equations to memorize

Question 1

how to calculate patients alveolar ventilation rate

Answer 1

AVR = (tidal volume- anatomical dead space) x ventilation frequency
norm: TV= 500 ml, anat. dead space= 150 ml, vent freq= 12
AVR= 4.2 L/min

Question 2

calculating dead space

Answer 2

VD/VT = (PaCO2 - PECO2)/PaCO2

Question 3

estimate AVR based on PaCO2

Answer 3

AVR = 1/PaCO2

Question 4

alveolar gas equation for calculating PAO2

Answer 4

PAO2 = PIO2 - (PaCO2/.8)

Question 5

PIO equation

Answer 5

FIO2 (PB-PH2O)

norm: PIO=150, PB = 760, PH2O= 47, FIO2: 21

Question 6

P(A-a)O2

Answer 6

norm: (age +10)/4, or 5-15 mmHg

Question 7

Fick’s principle

Answer 7

Q = VO2/(CaO2 - CvO2)

Cardiac out put = rate of O2 uptake over difference in content of O2

Question 8

Fick’s law

Answer 8

(AxD)/T or Vgas/(P1x - P2x) = Dlx

A= area, D= diffusion constant, T= thickness
Vgas= rate of gas exchange, over difference of gas on each side of membrane

Question 9

henderson hasselbalch equation

Answer 9

pH= pKa + log10 (HCO3-/.03 x PaCO2)

norm: pH= 7.4, PaCO2= 40 mmHg, HCO3-= 24 mEq/L

Question 10

O2 content

Answer 10

O2 sat x Hb concentration x 1.34 plus dissolved O2

Question 11

O2 capacity

Answer 11

Hb concentration x 1.34 + dissolved

norm: Hb= 13.5

Question 12

dissolved O2

Answer 12

.003 x PO2

Question 13

Ptp

Answer 13

PTP = PALV -PIP
PALV = 0 in open systems
PALV = system in closed system with relaxed muscles
PIP= lung only when using chest wall muscles