Shunts

Valve Area

Coronary Artery Anatomy

Figure A-1. Coronary arteries.

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 = P_AO₂ – P_aO₂ [normal A-a gradient ≈ 4 + (age/4)]

Minute ventilation ( V._E) = Tidal volume (  V_T) × Respiratory rate (RR) (normal 4–6 L/min)

Tidal volume (V_T) = Alveolar space (  V_A) + Dead space (  V_D)

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) = (U_Na + U_K) – U_Cl

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

SENSITIVITY AND SPECIFICITY CALCULATIONS

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