Medical

Anesthesia for the obese patient undergoing non-cardiac surgery

Anesthesia for the obese patient undergoing non-cardiac surgery

Author
Roman Schumann, MD
Section Editor
Stephanie B Jones, MD
Deputy Editor
Kathryn A Collins, MD, PhD, FACS

Disclosures

Last literature review version 19.3: Fri Sep 30 00:00:00 GMT 2011 | This topic last updated: Fri Apr 08 00:00:00 GMT 2011 (More)

INTRODUCTION — Worldwide, it is estimated that a billion adults are overweight [1]. In the United States, more than 75 million American adults are obese and it is not uncommon for the anesthesiologist to administer anesthesia to patients who meet the criteria for morbid obesity (ie, body mass index >40 kg/m2) for routine elective surgery or surgery for weight loss. The increase in the number of bariatric procedures over the past decade has contributed to interest in this area of anesthesia and improved knowledge and experience in the perioperative management of obese patients [2]. However, perioperative care guidelines are predominantly based upon retrospective review or expert opinion. Best practice policies based upon the results of randomized trials that show direct improvement in clinically important outcome measures are needed.

The perioperative anesthetic management of the obese patient will be reviewed. Anesthetic principles and general anesthetic management are discussed in separate topic reviews. The surgical management of severe obesity and its complications are discussed elsewhere. (See “Surgical management of severe obesity” and “Complications of bariatric surgery”.)

OBESITY-RELATED PHYSIOLOGIC CHANGES — Perioperative morbidity related to obesity may be related to physiologic changes that impact the delivery of anesthesia and perioperative analgesia, including the following:

  • Control of the airway is potentially hampered by reduced neck mobility and altered oropharyngeal anatomy [3-5]. The pharyngeal space is narrowed due to increased soft tissue within the confines of the maxilla-mandibular space [6]. (See ‘Airway management’ below.)
  • Altered respiratory mechanics and decreased chest wall compliance interfere with oxygenation and ventilation [7]. Severe obesity causes a reduction in functional residual capacity (FRC) and expiratory reserve volume, particularly in the supine position. The work of breathing is increased because of decreased chest wall compliance [8]. In obese patients, intraoperative and postoperative tissue oxygen tension may be significantly reduced compared with baseline, even with supplemental oxygen [9]. (See “Diseases of the chest wall”, section on ‘Obesity’ and ‘Airway management’ below.)
  • The factors that determine drug distribution into the tissues include plasma protein binding, regional blood flow and body composition [10]. Some or all of these components may be altered in severe obesity including the volume of distribution for specific drugs. The pharmacodynamics and pharmacokinetics of many medications are unknown for severely obese individuals. Initial dosing may be based on total body weight (TBW), lean body weight (LBW, similar to lean body mass) (calculator 1 and calculator 2), or ideal body weight (IBW) (calculator 3) depending upon the agent chosen and presence of comorbidities [11,12]. When drug pharmacokinetic and pharmacodynamic parameters are unknown, initial dosing in obese patients should begin based upon LBW (table 1).

ANESTHESIA CONSULTATION — For major surgery in the severely obese patient, the preoperative evaluation should include consultation with an anesthesiologist [11,13]. Major surgery is any procedure that accesses the chest or abdominal cavities, including minimally invasive bariatric surgery. However, clinical judgment taking into account the patient’s degree of obesity, apparent comorbidities, type of surgery and anesthesia, and postoperative needs may indicate the need for anesthesia consultation for any type of surgery.

A history and physical examination and selective preoperative testing can identify patients with silent comorbidities and those at risk for complications due to possible underlying obstructive sleep apnea during and following anesthesia (table 2A-B). Other advantages of anesthesia consultation include improved patient education and early identification of airway and vascular access issues. With appropriate preoperative management, airway complications and the need to cancel cases due to previously undetected or inadequately controlled medical conditions can be reduced [14].

There are presently no data in the literature providing clear, evidence-based guidance regarding the need and appropriateness of an advance preoperative anesthesiology consultation based on obesity alone. Likewise, it has not been determined when such consultation is definitively not needed. For example, advance anesthesia consultation is unlikely to be necessary in a younger patient (<50 years) with a BMI of <35 kg/m2 and without obvious comorbidities who will undergo outpatient ophthalmologic surgery. On the other hand, for the same procedure, an anesthesiology consultation should be considered in the severely obese older patient who is unable to lie flat or who has obstructive sleep apnea, hypertension or diabetes, or a coronary stent. When in doubt, at a minimum, the preoperative charts of severely obese patients should be screened by an anesthesiologist ahead of time to determine the need for advance preoperative consultation. However, data to support such an approach are lacking.

Evaluation of comorbidities — Increased body mass index (BMI) (calculator 4) in the absence of comorbidities, also termed ‘simple obesity’, is not associated with adverse postoperative outcomes in patients undergoing noncardiac surgery, with the exception of venous thromboembolism. (See “Preoperative medical evaluation of the healthy patient”, section on ‘Obesity’ and “Overview of the causes of venous thrombosis”, section on ‘Cardiovascular risk factors’.)

Obesity has been associated with lowered morbidity and mortality [15-17]. The “obesity paradox” identified in many studies is likely due to the presence of two distinct populations of obese patients, those without and those with metabolic markers of obesity or the metabolic syndrome. Metabolic syndrome is characterized by central obesity, hypertension, hyperglycemia, dyslipidemia, and prothrombotic and proinflammatory states. (See “The metabolic syndrome (insulin resistance syndrome or syndrome X)”.)

