Capnography for EMS: Waveforms That Actually Matter

Capnography is the closest thing EMS has to a real-time window on ventilation, perfusion, and metabolism. Every AEMT and paramedic should be able to read the four common waveforms without hesitation.

Normal square waveform

Four phases: baseline, expiratory upstroke, alveolar plateau, and inspiratory downstroke. Normal ETCO₂ is 35–45 mmHg.

Shark-fin waveform — bronchospasm

Loss of the sharp plateau, replaced by a curved upslope. Classic for asthma and COPD exacerbations. Watch it flatten as your bronchodilators work.

Low ETCO₂ with tachypnea — DKA or sepsis

A patient breathing 30/min with an ETCO₂ of 18 is compensating for a metabolic acidosis. This is Kussmaul respiration in numeric form.

Sudden ETCO₂ jump during CPR — ROSC

A spike from 15 to 40 mmHg during compressions strongly suggests return of spontaneous circulation. Check a pulse at the next rhythm check, not immediately.

Sudden drop to zero

Dislodged tube, disconnected circuit, or cardiac arrest — in that order of likelihood. Look, listen, and troubleshoot the circuit before anything else.