Important Equations

Question 1

Sensitivity

Answer 1

^{<img></img>TP} / _{(TP + FN)}

_or

^A / _{(A + C)}

_{<span>or</span>}

_{1 - False Negative Rate}

Question 2

Specificity

Answer 2

^{<img></img>TN} / _{(TN + FP)}

_or

^D / _{(D + B)}

_{<span>or</span>}

_{1 - False Positive Rate}

Question 3

PPV

Answer 3

^{<img></img>TP} / _{(TP + FP)}

_or

^A / _{(A + B)}

Question 4

NPV

Answer 4

^{<img></img>TN} / _{(FN + TN)}

_or

^D / _{(C + D)}

Question 5

Odds Ratio

Answer 5

^{<img></img>A/C} / _B/D

_{<span>or</span>}

^{<img></img>A/B} / _C/D

_or

^{<img></img>AD} / _BC

FOR CASE CONTROL STUDIES

Question 6

Relative Risk

Answer 6

^{<img></img>A / (A + B)} / _{C / (C + D)}

Question 7

Attributable Risk

Answer 7

( ^A / _{(A + B)} ) - ( ^{<span>C</span>} / _{(C + D)} )

Question 8

RRR

Answer 8

1 - RR

Question 9

Attributable Risk Reduction

Answer 9

( ^C / _{(C + D)} ) - ( ^A / _{(A + B)} )

Question 10

Number Needed to Treat

Answer 10

¹ / _ARR

Question 11

Number Needed to Harm

Answer 11

¹ / _AR

Question 12

Hardy-Weinberg Equilibrium

Answer 12

p² + 2pq + q² = 1

p + q = 1

Question 13

Half-life

Answer 13

t½ = ^{.693 x Vd} / _CL

_{Vd= Volume of Distribution}

CL= Clearance

Question 14

Clearance

Answer 14

^{Rate of elimination of drug} / _{plasma drug concentration}

or

Vd x Ke (Ke=elimination constant)

or

^{U x V} / _P

Question 15

Loading Dose

Answer 15

^{Cp x Vd} / _F

Cp= Desired plasma concentration

Vd= Volume of distribution

F= Bioavailability

Question 16

Maintenance Dose

Answer 16

^{Cp x CL x t} / _F

Cp= Desired plasma concentration

CL= Clearance

t = infusion rate/frequency

F= Bioavailability

Question 17

Cardiac Output

Answer 17

CO= SV x HR

or

Ficks Equation:

^{Rate of O₂ Consumption} / _{arerial O² content - venous O² content}

Question 18

Mean Arterial Pressure

Answer 18

MAP = CO x TPR

_or

MAP = ²/₃ Diastolic + ¹/₃ Systolic

Question 19

Stroke Volume

Answer 19

SV= EDV - ESV

Question 20

Ejection Fraction

Answer 20

^SV / _EDV

_or

^{EDV - ESV} / _EDV

Question 21

Resistance

Answer 21

^{Driving Pressure (▲P)} / _{Flow (Q)}

_or

^{8n x length} / _πr⁴

n= viscosity

r= radius

Question 22

Capillary Fluid Exchange

Answer 22

Net Fluid Flow = K_f [(P_c - P_i) - σ(π_c - π_i)]

K_f= constant of filtration?

P_c/i = hydrostatic pressure of capillary or interstitium

π_c/i = oncotic pressure of capillary or interstitium

σ= Reflection coeficient

Postitive Net Fluid Flow = Filtration

Negtive Net Fluid Flow = Reabsorption

Question 23

Renal Clearance

Answer 23

^{Ux V} / _Px

Question 24

Glomerular Filtration Rate

Answer 24

^{Uinulin V} / _Pinulin

_or

GFR = K_f [(P_GC - P_{<span>BS</span>}) - (π_GC - π_BS)]

Question 25

Effective Renal Plasma Flow

Answer 25

eRPF = ^{UPAH V} / _PPAH

Question 26

Renal Blood Flow

Answer 26

^RPF / _{1 - Hct}

RPF can be determined from PAH

Question 27

Filtration Fraction

Answer 27

^GFR / _RPF

Question 28

Henderson Hasselbalch Equation

(for extraceullar pH)

Answer 28

pH = 6.1 + log( ^{[HCO<span>3</span>-]} / _{.03 PCO2} )

Question 29

Winters Formula

Answer 29

P_CO2 = 1.5 [HCO₃-] + 8 _{<strong>^+/-</strong>} 2

Question 30

Physiologic Dead Space

Answer 30

VD = VT x ( ^{PaCO2 - PECO2} / _{Pa<span>CO</span>2} )

Pa_CO2 = Arterial P_CO2 = Alveolar P_CO2

Pa_CO2 = P_CO2 of Expired Air

Question 31

Pulmonary Vascular Resistance

Answer 31

PVR = ^{(Ppulm artery - PL atrium)} / _{Cardiac Output}

Question 32

Alveolar Gas Equation

Answer 32

P_AO2 = P_iO2 - (^Paco2 / _R)

R= respiratory gas quotient (usually .8)

or

P_AO2 = P_iO2 - 1.2(P_{aCO<span>2</span>})

Question 33

Serum Osmolality Equation

Answer 33

Osm = 2Na + ^Glucose/₁₈ + ^BUN/_2.8 + ^EtOH/_4.6

Use in Anion Gap Metabolic Acidosis (MUDPILES)

If Actual Osm - Calculated Osm is > 10 : indicates presence of unaccounted osmoles

Indicates Ethylene Glycol, Propylene Glycol, or Methanol causing anion gap (all are active osmoles)