8/24/2023 0 Comments What is physiologic dead space![]() Patients who were invasively ventilated for less than 24 h were excluded from the analysis. ![]() The current analysis only included patients with ARDS diagnosis during the first 2 days of invasive mechanical ventilation. Patients aged under 18 years were excluded. The parent study had the following two inclusion criteria: (a) being admitted to one of the participating ICUs and (b) having an expected length of stay in ICU longer than 24 h. Patients were included via an opt-out method, approved by the medical ethical committees of both hospitals. 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 Academic Medical Center in Amsterdam, and the University Medical Center in Utrecht) The study was registered at (study identifier NCT01905033). In addition, we tested whether estimates of ventilatory impairment at day 2 outperform estimations at day 1. In this study, we hypothesized that indices of ventilatory impairment early during the course of ARDS would have independent predictive value for 30-day mortality. In patients with ARDS, VR positively correlates with dead space fraction, and could, therefore, function as a surrogate for dead space fraction. It can be calculated using routinely measured respiratory variables at bedside. Recently, a clinically practical method, the ventilatory ratio (VR), has been validated for estimating pulmonary dead space. Moreover, estimated dead space correlates well with mortality. Approximation methods for estimating dead space fraction do not require direct measurement of exhaled carbon dioxide, are less complicated to perform, and feasible to calculate at the bedside. ![]() Dead space measurements, however, are not utilized routinely in clinical practice, probably due to the added costs of direct measurement techniques. Indeed, dead space fraction ( V D/ V T) during the first week after the initial diagnosis is known to be a predictor of survival, independent of oxygenation. It results from endothelial injury, microvascular plugging with cellular aggregates and thrombi, and disordered pulmonary blood flow, as well as overdistention of alveolar units that may result from the heterogeneity within the injured lung and/or from the use of mechanical ventilation itself. More accurate markers are needed to predict outcome in the early course of ARDS.īoth increased V/Q heterogeneity and shunt are the more likely contributors to increased dead space in ARDS. The prognostic value of PaO 2/FiO 2 for mortality prediction, however, is limited. Arterial oxygen tension (PaO 2) to fraction of inspired oxygen (FiO 2) is the only measured physiological variable in the Berlin Definition for ARDS. The acute respiratory distress syndrome (ARDS) is an important cause of acute respiratory failure with a high mortality rate. ConclusionsĮstimated 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. The predicted validity of the estimated dead space fraction and the ventilatory ratio improved the baseline model based on PEEP, PaO 2/FiO 2, driving pressure and compliance of the respiratory system at day 2 (AUROCC 0.72 vs. Dead space fraction calculation using the estimate from physiological variables and the ventilatory ratio at day 2 showed independent association with mortality at 30 days (odds ratio 1.28, p < 0.03 and 1.20, p < 0.03, respectively) whereas, the Harris–Benedict and Penn State estimations were not associated with mortality. Estimated dead space fraction and the ventilatory ratio at days 1 and 2 were significantly higher among non-survivors ( p < 0.01). Individual patient data from 940 ARDS patients were analyzed. The present study is a post hoc analysis of a prospective observational cohort study of ICUs of two tertiary care hospitals in the Netherlands. 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. 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.
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