# Hypercapnia outcome in COVID-19 acute respiratory distress syndrome patients on mechanical ventilator: A retrospective observational cohort

## TL;DR

This study found that high carbon dioxide levels in the blood (hypercapnia) are not linked to higher death rates in COVID-19 patients with severe lung disease on ventilators.

## Contribution

The study clarifies the conflicting evidence on hypercapnia's role in mortality among mechanically ventilated COVID-19 ARDS patients.

## Key findings

- Severe hypercapnia is associated with worse lung function and higher disease severity.
- After adjusting for disease severity, hypercapnia is not linked to increased mortality.
- Weighted regression analysis also found no significant effect of hypercapnia on mortality.

## Abstract

Acute respiratory distress syndrome (ARDS) is characterized by progressive lung inflammation which leads to increased dead space that can cause hypercapnia and can increase the risk of patient morbidity and mortality. In an attempt to improve ARDS patient outcomes provision of protective lung ventilation has been shown to improve patient mortality but increases the incidence of hypercapnia. Therefore, the role of carbon dioxide in ARDS remains contradicted by conflicted evidence. This study aims to examine this conflicting relationship between hyper-capnia and mortality in mechanically ventilated COVID-19 ARDS patients.

We conducted a retrospective cohort study. The data was collected from the medical records of the patients admitted with COVID-19 ARDS in Sindh Infectious Disease Hospital & Research Centre (SIDH & RC) from August 2020 to August 2022 and who received mechanical ventilation for more than 48 hours. The patients were grouped into severe and no severe hypercapnia groups based on their arterial blood carbon dioxide levels (PaCO2). To understand the effect of hypercapnia on mortality we performed multivariable logistic regression, and inverse probability-weighted regression to adjust for time-varying confounders.

We included 288 patients to detect at least 3% of the effect on mortality. Our analysis revealed an association of severe hypercapnia with severe lung injury, low PaO2/FiO2, high dead space, and poor compliance. In univariate analysis severe hypercapnia showed higher mortality: OR=3.50, 95% CI (1.46–8.43). However, after, adjusting for disease severity hypercapnia is not found to be associated with mortality: OR=1.08, 95% CI (0.32–3.64). The sensitive analysis with weighted regression also shows no significant effect on mortality: OR=1.04, 95% CI (0.95–1.14).

This study showed that hypercapnia is not associated with mortality in COVID-19 ARDS patients.