anesthesia case management for bariatric surgery - american

AANA Journal CourseUpdate for Nurse Anesthetists

Anesthesia Case Management for Bariatric Surgery

Jennifer Thompson, CRNA, MSNSandra Bordi, CRNA, MSNMichael Boytim, CRNA, EdDSass Elisha, CRNA, EdDJeremy Heiner, CRNA, MSNJohn Nagelhout, CRNA, PhD, FAAN

ObjectivesAt the completion of this course, the reader should be able to:

1. Describe the pathophysiologic changes that are as-sociated with morbid obesity.

2. Discuss commonly used weight-reduction drugs and the dosing of commonly administered anes-thetic drugs given to morbidly obese patients.

3. Compare and contrast the various surgical proce-dures used for bariatric surgery.

4. List perioperative strategies that can be used to op-timize oxygenation/ventilation in morbidly obese patients.

5. Identify the postoperative complications associated with bariatric surgery.

IntroductionObesity is an epidemic that threatens the health of people all over the world. By estimation of the International

Obesity Task Force, more than 1.7 billion people are overweight or obese. Decreased physical activity and overconsumption of high-fat foods are the main con-tributing factors to the obesity epidemic. Conservative interventions to the treatment of obesity include early education, low-calorie diet, increased physical activity, and, sometimes, medications. However, these treatments are not always effective, and many obese people undergo bariatric surgical procedures. There is a myriad of an-esthesia challenges associated with these surgeries. A thorough understanding of the anesthetic considerations is essential to facilitate positive outcomes for the patients.

Pathophysiologic Changes of ObesityObesity is commonly associated with a variety of co-morbidities, including diabetes, cardiovascular disease, endocrinopathies, and osteoarthritis (Figure 1).1 The mechanisms underlying these complications are complex and most often are interrelated.

*AANA Journal Course No. 31 (Part 1): AANA Journal course will consist of 6 successive articles, each with objectives for the reader and sources for additional reading. At the conclusion of the 6-part series, a final examination will be published on the AANA website. Successful completion will yield the participant 6 CE credits (6 contact hours).

6 CE Credits*

1

An increasing number of bariatric surgeries are per-formed every year. A thorough understanding of the pathophysiologic changes, surgical procedure, and anesthesia case management for morbidly obese patients and of the pharmacology of weight-reduction and anesthetic drugs is essential to provide high-quality anesthetic care. The various comorbidities associated with obesity may complicate anesthetic management. Anesthetists must perform a thorough preoperative assessment to identify potential risk fac-tors related to anesthesia and adequately prepare for

intraoperative management. Intubation, maintenance of oxygenation, and pain management may be particu-larly challenging, and various strategies are presented. In addition, an obese patient is at higher risk for post-operative complications. Signs and symptoms of sur-gical complications may mimic medical complications, making diagnosis difficult.

Keywords: Bariatric surgery, gastric banding, gastric bypass, metabolic syndrome, obesity.

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Figure 1. Pathology of Obesity CVA indicates cerebrovascular accident; DVT, deep venous thrombosis; PE, pulmonary embolism.


The combination of related cardiovascular risk factors, including central obesity, hyperglycemia, hypertension, and dyslipidemia, is referred to as metabolic syndrome.Patients with metabolic syndrome are at higher risk for coronary artery disease (CAD) and experiencing major cardiovascular events. Although each component is rec-ognized as an individual risk factor, the clustering of these risk factors puts a patient at an even greater surgical risk.2

One of the most prevalent disorders associated with obesity is type 2 diabetes resulting from insulin re-sistance and hyperinsulinemia.1 Hyperinsulinemia fre-quently results in sodium retention, excessive circulating catecholamines, and increased blood volume.3 Patients commonly have hypertriglyceridemia and low high-density lipoprotein levels, which may contribute to CAD. The American Heart Association reports that obesity may be a major factor for developing heart disease.1

Concentric ventricular hypertrophy, which develops over time, results from increased systemic vascular resis-tance. The incidence of hypertension increases propor-tionally as body mass index (BMI) increases.

Fatty changes in the liver may lead to fibrosis and hepatic failure. Nonalcoholic steatohepatitis often occurs in obese children. Cholelithiasis is 6 times more common in people who are obese as in normal-weight people.3

Formation of gallstones also occurs at a higher rate due to the increase in the total body cholesterol level and greater biliary cholesterol excretion.4

Commonly occurring respiratory abnormalities include Pickwickian syndrome, obstructive sleep apnea, decreased functional residual capacity, and increased closing capacity, which all contribute to atelectasis and rapidly occurring hypoxemia.1 These respiratory changes may also lead to polycythemia and cor pulmonale.

