Estimated dead space fraction and the ventilatory ratio are associated with mortality in early ARDS

Luis Morales-Quinteros,Antonio Artigas,Janneke Horn,Marcus J Schultz,Josep Bringué,Tom Van Der Poll,Carolyn S Calfee,Pratik Sinha,Marta Camprubí,Olaf L Cremer,Lieuwe D Bos

doi:10.1186/s13613-019-0601-0

Abstract

BackgroundIndirect indices for measuring impaired ventilation, such as the estimated dead space fraction and the ventilatory ratio, have been shown to be independently associated with an increased risk of mortality. This study aimed to compare various methods for dead space estimation and the ventilatory ratio in patients with acute respiratory distress syndrome (ARDS) and to determine their independent values for predicting death at day 30. The present study is a post hoc analysis of a prospective observational cohort study of ICUs of two tertiary care hospitals in the Netherlands.ResultsIndividual patient data from 940 ARDS patients were analyzed. Estimated dead space fraction and the ventilatory ratio at days 1 and 2 were significantly higher among non-survivors (p < 0.01). Dead space fraction calculation using the estimate from physiological variables [VD/VT phys] and the ventilatory ratio at day 2 showed independent association with mortality at 30 days (odds ratio 1.28 [95% CI 1.02–1.61], p < 0.03 and 1.20 [95% CI, 1.01–1.40], p < 0.03, respectively); whereas, the Harris–Benedict [VD/VT HB] and Penn State [VD/VT PS] estimations were not associated with mortality. The predicted validity of the estimated dead space fraction and the ventilatory ratio improved the baseline model based on PEEP, PaO2/FiO2, driving pressure and compliance of the respiratory system at day 2 (AUROCC 0.72 vs. 0.69, p < 0.05).ConclusionsEstimated methods for dead space calculation and the ventilatory ratio during the early course of ARDS are associated with mortality at day 30 and add statistically significant but limited improvement in the predictive accuracy to indices of oxygenation and respiratory system mechanics at the second day of mechanical ventilation.

Highlights

Indirect indices for measuring impaired ventilation, such as the estimated dead space fraction and the ventilatory ratio, have been shown to be independently associated with an increased risk of mortality
Study design and ethical considerations The study design was a post hoc analysis of the ‘Molecular Diagnosis and Risk Stratification of Sepsis’ (MARS) project, a prospective observational cohort study in the mixed medical–surgical intensive care units (ICUs) of two tertiary teaching hospitals in the Netherlands The study was registered at ClinicalTrials.gov [14]
Patients A total of 6994 admissions were included in MARS from January 2011 until December 2013. 965 patients fulfilled the criteria of acute respira‐ tory distress syndrome (ARDS), of whom 940 patients were mechanically ventilated for longer than 24 h (Additional file 1: Figure S1)

Summary

Introduction

Indirect indices for measuring impaired ventilation, such as the estimated dead space fraction and the ventilatory ratio, have been shown to be independently associated with an increased risk of mortality. This study aimed to compare various methods for dead space estimation and the ventilatory ratio in patients with acute respira‐ tory distress syndrome (ARDS) and to determine their independent values for predicting death at day 30. Arterial oxygen tension (PaO2) to fraction of inspired oxygen (FiO2) is the only measured Both increased V/Q heterogeneity and shunt are the more likely contributors to increased dead space in ARDS. A clinically practical method, the ventilatory ratio (VR), has been validated for estimating pulmonary dead space. It can be calculated using routinely measured respiratory variables at bedside. In patients with ARDS, VR positively correlates with dead space fraction [13], and could, function as a surrogate for dead space fraction

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