Acute Kidney Injury in the Critically Ill, Morbidly Obese Patient: Diagnostic and Therapeutic Challenges in a Unique Patient Population

Perioperative Rhabdomyolysis in Obese Individuals Undergoing Bariatric Surgery: Current Status

One potential complication in bariatric surgery is rhabdomyolysis, which is a condition involving muscle tissue damage that can significantly impact a patient's health. The causes of rhabdomyolysis can be broadly classified into two major categories: traumatic and non-traumatic. Early investigations into the development of intraoperative rhabdomyolysis in bariatric surgery identified the main risk factors as tissue compression-primarily affecting the lower extremities, gluteal muscles, and lumbar region-as well as prolonged periods of immobilization. Clinically, rhabdomyolysis is typically suspected when a patient presents with muscle pain, weakness, and potentially dark urine or even anuria. However, the most reliable biomarker for rhabdomyolysis is elevated serum creatine kinase levels. The primary goal in managing hydration is to correct intravascular volume depletion, with solutions such as Lactated Ringer's or 0.9% saline being appropriate options for resuscitation. Perioperative diagnosis of rhabdomyolysis poses a significant challenge for anesthesiologists, requiring a high degree of clinical suspicion, particularly in bariatric patients. In this vulnerable population, prevention is crucial. The success of treatment depends on its early initiation; however, there are still significant limitations in the therapies available to prevent renal injury secondary to rhabdomyolysis.

No sex differences in the incidence, risk factors and clinical impact of acute kidney injury in critically ill patients with sepsis

Background

Sex-stratified medicine is an important aspect of precision medicine. We aimed to compare the incidence and risk factors of acute kidney injury (AKI) for critically ill men and women with sepsis. Furthermore, the short-term mortality was compared between men and women with sepsis associated acute kidney injury (SA-AKI).

Method

This was a retrospective study based on the Medical Information Mart for Intensive Care IV database. We used the multivariable logistic regression analysis to evaluate the independent effect of sex on the incidence of SA-AKI. We further applied three machine learning methods (decision tree, random forest and extreme gradient boosting) to screen for the risk factors associated with SA-AKI in the total, men and women groups. We finally compared the intensive care unit (ICU) and hospital mortality between men and women with SA-AKI using propensity score matching.

Results

A total of 6463 patients were included in our study, including 3673 men and 2790 women. The incidence of SA-AKI was 83.8% for men and 82.1% for women. After adjustment for confounders, no significant association was observed between sex and the incidence of SA-AKI (odds ratio (OR), 1.137; 95% confidence interval (CI), 0.949-1.361; p=0.163). The machine learning results revealed that body mass index, Oxford Acute Severity of Illness Score, diuretic, Acute Physiology Score III and age were the most important risk factors of SA-AKI, irrespective of sex. After propensity score matching, men had similar ICU and hospital mortality to women.

Conclusions

The incidence and associated risk factors of SA-AKI are similar between men and women, and men and women with SA-AKI experience comparable rates of ICU and hospital mortality. Therefore, sex-related effects may play a minor role in developing SA-AKI. Our study helps to contribute to the knowledge gap between sex and SA-AKI.

Predictors of Augmented Renal Clearance in a Heterogeneous ICU Population as Defined by Creatinine and Cystatin C

INTRODUCTION

The incidence of augmented renal clearance (ARC) in the intensive care unit (ICU) is highly variable, and identification of these patients remains challenging.

OBJECTIVE

The objective of this study was to define the incidence of ARC in a cohort of critically ill adults, using serum Cr and cystatin C, and to identify factors associated with its development.

METHODS

This is a retrospective cohort study of critically ill patients without stage 2 or 3 acute kidney injury with both serum Cr and cystatin C available. The incidence of ARC was defined as a Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)Cr-cystatin C-estimated glomerular filtration rate >130 mL/min. A multivariable logistic regression model using a penalized Lasso method was fit to identify independent predictors of ARC.

RESULTS

Among the 368 patients included in the study, indication for ICU admission was nonoperative in 55% of patients, and 9% of patients were admitted for major trauma. The overall incidence of ARC was low at 4.1%. In a multivariable logistic regression model, Charlson comorbidity index, major trauma, intracerebral hemorrhage, age, and Sequential Organ Failure Assessment score were found to predict ARC.