Obesity predisposes to osteoarthritis. Increased body weight stresses bones and joints, and this condition is especially common in elderly people. An increased risk of stroke and thromboembolic disease is also prevalent.4

A recent study determined that there may be an as-sociation between obesity and various forms of cancer, including esophageal, colon, rectum, liver, prostate, breast, uterus, cervix, and non-Hodgkin lymphoma. Many of these phenomena are hypothesized to be caused by increased estrogen levels.5

Pharmacology of Obesity-Related Drugs and of Anesthetics

• Antiobesity Medications. Medications that promote weight loss have limited efficacy. Despite the enormous potential market, efforts to develop effective drug thera-pies have been disappointing. The US Food and Drug Administration guidance for long-term weight-loss drugs recommends that a 5% weight reduction be maintained for 12 months after treatment initiation. Two drugs are available for use: orlistat (Xenical [prescription form, Roche, Basel, Switzerland]; Alli [over-the-counter form, GlaxoSmithKline, Brentford, England]) and phentermine (Adipex-P [North Wales, Pennsylvania]; others). When used in combination with a comprehensive weight-loss program, they can occasionally be effective in producing weight loss in the range of 4 to 5.5 kg.6

Orlistat is a lipase inhibitor that decreases the absorp-tion of fat in the gastrointestinal tract. It has recently been released as an over-the-counter medication. Side effects are minor and mostly related to gastrointestinal discomfort (Table 1). Phentermine, a sympathomimetic agent, is approved for short-term use (up to 12 weeks) as a weight-management drug. Tolerance, dependence, abuse, and a relatively high number of adverse effects limit its usefulness. Several antidepressant, antiepileptic, and antidiabetic drugs may promote weight loss and are used off-label for this indication.6,7

• Anesthesia Drugs and Obesity. Obesity causes physi-ologic changes that can affect the pharmacokinetics and pharmacodynamics of anesthetic agents. An overview of these changes is given in Table 2. The common approach to anesthetic drug administration is to dose water-soluble drugs according to ideal body weight and lipid-soluble drugs according to total body weight. Lean body mass in-creases approximately 20% to 40% in obesity, so adding 30% to the ideal body weight is a convenient dose adjust-ment. Table 3 shows weight calculations commonly used for the dosing of medications.

Contradictory results from individual drug studies in small patient groups are common; therefore, specific rec-ommendations are frequently conflicting. A few general observations can be made. Postoperative respiratory depression is especially problematic in obese patients; therefore, most clinicians favor short-acting drugs that

Drug Mechanism Side or adverse effects Precautions

Orlistat (Xenical; Alli) Lipase inhibitor: inhibits intestinal Fecal urgency, diarrhea, and abdominal May interfere with absorption fat absorption by blocking hydrolysis pain; case reports of liver injury under of fat-soluble vitamins A, D, of dietary triglycerides into free fatty investigation E, and K, requiring supple- acids mentation

Phentermine Sympathomimetic agent similar Primary pulmonary hypertension and Rarely used; only for short- (Adipex-P; others) to amphetamines many other sympathomimetic adverse term use; however, has a effects possible; contraindicated in poor risk-benefit ratio hypertension and diabetes

Table 1. Pharmacotherapy for Obesity


allow for fast recovery. The inhalation agents desflurane and sevoflurane produce excellent recovery profiles in obese patients. Although desflurane is less soluble than sevoflurane, clinical differences are minimal. Nitrous oxide can be safely used in patients in whom a require-ment for high oxygen concentrations does not preclude its administration. Succinylcholine doses for intubation are given according to total body weight to ensure excel-lent intubating conditions, whereas the nondepolarizing muscle relaxants used for operative maintenance are given according to ideal body weight. Use of a nerve stimulator to guide relaxant administration assists in minimizing residual paralysis and reversal concerns. Remifentanil infusion is an especially popular analge-sic because of the drugs titratability and rapid offset and is administered according to ideal body weight.

Dexmedetomidine is also a useful adjunct for sedation, amnesia, and analgesia.8 Specific dosing recommenda-tions for some common anesthetic agents in obesity are listed in Table 4.

Surgical ProcedureBecause of the epidemic proportions of obesity within the United States, the number of bariatric surgical pro-cedures performed each year has increased. Bariatric surgical programs mandate that before surgery, patients participate in lifestyle modifications to lose weight and learn how to incorporate healthy choices into daily life. It has been demonstrated that preoperative weight loss decreases all of the complications associated after laparo-scopic gastric bypass.9 Psychologists, dieticians, physical therapists, and exercise specialists work with patients

Increased fat mass

Increased cardiac output

Increased blood volume

Increased lean body weight

Changes in plasma protein binding

Reduced total body water

Increased renal clearance

Increased volume of distribution of lipid-soluble drugs

Table 2. Pathophysiologic Changes in Obesity That May Affect Pharmacokinetics

Table 3. Simplified Weight CalculationsBMI indicates body mass index; TBW, total body weight; IBW, ideal body weight; and LBW, lean body weight.

BMI

BMI = TBW in kg/height in m2

IBW in kg

IBW = height (cm) – 100 for men or 105 for women

or

IBW = 0.8 × TBW for men or 0.75 × TBW for women

LBW

LBW = IBW × 1.3

Table 4. Dosing Recommendations for Some Common Anesthetic Drugs in ObesityTBW indicates total body weight; LBW, lean body weight; and IBW, ideal body weight.

Drug Dose recommendation Comments

Propofol Induction dose based on LBW; maintenance Increased fat mass does not affect initial dose based on TBW distribution/redistribution during induction. Cardiac depression at high doses is a concern.

