Question

Which of the following does the capnograph image below depict?

• A. During inspiration
• B. Inspiration with cardiac oscillations
• C. During expiration
• D. Spontaneous respiration

Hint:

A single notch dipping into the phase III plateau points to returning patient effort.

Answer 1

The Correct Option is D

Step 1: Read the trace. The capnograph shows a notch or cleft dipping into the plateau of phase III (the alveolar plateau, the part of the curve after the expired CO2 has stabilised).
Step 2: Name the sign. This dip is the curare cleft (also called the curare notch). It appears when the diaphragm contracts during the inspiratory pause and briefly pulls in fresh gas, lowering the CO2 reading for a moment.
Step 3: Interpret it. A curare cleft means the patient is making spontaneous breathing efforts while on controlled mechanical ventilation, often as the effect of a muscle relaxant wears off.
Why the others are wrong: Cardiac oscillations are small regular ripples near the end of expiration, not a single deep cleft. Inspiration and expiration describe the limbs of the waveform, not this specific notch.
Ref: Miller's Anesthesia, 8th edition, Page 1554.