Question 31

Which of the following causes a RIGHT shift in the O2 dissociation curve?

A. Sevoflurane

B. Hypothermia

C. Alkalosis

D. elevated 2,3-DPG

Answer 31

A. Sevoflurane

RIGHT SHIFT:

ACIDOSIS
Hyperthermia
Pregnancy

Volatile anesthetics
Dereased 2,3-DPG

Question 32

This phenomenon happens when Hg is deoxygenated and bind more CO2:

A. Haldane Effect

B. Bohr Effect

Answer 32

A. Haldane Effect

Question 33

TRUE or FALSE

The “normal” value for arterial oxygen tension (PaO2) decreases with age.

Answer 33

TRUE

Question 34

Which of the following parameters is MOST likely to be part of the orders for pressure support ventilation PSV?

(A)	Tidal volume
(B)	Rate
(C)	Inspiratory pressure
(D)	Inspiratory flow rate

Answer 34

(C) Inspiratory pressure

Pressure support ventilation (PSV) is intended to facilitate spontaneous inspiration. When a patient initiates a spontaneous breath, the ventilator provides an inspiratory assist by increasing flow in the circuit until the designated level of PSV is achieved.

A pressure support breath may be triggered by changes in pressure, flow, or volume. The physician orders the level of inspiratory pressure to be maintained during spontaneous inspiration.

Question 35

Which statement about age-related physiologic changes in geriatric patients (age ≥ 65) is MOST likely true?

(A) The closing volume increases with age

(B) The response to beta-adrenergic agonists increases with age.

(C) There is progressive atrophy of the left ventricle with age.

(D) There is a steady increase in the chest wall compliance with age.

Answer 35

(A) The closing volume increases with age

The closing volume is the volume at which dynamic compression and closure of small airways occur. As individuals age, they lose lung elasticity and their closing volume increases linearly, eventually exceeding expiratory reserve volume.

Consequently by the age of 65, airway closure occurs at the end of a normal tidal volume breath even in the upright position (Figure 1). The age-related changes result in atelectasis, airway collapse, and a reduced physiologic oxygen reserve

Question 36

Which of the following is MOST likely to be INCREASED as a result of administration of 100% oxygen to a normal, healthy patient for six hours?

(A)	Pulmonary compliance
(B) 	Vital capacity
(C)	Shunt fraction
(D)	PaCO2

Answer 36

(C) Shunt fraction

Absorption atelectasis occurs in lung units with low ventilation:perfusion ratios when absorption of oxygen from the alveolus exceeds the rate of inflow of gas into the alveolus.

When breathing room air—even if all the oxygen is absorbed from the alveolus—the presence of nitrogen prevents collapse of the lung unit (nitrogen splint) under normal circumstances.

Absorption atelectasis can be demonstrated within 30 minutes of breathing 100% oxygen. Atelectasis produces an increase in shunt fraction and a decrease in lung compliance.

prolonged 100% O2 > Absorption atelectasis > Increase SHUNT fraction > decrease COMPLIANCE

Question 37

Positive end-expiratory pressure is effective for treatment of hypoxia resulting from each of the following EXCEPT

(A) cardiogenic pulmonary edema
(B) intraoperative Trendelenburg position
(C) lateral position during total hip replacement
(D) lung contusion
(E) status asthmaticus

Answer 37

(E) status asthmaticus

Why?

As with virtually everything in mechanical ventilation of asthma, this topic is somewhat controversial. The conventional teaching is to minimize the PEEP for these patients. In fact you’re often ventilating them with zero PEEP (ZEEP).

The rationale for this is:
In terms of getting all the beneficial PEEP effects (eg. increased FRC, better oxygenation), there is no need for any additional ventilator-generated PEEP because the patient already has plenty of intrinsic PEEP.

Oxygenation is not the issue in any case.

The gradient between intrathoracic pressure (intrinsic PEEP) and extra-thoracic pressure (ventilator-generated PEEP) is what drives expiratory flow, and therefore surely we would want to maximize this gradient to promote expiratory CO2 clearance.

Question 38

The carbon dioxide/ventilation response curve:

(A) is primarily a measure of the integrity of the peripheral chemoreceptors

(B) shows parallel displacement to the left in the presence of opioids

(C) is linear between a PaCO2 of 20 and 120 mmHg

(D) shows progressive changes in slope with increased doses of halogenated anesthetics

(E) is unaffected by a decrease in PaO2 to 60 mmHg

Answer 38

(D) shows progressive changes in slope with increased doses of halogenated anesthetics

Question 39

A previously healthy 28-year-old man is admitted to the emergency department with a probable opioid overdose. Arterial blood gas values are: PaO2 49 mmHg, PaCO2 76 mmHg, and pH 7.12 while breathing room air. Which of the following statements is true?

(A) Aspiration of gastric contents must have occurred
(B) Hypoventilation alone can explain the acidosis and hypoxemia
(C) The hypoxemia is probably due to noncardiogenic pulmonary edema
(D) Naloxone should be administered only if the patient is normothermic
(E) Pure oxygen is contraindicated

Answer 39

(B) Hypoventilation alone can explain the acidosis and hypoxemia