ETCO2 patterns — what they mean
Capnography interpretation
Mnemonic device
Sudden ↓ vs gradual ↓ vs ↑
Mapping
Sudden ↓ to 0
ETT dislodgement, complete circuit disconnect, complete obstruction, cardiac arrest (no flow)
Sudden ↓ but waveform present
PE, air embolism, sudden ↓ CO, hypovolemia, hyperventilation, decreased sample line flow
Gradual ↓
Hyperventilation (alveolar), ↓ metabolic rate (hypothermia, deep sedation), ↓ pulmonary perfusion gradual
Gradual ↑
Hypoventilation, ↑ metabolism (fever, MH early), CO2 absorbent exhausted, rebreathing
Sudden ↑
Tourniquet release, IV bicarbonate, laparoscopic CO2 absorption, MH onset (sustained ↑ refractory to ↑ MV)
Steeple/curare cleft
Spontaneous breath through paralyzed → notch in plateau (residual paralysis returning)
Shark fin
Bronchospasm — sloped expiratory phase (asthma, COPD)
Clinical note: Capnography is the single most useful intraop monitor — confirms intubation, ventilation, perfusion, CO2 production. Sudden changes ALWAYS deserve immediate workup.