Acute kidney injury in elderly patients receiving invasive mechanical ventilation: early versus late onset

Background Acute kidney injury (AKI) is a severe complication in critical patients receiving invasive mechanical ventilation (MV). However, AKI which occurs in the first 48 h after MV (early AKI) and thus likely associated with the MV settings is probably different from AKI occurring following 48 h (late AKI). This study is aimed at exploring the incidence of early and late AKI in elderly patients receiving MV and identifying their different risk factors and outcomes. Methods This retrospective, observational, multicenter cohort study consecutively included 3271 elderly patients (>= 75 years) receiving invasive MV at four medical centers of Chinese PLA General Hospital from 2008 to 2020. The diagnosis of AKI was made following the 2012 KDIGO criteria and categorized into early (<= 48 h) or late (> 48 h-7 days) according to the time from MV. Results There were totally 1292 cases enrolled for the final analysis. Among them, 376 patients (29.1%) developed early AKI versus 132 (10.2%) developed late AKI. The 28-day mortality rates of the non-AKI, early AKI, and late AKI patients were 14.4, 46.8, and 61.4%, respectively. After 90 days, mortality rates of three groups were 33.2, 60.6, and 72.7%, respectively. Risk factors for early AKI included PaO2/FIO2, serum creatinine, hemoglobin, and positive end-expiratory pressure at the beginning of MV, while those for late AKI were PaO2/FIO2, serum creatinine, and hemoglobin. In the multivariable adjusted analysis, both early AKI (HR = 4.035; 95% CI = 3.166-5.142; P < 0.001) and late AKI (HR = 6.272; 95% CI = 4.654-8.453; P < 0.001) were related to the increased 28-day mortality relative to non-AKI. AKI was significantly related to 90-day mortality: early AKI (HR = 2.569; 95% CI = 2.142-3.082; P < 0.001) and late AKI (HR = 3.692; 95% CI = 2.890-4.716; P < 0.001). Conclusions AKI mostly develops in the initial 48 h following MV, which is related to the health and MV settings; while AKI occurring following 48 h is not associated with MV settings. Therefore, a strategy for kidney protection in patients with MV should take these differences into consideration.