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

Abrupt end-tidal CO 2 surges during thoracoscopic surgery with capnothorax Clinical Procedure:-Specialty: Anesthesiology Objective: Diagnostic / therapeutic accidents Background:During minimally invasive thoracic surgery with intrathoracic carbon dioxide (CO 2 ) insufflation, an abrupt rise in end-tidal CO 2 (EtCO 2 ) alone cannot distinguish true hypercapnia from artifactual or exogenous CO 2 contamination.We report 2 contrasting cases in which the direction of the arterial-to-end-tidal CO 2 gradient, D(PaCO 2 -EtCO 2 ), guided differential diagnosis. Case Reports:Case 1: A 62-year-old man undergoing robot-assisted right lower lobectomy developed an abrupt EtCO 2 rise from 40 to 130 mm Hg immediately after CO 2 insufflation, with severe hypotension and bradycardia.Arterial blood gas (ABG) analysis showed pH 6.79, PaCO 2 228.0 mm Hg, and D(PaCO 2 -EtCO 2 ) +98.0 mm Hg, suggesting a possible contribution of low cardiac output to the widened gradient.Insufflation was stopped, 2-lung ventilation resumed, and surgery completed without re-insufflation.Case 2: A 77-year-old man undergoing thoracoscopic subtotal esophagectomy developed an EtCO 2 rise from 54 to 99 mm Hg while hemodynamically stable.After excluding circuit and sampling-line artifacts, ABG analysis showed pH 7.21, PaCO 2 72.5 mm Hg, and D(PaCO 2 -EtCO 2 ) -26.5 mm Hg, suggesting exogenous CO 2 contamination of expiratory gas rather than systemic retention alone.Surgical exploration confirmed a partial injury to the left main bronchus.Conclusions:During abrupt EtCO 2 surges under 1-lung ventilation with capnothorax, the direction of D(PaCO 2 -EtCO 2 ) on prompt ABG analysis may help prioritize the differential diagnosis between systemic retention and exogenous contamination, provided hemodynamics and circuit integrity are concurrently assessed.A markedly positive gradient during shock may indicate systemic CO 2 loading with reduced pulmonary perfusion, whereas a negative gradient after artifact exclusion suggests pleuro-airway communication or peri-device leakage.This hypothesis-generating approach remains unvalidated as a standalone diagnostic tool.