Perioperative Assessment and Risk Stratification of the Obese Patient

Abstract

Obesity has risen to epidemic proportions in the United States and is increasing among all populations. The complications associated with obesity have a tremendous impact on healthcare and hospital costs. The diagnosis of obesity alone is believed to present an independent risk for surgical morbidity and mortality. Obese patients frequently have multiple comorbidities, which present a unique challenge for healthcare teams responsible for their perioperative and postoperative assessment and management. This article highlights critical elements of the perioperative assessment of the adult obese patient, considerations for further risk stratification in the perioperative period, and potential complications of the obese patient postoperatively.

Introduction

Obesity has become an epidemic in the United States, and our rate of obesity is among the highest rates in the world.¹ More than two thirds of U.S. adults are overweight or obese: 68% of all adults, 64.1% of women, and 72.3% of men.^1,2 The obesity epidemic in the United States has become so serious that the Centers for Disease Control and Prevention (CDC) has labeled America as an “obesogenic” society, referring to the societal promotion of increased food intake, unhealthy foods, and physical inactivity.¹

The complications associated with obesity have a tremendous impact on healthcare and hospital costs. Specifically, the costs of healthcare in 2008 for obesity-related medical care was approximately $147 billion. In 2006, obese people spent $1,400 more in medical care costs than people at normal weight.¹

Obesity is associated with major health risks, including diabetes, heart disease, hypertension, and certain types of cancers (colon, breast, endometrial, gallbladder), sleep apnea, stroke, metabolic syndrome, osteoarthritis, and reproductive problems. Obese patients have an increased risk of death from all causes compared with non-obese individuals.³ Morbidity and mortality rise sharply with increasing age and body mass index (BMI).⁴

Obese patients who undergo surgical procedures are at higher risk for complications both intraoperatively and postoperatively, including increased risk of mortality during these periods.¹ Healthcare providers, particularly those whose roles routinely include the perioperative assessment of the obese patient undergoing any surgical procedure, must become familiar with the associated risks and the recommendations for enhancing the patient's surgical outcomes. The purpose of this article is to highlight the essential elements of the preoperative assessment of the adult obese patient and to discuss the potential complications and interventions for the adult obese patient postoperatively.

Obesity Defined

BMI has become a national standard and reliable indicator for measuring obesity (see Table 1).¹ Obesity is defined as a BMI of 30 kg/m² or greater. An additional stratification system, to reflect those individuals with more severe obesity, has been proposed by the American Heart Association (see Table 2).⁵

Table 1.

Definitions of Obesity Based on Body Mass Index ⁵

Normal weight range BMI	≥18.5 to <25 kg/m²
Overweight BMI	25–29.9 kg/m²
Obese BMI	>30 kg/m²
Morbid obesity BMI	>40 kg/m²

Table 2.

The Revised Cardiac Risk Index ⁵

Emergency surgeries or major thoracic, abdominal, or vascular surgery

History of coronary heart disease

History of congestive heart failure

History of cerebrovascular disease

Preoperative treatment with insulin

Preoperative serum creatinine levels >2.0 mg/dl

Preoperative Evaluation of the Obese Patient

The goal of the preoperative evaluation of the obese patient is to identify preexisting unrecognized problems, to detect comorbidities, to determine risk factors, and to risk stratify the patient.⁶ Ideally, the patient's comorbidities will be treated and the patient optimized prior to surgical intervention. In most situations, preoperative management of medical comorbidities will reduce operative risks to acceptable levels.⁷ During the preoperative phase, it is also essential to educate the patient and the family about the risks, the surgical procedure, and the postoperative course.

History

A thorough history is an essential component of the preoperative assessment. The provider focuses the history on those aspects that pose an increased risk for the obese patient. For example, an accurate smoking history is key information to obtain because obese patients are at increased risk of pulmonary complications from hypoventilation. Often, obese patients have poor eating habits, so a nutritional assessment is important, and interventions may be used to optimize the patient's nutritional status prior to surgery. A complete list and dosage of all medication, both prescribed and over the counter, is needed. It may be necessary to stop some of these medications before the surgical procedure. For example, patients with known or newly diagnosed cardiac dysrhythmias may require changes or additions to medications (anticoagulants, beta-blockers, anti-arrhythmics), which necessitates consultation and management by a cardiologist.⁵ The pharmacokinetics of certain drugs are affected by obesity. This is due to factors that not only influence the distribution of drugs to the tissues (such as regional blood flow and body composition), but also because of the association of obesity with liver and gallbladder disease.⁸ Consequently, the metabolism and clearance of various drugs can be altered. The typical classes of drugs affected include anticoagulants, steroid hormones, sedatives, and analgesics.⁹

Assessment of Comorbidities

The review of systems is one of the most vital components of the history because the obese patient is likely to have numerous comorbidities that impact the risk of surgical intervention.

