Bariatric Surgery: What Your Anesthesiologist Needs to Know and Do

by Babatunde Ogunnaike, MD
Dr. Ogunnaike is Associate Professor and Chief of Anesthesia Services at Parkland Health and Hospital System, Southwestern Medical School, Dallas, Texas.

The success of bariatric perioperative care depends on a team of dedicated healthcare personnel working together toward optimal patient care. Important aspects of the bariatric surgery that are crucial to the success of the process are discussed in this article.

Preoperative Evaluation: Where is the Focus?
Issues unique to the obese patient should be the focus of attention during the preoperative assessment of the bariatric surgery patient. The systems that are most commonly affected by obesity, including cardiovascular, respiratory, endocrine, and the airway, are of major interest to anesthesiologists and should be emphasized to surgeons and other personnel who screen patients for bariatric surgery.[1] Sleep-disordered breathing, including obstructive sleep apnea (OSA) and obstructive sleep hypopnea (OSH) syndromes, is often present in individuals with morbid obesity. Other syndromes include type 2 diabetes and cardiovascular diseases, such as systemic and pulmonary hypertension, right and/or left ventricular failure, and ischemic heart disease. Also, the surgical approach to bariatric surgery should be clearly discussed during the preoperative phase. Information regarding what the surgeon plans to do and how he or she plans to do it is beneficial to both the patient and anesthesia personnel as it helps anticipate events such as degree of postoperative pain— which is important so that analgesic techniques may be discussed with the patient. Peripheral and central venous access and arterial cannulation sites should be identified during the preoperative evaluation and the degree of difficulty noted. This is a particularly important cause of delay in surgical start times. Certain problems, such as rhabdomyolysis and nerve palsies, are associated with prolonged duration of surgery.

Obstructive Sleep Apnea: Not a Silent Killer
Sixty to ninety percent of people with OSA are obese and up to four percent of men, and two percent of women in the middle-aged population have clinically significant OSA. One particular review clearly describes the pathophysiology of OSA as follows: loss of pharyngeal muscle tone during deep sleep may cause partial or total pharyngeal collapse leading to hypopnea (and snoring) or apnea (and silence).[2] Apnea and hypopnea are defined respectively as no airflow for greater than 10 seconds despite continuing ventilatory effort and a decrease in airflow more than 50 percent of awake value for more than 10 seconds.[3] Mini-arousals during the obstructive episodes activate the pharyngeal muscles to open the airway and allow the patient to go back into a deep sleep that in turn causes pharyngeal collapse, and obstruction, leading to a recurring cycle. Sympathetic nervous system stimulation occurs during each arousal. leading to systemic and pulmonary hypertension, which may subsequently lead to right or left ventricular hypertrophy and eventual congestive cardiac failure. Myocardial ischemia leading to arrhythmias and sudden death can result from hypoxemia due to the obstructive episodes. Perioperative management of patients with OSA presents a major problem for anesthesia personnel due to well-documented, adverse respiratory outcomes. These adverse events usually occur in the form of failure to secure the airway and postoperative airway obstruction or respiratory arrest from sedatives and/or opioids.[2]

Many bariatric surgery patients are not aware of their sleep-disordered status and the preoperative assessment team may be the first to diagnose OSA in patients for bariatric surgery. Look for features to help make a tentative clinical diagnosis, such as a history of snoring or apnea during sleep, frequent arousals, and daytime sleepiness.[4] If these are associated with a large neck circumference (>40 cm), history of hypertension, nocturnal diaphoresis, and frequent nocturia, a presumptive diagnosis may be made.[4] Patients who have not been previously diagnosed as having OSA, but have screened positive, may have elective surgery delayed so as to obtain proper workup to help determine severity and begin treatment. If the procedure permits, treatment with continuous positive airway pressure (CPAP) may be started. Four to 6 weeks of CPAP treatment before surgery has been shown to increase pharyngeal size and reduce tongue volume in patients with OSA.[5] Treatment should continue in the perioperative period and patients should be encouraged to bring their CPAP equipment with them to use postoperatively.