CONCLUSION

The incidence of ARC in this study was low, but prediction models identified several factors for early identification of patients with risk factors for or who develop ARC, particularly in a cohort with a low baseline risk of ARC. These factors could be used to help identify patients who may develop ARC.

Low, rather than High, Body Mass Index Is a Risk Factor for Acute Kidney Injury in Multiethnic Asian Patients: A Retrospective Observational Study

Background

Acute kidney injury (AKI) is common in hospitalised patients. The relationship between body mass index (BMI) and the risk of having AKI for patients in the acute hospital setting is not known, particularly in the Asian population.

Methods

This was a retrospective, single-centre, observational study conducted in Singapore, a multiethnic population. All patients aged ≥21 years and hospitalised from January to December 2013 were recruited.

Results

A total of 12,555 patients were eligible for the analysis. A BMI of <18.5 kg/m² was independently associated with the development of AKI in hospitalised patients (odds ratio (OR): 1.23 [95% confidence interval [CI]: 1.04–1.44, P = 0.01]) but not for overweight and obesity. Subgroup analysis further revealed that underweight patients aged ≥75 and repeated hospitalisation posed a higher risk of AKI (OR: 1.25 [CI: 1.01–1.56], P = 0.04; OR: 1.23 [CI: 1.04–1.44], P = 0.01, resp.). Analyses by interactions between different age groups and BMI using continuous or categorised variables did not affect the overall probability of developing AKI.

Conclusions

Underweight Asian patients are susceptible to AKI in acute hospital settings. Identification of this novel risk factor for AKI allows us to optimise patient care by prevention, early detection, and timely intervention.

Overestimation of Glomerular Filtration Rate Among Critically Ill Adults With Hospital-Acquired Oligoanuric Acute Kidney Injury

BACKGROUND

Medication use in the intensive care unit (ICU) depends on creatinine-based glomerular filtration rate (GFR) estimates. Urine output deterioration may precede the creatinine rise resulting in delayed recognition of GFR reductions. Our objective was to quantify the disparity between estimated GFR (eGFR) and true GFR in ICU patients with hospital-acquired oligoanuric acute kidney injury (hAKI).

METHODS

This single-center cohort study examined adults who met the Acute Kidney Injury Network stage III urine output criterion ≥48 hours after ICU admission. True GFR was ≤15 mL/min/1.73 m(2), and eGFR was described by 6 different creatinine-based equations. True GFR and eGFR were compared on the day of hAKI diagnosis and followed for 4 days using multivariable linear regression with generalized estimating equations, adjusting for day and method.

RESULTS

Of the 691 patients screened, we enrolled 61 patients. After adjustment for multiple comparisons and day, there were significant differences in eGFR between the estimation methods and true GFR (P < .001). After day adjustment, eGFR overestimated true GFR by 17 to 50 mL/min/1.73 m(2) and overestimation persisted through the fourth day of hAKI (P ≤ .001).

CONCLUSION

Creatinine-based equations overestimated GFR in ICU patients with hAKI. This study highlights a population at risk of medication misadventures in whom systems optimization should be considered.

Computed tomography-defined abdominal adiposity is associated with acute kidney injury in critically ill trauma patients*

OBJECTIVES

Higher body mass index is associated with increased risk of acute kidney injury after major trauma. Since body mass index is nonspecific, reflecting lean, fluid, and adipose mass, we evaluated the use of CT to determine if abdominal adiposity underlies the body mass index-acute kidney injury association.

DESIGN

Prospective cohort study.

SETTING

Level I Trauma Center of a university hospital.

