Shunts
Valve Area
Coronary Artery Anatomy
PULMONARY
Dead space = Lung units that are ventilated but not perfused
Intrapulmonary shunt = Lung units that are perfused but not ventilated
Alveolar gas equation:
A-a gradient = PAO2 – PaO2 [normal A-a gradient ≈ 4 + (age/4)]
Minute ventilation ( V.E) = Tidal volume ( VT) × Respiratory rate (RR) (normal 4–6 L/min)
Tidal volume (VT) = Alveolar space ( VA) + Dead space ( VD)
Fraction of tidal volume that is dead space
NEPHROLOGY
Anion gap (AG) = Na – (Cl + HCO3) (normal = [alb] × 2.5; typically 12 ± 2 mEq)
Delta-delta (δδ) = [δ AG (i.e., calc. AG – expected)/δ HCO3 (i.e., 24 – measured HCO3)]
Urine anion gap (UAG) = (UNa + UK) – UCl
Osmolal gap (OG) = Measured osmoles – Calculated osmoles (normal <10)
Corrected Na in hyperglycemia
Estimate in all pts: Corrected Na = Measured Na +
However, δ in Na depends on glc (Am J Med 1999;106:399)
δ is 1.6 mEq per each 100 mg/dL ↑ in glc ranging from 100–440
δ is 4 mEq per each 100 mg/dL ↑ in glc beyond 440
Total body water (TBW) = 0.60 × IBW (× 0.85 if female and × 0.85 if elderly)
HEMATOLOGY
• PTT q6h after every change (half-life of heparin is ∼90 min)
• PTT qd or bid once PTT is therapeutic
• CBC qd (to ensure that Hct and plt counts are stable)
OTHER
Ideal body weight (IBW) = [50 kg (men) or 45.5 kg (women)] + 2.3 kg/in. over 5 ft