The apparent protective effect of obesity may be due to the large number of metabolically healthy but obese patients included in cohorts of obese patients being studied [18]. Compared with normal patients or obese patients without metabolic syndrome, obese patients with metabolic syndrome undergoing noncardiac surgery do appear to be at increased risk for perioperative morbidity and mortality and the degree of risk correlates with BMI.

A large National Surgical Quality Improvement Program (NSQIP) database study that included more than 310,000 patients undergoing non-cardiac surgery, compared normal weight patients with obese patients who did or did not have metabolic syndrome [18]. There were no significant differences in the risk for perioperative morbidity or mortality between normal weight and metabolically healthy, obese patients. In this study, the following classifications of BMI [kg/m2] were used: Overweight: 25 to 29.9; Obese: 30 to 39.9; Morbidly obese: 40 to 49.9; Super Obese: >50.

Standardized classification of BMI endorsed by the National Institute of Health (NIH) and World Health Organization (WHO) are presented elsewhere. (See “Screening for and clinical evaluation of obesity in adults”, section on ‘Classification of BMI’.)

For obese patients with metabolic syndrome, the adjusted odds ratios (AOR) for adverse cardiac events compared with normal-weight patients were as follows: obese, 1.7 (95% CI 1.40-2.07), morbidly obese, 2.0 (95% CI 1.48-2.73), and super obese 2.66 (95% CI 1.68-4.19). The risks for acute kidney injury were obese 3.30 (95% CI 2.75-3.94), morbidly obese 5.0, (95% CI 3.87-6.49), and super obese 7.29 (95% CI 5.27-10.1).

Thus, it is important to evaluate the patient preoperatively for metabolic syndrome and its associated conditions including cardiovascular disease, hypertension, type 2 diabetes mellitus and kidney disease. These conditions and obstructive sleep apnea (OSA) may be undiagnosed prior to consideration for surgery, particularly if the patient has a poor record of engaged health maintenance, including regular primary care visits. (See “Health hazards associated with obesity in adults”.)

  • The prevalence of silent cardiac ischemia may approach 10 percent for those with two or more major coronary risk factors, including obesity, smoking, family history of heart disease, age over 45 years, diabetes, hypertension, and hypercholesterolemia. Such patients may be identified by appropriate cardiac evaluation including EKG and stress tests as indicated. (See “Silent myocardial ischemia: Epidemiology and pathogenesis”, section on ‘Asymptomatic patients’.)
  • For all ages, the risk of type 2 diabetes increases with increasing body weight. Abnormal glucose metabolism can be documented years before the onset of overt diabetes. Determination of HbA1C may detect these patients. (See “Risk factors for type 2 diabetes mellitus”, section on ‘Obesity’ and “Prediction and prevention of type 2 diabetes mellitus”.)
  • The risk of chronic kidney disease is increased (relative risk 2.3, 95% CI 1.1-4.9) in patients with severe obesity (BMI ≥35 kg/m2) compared with normal weight persons [19]. This risk appears to be largely mediated by the presence of diabetes and hypertension. Standard preoperative laboratory testing including the creatinine value within a reasonable time frame prior to surgery (eg, six months) may assist recognition of these patients [11]. (See “Health hazards associated with obesity in adults”, section on ‘Kidney disease’ and “Screening for chronic kidney disease”, section on ‘Methods of screening’.)
  • Obstructive sleep apnea is the predominant form of sleep disordered breathing in severely obese patients [20]. Obstructive sleep apnea occurs when airflow is absent or nearly absent due to upper airway obstruction, but ventilatory effort is normal. Obstructive sleep apnea often goes undiagnosed and the preoperative history and physical examination should specifically assess for its signs and symptoms (table 3A-B). (See “Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea”.)

Preoperative testing — Specific preoperative testing should be decided on an individual basis depending upon the nature of the planned surgical procedure and the obese patient’s medical comorbidities following the published practice advisory of the American Society of Anesthesiologists (ASA) [21,22]. The preoperative medical evaluation of the obese patient without cardiovascular risk factors or medical comorbidities is similar to normal-weight patients being evaluated for surgery and is discussed in detail elsewhere. Highlights of the preoperative evaluation as it pertains to the obese patient in general are summarized below. (See “Preoperative medical evaluation of the healthy patient”.)

We prefer to obtain basic preoperative laboratory tests for all obese patients including a recent (within six months) hematocrit, glucose, blood urea nitrogen (BUN) and creatinine [11]. Other blood work (eg, HbA1C), noninvasive cardiac testing, chest radiograph and pulmonary function tests should be obtained selectively [23]. (See “Preoperative medical evaluation of the healthy patient”, section on ‘Rationale for selective testing’.)