Thiopental Induction dose based on TBW High cardiac output, volume of distribution, and lean body mass suggest a higher dose require- ment. Reduce doses when excess cardiac depression is a concern.

Succinylcholine Intubating dose based on TBW Increased fluid compartment and pseudocholin- esterase levels require higher doses to ensure adequate paralysis.

Rocuronium, All doses based on IBW Hydrophilic drugs given according to IBW will vecuronium; ensure shorter duration and a more predictable cisatracurium recovery in this respiratory challenged population.

Fentanyl Loading dose based on TBW; maintenance Increased distribution volume and elimination dose based on LBW and response time correlate with degree of obesity.

Remifentanil Infusion rates based on IBW Distribution volumes and elimination rates are similar to those for normal-sized people. Fast offset requires planning for postoperative analgesia.

Dexmedetomidine Infusion rates of 0.2 µg/kg/min Useful as an adjunct. Lower than usual infusion rates are recommended to minimize adverse cardiac side effects.


to change their habits and behaviors that contribute to obesity. Furthermore, medical optimization of the pa-tients’ coexisting morbidities is essential before surgical intervention.

There are several variations related to the surgical procedures that can be performed. Presently, the most common surgical approach for bariatric surgery is lapa-roscopy. Furthermore, there is a decrease in the morbid-ity and mortality associated with laparoscopic gastric bypass with robotic assistance.10 The goal of bariatric surgery is to reduce the patient’s caloric intake by re-stricting the amount of food that is able to be consumed (gastric restriction procedure) or, by a dual mechanism, to restrict and decrease the amount of absorption from the gastrointestinal tract (mixed restrictive and malab-sorptive procedure).11 Operative mortality (≤ 30 days postoperatively) is estimated to be approximately 0.1% for restrictive procedures and 1% for mixed restrictive and malabsorptive procedures.12 The most common types of bariatric surgical procedures are laparoscopic adjustable gastric banding and the Roux-en-Y technique.

Types of Gastric Bypass Procedures• Restrictive Procedures. Vertical banded gastroplasty is

a restrictive procedure that involves the surgical creation of a gastric pouch. The procedure involves making a hole in the middle of the body of the stomach. Stapling of the stomach from the superior aspect of the fundus to the newly created hole is accomplished. The surgeon then fashions a tissue band through the hole that surrounds the remainder of the gastric body near the esophago-

gastric junction. Thus, a gastric pouch remains that can accommodate 25 to 30 mL and restricts the amount of food that can be consumed. An illustration of vertical banded gastroplasty is shown in Figure 2A.

Vertical banded gastroplasty was the most popular surgical intervention for bariatric surgery from the mid 1980s until the early 1990s. Disadvantages to vertical banded gastroplasty include difficulty eating foods that are high in protein, which facilitates the consumption of soft calorie-dense foods, gastroesophageal reflux, and abdominal discomfort. Patients would frequently regain weight, and only 26% were satisfied with the result of the surgery.12

• Laparoscopic Adjustable Gastric Banding (LAGB)has become a popular alternative to more invasive mal-absorptive surgical procedures and is one of the most common restrictive weight-loss surgeries performed in the United States. This system offers 2 distinct advan-tages compared with vertical banded gastroplasty: The tension on the band is adjustable, and the system is removable. Laparoscopic adjustable gastric banding is associated with a shorter duration of hospitalization, de-creased pulmonary complications, and overall decreased morbidity and mortality compared with other bariatric surgical options.13 There are several adjustable bands, including Lap Band (Alleran Inc, Irvine, California), Realize Adjustable Gastric Band (Ethicon Endo-Surgery Inc, Cincinnati, Ohio), and the Swedish adjustable gastric band. The gastric band is placed immediately distal to the gastroesophageal junction. An illustration of the LAGB is shown in Figure 2B. Contained within the silicone band,

Figure 2. Restrictive Bariatric Surgical ProceduresA. Vertical banded gastroplastyB. Laparoscopic adjustable gastric bandC. Sleeve gastrectomy


a balloon is inflated to decrease the size of the proximal aspect of the stomach. The balloon is inflated with saline via an access port that is positioned subcutaneously. The pouch that is created holds approximately 100 to 200 g of food. Distention of the pouch causes satiety resulting from afferent sensory and visceral neural innervation.

Identification of patients who are ideal candidates for LAGB improves the postoperative percentage of weight loss. Increased age, increasing BMI, hyperinsulinemia, type 2 diabetes, and polycystic ovarian syndrome are as-sociated with a lower percentage of weight lost after sur-gical intervention.14 It has been demonstrated that weight loss with LAGB frequently results in complete resolution or improvement of type 2 diabetes, hypertension, and dyslipidemia.15 The indications and contraindications for having LAGB are included in Table 5.14

