Anestesia en Cirugia Bariatricax

8/11/2019 Anestesia en Cirugia Bariatricax

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AANA Journal CourseUpdate for Nurse Anesthetists

Anesthesia Case Management for BariatricSurgery

Jennifer Thompson, CRNA, MSN

Sandra Bordi, CRNA, MSN

Michael Boytim, CRNA, EdD

Sass Elisha, CRNA, EdD

Jeremy Heiner, CRNA, MSN

John Nagelhout, CRNA, PhD, FAAN

Objectives

At the completion of this course, the reader should beable to:

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

2. Discuss commonly used weight-reduction drugsand 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 obesepatients.

5. Identify the postoperative complications associated

with bariatric surgery.

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

Obesity Task Force, more than 1.7 billion people are

overweight or obese. Decreased physical activity andoverconsumption of high-fat foods are the main con-tributing factors to the obesity epidemic. Conservativeinterventions to the treatment of obesity include earlyeducation, low-calorie diet, increased physical activity,and, sometimes, medications. However, these treatmentsare not always effective, and many obese people undergobariatric surgical procedures. There is a myriad of an-esthesia challenges associated with these surgeries. Athorough understanding of the anesthetic considerationsis essential to facilitate positive outcomes for the patients.

Pathophysiologic Changes of Obesity

Obesity is commonly associated with a variety of co-morbidities, including diabetes, cardiovascular disease,endocrinopathies, and osteoarthritis (Figure 1).1 Themechanisms underlying these complications are complexand most often are interrelated.

*AANA Journal Course No. 31 (Part 1):AANA Journalcourse 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 thepathophysiologic 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.

www.aana.com/aanajournalonline.aspx AANA JournalApril 2011 Vol. 79, No. 2 147


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148 AANA JournalApril 2011 Vol. 79, No. 2 www.aana.com/aanajournalonline.aspx

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


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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 forcoronary artery disease (CAD) and experiencing majorcardiovascular events. Although each component is rec-ognized as an individual risk factor, the clustering of theserisk factors puts a patient at an even greater surgical risk.2

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

Concentric ventricular hypertrophy, which developsover 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 andhepatic failure. Nonalcoholic steatohepatitis often occursin obese children. Cholelithiasis is 6 times more commonin people who are obese as in normal-weight people.3

Formation of gallstones also occurs at a higher rate dueto the increase in the total body cholesterol level andgreater biliary cholesterol excretion.4

Commonly occurring respiratory abnormalitiesinclude Pickwickian syndrome, obstructive sleep apnea,decreased functional residual capacity, and increasedclosing capacity, which all contribute to atelectasis andrapidly occurring hypoxemia.1These respiratory changesmay also lead to polycythemia and cor pulmonale.

Obesity predisposes to osteoarthritis. Increased bodyweight stresses bones and joints, and this condition isespecially common in elderly people. An increased riskof 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 causedby increased estrogen levels.5

Pharmacology of Obesity-Related Drugs andof Anesthetics

Antiobesity Medications. Medications that promoteweight loss have limited efficacy. Despite the enormouspotential market, efforts to develop effective drug thera-pies have been disappointing. The US Food and DrugAdministration guidance for long-term weight-loss drugsrecommends that a 5% weight reduction be maintained

for 12 months after treatment initiation. Two drugs areavailable 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). Whenused in combination with a comprehensive weight-lossprogram, they can occasionally be effective in producingweight 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 recentlybeen released as an over-the-counter medication. Sideeffects are minor and mostly related to gastrointestinaldiscomfort (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 effectslimit its usefulness. Several antidepressant, antiepileptic,and antidiabetic drugs may promote weight loss and areused off-label for this indication.6,7

Anesthesia Drugs and Obesity.Obesity causes physi-ologic changes that can affect the pharmacokinetics andpharmacodynamics of anesthetic agents. An overview ofthese changes is given in Table 2. The common approachto anesthetic drug administration is to dose water-solubledrugs according to ideal body weight and lipid-solubledrugs according to total body weight. Lean body mass in-

creases approximately 20% to 40% in obesity, so adding30% to the ideal body weight is a convenient dose adjust-ment. Table 3 shows weight calculations commonly usedfor the dosing of medications.