  • The American Heart Association (AHA) 2009 scientific advisory on cardiovascular evaluation and management of severely obese patients (BMI ≥40 kg/m2) undergoing surgery states that an electrocardiogram is reasonable in obese patients with at least one risk factor for coronary heart disease (diabetes, smoking, hypertension, or hyperlipidemia) or poor exercise tolerance [24]. Additional testing is selectively obtained based upon the electrocardiogram results. (See “Preoperative medical evaluation of the healthy patient”, section on ‘Electrocardiogram’.)
  • The American College of Physicians (ACP) recommends chest radiograph for patients with cardiopulmonary disease, and patients older than 50 years of age undergoing abdominal aortic aneurysm surgery, or upper abdominal or thoracic surgery [25]. Posteroanterior and lateral chest x-ray is also suggested by the AHA for patients with severe obesity (BMI ≥40 kg/m2) [24]. However, in the absence of a medical history or clinical symptoms (eg, dyspnea, cough, fever) that might suggest cardiopulmonary disease (eg, pneumonia, heart failure), findings on preoperative chest radiograph have not been found to affect perioperative outcomes. (See “Preoperative medical evaluation of the healthy patient”, section on ‘Chest radiograph’.)
  • Mandatory polysomnography (ie, sleep study) has been proposed for patients undergoing bariatric surgery, but it is unclear if information gained from testing is associated with improved outcomes [26]. Routine preoperative polysomnography is not advocated for all patients with obstructive sleep apnea [27]. The decision to pursue testing primarily depends upon the patient’s history, physical examination, and type of surgery planned. The preoperative evaluation of the patient with obstructive sleep apnea is discussed in detail elsewhere. (See “Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea”.)

    Rather than mandatory polysomnography, another approach involves the use of clinical questionnaires or prediction scores [28-30]. The STOP questionnaire and the modified version called the STOP-Bang questionnaire are practical for clinicians and have emerged as frequently-used and cost-effective approaches to identify patients with obstructive sleep apnea. STOP assesses Snoring, Tiredness, Observed apnea and high blood Pressure, and Bang adds BMI, age, neck circumference and gender. In a systematic review of preoperative questionnaires that included 10 studies with a total of 1484 patients, both the STOP and STOP-Bang questionnaires were found to have the best methodological quality and ease of use [29]. In a study of 2467 adult patients without a prior diagnosis of sleep apnea, the sensitivities of the STOP questionnaire in diagnosing sleep apnea were 65.6, 74.3, and 79.5 percent, using apnea-hypopnea index (AHI) (monitored polysomnography) cutoffs of >5, >15, and >30, respectively (table 2A) [31]. When incorporating Bang, sensitivities increased to 84, 93, and 100 percent with the same AHI cutoffs.

Preoperative counseling

Positive airway pressure therapy — Obese patients with a diagnosis of obstructive sleep apnea (OSA) or obesity-hypoventilation syndrome who have been using continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) therapy should be instructed to adhere to their treatment regimen prior to elective surgery to maintain the benefits of treatment on their physical status. Furthermore, patients are instructed to bring their breathing equipment with them on the day of surgery for use postoperatively. (See ‘Respiratory care’ below.)

The treatment of patients with newly diagnosed OSA as a result of preoperative evaluation and testing depends upon the severity of OSA, and risk for postoperative respiratory compromise (table 2B). (See “Overview of obstructive sleep apnea in adults”, section on ‘Disease spectrum’.)

Patients with severe sleep apnea derive the most benefit from preoperative therapy and the authors prefer to initiate positive airway pressure therapy for four to six weeks prior to surgery, time permitting. Many OSA-associated medical conditions will improve within such a time frame, and their preoperative treatment may reduce postoperative complications [32]. Preoperative positive airway pressure therapy is associated with several physiologic benefits that improve delivery of anesthesia and overall anesthetic management. The most important of these include reduced tongue volume and increased volume of the pharyngeal space (an effect that occurs following four to six weeks of therapy) [33], improved cardiac parameters [34-36], and improved ventilatory drive in patients with obesity-hypoventilation syndrome [35]. (See “Management of obstructive sleep apnea in adults”, section on ‘Positive airway pressure’ and “Noninvasive positive pressure therapy of the obesity hypoventilation syndrome” and “Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea”, section on ‘Preoperative management’.)

Smoking cessation — Smoking is an independent risk factor for postoperative pulmonary complications with significant reductions in these complications when smoking has been stopped, ideally for eight weeks. Shorter periods of smoking cessation may provide short-term benefits, such as decreased carboxyhemoglobin levels on the day of surgery, but in some patients the risk of pulmonary complications increases due to reduced mucociliary clearance of secretions [37]. (See “Strategies to reduce postoperative pulmonary complications”, section on ‘Smoking cessation’.)

The preoperative evaluation provides an opportunity to discuss the benefits of smoking cessation. The anesthesiologist is an important part of the multidisciplinary team responsible for advocating smoking cessation for the patient’s and the public’s long-term benefit. The American Society of Anesthesiologists (ASA) smoking cessation initiative task force is exploring systematic approaches that could increase the anesthesiologist’s impact on smoking cessation rates [38]. (See “Management of smoking cessation in adults”.)

Ambulatory versus inpatient surgery — Anesthesia in the ambulatory surgery setting for obese patients is very safe. More and more, ambulatory surgery is being offered to populations with comorbidities, with many ambulatory surgery units routinely anesthetizing patients with a body mass index (BMI) >30 [39-42]. There are, however, no high-quality studies to guide patient or procedure selection for this operative setting in severely obese patients [43]. Although a diagnosis of obstructive sleep apnea (OSA) is not a contraindication to ambulatory surgery, there remains an ongoing debate over what types of procedures can be safely performed in the ambulatory care setting in morbidly obese OSA patients [44]. A retrospective review assessed outcomes in 1780 morbidly obese patients undergoing outpatient laparoscopic gastric banding in a freestanding ambulatory surgical center [44]. No hospital admissions were required in 320 patients who had OSA and BMI of >50 kg/m2.

