Fluid Balance is Associated with Differential Effects on Respiratory Failure between Critically Ill and Noncritically...

Conservative fluid management improves outcomes in mechanically ventilated adults with acute respiratory distress syndrome, but its impact across the broader spectrum of acute respiratory failure is less clear. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic provided an opportunity to assess the relationship between daily fluid balance and respiratory status across varying degrees of respiratory impairment with a relatively uniform lung injury mechanism.

Retrospective study of adults hospitalized with SARS-CoV-2 within ±7 days of hospital admission in an academic medical system (March 2020-July 2022). The primary outcome was a modified World Health Organization Clinical Scale from 1 (Hospitalized, no respiratory support) to 5 (Death or discharge to hospice). Associations between daily net fluid balance and next-day modified World Health Organization Clinical Scale were tested using cumulative logistic regression and adjacent-categories logistic regression, adjusting for demographics, comorbidities, hospital type, vasopressors, inotropes, renal replacement therapy, and unmeasured urine outputs.

Among 4,254 patients (median age 58 [41-70]; 52.9% male; median hospital stay 4.5 [2.5-8.1] days), 2,860 (67.2%) required respiratory support, 539 (12.7%) received invasive ventilation, and 571 (13.4%) died. In critically ill adults, positive fluid balance was associated with higher odds of subsequent mechanical ventilation (odds ratio [OR] per L 1.48, 95% confidence interval [CI] 1.41-1.55) or death (OR 1.15, 95% CI 1.08-1.23). Among noncritically ill patients on low-flow oxygen, positive fluid balance was associated with improved respiratory status (OR 0.89, 95% CI 0.86-0.92).

Positive fluid balance had divergent effects by illness severity, suggesting distinct physiologic or clinical mechanisms across the spectrum of SARS-CoV-2 respiratory failure.