Contradictory results from individual drug studies insmall patient groups are common; therefore, specific rec-ommendations are frequently conflicting. A few generalobservations can be made. Postoperative respiratorydepression 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 aeffects possible; contraindicated in poor risk-benefit ratio

hypertension and diabetes

Table 1. Pharmacotherapy for Obesity


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allow for fast recovery. The inhalation agents desfluraneand sevoflurane produce excellent recovery profiles inobese patients. Although desflurane is less soluble thansevoflurane, clinical differences are minimal. Nitrousoxide can be safely used in patients in whom a require-ment for high oxygen concentrations does not preclude

its administration. Succinylcholine doses for intubationare given according to total body weight to ensure excel-lent intubating conditions, whereas the nondepolarizingmuscle relaxants used for operative maintenance aregiven according to ideal body weight. Use of a nervestimulator to guide relaxant administration assists inminimizing residual paralysis and reversal concerns.Remifentanil infusion is an especially popular analge-sic because of the drugs titratability and rapid offsetand 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 arelisted in Table 4.

Surgical Procedure

Because of the epidemic proportions of obesity withinthe United States, the number of bariatric surgical pro-cedures performed each year has increased. Bariatricsurgical programs mandate that before surgery, patientsparticipate in lifestyle modifications to lose weight andlearn how to incorporate healthy choices into daily life.It has been demonstrated that preoperative weight lossdecreases all of the complications associated after laparo-scopic gastric bypass.9Psychologists, dieticians, physicaltherapists, 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 = 0.8TBW 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 off-

set requires planning for postoperative analgesia.

Dexmedetomidine Infusion rates of 0.2 g/kg/min Useful as an adjunct. Lower than usual infusion

rates are recommended to minimize adverse

cardiac side effects.


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to change their habits and behaviors that contribute toobesity. Furthermore, medical optimization of the pa-tients coexisting morbidities is essential before surgicalintervention.

There are several variations related to the surgicalprocedures that can be performed. Presently, the mostcommon surgical approach for bariatric surgery is lapa-roscopy. Furthermore, there is a decrease in the morbid-

ity and mortality associated with laparoscopic gastricbypass with robotic assistance.10 The goal of bariatricsurgery is to reduce the patients 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 fromthe gastrointestinal tract (mixed restrictive and malab-sorptive procedure).11 Operative mortality ( 30 dayspostoperatively) is estimated to be approximately 0.1%for restrictive procedures and 1% for mixed restrictiveand malabsorptive procedures.12 The most commontypes of bariatric surgical procedures are laparoscopicadjustable 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 creationof a gastric pouch. The procedure involves making a holein the middle of the body of the stomach. Stapling of thestomach from the superior aspect of the fundus to thenewly created hole is accomplished. The surgeon thenfashions a tissue band through the hole that surroundsthe remainder of the gastric body near the esophago-

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

Vertical banded gastroplasty was the most popularsurgical intervention for bariatric surgery from the mid1980s until the early 1990s. Disadvantages to verticalbanded gastroplasty include difficulty eating foods that

are high in protein, which facilitates the consumptionof soft calorie-dense foods, gastroesophageal reflux, andabdominal discomfort. Patients would frequently regainweight, and only 26% were satisfied with the result ofthe surgery.12

