CCP Hemodynamic Monitoring During Bypass 3 — Questions and Answers
Question 1: A perfusionist notices the reservoir level is falling despite adequate venous return. Which hemodynamic sign would first alert the team to impending venous air entrainment?
- Rising arterial line pressure
- Decreasing SvO2 with stable pump flow
- Visible air bubbles in the venous line (Correct answer)
- Sudden increase in venous return
Correct answer: Visible air bubbles in the venous line
Visible air bubbles in the venous line are the earliest direct sign of air entrainment before it reaches the oxygenator or arterial circuit.
Question 2: During CPB, systemic vascular resistance (SVR) is calculated using which formula?
- (MAP – CVP) / CO × 80 (Correct answer)
- (MAP – PAOP) / CO × 80
- (SAP – DAP) / HR
- (CVP – MAP) / SV × 80
Correct answer: (MAP – CVP) / CO × 80
SVR = (MAP – CVP) / CO × 80, where the pressure gradient across the systemic circulation is divided by cardiac output and converted to dyne·s·cm⁻⁵.
Question 3: An arteriovenous oxygen content difference (AVDO2) greater than 6.0 mL/dL during CPB most likely reflects:
- Excessive pump flow causing hyperoxia
- Inadequate perfusion flow relative to oxygen demand (Correct answer)
- A left-to-right intracardiac shunt
- Correct oxygen delivery with normal extraction
Correct answer: Inadequate perfusion flow relative to oxygen demand
An AVDO2 above 6 mL/dL indicates tissues are extracting an unusually large fraction of delivered oxygen, consistent with inadequate perfusion flow.
Question 4: Which variable, when monitored continuously, provides the most direct real-time index of global oxygen delivery adequacy during CPB?
- Arterial pH
- Mixed venous oxygen saturation (SvO2) (Correct answer)
- Lactate concentration
- Mean arterial pressure
Correct answer: Mixed venous oxygen saturation (SvO2)
Continuous SvO2 monitoring reflects the real-time balance between oxygen delivery and consumption across the entire body, making it the best continuous global index.
Question 5: During rewarming on CPB, a perfusionist observes a gradual decline in MAP from 65 to 45 mmHg. The most appropriate first intervention is:
- Increase pump flow rate
- Administer a vasopressor such as phenylephrine (Correct answer)
- Decrease the rewarming rate
- Increase FiO2 to the oxygenator
Correct answer: Administer a vasopressor such as phenylephrine
Vasodilation during rewarming commonly causes hypotension; administering a vasopressor to restore SVR is the primary hemodynamic intervention.
Question 6: Left atrial pressure monitoring during CPB is most valuable for detecting:
- Right ventricular failure
- Left ventricular distension from aortic insufficiency (Correct answer)
- Pulmonary hypertension
- Systemic venous hypertension
Correct answer: Left ventricular distension from aortic insufficiency
Elevated left atrial pressure during a cross-clamped, non-ejecting heart indicates LV distension, often from aortic regurgitation allowing blood to pool in the ventricle.
Question 7: Which condition would cause a falsely elevated arterial blood pressure reading from a radial arterial line during CPB?
- Peripheral vasoconstriction with radial-to-aortic pressure gradient (Correct answer)
- Systemic hypertension from excessive vasopressor
- High pump flow rate
- Hypothermia reducing peripheral vascular tone
Correct answer: Peripheral vasoconstriction with radial-to-aortic pressure gradient
Peripheral vasoconstriction can create a radial-to-aortic gradient where the radial artery reads lower than central aortic pressure, but in some hypothermic states the reverse occurs, yielding a falsely high peripheral reading.
CCP Hemodynamic Monitoring During Bypass 3
A perfusionist notices the reservoir level is falling despite adequate venous return.
Which hemodynamic sign would first alert the team to impending venous air entrainment?