Acute Respiratory Distress Syndrome Mortality Based on Arterial CO2 Management

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Patients with mild ARDS and sustained hypercapnia had higher mortality rates than those with more severe ARDS.

Patients with mild acute respiratory distress syndrome (ARDS) and sustained hypocapnia had higher mortality rates than those with more severe ARDS, according to study results published in the journal CHEST.

Researchers examined how arterial CO2 was managed in patients with ARDS who were enrolled in the Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG-SAFE; Identifier: NCT02010073).  These patients were admitted to the intensive care unit and underwent invasive or noninvasive ventilation for ARDS. The researchers sought to determine the prevalence of day 1 and sustained (day 1 and 2) of hypocapnia, normocapnia, and hypercapnia. Associations between clinical outcomes and arterial CO2 levels were compared between groups. 

Of the 2813 patients with ARDS analyzed, 551 were hypocapnic, 1018 were normocapnic, and 1214 were hypercapnic, on day 1. Meanwhile, sustained hypocapnia was observed in 252 patients, sustained normocapnia in 544 patients, and sustained hypercapnia in 654 patients. Overall, hypocapnia was more frequent and severe in patients receiving noninvasive ventilation, while hypercapnia was more frequent in patients with moderate or severe ARDS (PF ratio [partial pressure arterial oxygen/fraction inspired oxygen], <150 mm Hg). A higher prevalence of chronic obstructive pulmonary disease, lower frequency of immune incompetence, and more pneumonia were seen in patients with sustained hypercapnia.

When hospital outcomes were analyzed, there was no association between arterial CO2 levels and clinical outcomes. However, ICU mortality was higher in patients with mild to moderate ARDS with sustained hypocapnia vs sustained normocapnia (38% vs 27%, respectively).

“There was no evidence for benefit or harm with hypercapnia in our cohort,” the researchers wrote. “In contrast, ICU mortality was higher in patients with mild to moderate ARDS receiving sustained hypocapnia, suggesting the need for caution regarding ARDS patients with sustained hypocapnia.”


Madotto F, Rezoagli E, McNicholas BA, et al; on behalf of the LUNG SAFE Investigators and the ESICM Trials Group  Patterns and impact of arterial CO2 management in patients with acute respiratory distress syndrome: insights from the LUNG SAFE study [published online June 23, 2020]. CHEST. doi:10.1016/j.chest.2020.05.605