Hemodynamic Monitoring During Bypass Flashcards

When using alpha-stat pH management during hypothermic CPB, the arterial PCO2 measured at 37°C is maintained at 40 mmHg, which means the actual in vivo PCO2 at 28°C is:

Answer: Higher than 40 mmHg because CO2 solubility increases with cooling

As blood cools, CO2 becomes more soluble, so the in vivo PCO2 at 28°C is lower than the 37°C-measured value — but alpha-stat intentionally maintains pH relative to neutral water at each temperature.

A sudden increase in arterial line pressure during CPB accompanied by an increase in pump outlet pressure most likely indicates:

Answer: High arterial outflow resistance, such as aortic stenosis or cannula malposition

Both arterial line and pump outlet pressure rise when the outlet circuit faces increased resistance, pointing to outflow obstruction rather than a vasodilatory process.

During CPB, which combination of findings best indicates adequate organ perfusion?

Answer: MAP 55 mmHg, SvO2 72%, urine output 1 mL/kg/hr, lactate 1.2 mmol/L

MAP 55 mmHg with SvO2 72%, adequate urine output, and normal lactate collectively confirm that oxygen delivery meets metabolic demand without tissue ischemia.

Which pharmacological intervention is most appropriate when SVR is excessively elevated (>1800 dyne·s·cm⁻⁵) during normothermic CPB, limiting adequate pump flow at safe pressures?

Answer: Sodium nitroprusside or nitroglycerin to reduce afterload

Vasodilators such as sodium nitroprusside lower SVR, allowing adequate pump flow to be maintained at safe arterial pressures when vascular tone is pathologically elevated.

In a patient with severe peripheral vascular disease on CPB, femoral arterial pressure reads 95 mmHg while a simultaneous radial arterial line reads 60 mmHg. Which statement is most accurate?

Answer: The radial line is underestimating central aortic pressure due to peripheral vasoconstriction

In peripheral vascular disease with significant vasoconstriction, the radial artery may underestimate central pressure due to dampening of flow in diseased vessels.

Transesophageal echocardiography (TEE) during CPB is most useful for identifying which hemodynamic complication before weaning from bypass?

Answer: Intracardiac air, ventricular wall motion abnormalities, and valve function

TEE before weaning detects intracardiac air, regional wall motion abnormalities suggesting ischemia, and valve function — all critical determinants of successful separation from CPB.

A perfusionist observes that the calculated oxygen delivery index (DO2I) is 280 mL/min/m² during normothermic CPB. Given a normal oxygen consumption index (VO2I) of approximately 120 mL/min/m², the oxygen extraction ratio (O2ER) is:

Answer: 43%

O2ER = VO2I / DO2I × 100 = 120 / 280 × 100 ≈ 43%, which is mildly elevated above the normal 25–30% range, suggesting borderline adequate delivery.