Laparoscopic Adjustable Gastric Banding (LAGB)has become a popular alternative to more invasive mal-absorptive surgical procedures and is one of the mostcommon restrictive weight-loss surgeries performed inthe United States. This system offers 2 distinct advan-tages compared with vertical banded gastroplasty: Thetension on the band is adjustable, and the system isremovable. Laparoscopic adjustable gastric banding is

associated with a shorter duration of hospitalization, de-creased pulmonary complications, and overall decreasedmorbidity and mortality compared with other bariatricsurgical options.13 There are several adjustable bands,including Lap Band (Alleran Inc, Irvine, California),Realize Adjustable Gastric Band (Ethicon Endo-SurgeryInc, Cincinnati, Ohio), and the Swedish adjustable gastricband. The gastric band is placed immediately distal to thegastroesophageal junction. An illustration of the LAGB isshown in Figure 2B. Contained within the silicone band,

Figure 2. Restrictive Bariatric Surgical ProceduresA. Vertical banded gastroplasty

B. Laparoscopic adjustable gastric band

C. Sleeve gastrectomy


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a balloon is inflated to decrease the size of the proximalaspect of the stomach. The balloon is inflated with salinevia an access port that is positioned subcutaneously. Thepouch that is created holds approximately 100 to 200 gof food. Distention of the pouch causes satiety resultingfrom afferent sensory and visceral neural innervation.

Identification of patients who are ideal candidates forLAGB improves the postoperative percentage of weightloss. 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.14It has been demonstrated that weightloss with LAGB frequently results in complete resolutionor improvement of type 2 diabetes, hypertension, anddyslipidemia.15The indications and contraindications forhaving LAGB are included in Table 5.14

Numerous potential complications are associated withLAGB surgery. An analysis of 7 years of data from 2,909patients related to the safety of the LAGB includes the

following complications and frequencies: band slippage,4.5%; port-related problems, 3.3%; and reoperation forweight gain, 0.4%. One or more of these complicationswere experienced by 12.2% of patients.12 The overallincidence of erosion of the stomach under the gastricband is 1.96%. Postoperative mortality within 30 days orfewer is approximately 0.06% to 0.1%.12,16A rare com-plication called Barrett esophagus can occur after LAGB.Barrett esophagus occurs due to chronic gastroesophagealreflux, which causes esophageal erosion and predisposes

patients to malignant changes. The overall incidence isunknown; however, cellular dysplasia and esophagealadenocarcinoma that is related to gastroesophageal refluxdisease can occur after gastric banding.17 A compre-hensive list of complications associated with LAGB areincluded in Table 6.12

Sleeve Gastrectomy is accomplished by decreasingthe size of the stomach to approximately 20% of itsoriginal size by removing a substantial portion of thestomach. This procedure is most frequently performedlaparoscopically and involves resection of a substantialportion of the gastric fundus and body to create a tube-like opening from the gastroesophageal junction to the

pyloric valve. The reconstructed stomach ideally willhave 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 weightwithin 1 year.

Combined Restrictive and Malabsorptive Procedures.Roux-en-Y gastric bypass (RYGB) is the most commoncombined restrictive and malabsorptive form of gastricbypass surgery in the United States. The NationalInstitutes 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 procedures

Bowel obstruction

Wound dehiscence

Leakage and/or ulcers at the sites of anastomosis

Nutritional deficiency

Incisional hernia

Gastrojejunostomy stenosis

Potential complications of both types ofprocedures

Hemorrhage

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 OBrien.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 restrictionsAcceptable 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


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fective surgical treatment for obesity is RYGB.19 Theprocedure is frequently accomplished via a laparoscopicapproach with or without robotic assistance, and thereare a number of variations of this technique.10A smallgastric pouch (15-20 mL) is constructed from the cardiaportion of the stomach near the gastroesophageal junc-

tion and restricts the amount of food that the patientcan eat at one time. The pouch is attached to the distalduodenum and becomes the Roux limb or alimentarylimb, where food and fluids travel and are absorbed.The biliopancreatic limb is formed proximally from theduodenum, and the distal resected end is anastomosed tothe ileum to form a common small intestinal limb. Thisprocedure is illustrated in Figure 3A.