For morbidly obese patients, logistical factors are important in determining the feasibility of outpatient surgery performed at a freestanding facility. Some considerations include the immediate availability of emergency difficult airway equipment, advanced respiratory care equipment, access to laboratory and radiology facilities, and transfer agreements with external facilities. In addition, the presence of an established clinical pathway for the care of the morbidly obese patient with tailored discharge criteria is ideal [45-47]. (See ‘Discharge criteria’ below.)

A scoring system can be used to estimate the risk of adverse perioperative outcomes in patients with OSA based upon severity of sleep apnea, the need for systemic or neuraxial opioids, site and invasiveness of the surgical procedure and type of anesthesia administered (table 2A-B). This scoring system is based upon the ASA practice guidelines for the perioperative management of patients with obstructive sleep apnea but has not been prospectively validated [27]. A risk score of >5 indicates a significantly increased risk for perioperative complications, and such patients are not good candidates for outpatient surgery. Additional factors for risk assessment include patient age, anatomic and physiologic abnormalities, and comorbidities. Superficial surgeries performed with local or regional anesthesia, or procedures such as lithotripsy can be performed safely on an outpatient basis in most patients with OSA [27,48]. (See “Intraoperative management of adults with obstructive sleep apnea”.)

ANESTHETIC MANAGEMENT — The choice of anesthetic technique for obese patients should be guided by the requirements of the surgical procedure, comorbidities and patient preferences. General anesthesia, regional anesthetic and sedation techniques have all been employed safely in obese patients, and no technique has been found to be superior over another with respect to important patient outcomes (eg, mortality, cardiopulmonary complications). Common goals for anesthetic management of obese patients, regardless of technique chosen, but particularly in the presence of sleep apnea, include minimizing sedation and opioid administration to decrease the risk of respiratory depression and allow rapid emergence from anesthetic or sedative effects. (See “Overview of anesthesia and anesthetic choices”.)

Inhalational agents — Inhaled potent volatile anesthetic agents are the most frequently used drugs for maintenance of general anesthesia, including for obese patients. Minimal alveolar concentration (MAC) is a measure of drug potency and is affected by many factors, including age, medications, and patient-specific factors including body weight. Both MAC and the solubility of inhalational agents in the blood and tissues differ among the various agents. Those with low solubility have a rapid onset, and rapid offset of effect which may allow for faster recovery [49]. (See “Awareness with recall following anesthesia”, section on ‘Minimum alveolar concentration monitoring’.)

The potent volatile anesthetic agents including isoflurane, desflurane and sevoflurane have been used safely for the maintenance of general anesthesia in severely obese patients. In the available studies, no significant differences between the agents have been identified [50]. Several small trials have compared sevoflurane to desflurane in morbidly obese patients focusing on emergence and recovery characteristics [51-54]. Desflurane should facilitate the speed of emergence and the reestablishment of airway reflexes due to its low blood solubility. In two of these trials, faster emergence and recovery was found for desflurane, but the clinical difference was small and it is unclear whether any identified differences would impact patient safety or other outcomes [51,52]. A retrospective study compared morbidly obese with super obese patients (BMI >50 kg/m2) and found no difference in outcomes and hospital course following general anesthesia with desflurane, sevoflurane or propofol infusion for weight-loss surgery [55].

Nitrous oxide has frequently been used to complement potent volatile agents. Because of its physicochemical properties, it is able to quickly diffuse into and distend gas filled compartments, such as the bowel. A study comparing the use of inhalational agents with or without nitrous oxide during laparoscopic bariatric surgery found that the addition of nitrous oxide did not cause noticeable bowel distention [56]. However, some obese patients may not tolerate the decreased inspired oxygen concentration that accompanies the use of nitrous oxide, and the anesthetic may need to be adjusted accordingly.

Neuraxial anesthesia — Neuraxial anesthetic techniques (spinal, epidural) minimally affect respiratory drive and sleep patterns and are safe and appropriate choices for obese patients [57,58]. However, sympathetic blockade can spread to higher levels in obese compared with normal weight patients. For spinal blockade, this is thought to be due to a relatively smaller spinal compartment. Compression of the spinal compartment by an epidural space that is expanded from increased epidural adipose tissue facilitates spread of intrathecally administered local anesthetics. The reasons for augmented sympathetic epidural blockade in this population are unclear.

High regional blocks may result in comparatively greater respiratory impairment in obese patients due to their altered respiratory mechanics [59]. Also, regional techniques may technically be more difficult to perform in obese patients [10,59-61]. The risks and benefits of adding opioid to local anesthetic solutions for neuraxial anesthesia and analgesia in patients with OSA need to be carefully appraised to minimize the risk for delayed respiratory depression [27,62].

Epidural catheters can be maintained postoperatively for analgesia. Postoperative pain management with epidural catheters improves respiratory function in obese individuals. (See “Management of postoperative pain”, section on ‘Morbid obesity’.)

  • In one study of 84 obese patients that included obese subjects undergoing midline laparotomy, postoperative vital capacity and FEV1 decreased less and returned to baseline faster in patients with epidural catheters compared with patients receiving systemic opioids [63].
  • In a randomized trial of 915 high-risk patients that included patients who were morbidly obese, the incidence of respiratory failure was significantly lower in the epidural group compared with patients who received standard analgesic therapy (23 versus 30 percent) [64].
  • In another trial, 60 obese patients were randomly assigned to general anesthesia with or without thoracic epidural analgesia (TEA). Tracheal extubation time and intensive care unit stay were significantly less in patients who had TEA [65].