Numerous potential complications are associated with LAGB surgery. An analysis of 7 years’ of data from 2,909 patients related to the safety of the LAGB includes the following complications and frequencies: band slippage, 4.5%; port-related problems, 3.3%; and reoperation for weight gain, 0.4%. One or more of these complications were experienced by 12.2% of patients.12 The overall incidence of erosion of the stomach under the gastric band is 1.96%. Postoperative mortality within 30 days or fewer is approximately 0.06% to 0.1%.12,16 A rare com-plication called Barrett esophagus can occur after LAGB. Barrett esophagus occurs due to chronic gastroesophageal reflux, which causes esophageal erosion and predisposes

patients to malignant changes. The overall incidence is unknown; however, cellular dysplasia and esophageal adenocarcinoma that is related to gastroesophageal reflux disease can occur after gastric banding.17 A compre-hensive list of complications associated with LAGB are included in Table 6.12

• Sleeve Gastrectomy is accomplished by decreasing the size of the stomach to approximately 20% of its original size by removing a substantial portion of the stomach. This procedure is most frequently performed laparoscopically and involves resection of a substantial portion of the gastric fundus and body to create a tube-like opening from the gastroesophageal junction to the pyloric valve. The reconstructed stomach ideally will have a total gastric volume of between 100 and 200 mL.18

This procedure is shown in Figure 2C. In general, pa-tients lose between 30% and 50% of excess body weight within 1 year.

• Combined Restrictive and Malabsorptive Procedures. Roux-en-Y gastric bypass (RYGB) is the most common combined restrictive and malabsorptive form of gastric bypass surgery in the United States. The National Institutes of Health has determined that the most ef-

Table 6. Complications Associated With Bariatric Surgery(Adapted from Matarasso et al.12)

Adjustable gastric band Gastric mucosal erosion around the band

Gastritis

Erosion of gastric mucosa under the band, causing perforation

Filling port malfunction

Gastric prolapse

Malposition of the band

Barrett esophagus

Dysphagia

Gastroesophageal reflux

Malabsorptive proceduresBowel obstruction

Wound dehiscence

Leakage and/or ulcers at the sites of anastomosis

Nutritional deficiency

Incisional hernia

Gastrojejunostomy stenosis

Potential complications of both types of proceduresHemorrhage

Dumping syndrome (more common in gastric bypass)

Postoperative respiratory insufficiency

Deep vein thromboembolism

Pulmonary embolism

Sepsis

Table 5. Indications and Contraindications to Laparo-scopic Adjustable Gastric Banding(Adapted from Dixon and O’Brien.14)

IndicationsBody mass index ≥ 40 kg/m2

Failure to lose weight with dietary restrictions and pharmaco-logic therapy for > 1 y

Obesity for > 5 y

Understanding of the surgical and anesthetic risks and benefits

Willingness to adhere to lifelong dietary restrictions

Acceptable operative risk

Comorbid diseases that improve with weight loss (eg, diabe-tes, metabolic syndrome, cardiovascular disease)

ContraindicationsUnreasonable surgical risk

Untreated hypothyroidism

Gastrointestinal inflammatory disease (eg, ulcers, Crohn dis-ease, ulcerative colitis)

Severe cardiopulmonary disease

Pain intolerance to implantable devices

Alcohol and/or drug addiction

Severe cognitive disabilities

Allergy to silicone


fective surgical treatment for obesity is RYGB.19 The procedure is frequently accomplished via a laparoscopic approach with or without robotic assistance, and there are a number of variations of this technique.10 A small gastric pouch (15-20 mL) is constructed from the cardia portion of the stomach near the gastroesophageal junc-tion and restricts the amount of food that the patient can eat at one time. The pouch is attached to the distal duodenum and becomes the “Roux limb” or “alimentary limb,” where food and fluids travel and are absorbed. The biliopancreatic limb is formed proximally from the duodenum, and the distal resected end is anastomosed to the ileum to form a common small intestinal limb. This procedure is illustrated in Figure 3A.

A polypeptide called ghrelin is primarily secreted by the stomach and small intestine. When secreted, this hormone stimulates appetite. Since removal of various portions of the stomach and duodenum occurs as part of malabsorptive procedures for obesity, another mecha-nism of weight loss is associated with decreased plasma ghrelin levels. It has been demonstrated that ghrelin values are up to 47% lower in patients who have under-gone the RYGB procedure compared with equally obese nonsurgical patients.20

There has been substantial interest in which bariatric surgical procedure is most effective, LAGB or RYGB. The major advantage of the LAGB is that it is revers-ible; however, the percentage of excess body weight loss is less variable and consistently greater with the

RYGB.18,21 Reversal of comorbidities is greatest after LAGB. Perioperative complications were more likely to occur during RYGB than during LAGB, but long-term reoperation rates were lower and patient satisfaction was higher with the RYGB gastric bypass procedure.21 Adams and colleagues22 determined that the long-term mortality after RYGB is decreased from any cause and from diseases specifically attributed to obesity. A list of bariatric surgi-cal procedures and the percentage of excess body weight lost within the first year is listed in Table 7.21

Because of the intricacy associated with this pro-cedure, complications such as leaks from the distal and proximal sites of anastomosis, bowel obstruction, vitamin deficiency, and intestinal stenosis can occur.12,18

Dumping syndrome occurs in approximately 10% of pa-tients who undergo any type of gastric bypass surgery.18

