0. Physiology Equations

Question 1

What are the equations for calculating whether or not respiratory acidosis is acute or not?

Answer 1

Acute:

HCO3 = 24 + (PaCO2 - 40)/10

Chronic:

HCO3 = 24 + 4(PaCO2 - 40)/10

Question 2

What is the equation for calculating whether or not a patient is compensated adequately for metabolic alkalosis?

Answer 2

Expected change in PaCO2 = (.5 to 1.0) change in HCO3

Question 3

What is the equation for calculating whether or not a patient is compensated adequately for metabolic acidosis?

Answer 3

PaCO2 = 1.5(HCO3) + 8 +/- 2

Question 4

What are the equations for calculating whether or not respiratory alkalosis is acute or not?

Answer 4

Acute

Expected HCO3 = 24 - 2(40 - PaCO2)/10

Chronic:

Expected HCO3 = 24 - 5(40 - PaCO2)/10

Question 5

What is the equation for calculating anion gap?

Answer 5

Anion gap = [Na] - ([Cl] + [HCO3])

Question 6

What is the equation for minute ventilation?

Answer 6

Tidal volume x frequency

Question 7

What is the equation for minute alveolar volume?

Answer 7

(Tidal Volume - Dead space) x frequency

Question 8

What is the equation for blood pressure in terms of cardiac output?

Answer 8

BP = CO x Resistance (pulmonary or peripheral)

Question 9

What is the equation for the respiratory quotient?

Answer 9

Volume of CO2 produced / Volume of O2 consumed

OR

Minute ventilation CO2 / Minute ventilation O2

Question 10

What is the (solvable) equation for alveolar O2 given arterial PaCO2?

Answer 10

PAO2 = P_IO₂ - [PaCO2/RQ]

P_IO₂ = Pressure of air (760 at sea level) - Pressure of water (47) x percentage of oxygen (21 in room air)

Question 11

What is the equation for airway resistance?

Answer 11

8nL/r⁴

n = viscosity

L = length of the tube

r = radius of the tube

Question 12

What is the relationhip between pressure and surface tension?

Answer 12

LaPlace’s law

Pressure = 2(tension)/radius