THE BARIATRIC SURGERY PATIENT
| ANESTHETIC IMPLICATIONS —Ashish C. Sinha, MD, PhD, Assistant Professor of Anesthesiology and Critical Care,
University of Pennsylvania School of Medicine, Philadelphia
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| Statistics: two-thirds of adult Americans overweight; 1 in 5 characterized as obese; 1 in 20 morbidly obese (>100 lb overweight);
≈120,000 bariatric surgery procedures performed in United States in 2005; two-thirds of bariatric surgeries done
in world done in United States
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| Obesity: body mass index (BMI) >30
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| Preoperative factors: cardiopulmonary status and airway; evaluation—systemic and pulmonary hypertension (HTN),
right and left heart failure, and ischemic heart disease; nutritional status (especially vitamin B12 , iron, calcium, and
folate) concern if patient returns to operating room (OR) after bariatric surgery; coagulation profile and electrolyte status
worrisome; vitamin K deficiency increases prothrombin time (PT) but partial thromboplastin time (PTT) normal (treat
with vitamin K or fresh frozen plasma)
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| Childhood obesity: 1 in 4 to 1 in 5 children obese; poor nutrition combined with obesity responsible for increasing incidence
of type 2 diabetes; obese children have HTN, diabetes, and abnormal lipid profiles; obesity and weight-related conditions
cause ≈300,000 preventable deaths (second leading cause of death)
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| Obesity-related conditions: type 2 diabetes; two thirds of coronary heart disease; 1 in 9 breast cancers (multiple etiologies;
ineffective mammography; estrogen and progesterone levels stimulate mammary tissue towards malignancy); 10%
of colon cancers; HTN; gout; osteoarthritis; cost to society—$100 billion annually
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| Medical treatment options: for those with BMI >30, or 27 to 30 with obesity-related medical complications; fenfluramine
and phentermine (Fen-phen; complicated by pulmonary HTN, taken off market); sibutramine—inhibits reuptake
of norepinephrine, serotonin, and dopamine, causing anorexia; Orlistat (Xenical)—lipase inhibitor; blocks digestion and
absorption of dietary fat
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| Surgical treatment: who qualifies—failure of medically supervised treatment (medical treatment program costs $7000
to $8000/yr); those with <5% to 10% weight loss with diet, exercise, or medical therapy or no change in comorbidities
(typically, 5%㪢% weight loss causes improvement in type 2 diabetes, HTN, and lipid profile); cost of surgery
≈$25,000
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| Comorbidities: obesity and depression go hand in hand; hepatic effects—majority have histologic abnormalities; elevated
liver function tests (LFTs), especially alanine aminotransferase (ALT; 1% decrease in weight loss improves
ALT by 8%); elevated LFT does not linearly correlate with ability of liver to metabolize drugs; renal effects—increased
renal blood flow and increased glomerular filtration rate; increased renal clearance of drugs; higher incidence
of proteinuria; cardiac effects—cardiac failure difficult to identify because of inability to detect signs (increased jugular
venous pressure [JVP]; additional heart sounds; peripheral edema; liver enlargement; pulmonary crackles); pulmonary
HTN—dyspnea, fatigue, and syncope (difficult to detect if patient does not get out of bed; unable to assess
cardiac output on exertion); echocardiography (ECG) with tricuspid regurgitation (TR), along with characteristic ECG
changes; more severe the TR, the better the correlation with ECG changes
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| Preoperative medications: need “everything,” except insulin and oral hypoglycemic agents; antibiotic prophylaxis;
anxiolytic (titrate to effect); analgesia; aspiration prophylaxis; deep venous thrombosis (DVT) prophylaxis
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| Positioning: special table (designed to hold up to 1000 lb) or 2 tables together if >450 lb; straps to hold patients during
tilting of table; bean bag if possible; pressure areas (brachial plexus and sciatic) need protection (document steps taken)
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| Pneumoperitoneum: usually with CO2 ; worsens in Trendelenburg position; systemic vascular resistance (SVR) increases
with intra-abdominal pressure (IAP); if IAP <10 mm Hg—get splanchnic squeeze (increased venous return, cardiac
output, and blood pressure [BP]); if IAP >20 mm Hg—get compression of inferior vena cava (IVC; decreased
venous return, cardiac output, and BP); femoral vein compression
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| Monitors: arterial monitoring if super morbidly obese (BMI >50), cuff difficult to apply, patient has cardiopulmonary
disease, and preoperative arterial blood gases used to guide maintenance and extubation; place central line if peripheral
access difficult; pulmonary artery catheter if serious cardiopulmonary disease present
