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Flashcards in M5 Equations Deck (44):
1

Alveolar Gas Equation

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

2

Dead Space (Bohr Equation)

VD/VT = (PaCO2 –PECO2) / (Pa CO2)

3

Ohm’s Law

Pressure Gradient = Air Flow x Airway Resistance

4

Airway Resistance for Laminar Flow (Poiseuille’s Law)

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

5

Reynold’s Number

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

>2000 consistent with turbulent flow

6

Static Compliance

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

7

Dynamic Compliance

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

8

Law of LaPlace

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

Note: wall thickness is typically not considered for alveoli

9

Transpulmonary Pressure

Transpulmonary pressure = Alveolar pressure – Pleural pressure

10

Transthoracic Pressure

Transthoracic pressure = Pleural pressure – Atmospheric pressure

11

Predicted PaO2 by Age

Predicted PaO2 = 110-(age • 0.4)

12

Boyle’s Law

Pressure1 • Volume1 = Pressure2 • Volume2

13

Ohm’s Law

Pressure = Cardiac Output • Resistance

14

Myocardial Perfusion Pressure

MPP = Aortic diastolic pressure – LVEDP

15

LaPlace Law

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

16

Poiseuille’s Law

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.

17

Fick Principle

CO = VO2/(CaO2 – CmvO2)

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

18

Consumption of Oxygen

VO2 = Hb • (Sata - Satmv) X 1.34 • CO

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

19

Arterial Content of Oxygen

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

20

Respiratory Quotient

RQ = VCO2/VO2

VCO2 = Elimination of CO2
VO2 = Oxygen consumption

21

Oxygen Delivery

DO2 = CaO2 • CO

CaO2 = Arterial content of oxygen

22

Oxygen Extraction Ratio

ER = VO2/DO2

23

Pulmonary Vascular Resistance

PVR = [(PAP-Wedge)/CO] • 80

PAP = Pulmonary Arterial Mean Pressure

24

Stroke Work

SW = Stroke volume • mean arterial pressure

25

Cardiac Index

CI = CO/BSA

26

Systemic Vascular Resistance

SVR = [(MAP-CVP)/CO] • 80

27

Starling Equation

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.

28

Allowable Blood Loss

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

EBV = Estimated Blood Volume

29

Cerebral Perfusion Pressure

CPP = MAP – ICP

30

Perfusion Pressure

PP = MAP – Venous Presure

31

Volume of Distribution

VD = Dose / Concentration

32

Half Life

Half-life = Volume of distribution / Rate of clearance

33

Clearance

Clearance = dose / area under time concentration curve

Clearance = (Urine concentration x Urine flow) / (Plasma concentration)

34

Opioid Conversions

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

35

Gas Tanks (E)

Gas Volume Pressure

Oxygen 625 L 2200 psig
Nitrous Oxide 1590 L 745 psig

36

Incidence & Prevalence

Incidence = Number of occurrences / Sum of person-time at risk

Prevalence = Number of cases/ Number of individuals sampled

37

Measure of Effect

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

38

Sensitivity

Sensitivity = TP/ (TP + FN)

39

Specificity

Specificity = TN/ (TN + FP)

40

PPV

Positive Predictive Value = TP/ (TP + FP)

41

NPV

Negative Predictive Value = TN/ (TN + FN)

42

Odds Ratio

Odds Ratio = AD/BC

43

Relative Risk

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

44

Number needed to Treat

NNT = 1 / ARR