Formulas

Question 1

What is the Alveolar Air Equation?

PA02

Answer 1

PAO2 = FIO2(PB - PH2O) - [PaCO2/.8]

If fio2 >= .60

PA02 = fi02(PB-Ph20)-(PaC02/1)

Question 2

What is the formula for Arterial Oxygen Content?

Ca02

Answer 2

CaO2 % = [Sa02 x Hb x 1.34] + (PaO2 x 0.003 mL/dL)

Question 3

What is the Physiological Shunt formula?

Qs/Qt

Answer 3

QS/QT = CcO2 – CaO2
—————–
CcO2 – CvO2

Question 4

What is the formula for Venous Oxygen Content?

Cv02

Answer 4

CvO2 % = [(Venous 02 Sat) x Hb x 1.34] + (PvO2 x 0.003 mL/dL)

Question 5

What is the formula for Capillary oxygen content?

Cc02

Answer 5

CcO2 = [Hb x 1.34] + (PAO2 x 0.003 mL/dL)

in % form

Question 6

What is the formula for P/F ratio?

Answer 6

Pa02/Fi02

Question 7

What are the ranges and interpretation for P/F ratio?

Answer 7

> 400 normal

Question 8

How do you calculate for oxygen gradients between alveolar and blood? whats the formula?

What is the range for normal healthy individuals?

Answer 8

Aa Gradient.
P(A-a)02 = PA02 - Pa02 (answer in mm Hg)

5-10 mmhg

Question 9

What is the normal amount of shunting?

Answer 9

2-3%

Question 10

What is a severe amount of shunting?

Answer 10

> 30%

Question 11

What is the equation for PaC02 production?

Answer 11

PaC02 = 0.863(Vc02[minute C02 prod in ml])
—————————————–
VA[Alveolar vent]

Question 12

What is the equation for Alveolar Ventilation? (VA)

Answer 12

(Tidal Vol - Dead Space) x RR = VA

Question 13

What is the Physiological Dead Space equation? (Vd/Vt)

Answer 13

Vd/Vt = (PAC02-PeC02)/PAC02)

PaC02 can also be used as a substitute.

Question 14

How can you calculate estimated changes in HC03 in acute alveolar hypoventillation?

Answer 14

A increase in Pac02 of 10 mmHg will immediately increase HC03 by 1 mEq/L.

the equation to use is:
ΔHCO3 = 0.10 x ΔPaCO2

Question 15

How can you calculate estimated changes in HC03 in acute alveolar hyperventillation?

Answer 15

As PaCO2 decreases by 10mm Hg the HCO3– will immediately decrease by 2 mEq/L

The equation is:
ΔHCO3– = 0.20 x ΔPaCO2

Question 16

How is pH affected when PaC02 is increased by 10 mmhg?

Answer 16

pH will DECREASE by 0.06

Question 17

How is pH affected when PaC02 is decreased by 10 mmhg?

Answer 17

pH will INCREASE by 0.10

Question 18

How do you calculate for Time Constants?

Answer 18

Static Compliance (in L/Cm H20) x Airway Resistance = Time Constant in secs.

This is only 1 unit as you’ll need to multiply it by a constant of 1-5 depending on target % volume inspiration or expiration

Question 19

what is the conversion from mmHg to cm H20

Answer 19

1mm = 1.36 cm h20

760 mmHg = 1034 cm H20

Question 20

What is the equation for TransPULMONARY pressure? (PL)

What does it measure?

Answer 20

PL = P alv - P PLURAL
Pressure difference between alveolus and PLURAL space
Maintains alveolar inflation

Question 21

What is the equation for transAIRWAY pressure?
(P ta)
What does it measure?

Answer 21

P ta = P (AIRWAY opening) - P (alv) or (PIP - Plat)

Pressure difference between airway opening and avleolus Airway Resistance

Question 22

What time constant factors and their receptive % of volume (inspiration or expiration) equivalent.

Answer 22

1: 63%
2: 86%
3: 95%
4: 98%
5: 100%

Question 23

For every increase in PaC02, what is the Change in Pa02?

Answer 23

As PaCO2 increases by 1mm Hg,

PaO2 decreases by 1.25mm Hg

Question 24

PIP is the sum of what 2 pressures at the end of inspiration?

Answer 24

TransAIRWAY (P ta) and Pressure in the alveoli (P alv)

Question 25

What is the equation for a/A ratio?

What is the normal range?

Answer 25

a/A ratio = Pa02/PA02

Normal is > .80
Elderly > .75

Question 26

What is the equation for predicted Pa02?

Answer 26

PaO2 = 104.2 – (0.27 x Age)