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OBESITY AND ICU HAMIDREZA JAMAATI MD, FCCP, FCCM CARDIOVASCULAR PHYSIOLOGY IN OBESITY PULMONARY PHYSIOLOGY IN OBESITY IMMUNOLOGIC CHANGES IN OBESITY CARDIOVASCULAR PHYSIOLOGY IN OBESITY PULMONARY PHYSIOLOGY IN OBESITY IMMUNOLOGIC CHANGES IN OBESITY IMMUNOLOGIC CHANGES IN OBESITY Adipocytes are now known to produce signaling molecules, called adipokines, that can significantly alter inflammatory cell and immune function. (Honiden & McArdle Clin Chest Med 2009) The percentage of macrophages is substantially higher in obese persons. (Dixit VD. J Leukoc Biol 2008) Pre-adipocytes produce macrophage colony stimulating factor (M-CSF) and peroxisome proliferation activated receptor gamma (PPARg), both of which promote macrophage activation. (Karagiannides. Curr Opin Gastroenterol 2007) IMMUNOLOGIC CHANGES IN OBESITY Increased monocyte and granulocyte oxidative burst, have been found in obese subjects. (Lamas O, Eur J Clin Nutr 2002) One such adipokine is leptin, which acts to decrease food intake and increase energy consumption by promoting production of anorexigenic factors. (Marti A,Obes Rev2001) Leptin involvement in immunoregulation COMMON DISORDERS IN CRITICALL ILL OBESE PATIENTS Thromboembolic Disease Aspiration Abdominal Compartment Syndrome CHALLENGES IN THE CARE OF CRITICALLY ILL OBESE PATIENTS Airway Management Central Venous Access Surgical Airways Hemodynamic Monitoring Imaging and Tests Nutritional Support DRUG DOSING NURSING CARE Thromboembolic Disease The incidence of thromboembolic disease (TED) varies:10% to 20% in general ward to 40% in pts with major trauma and as high as 80% in critical care patients. (Geerts WH. Chest 2004) Stein and colleagues found an increased risk for VTE in obese men and women compared with nonobese patients. (Stein PD. Am J Med 2005) Alterations in PAI-1 and fibrinolytic activity in obese patients may contribute to their increased risk for VTE. (Loskutoff DJ.Thromb Vasc Biol 1998) Abdominal obesity may predispose obese patients to atelectasis and arterial hypoxemia,particularly when immobile and in the supine position. PE may be a concern in these situations,but diagnosis of PE is a challenge in patients with morbid obesity. Thromboembolic Disease Compression ultrasonography with venous imaging is not as sensitive in patients with severe obesity and/or significant leg edema. Morbid obesity may limit CT angiography. Ventilation-perfusion scanning or perfusion scanning alone is a potential alternative, but neither modality can give a definitive diagnosis. (Tapson VF. Am J Respir Crit Care Med 1999) Aspiration Obesity, especially central adiposity, is a significant risk factor for gastroesophageal reflux disease (GERD). (Corley DA.Gut 2007) Proposed mechanisms include increased intra-abdominal pressure, decreased lower esophageal sphincter pressure,increased frequency of hiatal hernia, and perhaps alterations in esophageal motility and gastric emptying in the obese. (Friedenberg FK. Am J Gastroenterol 2008) Aspiration Histamine H2 antagonists and proton pump inhibitors might minimize the deleterious effects of gastric acid aspiration on the lung, but the loss of the antimicrobial effects of gastric acid has been suggested as a potential risk factor for pneumonia. (Nishina K. Anesth Analg 1996) Elevation of the patient’s head and the use of special endotracheal tubes that allow for continuous suctioning of subglottic secretions may also decrease the risk for aspiration and VAP , although the use of these devices has not been studied in obese patients. (Valles J. Ann Intern Med 1995) Abdominal Compartment Syndrome Obese patients have higher IAP than nonobese control subjects. The incidence of clinically significant abdominal compartment syndrome in critically ill obese patients is unknown. The abdominal compartment syndrome should be suspected in the setting of increased IAP with attendant poor urine output, respiratory acidosis, or metabolic acidosis. In these settings, abdominal decompression should be considered, with treatment of ileus, large volume paracentesis, or laparotomy. CHALLENGES IN THE CARE OF CRITICALLY ILL OBESE PATIENTS Airway Management Morbidly obese patients often have anatomic changes that make intubation difficult, such as a short and thick neck, redundant soft tissue in the oropharynx, and limited mouth opening, and the availability of two experienced intubators is preferable. Several studies have established an association between increasing BMI and difficulties with intubation. (Grant P. Emerg Med Australas 2004) Proper positioning,with the head elevated above the shoulders in the ‘‘sniffing position,’’ is important. (Rao SL. Anesth Analg 2008) Airway Management Bilevel positive airway pressure (BiPAP) has been used to oxygenate patients before rapid sequence intubation when conventional methods of preoxygenation have failed to bring the saturation above 90%. (El-Khatib MF.Can Anesth 2007) Ultimately,when other advanced airway techniques fail,skilled operators may need to intubate under fiberoptic guidance or with the aid of newer devices (for example, LMA CTrach, Airtraq, Glidescope) that allow for video-assisted intubation without the need to align the oral and pharyngeal axes. If such methods are not successful, an emergent tracheostomy should be considered. (Dhonneur G. Obes Surg 2008) Central Venous Access Because of the distortion of normal anatomic landmarks in obese patients, establishing central venous access can be timeconsuming and challenging. In a randomized, crossover study in obese or anticoagulated patients, real-time ultrasound guidance improved success rates at cannulation and led to fewer complications. (Gilbert TB. Crit Care Med 1995) Central Venous Access Longer needles (for example, spinal needles) may be required in obese patients because standard needles may be too short to clear excessive soft tissue. Vigilance for infection and catheter-related phlebitis and thrombosis is important as well because intertriginous folds predispose these patients to local skin infections. Surgical Airways Longer tubes with sharper angles may be required for tracheostomy in obese patients because of their increased soft tissue, but such tubes carry a higher risk of becoming dislodged or occluded. Higher