Prognostic value of the dead space fraction in invasive mechanical ventilation using the Enghoff equation: a single center retrospective cohort study

Rietveld, P.J.; Meiracker, B.T.R.M. van den; Brunsveld-Reinders, A.H.; Smits, F.E.; Snoep, J.W.M.; Westerloo, D.J. van; Schoe, A. (2026)

Article / Letter to editor

Background: The 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. Objectives: To 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 Methods: This single center retrospective cohort study included adults >= 18 (years) ventilated for >= 24 h 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 h. 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. Results: Higher Enghoff ratios were independently associated with increased hospital mortality (Chi(2) = 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) = 2.54, df = 2, p = 0.280; HR 1.01, 95% CI 0.89-1.08). Conclusion: The 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.

• Mechanical ventilation
• Dead space
• Enghoff ratio
• Volumetric capnography
• VCO2

• All authors: Rietveld, P.J.; Meiracker, B.T.R.M. van den; Brunsveld-Reinders, A.H.; Smits, F.E.; Snoep, J.W.M.; Westerloo, D.J. van; Schoe, A.
• Date: 2026-04-09
• Journal: Respiratory Medicine
• Volume: 256
• DOI: doi:10.1016/j.rmed.2026.108809
• Link: https://www.sciencedirect.com/science/article/pii/S0954611126001770?via%...