Acute kidney injury and mortality 1 year after major non-cardiac surgery.

BACKGROUND: Even mild and transient acute kidney injury (AKI), defined by increases in serum creatinine level, has been associated with adverse outcomes after major surgery. However, characteristic decreases in creatinine concentration during major illness could confound accurate assessment of postoperative AKI. METHODS: In a single-hospital, retrospective cohort study of non-cardiac surgery, the association between postoperative AKI, defined using the Kidney Disease: Improving Global Outcomes criteria, and 1-year survival was modelled using a multivariable Cox proportional hazards analysis. Factors associated with development of AKI were examined by means of multivariable logistic regression. Temporal changes in serum creatinine during and after the surgical admission in patients with and without AKI were compared. RESULTS: Some 1869 patients were included in the study, of whom 128 (6·8 per cent) sustained AKI (101 stage 1, 27 stage 2-3). Seventeen of the 128 patients with AKI (13·3 per cent) died in hospital compared with 16 of 1741 (0·9 per cent) without AKI (P < 0·001). By 1 year, 34 patients with AKI (26·6 per cent) had died compared with 106 (6·1 per cent) without AKI (P < 0·001). Over the 8-365 days after surgery, AKI was associated with an adjusted hazard ratio for death of 2·96 (95 per cent c.i. 1·86 to 4·71; P < 0·001). Among hospital survivors without AKI, the creatinine level fell consistently (median difference at discharge versus baseline -7 (i.q.r. -15 to 0) µmol/l), but not in those with AKI (0 (-16 to 26) µmol/l) (P < 0·001). CONCLUSION: Although the majority of postoperative AKI was mild, there was a strong association with risk of death in the year after surgery. Underlying decreases in serum creatinine concentration after major surgery could lead to underestimation of AKI severity and overestimation of recovery.

Incidence and associations of acute kidney injury after major abdominal surgery.

PURPOSE: Acute kidney injury (AKI) is a recognised risk factor for adverse outcomes in critical illness and hospitalised patients in general. To understand the incidence and associations of AKI as a peri-operative complication of major abdominal surgery, we conducted a systematic literature review and meta-analysis. METHODS: Using a systematic strategy, we searched the electronic reference databases for articles describing post-operative renal outcomes using consensus criteria for AKI diagnosis (RIFLE, AKIN or KDIGO) in the setting of major abdominal surgery. Pooled incidence of AKI and, where reported, pooled relative risk of death after post-operative AKI were estimated using random effects models. RESULTS: From 4287 screened titles, 19 articles met our inclusion criteria describing AKI outcomes in 82,514 patients undergoing abdominal surgery. Pooled incidence of AKI was 13.4% (95% CI 10.9-16.4%). In eight studies that reported the short-term mortality, relative risk of death in the presence of post-operative AKI was 12.6 fold (95% CI, 6.8-23.4). Where reported, length of stay was greater and non-renal post-operative complications were also more frequent in patients experiencing AKI. CONCLUSIONS: Using modern consensus definitions, AKI is a common complication of major abdominal surgery that is associated with adverse patient outcomes including death. While a causative role for AKI cannot be concluded from this analysis, as an important signal of peri-operative harm, AKI should be regarded as an important surgical outcome measure and potential target for clinical interventions.

Acute kidney injury reduces the hepatic metabolism of midazolam in critically ill patients.

INTRODUCTION: Acute kidney injury (AKI) is a common and serious complication increasing morbidity and mortality from all causes of hospital admission. We have previously shown that AKI decreases midazolam metabolism, a substrate of the cytochrome P450 3A (CYP3A) enzymes and our primary aim was to determine if this effect is dependent on the severity of AKI. We also present preliminary data on the functional impact of different genotypes of CYP3A. METHODS: Critically ill patients at risk of AKI and admitted to a general intensive care unit were categorised after initial resuscitation according to the RIFLE criteria for AKI. Midazolam (1mg) was administered and the serum concentration of midazolam measured at 4 h. Samples were taken for CYP3A genotyping. RESULTS: Seventy-three patients were assigned to categories R, I and F of the RIFLE criteria or C (controls). Midazolam concentrations (ng mL(-1)) increased significantly (p = 0.002) as the severity of AKI worsened [control 3.1 (1.4-5.9), risk 4.7 (1.3-10.3), injury 3.9 (2.0-11.1) and failure 6.8 (2.2-113.6)] and were predicted by the duration of AKI (p = 0.000) and γ-glutamyl transferase (p = 0.005) concentrations. Increasing BMI negatively predicted the midazolam concentration (p = 0.001). Preliminary data suggest this effect is diminished if the patient expresses functional CYP3A5. CONCLUSION: Increasing severity and duration of AKI are associated with decreased midazolam elimination. We propose that this is caused by impaired CYP3A activity secondary to AKI. The exact mechanism remains to be elucidated. This may have important implications for our drug treatment of critically ill patients.