Key result
Each 5-mmHg increase in baseline PaCO2 below 37 mmHg was associated with a 16% reduction in 60-day ICU mortality (HR 0.84, 95% CI 0.72-0.98, p=0.0274) in critically ill acute heart failure patients.
Why the study?
Existing studies on the association between arterial partial pressure of carbon dioxide (PaCO2) and outcomes in acute heart failure (AHF) were controversial and limited by small sample sizes.
Is baseline arterial partial pressure of carbon dioxide (PaCO2) within 24 hours of ICU admission associated with ICU 60-day mortality in critically ill patients aged ≥60 years with acute heart failure?
Cohort (n=4,271)
No
Is baseline arterial partial pressure of carbon dioxide (PaCO2) within 24 hours of ICU admission associated with ICU 60-day mortality in critically ill patients aged ≥60 years with acute heart failure?
In critically ill older patients with acute heart failure admitted to the ICU, baseline hypocapnia (PaCO2 <37 mmHg) is inversely associated with 60-day mortality, suggesting low admission PaCO2 is an independent marker of poor short-term prognosis.
Low PaCO2 at admission signals higher mortality risk in acute HF; hypothesis-generating and requires prospective validation before clinical use.
Background: The association of the arterial partial pressure of carbon dioxide (PaCO2) with poor outcomes in acute heart failure (AHF) patients has been observed. Nevertheless, the existing studies are controversial and limited by small sample sizes. We assessed whether PaCO2 is associated with intensive care unit (ICU) 60-day mortality in AHF patients. Methods: We extracted and analyzed data from a quality public database, the Medical Information Mart for Intensive Care IV database. We used a smooth curve fitting method to assess a potential curvilinear relationship. Multivariate regression analyses incorporating a two-stage linear regression model were used to investigate the associations of PaCO2 with prognosis. Results: Overall, 4,271 participants were included, comprising 825 ICU 60-day non-survivors and 3,446 ICU 60-day survivors. Smooth curve fitting revealed a U-shaped relationship between PaCO2 and prognosis, with an inflection point of PaCO2 at 37 mmHg that was used to establish a two-stage linear regression model. When PaCO2 was <37 mmHg, the multivariate regression analysis showed that for every 5-mmHg increase in the PaCO2, the ICU 60-day mortality decreased by 16% (p=0.0274). There was no significant association between PaCO2 and ICU 60-day mortality (p=0.4685) when PaCO2 was ≥37 mmHg. Conclusions: These findings suggest that low PaCO2, but not high PaCO2, at ICU admission might help determine the short-term prognosis in critically AHF patients.
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Xiao et al. (2023) conducted a cohort in Acute heart failure (n=4,271). Baseline arterial partial pressure of carbon dioxide (PaCO2) per 5-mmHg increase when PaCO2 <37 mmHg vs. PaCO2 ≥37 mmHg (and continuous evaluation across inflection point of 37 mmHg) was evaluated on ICU 60-day all-cause mortality (per 5-mmHg increase in PaCO2 when PaCO2 <37 mmHg in fully adjusted model) (HR 0.84, 95% CI 0.72, 0.98, p=0.0274). Each 5-mmHg increase in baseline PaCO2 below 37 mmHg was associated with a 16% reduction in 60-day ICU mortality (HR 0.84, 95% CI 0.72-0.98, p=0.0274) in critically ill acute heart failure patients.
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