Abstract
Background: The aim of this study was to evaluate the incidence and outcome of postoperative acute kidney injury (AKI) after major noncardiac surgery in Hungarian intensive care units (ICUs). Methods: We conducted an analysis of a multicenter survey on the epidemiology of AKI in Hungarian ICUs in respect of surgical interventions. The cohort study consisted of all patients (n = 295) over the age of 18 years who were admitted to ICUs after surgery between 1 October 2009 and 30 November 2009. AKI was defined and classified by the acute kidney injury network (AKIN) criteria. Results: Forty-eight (18.1%) patients had AKI during their ICU stay. By AKIN criteria, 27 (10.2%) patients were in Stage 1, 11 (4.2%) patients in Stage 2, and 10 (3.8%) patients in Stage 3. The overall mortality rate of AKI was 39.6% (AKI 1: 25.9%, AKI 2: 40%, and AKI 3: 54.5%; p < 0.001) and the ICU mortality rate was 33.3% (AKI 1: 18.5%, AKI 2: 10%, and AKI 3: 54.5%; p < 0.001). According to logistic regression analysis, age (OR: 1.048; CI: 1.014–1.082; p = 0.005), vasopressor treatment (OR: 9.751; CI: 8.579–10.923; p < 0.001), sepsis (OR: 10.791; CI: 9.353–12.233; p = 0.001), serum-creatinine peak-concentration (OR: 1.035; CI: 1.021–1.047; p < 0.001), and intra-abdominal surgery (OR: 2.558; CI: 1.75–3.366; p = 0.020) were independent predictors for AKI. Conclusions: The results of this study confirm that there is a high incidence of AKI following major noncardiac surgery, which is associated with higher ICU and in-hospital mortality.
INTRODUCTION
Acute kidney injury (AKI) is commonly seen in the perioperative period and in the intensive care unit (ICU). AKI is associated with a prolonged hospital stay and high morbidity and mortality.Citation1–3 Many studiesCitation4–8 describe a wide range of postoperative AKI (0.8–17%), which varies across ICUs and admission diagnoses. Several independent preoperative predictors (age, emergent surgery, liver disease, high body mass index, high-risk surgery, and so on) and intraoperative management variables (use of vasopressor and diuretics) have been identified as independent predictors of AKI, but the incidence of AKI following different types of surgery has not been evaluated. Postoperative AKI is a leading cause of morbidity, mortality, prolonged hospital stay, and increased hospital cost.Citation5 Despite the widespread recognition of the increased risk for AKI following a variety of surgical procedures, the pathogenesis of this syndrome is poorly understood.
Because we have no controlled data on the epidemiology of postoperative AKI in critically ill patients in Hungary, the aims of our study were to examine the incidence of postoperative AKI depending on type of surgery and to evaluate its impact, in the context of other risk factors, on outcomes (mortality and hospital- and ICU stay) and to compare the findings to international experience.
METHODS
We analyzed our prospectively collected databaseCitation1 with respect to surgical interventions. Medical patients (164), chronic kidney disease patients on dialysis (n = 3), theoretically the renal transplant patients (n = 0), polytraumatic patients (n = 17), and the patients who were after several body cavities affecting surgical intervention (n = 10) were excluded from the analysis. Those included (n = 265) were categorized by serum creatinine and/or urine output into the acute kidney injury network (AKIN) stagesCitation9 and the highest AKIN stage during ICU staying was evaluated. Serum creatinine on ICU admission was used as a reference value; staging was based on the appropriate increase within the 48-h observation period. Declines in serum creatinine level were not coded as AKI. Twelve patients had a creatinine level >300 μmol/L on admission. Serum creatinine was determined at least once a day and urine output recorded hourly, for all patients. AKI was defined and classified by the AKIN criteria. The Simplified Acute Physiology Score version II (SAPS II)Citation10 and the Sepsis-related Organ Failure Assessment Score (SOFA)Citation11 were used to evaluate the severity of illness, and were calculated on the basis of worst variables recorded during the first 24 h of ICU admission. The data were collected using an Excel-based data collection file.
