Internal Consistency for ABG
[H+]=24 x PaCO2/HCO3
Alveolar Gas Equation
PAO2= FiO2 (Pb-PH2O)-PaCO2/R
FiO2 fraction of inspired oxygen, Pb barometric pressure, pH2O water vapor partial pressure, R= CO2 eliminated/O2 consumed
O2 delivery to tissues
DO2= CaO2 xCO
CaO2= arterial oxygen content; CO= cardiac output (SV x HR)
CaO2 (mL/dL)= (Hg x 1.34 x O2sat%)+(0.003 x PaO2)
Calculated Osm
Calculated Osm= 2[Na+] + BUN/2.8 + glucose/18
Appropriateness of compensation for Acid-Base Disturbance:
- Met Acidosis
- Met alkalosis
- Resp Acidosis
- Resp Alkalosis
- Winter’s Formula: pCO2= 1.5 (bicarb) + 8 +/- 2
- change in pCO2= 0.6 x (change in bicarb) +/-2
- Inc in bicarb by 1 (acute) to 4 (chronic) for each change in 10 of pCO2
- Dec in bicarb by 2 (acute) and 4 (chronic) for each dec of pCO2 by 10
Expected anion gap=
12-2.5(4-alb)
Sensitivity
Proportion of patient that have the disease that test positive
TP/(TP+FN)
Specificity
The proportion of people that don’t have the disease that test negative
TN/(TN+ FP)
PPV
Proportion of people that test positive that actually have the disease
TP/(TP+FP)
NPV
Proportion of people that test negative that actually do not have the disease
TN/(TN+FN)
Type I error
error when research reject null hypothesis that is actually true
- alpha
- reflected by p-value (probability of comitting type I error), alpha 5% is p=0.05
Type II error
beta- function of study power
one does not reject null hypothesis that is false
Change with prevalence of disease
PPV and NPV
Prevalence=
TP+FN/(TP+FN+FP+TN)
LR+
TP/FP (sens/(1-spec))
LR-
FN/TN= (1-sens)/spec
AR
contributing risk of particular exposure
- 2x2 with Exposure and Disorder
- [a/(a+b)]-[c/(c+d)]
Dead space vent calculation
VD/Vt= (PaCO2 -PECO2)/PaCO2
ratio of dead space to Vt