Peripheral nerve block — Peripheral nerve blocks can also be used safely in morbidly obese patients and are effective in minimizing or eliminating the need for opioids. A variety of peripheral nerve blocks have been used in the obese population including interscalene block, supraclavicular block, and axillary block [66-69]. (See “Peripheral nerve block: Techniques”.)

Obese patients with BMI >30 kg/m2 were 1.62 times more likely to have a failed block and the rate of acute complications was higher in obese patients (BMI >30 kg/m2) compared with normal weight patients in one retrospective study of 6920 patients [66].

The use of ultrasound-guided regional techniques has been shown to reduce the number of attempts and time needed for peripheral block placement in normal weight patients. There are no trials comparing traditional and ultrasound-guided regional techniques in obese patients. In a retrospective study of 70 patients, the success rate of ultrasound-guided interscalene nerve blocks was similar in obese and nonobese individuals [67]. The technical aspects of ultrasound-guided peripheral nerve block are discussed elsewhere. (See “Overview of peripheral nerve blocks”, section on ‘Ultrasound guidance’ and “Peripheral nerve block: Techniques”.)

Intravenous anesthesia — Intravenous anaesthetic agents and adjuncts can also be used safely in obese patients to provide total intravenous anesthesia (TIVA), or to supplement inhalational or regional anesthetic techniques [70,71]. For patients with obstructive sleep apnea (OSA) under light to moderate sedation, carbon dioxide levels are continuously monitored, and an oral airway appliance (and potentially continuous positive airway pressure) used to prevent airway collapse and hypoxemia [27]. For deep sedation, a secure intubated airway is preferable in most cases.

Dosing of medications used for intravenous anesthesia (eg, propofol, opioids) is based upon total body weight (TBW), ideal body weight (IBW) or lean body weight (LBW) depending upon the agent [72]. However, clinical judgment and titration to clinical effect will be the guiding principles of dosing. (See ‘Monitoring’ below and “Management of the critically ill obese patient”, section on ‘Weight based dosing of medications’.)

As examples, propofol is initially based upon lean body weight (LBW) (calculator 1 and calculator 2) to achieve an acceptable level of anesthesia (table 4). Propofol accumulation does not appear to occur to a significant degree [73]. In contrast, opioid dosing is variable with the shorter-acting agents based upon IBW or LBW (eg, fentanyl, remifentanil), while others can initially be based upon LBW or TBW (eg, sufentanil) [74,75]. For the ultrashort-acting agent remifentanil, we suggest initially dosing according to IBW and titrating to clinical effect. [76-84]

The alpha-2 agonists, clonidine and dexmedetomidine, are adjuncts to anesthesia that can reduce intraoperative as well as postoperative opioid requirements. Given the high prevalence of obstructive sleep apnea in the morbidly obese population, minimization of opioid use and therefore its sedative effects is desirable. Unless medically or surgically contraindicated, alpha-2 agonists can be used as a part of a multimodal anesthetic regimen. Further studies are needed to determine optimal perioperative dosing and safety in obese surgical patients. (See ‘Multimodal analgesia’ below.)

  • In a small randomized trial, preoperative oral clonidine administered to obese patients with obstructive sleep apnea at a dose of 2 mcg/kg on the evening before, and again two hours prior to surgery reduced anesthetic requirements and intraoperative and postoperative opioid requirements [85].
  • In three additional trials evaluating bariatric patients, intraoperative intravenous dexmedetomidine similarly decreased anesthetic and opioid requirements, decreased postoperative antiemetic requirements, and shortened stay in the post-anesthesia care unit [86-88]. At least one case report describes opioid-free intraoperative management in an extremely obese patient using perioperative dexmedetomidine [89].

ANALGESIA — General considerations for the management of postoperative pain are discussed in detail elsewhere. (See “Management of postoperative pain”.)

Multimodal analgesia — A multimodal approach to pain management reduces the risk for respiratory depression and also reduces opioid-related side effects (eg, nausea, pruritus, delayed bowel function). (See “Pain control in the critically ill adult patient”, section on ‘Opioid side effects’ and “Overview of anesthesia and anesthetic choices”.)

In severely obese patients, multimodal analgesia should be used whenever possible, using potent non-steroidal anti-inflammatory analgesics (NSAIDs) such as ketorolac, along with local anesthetic wound infiltration [10,12,27,90-93]. Additional agents being investigated to further augment multimodal analgesia include ketamine and alpha-2 agonists, although no clear regimens have evolved yet. When patient-controlled analgesia (PCA) is used for severely obese patients with obstructive sleep apnea (OSA), the American Society of Anesthesiologists (ASA) suggests avoiding continuous infusion, unless PCA is being used for the opioid-tolerant patient who has a basal requirement [27].

Several observational studies and three trials support the opioid-sparing effect of multimodal postoperative pain management strategies in severely obese patients; however, the optimal timing and dosing and specific protocols have yet to be determined in this population of patients [91-95].

