CCP Hemodynamic Monitoring During Bypass 2 — Questions and Answers
Question 1: During CPB, a sudden drop in arterial line pressure with unchanged pump flow most likely indicates which of the following?
- Aortic dissection at the cannulation site (Correct answer)
- Systemic vasodilation from rewarming
- Kinked arterial cannula
- Air lock in the oxygenator
Correct answer: Aortic dissection at the cannulation site
A sudden pressure drop with unchanged flow suggests aortic dissection, where blood tracks into the false lumen reducing effective forward perfusion.
Question 2: Which pulmonary artery catheter parameter is most useful for assessing right ventricular afterload during CPB?
- Pulmonary artery occlusion pressure
- Pulmonary vascular resistance (Correct answer)
- Cardiac output by thermodilution
- Central venous pressure
Correct answer: Pulmonary vascular resistance
Pulmonary vascular resistance (PVR) directly quantifies the impedance against which the right ventricle must eject, making it the best measure of RV afterload.
Question 3: A mixed venous oxygen saturation (SvO2) of 55% during normothermic CPB at a flow of 2.4 L/min/m² suggests:
- Adequate oxygen delivery
- Increased oxygen consumption or reduced flow (Correct answer)
- Hyperoxia from excessive FiO2
- Calibration error of the oximeter
Correct answer: Increased oxygen consumption or reduced flow
SvO2 below 65% at normothermia indicates oxygen extraction is elevated, reflecting either insufficient delivery or increased metabolic demand.
Question 4: When the arterial blood pressure waveform dampens and the pulse pressure narrows significantly during full CPB, the most likely explanation is:
- The roller pump is operating in pulsatile mode
- Complete occlusion of the aortic root vent
- Air in the arterial monitoring line transducer
- A kinked or partially occluded arterial pressure line (Correct answer)
Correct answer: A kinked or partially occluded arterial pressure line
A dampened waveform with narrow pulse pressure typically results from a mechanical obstruction or air bubble in the monitoring line rather than a true hemodynamic event.
Question 5: During hypothermic CPB at 28°C, the target mean arterial pressure recommended to ensure adequate cerebral perfusion in most adult patients is:
- 40–50 mmHg
- 50–70 mmHg (Correct answer)
- 70–90 mmHg
- 90–110 mmHg
Correct answer: 50–70 mmHg
Most guidelines recommend maintaining MAP between 50–70 mmHg during moderate hypothermic CPB, balancing cerebral perfusion with surgical field conditions.
Question 6: Which of the following best explains a sudden rise in venous line pressure during CPB without a change in pump speed?
- Systemic vasodilation
- Venous cannula obstruction or malposition (Correct answer)
- Hemodilution reducing blood viscosity
- Increased pump flow rate
Correct answer: Venous cannula obstruction or malposition
Elevated venous line pressure at constant pump speed suggests obstruction to venous drainage, often from cannula malposition, kinking, or cavitation.
Question 7: Cerebral oximetry (rSO2) monitoring during CPB primarily detects imbalances in:
- Coronary oxygen delivery
- Regional cerebral oxygen supply-demand ratio (Correct answer)
- Global mixed venous saturation
- Pulmonary oxygen transfer efficiency
Correct answer: Regional cerebral oxygen supply-demand ratio
Near-infrared spectroscopy-based cerebral oximetry measures regional cortical oxygen saturation, reflecting the local balance between cerebral O2 supply and demand.
CCP Hemodynamic Monitoring During Bypass 2
During CPB, a sudden drop in arterial line pressure with unchanged pump flow most likely indicates which of the following?