Background: Venovenous ECMO is a lifesaving technique for patients with severe respiratory failure. Management of carbon dioxide (CO₂) levels at ECMO start is crucial, as recent studies found an association between rapid CO₂ shifts and increased incidence of neurological complications.

Purpose: To describe the role of end tidal CO₂ (etCO₂) monitoring at the ECMO start to minimize carbon dioxide shifts.

Research design: Retrospective cohort study.

Methods: We performed a retrospective analysis of patients who started venovenous ECMO support at our institution between 2011 and 2021. We analysed the minute-by-minute variations of etCO₂, ventilatory parameters and arterial blood gas before and after the ECMO start.

Results: 36 patients with a complete dataset of parameters were included. After the ECMO start, minute ventilation was progressively reduced from 10.8±;3.3 to 2.9±1.2 L/min (p<0.001). etCO₂ did not vary significantly (baseline 37±10 vs 35±9 mmHg 20 minutes after ECMO start, p = 0.36). Despite a stable etCO₂ level, a mild drop of arterial CO₂ tension (9.5 mmHg, corresponding to a 18% change) was recorded at the first ABG sampled after the ECMO start. No patient developed neurological complications after the ECMO commencement.

Conclusion: etCO₂ monitoring during ECMO start is feasible and allows to adjust gas flow and ventilator settings to limit changes in arterial CO₂ levels.