Cardiac output PA catheter and tailored therapy

• Thermodilution: saline injected in RA or intermittent heating of prox thermal filament in some PA lines (“continuous CO”). ∆ in temp over time measured at thermistor (in PA) used to calc CO. Inaccurate if ↓ CO, severe TR, or shunt.

• Fick method: O2 consumption (L/min) = CO (L/min) × ∆ arteriovenous O2 content ∴ CO = O2/C(a-v)O2

O2 ideally measured (esp. if ↑ metab demands), but freq estimated (125 mL/min/m2)

C(a-v)O2 = [10 × 1.36 mL O2/g of Hb × Hb g/dL × (SaO2 – SMVO2)]. SMVO2 is key var that ∆s.

If SMVO2 >80%, consider if the PAC is “wedged” (ie, pulm vein sat), L→R shunt, impaired O2 utilization (severe sepsis, cyanide, carbon monoxide), ↑↑ CO or FiO2.

PCWP waveform abnormalities: large a wave → ? mitral stenosis; large v wave → ? mitral regurgitation; blunted y descent → ? tamponade; steep x & y descents → ? constriction. Surrogates: RA ≈ JVP (1 mmHg = 1.36 cm H2O); pulmonary edema on CXR implies ↑ PCWP; UOP ∝ CO (barring AKI); delayed capillary refill (ie, >2–3 sec) implies ↑ SVR