A presentation on "End-Tidal to Arterial Pco₂ Ratio as Guide to Weaning from Venovenous Extracorporeal Membrane Oxygenation" @ISICEM explored the potential of the end-tidal to arterial carbon dioxide pressure ratio (PetCO₂/PaCO₂) as a predictor for successful weaning from venovenous extracorporeal membrane oxygenation (VV-ECMO) in patients suffering from severe acute respiratory distress syndrome (ARDS).
VV-ECMO is a critical support mechanism for patients with severe ARDS, facilitating gas exchange when conventional mechanical ventilation proves inadequate. Determining the optimal timing for weaning patients from VV-ECMO is crucial, as premature discontinuation can lead to respiratory failure, while unnecessary prolongation increases the risk of complications. Currently, there is no standardised approach to guide clinicians in making these weaning decisions. The PetCO₂/PaCO₂ ratio, reflecting the relationship between noninvasive end-tidal CO₂ measurements and arterial CO₂ levels, has been proposed as a potential indicator of pulmonary function and, by extension, a predictor of weaning outcomes.
A large prospective observational study conducted by the same research team involved two cohorts: a clinical cohort comprising 30 patients undergoing VV-ECMO weaning trials and a physiological cohort of 12 patients assessed for specific respiratory parameters. The primary objective was to evaluate the efficacy of the PetCO₂/PaCO₂ ratio in predicting successful weaning from VV-ECMO. Key measurements included arterial blood gases, ventilatory parameters, and the PetCO₂/PaCO₂ ratio, both at baseline and during weaning trials.
In the clinical cohort, 19 out of 30 patients (63%) were successfully weaned from VV-ECMO, while 11 patients (37%) experienced weaning failure. The physiological cohort exhibited a similar pattern, with 7 out of 12 patients (58%) successfully weaned and 5 patients (42%) encountering failure. Elevated inspiratory effort or increased respiratory rate was identified as the predominant cause of weaning failure in both cohorts. This suggests that patients who failed weaning required greater ventilatory effort to maintain adequate gas exchange, likely due to increased physiological dead space.
A higher baseline PetCO₂/PaCO₂ ratio was strongly associated with successful weaning outcomes. Specifically, the area under the receiver operating characteristic (ROC) curve for the baseline PetCO₂/PaCO₂ ratio was 0.87, indicating high predictive accuracy. Patients with a higher PetCO₂/PaCO₂ ratio demonstrated better pulmonary function and were more likely to be weaned successfully from VV-ECMO.
The study found that patients who failed weaning trials had increased physiological dead space, necessitating higher ventilatory effort to maintain similar PaCO₂ levels compared to those who were successfully weaned. This finding underscores the importance of assessing ventilatory efficiency and dead space ventilation when considering weaning from VV-ECMO.
The PetCO₂/PaCO₂ ratio is a valuable clinical variable for predicting successful weaning from VV-ECMO in patients with severe ARDS. Implementing this ratio in clinical practice could enhance weaning protocols, allowing for more individualised and timely decisions, potentially improving patient outcomes and resource utilisation. Future studies with larger sample sizes are warranted to validate these findings and to further refine weaning strategies based on the PetCO₂/PaCO₂ ratio.
Incorporating the PetCO₂/PaCO₂ ratio into routine clinical assessments could provide clinicians with a noninvasive, readily available tool to evaluate a patient's readiness for weaning from VV-ECMO. This approach aligns with the goal of minimising ventilator-induced lung injury by ensuring that patients are neither prematurely nor unnecessarily prolonged on ECMO support. Moreover, understanding the relationship between dead space ventilation and weaning outcomes highlights the need for comprehensive respiratory assessments in this patient population.
Source: American Journal of Respiratory and Critical Care Medicine
Image Credit: ISICEM 2025
References:
Lazzari S et al. (2022) End-Tidal to Arterial Pco2 Ratio as Guide to Weaning from Venovenous Extracorporeal Membrane Oxygenation. American Journal of Respiratory and Critical Care Medicine.