Up to 30 percent of patients with OSA have obesity hypoventilation syndrome (OHS).[6] OHS is defined as a combination of obesity (body mass index [BMI]>30kg/m[2]), chronic daytime hypercapnia (PaCO2>45 mmHg), and sleep-disordered breathing in the absence of other known causes of hypercapnia.[7] Serum bicarbonate level, in combination with other independent variables, such as the apnea-hypopnea index (AHI) and the lowest oxygen saturation during sleep, may help predict the presence of OHS. AHI is the total number of apneas and hypopneas per hour. It defines the severity of OSA with values of 5 to 15, 16 to 30, and >30, indicating mild, moderate, and severe, respectively. A normal serum bicarbonate level excludes hypercapnia, but an elevated level should encourage the practitioner to measure arterial blood gases.

Thromboprophylaxis and Other Perioperative Medications: What is Important?
Patients’ usual medications should be continued until the time of surgery.[8] Exceptions may be insulin and oral hypoglycemics. Careful titration of insulin is important to prevent hypoglycemia. Longer operative times, larger incisions, and relative inability of adipose tissue to resist infection lead to increased incidence of wound infections, making antibiotic prophylaxis very important, even during laparoscopic bariatric surgery. Wound infection rates after bariatric operations have been quoted to be as high as 5 to 15 percent.[9,10]

Acute postoperative pulmonary embolism from deep vein thrombosis (DVT) is a common cause of sudden death in surgery patients with morbid obesity. Most surgeons do not need to be reminded that thromboprophylaxis with unfractionated heparin or low molecular weight heparin (LMWH) should commence preoperatively and continue into the postoperative period until the patient is fully mobile to reduce the incidence of DVT. Postoperative use of LMWH does not increase the incidence of bleeding.[11] The bioavailability of LMWH after subcutaneous injection makes it an attractive choice for perioperative thromboprophylaxis. Subcutaneous heparin 5000 IU administered before surgery and repeated every 8 to 12 hours until the patient is fully mobile is still the preference of many surgeons.

Laparoscopy
Laparoscopy is rapidly becoming the standard technique of operation for bariatric surgery; however, it carries significant complications, especially in inexperienced hands. Attractions include less postoperative pain, lower morbidity, and faster recovery. It is expected that the surgeon would have informed the patient about certain significant side effects, such as the pneumoperitoneum causing shoulder pain that mimics pain of cardiac origin. Carbon dioxide, the gas most often used to produce pneumoperitoneum during laparoscopy, has systemic effects when absorbed and the pneumoperitoneum may produce hemodynamic changes, which may worsen with unfavorable patient positioning, such as Trendelenburg. Systemic vascular resistance increases with increased intra-abdominal pressure (IAP) while venous return and myocardial performance decrease. Compression of the inferior vena cava (IVC) occurs at IAP >20mmHg leading to decreased venous return from the lower body and consequent decreased cardiac output. Abdominal viscera further exert weight on the diaphragm during Trendelenburg positioning, causing a reduction in vital capacity and subsequent worsening of oxygenation.[12] The anesthesiologist should be very vigilant during pneumoperitoneum. I have witnessed a firmly secured endotracheal tube displace into one mainstem bronchus due to cephalad displacement of the diaphragm and carina from pneumoperitonium, leading to ventilation and oxygenation difficulties. Keeping laparoscopic bariatric patients kept profoundly relaxed is important to facilitate ventilation and to maintain an adequate working space for visualization and safe manipulation of laparoscopic instruments. Extraction of excised tissues is also facilitated. Collapse of the pneumoperitoneum and tightening of the patient’s musculature around port sites are early indications of inadequate muscle relaxation. On occasion, the surgeon may inform the anesthesiologist of diaphragmatic contractions even when no twitches are detected on the nerve stimulator.

