M5 Equations

Question 1

Alveolar Gas Equation

Answer 1

PAO2 = FIO2 (PATM – PH2O )– PaCO2 / RQ

Question 2

Dead Space (Bohr Equation)

Answer 2

VD/VT = (PaCO2 –PECO2) / (Pa CO2)

Question 3

Ohm’s Law

Answer 3

Pressure Gradient = Air Flow x Airway Resistance

Question 4

Airway Resistance for Laminar Flow (Poiseuille’s Law)

Answer 4

Laminar Flow Resistance = (8 Length • Viscosity of gas) / (πRadius^4 )

Question 5

Reynold’s Number

Answer 5

R = (Velocity x Density x Diameter) / (Viscosity)

> 2000 consistent with turbulent flow

Question 6

Static Compliance

Answer 6

Static compliance = Volume/Pressure = (Tidal volume delivered) / (Plateau pressure – PEEP)

Question 7

Dynamic Compliance

Answer 7

Dynamic compliance = Volume/Pressure = (Tidal volume delivered) / (Peak pressure – PEEP)

Question 8

Law of LaPlace

Answer 8

Pressure = (2 • Wall Tension) / (Radius)

Note: wall thickness is typically not considered for alveoli

Question 9

Transpulmonary Pressure

Answer 9

Transpulmonary pressure = Alveolar pressure – Pleural pressure

Question 10

Transthoracic Pressure

Answer 10

Transthoracic pressure = Pleural pressure – Atmospheric pressure

Question 11

Predicted PaO2 by Age

Answer 11

Predicted PaO2 = 110-(age • 0.4)

Question 12

Boyle’s Law

Answer 12

Pressure1 • Volume1 = Pressure2 • Volume2

Question 13

Ohm’s Law

Answer 13

Pressure = Cardiac Output • Resistance

Question 14

Myocardial Perfusion Pressure

Answer 14

MPP = Aortic diastolic pressure – LVEDP

Question 15

LaPlace Law

Answer 15

Tension = (Pressure • Radius)/(2 • Wall Thickness)

Note: Notice that as opposed to the equation in the Respiratory Section, the equation is solved for wall tension

Question 16

Poiseuille’s Law

Answer 16

Flow Rate = (π • Pressure • radius4)/(8 • viscosity • length)

Note: Notice that as opposed to the equation in the Respiratory Section, the equation is solved for flow.

Question 17

Fick Principle

Answer 17

CO = VO2/(CaO2 – CmvO2)

VO2 = Oxygen consumption
CaO2 = Arterial content of oxygen
CmvO2 = Mixed venous content of oxygen

Question 18

Consumption of Oxygen

Answer 18

VO2 = Hb • (Sata - Satmv) X 1.34 • CO

Rearranged: Satmv = Sata – [VO2/ (Hb • 1.34 • CO)]

Question 19

Arterial Content of Oxygen

Answer 19

CaO2 = [Hb • Sata • 1.34] + 0.003 • PaO2

Question 20

Respiratory Quotient

Answer 20

RQ = VCO2/VO2

VCO2 = Elimination of CO2
VO2 = Oxygen consumption

Question 21

Oxygen Delivery

Answer 21

DO2 = CaO2 • CO

CaO2 = Arterial content of oxygen

Question 22

Oxygen Extraction Ratio

Answer 22

ER = VO2/DO2

Question 23

Pulmonary Vascular Resistance

Answer 23

PVR = [(PAP-Wedge)/CO] • 80

PAP = Pulmonary Arterial Mean Pressure

Question 24

Stroke Work

Answer 24

SW = Stroke volume • mean arterial pressure

Question 25

Cardiac Index

Answer 25

CI = CO/BSA

Question 26

Systemic Vascular Resistance

Answer 26

SVR = [(MAP-CVP)/CO] • 80

Question 27

Starling Equation

Answer 27

Q = kA X [(Pc – Pi) + σ(πi-πc)] ``` Q = Net Fluid Filtration k = Capillary Filtration Coefficient (of water) A = Area of the Membrane σ = Reflection Coefficient (of albumin) Pc = Capillary Hydrostatic Pressure Pi = Interstitial Hydrostatic Pressure πi = Interstitial Colloid Osmotic Pressure πc = Capillary Colloid Osmotic Pressure. ```

Question 28

Allowable Blood Loss

Answer 28

ABL = EBV X [(Hb – Minimum allowable Hb)/Hb] EBV = Estimated Blood Volume

Question 29

Cerebral Perfusion Pressure

Answer 29

CPP = MAP – ICP

Question 30

Perfusion Pressure

Answer 30

PP = MAP – Venous Presure

Question 31

Volume of Distribution

Answer 31

VD = Dose / Concentration

Question 32

Half Life

Answer 32

Half-life = Volume of distribution / Rate of clearance

Question 33

Clearance

Answer 33

Clearance = dose / area under time concentration curve Clearance = (Urine concentration x Urine flow) / (Plasma concentration)

Question 34

Opioid Conversions

Answer 34

Drug IV Oral Morphine 10 mg 30 mg Hydromorphone 1.5 mg 7.5 mg Fentanyl 100 mcg NA Codeine N/A 200 mg Hydrocodone NA 30 mg Oxycodone NA 20-30 mg

Question 35

Gas Tanks (E)

Answer 35

Gas Volume Pressure Oxygen 625 L 2200 psig Nitrous Oxide 1590 L 745 psig

Question 36

Incidence & Prevalence

Answer 36

Incidence = Number of occurrences / Sum of person-time at risk Prevalence = Number of cases/ Number of individuals sampled

Question 37

Measure of Effect

Answer 37

Absolute measure of effect = Rate Difference = Rate of risk exposed – Rate of risk not exposed Relative measure of effect = Rate Ratio = Rate of risk exposed /Rate of risk not exposed

Question 38

Sensitivity

Answer 38

Sensitivity = TP/ (TP + FN)

Question 39

Specificity

Answer 39

Specificity = TN/ (TN + FP)

Question 40

PPV

Answer 40

Positive Predictive Value = TP/ (TP + FP)

Question 41

NPV

Answer 41

Negative Predictive Value = TN/ (TN + FN)

Question 42

Odds Ratio

Answer 42

Odds Ratio = AD/BC

Question 43

Relative Risk

Answer 43

Relative Risk = [A/(A+B)] / [C/(C+D)]

Question 44

Number needed to Treat

Answer 44

NNT = 1 / ARR