Statistical Analysis
All values were presented as mean ± SD or as median with interquartile range (IQR) as appropriate. The mean values of the different groups were compared using two-sided t-test, the median values using the Kolmogorov–Smirnov test and the occurrence rates using the chi-square test. A forward stepwise logistic regression analysis (conditional) was performed to determine the independent risk factors for AKI and mortality. The included variables were age, gender, vasopressor requirement, AKI stages, SOFA, SAPS II, creatinine level at ICU admission and the maximum level during ICU staying, sepsis, and mechanical ventilation, as appropriate. All analysis were performed using the SPSS statistical software package 15.0 (IBM, Armonk, NY, USA). Statistical significance was indicated by p < 0.05.
RESULTS
Baseline Characteristics
A total of 265 patients met the inclusion criteria and were followed for the development of AKI after ICU admission. Forty-eight (18.1%) patients had AKI during their ICU stay. Patients with AKI were older (median age 67 vs. 61 years, p = 0.002), with higher serum-creatinine level at ICU-admission (110 vs. 67 μmol/L, p < 0.001), than patients without AKI: Patients with AKI were more severely ill (median SAPS II 40 vs. 18, p < 0.001, SOFA 5 vs. 2, p < 0.001) and had higher ratio of respiratory support (60.4% vs. 18%, p = 0.002) and catecholamine needs (50% vs. 6.5%, p < 0.001). Sepsis occurred more frequently in the AKI group (45.8% vs. 2.3%, p < 0.001). The characteristics of the patients are summarized in .
Table 1. Baseline characteristics of patients.
Distribution of AKI Stages
By AKIN criteria, 27 (10.2%) patients were in Stage 1, 11 (4.2%) patients in Stage 2, and 10 (3.8%) patients in Stage 3. Among AKI Stage 3 patients, 40% (4/10) received renal replacement therapy.
Mortality and Lengths of Stay
The overall mortality rate of AKI was 39.6% (AKI 1: 25.9%, AKI 2: 40%, and AKI 3: 54.5%) and the ICU mortality rate was 33.3% (AKI 1: 18.5%, AKI 2: 10%, and AKI 3: 54.5%). Any degree of AKI was associated with a significantly increased all-cause ICU (6.9% vs. 33.3%, p < 0.001) and overall in-hospital mortality (8.8% vs. 39.6%, p < 0.001) compared with not having AKI. For patients with AKI admitted to the ICU, the median length of stay at the ICU increased by 200% (2 vs. 6 days, p < 0.0001) and the median length of hospitalization increased by 80% (10 vs. 18 days, p < 0.001) compared with patient without AKI ().
Table 2. Mortality and lengths of stay.
Analysis of Patients according to Type of Surgery
We analyzed the incidence of AKI according to different types of surgery and the characteristics of patients with and without AKI summarized in . The incidence of AKI occurred more frequently in abdominal surgery group (53.9%, p < 0.001), than in intracranial- (12.9%), thoracic-surgery (2.0%), or surgery outside the cavities (10%). We elaborated the different types of major abdominal procedures according to the occurrence of AKI and did not find significant differences among the different types of surgery (). The most frequent diagnosis was cancer, and this illness associated with significantly lower rate of AKI than was observed in the mechanical obstruction and perforation groups.
Table 3. Incidence and outcome of AKI according to the type of surgery.
Table 4. Distribution of AKI according to the types of abdominal procedures and diagnoses.
In the abdominal surgery group, we analyzed the incidence of AKI on the basis of serum creatinine level at ICU admission (under and above the normal laboratory limit values). About 110 patients had serum creatinine under the normal laboratory level and, during the ICU stay, AKI developed in 16 (14.5%) patients. The serum creatinine level during admission was above the normal limits in 35 patients and among them significantly higher ratio of AKI (n = 23; 65.7%) was observed (p < 0.005). The ICU and hospital stay and mortality did not differ significantly in respect of the creatinine level at admission.
Multivariate Analysis to Evaluate the Influencing Factors of the Development of AKI and the ICU Mortality
A logistic regression analysis was performed to analyze the predisposing factors for the incidence of AKI (). Among the analyzed parameters, vasopressor treatment, serum creatinine on ICU admission, and sepsis were the independent risk factors for the development of any stage of AKI. Multivariate analysis of different type of surgery for the determinants of AKI identified the intra-abdominal surgery as independent predictor (OR: 2.558; CI: 1.75–3.366; p = 0.020). According to the logistic regression analysis, age, vasopressor treatment, SAPS II Score, and serum-creatinine peak concentration were found to be independent risk factors for ICU mortality ().