Ambulatory and Short-Stay Surgery:  What are the Limits?
As the system pushes for more cases to be done at minimal expense, we are seeing a significant number of bariatric cases being done at free-standing ambulatory surgery facilities. The recent explosion of gastric banding and improvements in laparoscopic techniques have made this possible. Many anesthesiologists believe that patients with morbid obesity with comorbidities are unsuitable for ambulatory anesthesia.[13] On the contrary, there is no evidence to suggest any increased morbidity in patients with morbid obesity with stable concomitant diseases; therefore, they should not be excluded from ambulatory or short-stay surgery on the basis of absolute weight or BMI.[14] Individual evaluation and proper selection is the key to determining which patients with obesity can undergo ambulatory bariatric surgery and anesthesia. Patients with obesity do not have a higher incidence of contact with healthcare professionals after discharge from the ambulatory surgery unit; neither do they have a higher postambulatory surgery unplanned admission rate than the general population.[15] An almost four-fold increase in intraoperative and postoperative respiratory events (mostly bronchospasm and desaturation) is seen in patients with obesity and when obesity combines with obstructive OSA, the risk of difficult intubation, airway obstruction, and postoperative apnea is increased, a major reason to properly assess patients for OSA.[16,17] Anesthesia tailored specifically toward ambulatory bariatric surgery will help facilitate discharge from the outpatient surgery unit. Some anesthesiologists advocate the use of brain function monitors to accurately titrate anesthetics and facilitate rapid discharge after bariatric operations. Anxiolytic premedication and sedatives should be avoided if at all possible or reduced to a minimum. Use of short-acting and rapidly dissipating drugs, such as propofol, remifentanil, and desflurane, is paramount to the success of early discharge. Pain control with nonopioids, such as nonsteroidal anti-inflammatory agents (e.g. acetaminophen, etc.), and prophylactic prevention of postoperative nausea and vomiting will ensure rapid discharge from the postanesthesia care unit (PACU) and early mobilization. Overall, there should be a low threshold for extending the stay of bariatric surgery patients presenting for outpatient surgery, and a close postdischarge followup and readmission, when necessary, will result in better success rates.[18]

The Airway: Are You Well Prepared?

Tips for Successful Airway Management

Several anatomic changes of obesity may contribute to a potentially difficult airway. These include limitation of movement of the atlantoaxial joint and cervical spine by the upper thoracic and low, cervical fat pads; excessive tissue folds in the mouth and pharynx; short, thick neck; suprasternal, presternal, and posterior cervical fat; and a very thick submental fat pad. Obtaining a proper history from the patient and checking previous anesthesia records may help predict airway difficulties. A previous diagnosis of OSA should alert the anesthesiologist to airway difficulties. Excess pharyngeal tissue deposited in the patient’s lateral pharyngeal walls may not be noticed during routine airway examination.[19] The magnitude of BMI does not necessarily have much influence on the difficulty of laryngoscopy. Such difficulty correlates better with increased age, male sex, temperomandibular joint (TMJ) pathology, Mallampati classes 3 and 4, history of OSA, and abnormal upper teeth.[20] Neck circumference should probably be routinely measured at preoperative visit as this seems to be the single biggest predictor of problematic intubation in patients with morbid obesity.[21] The probability of a problematic intubation was found to approximate five percent with a 40-cm neck circumference compared with a 35-percent probability at 60-cm neck circumference. A larger neck circumference is associated with the male sex, a higher Mallampati score, grade 3 views at laryngoscopy, and OSA. OSA has also been implicated in some cases of difficult or impossible mask ventilation.[22]

Adequate preoxygenation up to saturation greater than at least 90 percent is vital in patients with obesity because of rapid desaturation after loss of consciousness due to increased oxygen consumption and a decreased FRC. Taking four vital capacity breaths with 100-percent oxygen within 30 seconds has been found to be useful when compared to the usually recommended three minutes of 100-percent preoxygenation in patients with obesity.[23] Application of positive pressure ventilation during preoxygenation decreases atelectasis formation and improves oxygenation in patients with morbid obesity.[24] Preoxygenation in the reverse Trendelenburg position provides a greater safety margin for airway control when compared with the supine position because it achieves higher oxygen tensions and a clinically significant increase in the desaturation safety period.[25] Utilize an awake intubation with topical or regional anesthesia, if significant doubt exists. Doses of sedative-hypnotic medications should be reduced to a minimum during awake intubation. Dexmedetomidine, a short-acting alpha-2 receptor stimulant, may be used during awake intubation to provide anxiolysis and analgesia without respiratory depression.[26]

