2026 FSA Podium and Poster Abstracts

Introduction / Background: End-tidal carbon dioxide (ETCO₂) monitoring provides real-time assessment of ventilation, perfusion, and metabolism during general anesthesia. A sudden decrease in ETCO₂ is an established sign of pulmonary embolism. Changes in waveform morphology may provide additional diagnostic insight. We report a case of intraoperative pulmonary embolism characterized by an acute reduction in ETCO₂ and prominent oscillatory distortion of the alveolar plateau.

Methods: A 53-year-old female with obesity (BMI 43), hypertension, obstructive sleep apnea not adherent to continuous positive airway pressure therapy, and a recent fall with right femoral neck fracture presented for right hip arthroplasty. Preoperative evaluation was notable for transthoracic echocardiography with normal ventricular systolic function and mildly elevated estimated right ventricular systolic pressure (40-49 mmHg). General anesthesia was induced uneventfully with standard intravenous induction and endotracheal intubation.

During transfer to the operating table and positioning in the left lateral decubitus position, prior to surgical manipulation, an acute decrease in ETCO₂ from the mid-30s mmHg to the low-20s mmHg was observed, accompanied by large-amplitude oscillatory distortion of the ETCO₂ waveform. The patient remained normotensive with mild tachycardia and preserved oxygen saturation. Endotracheal tube position, ventilator circuit integrity, and capnography sampling were evaluated systematically without improvement in ETCO₂. An independent defibrillator containing in-line capnography monitoring was used for comparison and demonstrated identical waveform morphology to the ventilator, supporting a true waveform rather than monitoring artifact.

Results: Arterial blood gas analysis revealed severe hypercapnia with a large arterial-to-end-tidal CO₂ gradient. Given concern for acute pulmonary embolism, the surgery was aborted and computed tomography pulmonary angiography was obtained. Imaging demonstrated an acute central pulmonary embolism completely occluding the distal right pulmonary artery with extension into the segmental branches of the right upper, middle, and lower lobes and features of right heart strain.

The patient remained hemodynamically stable without vasopressor support throughout transport and intensive care unit admission. Repeat echocardiography demonstrated right ventricular dilation with moderately reduced systolic function and preserved apical contractility. She underwent catheter-directed pulmonary thrombectomy with concomitant infrarenal inferior vena cava filter placement, after which ETCO₂ values improved. Following anticoagulation and interval monitoring, the patient underwent right hip arthroplasty without complication and was discharged to rehabilitation.

Discussion / Conclusion: This case illustrates that pronounced oscillatory distortion of the ETCO₂ waveform when accompanied by an abrupt reduction in ETCO₂ may indicate acute pulmonary embolism. One possible mechanism is severe ventilation-perfusion heterogeneity, in which carbon dioxide-poor gas from nonperfused lung regions variably mixes with carbon dioxide-rich gas from perfused lung regions, resulting in an irregular alveolar plateau.

Despite a large central pulmonary embolism with right ventricular strain, the patient remained hemodynamically stable. Preoperative echocardiographic evidence of mildly elevated right ventricular systolic pressure with preserved function suggests possible chronic pulmonary vascular loading, which may be related to obesity and untreated obstructive sleep apnea and may have contributed to preserved hemodynamics. In this case, alteration of capnographic waveform morphology aided early recognition of pulmonary embolism and informed intraoperative decision making.