Severe hypercapnia and outcome of mechanically ventilated patients with moderate or severe acute respiratory distress syndrome

Abstract

Purpose: To analyze the relationship between hypercapnia developing within the first 48 h after the start of mechanical ventilation and outcome in patients with acute respiratory distress syndrome (ARDS).

Patients and methods: We performed a secondary analysis of three prospective non-interventional cohort studies focusing on ARDS patients from 927 intensive care units (ICUs) in 40 countries. These patients received mechanical ventilation for more than 12 h during 1-month periods in 1998, 2004, and 2010. We used multivariable logistic regression and a propensity score analysis to examine the association between hypercapnia and ICU mortality.

Main outcomes: We included 1899 patients with ARDS in this study. The relationship between maximum PaCO2 in the first 48 h and mortality suggests higher mortality at or above PaCO2 of ≥50 mmHg. Patients with severe hypercapnia (PaCO2 ≥50 mmHg) had higher complication rates, more organ failures, and worse outcomes. After adjusting for age, SAPS II score, respiratory rate, positive end-expiratory pressure, PaO2/FiO2 ratio, driving pressure, pressure/volume limitation strategy (PLS), corrected minute ventilation, and presence of acidosis, severe hypercapnia was associated with increased risk of ICU mortality [odds ratio (OR) 1.93, 95% confidence interval (CI) 1.32 to 2.81; p = 0.001]. In patients with severe hypercapnia matched for all other variables, ventilation with PLS was associated with higher ICU mortality (OR 1.58, CI 95% 1.04-2.41; p = 0.032).

Conclusions: Severe hypercapnia appears to be independently associated with higher ICU mortality in patients with ARDS.

Trial registration: Clinicaltrials.gov identifier, NCT01093482.

Keywords: Acute respiratory distress syndrome; Hypercapnia; ICU mortality; Mechanical ventilation.

Figures

Fig. 1

Study flow chart. ARDS Acute respiratory distress syndrome, MV mechanical ventilation, PaCO2 partial pressure of carbon dioxide in arterial blood

Fig. 2

Adjusted effects of PaCO2 at 48 h from the beginning of the period of mechanical ventilation on mortality in the intensive care unit (ICU). Each black square represents the odds ratio for each PaCO2 interval adjusted by age, Simplified Acute Physiology Score II score, PaO2/fraction of inspirted oxygen (FiO2) ratio, pressure/volume limitation strategy, respiratory rate, presence of acidosis, dead space, and year of study, solid vertical lines 95% confidence intervals, horizontal dotted line threshold between non-significant and significant differences (odds ratio = 1)