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| Induction and intubation: difficult airway—prepare for it; towel placed under shoulder and head; surgeon present
ready for tracheostomy; Brodsky regression modeling—difficulty of intubation increases as neck size increases; 1-cm increase
in neck circumference increases odds of problematic intubation by 1.13; 40-cm neck circumference implies 5%
probability of difficult intubation (60 cm, 35%)
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| Medication dosing: lipophilic substances (eg, barbiturates, benzodiazepines) have increased volume of distribution;
remifentanil, digoxin, and procainamide exceptions; for medications with little lipophilicity, dose by ideal body weight or
lean body mass; volatile anesthetic—desflurane potential anesthetic of choice because of rapid and consistent recovery
profile; study—compared desflurane, propofol, and isoflurane; found that immediate recovery (eye opening, time to extubation,
and stating of own name) faster and more consistent with desflurane than with propofol or isoflurane; pulse
oximeter reading significantly higher, patients less sedated, and more mobile when admitted to postanesthesia care unit
with desflurane; psychometric testing, discharge time, nausea and vomiting, and pain scores similar between groups;
study—compared sevoflurane and desflurane; found fewer episodes of hypotension with desflurane; equivalent times to
spontaneous breathing; eye opening, extubation, airway maintenance, and orientation sooner in desflurane group
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| Trendelenburg position: abdominal contents displace diaphragm cephalad; endotracheal tube potentially displaced into
bronchial main stem; hypoxemia and hypercarbia possible because of ventilation and perfusion (.V/.Q) mismatch; fiberoptic
scope needed to adjust tube; air embolism and pneumothorax concerns
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| Neuromuscular blockade: complete relaxation necessary for ventilation and space for surgical visibility and manipulation;
collapse of pneumoperitoneum implies less than ideal relaxation
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| Ventilation: tidal volumes (TVs) of 15 mL/kg to 20 mL/kg thought to improve functional reserve capacity (FRC); in
these patients, FRC greater than closing volume, but oxygenation not improved significantly; study looking at larger TVs
on oxygenation and ventilation in morbidly obese people (up to 22 mL/kg) found increase in peak inspiratory pressure,
end expiratory airway pressure, and compliance without increase in PaO2 , causing severe hypocapnia and increasing risk
for trauma; TVs >13 mL/kg ideal body weight confer no added advantage; moderate positive end expiratory pressure
(PEEP) preferable (PEEP of 8 to 10 mm Hg, TV of 10 to 12 mL/Kg, and rate of 12 to 14/min); start with these and
change as necessary
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| Fluid requirements: usually larger than predicted; concern with acute tubular necrosis; 4 to 5L of fluid potentially required
for 2-hr procedure
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| Postoperative: continuous positive airway pressure (CPAP) recommended (50% of patients have atelectasis after surgery);
study showed respiratory dysfunction significantly reduced if patient given 12 cm of inspiratory pressure and 4 cm
of expiratory pressure with bi-level positive airway pressure (BiPAP); pain control—thoracic epidural with local anesthetic
with or without narcotics probably ideal (safe; effective; intrathecal option; decreases DVT; helps intestinal recovery;
decreases O2 consumption; decreases left ventricular stroke work); if unable to do thoracic epidural, use intravenous
patient controlled analgesia (IV PCA) and local infiltration
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| WHAT SHOULD BE INCLUDED IN A PREOPERATIVE ASSESSMENT ?—Michael H. Wall, MD, Associate Professor,
Vice Chairman, and Clinical Affairs Director, Cardiothoracic Anesthesia, ST “Buddy” Harris Distinguished Chair of
Cardiothoracic Anesthesiology, Department of Anesthesiology and Pain Management, University of Texas Southwestern
Medical Center, Dallas
|
| Definition: World Health Organization (WHO) classification; overweight—BMI of 25 to 29.9; Class I (obese)—BMI
of 30 to 34.9; Class II (morbidly obese)—BMI of 35 to 39.9; Class III (super obese)—BMI >40
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| Comorbid disease: depression may play role postoperatively in obese patients; obesity increases risk for diabetes, HTN,
coronary artery disease (CAD); being 30% overweight confers 40% increased chance of dying from heart disease and
50% increased chance of dying from stroke; in perioperative period, obesity associated with increased resource utilization
throughout hospital stay; some studies show higher perioperative morbidity and some do not (related to type of surgical
procedure and degree of obesity); obesity increases risk for severe complications (death, myocardial infarction, and
