Acute Kidney Injury Incidence, risk factors, renal recovery and outcome

Abstract

Acute kidney injury (AKI) is a common clinical problem both in the hospital and outpatient setting and is associated with increased morbidity and mortality. Chronic kidney disease (CKD) is a risk factor for developing AKI and AKI is a risk factor for development and progression of CKD. Renal recovery after AKI has been shown to be an independent determinant of patient morbidity and mortality, but studies have been impeded by lack of consensus on how to define renal recovery following AKI. A small absolute change in serum creatinine (SCr) of 26.5 μmol/L within 48 hours is included in the current diagnostic criteria of AKI. However, characteristics and long-term outcomes of the subgroup diagnosed with AKI solely by this part of the criteria, referred to as mild stage 1 AKI in this thesis, has not been studied. The aim of this thesis was to evaluate the incidence, long-term survival and renal recovery of hospital-acquired AKI (H-AKI) and examine time-trends in its incidence and survival. Also to assess the incidence, risk factors and short-term survival of AKI following abdominal surgery. Furthermore, to compare different definitions of renal recovery following postoperative AKI with respect to association with long-term survival, development of incident CKD and progression of preexisting CKD. Finally, to examine the characteristics of mild stage 1 AKI and whether it is associated with long-term survival, development of incident CKD or progression of preexisting CKD. All the studies reported in the papers were retrospective. Paper I included all patients with H-AKI over a 20-year period, from 1993 to 2013. All patients undergoing abdominal surgery in 2007-2014 were included in Paper II, and Paper III and IV included all patients undergoing abdominal, cardiothoracic, vascular or orthopedic surgery in 1998-2015. Data on patient characteristics, comorbidities, perioperative information and SCr measurements were collected from electronic hospital records, national registries and hospital databases. The SCr component of the KDIGO criteria was used to detect AKI in all Papers, except that the absolute increase in SCr of 26.5 μmol/L within 48 hours was excluded in Paper I. Multivariable logistic regression analyses were performed to evaluate risk factors and associations with one-year mortality. Cox proportional hazards regression analysis and propensity score matching were used to evaluate long-term survival, development of incident CKD and progression of preexisting CKD. The mean incidence of H-AKI was 25.8 per 1000 admissions/year and increased significantly over the 20-year study period. H-AKI associated with worse one-year survival that followed an inverse relationship with the severity of H-AKI. However, survival of H-AKI patients improved over the study period. AKI occurred following 6.8% of all abdominal surgeries and was most common following surgery on the esophagus, spleen, stomach and after explorative laparotomy. Independent risk factors for AKI following abdominal surgery were older age, male sex, preoperative CKD, higher ASA class and if the surgery was a reoperation. AKI following abdominal surgery was associated with longer length of stay, more short-term complications and worse 30-day survival. Lack of renal recovery after AKI to a SCr < 1.5 x baseline within 30 days was associated with worse one-year survival and lack of recovery to a SCr < 1.25 x baseline within 30 days was associated with increased risk of developing incident CKD and progression of preexisting CKD. One-third of all postoperative AKI patients had mild stage 1 AKI, which was associated with both development of incident CKD and progression of preexisting CKD, but no association was found with one-year survival. The four papers highlight that AKI is a common problem in both the general hospital population and following surgery. There are independent risk factors for development of AKI following abdominal surgery that can all be assessed preoperatively for patient risk stratification. AKI is associated with both short-term and long-term survival and development of incident CKD and progression of preexisting CKD. Moreover, lack of renal recovery to SCr below 1.5 x baseline value within 30 days associated with worse one-year survival and lack of recovery to SCr below 1.25 x baseline value was associated with development of CKD and progression of preexisting CKD. These results should be considered when a consensus on the definition of renal recovery is reached. Furthermore, mild stage 1 AKI was associated with short-term mortality and both development of CKD and progression of preexisting CKD. This supports the inclusion of small absolute increase in SCr in the AKI definition and the results emphasize the importance of meticulous follow-up of patients with AKI, particularly patients without renal recovery.