Arterial-to-End-Tidal CO₂ Gradient Direction as a Differential Diagnostic Clue During Sudden Hypercapnia in Thoracoscopic Surgery with Capnothorax: A Report of 2 Cases.
Yumi Nakao, Urara Hirano, Natsuki Anada et al.
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Case in brief
Two men undergoing thoracoscopic surgery with CO₂ insufflation developed abrupt rises in end-tidal CO₂ (EtCO₂). In the first, the rise coincided with severe hypotension and bradycardia; arterial blood gas showed PaCO₂ 228.0 mm Hg and a positive arterial-to-end-tidal gradient of +98.0 mm Hg. In the second, EtCO₂ rose despite stable hemodynamics; after circuit and sampling-line artifacts were excluded, PaCO₂ was 72.5 mm Hg and the gradient was negative at -26.5 mm Hg. Exploration found partial left main bronchus injury. Insufflation was stopped in the first case; surgery was completed without re-insufflation.
What made this case unusual
The contrasting gradient directions accompanied two different suspected mechanisms: a markedly positive gradient during shock, and a negative gradient with bronchial injury and suspected exogenous CO₂ contamination.
Diagnostic / clinical pearl
For sudden EtCO₂ elevation during capnothorax, prompt ABG assessment of the PaCO₂–EtCO₂ gradient may help distinguish systemic CO₂ retention from exogenous contamination. Interpret it alongside hemodynamics and circuit integrity; it is not a validated standalone diagnostic tool.