Cardiac comorbidities

There are six identified risk factors that place patients at greater risk of perioperative cardiovascular morbidity, documented in the Revised Cardiac Risk Index (see Table 2).¹⁰ Patients with three or more of these cardiac risk factors may require additional noninvasive testing.

Obesity is an independent risk factor for cardiovascular comorbidities, and the greater the BMI and the greater the age of the patient, the greater the risk for cardiovascular comorbidities.^4,5,11 An increase in BMI results in an increase in circulating blood volume leading to an increase in cardiac output. Even with normal peripheral vascular resistance, there is an elevation in blood pressure causing stress on the left ventricle leading to left ventricle hypertrophy.^4,11,12 In the early stages of obesity, the left ventricle compensates for the excess circulating volume load by thinning of the left ventricular wall. This compensatory mechanism preserves cardiac function. However, over time, it leads to remodeling of the heart.^11,13 Initially, this remodeling is a beneficial response to help the heart meet the increased demand on perfusion, but over time, the stress on the myocardial wall leads to chamber dilatation, myocardial and endothelial cell death, interstitial myocardial fibrosis, increases in collagen deposits, contractile dysfunction, and further remodeling.^11,14

Atrial fibrillation is another cardiovascular comorbidity associated with obesity. Atrial fibrillation frequently occurs in the obese individual with hypertension and heart failure. This arrhythmia develops when there is heart remodeling compensating for the overload due to obesity. The areas of fibrosis within the heart and the dilation of the chambers interfere with the normal conduction pathway leading to atrial fibrillation.¹⁵

Obesity is also identified as a state of inflammation contributing to the development of atherosclerotic cardiac disease.⁵ Atherosclerotic cardiac disease is prevalent in obese individuals and occurs over years without any symptoms.¹⁶ Insulin resistance, increase in serum low density lipoprotein, cholesterol, triglyceride levels, and decrease in the serum high density lipoprotein contribute to the development of atherosclerotic plaques that cause vessel stenosis overtime.

Ischemic heart disease in the obese population is correlated with interference of microcirculation caused by development of the atherosclerotic patches.¹⁶ Hypertension and heart remodeling, causing myocardial hypertrophy and dilated chambers that interfere with microcirculation, contribute to ischemic heart disease.¹⁶

Respiratory comorbidities

Respiratory abnormalities are common in the obese patient and must be determined as part of the assessment of comorbidities.^5,11 These abnormalities include an increased demand for ventilation and breathing workload, decreased functional reserve capacity and expiratory reserve volume, closure of peripheral lung units, inefficient respiratory muscles due to fatty infiltrates, and increased intra-abdominal pressure, which places stress on the diaphragm.^5,17–19 As obesity is a disease of systemic inflammation, airway reactivity can be increased by elevated C-reactive protein, tumor necrosis factor, and interleukin-6.¹⁷ In the perioperative setting, these abnormalities can become further accentuated when patients are placed in the supine position or are mechanically ventilated and medically paralyzed.^4,18–21

Gastrointestinal comorbidities

Obese patients, despite excess body fat stores, remain at risk to develop energy malnutrition in response to the stress of surgery. They metabolize more protein and less fat compared to non-obese patients.⁹ Hypoproteinemia contributes to poor surgical wound healing and an increase in wound dehiscence.

Another metabolic abnormality associated with obesity and fostered by a chronic, pro-inflammatory state is nonalcoholic steatohepatitis (NASH) and its precursor, nonalcoholic fatty liver disease (NAFLD). The incidence of NASH in the general population is estimated at 2–4%; while NAFLD is found in 16–23%.²² Higher percentages of both conditions occur in the obese population. NAFLD and NASH can progress to fibrosis and cirrhosis of the liver and lead to increased perioperative morbidity and mortality. Fat cells engorged with triglycerides stimulate the release of cytokines. This produces a pro-inflammatory state and impacts the hepatic and vascular systems. Free fatty acids are released due to impaired glucose utilization. Fat is then deposited in non-adipose tissues such as the liver, muscle, and pancreas.²² The obese patient may complain of mild fatigue, right upper quadrant pain, or mild jaundice. Signs of hypergonadism, hirsutism, anovulation, and infertility may or may not be evident.²²

