Morbid obesity is an independent determinant of death amongsurgical critically ill patients

From: Crit Care Med 2006 Vol. 34, No. 4By: Stanley A. Nasraway Jr, MD, FCCM

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Introduction

National Health and Nutrition Examination Survey conducted in 1999–2002 65.7% of adult is overweight ([BMI]> 25 kg/m2); obesity (BMI 30 kg/m2) in 2000 ---30.6% extreme obesity (BMI 40 kg/m2) morbid or class III obesity 5.1% in USA, an increase of 570% over the last 4 decades

obesity to be an independent predictor of death in critically ill patients…….. Bercault N, Boulain T, Kuteifan K, et al: Obesity-related excess mortality rate in an adult intensive care unit: A risk-adjusted matched cohort study. Crit Care Med 2004; 32:998–1003

Hypothesized that morbid obesity is an independent determinant of death among critically ill surgical patients, as it is in the general population

MethodsStudy PopulationJanuary 1998 to March 2001 in the Tufts-New England Medical Center SICU1471 patients but exclude 98( no height and weight data)1,373 patients for final analysisStudy Design Sociodemographic data were entered into the database on admission including age, gender, and coexisting diseases.

Severity of illness the Simplified Acute Physiology Score II as assigned at the time of SICU admission and Mortality Prediction Model (MPM)-24 as determined 24 hrs after SICU admissionNational Institutes of Health and World Health Organization criteria for BMI Underweight-- BMI 18.5 kg/m2; normals ---18.5–24.9 kg/m2; overweight --- 25–29.9 kg/m2; obese -- 30–39.9 kg/m2; extreme or morbid obesity – 40 kg/m2.

Prolonged critical illness was defined as an ICU length of stay (LOS) 4 days406 critically ill surgical patientsStatistical Analysis Demographic characteristics, severity of illness, and outcomes were compared among 5 BMI groups, Statistical comparisons were done between the extremely obese (BMI 40) patients and patients with BMI < 40 using the Student’s t-test (age), Kruskal- Wallis test (Simplified Acute Physiology Score II, MPM-24), or Fisher’s exact and chi-square tests

Multivariable models of ICU using a stepwise selection process, with p values for entry and retention in the model of .15 and .10 to pick among all potential determinants of ICU death (other than BMI). BMI was then added to this covariate model of mortality to estimate the relationship of extreme obesity (BMI> 40) and ICU mortality after adjusting for the final subset of covariates also related to mortality.

univariate relationships of characteristics with the ICU mortality using logistic regressionnonparametric smoothing spline plot based on a generalized additive model, where the value of the smoothing parameter was selected by generalized cross-validationshow nonlinear relationship between BMI as a continuous variable and the probability of death in the ICUSAS system for Windows, version 8.0 (SAS Institute, Cary, NC)

Results( general : prolonged stay) neurosurgery (25%, 17%), general surgery (21%, 29%), cardiothoracic surgery (18%, 19%), vascular surgery (13%, 12%), transplantation (12%, 15%), and all others combined (12%, 7%)Patients with extreme obesity were younger, female and diabetic, and higher severity of illness median ICU LOS was short, between 2.0 and 2.2 days, and there were no differences in ICU or hospital mortality compared with all other patients

mortality was seen with BMI, also related to mortality, including age, gender, and MPM-24. Morbidly obese critically ill surgical patients had a greater than 7-fold likelihood of death over nonmorbidly obese critically ill patients.

Discussions26.7% of all SICU admissions were obese or extremely obese(6.8%)Extreme obesity was an independent risk factor for death in critically ill patients who sustained a protracted stay, increasing the odds of death 700%

Galanos and associates concluded that high BMI was not significantly related to risk of death in seriously ill hospitalized patients-------Relationship of body mass index to subsequent mortality among seriously ill hospitalized patients. Crit Care Med 1997; 25: 1962–1968

Obese patients undergoing surgery are more susceptible to postoperative complications, including wound dehiscence and infection, CHF, and pulmonary failure-------Pasulka PS, Bistrian BR, Benotti PN: The risks of surgery in obese patients. Ann Intern Med 1986; 104:540–46

Obese trauma patients have an 8-fold greater mortality rate than non-obese , the most severely overweight are most likely to sustain irreversible deteriorationSawyer and colleaguesintra-operative transfusion requirements, wound infections, and early death from multiple organ failure were more common in morbidly obese (defined in that study as BMI 35 kg/m2) in liver transplant recipients

Relationship between BMI and outcome in 41,011 critically ill patients using the Project Impact ICU database. High BMI was not associated with an increased risk of death; however, the median ICU LOS in this study was very short, 2.0 days----Tremblay A, Bandi V: Impact of body mass index on outcomes following critical care. Crit Care Med 2003; 1202–1207

(N= 2148 in MICU )…no differences observed in severity of illness, mortality, length of mechanical ventilation, ICU LOS, or ICU-related complications among groups stratified by BMI. The investigators concluded BMI has little effect on overall ICU outcome---Ray DE, Matchett SC, Baker K, et al: The effect of body mass index on patient outcomes in a medical ICU. Chest 2005; 127: 2125–2131………

mean ICU LOS in these patients was 5 days, maybe not sick enough

2 groups each of 170 patients (89% admitted to ICU with medical pathology) with MV for 48 hrs --- Obesity doubled odds of death (odds ratio, 2.1; 95% confidence interval, 1.6 –3.6)--- 4-fold increase in likelihood of nosocomial infections and other ICU-related complications, likely explaining increased death rate in the obese----Bercault et al: Obesity-related excess mortality rate in an adult intensive care unit: A risk-adjusted matched cohort study. Crit Care Med 2004; 32:998–1003

In the present studyextreme obesity in a critically ill surgical population was independently associated with an increased risk of death esp. in prolonged critical illness

Complications of obesity ventilatory and cardiac failure, increased challenges in safely obtaining vascular access, and wound infection and dehiscence. increased insulin resistance and hyperglycemia( may risk of death by severe sepsis) Extreme obesity is frequently associated with LV hypertrophy with resultant systolic and diastolic dysfunction and sudden death

Respiratory disorders --- obesity hypoventilation syndrome and pulmonary emboli are a frequent cause of sudden death ….mean BMI 50 kg/m2 1/3 were classified as having severe sleep apnea(41% with arrhythmia), lung volumes , work of breathing is increased, and difficult weaning , aspiration pneumonia (greater gastric volume of acidic juices and an increased incidence of GERD)

Appropriate weight-related dosage adjustment in obese patients ---ESP. antibiotics generally tend to be significantly under-dosed, inaccurate CCrSimple tasks of daily nursing care require more manpower and resources----nosocomial pneumonia, venous thromboembolism, and pressure sores, difficult venous access and its complicationsDifficult imaging studies

Clinicians and hospitals generally underestimate the practical difficulties imposed in caring for increasing numbers of obese patients and can misjudge the necessary infrastructural resources required to support these demanding patients----need to redesign hospital systems, devote more resources, and put into place infrastructure more tailored to the demands of the morbidly obese, acutely ill patient

Thank you for your attention