Plasma sodium during the recovery of renal function in critically ill adult patients: Multicenter prospective cohort study

Background: Sodium increases during acute kidney injury (AKI) recovery. Both hypernatremia and positive fluid balances are associated with increased mortality. We aimed to evaluate the association between daily fluid balance and daily plasma sodium during the recovery from AKI among critical patients. Methods: Adult patients with AKI were enrolled in four ICUs and followed up for four days or until ICU discharge or hemodialysis initiation. Day zero was the peak day of creatinine. The primary outcome was daily plasma sodium; the main exposure was daily fluid balance. Results: 93 patients were included. The median age was 66 years; 68% were male. Plasma sodium increased in 79 patients (85%), and 52% presented hypernatremia. We found no effect of daily fluid balance on plasma sodium (beta -0.26, IC95%: - 0.63-0.13; p = 0.19). A higher total sodium variation was observed in patients with lower initial plasma sodium (beta -0.40, IC95%: -0.53 to -0.27; p < 0.01), higher initial urea (beta 0.07, IC95%: 0.04-0.01; p < 0.01), and higher net sodium balance (beta 0.002, IC95%: 0.0001-0.01; p = 0.05). Conclusions: The increase in plasma sodium is common during AKI recovery and can only partially be attributed to the water and electrolyte balances. The incidence of hypernatremia in this population of patients is higher than in the general critically ill patient population.