A patient is anaesthetised using a circle breathing system. At the end of the case, the inspired sevoflurane concentration is zero but the patient is not waking up. Capnography shows a flat CO2 waveform despite the ventilator cycling. Which of the following is the MOST likely explanation?

• A Oesophageal intubation ✓
• B Carbon dioxide absorber exhaustion
• C Complete disconnection of the breathing circuit
• D Residual neuromuscular blockade

Explanation

A flat capnography trace (no CO2 waveform) despite chest movement by the ventilator is the classic sign of oesophageal intubation; CO2 is not exhaled from the stomach in significant amounts after more than a few breaths. The patient not waking is because no anaesthetic has been delivered to the lungs. Carbon dioxide absorber exhaustion would cause rising inspired CO2, not a flat trace. Circuit disconnection would prevent ventilation, which should trigger a low-pressure alarm. Residual neuromuscular blockade does not affect the CO2 waveform.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.