complication rates have also been reported with tube placement itself (whether via a surgical77 or percutaneous route), although the magnitude of excess risk in experienced hands is not clear. (Byhahn C. Anaesthesia 2005) Hemodynamic Monitoring Noninvasive blood pressure monitoring by cuff sphygmomanometer has unpredictable accuracy because of difficulties with cuff size selection. Inaccuracies may persist, even when an appropriately sized cuff is available. (Maxwell MHf.Lancet 1982) Hemodynamic parameters are often adjusted according to body surface area. Hemodynamic Monitoring Beutler and colleagues highlight the potential variations in calculated indexed values depending on weight chosen (actual, adjusted, or ideal), which could lead to different conclusions regarding a patient’s status, and, ultimately, treatment. Ideal body weight is not optimal because oxygen demand and cardiac output are higher in obese patients than in nonobese patients. As a compromise, a 40% adjustment for weight above ideal body weight is commonly used as in drug dosing, but no study has rigorously validated this adjustment. Imaging and Tests Variable lead positioning owing to indistinct landmarks and excessive soft tissue can lead to low voltages and make accurate interpretation of electrocardiograms (ECG) difficult. Specifically,application of ECG-based criteria for the assessment of left ventricular hypertrophy and chamber enlargements is limited. Similarly, image acquisition using an echocardiogram is poor. Inadequate soft tissue penetration makes interpretation of portable radiographs difficult. Imaging and Tests Confluence of shadows from overlying soft tissue can mimic abnormalities such as pleural thickening. Distinguishing the nature of parenchymal opacities (infiltrate versus edema, for example) can be difficult. Computed tomography (CT) is limited by load limits of the scanning tables as well as the diameter of the aperture. Some veterinary hospitals have specialized CT equipment to accommodate large animals may be willing to perform scans in morbidly obese patients who cannot fit into conventional human scanners. Nutritional Support Obesity and malnutrition can coexist, particularly in the setting of critical illness, and appropriate nutritional support of obese patients is essential. Accelerated protein breakdown can lead to a rapid reduction in lean body mass. Hypocaloric,high-protein feeding theoretically prevents overfeeding (and its consequences, such as hyperglycemia) and allows for net protein anabolism and secondary fat weight loss. (Malone AM. Curr Gastroenterol Rep 2007) Nutritional Support Although small studies have suggested improved morbidity end points with this approach, including shorter ICU stay and ventilator days, it remains controversial. Estimation of the metabolic need of the critically ill obese patient is difficult. Some investigators have advocated the use of an obesity-adjusted weight with a 25% correction for excess weight above ideal body weight as follows: adjusted body weight =(actual weight- IBW) 0.25 + IBW This approach has not been validated for standard practice. DRUG DOSING The physiologic changes in obesity markedly affect distribution, binding, and elimination of medications commonly prescribed in the ICU. Although systemic absorption of oral drugs is not significantly altered in obese patients, the increase in fat body mass and relative decrease in percentage contribution of lean mass and water can cause dramatic changes in the volume of distribution. Other important changes include increases in total blood volume and cardiac output, alterations in plasma protein binding, and obesity-induced changes in liver and kidney function that may affect drug elimination. (Casati A. J Clin Anesth 2005) DRUG DOSING For many lipophilic medications, such as aminoglycosides, with a large volume of distribution, the use of adjusted body weight is recommended. The distribution is presumed to be approximately 20% to 50% of the weight above ideal body weight. A typical calculation using 40% of excess weight is as follows: adjusted body weight = (Actual body-weight IBW) 0.41+ IBW However in the ICU,measurement of weight itself can be affected by temporary changes in body water from third spacing, which may or may not influence the distribution of medications. Dr. Who’s Dr. Who’s Adipose monsters Shyoko Hoinden.Clin Chest Med 2009 Nursing Care All staff caring for the obese ICU patient should be aware of the potential effect of personal prejudices toward the obese, who may have insecurities about body image. (Charlebois D.Crit Care Nurse 2004) Skin integrity can be particularly problematic in obese patients. (Winkelman C. Clin Nurs Res 2005) Multiple skinfolds can lead to the buildup of moisture, posing a threat to skin integrity. Limited mobility, difficulty in nurseassisted turning, decreased vascularity within adipose tissue, and excessive weight all contribute to pressure ulcer risk. (El-Solh AA.Am J Respir Crit Care Med 2004) Nursing Care Pressure ulcers that begin in skin folds may go undetected during their early stages unless all such regions are examined carefully during routine turning. Patients with a BMI greater than 40 generally require at least four staff members to assist with repositioning. (Hurst S. Dimens Crit Care Nurs 2004) Mobilization and rehabilitation in obese patients may require increased personnel andequipment. SUMMARY Obesity poses unique challenges for the ICU team. Important changes in cardiovascular, pulmonary, and immunologic physiology predispose such patients to respiratory failure, thromboembolic disease, abdominal compartment syndrome, and aspiration. Special attention is required when performing routine ICU procedures, such as intubation and insertion of central venous catheters, and limitations in testing capabilities may lead the astute ICU clinician to rely solely on clinical suspicion when making therapeutic decisions. Daily management can be further hampered by uncertainties regarding drug metabolism and pharmacokinetics, nutritional needs, and challenges in bedside nursing care. Dedicated research is much needed in obese patients to allow for formulation of evidence-based guidelines that would further enhance delivery of ICU care for this challenging population. Thank you