Hypotension as a Risk Factor for Acute Kidney Injury in ICU Patients

Abstract

In the context of critical illness, hypotension may be associated with acute kidney injury (AKI). Using the MIMIC II database, we studied the risk of AKI in ICU patients as a function of both the severity and duration of hypotension. Multivariate logistical regression was performed to find correlations between hypotension and AKI. Minimum mean arterial blood pressure (MAP) and the amount of time MAP was below a range of hypotension thresholds in a target 48-hour window (prior to AKI onset) were used as primary predictive variables in the multivariate model. Our results indicate that the risk of AKI was related to the severity of hypotension with an odds ratio (OR) of 1.03, 95% CI 1.02-1.04 (p < 0.0001) per 1 mmHg decrease in minimum MAP ≥ 80 mmHg. For each additional hour MAP was less than 70, 60, 50 mmHg, the risk of AKI increased by 2% (OR 1.02, 95% CI 1.00-1.03, p = 0.0034), 5% (OR 1.05, 95% CI 1.02-1.08, p = 0.0028), and 22% (OR 1.22, 95% CI 1.04-1.43, p = 0.0122) respectively.

Figures

Figure 1

Mean arterial blood pressure up to 3 days prior to AKI onset for the AKI cohort, or prior to the last creatinine measurement time for the no AKI group. Plot shows mean and standard error of patients’ median MAP in 3-hour bins. Circadian variations are apparent and reflect the timing of the creatinine measurements, which are usually taken in the early morning.

Figure 2

Fraction of patients who developed AKI as a function of minimum blood pressure in the 48-hour target window. N = 3,658 (34% AKI).

Figure 3

Fraction of patients who developed AKI as a function of hypotension duration in the target 48-hour window using various MAP values as thresholds. A third of the 3613 patients included in this plot developed AKI, as indicated by the black dashed line. Prolonged hypotension increased the incidence of AKI in these patients. The duration of hypotension associated with a 5% increase in AKI incidence (indicated by the dotted blue line) varies with severity of hypotension (see text).