The majority of bariatric surgery patients can still undergo endotracheal intubation under general anesthesia without difficulty. Hypoxia and aspiration of gastric contents should, however, be prevented at all costs. Higher BMI is a weak but statistically significant predictor of difficult tracheal intubation when compared to other risk factors, such as previous difficult intubation, higher Mallampati score, and increased neck circumference.[27] An experienced colleague as an assistant in the room during induction and airway management is of immense help during a difficult intubation. Ensure that a surgeon capable of accessing the airway surgically will be in the operating room during airway management.

Anesthesiologists should do everything possible to facilitate a successful airway, including proper positioning and other special intubation equipment. Towels or folded blankets under the shoulders and head will help compensate for the exaggerated flexed position due to posterior cervical fat. This maneuver, known as stacking, positions the patient so that the tip of the chin is at a higher level than the chest, helping to facilitate laryngoscopy and intubation. The head-elevated laryngoscopy position (HELP) goes a step beyond stacking as it significantly elevates the patient’s head, upper body, and shoulders above the chest to the extent that an imaginary horizontal line connects the sternal notch with the external auditory meatus to better improve laryngoscopy and intubation.[28] To facilitate proper HELP placement, a  preformed elevation device, for example, the Troop® Elevation Pillow (C&R Enterprises, Frisco, Texas), may be used in place of folded towels or blankets. The advantage of a preformed pillow is that it can be prepositioned, inserted, and removed much faster with less effort than that required to build and dismantle a ramp made from blankets and towels.29 Current advances in various video laryngoscopic techniques for indirect and global view of the pharyngo-laryngeal area help facilitate intubation in bariatric surgery patients with morbid obesity.

Repeat Bariatric Surgery or Postbariatric Cosmetic Surgery
As the rate of bariatric operations increases exponentially, anesthesiologists will frequently come across previously operated bariatric patients who may have long-term metabolic and nutritional deficiencies. The most common include, vitamin B12, iron, folate, and calcium deficiencies. Acute postgastric reduction surgery (APGARS) neuropathy, a collective form of polynutritional multisystem disorder, is characterized by protracted vomiting, hyporeflexia, and muscular weakness resulting from vitamin and nutritional deficiency.[30] Patients with hyporeflexia may require less aggressive muscle relaxant therapy. Protein depletion may occur with rapid weight loss, leading to inadequate synthesis of essential proteins and factors. Close attention should also be paid to coagulation indices, particularly in noncompliant or acutely ill patients who may have chronic vitamin K deficiency, which can lead to coagulation abnormalities.

Positioning
Specially designed tables or two regular operating tables may be required for safe anesthesia and surgery in patients with obesity. Operating tables capable of holding up to 1,000 pounds (455kg), with a little extra width to accommodate the extra girth, are available. Securing patients with obesity to the operating table with the aid of straps, in combination with a malleable beanbag may help keep them from falling off.

Pay particular attention to pressure areas to prevent pressure sores, neural injuries, and possible rhabdomyolysis. Rhabdomyolysis is more common in patients with morbid obesity who undergo laparoscopic bariatric procedures as opposed to open. Long duration of surgery is a major risk factor. If a patient has unexplained elevations in serum creatinine and creatine phosphokinase (CPK) levels, and complains of buttock, hip, or shoulder pain in the postoperative period, rhabdomyolysis should be suspected. Postoperative measurement of serum CPK aids in early diagnosis and treatment. The complication of myoglobinuric acute renal failure can be as high as 30 percent in patients with serum CPK >5,000 IU/L.[31]

