Equations

Question 1

Alveolar gas equation

Answer 1

(Patm - Ph20)x(FiO2) - PaCO2/R

Question 2

Respiratory Quotient (R)

Answer 2

0.8 - given by CO2 production/O2 consumption

Question 3

Patm

Answer 3

Denver = 630

Sea level = 760

Question 4

Ph20

Answer 4

47

Question 5

Aa gradient

Answer 5

PAO2 - PaO2

normal = 5-15 (but increases to ~100 at 100% O2)

Question 6

PaO2/FiO2 ratio

Answer 6

normal > 300
ALI 300-200
ARDS < 200

Question 7

Oxygenation index (OI)

Answer 7

(MAP x FiO2) / PaO2

Question 8

DO2

Answer 8

CO x CaO2 x 10

Question 9

CaO2

Answer 9

(Hgb x SaO2 x 1.34) + (PaO2 x 0.003)

Question 10

CO

Answer 10

HR x SV

Question 11

CI

Answer 11

CO/BSA

Question 12

SVR

Answer 12

(MAP-CVP)/CO

Question 13

PVR

Answer 13

(MPAP - PCWP)/CO

Question 14

% dead space ventilation (Bohr Equation)

Answer 14

(PaCO2 - ETCO2)/ PaCO2

normal = 30%

Question 15

Alveolar gas equation: units!

Answer 15

DO2 = mLO2/min
CO = L/min
CaCO = mLO2/dL
Hgb = g/dL
1.34 mLO2/gHgb
0.003 mLO2/dL/mmHg

Question 16

Fick Equation

Answer 16

Vgas = Area/Thickness x D x (P1 - P2)
D = solubility/square root of molecular weight

Question 17

Diffusing capacity

Answer 17

DL = Vco/PAco

Question 18

Laplace’s law

Answer 18

P = (4 x surface tension)/radius

Question 19

Poiseuille’s law

Answer 19

Pressure-flow characteristics for laminar flow

V = (P x 3.14 x r4)/(8 x n x l)
R = (8 x n x l)/(3.14 x r4)

P = pressure, r = radius, n = viscosity, l = length

Question 20

Resistance

Answer 20

change in P / flow

Question 21

Reynolds number (Re)

Answer 21

Determines if flow is laminar or turbulent - higher = more likely to be turbulent

(2 x r x v x d)/n

r = radius, v = velocity, d = density, n = viscosity