A sudden decrease in PetCO2 most commonly indicates which event?

• A. Pulmonary Embolism
• B. Bronchospasm
• C. Circuit Disconnect
• D. Ventilator Failure

Answer: (A)

A sudden drop in end-tidal CO2 reflects a rapid loss of CO2 delivery from the lungs, meaning ventilation is occurring but perfusion to ventilated units has suddenly decreased. A pulmonary embolism fits this pattern because a clot abruptly obstructs blood flow in the pulmonary arteries, cutting off perfusion to part of the ventilated lung. With less blood reaching alveoli to pick up and carry CO2 to the airways, the amount of CO2 exhaled decreases quickly, so the end-tidal CO2 falls sharply.

In contrast, a circuit disconnect would typically cause the PetCO2 to fall toward near zero because no gas reaches the sensor, and ventilator-related problems or bronchospasm usually produce different patterns or more gradual changes rather than an abrupt drop.