  • In a pilot study of 20 severely obese patients undergoing open gastric bypass surgery, patients were randomly assigned to receive preoperative ketorolac (30 mg, intravenous) plus incisional infiltration of a local anesthetic mixture (bupivacaine and epinephrine) or neither of these measures [94]. The postoperative analgesic requirements were 40 percent lower in the treated group.
  • Another trial of 114 patients undergoing open gastric bypass surgery compared multimodal therapy using wound infiltration with local anesthetic plus patient-controlled opioid analgesia, thoracic epidural analgesia, or patient-controlled opioid analgesia [95]. Pain scores were similar for the multimodal analgesia and thoracic epidural analgesia groups but lower compared with the group that received only patient-controlled opioid analgesia.
  • Another trial randomly assigned 50 patients undergoing bariatric surgery to clonidine plus an infusion of ketamine before anesthetic induction, or no pre-treatment. The treated group had significantly lower anesthetic requirements, faster time to extubation (15 versus 28 minutes), lower total tramadol dose (138 versus 252 mg), and lower pain scores compared with control patients [93].

Alternative analgesic therapies — Complementary strategies, including transcutaneous electrical nerve stimulation and acupuncture, can be used to supplement pharmacologic therapy to treat pain, further reducing opioid requirements. These modalities are considered to be virtually risk free. Transcutaneous electrical nerve stimulation (TENS) uses a small battery-operated device to provide continuous electrical impulses via surface electrodes, with the goal of providing symptomatic relief by modifying pain perception. Acupuncture consists of a family of procedures used to stimulate anatomical points with the goal of reducing pain. A systematic review of the literature evaluating these alternative analgesic therapies for postoperative pain found many high-quality studies documenting a positive effect for both modalities [96]. However, these strategies have not been specifically explored for the severely obese patient.

PERIOPERATIVE MANAGEMENT

Airway management — Endotracheal intubation of the severely obese patient can be difficult, even for an experienced anesthesiologist, due to anatomic oropharyngeal changes that compromise laryngoscopic visualization. (See ‘Obesity-related physiologic changes’ above.)

A ramped position is preferred for intubation and extubation and is optimal in the event of reintubation (picture 1). In one study of morbidly obese patients undergoing bariatric surgery in the “ramped position,” there was no relationship between the presence and severity of obstructive sleep apnea, body mass index or neck circumference and difficulty of intubation or laryngoscopy grade [97]. Only a Mallampati score of 3 or 4 or male gender predicted difficult intubation. (See “The difficult airway in adults”, section on ‘The LEMON© approach to difficult airway assessment’.)

Although trials evaluating the significance of a team approach to the potential difficult airway management in this patient population are lacking, an additional anesthesia clinician, the surgeon and the circulating nurse should be present during induction and emergence from general anesthesia to assist with any unforeseen airway crisis [11]. Strategies for intubating the obese patient and airway management are discussed in detail elsewhere. (See “Emergency airway management in the morbidly obese patient”.)

Respiratory care — Morbidly obese patients are at risk for adverse intraoperative and postoperative respiratory events [98-100]. Morbid obesity results in a restrictive pulmonary physiology that includes decreased functional residual capacity. (See ‘Obesity-related physiologic changes’ above.)

General anesthesia further decreases functional residual capacity, and gas exchange is altered more profoundly in morbidly obese patients than in nonobese patients [101]. Moreover, these changes persist longer during the postoperative period, rendering obese patients vulnerable to postoperative respiratory complications.

For intubated patients undergoing general anesthesia, oxygenation can be improved by vital capacity or recruitment maneuvers, which consists of the application of a positive inspiratory pressure between 35 and 55 cm H2O for a brief period, possibly followed by positive end-expiratory pressure of 10 cm H2O [7,8,102-104]. Recruitment maneuvers should not be performed until after hemodynamic stabilization following induction of general anesthesia has been achieved, and the patient is euvolemic. During laparoscopic surgery in morbidly obese patients, a positive end-expiratory pressure (PEEP) of approximately 15 cm H2O is effective in maintaining functional residual capacity and improving oxygenation [105,106]. However, higher levels of PEEP can induce hypotension due to decreased venous return, and patients may require increased fluid administration or vasopressors to maintain their blood pressure [103,105,107]. (See “Intraoperative management of adults with obstructive sleep apnea” and “Postoperative management of adults with obstructive sleep apnea”.)

At the completion of the procedure, the endotracheal tube should be removed in the operating room only if the patient is fully awake, reversed from neuromuscular blockade, and meets standard extubation criteria. Some patients may be slow to emerge from anesthesia, and will need to remain intubated for a short period of time in the recovery room. The severely obese patient who requires early re-intubation following surgery may have swelling and edema due to the prior surgical intervention and airway manipulation. These changes can pose unexpected challenges for repeat airway management and should be anticipated. Availability of adequate airway equipment and personnel to assist in airway management should be arranged, up to and including the potential need for a surgical airway. (See “Devices for difficult emergency airway management in adults”.)

A trial of 209 normal-weight patients at risk for respiratory failure found that early treatment of postoperative hypoxemia with noninvasive positive pressure ventilation (NIPPV) significantly reduced the incidence of reintubation, ICU length of stay, pneumonia, infection and sepsis [108]. In morbidly obese patients with obstructive sleep apnea undergoing laparoscopic bariatric surgery, NIPPV given immediately after extubation was found to significantly improve lung spirometry values at one hour and one day postoperatively, compared with continuous positive airway pressure (CPAP) started in the PACU [109]. The use of NIPPV is feasible in previously untrained patients in the presence of a trained respiratory technician [110].

