OBJECTIVES: Compare ICU outcomes and respiratory system mechanics in patients with and without acute kidney injury during invasive mechanical ventilation. DESIGNS: Retrospective cohort study. SETTINGS: ICUs of the University of California, San Diego, from January 1, 2014, to November 30, 2016. PATIENTS: Five groups of patients were compared based on the need for invasive mechanical ventilation, presence or absence of acute kidney injury per the Kidney Disease: Improving Global Outcomes criteria, and the temporal relationship between the development of acute kidney injury and initiation of invasive mechanical ventilation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 9,704 patients were included and 4,484 (46%) required invasive mechanical ventilation; 2,009 patients (45%) had acute kidney injury while being treated with invasive mechanical ventilation, and the mortality rate for these patients was 22.4% compared with 5% in those treated with invasive mechanical ventilation without acute kidney injury (p < 0.01). Adjusted hazard of mortality accounting for baseline disease severity was 1.58 (95% CI, 1.22–2.03; p < 0.001]. Patients with acute kidney injury during invasive mechanical ventilation had a significant increase in total ventilator days and length of ICU stay with the same comparison (both p < 0.01). Acute kidney injury during mechanical ventilation was also associated with significantly higher plateau pressures, lower respiratory system compliance, and higher driving pressures (all p < 0.01). These differences remained significant in patients with net negative cumulative fluid balance. CONCLUSIONS: Acute kidney injury during invasive mechanical ventilation is associated with increased ICU mortality, increased ventilator days, increased length of ICU stay, and impaired respiratory system mechanics. These results emphasize the need for investigations of ventilatory strategies in the setting of acute kidney injury, as well as mechanistic studies of crosstalk between the lung and kidney in the critically ill.

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Acute kidney injury (AKI) is a common complication of critical illness, and the mortality rate of AKI in the intensive care unit (ICU) is 30-50%. Recent studies have demonstrated that mechanical ventilation (MV) contributes to the development of AKI, yet few studies have investigated the impact of AKI during MV on ICU outcomes. We performed a retrospective analysis of a large ICU cohort to investigate the hypothesis that AKI would lead to increased duration of MV, length of ICU stay, and mortality. METHODS: Medical records of all patients admitted to the University of California, San Diego (UCSD) ICU between January 1, 2014 and November, 30 2016 were screened. Patients with ESRD were excluded, and those with AKI were identified based on KDIGO criteria. Outcomes were evaluated in 6 groups; 1) No MV or AKI, 2) No MV+AKI, 3) MV with no AKI, 4) AKI at initiation of MV, 5) AKI during MV, and 6) AKI post-MV. After tests for normality, differences in continuous, categorial and independent proportions were compared using two tailed Ttest or Mann Whitney U; Fisher's exact test; and Z-test respectively at a 0.05 level of significance. Kaplan-Meier time to event analysis was used to plot trends in ICU survival among the groups. RESULTS: 9704 patients were included in our analysis, and 4275 patients had AKI. The incidence of AKI in patients not treated with MV was 32% vs 58% in those who were (p-value :<0.001). Total days with AKI and need for CRRT were increased in groups who had AKI while on MV compared to the No MV+AKI (23.6% vs 0.6%, p and 16.3% vs 0.6, p) and AKI post-MV (23.6% vs 1.9%, p< 0.001 and 16.3% vs 1.9, p< 0.001) groups. Patients in the AKI at the initiation of MV and AKI during MV groups required significantly longer durations of ventilation days (4[2-8] vs. 2[2-3], p < 0.001; and 6[3 -12] vs. 2[2-3], p < 0.001); and lengthier ICU stays (12 [8-20] vs 4[3-6], p <0.001; and 9[5-17] vs 4[3-6], p <0.001) compared to MV patients without AKI. Mortality was also significantly increased in the MV+AKI groups (28.4% vs 6.2%, p <0.001 and 21.5% vs 6.2%, p<0.001). CONCLUSIONS: MV was associated with higher rates of AKI. AKI during MV prolongs MV duration and significantly increases mortality. This study highlights the need for mechanistic studies focused on ventilator-kidney interactions that may lead to novel preventative strategies.