Improper positioning may lead to brachial plexus and lower extremity nerve injuries. Carpal tunnel syndrome is a very common mononeuropathy after bariatric surgery.[32] Simply changing the patient from a sitting to supine position significantly increases oxygen consumption and cardiac output. The reverse Trendelenburg position provides for an extended safe apnea period (SAP) during induction of anesthesia gaining some extra time, which may help prevent hypoxemia if intubation is delayed.[33] Both intraoperative, positive end-expiratory pressure (PEEP) and the head-up position significantly decrease alveolar-arterial oxygen tension difference and increase total respiratory compliance to a similar degree in the patient, but the head-up position results in lower airway pressures.[34] PEEP is the only maneuver that has consistently been shown to improve oxygenation during anesthesia in the obese patient. Prone positioning, rarely needed for bariatric surgery, should be correctly performed with freedom of abdominal movement to prevent detrimental effects on lung compliance, ventilation, and arterial oxygenation.

Postoperative Course: Keeping the patient alive and pain-free
The immediate 12- to 24- hour postanesthetic period is critical for the development of significant morbidity and mortality. Inadequate pain control is a major cause of morbidity and perioperative use of regional anesthesia and analgesia reduces the incidence of postoperative respiratory complications. Epidural analgesia with local anesthetics, opioids, or both is an effective form of analgesia. Intrathecal opioid is also a viable option. Potential advantages of epidural analgesia in patients with obesity include prevention of DVT, improved analgesia, and earlier recovery of intestinal motility. Lesser oxygen consumption and decreased left ventricular stroke work are other benefits. PCA morphine compares favorably to low-thoracic/highlumbar, continuous infusions of bupivacaine/fentanyl epidural analgesia in patients with morbid obesity undergoing gastric bypass surgery with regard to the quality of pain control at rest, the frequency of nausea and pruritius, the time to ambulation, time to return of gastrointestinal function, and the length of hospital stay.[35] Local wound infusion may be all that is necessary after laparoscopic bariatric surgery.[36] Many centers now use multimodal analgesia, which includes incisional local anesthetic infiltration plus PCA to produce lower pain scores in comparison to epidural analgesia and postoperative PCA for bariatric surgery since it offers a simple, safe, and inexpensive alternative to epidural analgesia.[37] A form of multimodal analgesia combines intraoperative nonopioid analgesics and anesthetic adjuvants (ketorolac, clonidine, ketamine, lidocaine, magnesium sulfate, and methylprednisolone) to produce analgesia by mechanisms different from that of opioids in order to decrease sedation during recovery from anesthesia and reduce postoperative opioid requirements.[38] Delayed respiratory depression is a known complication of central neuraxial opioids. When coupled with a potentially difficult airway in the patient, closer monitoring in a step-down or intensive care unit is a prudent choice until this complication is no longer a threat.

An increased incidence of atelectasis in patients with morbid obesity who have general anesthesia persists into the postoperative period consequently and initiation of continuous positive airway pressure (CPAP) is advocated. Postoperative CPAP may improve oxygenation but does not facilitate carbon dioxide elimination and also does not increase the incidence of major anastomotic leakage after gastric bypass surgery despite a theoretical risk.[39] CPAP should not be applied immediately upon arrival in PACU because it blocks access to communication with the patient and it is also a period when nausea and vomiting are very likely to occur.[4] The patient may avoid taking deep breaths because of pain after abdominal surgery. Adequate analgesia, use of a properly fitted elastic binder for abdominal support, early ambulation, deep breathing exercises, and incentive spirometry are all useful adjuncts.

Conclusion
Bariatric surgery continues to challenge the healthcare system as more people attain obesity status worldwide. Close attention to the important aspects of perioperative care of such patients needing bariatric surgery and staff education, goes a long way to achieve successful outcomes. Proper preoperative evaluation is a key initial step that needs to be followed later by vigilant monitoring and team care in the postoperative period to prevent disastrous outcomes.

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Category: Anesthetic Aspects of Bariatric Surgery, Past Articles