It occurs when food from the stomach is rapidly trans-ported or “dumped” into the duodenum. The severity of the abdominal cramping and nausea associated with this phenomenon varies from mild to severe. This side effect is more common after gastric bypass compared with LAGB. Treatment includes medications such as acarbose (Precose, Bayer Corp, West Haven, Connecticut) or surgical reintervention. A comprehensive list of compli-cations associated with malabsorptive bariatric surgical procedures is listed in Table 6.12

• Biliopancreatic Diversion With Duodenal Switch in-cludes a hemigastrectomy or sleeve gastrectomy to create a 75- to 100-mL pouch. The ileum is connected directly

Figure 3. Mixed Restrictive and Malabsorptive Bariatric Surgical ProceduresA. Roux-en-Y gastric bypassB. Biliopancreatic diversion with duodenal switch


to the gastric pouch, completely bypassing the duode-num and jejunum (alimentary limb). The distal portion of the biliopancreatic limb is then reconnected 100 cm from the ileocecal valve.18 Thus, in addition to being restrictive due to the gastric sleeve, the now substantially shorter small intestine offers less intestinal surface area for absorption to occur. A representation of this proce-dure is shown in Figure 3B.

Biliopancreatic diversion with duodenal switch is most often performed for patients who are described as superobese (BMI ≥ 55 kg/m2). Prachand and colleagues23

determined that excess body weight loss of more than 50% was achieved in 83.9% of patients having biliopan-creatic diversion with duodenal switch and 70.4% with Roux-en-Y 1 year postoperatively.

The development of gallstones commonly occurs after gastric bypass procedures, and some surgeons perform a cholecystectomy simultaneously. Inadequate absorption of proteins, iron, calcium, and fat-soluble vitamins (A, D, E, and K) can occur, and multivitamin supplementation is recommended.18

A new procedure under investigation to determine the safety and efficacy in treating obesity is an implantable gastric stimulator. A pulse generator the size of a cardiac pacemaker is implanted on the surface of the stomach. The afferent impulses that are sensed by the brain allow the person to feel satiated. In the future, as new surgical techniques, technological advances, and the discovery of new medications occur, the treatment of obesity will become safer and more effective.

Anesthetic Management• Preoperative Evaluation. Preoperative evaluation of

a bariatric surgical patient should include an evaluation by a multidisciplinary team and focus on the identifica-tion, treatment, and optimization of modifiable health concerns. Many bariatric surgical candidates have already been diagnosed and medically managed for comorbid conditions by their primary care physicians; therefore, the additional need to perform extensive diagnostic tests is minimal. A candid discussion between the surgeon and patient regarding realistic expectations, lifestyle alterations, diet modifications, and exercise is neces-sary. Common criteria for bariatric surgery include the

following: a BMI of 40 kg/m2 or more or of 35 kg/m2 or more with comorbid conditions, failure of nonoperative weight-loss efforts, absence of contraindications, and a well-informed, compliant, and motivated patient with a good support system.24 Absolute contraindications for bariatric surgery include a lack of understanding of the procedural risks, severe liver disease with accompany-ing portal hypertension, uncontrolled severe obstructive sleep apnea with pulmonary hypertension, and unstable or terminal illness.25

A thorough history and physical examination, vital signs, baseline laboratory studies, and informed consent should be obtained during the initial assessment, and, if needed, referral to and consultation with appropriate subspecialties should be accomplished. Risk identifica-tion and risk reduction should be priorities that can assist in the identification of appropriate surgical candidates. The Obesity Surgery–Mortality Risk Score has been de-signed and validated to predict the risk of mortality in patients undergoing bariatric surgery.26 One point is as-signed to each of 5 preoperative variables:

1. BMI 50 kg/m2 or more2. Male gender3. Hypertension4. Risk for pulmonary embolism (history of venous

thromboembolism, pulmonary hypertension, and/or obesity hypoventilation)

5. Older than 45 yearsA score of 0 or 1 is classified as “A” or lowest risk,

2 or 3 as “B” or intermediate risk, and 4 or 5 as “C” or high risk, with mortality ranging from 0.2% for an A clas-sification, to 1.3% for a B classification, to 2.4% for a C classification.26

A primary goal of the preoperative assessment is treat-ment and optimization of comorbid conditions. Obese patients frequently have comorbid conditions such as hypertension, CAD, diabetes, venous thromboembolism, and/or obstructive sleep apnea. Patients referred to cardi-ology for suspicion of CAD should undergo an exercise or dobutamine stress echocardiogram to evaluate cardiac function.25 Bariatric surgery can be safely performed on patients with known CAD without major increases in perioperative mortality and cardiac complications, pro-vided the patients have been thoroughly evaluated and appropriately managed.27

Patients suspected of having obstructive sleep apnea should undergo polysomnography and receive treatment preoperatively and throughout the perioperative period. Treatment modalities include continuous positive airway pressure, noninvasive positive-pressure ventilation, and bilevel positive airway pressure.24,28 Pulmonary function should be evaluated to anticipate the need for postopera-tive controlled ventilation.

