Anesthesia in Bariatric Surgery

1. Cardiovascular system

(a) Hypertension (both systemic and pulmonary)

(b) Atherosclerosis and hyperlipidemia

(d) Coronary artery disease

(e) Peripheral vascular disease and chronic venous insufficiency

2. Respiratory system

(a) Dyspnea (restrictive lung disease)

(b) Altered sleep disorders (obstructive sleep apnea, obesity hypoventilation syndrome)

3. Gastrointestinal system

(a) Hepatic steatosis and abnormal liver function tests

(b) Cholelithiasis

(d) Higher incidence of gall bladder cancer (females)

(e) Higher incidence of colon cancer (males)

4. Reproductive system

(a) Female infertility, disrupted menstruation, and ovulation

(b) Urinary incontinence

(d) Higher incidence of cervical, endometrial, ovarian, and breast cancer

(e) Higher incidence of prostate cancer

5. Endocrine system

(a) Type 2 diabetes mellitus

(b) Disorders of plasma cortisol and growth hormone

6. Musculoskeletal system

(a) Osteoarthritis (hips, knees)

(b) Hyperuricemia and gout

(d) Spinal column problems

7. Dermatologic system

(a) Acanthosis nigricans

(b) Fungal skin infections

8. Psychiatric

(a) Depression

(b) Low self-esteem

Increasing obesity is associated with pathophysiologic changes in all organ systems and with many associated medical co-morbidities. These conditions should be sought during the preoperative evaluation and should be optimized before surgery when possible

Table 11.2

Metabolic Syndrome (MetS)

1. Abnormal glucose metabolism (must be present)

(a) Diabetes mellitus

(b) Impaired glucose tolerance

Plus at least two of the following

2. Hypertension (blood pressure >140/90 mmHg)

3. Dyslipidemia:

(d) Triglycerides ≥1.695 mmol l⁻¹

(e) High-density lipoprotein cholesterol

(i) ≤0.9 mmol l⁻¹ (male)

(ii) ≤1.0 mmol l⁻¹ (female)

4. Central obesity: large waist; waist:hip ratio

(iii) >0.90 (male)

(iv) >0.85 (female)

5. Microalbuminuria

(f) Urinary albumin excretion ratio ≥2 min⁻¹

(g) Albumin:creatinine ratio 30 mg g⁻¹

Metabolic syndrome: World Health Organization (WHO) definition (1999)

Patients with the metabolic syndrome have a much greater incidence of serious medical problems than do patients of similar weight

Most obese patients, especially younger ones without serious medical co-morbidities scheduled for elective bariatric procedures, do not require an expensive and complex preoperative workup [1]. A comprehensive metabolic panel, a chest radiograph, and perhaps an EKG in older patients are usually all that need to be routinely obtained. Any patient who has had previous bariatric surgery should be evaluated for metabolic changes that can include protein, vitamin, iron, and calcium deficiencies. Patients with MetS, with sleep-disordered breathing problems, and with other significant cardiovascular conditions are of special concern, and when present may indicate the need for further diagnostic evaluation and perhaps consultation with a cardiologist, endocrinologist, or sleep physician.

The most common sleep-disordered breathing condition is obstructive sleep apnea (OSA). Patients maintain a normal PaCO₂ during the day but have CO₂ retention, sleep disturbances, intermittent airway obstruction with hypoxemia, and cardiac arrhythmias at night. OSA is characterized by frequent episodes of apnea (>10 s cessation of airflow despite continuous respiratory effort against a closed airway) and hypopnea (50 % reduction in airflow or reduction associated with a decrease of oxyhemoglobin saturation (SpO₂) >4 %). OSA is very common in obesity and has been reported to be present in as many as 70 % of morbidly obese (BMI > 40 kg/m²) patients undergoing bariatric surgery [2]. OSA is associated with many potentially serious conditions including systemic and pulmonary hypertension, coronary artery disease, congestive heart failure, and stroke. Polysomnography (PSG) will give a definitive diagnosis of OSA; however, preoperative testing has not been shown to be cost effective or to actually improve operative outcomes in bariatric patients. In the absence of a PSG diagnosis, we use the STOP-BANG questionnaire to identify patients with OSA [3] (Table 11.3). Many of the anatomic and pathophysiologic consequences that are associated with OSA can be reduced or corrected by applying nasal continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) devices, but only if the treatment is instituted weeks or months before surgery. Unfortunately, many OSA patients do not use their prescribed CPAP masks. Those patients who do have their own devices should be instructed to bring them to the hospital on the day of surgery for use during their recovery.

Table 11.3

STOP-BANG Questionnaire for Identifying Patients with Obstructive Sleep Apnea (OSA)

SNORE:	Do you snore loudly? (snoring can be heard through closed door)
TIRED:	Do you feel tired, sleepy, fatigued, during daytime?
OBSERVED:	Has anyone seen you stop breathing during sleep?
BLOOD PRESSURE:	Do you have, or are you being treated, for high blood pressure?
BMI:	Is your BMI >35 kg/m²?
AGE:	Are you older than 50?
NECK CIRCUMFERENCE:	Is your neck circumference >40 cm?
GENDER:	Are you a male?

Modified from: Chung and Elsaid [34]

This questionnaire is used to identify patients with OSA who have not undergone diagnostic polysomnography. If the answer to any three of these questions is “yes”, then a presumptive diagnosis of OSA can be made. If the answer to five or more is “yes,” a more “definitive” diagnosis of OSA can be made

11.1.2 Premedication

As a rule sedative premedication should be avoided, especially for patients with OSA. We occasionally give small amounts of an anxiolytic (e.g., midazolam) for very anxious patients. We usually continue most medications for chronic hypertension. The exception are angiotensin-converting enzyme (ACE) inhibitors (e.g., lisinopril, captopril, losartan), which are stopped for the day of surgery. These drugs can cause profound hypotension following induction of general anesthesia. The preoperative administration of a beta-blocker remains controversial, and it we do routinely use them.