A polypeptide called ghrelin is primarily secreted bythe stomach and small intestine. When secreted, thishormone stimulates appetite. Since removal of variousportions of the stomach and duodenum occurs as partof malabsorptive procedures for obesity, another mecha-

nism of weight loss is associated with decreased plasmaghrelin levels. It has been demonstrated that ghrelinvalues are up to 47% lower in patients who have under-gone the RYGB procedure compared with equally obesenonsurgical patients.20

There has been substantial interest in which bariatricsurgical 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 weightloss is less variable and consistently greater with the

RYGB.18,21 Reversal of comorbidities is greatest afterLAGB. Perioperative complications were more likely tooccur during RYGB than during LAGB, but long-termreoperation rates were lower and patient satisfaction washigher with the RYGB gastric bypass procedure.21Adamsand colleagues22determined that the long-term mortality

after RYGB is decreased from any cause and from diseasesspecifically attributed to obesity. A list of bariatric surgi-cal procedures and the percentage of excess body weightlost 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 distaland 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 ofthe abdominal cramping and nausea associated with this

phenomenon varies from mild to severe. This side effectis more common after gastric bypass compared withLAGB. Treatment includes medications such as acarbose(Precose, Bayer Corp, West Haven, Connecticut) orsurgical reintervention. A comprehensive list of compli-cations associated with malabsorptive bariatric surgicalprocedures is listed in Table 6.12

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

Figure 3. Mixed Restrictive and Malabsorptive Bariatric Surgical ProceduresA. Roux-en-Y gastric bypass

B. Biliopancreatic diversion with duodenal switch


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to the gastric pouch, completely bypassing the duode-num and jejunum (alimentary limb). The distal portionof the biliopancreatic limb is then reconnected 100 cmfrom the ileocecal valve.18 Thus, in addition to beingrestrictive due to the gastric sleeve, the now substantiallyshorter small intestine offers less intestinal surface areafor absorption to occur. A representation of this proce-dure is shown in Figure 3B.

Biliopancreatic diversion with duodenal switch ismost often performed for patients who are described assuperobese (BMI 55 kg/m2). Prachand and colleagues23

determined that excess body weight loss of more than50% was achieved in 83.9% of patients having biliopan-creatic diversion with duodenal switch and 70.4% withRoux-en-Y 1 year postoperatively.

The development of gallstones commonly occurs aftergastric bypass procedures, and some surgeons perform acholecystectomy simultaneously. Inadequate absorptionof proteins, iron, calcium, and fat-soluble vitamins (A, D,E, and K) can occur, and multivitamin supplementationis recommended.18

A new procedure under investigation to determine thesafety and efficacy in treating obesity is an implantablegastric stimulator. A pulse generator the size of a cardiacpacemaker is implanted on the surface of the stomach.The afferent impulses that are sensed by the brain allowthe person to feel satiated. In the future, as new surgicaltechniques, technological advances, and the discoveryof new medications occur, the treatment of obesity willbecome 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 healthconcerns. Many bariatric surgical candidates have alreadybeen diagnosed and medically managed for comorbidconditions by their primary care physicians; therefore,the additional need to perform extensive diagnostic testsis minimal. A candid discussion between the surgeonand patient regarding realistic expectations, lifestylealterations, diet modifications, and exercise is neces-sary. Common criteria for bariatric surgery include the

following: a BMI of 40 kg/m2or more or of 35 kg/m2ormore with comorbid conditions, failure of nonoperativeweight-loss efforts, absence of contraindications, and awell-informed, compliant, and motivated patient with agood support system.24 Absolute contraindications forbariatric surgery include a lack of understanding of the

procedural risks, severe liver disease with accompany-ing portal hypertension, uncontrolled severe obstructivesleep apnea with pulmonary hypertension, and unstableor terminal illness.25