Patients at risk for postoperative venous thromboem-bolism (venous stasis disease, BMI ≥ 60 kg/m2, truncal

Adjustable gastric banding, 25%-80%

Sleeve gastrectomy, 65%-75%

Vertical gastric banding, 50%-60%

Roux-en-Y gastric bypass, 50%-70%

Biliopancreatic diversion with duodenal switch, 65%-75%

Table 7. Percentage of Excess Body Weight Lost by Type of Bariatric Surgery Within the First Year(Adapted from Maggard et al.21)


obesity, prior venous thromboembolism, and known hypercoagulable states) may be considered for placement of an inferior vena cava filter before bariatric surgery. Although expert consensus concerning dosing guidelines does not exist, prophylactic anticoagulation is commonly ordered by most bariatric surgeons.25 Heparin, 5,000 IU, is administered subcutaneously before surgery and then every 12 hours in combination with the use of pneumatic compression devices. Early ambulation is also suggested for effective thromboprophylaxis.29 Some surgeons prefer the administration of low-molecular-weight heparin such as enoxaparin.

Preoperative endoscopy is not routinely performed and is reserved for patients with symptomatic reflux, dyspepsia, or dysphagia. As mentioned earlier, lipid deposition in hepatocytes may induce liver damage and cause simple fatty infiltration or cirrhosis. The terms nonalcoholic fatty liver disease and nonalcoholic steato-hepatitis are used to describe inflammatory changes that occur in the liver with or without fibrosis. Some bariatric surgeons routinely perform liver biopsies during bariatric procedures to diagnose and stage nonalcoholic fatty liver disease/nonalcoholic steatohepatitis.24

It is suggested that each bariatric surgical candidate undergo an electrocardiogram and chest radiograph testing to further investigate cardiopulmonary risk.24,25

In patients with diabetes, the serum glucose level should be maintained at less than 150 mg/dL. A hemoglobin A1c

value of less than 7% is desirable to reduce surgical risk.24

Commonly recommended laboratory tests are listed in Table 8.

With the exception of insulin and oral hypoglycemic agents, patients should continue their usual medication regimen.29 Antibiotic therapy is instituted to decrease the risk of postoperative wound infection. Medications for anxiolysis, analgesia, and aspiration and venous thromboembolism prophylaxis are commonly adminis-tered preoperatively. Aspiration prophylaxis medications include histamine-2 blockers, antacids, and metoclo-pramide.

A thorough airway examination should be completed to identify the possibility of a difficult airway. There is controversy regarding whether obesity is a predictor of difficult endotracheal intubation. Mallampati scores of 3 or greater, neck circumferences greater than 43 cm at the thyroid cartilage, a decreased thyromental distance, and a high BMI are all predictors of potential difficult endo-tracheal intubation.30 Invasive monitoring using arterial and central venous pressures should be considered in patients with poor cardiopulmonary function. In addi-tion, a central venous catheter should be considered in obese patients in whom venous access is challenging or as otherwise indicated from the patient’s health history.

• Intraoperative Anesthetic Management. Morbidly obese (MO) patients present many challenges during the

intraoperative period. Major areas of concern include airway management, maintenance of oxygenation, patient positioning, and monitoring.

General endotracheal anesthesia is the technique of choice for laparoscopic bariatric surgery. Rapid-sequence induction with cricoid pressure remains important to avoid gastric aspiration in obese patients with symp-tomatic gastroesophageal reflux or other predisposing conditions such as diabetes mellitus and gastrointestinal disorders.31 However, the necessity of rapid-sequence in-duction with cricoid pressure because of a presumed risk of aspiration in an obese, fasting patient with no other risk factors is controversial.32

A prudent approach to a known or highly suspected difficult airway would be an awake, fiberoptic intuba-tion. If tracheal intubation with direct laryngoscopy is planned, appropriate positioning, preoxygenation, and preparation of emergency airway equipment is essential. Traditional teaching has emphasized the supine sniff-ing position to aid in airway instrumentation. In MO patients, multiple studies have demonstrated that creat-ing a blanket ramp or reconfiguring the operating table to a 30° back-up position provides optimal conditions for successful intubation.29,33 In these studies, aligning the external auditory meatus with the sternum horizon-tally has been shown to improve the laryngoscopic view (Figure 4). If airway management and intubation prove difficult, emergency airway adjuncts, including a gum elastic bougie, laryngeal mask airway, video laryngo-scope, or fiberoptic endoscope, may be used.

