Syllabus Equations

Question 1

What is normal PAO2? Normal PACO2? Normal PAH2O?

Answer 1

PAO2 = 104 mmHg
PACO2 = 40 mmHg
PAH2O = 47 mmHg

Question 2

What is normal physiologic pH?

Answer 2

7.40 (arterial) - 7.37 (mixed venous)

Question 3

What is the O2 saturation of hemoglobin in arterial blood? In mixed venous blood?

Answer 3

97% in arterial, 75% in venous

Question 4

What is the equation for dead space ventilation?

Answer 4

VD/VT = (PaCO2-PECO2)/PaCO2

Question 5

What is the equation for alveolar gas? What are the normal values of the variables?

Answer 5

PAO2 = (PB-PH2O)(FiO2) - PaCO2/R

PB = barometric pressure, usually 760 mmHg
PH2O = 47 mmHg
FiO2 = 0.21
R = 0.8

Question 6

What is the equation for A-a gradient? What are the normal values of the variables?

Answer 6

A-a gradient = (PB-PH20)(FiO2) - [PaO2 + (PaCO2/R)]

PB = barometric pressure, usually 760 mmHg
PH2O = 47 mmHg
FiO2 = 0.21
R = 0.8

Question 7

What is a normal A-a gradient?

Answer 7

A-a < 10

Question 8

What are the equations for PaCO2? What do the variables stand for?

Answer 8

PaCO2 = (KVCO2)/VA = (KVCO2)/[VE*(1-VD/VT)

K = a constant = 0.863
VCO2 = CO2 production
VA = alveolar ventilation
VE = total minute ventilation
VD/VT = dead space ventilation

Question 9

What is the equation for compliance?

Answer 9

C = ∆V/∆P

Question 10

What is the equation for pulmonary artery pressure? What do the variables stand for?

Answer 10

PA = (PVR*CO) + PCWP

PVR = pulmonary vascular resistance
CO = cardiac output
PCWP = pulmonary capillary wedge pressure

Question 11

What is the normal content of hemoglobin in the blood?

Answer 11

15g/100ml

Question 12

What is the equation for total oxygen content in the blood? What do the variables stand for?

Answer 12

CxO2 = (1.34HgbSxO2) + (0.003*PxO2)

x = either arterial (a) or venous (v)
Hgb = hemoglobin, usually 15g/100ml
S = saturation

Question 13

What is the equation for acute respiratory acidosis?

Answer 13

∆pHa = ∆PaCO2 x 0.008 (subtract ∆pHa from starting pHa)

Question 14

What is the equation for chronic respiratory acidosis?

Answer 14

∆pHa = ∆PaCO2 x 0.003 (subtract ∆pHa from starting pHa)

Question 15

What is the equation for acute respiratory alkalosis?

Answer 15

∆pHa = ∆PaCO2 x 0.008 (add ∆pHa to starting pHa)

Question 16

What is the equation for chronic respiratory alkalosis?

Answer 16

∆pHa = ∆PaCO2 x 0.0017 (add ∆pHa to starting pHa)

Question 17

What is the mnemonic for restrictive lung disease? What does it stand for?

Answer 17

P - pleural
A - alveolar filling
I - interstitial
N - neuromuscular
T - thoracic cage

Question 18

What is the mnemonic for obstructive lung disease? What does it stand for?

Answer 18

F - foreign body or upper airway disease
A - asthma
C - chronic bronchitis or bronchiectasis
E - emphysema
S - small airway disease