Researchers identify clinical variable that predicts ability to wean from ECMO
A high effort to eliminate carbon dioxide was linked to a greater likelihood of failing to wean from venovenous extracorporeal membrane oxygenation, according to study results.
Further, end-tidal partial carbon dioxide pressure/partial pressure of carbon dioxide (PETCO2/PaCO2) ratio was strongly linked to weaning success and can be used in practice to predict when weaning is safe and likely to be successful, Stefano Lazzari, MD, of the University Medical Center Göttingen in Göttingen, Germany, and colleagues wrote in American Journal of Respiratory and Critical Care Medicine.
For the multicenter study designed to measure variables and physiological reasons for ECMO weaning failure, Lazzari and colleagues enrolled mechanically ventilated adults with severe acute respiratory distress syndrome who were receiving venovenous ECMO (VV-ECMO) into two cohorts: a prospective interventional study of a physiological cohort (n = 26; median age, 57 years; 80% men) and a retrospective clinical cohort (n = 638; median age, 44 years; 57% men).
Data revealed a weaning failure rate of 37% in the clinical cohort and 42% in the physiological cohort.
In the physiological arm, the main cause of failure was high inspiratory effort or respiratory rate, at 70% — as exhaled minute ventilation increased in response to the decreased C02 removed extracorporeally to maintain PaCO2 — followed by hypoxemia in 30%.
Furthermore, patients who failed the weaning trial demonstrated an increased effort to eliminate a one unit-volume of carbon dioxide (68.9 cm H2O L/minute vs. 39 cm H2O L/minute; P = .007), which researchers attributed to higher physiological dead space ventilation (68% vs. 54%; P = .012).
Of variables that differed at baseline between those who succeeded or failed at weaning in the physiological cohort, PetCO2/PaCO2 ratio was the only to maintain significance in univariate logistic regression, with a 0.87 (95% CI, 0.71-1) area under the receiver operating characteristic curve. A PetCO2/PaCO2 ratio of 0.84 or higher for prediction of weaning success showed a sensitivity of 91.7% and a specificity of 80%.
Moreover, the PetCO2/PaCO2 ratio also predicted weaning outcome in the clinical arm, both when measured before the weaning trial (OR = 4.14; 95% CI, 1.32-12.2) and at a sweep gas flow of zero (OR = 13.1; 95% CI, 4-44.4). In this cohort, area under the receiver operating characteristic curve was 0.58 (95% CI, 0.53-0.63), with a 0.83 or higher ratio cutoff showing 54% sensitivity and 66% specificity.
“This large multicenter physiological and clinical study shows that weaning failure is frequent and associated with the respiratory effort to control carbon dioxide exchange,” the researchers wrote.
“A higher PETCO2/PaCO2 ratio — a bedside measure of the overall gas exchanging performance of the natural lung — was associated with greater likelihood of weaning from VV-ECMO,” they added. “Its calculation before weaning initiation may decrease the potentially detrimental effects of high inspiratory effort and increase the likelihood of successful weaning from VV-ECMO.”
In an accompanying editorial, Ricardo Teijeiro Paradis, MD, a clinical fellow in the interdepartmental division of critical care medicine at University of Toronto, and colleagues wrote that, as with mechanical ventilation, it is unlikely that a single predictor will be the answer to promptly and safely liberating patients from ECMO.
“No predictive test for liberation has greater predictive ability than the liberation test itself,” Teijeiro Paradis and colleagues wrote. “We should instead direct our efforts to adopt a standardized approach to liberation, and to define criteria for when to test, how to test, how to define successful liberation, and how to approach liberation failure. Only then will we understand the outcomes of liberation and can attempt to seek weaning predictors for specific clinical scenarios.”