Pass Machine - Pulm

Question 1

Average FRC volume
Average VC volume
Average TLC volume

Answer 1

40 cc/kg (3L in 70kg)
70 cc/kg (5L)
90 cc/kg (6.5L)

Question 2

Acronym for things that cause decreased FRC

Answer 2

PANGOS
Pregnancy
Ascites
Neonates
GA
Obesity
Supine

Question 3

Laplace’s law - importance? surfactant?

Answer 3

P (pressure to keep open a sphere) = surface tension / radius

Larger alveoli = less distending pressure necessary to keep open = inspiration easier after initial airway opening

More surfactant = less surface tension = less pressure required to open a sphere further (counteracting LaPlace’s law)

Result: easier to inhale, and alveoli want to stay open

ARDS: less surfactant = more alveolar collapse

Question 4

How to calculate dead space:tidal volume ratio from PaCO2 and EtCO2

Answer 4

(PaCO2 - EtCO2)/PaCO2 = % of TV that is dead space

Question 5

Why might Zone 3 have more compliance than Zone 1?

Answer 5

Assuming that zone 1 is already distended from never emptying, cannot fill further

Question 6

How does neuromuscular blockade affect A-a gradient?

Answer 6

Worsens it: increases ventilation of Zone 1 -> more dead space ventilation

Question 7

Explain why dependent (zone 3) lung zones have more shunt than upper zones

Answer 7

Even though ventilation and perfusion are BOTH the highest in Zone 3, the difference in perfusion is much greater than the difference in ventilation. SO you get a RELATIVE SHUNT in Zone 3 and RELATIVE DEAD SPACE in Zone 1

Question 8

Why is there more ventilation in Zone 3 than Zone 1?

Answer 8

The pleural pressure at the apex is MORE negative due to less gravity, etc. So at baseline, Zone 1 alveoli are larger and more filled. This negative pressure is harder to overcome during exhalation, so less air is exchanged

Question 9

GA and hypoxic pulmonary vasoconstriction

Answer 9

Inhaled anesthetics inhibit it

Question 10

What is the CO2 response curve?

Answer 10

Relationship between PaCO2 and alveolar ventilation response

Question 11

Things that shift CO2 response curve to the right?

Answer 11

Sleep, narcotics, inhaled anesthetics, barbiturates, metabolic alkalosis, COPD

R-shift: higher paCO2 needed to achieve the same level of ventilation response

Question 12

DRG, VRG, apneustic center, pneumotaxic center

Answer 12

DRG (medulla) = basic resp rate (12-15)
VRG (medulla) = adjust based on exercise, etc
Apneustic (pons) = apneustic breathing (pathologic)
Pneumotaxic (pons) = stretch receptors (CV X) -> stop inhalation

Question 13

Where/how is majority of CO2 stored in the blood?

Answer 13

(1) As HCO3 inside RBCs (60%)

2) Inside RBCs on Hb (20%

Question 14

Explain this ABG in a person on heroin in ED:

• pH 7.33
• paCO2 60
• HCO3 30

Answer 14

Acute respiratory acidosis (hypoventilation) + chronic use causing compensatory metabolic alkalosis (excrete Cl and retain HCO3)

Question 15

Pink puffer vs Blue bloater

Answer 15

Pink puffer (emphysema) = respiratory compensation is adequate via hyperventilation to maintain normal PaCO2

Blue bloater (chronic bronchitis) = chronic elevated PaCO2 and PaO2 low due to airway flow problem

Question 16

What is strong ion difference? Explain

Answer 16

SID = (Na + K + Mg + Ca) - (Cl + lactate)
SID = Na - Cl (basically) --> normal is about 40

Rules of any aqueous solution:

(1) total electrical charge must = 0
(2) strong ions are completely dissociated regardless of pH, thus their concentrations are constant
(3) So, SID must = [all other anions] (bicarb, albumin, PO4, organic acids)

Rules of SID:

(1) SID > 0 = pH > 7 (thus blood pH is 7.4 since SID is 40)
(2) SID < 0 = pH < 7

So a change in SID means some change in hidden anions in the body. Thus, any pathologic process that alters a strong ion concentration (including organic acids which = anions) will alter the pH

Question 17

Morphine, mivacurium, and sevo on airway resistance

Answer 17

Morphine -> histamine -> potential worsening
Mivacurium -> same
Sevo -> airway dilation