The anaesthesia ventilator bellows do not ascend to the top of the bellows housing during the expiratory phase. Which of the following is the most likely cause?

• A High fresh gas flow causing bellows over-distension
• B Excessive soda lime resistance
• C A leak in the patient circuit, bellows, or around the bellows housing ✓
• D Ventilator cycling rate set too high

Explanation

In ascending (standing) bellows anaesthesia ventilators, the bellows should fully ascend to the top of the housing during expiration when the driving gas fills below the bellows. Failure to ascend fully indicates a gas leak — either from the breathing circuit, ETT cuff, bellows itself, or the seal between bellows and housing. Ascending bellows designs provide a safety advantage: a leak is visible as partial filling, whereas descending (hanging) bellows ventilators can continue to look normal even with a significant circuit leak (the bellows descend by gravity). Leak testing includes checking the bellows does not continue to move and fully ascends at baseline PEEP.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.