Because of alterations in pulmonary function, such as reduced functional residual capacity and oxygen re-serves, MO patients are likely to experience rapid oxygen desaturation during the induction of general anesthesia, and increased atelectasis may develop throughout the case (Figure 5). Maximizing the oxygen content in the lungs before tracheal intubation is important to decrease these risks. The application of continuous positive airway pressure during preoxygenation, induction with the patient in a head-up position, along with the addition of positive end-expiratory pressure (PEEP) and mechanical ventilation by mask after induction have been shown to prevent atelectasis and desaturation.34,35

Safe intraoperative ventilation of MO patients poses a substantial challenge to anesthesia providers. This chal-

Complete blood cell count

Comprehensive metabolic panel

Liver function tests

Glucose/hemoglobin A1c

Prothrombin time/partial thromboplastin time

Lipid profile

Table 8. Suggested Preoperative Laboratory Testing


lenge is especially important when considering the nega-tive pulmonary effects of the pneumoperitoneum during bariatric surgery. Complete muscle relaxation is crucial during these procedures to facilitate ventilation and prevent collapse of the pneumoperitoneum. Numerous strategies to maintain intraoperative oxygenation and lung volumes in MO patients have been recommended. The use of high tidal volumes, alveolar recruitment maneuvers, positive end-expiratory pressure, and high oxygen concentrations have been studied extensively, and none are conclusively superior. Increasing tidal volumes more than 13 mL/kg in MO patients has been found to increase peak inspiratory pressures and end-expiratory airway pressures but does not substantially improve arterial oxygen tension.36 When compared with the supine position, the use of a 30° reverse Trendelenburg position during bariatric surgery reduces the alveolar-to-arterial oxygen difference, increases total ventilatory compliance, and reduces peak airway pressures. Alveolar

recruitment by repeated sustained lung inflation to 50 cm/H2O followed by the addition of 12 cm/H2O of posi-tive end-expiratory pressure during mechanical ventila-

Figure 4. Optimal Body Position for Successful Intubation of Morbidly Obese Patients

Figure 5. Oxygen Desaturation in Morbidly Obese Patients


tion can increase intraoperative PaO2 but may result in hypotension that requires vasopressor support.37

Mechanical ventilation using pressure-controlled instead of volume-controlled ventilation results in improved ox-ygenation in MO patients.38 Table 9 summarizes various strategies for intraoperative ventilatory management while protecting against ventilator-induced lung injury.39

Safe positioning of obese patients may require a spe-cially designed operating table or 2 regular tables joined together. Standard-size operating tables have a maximum weight limit of approximately 200 kg, but operating tables with a weight maximum of 455 kg are available. Pressure sores, neural injuries, and rhabdomyolysis are more common in MO patients and patients with dia-betes.25 Special care should be given to positioning and padding pressure points before and throughout the surgi-cal process because changes in operating table position or surgical manipulation may cause body shifts.

As with all patients, invasive arterial monitoring may be considered for obese patients with concomitant car-diopulmonary disease. The conical shape of the upper arm may present difficulties in obtaining an accurate noninvasive blood pressure reading, and invasive moni-toring may be deemed necessary. To avoid inaccurate readings, appropriate cuff size includes a bladder that encircles a minimum of 75% of the upper arm circumfer-

ence or the entire arm.25 Comparable and accurate blood pressure readings can be obtained from the wrist or ankle with appropriately sized cuffs.

Patients may be admitted to the surgical suite with hypovolemia due to bowel preparation and preoperative fasting. In addition, obese patients are frequently receiv-ing antihypertensive medications that increase the po-tential for hypotension during induction. This potential, coupled with the propensity for postoperative acute renal failure, highlights the importance of fluid replacement. Because of higher blood volumes in MO patients, abso-lute values calculated for fluid requirements during bar-iatric surgery may seem high (eg, 4-5 L). Regardless, the development of fluid overload is possible, and vigilance in monitoring volume status is imperative.

Delayed recovery from anesthesia may occur due to sequestration of lipid-soluble anesthetic drugs in MO patients. Special consideration should be taken to ensure the patient has fully recovered protective airway reflexes, adequate respirations, and complete muscle strength before extubation. In addition, placing the patient in the reverse Trendelenburg position improves alveolar re-cruitment and distention, decreases atelectasis, and may help to improve oxygenation throughout emergence.25

• Postoperative Management. Pathophysiologic changes in obese patients, along with coexisting diseases, affect

Table 9. Ventilatory Management of Morbidly Obese PatientsHOB indicates head of bed; CPAP, continuous positive airway pressure; FIO2, fractional inspired oxygen concentration; PEEP, positive end-expiratory pressure; BiPAP, bilevel positive airway pressure.(Adapted from Sprung et al.39)

Goal/recommendation Rationale/additional information

Prevent hypoxemia during induction HOB elevated (back-up Fowler or reverse Trendelenburg) 30° May increase the safe apnea period during induction Use of CPAP during induction Preoxygenate with 100% O2

Prevent/reverse atelectasis Restrict the use of FIO2 to < 0.8 during maintenance of anesthesia Use of a high FIO2 concentration during anesthesia accelerates

the onset and the amount of atelectasis.

Recruitment (“vital capacity”) maneuver after intubation by using Monitor for adverse effects (bradycardia, hypotension). sustained (8-10 seconds) pressure ≥ 40 cm/H2O

Maintain lung recruitment Use PEEP (10-12 cm/H2O) Monitor for hypotension or decreasing arterial oxygenation (PEEP-induced increase in pulmonary shunt fraction).