Immediate postoperative use of continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) treatment of obese patients, particularly following intestinal surgery, should no longer be regarded as controversial. Based on data in nonobese and obese patients, CPAP can be recommended for the treatment of hypoxemia in the immediate postoperative period for most obese patients. Following gastrointestinal surgery such as gastric bypass, we prefer early joint decision between anesthesiologist, surgeon, respiratory technician and nurse to determine CPAP use in selected patients, emphasizing the team concept for the perioperative care of these patients [12]. Institutions are encouraged to develop protocols and pathways for perioperative care of obese patients that include standardized procedures for the use of CPAP or BiPAP.

Aspiration of air during CPAP treatment with possible disruption of fresh anastomotic suture lines was thought to be a concern and supported by at least one case report following gastric bypass surgery [111]. However, in a prospective study of 1067 gastric bypass patients, 15 anastomotic leaks occurred but only two were in patients using CPAP [112]. The authors concluded that CPAP is useful for treating hypoventilation without significantly increasing the risk for anastomotic leak. In another study in 310 patients undergoing gastric bypass surgery, 91 patients were treated postoperatively with CPAP and no anastomotic leaks occurred [113].

Some clinicians would still prefer to avoid immediate postoperative positive airway pressure therapy. In a prospective study of 1095 patients who underwent laparoscopic gastric bypass surgery, 811 patients had no known history of OSA and 284 patients had confirmed OSA. Of these 284 patients, 144 were considered CPAP or BiPAP dependant [114]. Postoperative positive airway pressure therapy was withheld in all cases, but aggressive incentive spirometry and early ambulation were instituted. No significant differences were found in length of stay or pulmonary complications between groups. No anastomotic leaks or deaths occurred in any of the patients and the authors concluded that postoperative positive pressure therapy can be safely omitted following laparoscopic gastric bypass surgery.

Fluid management — Optimal fluid management remains an unresolved issue in the general surgical population, let alone the population of obese surgical patients. Little to no generalizable evidence exists, other than accepted practice standards [12,115]. Intraoperative and perioperative fluid strategies in severely obese patients aim to maintain euvolemia [12]. However, euvolemia in this population is poorly defined, and clinical judgment based upon available measures of volume status and tissue perfusion remains the most important factor. (See “Intraoperative fluid management”.)

Monitoring — No high-quality evidence is available to suggest that intraoperative monitoring in the obese patient should be any different compared with normal-weight individuals. The intensity of intraoperative patient monitoring should be guided by the type of surgery and the patient’s comorbidities [12].

For the majority of patients, we use standard intraoperative monitoring, including oxygenation, ventilation, blood pressure, heart rate and body temperature. An appropriately-sized and possibly conically-shaped blood pressure cuff for noninvasive blood pressure (NIBP) measurement is desirable. However, alternative cuff location (eg, forearm or lower leg) is acceptable for most situations when body habitus prevents correct cuff positioning [12]. No studies are available that have determined the accuracy of alternative NIBP cuff locations and possible size mismatches. However, widespread use of NIBP assessment rather than routine invasive monitoring has shown this clinical practice to be safe for the majority of obese patients. If noninvasive blood pressure monitoring is technically not feasible, the threshold for arterial catheter placement should be low. As with the placement of peripheral nerve blocks or neuraxial anesthetics, ultrasound guidance may also be useful for arterial catheter placement. (See “Arterial catheterization techniques for invasive monitoring”, section on ‘Ultrasound guidance’.)

Brain monitoring devices using a processed EEG to assess depth of anesthesia can provide useful information during anesthetic delivery and recovery in morbidly obese patients [86,87,116,117]. These devices allow anesthetic agents to be titrated to achieve and maintain a desired level of anesthesia. Brain monitoring devices and monitoring for anesthetic underdosing are discussed in detail elsewhere. (See “Awareness with recall following anesthesia”.)

The obese patient requiring emergency surgery or returning emergently to the operating room within 24 to 48 hours of the initial major surgery can be a unique challenge to the care team. The patient’s physical status is often altered and the patient may exhibit signs of an early systemic inflammatory response following major surgery. There is essentially no literature to guide the caregivers in this situation. (See “Sepsis and the systemic inflammatory response syndrome: Definitions, epidemiology, and prognosis”, section on ‘Systemic inflammatory response syndrome’.)

The anesthesia and surgical teams should have a low threshold to establish additional vascular access and implement invasive arterial blood pressure monitoring, preferably prior to the induction of general anesthesia. Central venous access may be helpful for drug and fluid administration as well as assessment of the patient’s fluid status. (See “Placement of central venous catheters”.)

Positioning — The improperly positioned obese surgical patient can experience serious physiologic impairment, and even physical injury. Certain surgical positions are more hazardous than others in altering baseline cardiovascular and pulmonary function. (See ‘Obesity-related physiologic changes’ above.)

There is little evidence in the literature evaluating specific measures particular to positioning of morbidly obese patients during surgery or in the recovery room. Therefore, a common-sense approach should be taken that includes positioning the patient on an appropriately-sized operating room table, recovery stretcher or bed, and carefully padding pressure points especially between exposed limbs and guard-rails. Intraoperative positioning focuses on prevention of peripheral nerve injuries. (See “Nerve injury associated with pelvic surgery”.).

A comprehensive review of different intraoperative surgical positions and their impact on cardio-pulmonary function in obese patients is available [118], but there are no studies that address specific strategies that conclusively prevent or ameliorate potential detrimental effects beyond what is known for the surgical population in general. However, the Trendelenburg, lithotomy and particularly the prone position should be avoided in the morbidly obese patient whenever possible, because these exacerbate restrictive pulmonary physiology. In selected morbidly obese patients requiring prone positioning for surgery, we have successfully practiced awake fiberoptic intubation and self-prone positioning [119]. This strategy avoids the need for extended personnel for assistance with positioning and allows the patient to assume a comfortable position prior to induction of general anesthesia. During lateral positioning, care must be taken to avoid compression of the groin region as lower extremity ischemia has been reported in the dependent extremity [120].