A thorough history and physical examination, vitalsigns, baseline laboratory studies, and informed consentshould be obtained during the initial assessment, and,if needed, referral to and consultation with appropriatesubspecialties should be accomplished. Risk identifica-tion and risk reduction should be priorities that can assistin the identification of appropriate surgical candidates.The Obesity SurgeryMortality 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/m2or more2. Male gender3. Hypertension4. Risk for pulmonary embolism (history of venous

thromboembolism, pulmonary hypertension, and/orobesity 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 orhigh 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.26A primary goal of the preoperative assessment is treat-

ment and optimization of comorbid conditions. Obesepatients frequently have comorbid conditions such ashypertension, CAD, diabetes, venous thromboembolism,and/or obstructive sleep apnea. Patients referred to cardi-ology for suspicion of CAD should undergo an exerciseor dobutamine stress echocardiogram to evaluate cardiacfunction.25Bariatric surgery can be safely performed onpatients with known CAD without major increases inperioperative mortality and cardiac complications, pro-vided the patients have been thoroughly evaluated andappropriately managed.27

Patients suspected of having obstructive sleep apneashould undergo polysomnography and receive treatmentpreoperatively and throughout the perioperative period.Treatment modalities include continuous positive airwaypressure, noninvasive positive-pressure ventilation, andbilevel positive airway pressure.24,28Pulmonary functionshould 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)


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lenge is especially important when considering the nega-tive pulmonary effects of the pneumoperitoneum duringbariatric surgery. Complete muscle relaxation is crucialduring these procedures to facilitate ventilation andprevent collapse of the pneumoperitoneum. Numerousstrategies to maintain intraoperative oxygenation andlung volumes in MO patients have been recommended.The use of high tidal volumes, alveolar recruitmentmaneuvers, positive end-expiratory pressure, and high

oxygen concentrations have been studied extensively, andnone are conclusively superior. Increasing tidal volumesmore than 13 mL/kg in MO patients has been found toincrease peak inspiratory pressures and end-expiratoryairway pressures but does not substantially improvearterial oxygen tension.36 When compared with thesupine position, the use of a 30 reverse Trendelenburgposition during bariatric surgery reduces the alveolar-to-arterial oxygen difference, increases total ventilatorycompliance, and reduces peak airway pressures. Alveolar

recruitment by repeated sustained lung inflation to 50cm/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


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

Mechanical ventilation using pressure-controlled instead

of volume-controlled ventilation results in improved ox-ygenation in MO patients.38Table 9 summarizes variousstrategies for intraoperative ventilatory managementwhile protecting against ventilator-induced lung injury.39

Safe positioning of obese patients may require a spe-cially designed operating table or 2 regular tables joinedtogether. Standard-size operating tables have a maximumweight limit of approximately 200 kg, but operatingtables with a weight maximum of 455 kg are available.Pressure sores, neural injuries, and rhabdomyolysis aremore common in MO patients and patients with dia-betes.25Special care should be given to positioning andpadding pressure points before and throughout the surgi-

cal process because changes in operating table position orsurgical manipulation may cause body shifts.

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

ence or the entire arm.25Comparable and accurate bloodpressure readings can be obtained from the wrist or anklewith appropriately sized cuffs.

Patients may be admitted to the surgical suite withhypovolemia due to bowel preparation and preoperativefasting. 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 renalfailure, 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, thedevelopment of fluid overload is possible, and vigilancein monitoring volume status is imperative.

Delayed recovery from anesthesia may occur due to

sequestration of lipid-soluble anesthetic drugs in MOpatients. Special consideration should be taken to ensurethe patient has fully recovered protective airway reflexes,adequate respirations, and complete muscle strengthbefore extubation. In addition, placing the patient in thereverse Trendelenburg position improves alveolar re-cruitment and distention, decreases atelectasis, and mayhelp to improve oxygenation throughout emergence.25

Postoperative Management. Pathophysiologic changesin 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 FIO

2to < 0.8 during maintenance of anesthesia Use of a high FIO

2concentration during anesthesia acceleratesthe 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.


