Acute Kidney Injury, Renal Function, and the Elderly Obese Surgical Patient A Matched Case-Control Study

Departments of *Surgery †The Leonard Davis Institute of Health Economics, The University of Pennsylvania ‡Department of Statistics, The Wharton School, The University of Pennsylvania §Center for Outcomes Research, The Children's Hospital of Philadelphia ¶Medicine ‖Anesthesiology and Critical Care
Annals of surgery (Impact Factor: 8.33). 05/2013; 258(2). DOI: 10.1097/SLA.0b013e31829654f3
Source: PubMed


OBJECTIVE:: To investigate the association between obesity and perioperative acute kidney injury (AKI), controlling for preoperative kidney dysfunction. BACKGROUND:: More than 30% of patients older than 60 years are obese and, therefore, at risk for kidney disease. Postoperative AKI is a significant problem. METHODS:: We performed a matched case-control study of patients enrolled in the Obesity and Surgical Outcomes Study, using data of Medicare claims enriched with detailed chart review. Each AKI patient was matched with a non-AKI control similar in procedure type, age, sex, race, emergency status, transfer status, baseline estimated glomerular filtration rate, admission APACHE score, and the risk of death score with fine balance on hospitals. RESULTS:: We identified 514 AKI cases and 694 control patients. Of the cases, 180 (35%) followed orthopedic procedures and 334 (65%) followed colon or thoracic surgery. After matching, obese patients undergoing a surgical procedure demonstrated a 65% increase in odds of AKI within 30 days from admission (odds ratio = 1.65, P < 0.005) when compared with the nonobese patients. After adjustment for potential confounders, the odds of postoperative AKI remained elevated in the elderly obese (odds ratio = 1.68, P = 0.01.) CONCLUSIONS:: Obesity is an independent risk factor for postoperative AKI in patients older than 65 years. Efforts to optimize kidney function preoperatively should be employed in this at-risk population along with keen monitoring and maintenance of intraoperative hemodynamics. When subtle reductions in urine output or a rising creatinine are observed postoperatively, timely clinical investigation is warranted to maximize renal recovery.

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    ABSTRACT: In the general population, obesity is associated with an increased mortality risk, whereas several epidemiological studies demonstrated a protective effect of obesity in critically ill patients. In this context, Sleeman and colleagues investigated the effects of obesity on kidney function in a well-established porcine model of cardiopulmonary bypass. The authors confirm literature data that obesity per se is associated with a chronic hyper-inflammatory status. Nevertheless, obese swine undergoing the surgical procedure presented with attenuated kidney dysfunction and tissue apoptosis. The authors suggest that the chronic inflammation causes pre-conditioning against excessive acute hyper-inflammation. The authors have to be commended for using a long-term, clinically relevant model that, moreover, addresses a variety of putative mechanisms. The study is discussed in the context of the controversial findings that, in contrast to the existing literature on improved survival, most studies available suggest a higher incidence and severity of acute kidney injury in obese patients when compared with lean controls.
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    ABSTRACT: Obesity has reached epidemic proportions in the developed world today. Obesity is a significant risk factor for cardiovascular disease, hypertension, diabetes mellitus, and chronic kidney disease. There has been renewed interest in the role of perioperative renal dysfunction with the establishment of new diagnostic criteria for kidney dysfunction such as the AKIN criteria and the RIFLE criteria. There is increasing evidence pointing to the role of visceral adipose tissue and adipokines in the pathophysiology of obesity. Furthermore, the traditional methods of quantifying obesity such as BMI are increasing being questioned since they may not accurately reflect true visceral obesity and may skew epidemiological classification of metabolically healthy patients. Recent epidemiologic studies suggest the existence of an obesity paradox wherein obese patients seem to have superior perioperative outcomes compared to normal and low BMI patients. We seek to review the epidemiologic, and pathophysiologic aspects of obesity especially with respect to structural and functional changes in kidney function and their impact on perioperative outcomes.
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    ABSTRACT: Introduction: Patients with renal cell carcinoma who were treated with radical nephrectomy (RN) or partial nephrectomy (PN) are at risk of postoperative acute kidney injury (AKI), and in consequence, short- and long-term adverse outcomes. We sought to identify independent predictors of 30-day AKI in patients undergoing RN or PN. Materials and methods: Between 2005 and 2011, patients who underwent RN or PN for renal cell carcinoma within the National Surgical Quality Improvement Program data set were identified. Patients with preexisting severe renal failure, defined as a preoperative estimated glomerular filtration rate<30 ml/min/1.73 m(2), were excluded from the analyses. AKI was defined as an elevation of serum creatinine>2mg/dl above baseline or the need for dialysis within 30 days of surgery. Univariable and multivariable logistic regression analyses were used to examine the association between preoperative factors and the risk of postoperative AKI. Results: Overall, 1,944 (58.6%) and 1,376 (41.4%) patients underwent RN and PN, respectively. Overall, 1.8% of the patients included in the study experienced AKI within an average of 5.4 days after RN or PN. Independent predictors for AKI included obesity (odds ratio [OR] = 2.24, P = 0.04), history of neurovascular disease (OR = 5.29, P<0.001), and a preoperative chronic kidney disease stage II (OR = 10.00, P = 0.03) or stage III (OR = 26.49, P = 0.02). Furthermore, RN (OR = 2.87, P = 0.02) or the open approach (OR = 2.18, P = 0.04) was significantly associated with postoperative AKI. AKI was significantly associated with adverse postoperative outcomes, such as prolonged length of stay, occurrence of any complication, and mortality (all P <0.001). Conclusions: The assessment of preoperative kidney function and comorbidity status is essential to identify patients at risk of postoperative AKI. In addition to preoperative chronic kidney disease stages II and III, neurovascular disease, obesity, and surgical approach (RN or open) represent predictors of 30-day AKI. Careful patient selection as well as preoperative planning may help reduce this unfavorable postoperative outcome.
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