Ten minutes after induction, the capnograph suddenly displays a flat line with end-tidal CO2 falling abruptly from 34 mmHg to 2 mmHg. The airway pressure alarm shows low pressure and the reservoir bag is empty. The most likely cause is:
- A Massive pulmonary embolism
- B Malignant hyperthermia crisis
- C Disconnection in the breathing circuit ✓
- D Total airway obstruction by the surgeon's retractor
Correct answer: C. Disconnection in the breathing circuit
Explanation
Abrupt loss of the entire carbon dioxide waveform together with low airway pressure and an empty reservoir bag indicates a leak or disconnection between the tracheal tube and the breathing system, so exhaled gas never reaches the analyser. Pulmonary embolism also drops end-tidal CO2 sharply but raises airway pressures and preserves the circuit integrity, and the waveform usually falls to a low nonzero value rather than flatlining with circuit collapse. Obstruction and malignant hyperthermia both raise end-tidal CO2.
Reference: Morgan and Mikhail's Clinical Anesthesiology, 5th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.