Table 5. Logistic regression analysis to evaluate the influencing factors of AKI development and ICU mortality.
DISCUSSION
Epidemiological studies for postoperative AKI have been conducted in different populations using various criteria and reported a wide range of incidence (0.8–17.0%).Citation1–5,12–14 There is only one study that assessed the prevalence of postoperative kidney injury in noncardiac surgery according to the AKIN criteria. Abelha and co-workersCitation5 have found it 7.5%, but they did not assess the different degrees of severity. While they reported the incidence of AKI among patients with normal preoperative renal function, in our study chronic kidney disease and a higher serum-creatinine value were not exclusion criteria in classification by AKIN. We used serum creatinine on ICU admission as a reference value. The overall incidence of AKI in their study was lower than that in our analysis (7.5% vs. 18.1%).
We have demonstrated that the incidence of AKI is the highest in elderly patients who make up an ever-growing segment of the surgical population.Citation15,16 In our study, patients with AKI were significantly older with a higher severity of illness (SAPS II and SOFA score), which was found to be an independent risk factor for AKI and ICUs mortality.
We found that the incidence of AKI was the highest after abdominal surgery. Inadequate renal perfusion pressure caused by complicated abdominal surgery was one of the potential key factors in the development of high intra-abdominal pressure—induced kidney injury.Citation17–19 Badin and coworkersCitation20 showed that in septic shock patients with an initial renal insult, a time-averaged mean arterial pressure (MAP) between 72 and 82 mmHg during the first 24 h was associated with a lower incidence of acute kidney insufficiency. This MAP level is higher than the universally recommended level of 65 mmHg. Our study indirectly confirms the importance of inadequate blood pressure in the development of AKI in that vasopressor requirements were significantly higher in patients with AKI than in those without AKI.
Vasopressor treatment was identified to be an independent risk factor for the development of all stages of AKI and for ICU mortality.
Severe sepsis and septic shock are the most common causes of mortality in postoperative ICUs. The combination of AKI and severe sepsis was reported to carry a mortality of up to 70%, whereas the mortality of AKI alone is 40–45%.Citation21 The multicenter European Sepsis Occurrence in Acutely Ill Patients (SOAP) studyCitation22 found that ∼51% of septic patients developed AKI. In our study, sepsis was also the leading etiologic factor (in 45.8% of patients) of AKI, and was a highly significant independent risk factor for AKI.
The incidence of AKI was similar in the different abdominal procedures, but it was significantly lower when the operation was due to cancer. We suppose that the higher occurrence of AKI in the perforation and mechanical obstruction groups was due to the emergent surgery, where there was not enough time to prepare the patients adequately for the operation.
There are limitations to our study. Most importantly, we did not routinely measure postoperative intra-abdominal pressure following intra-abdominal surgery. Secondly, we did not separate patients preoperatively with normal kidney function and chronic renal failure. Thirdly, Hungarian ICUs have no standardized protocol for the treatment of AKI, so we could not meaningfully compare different ICUs in this respect. Finally, we did not distinguish early AKI from late AKI.
CONCLUSION
For the first time, we have established the incidence of postoperative AKI using the AKIN criteria at Hungarian ICUs. The results of this study confirm that postoperative AKI has a high incidence and is associated with high ICU and in-hospital mortality. The independent risk factors for the development of AKI were age, serum creatinine on ICU admission, sepsis, vasopressor treatment, and intra-abdominal surgery. Age, sepsis-related variables (vasopressor treatment, serum-creatinine peak concentration, and SAPS II score), and AKI were highly significant risk factors for the ICU mortality.
ACKNOWLEDGMENTS
The authors thank Drs. Csaba Antek, Balazs Paloczi, Szilvia Kocsi, Bela Gartner, Zsuzsanna Marjanek, Gabor Bencsik, and Peter Kanizsai for their contribution to data collection.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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