stroke) after gynecologic, orthopedic, urologic, and transplant surgeries; controversy exists about whether obesity independent
risk factor for adverse outcome after cardiac surgery; across all surgical disciplines and procedures, obesity increases
risk for perioperative wound infection (degree of obesity correlates with risk)
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| Obesity and outcome after surgery: study (2001)—large retrospective study of obese patients (BMI >35) vs nonobese
patients, who underwent gynecologic, orthopedic, general surgery, and otolaryngologic day surgery; showed no
difference in nausea, pain, and vomiting, no increase in bleeding, no increased unplanned admissions, and no increase in
unplanned contact with health care workers; study (2003)—elective general surgery; 6000 patients (800 obese, 500
mildly obese, and 200 severely obese); groups excluded vascular, thoracic, bariatric, and transplant surgery patients;
study showed no increase in mortality, but increase in wound infections
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| Preoperative testing: American Society of Anesthesiologists (ASA) practice advisory (2002) described “routine test”
as test ordered on everyone in absence of medical condition, and “indicated test” as test ordered for someone with specific
condition; no routine testing recommended, just indicated testing; study showed having patients attempt to lose
weight before surgery ineffective
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 | Airway: obese patients at increased risk for difficult intubation and difficult mask airway; increased risk for rapid desaturation
during airway manipulation; physical examination important looking at range of motion; check for history of obstructive
sleep apnea (OSA) or obesity hyperventilation syndrome (OHS)
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| Pulmonary: risk for hypoxemia (low resting lung volume and early airway closure resulting in worsening V/Q mismatch,
coupled with decreased FRC [often lower than closing volume], leads to hypoxemia; V/Q mismatch and low airway
volume become worse when supine and even more so when supine during mechanical ventilation); hypoventilation—
another cause of hypoxemia in postoperative period; decreased time of “safe apnea”; pulmonary function tests
(PFTs)—marked changes in obese patients (effective residual volume 40% decreased; if anesthetized, supine, and
mechanically ventilated, becomes 50% worse); marked increase in airway resistance (chest wall compliance issues);
forced expiratory volume in 1 sec (FEV1 ) or maximum voluntary ventilation significantly decreased in obese patient;
significant changes in PaO 2 due to positioning and having surgery; OSA—occurs in 40% of obese women and 70% of
obese men; no breathing problems during day; at night, have snoring, interrupted breathing, nighttime events, daytime
sleepiness (sleep fragmentation; lack of rapid eye movement cycle), and morning headache and irritability; sleep partner
good source of history; episodic asphyxia—leads to increase in sympathetic activity, increased lipid and catecholamine
levels, and increased platelet activation; chronic recurring asphyxia—patient becomes hypoxemic and
hypercarbic, leading to pulmonary hypertension, right ventricular (RV) overload, increased left ventricular (LV) afterload,
decreased LV stroke volume, and decreased cardiac output; OHS—chronic daytime hypoventilation; partial
pressure of carbon dioxide (PCO 2 ) >45 mm Hg; associated with hypoxemia (PaO 2 <65 mm Hg or O2 saturation
<96%); potentially exclusive from sleep-disordered breathing; incidence increases in OSA and OHS with increase in
BMI; hypoxemia and hypercarbia during day leads to same problems as asphyxia at night; Pickwickian syndrome triad
of obesity, hypersomnolence during day, and associated RV failure; CPAP and BiPAP improve long-term sequelae of
OSA and OHS; no prospective trials looking at delaying surgery for BiPAP or CPAP prior to surgery in obese patients
(takes weeks for BiPAP to improve systemic problems of asphyxia); PFTs—obtain room air O2 saturation; other PFTs
indicated only if other reversible disease present
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| Cardiac: obesity associated with HTN, LV hypertrophy, pulmonary HTN, and RV hypertrophy; work-up of patients with
concomitant cardiovascular disease should follow American College of Cardiology/ American Heart Association
(ACC/AHA) guidelines (revised 2006)
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| Gastrointestinal (GI): obesity associated with reflux (increased volume and acidity of gastric contents), liver abnormalities
(increased risk for cirrhosis; check LFTs in patients presenting for surgery); drug selection (cimetidine decreases
pH and gastric volume if given before surgery)
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| Metabolic, endocrine, and renal: diets; diuretic use; electrolyte abnormalities; increased risk for diabetes and dyslipidemia;
electrolyte panel and renal function tests
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| DVT: pulmonary embolism (PE) most significant cause of 30-day mortality after bariatric surgery; preoperative prophylaxis