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

The pulmonary changes in obese patients, such asincreased chest wall resistance, decreased functional re-sidual capacity, and forced vital capacity, along with theeffects of intraoperative mechanical ventilation result ina substantial incidence of postoperative atelectasis andhypoxemia. Therefore, optimizing oxygen administrationby placing the patient in the head-up position increasesfunctional residual capacity and decreases the work ofbreathing.

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

ASA practice guidelines suggest that patients receivingcontinuous positive airway pressure or bilevel positive

airway pressure preoperatively should receive it imme-diately postoperatively.41These ventilatory support mo-dalities prevent alveolar collapse during expiration andallow alveolar recruitment during inspiration.40,42Theyalso act to displace the tongue and soft tissues, therebypreventing airway obstruction. Concerns that continu-ous positive airway pressure may cause gastric insuffla-tion and distention resulting in anastomotic failure havelargely been discredited.43

The surgical approach for bariatric surgery also con-tributes to postoperative pulmonary complications. Openabdominal 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 laparoscopicapproaches, resulting in tachypnea, shallow breathing,and impairment of respiratory mechanics.42 Regardlessof the surgical approach, inadequate postoperative painmanagement can lead to hypoxemia, hypercarbia, andatelectasis.44

Management of postoperative pain in MO patients ischallenging. Morbidly obese patients have exaggeratedrespiratory depression from opioids. A multimodal ap-proach to postoperative pain may be superior. However,in patients with obstructive sleep apnea, the respiratorydepressant effects are more pronounced; therefore, opioid-

sparing techniques help avoid respiratory complications.41Multimodal approaches to postoperative pain manage-

ment include intravenous opioid administration basedon ideal body weight, local anesthetics injected into thewound or port site, neuraxial anesthesia, and the use ofnonsteroidal anti-inflammatory agents.45,46Investigationshave shown that an infusion of dexmedetomidine de-creases postoperative opioid requirements.8,45,46Anothercurrent pain management alternative is the continuousintraperitoneal infusion of bupivacaine.47

Anastomotic leak is the most common cause of sur-

gically related mortality in bariatric patients.48,49

Signsand symptoms of an anastomotic leak are listed in Table10. These symptoms are often subtle and nonspecific,making early diagnosis difficult.49

Other physiologic changes associated with morbidobesity, such as greater blood volume, polycythemia,sedentary lifestyle, and venous stasis, increase the riskof deep venous thrombosis and pulmonary embolism.Consequently, pulmonary embolism is the secondmost common cause of mortality related to bariatricsurgery.44,48

Postoperative signs and symptoms of pulmonaryembolism include tachypnea, tachycardia, chest pain,

hypoxemia, arrhythmias, and a feeling of doom.43Differential diagnosis of pulmonary embolism may bechallenging because many of these symptoms mimic abowel leak.48

The anesthetic management for bariatric surgery pres-ents many challenges. These include managing comorbidconditions, airway management, oxygenation, fluid andmedication calculation, and postoperative pain manage-ment. A thorough understanding of the pathophysiologicchanges, 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

Unexplained oliguria

Hiccups

Restlessness

Table 10. Signs and Symptoms of Anastomotic Leak


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AUTHORS

Jennifer Thompson, CRNA, MSN, is academic and clinical instructor atKaiser Permanente School of Anesthesia/California State University Fuller-ton Department of Nursing, Pasadena, California. Email: [email protected].

Sandra Bordi, CRNA, MSN, is academic and clinical instructor at Kai-

ser Permanente School of Anesthesia/California State University FullertonDepartment 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 PermanenteSchool of Anesthesia/California State University Fullerton Department ofNursing.

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

John Nagelhout, CRNA, PhD, FAAN, is director of Kaiser PermanenteSchool of Anesthesia/California State University Fullerton Department ofNursing.

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Anestesia en Cirugia Bariatricax