PATIENTS

Patients older than 13 years with an Injury Severity Score greater than or equal to 16 admitted to the trauma ICU were followed for development of acute kidney injury over 5 days. Those with isolated severe head injury or on chronic dialysis were excluded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Clinical, anthropometric, and demographic variables were collected prospectively. CT images at the level of the L4-5 intervertebral disc space were extracted from the medical record and used by two operators to quantitate visceral adipose tissue and subcutaneous adipose tissue areas. Acute kidney injury was defined by Acute Kidney Injury Network creatinine and dialysis criteria. Of 400 subjects, 327 (81.8%) had CT scans suitable for analysis: 264 of 285 (92.6%) blunt trauma subjects and 63 of 115 (54.8%) penetrating trauma subjects. Visceral adipose tissue and subcutaneous adipose tissue areas were highly correlated between operators (intraclass correlation > 0.99, p < 0.001 for each) and within operator (intraclass correlation > 0.99, p < 0.001 for each). In multivariable analysis, the standardized risk of acute kidney injury was 15.1% (95% CI, 10.6-19.6%), 18.1% (14-22.2%), and 23.1% (18.3-27.9%) at the 25th, 50th, and 75th percentiles of visceral adipose tissue area, respectively (p = 0.001), with similar findings when using subcutaneous adipose tissue area as the adiposity measure.

CONCLUSIONS

Quantitation of abdominal adiposity using CT scans obtained for clinical reasons is feasible and highly reliable in critically ill trauma patients. Abdominal adiposity is independently associated with acute kidney injury in this population, confirming that excess adipose tissue contributes to the body mass index-acute kidney injury association. Further studies of the potential mechanisms linking adiposity with acute kidney injury are warranted.

Serum cystatin C predicts vancomycin trough levels better than serum creatinine in hospitalized patients: a cohort study

INTRODUCTION

Serum cystatin C can improve glomerular filtration rate (GFR) estimation over creatinine alone, but whether this translates into clinically relevant improvements in drug dosing is unclear.

METHODS

This prospective cohort study enrolled adults receiving scheduled intravenous vancomycin while hospitalized at the Mayo Clinic in 2012. Vancomycin dosing was based on weight, serum creatinine with the Cockcroft-Gault equation, and clinical judgment. Cystatin C was later assayed from the stored serum used for the creatinine-based dosing. Vancomycin trough prediction models were developed by using factors available at therapy initiation. Residuals from each model were used to predict the proportion of patients who would have achieved the target trough with the model compared with that observed with usual care.

RESULTS

Of 173 patients enrolled, only 35 (20%) had a trough vancomycin level within their target range (10 to 15 mg/L or 15 to 20 mg/L). Cystatin C-inclusive models better predicted vancomycin troughs than models based upon serum creatinine alone, although both were an improvement over usual care. The optimal model used estimated GFR by the Chronic Kidney Disease Epidemiology Collaborative (CKD-EPI) creatinine-cystatin C equation (R(2) = 0.580). This model is expected to yield 54% (95% confidence interval 45% to 61%) target trough attainment (P <0.001 compared with the 20% with usual care).

CONCLUSIONS

Vancomycin dosing based on standard care with Cockcroft-Gault creatinine clearance yielded poor trough achievement. The developed dosing model with estimated GFR from CKD-EPIcreatinine-cystatin C could yield a 2.5-fold increase in target trough achievement compared with current clinical practice. Although this study is promising, prospective validation of this or similar cystatin C-inclusive dosing models is warranted.

Body mass index as a predictor of complications and mortality after lumbar spine surgery

STUDY DESIGN

Retrospective analysis.

OBJECTIVE

A national population-based database was analyzed to characterize the risks of postoperative complications and mortality associated with the patient's body mass index (BMI) after lumbar spinal surgery.

SUMMARY OF BACKGROUND DATA

Obesity has been associated with greater perioperative complications and worsened surgical outcomes after lumbar spinal surgery. However, the stratified BMI risks of postoperative complications relative to normal weight patients have not been well characterized.

METHODS

The American College of Surgeons National Surgical Quality Improvement Program database was queried to identify patients who underwent lumbar spinal surgery between 2006 and 2011. Patients were stratified into BMI cohorts: normal (18.5-24.99 kg/m), overweight (25.00-29.99 kg/m), class 1 (30.00-34.99 kg/m), class 2 (35.00-39.99 kg/m), and class 3 (≥40 kg/m) obesity. Preoperative patient characteristics and perioperative outcomes were assessed. The relative risks of 30-day postoperative complications and mortality for each BMI cohort were calculated in reference to the normal weight cohort using a 95% confidence interval.

