['Hypophosphatemia is common in critically ill patients and has been associated with generalized muscle weakness, ventilatory failure and myocardial dysfunction. Continuous renal replacement therapy causes phosphate depletion, particularly with prolonged and intensive therapy. In a prospective observational cohort of critically ill patients with acute kidney injury (AKI), we examined the incidence of hypophosphatemia during dialysis, associated risk factors and its relationship with prolonged respiratory failure and 28-day mortality.', 'This is a single-center prospective observational study. Included in the study were 321 patients with AKI on continuous dialysis as initial treatment modality.', 'Four per cent of the patients had a phosphate level <2 mg/dL at initiation and 27% during dialysis. Low baseline phosphate was associated with older age, female gender, parenteral nutrition, vasopressor support, low calcium, and high urea, bilirubin and creatinine, whereas hypophosphatemia during dialysis correlated with the ischemic acute tubular necrosis etiology of renal failure, intensive dose and longer therapy. Serum phosphate decline during dialysis was associated with higher incidence of prolonged respiratory failure requiring tracheostomy [odds ratio (OR) = 1.81; 95% confidence interval (CI) = 1.07-3.08], but not 28-day mortality (OR = 1.16; 95% CI = 0.76-1.77) in multivariable analysis.'] Is hypophosphatemia during continuous hemodialysis associated with prolonged respiratory failure in patients with acute kidney injury?