recommended or at worst, given intraoperatively; Seventh American College of Chest Physicians (ACCP) Conference
stated risk factors for PE in DVT include obesity, surgery, cancer, previous venous thromboembolic disease,
age >40 yr, birth control pills with estrogen, acute illness, smoking, varicose veins, central line placement, and immobility
or paresis; those considered high-risk include patients having surgery at >60 yr of age and patients having surgery
at >40 yr of age and with 1 risk factor; most obese patients in high-risk category for risk for PE in surgery;
prophylaxis recommended for these patients consists of low-dose unfractionated heparin (LDUH) q8h or low molecular
weight heparin (LMWH) or intermittent compression stockings; highest risk if multiple risk factors present (most
obese patients have multiple risk factors and should receive LMWH); other options warfarin (Coumadin) or compression
stockings and LDUH
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| Musculoskeletal: associated with degenerative joint disease (DJD), low back pain, and increased risk for ulnar neuropathy;
history and careful positioning important
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| Super obese: special OR tables or 2 tables; potentially need longer central line; hospital beds, stretchers, wheelchairs,
and toilets have weight limits (500 lb)
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Suggested Reading
Akbay BK, et al: Anaesthetic management of an extremely obese woman undergoing open gastric bypass. Eur J Anaesthesiol
23:983, 2006; Ali MR, et al: Assessment of obesity-related comorbidities: a novel scheme for evaluating bariatric
surgical patients. J Am Coll Surg 202:70, 2006; Banerjee D, et al: Obesity hypoventilation syndrome: hypoxemia during
continuous positive airway pressure. Chest 131:1678, 2007; Cartagena R: Preoperative evaluation of patients with
obesity and obstructive sleep apnea. Anesthesiol Clin North America 23:463, 2005; Chalhoub V, et al: Effect of vital
capacity manoeurvres on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery. Eur J Anaesthesiol
24:283, 2007; Cuvelier A, Muir JF: Obesity-hypoventilation syndrome and noninvasive mechanical ventilation:
new insights in the Pickwick papers? Chest 131:7, 2007; Ebert TJ, et al: Perioperative considerations for patients
with morbid obesity. Anesthesiol Clin 24:621, 2006; Leykin Y, et al: Anesthetic management of morbidly obese and super-morbidly
obese patients undergoing bariatric operations: hospital course and outcomes. Obes Surg 16:1563, 2006;
Mertens E: Anesthesia for bariatric surgery. Acta Anaesthesiol Belg 57:387, 2006; Mokhlesi B: Positive airway pressure
titration in obesity hypoventilation syndrome: continuous positive airway pressure of bilevel positive airway pressure.
Chest 131:1624, 2007; Quint JK, et al: Previously undiagnosed obesity hypoventilation syndrome. Thorax 62:462,
2007; Saravanakumar K, et al: The challenges of obesity and obstetric anaesthesia. Curr Opin Obstet Gynecol
18:631, 2006; Servin F: Ambulatory anesthesia for the obese patient. Curr Opin Anaesthesiol 19:597, 2006; Setzer N,
et al: Childhood obesity and anesthetic morbidity. Paediatr 17:321, 2007; Thurnheer R: Obstructive sleep apnea and
cardiovascular disease—time to act! Swiss Med Wkly 137:217, 2007; Vallejo MC, et al: Desflurane versus sevoflurane
for laparoscopic gastroplasty in morbidly obese patients. J Clin Anesth 19:3, 2007; Wolf J, et al: Obstructive sleep apnea:
an update on mechanisms and cardiovascular consequences. Nutr Metab Cardiovasc Dis 17:233, 2007.
Educational Objectives
The goal of this program is to educate the listener about anesthesia implications in bariatric surgery and preoperative assessment
in the obese patient. After hearing and assimilating this program, the clinician will be better able to:
| 1. Discuss the classification of obese patients.
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| 2. Recognize the effects of obesity on different systems of the body.
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| 3. Choose the appropriate anesthesia option for the obese patient.
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| 4. Perform an adequate preoperative evaluation of the obese patient.
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| 5. Determine the unique needs of a super-obese patient as they pertain to surgery and hospital stay.
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Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue, the faculty
reported nothing to disclose.
Acknowledgements
Dr. Sinha was recorded at the 57th Annual Postgraduate Symposium of Anesthesiology, held April 13-15, 2007, in
Kansas City, MO, and sponsored by University of Kansas Medical Center, Department of Anesthesiology and University
of Kansas Medical Center Continuing Education. Dr. Wall was recorded at the American Society of Anesthesiologists
Annual Meeting, held October 14-18, 2006, in Chicago, IL. The Audio-Digest Foundation thanks the
speakers and the sponsors for their cooperation in the production of this program.
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