During laparoscopic cholecystectomy, EtCO2 rises from 35 to 52 mmHg despite unchanged ventilator settings at 30 minutes. The arterial CO2 is confirmed at 55 mmHg. Which is the MOST likely cause?
- A Endobronchial intubation causing right lung only ventilation
- B Capnograph sampling tube occlusion causing falsely elevated reading
- C Absorption of CO2 from pneumoperitoneum insufflation ✓
- D Rebreathing of CO2 due to exhausted soda lime in the circle system
Explanation
During laparoscopic surgery, CO2 is used as the insufflation gas for pneumoperitoneum. Peritoneal absorption of CO2 is significant and predictable, causing a rise in PaCO2 and EtCO2 proportional to the absorption rate. This typically increases ventilation requirements by 15–25%. The rise is expected, and the response is to increase minute ventilation (raise respiratory rate or tidal volume) to maintain normocapnia. Endobronchial intubation would cause hypoxia and unilateral breath sounds. Rebreathing shows an elevated EtCO2 baseline between breaths. Sampling tube occlusion would produce a dampened waveform or error message.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.