Renal comorbidities

Obesity impacts renal function by adversely affecting natriuresis (sodium excretion by the kidneys) and contributing to hypertension. This occurs because of glomerular hyperfiltration from increased renal plasma flow. Additionally, nephron function is compromised from shear physical compression of the kidneys due to increased body mass. The more nephron function is diminished, the more natriuresis is impaired. Eventually, this process contributes to increased arterial pressure by activation of the sympathetic and renin angiotensin systems.²³

Endocrine comorbidities

It is estimated that subclinical hypothyroidism may be present in up to 25% of all morbidly obese paitents.²³ Chronically elevated thyroid stimulating hormone levels can lead to a state of thyroid hormone resistance in peripheral tissues. This resistance is associated with hypoglycemia, hyponatremia, impaired hepatic metabolism, and an increased susceptibility to depressant drugs.²³ These physiologic changes may require adjustment of the dosing of anesthetic and analgesic agents. Preoperative screening for hypothyroidism is recommended, particularly in older females, those with a positive family history of thyroid disease, and if clinical signs and symptoms are suggestive of a thyroid disorder.⁷

Diabetes is also an independent risk factor for postoperative morbidity.²⁴ Hyperglycemia, whether from the release of catecholamines during the stress response or from insulin resistance, hinders surgical recovery, impairs wound healing, and interferes with collagen synthesis.²⁵ Therefore, it is important to attain glycemic control.⁹ This is best achieved with insulin by infusion rather than with oral agents.⁸ An accepted blood glucose range lies between 100 and 200 mg/dl.²⁵ A perioperative blood glucose protocol can provide guidance for titration of insulin infusions or sliding scale coverage and criteria for transitioning to oral agents or back to the patient's preoperative regimen.

Integumentary comorbidities

Obesity is an independent risk factor for surgical site infection.²⁴ As BMI increases, so does the incidence of superficial wound infections.²⁶ Decreased oxygen tension, immune system impairment, tension and secondary ischemia along suture lines, poor blood supply to the skin, and diabetes mellitus are contributing factors.²⁴ If a wound infection occurs, the surgical site weakens, and there is an increased incidence of incisional hernia.²⁰ A laparoscopic approach, with typically smaller incisions, affords a much lower rate of wound infection compared to open technique.⁶ However, many surgical procedures require large incisions for adequate exposure, and many procedures cannot be performed with a minimally invasive approach. Additionally, moisture in skin folds, particularly in the abdominal pannus, groin, or under the breasts, provides an excellent medium for fungal growth.²⁵ Appropriate antibiotic prophylaxis should be administered intravenously (IV) 30 minutes prior to the creation of the surgical incision. This ensures time for adequate tissue penetration.⁶

Immune comorbidities

Immunologic abnormalities found in the obese patient suggest the existence of a chronic pro-inflammatory state. This is defined as a persistent elevation in circulating cytokines causing endothelial inflammation, changes in cellular immunity, hypercoagulability, and insulin resistance.⁹

Physical Examination

A complete physical examination is another critical step in the preoperative evaluation of the obese patient. The most essential first step of the examination by the healthcare team is to obtain an accurate measurement of height and weight; these measurements will both ensure correct BMI calculation and further ensure the correct classification of the patient's morbidity status (obese vs. morbidly obese). In addition, a careful physical examination can detect clues to underlying comorbidities that may be unknown to the patient. When assessing the vital signs, blood pressure readings may be difficult to measure. An adequate size blood pressure cuff must be used to obtain an accurate reading because a standard cuff that does not fit properly may overestimate both systolic and diastolic readings.²⁵ Alternative sites such as the wrist, forearm, or ankle can be used. It should be noted, however, that distal sites for blood pressure measurement, such as the forearm, wrist, or ankle, can falsely elevate the true blood pressure compared with using the brachial site. An equation to correct for this disparity is useful to obtain accurate measurements.⁶ During the intraoperative and immediate postoperative phase, invasive arterial monitoring is recommended for those patients with a BMI >60 kg/m², severe cardiopulmonary disease, or if the noninvasive cuff cannot provide a reliable reading.⁶ Additionally, the patient may have an underlying tachycardia because obese patients have an increased cardiac output. An irregular rhythm is a clue to underlying dysrhythmias such as atrial fibrillation.

