Anesthetic Considerations in Bariatric Endoscopy

Patients are evaluated in the bariatric endoscopy clinic and subsequently in the preoperative anesthesia clinic. A thorough medical history, physical examination, and laboratory evaluation are performed as indicated. Although it is classified as a low-risk procedure, patients undergoing bariatric endoscopy often have multiple comorbidities, so additional investigations such as echocardiogram (ECG) or a stress test may be warranted.

Obesity, per se, may not be associated with increased gastric volumes – and, hence, increased risk of aspiration. The risk of aspiration is increased in association with hiatal hernia or diabetes mellitus with autonomic neuropathy causing delayed gastric emptying. A history of the exact bariatric surgery that the patient may have undergone in the past is also important. Simple gastric banding can cause diminished esophageal-gastric peristalsis as well as impairment of lower esophageal sphincter tone, increasing the risk of aspiration. Vertical banded gastroplasty can also cause a decrease in basal lower esophageal sphincter pressure and an increase in acid reflux, increasing risk of perioperative aspiration.

Unlike subcutaneous fat, intra-abdominal fat is metabolically very active and is known to contribute to several disease states. These states can lead to nonalcoholic fatty liver disease (NAFLD), which affects metabolism of lipids and fat-soluble drugs as the disease advances (Drug Metab Rev 2011;43:317-34). Sometimes in advanced cases of fatty liver, fibrosis is so extensive that even occult cirrhosis can be present. Hence, liver function tests are often performed prior to these procedures. Even in the presence of normal liver function tests, it has been established that sedation requirement is increased following Roux-en-Y gastric bypass surgery (RYGB). This is true of post-bypass patients who have undergone weight loss compared to their counterparts of similar weight who have not (Clinical Gastroenterology and Hepatology 2015:1432-6). Thus, a careful history in anticipation of dosing requirements is crucial.

The risk of obstructive sleep apnea (OSA) is directly proportional to increasing BMI, due to anatomic changes and fat deposition in the posterior pharynx (JAMA 2000; 284:3015-21). Obesity can lead to physical impingement on lung volumes and chest movement, thereby decreasing lung, chest wall, and total respiratory system compliance. Increased metabolic requirements are also noted. Obesity is associated with an increased breathing effort, oxygen consumption, carbon dioxide (CO2) production, and increased baseline respiratory rate. Due to increased basal atelectasis, the VQ mismatch is amplified in obese patients. This, coupled with decreased functional residual capacity (FRC) and expiratory reserve volume (ERV) even in mild obesity, results in faster desaturation with apnea or hypopnea. Although residual volume and closing capacity are normal in obesity, as the FRC falls to or below the closing capacity, airway closure can occur even during respiration at rest, especially in the supine position. The reduction in FRC is proportional to the severity of obesity – overweight, mildly obese, and severely obese subjects without asthma demonstrate reductions of up to 10%, 22%, and 33%, respectively (Acta Anaesthesiol Scand 1976;20:334-42). Smaller alveoli and airways may close in spontaneous ventilation; hence, SpO₂ recovery can be slow even when spontaneous ventilation resumes. Proper positioning, monitoring, and lung recruitment maneuvers may be necessary to prevent these complications.

Rather than BMI, recent evidence suggests that BMI years or the number of years that a person has been obese and the height-waist ratio are better predictors of cardiovascular morbidity (Obes 2015;23:879-85). Chronicity of obesity is therefore of extreme importance when predicting a possible major adverse cardiac event (MACE) perioperatively. These patients often have significant cardiac comorbidities, so a thorough history and further investigation in the presence of any symptoms are warranted even though the surgery is a low-risk procedure.

Bariatric endoscopic therapies – best known as endoscopic bariatric and metabolic therapies, or EBMTs – can be broadly classified as primary, if done in a native GI tract, and revisional if performed in a patient who has already undergone bariatric surgery or endoscopy. Some of the common procedures are shown in the Table.

POSE is an EBMT performed with The OverStitch™ Endoscopic Suturing System of Apollo Endosurgery. This is an endoscopically placed conduit through which full thickness sutures or staples are placed in the stomach lining, plicating and decreasing the size of the lumen, which leads to early satiety and therefore weight loss. This procedure is usually done under general anesthesia with full airway protection due to increased risk of aspiration and bleeding intraoperatively. Moreover, full thickness sutures are used in the stomach. During the process, CO2 is often used at extremely high rates, such as up to 10-12 L/ min through the scope to insufflate the stomach and improve visualization. Hence, the ability to ventilate adequately and eliminate CO2 is of utmost importance. Rarely, CO2 may escape through the stomach lining prior to gastric closure, resulting in peritoneal CO2 accumulation and increased airway pressures. As the patient is in the left lateral position and fully covered face down, abdominal distension may often go unnoticed until the airway pressure alarms go off. Endoscopic sleeve gastrectomy is a similar procedure where full-thickness bites and clips are placed.

Many of these patients have OSA and are on CPAP prior to the procedure. Postoperatively, CPAP must be used with caution. Though CPAP has been safely used after laparoscopic gastric sleeve procedures, it has not yet been proven to be safe with endoscopically placed sutures.