A mechanically ventilated patient on a circle absorber system shows a progressive rise in the baseline of the capnograph trace over 40 minutes, now reading 6 mmHg during inspiration. Expiratory tidal volume and airway pressures are unchanged. The most likely cause is:

• A Tracheal tube disconnection from the circuit
• B Acute pulmonary embolism
• C Exhaustion of the soda lime absorber causing rebreathing of carbon dioxide ✓
• D Malposition of the sampling line inside the bronchus

Explanation

In a properly functioning circle system the inspiratory limb contains essentially no carbon dioxide, so the capnogram baseline sits at zero. A rising baseline means carbon dioxide is present during inspiration, classically from exhausted soda lime allowing rebreathing. Disconnection produces a fall toward zero ETCO2, pulmonary embolism causes an abrupt stepwise decrease in ETCO2, and endobronchial sampling alters the waveform shape rather than elevating the baseline, which eliminates the other three options.

Reference: Morgan and Mikhail's Clinical Anesthesiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.