BackgroundThe physiological dead space fraction, particularly when estimated with the Enghoff equation, reflects global gas exchange by integrating all aspects of V/Q mismatch.Elevated dead space fractions have been associated with worse outcomes in ARDS, but their prognostic value beyond ARDS remains unclear. ObjectivesTo evaluate the prognostic value of the dead space fraction, calculated using the Enghoff equation, for hospital mortality among critically ill patients in the ICU. Study Design and MethodsThis single center retrospective cohort study included adults 18 (years) ventilated for 24 hours in the ICU of Leiden University Medical Center (October 2018 and September 2024).The Enghoff ratio was calculated from volumetric capnography and arterial blood gases, averaged over the first 24 hours.The primary outcome was hospital mortality; time until extubation was secondary.Cox regression with adjustment for APACHE IV score, Body Mass Index (BMI) and gender; non-linear effects were modeled using restricted cubic splines. ResultsHigher Enghoff ratios were independently associated with increased hospital mortality (Chi = 16.32,df = 2, p < 0.001, adjusted HR 1.42, 95% CI 1.22-1.67).The relationship was non-linear, with risk rising above 70%.No significant association was found with time until extubation (Chi = 2.54, df = 2, p = 0.280; HR 1.01, 95% CI 0.89-1.08). ConclusionThe Enghoff ratio was independently associated with hospital mortality in mechanically ventilated ICU patients, particularly above 70%.Although not predictive for time until extubation, it may serve as a complementary marker of gas exchange impairment and aid in risk stratification.
Rietveld et al. (Wed,) studied this question.