Hypophosphatemia and duration of respiratory failure and mortality in critically ill patients

Hypophosphatemia has been associated with prolonged duration of respiratory failure and increased mortality in critically ill patients, but there is very limited evidence supporting the negative effects of low phosphate. We examined the association between hypophosphatemia at ICU admission and time to successful weaning and 28-day mortality.

This was a cohort study that included all mechanically ventilated adult patients admitted to the ICU in 2013 at Nordsjællands Hospital. Hypophosphatemia was defined as a serum level below 0.80 mmol/L. Multivariate Cox-regression was used to evaluate the effect of hypophosphatemia on mechanical ventilation and 28-day mortality. Multiple imputation was used to adjust for missing values.

A total of patients were admitted during the study period, of whom 190 were eligible. 122 (64.2%) had serum phosphate levels measured during the first 24 hours of admission, of whom 25 (20.5%) were found to be hypophosphatemic. About 74% of patients were successfully weaned from the ventilator within 28 days. Hypophosphatemia was not associated with this outcome (HR: 0.56; 95% CI: 0.30-1.04; P = .067). All-cause 28-day mortality was 32.6%. Hypophosphatemia was also not associated with 28-day mortality (HR: 1.64; 95% CI: 0.65-4.17; P = .447). Similar results were present in supplementary analysis where missing data were included by means of multiple imputation.

Hypophosphatemia at ICU admission was not associated with prolonged respiratory failure nor mortality. Further studies are warranted, where phosphate is measured systematically on all patients to elucidate the effect of low phosphate on relevant outcomes.