MO patients were once considered at risk for gastric acid aspiration because of their increased intra-abdominal pressure and a high incidence of gastro-esophageal reflux disease (GERD). Recent studies and clinical experience have not demonstrated a need for routine aspiration prophylaxis. For patients with severe GERD and for those who have previously undergone gastric banding procedures, an H₂-receptor antagonist (e.g., ranitidine, famitidine) is given preoperatively.

Diabetic medications (e.g., insulin, oral hypoglycemics) are also withheld on the day of surgery. Prophylaxis, with an antibiotic against wound infection and with heparin to prevent deep venous thrombosis, is usually given at the surgeon’s request. An anti-sialogogue (e.g., atropine, glycopyrrolate) can also be administered if a fiber-optic tracheal intubation is planned.

11.2 Intraoperative Considerations

11.2.1 Positioning

Extremely obese patients have a marked reduction in lung volume, which is further exaggerated when they lie flat. Once a patient is moved onto the operating room table, they should be positioned with pillows, blankets, or a commercial “elevation” device so that their head, upper body, and shoulders are in the head elevated laryngoscopy position (HELP). In this position the patient’s ears should be level with their sternum. When compared to MO patients placed in the conventional “sniff” intubating position, HELP facilitates gas exchange while improving visual exposure during direct laryngoscopy (DL) [4].

The position of the operating room table influences the size of the surgical workspace in obese patients (BMI > 35 kg/m²) undergoing laparoscopy. In one study the operating room table was placed, in random order, in five different positions: (1) table horizontal with the legs flat, i.e., supine position, (2) table in 20° reverse Trendelenburg (RT) with the legs flat, (3) table in 20° RT with the legs flexed 45° upward at the hips, i.e., beach chair position, (4) table horizontal with the legs flexed 45° upward at the hips, and (5) table in 20° Trendelenburg with the legs flat. This study found that the mean inflated intra-abdominal volume in the supine position was about 3.2 l, and that volume increased by 900 ml in both the Trendelenburg position or when the legs were flexed at the hips with RT. Intra-abdominal volume decreased by 230 ml in the RT position. The conclusion was that the Trendelenburg position was best for lower abdominal surgery, and RT combined with leg flexion at the hips gave the largest workspace for upper abdominal surgery [5]. They noted that although the Trendelenburg position increased intra-abdominal space, it should not be used during bariatric surgery because ventilation of the MO patient could be significantly compromised in this position.

All pressure points must be carefully padded to prevent pressure sores, neurologic injury, and rhabdomyolysis (RML), each of which occurs more frequently in obese surgical patients. The patient’s neck, arms, and legs should also be supported to avoid stretch injuries and subsequent peripheral nerve damage.

11.2.2 Physiologic Monitoring

Standard physiologic monitors (EKG, noninvasive blood pressure cuff, pulse oximetry, end-tidal capnography, and temperature probe) are always applied.

An indwelling urinary catheter is important in order to monitor urine output. There is normally a transient decrease in urine production during laparoscopy, with return of normal kidney function following release of the pneumo-peritoneum.

An arterial line is usually unnecessary for continuous blood pressure monitoring, except in patients with significant hypertension or other cardiovascular conditions. When intraoperative blood tests are planned, an indwelling arterial line allows frequent sampling for blood gas analysis and for intermittent serum glucose monitoring. Central venous or pulmonary artery lines and trans-esophageal echocardiography (TEE) are seldom indicated, except in patients with significant cardiopulmonary disease or to guide fluid resuscitation. A central venous line may be necessary when peripheral venous access is limited. Ultrasonography greatly increases the success rate of internal jugular vein cannulation in obese patients.

A nerve stimulator is very important to assess the degree of neuromuscular blockade. Many anesthesiologists routinely use an electroencephalography (EEG) depth of anesthesia monitor, especially to titrate down the concentration of inhalational and intravenous anesthetics toward the end of surgery prior to emergence [6].

The anesthesiologist is responsible for proper placement of gastric tubes, used to decompress the stomach, to size the gastric pouch, and to test for anastomotic leaks. Any foreign body in the esophagus (gastric tube, temperature probe, TEE probe) must be completely withdrawn before the gastric pouch is stapled.

11.2.3 Fluid Management

Intraoperative fluid requirements in obese patients are usually greater than for normal-weight patients undergoing similar laparoscopic procedures. Obese patients receiving several liters of intravenous crystalloid had a faster recovery and fewer complications after laparoscopic cholecystectomy than those with restrictive fluid replacement [7]. There are few studies of fluid replacement in MO patients. Liberal amounts of intra-operative intravenous fluid may reduce the incidence of postoperative nausea and vomiting (PONV) in bariatric patients [8]. Generous amounts of intravenous fluid should also be given intraoperatively to reduce the risk of RML and postoperative renal failure [9].

11.2.4 Temperature Maintenance

All anesthetized patients lose heat and become poikilothermic during surgery. Even though adipose tissue is a thermal insulator, heat loss is increased during laparoscopy in obese patients due to the cool, dry CO₂ that is used for the pneumo-peritoneum and when cold irrigating fluids are used. Forced-air heating blankets are always applied, and warmed intravenous and irrigating fluid are occasionally needed. Attempts to minimize heat loss using heated and humidified gas for the pneumo-peritoneum have not been successful [10].