Avoid lung overdistension Use tidal volume of 6-10 mL/kg of ideal body weight

Keep peak-inspiratory pressure < 30 cm/H2O

Consider mild permissive hypercapnia if necessary

Maintain postoperative lung expansion Use CPAP or BiPAP immediately after tracheal extubation

Keep upper body elevated

Maintain good pain control

Use incentive spirometry

Encourage early ambulation

Increase the ventilation rate to control excessive hypercapnia instead of using large tidal volumes or high ventilatory pres-sures.


not only the intraoperative management but also the postoperative management. Early identification of com-plications is essential. Postoperative complications in MO bariatric surgical patients are derived from pathophysi-ologic changes due to obesity, coexisting diseases, and the surgical procedure.

The pulmonary changes in obese patients, such as increased chest wall resistance, decreased functional re-sidual capacity, and forced vital capacity, along with the effects of intraoperative mechanical ventilation result in a substantial incidence of postoperative atelectasis and hypoxemia. Therefore, optimizing oxygen administration by placing the patient in the head-up position increases functional residual capacity and decreases the work of breathing.

Patients who have obstructive sleep apnea are at increased postoperative risk for respiratory failure.40,41

ASA practice guidelines suggest that patients receiving continuous positive airway pressure or bilevel positive airway pressure preoperatively should receive it imme-diately postoperatively.41 These ventilatory support mo-dalities prevent alveolar collapse during expiration and allow alveolar recruitment during inspiration.40,42 They also act to displace the tongue and soft tissues, thereby preventing airway obstruction. Concerns that continu-ous positive airway pressure may cause gastric insuffla-tion and distention resulting in anastomotic failure have largely been discredited.43

The surgical approach for bariatric surgery also con-tributes to postoperative pulmonary complications. Open abdominal approaches reduce functional residual capac-ity and forced expiratory volume in 1 second more than laparoscopic approaches. In addition, they are also as-sociated with more postoperative pain than laparoscopic approaches, resulting in tachypnea, shallow breathing, and impairment of respiratory mechanics.42 Regardless of the surgical approach, inadequate postoperative pain management can lead to hypoxemia, hypercarbia, and atelectasis.44

Management of postoperative pain in MO patients is challenging. Morbidly obese patients have exaggerated respiratory depression from opioids. A multimodal ap-proach to postoperative pain may be superior. However, in patients with obstructive sleep apnea, the respiratory depressant effects are more pronounced; therefore, opioid-sparing techniques help avoid respiratory complications.41

Multimodal approaches to postoperative pain manage-ment include intravenous opioid administration based on ideal body weight, local anesthetics injected into the wound or port site, neuraxial anesthesia, and the use of nonsteroidal anti-inflammatory agents.45,46 Investigations have shown that an infusion of dexmedetomidine de-creases postoperative opioid requirements.8,45,46 Another current pain management alternative is the continuous intraperitoneal infusion of bupivacaine.47

Anastomotic leak is the most common cause of sur-gically related mortality in bariatric patients.48,49 Signs and symptoms of an anastomotic leak are listed in Table 10. These symptoms are often subtle and nonspecific, making early diagnosis difficult.49

Other physiologic changes associated with morbid obesity, such as greater blood volume, polycythemia, sedentary lifestyle, and venous stasis, increase the risk of deep venous thrombosis and pulmonary embolism. Consequently, pulmonary embolism is the second most common cause of mortality related to bariatric surgery.44,48

Postoperative signs and symptoms of pulmonary embolism include tachypnea, tachycardia, chest pain, hypoxemia, arrhythmias, and a feeling of “doom.”43

Differential diagnosis of pulmonary embolism may be challenging because many of these symptoms mimic a bowel leak.48

The anesthetic management for bariatric surgery pres-ents many challenges. These include managing comorbid conditions, airway management, oxygenation, fluid and medication calculation, and postoperative pain manage-ment. A thorough understanding of the pathophysiologic changes, pharmacology of weight-loss drugs and anes-thetic agents, and perioperative course will allow a high-quality, safe surgical experience.

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Unexplained tachycardia (sustained heart rate >120/min)

Shoulder pain (usually left)

Abdominal pain

Pelvic pain

Substernal pressure

Shortness of breath

Fever

Increased thirst

Hypotension

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Hiccups

Restlessness

Table 10. Signs and Symptoms of Anastomotic Leak


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AUTHORSJennifer Thompson, CRNA, MSN, is academic and clinical instructor at Kaiser Permanente School of Anesthesia/California State University Fuller-ton Department of Nursing, Pasadena, California. Email: Jen.l.thompson @kp.org.

Sandra Bordi, CRNA, MSN, is academic and clinical instructor at Kai-ser Permanente School of Anesthesia/California State University Fullerton Department of Nursing.

Michael Boytim, CRNA, EdD, is assistant director at Kaiser Perma-

nente School of Anesthesia/California State University Fullerton Depart-ment of Nursing.

Sass Elisha, CRNA, EdD, is assistant director at Kaiser Permanente School of Anesthesia/California State University Fullerton Department of Nursing.

Jeremy Heiner, CRNA, MSN, is academic and clinical instructor at Kaiser Permanente School of Anesthesia/California State University Ful-lerton Department of Nursing.

John Nagelhout, CRNA, PhD, FAAN, is director of Kaiser Permanente School of Anesthesia/California State University Fullerton Department of Nursing.

anesthesia case management for bariatric surgery - american

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