Preoperatively, a thorough skin assessment is essential to establish a baseline for postoperative comparison. Skin conditions such as rashes, areas of maceration, infection, or breakdown can be identified. If intertriginous candida is present, it should be treated before surgery.²⁴ Other clinical signs indicative of venous insufficiency and ulceration, dermatitis, pressure ulcers, or lymphedema can provide insight into the overall status of the skin and provide clues for systemic arterial or venous disease. The assessment also affords the opportunity to educate the patient about the importance of skin care and good hygiene.

During the skin assessment, potential venous and arterial access sites can be identified. Yet, due to the profound amount of excess adipose and subcutaneous tissue, even the most superficial blood vessels become indiscernible. Central venous catheters should be used when peripheral access is not possible.^6,24 The patient should be fully informed of the rationale for this option to allay anxiety.

The head and neck of the patient are thoroughly inspected because obese patients often have abnormal airways and limited range of motion of the neck. The use of the Mallampati score (visual grading of the oropharynx) is a reliable predictor of potential intubation difficulty. These findings are also important in determining how the airway will be managed intra- and postoperatively.¹⁷ Jugular venous distension may be difficult to distinguish due to the size of the patient's neck.

The cardiac exam may be challenging because the heart sounds are often distant. The exam may reveal abnormal heart sounds indicating structural abnormalities. Obese patients are at risk for ventricular hypertrophy as a result of long-term hypertension resulting in a displacement of the apical pulse.

A thorough assessment of the lungs is an essential part of the examination. Diminished breath sounds and wheezing (both spontaneous and forced expiratory wheezing) from the lung assessment may indicate hypoventilation syndrome or other underlying airway/pulmonary conditions that are common among obese patients. During this aspect of the physical examination, additional history from the patient, to include intolerance of lying flat due to increased respiratory effort (obstructive airway disease or compression of the oropharynx due to obesity) can be elucidated.

Assessment of the extremities for evidence of reddened, warm, or swollen calves may indicate a preexisting deep vein thrombosis (DVT). This evaluation is important because obesity is an independent risk factor for DVT. Evidence of edema in the extremities may be a clue to heart or renal failure.

Laboratory and Diagnostic Tests

Laboratory tests are another key element in the preoperative assessment. The tests should include a complete blood count, chemistry panel, coagulation profile, and urinalysis. An elevated glucose may indicate diabetes mellitus, and a hemoglobin A1C may be ordered for further evaluation of a diabetic patient. Polycythemia may occur secondary to chronic hypoventilation that is common in obese patients.²⁵ Checking a pre-albumin level preoperatively can provide insight to the nutritional status.

Liver functions tests (LFTs) may be ordered as part of the preoperative assessment. If abnormalities are present then it is important to determine the source and scope of hepatic impairment. Further imaging studies such as ultrasound (U/S) or computerized tomography (CT) scan may be warranted. Liver biopsy remains the gold standard to determine the extent of disease.⁷ Underlying causes such as hepatitis B or C may be identified and treatment initiated. While there is no clear correlation between abnormal LFTs and the liver's ability to metabolize drugs, it is important to consider the extent of liver disease and potential complications or possibility of failure.²³

It may become necessary to perform further diagnostic testing, based on the analysis of the history and physical exam, to optimize risk stratification of this patient population. The American Heart Association has developed guidelines on cardiac risk stratification of the obese patient undergoing surgery.⁵ The guideline indicates that exercise stress testing continues to be the foundation of noninvasive, provocative, assessment for occult cardiac ischemia. For patients unable to tolerate exercise stress testing, due to functional limitations (morbid obesity, respiratory, musculoskeletal limitations), transesophageal dobutamine stress echocardiography and radionuclide ventriculography may be useful to unmask ischemic heart disease, perioperatively.⁵ An echocardiogram may be indicated to evaluate left ventricular status.

The preoperative pulmonary evaluation of an obese patient should also include a posterior-anterior and lateral chest x-ray. Pulmonary function tests or spirometry and a screening test for obstructive sleep apnea may be performed. Arterial blood gasses in a severely obese patient with hypoventilation provide useful preoperative data. If available, preoperative consultation with an anesthesia team is suggested to identify any potential airway concerns ahead of time. Consultation with a pulmonologist, for newly diagnosed or poorly managed airway disease, is ideal.