RESULTS

A total of 24,196 patients underwent lumbar spine surgery between 2006 and 2011 of which 19,195 (79.3%) were overweight or obese. The risk for deep vein thrombosis increased beginning with overweight patients and compounded for the subsequent obesity classes. The risk for superficial wound infection and pulmonary embolism increased beginning with the class 1 obesity cohort. Furthermore, the relative risk increase for urinary tract infection, acute renal failure, and sepsis was significantly increased only among class 3 obesity patients. Lastly, there was no relative risk increase in 30-day mortality in any cohort after lumbar spine surgery.

CONCLUSION

Overweight and obese patients demonstrated an increased risk of postoperative complications relative to normal weight patients. Despite these findings, a BMI 25 kg/m or more was not associated with a greater risk of mortality. Further studies are warranted to characterize the impact of postoperative complications associated with overweight and obese patients on hospital resource utilization and costs after lumbar spine surgery.

Predicting the glomerular filtration rate in bariatric surgery patients

BACKGROUND/AIMS

Identifying the best method to estimate the glomerular filtration rate (GFR) in bariatric surgery patients has important implications for the clinical care of obese patients and research into the impact of obesity and weight reduction on kidney health. We therefore performed such an analysis in patients before and after surgical weight loss.

METHODS

Fasting measured GFR (mGFR) by plasma iohexol clearance before and after bariatric surgery was obtained in 36 severely obese individuals. Estimated GFR was calculated using the Modification of Diet in Renal Disease equation, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation using serum creatinine only, the CKD-EPI equation using serum cystatin C only and a recently derived equation that uses both serum creatinine and cystatin C (CKD-EPIcreat-cystC) and then compared to mGFR.

RESULTS

Participants were primarily middle-aged white females with a mean baseline body mass index of 46 ± 9, serum creatinine of 0.81 ± 0.24 mg/dl and mGFR of 117 ± 40 ml/min. mGFR had a stronger linear relationship with inverse cystatin C before (r = 0.28, p = 0.09) and after (r = 0.38, p = 0.02) surgery compared to the inverse of creatinine (before: r = 0.26, p = 0.13; after: r = 0.11, p = 0.51). mGFR fell by 17 ± 35 ml/min (p = 0.007) following surgery. The CKD-EPIcreat-cystC was unquestionably the best overall performing estimating equation before and after surgery, revealing very little bias and a capacity to estimate mGFR within 30% of its true value over 80% of the time. This was true whether or not mGFR was indexed for body surface area.

CONCLUSIONS

In severely obese bariatric surgery patients with normal kidney function, cystatin C is more strongly associated with mGFR than is serum creatinine. The CKD-EPIcreat-cystC equation best predicted mGFR both before and after surgery.

Nutrition delivery for obese ICU patients: delivery issues, lack of guidelines, and missed opportunities

The most appropriate enteral formula for the severely obese population has yet to be determined. The obese patient in the intensive care unit (ICU) creates numerous difficulties for managing care, one being the ability to deliver appropriate and timely nutrition. Access for nutrition therapy, either enteral or parenteral, can also create a challenge. Currently, no specific guidelines are available on a national or international scale to address the issues of how and when to feed the obese patient in the ICU. A bias against feeding these patients exists, secondary to the perception that an enormous quantity of calories is stored in adipose tissue. Making a specialty enteral formula for obesity from existing commercial formulas and other modular nutrient components is not practical, secondary to difficulty with solubility issues, dilution of the formula, and safety concerns. Using today's concepts and current metabolic data, a formula could be produced that would address many of the specific metabolic derangements noted in obesity. This formula should have a high-protein, low-carbohydrate content with at least a portion of the lipid source coming from fish oil. Specific nutrients that may be beneficial in obesity include arginine, glutamine, leucine, L-carnitine, lipoic acid, S-adenosylmethionine, and betaine. Certain trace minerals such as magnesium, zinc, and selenium may also be of value in the obese population. The concept of a specific bariatric formulation for the ICU setting is theoretically sound, is scientifically based, and could be delivered to patients safely.