Background

Separation from venovenous extracorporeal membrane oxygenation (VV-ECMO) is a pivotal transition for patients with acute respiratory distress syndrome (ARDS). Impaired alveolar ventilation more so than oxygenation may be implicated in weaning failure. The ventilatory ratio (VR), a simple marker of patient ventilatory efficiency, correlates with physiological dead space and ARDS outcomes. We hypothesised that elevated VR measured during sweep gas off trials (SGOT) predicts unsafe liberation from VV-ECMO.

Methods

In this monocentric retrospective study, adult patients undergoing VV-ECMO for ARDS between July 2019 and August 2023 were recruited. Patients who died on ECMO or were palliatively separated were excluded. Physiological, ventilatory and ECMO data were extracted from the electronic medical record. VR was calculated as VE [minute ventilation] × PaCO₂/(predicted body weight × 100 × 37.5). Safe wean was defined as ECMO free survival without predefined “unsafe criteria” (hypoxia, hypercapnia with acidosis, escalations in mechanical ventilation, or haemodynamic deterioration) occurring during SGOT (sweep gas off trial) or within 48 h of ECMO separation.

Results

Thirty-nine patients (median age 47 years; 76.9% male) were included. Twenty-four patients separated safely from ECMO following a single SGOT, the remaining 15 patients underwent 36 unsafe trials before decannulation, 69.4% of which failed due to hypercapnia. Safe wean trials were longer (19 [5.7–25.0]hr vs. 5 [0.3–13.3]hr; p = 0.01) and preceded by lower fractional delivered oxygen (FdO₂) (65 [40–85]% vs. 100 [60–100]%; p = 0.03). During unsafe SGOT, VR was higher at both early (1.7 vs. 1.4; p = 0.02), and late time points (2.6 vs. 1.7; p = 0.01) in unsafe trials. Hypercapnia following separation was associated with prolonged post-ECMO ventilation (β = 1.4 [0.21–2.59]; p = 0.02). No deaths or re-initiations occurred within 48 h of ECMO removal.

Conclusions

Elevated ventilatory ratio during SGOT was associated with unsafe weaning from VV-ECMO in this retrospective cohort of patients with ARDS. Prospective validation is warranted to inform future weaning practice.