The preoperative evaluation concludes with patient and family education. The provider explains strategies that may help prepare the patient for the surgical intervention. If time allows, a preoperative nutrition consult can serve to educate the patient to make better diet choices and help correct deficiencies. Postoperatively, the consult can provide a baseline for providing diets and supplements to ensure nitrogen equilibrium, prevent fatty acid deficiency, and avoid hyperglycemia.⁹

For the patient with obstructive sleep apnea, review of the correct use of a continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) device is essential. The patient may be instructed to bring their device with them for use during the postoperative phase.

A comprehensive review of the operative procedure with the patient and family, as well as a description of the postoperative course and potential complications, is essential. This is an important time for the patient and family to ask questions, gain helpful information that will promote the patient's recovery, and to develop realistic expectations regarding the recovery phase.

Additionally, an individualized plan of care, both preoperatively and postoperatively, is documented by the entire healthcare team, ideally, on the appropriate institutional form, for efficient and seamless communication with the preoperative and operative teams (surgical attendings, anesthesia attendings, nursing staff, and technician staff). This plan of care is reviewed at each phase of patients' progression through the operative course. It is critical that this information is also shared with patients and their families to ensure transparency and appropriate patient anticipation of interventions.

Postoperative Complications

Obese patients are at higher risk for many postoperative complications, underscoring the need for a thorough perioperative work-up to identify potential hidden risks. From a postoperative standpoint, obesity is thought to be a standalone risk factor for both morbidity and mortality, but postoperative risks are also related to existing comorbidities. Possible complications related to these comorbidities can include; difficult intubation, aspiration, hypoxemia, myocardial infarction, hyperglycemia, acute renal failure, hemorrhage, wound infection, wound dehiscence, nerve injury, and urinary tract infections.²⁶ Of particular concern is the need for airway and respiratory support in the immediate postop period. Postoperative extubation carries a risk of a lost airway and the possibility of a difficult re-intubation, leading to the onset of hypoxemia and the risk of pulmonary aspiration.²⁶ Careful continuous monitoring of cardiovascular and respiratory status in the postoperative period is essential.

Postoperative peripheral nerve injuries, observed particularly in the obese population, are believed to be related to protracted surgical procedures and prolonged immobilization after surgery. Specific sites of vulnerability for injury, due to pressure, included the elbow (ulnar nerve) and knee (peroneal nerve).²⁶ Therefore, measures should be taken to protect these areas during and after surgery, to avoid pressure and prolonged traction. Hyperglycemia is a frequent problem in the obese patient population. Meticulous regimens, according to institutional protocol, for perioperative and postoperative glycemic management are essential to lessen the risk for postoperative infections.²⁶

As mentioned earlier, obesity is an independent risk factor for DVT occurrence. Therefore, in addition to mechanical prophylaxis (anti-embolic stockings, devices), surgical consultation for consideration of pharmacologic prophylaxis during the postoperative period is recommended. With respect to the preoperative, individualized plan of care, DVT risk stratification and plans for prophylaxis are critical aspects for plan of care documentation and to include in discussions with the patient and family.

Finally, it is essential that both staff and facilities are chosen that can support obese patients in the event of an intraoperative or postoperative complication. Bariatric patients considering any type of surgical procedure may benefit from discussing with the surgeon and staff individual institutional readiness to accommodate physical dimensions for pre- and postoperative care appropriately and safely. Additional resources, such as the American College of Surgeons, Bariatric Accreditation Network (www.acsbscn.org/Public/index.jsp) may be particularly useful. Institutional readiness for the care of bariatric patients should include; adequate equipment (appropriate blood pressure cuff sizes, beds, lifts) and personnel, such as a postoperative care unit, intensive care unit, or telemetry unit, which are necessary to support the post-operative obese patient fully, until he or she is fully recovered.¹²

Conclusion

Rising U.S. obesity rates and their subsequent impact on healthcare costs are well documented. This increasing epidemic also increases the numbers of obese patients facing surgical procedures. The concomitant comorbidities frequently occurring in the obese population present a unique challenge for those healthcare teams responsible for the assessment and management of their perioperative surgical care.

A comprehensive patient history, physical exam, and baseline laboratory and diagnostic testing are essential to detect and manage comorbidities. Based on these findings, risk stratification is an essential next step of the perioperative evaluation. This comprehensive approach is vital for the prevention of many associated postoperative complications.

Footnotes

Disclosure Statement

No competing financial interests exist.

References

Centers for Disease Control. Vital Signs: State Specific Obesity Prevalence Among Adults—United States 2009. www.cdc.gov/mmwr/preview/mmwrhtml/mm5930a4.htm?s_cid=mm5930a4_w. 2011 June 10.

