Metabolic
Anion Gap: Na – (Cl + Bicarb)
Delta/Delta = (actual anion gap – normal gap)/(normal HCO3 – actual HCO3)
Total body water (TBW) = weight (kg) × 0.6 (use 0.5 if female/elderly, 0.6 for infants)
Corrected Na = measured Na + [2.4 × (measured glucose –100)]
Calculated osmoles = (2 × Na) + (glucose/18) + (BUN/2.8) + (EtOH/4.6)
Osmolal gap = measured osmoles – calculated osmoles (nl)
Estimated Cr clearance = 
Pediatric fluid maintenance (4-2-1 Rule):
(4 cc/kg for 1st 10 kg) + (2 cc/kg for 2nd 10 kg) + (1 cc/kg for remainder kg)
Hyponatremia:
Rate of infusion (mL/h) = 
Hypernatremia:
Free water deficit = total body water × [(140/serum Na) – 1]
Δ[Na]/liter infusate = 
Total infusion (L) = 
Rate of infusion (mL/h) = total infusion (mL)/24 h
CARDIAC
A-a gradient = PAO2 – PaO2 (nl ≈ 4 + (age/4))
Stroke volume = cardiac output/heart rate
Mean arterial pressure = 