Equation Review Flashcards
Volume of distribution
Vd = amount of drug in the body/plasma drug concentration
Half-life
t 1/2 = (0.7 x Vd)/Cl
Drug clearance
Cl = rate of elimination of drug/plasma drug concentration = Vd x Ke Ke = elimination constant
Loading dose
LD = (Cp x Vd)/F
Maintenance dose
D = (Cp x Cl x t)/F
Sensitivity
Sensitivity = TP/(TP+FN)
Specificity
Specificity = TN/(TN+FP)
Positive predictive value
PPV = TP/(TP+FP)
Negative predictive value
NPV = TN/(FN+TN)
Odds ratio (for case-control studies)
OR = (a/c)/(b/d) = ad/bc
Relative risk
RR = (a/(a+b))/(c/(c+d))
Attributable risk
AR = (a/(a+b)) - (c/(c+d))
Relative risk reduction
RRR = 1 - RR
Absolute risk reduction
ARR = (c/(c+d)) - (a/(a+b))
Number needed to treat
NNT = 1/ARR
Number needed to harm
NNH = 1/AR
Cardiac output
CO = rate of O2 consumption/(arterial O2 content - venous O2 content) CO = SV x HR
Mean arterial pressure
MAP = CO x TPR MAP = 2/3diastolic BP + 1/3systolic BP
Ejection fraction
EF = SV/EDV = (EDV-ESV)/EDV
Resistance
R = driving pressure/flow = (8n x l)/(pi x r to the 4th)
Stroke volume
SV = EDV-ESV
Renal clearance
Cx = UxV/Px
Capillary fluid exchange
Jv = net fluid flow = some insanity (look it up)
GFR
GFR = Uinulin x V/P inulin = Cinulin
Effective renal plasma flow
eRPF = Upah x (V/Ppah) = Cpah
Renal blood flow
RBF = RPF/(1 - Hct)
Filtration fraction
FF = GFR/RPF
Henderson-Hasselbalch equation (for extracellular pH)
pH = 6.1 + log [HCO3/0.03Pco2]
Winters formula
PCo2 = 1.5[HCO3-] + 8 +/- 2
Physiologic dead space
Vd = Vt x ((PaCO2 - PECO2)/PaCO2)
Pulmonary vascular resistance
PVR = (Ppulm artery - Pl atrium)/cardiac output
Alveolar gas equation
PAo2 = PIo2 - (Paco2/R)