Hammond

. Complex systems modeling for obesity research. Prev Chronic Dis, 2009; 6131.

American Medical Association. Assessment and management of adult obesity: a primer for physicians 2006. Jaffe

, Samuels

. Anesthesiologist's Manual of Surgical Procedures, fourth. Philadelphia, PA: Lippincott Williams & Wilkins, 2009; 7.

Poirier

, Alpert

, Fleisher

, Thompson

, Sugerman

et al. Cardiovascular evaluation and management of severely obese patients undergoing surgery: a science advisory from the American Heart Association. Circulation, 2009; 120:86–95.

Abir

, Bell

. Assessment and management of the obese patient. Crit Care Med, 2004; 32:S87–S91.

Collazo-Clavell

, Clark

, McAlpine

, Jensen

. Assessment and preparation of patients for bariatric surgery. Mayo Clin Proc, 2006; 81:S11–S17.

Buchwald

. Surgical options. J Fam Pract, 2005; 10–17.

Levi

, Goodman

, Patel

, Savransky

. Critical care of the obese and bariatric surgical patient. Crit Care Clin, 2003; 19:11–32.

Lee

, Marcantonio

, Mangione

, Thomas

, Polanczyk

et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation, 1999; 100:1043–1049.

10.

Roberts

, Clark

, Witte

. Left ventricular dysfunction and heart failure in metabolic syndrome and diabetes without overt coronary disease—do we need to screen our patients? Diab Vasc Dis Res, 2009; 6:153–156.

11.

O'Neill

, Allam

. Anaesthetic considerations and management of the obese patient presenting for bariatric surgery. Curr Anaesth Crit Care, 2009; 1–8.

12.

Stoelting

, Miller

. Special Considerations in Basics of Anesthesia, fifth. Philadelphia, PA: Churchill Livingstone Elsevier, 2007; 448–451.

13.

Hutchinson

, Stewart

, Lucchesi

. Extracellular matrix remodeling during the progression of volume overload-induced heart failure. J Mol Cell Cardiol, 2010; 48:564–569.

14.

Prystowsky

, Benson

, Fuster

et al. Management of patients with atrial fibrillation. Circulation, 1996; 93:1262–1277.

15.

Orsini

, Zito

. Matching pathophysiology and evidence-based medicine for optimal management of ischemic heart disease. Ital Fed Cardiol, 2010; 1158–2027.

16.

Davis

, Patel

, Gagne

. Pulmonary considerations in obesity and the bariatric surgical patient. Med Clin N Am, 2007; 91:433–442.

17.

Lin

. Endocrine and nutritional disease. Stoelting

, Miller

. Basics of Anesthesia, fifth. Philadelphia, PA: Churchill Livingston Elsevier, 2007; 29.

18.

Kaw

, Aboussouan

, Auckley

, Bae

, Gugliotti

et al. Challenges in pulmonary risk assessment and perioperative management in bariatric surgery patients. Obes Surg, 2008; 18:134–138.

19.

McGlinch

, Que

, Nelson

, Wrobleski

, Grunt

, Collazo-Clavell

. Perioperative care of patients undergoing bariatric surgery. Mayo Clin Proc, 2010; 1–14.

20.

The Association of Anaesthetists of Great Britain and Ireland. Peri-Operative Management of the Morbidly Obese Patient. Peri-Operative Management of the Morbidly Obese Patient. www.aagbi.org/sites/default/files/Obesity07.pdf. 2011 May 2.

21.

Richardson

, Vinik

. Metabolic implications of obesity: before and after gastric bypass. Gastroenterol Clin North Am, 2005; 34:9–24.

22.

Barash

, Cullen

, Stoelting

, Cahalan

, Stock

. Clinical Anesthesia, sixth. Philadelphia: Lippincott Williams & Wilkins, 2009.

23.

DeMaria

, Carmody

. Perioperative management of special populations: obesity. Surg Clin North Am, 2005; 85:1283–1287.

24.

Baugh

, Zuelzer

, Meador

, Blankenship

. Wounds in surgical patients who are obese. Am J Nurs, 2007; 107:40–50.

25.

Mullen

, Moorman

, Davenport

. The obesity paradox: body mass index and outcomes in patients undergoing nonbariatric general surgery. Ann Surg, 2009; 250:166–172.

26.

Bamgbade

, Rutter

, Nafiu

, Dorje

. Postoperative complications in obese and nonobese patients. World J Surg, 2007; 31:556–560.