Postoperatively, strictly supine positioning should be avoided in obese patients. A 30˚ upper body and head elevated position should be chosen. This position reduces the negative effects associated with a horizontal supine position including hypoxemia due to the restrictive pulmonary physiology, decreased functional residual capacity and airway obstruction.

The semi-upright position and avoiding the supine position whenever possible are also recommended by the American Society of Anesthesiologists for postoperative recovery in patients with obstructive sleep apnea [27]. In one study of patients with obstructive sleep apnea, the lateral decubitus position maintained airway patency by increasing the diameter of the pharyngeal airway compared with supine positioning [121]. The lateral decubitus position combined with head and upper body elevation should be used during recovery from general anesthesia unless contraindicated due to the nature of the surgery.

Discharge criteria — There is very little objective evidence in the literature to guide clinical decision-making regarding duration of postoperative monitoring in morbidly obese patients. Standards for the postoperative care of surgical patients published by the American Society of Anesthesiologists (ASA) should be followed [122]. However, the ASA recently published practice guidelines for the perioperative care of patients with obstructive sleep apnea (OSA), mostly based on expert opinion consensus [27]. These guidelines suggest that prior to transfer of the patient to an unmonitored setting, their oxygen saturation on room air should return to their baseline, and when left undisturbed the patient should not develop clinical hypoxemia or airway obstruction.

It has been suggested that patients with OSA may need to be continuously monitored with pulse oximetry for a median of three hours longer than their non-OSA counterparts, and that monitoring should continue for a median of seven hours after the last episode of hypoxemia or airway obstruction. There are no studies examining whether this monitoring reduces risk or improves outcomes in OSA patients. In our practice, we adhere to the ASA standards with a low threshold for prolonged recovery room monitoring based upon the individual patient’s course.

 

SUMMARY AND RECOMMENDATIONS

  • The percentage of severely obese and morbidly obese patients in the population is increasing and it is relatively common for the anesthesiologist to administer anesthesia to patients who meet criteria for morbid obesity (ie, body mass index [BMI] >40 kg/m2) for routine elective surgery or surgery for weight loss. (See ‘Introduction’ above.)
  • Severe obesity is associated with physiologic changes that impact the delivery of anesthesia. These include alterations in oropharyngeal anatomy, pulmonary mechanics and the pharmacokinetics of drug absorption and elimination. (See ‘Obesity-related physiologic changes’ above.)
  • The preoperative evaluation of severely obese patients undergoing major surgery should include consultation with an anesthesiologist. Although increased body mass index in the absence of comorbidities is not associated with adverse postoperative outcomes in patients undergoing noncardiac surgery (except for thromboembolism), the presence of metabolic syndrome, cardiovascular disease, hypertension, type 2 diabetes mellitus, obstructive sleep apnea, and kidney disease increase the risk for complications. (See ‘Anesthesia consultation’ above.)
  • The anesthesiology consultation, including history and physical examination and selective preoperative testing, aims to identify those severely obese patients who have silent comorbidities and those at risk for airway and respiratory compromise during and following anesthesia. (See ‘Preoperative testing’ above.)
  • Preoperative nocturnal positive pressure airway therapy is beneficial in severely obese patients with established or newly diagnosed obstructive sleep apnea. Preoperative positive airway pressure therapy is associated with improvements in physiology that facilitate anesthetic management. (See ‘Positive airway pressure therapy’ above and “Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea”, section on ‘Preoperative evaluation’.)
  • The choice of anesthetic technique for severely obese patients should be guided by the requirements of the surgical procedure, comorbidities and patient preferences. General anesthesia, regional anesthetic and sedation techniques have all been employed safely in obese patients, and no technique has been found to be superior over another with respect to important clinical outcomes. Regardless of technique chosen, the goals for anesthetic management of obese patients (and particularly in the presence of sleep apnea) include minimizing opioid administration to decrease the risk of respiratory depression, and when using general anesthesia, to allow rapid emergence. (See ‘Anesthetic management’ above.)
  • Prone, flat supine and Trendelenburg positioning should be avoided in severely obese patients whenever possible. Postoperatively, a head up 30° position combined with a lateral decubitus positioning, when possible, minimizes compromise to airway and respiratory function. (See ‘Positioning’ above.)
  • In severely obese patients, we suggest using multimodal analgesia that is opioid-sparing (Grade 2B). Multimodal analgesia including the use of non-steroidal anti-inflammatory drugs, alpha-2 agonists and wound infiltration with local anesthetic reduces the risk for respiratory depression and other opioid-related side effects. (See ‘Multimodal analgesia’ above.)
  • Postoperatively, strategies to reduce pulmonary complications in severely obese patients include early institution of noninvasive positive pressure ventilation (NIPPV) for hypoxemia, and other measures to decrease postoperative atelectasis (eg, head-up positioning, positive airway pressure therapy, incentive spirometry). (See ‘Respiratory care’ above.)
  • Body mass index >30 kg/m2 does not appear by itself to be a contraindication to outpatient surgery in severely obese patients. However, there are no high-quality studies to guide patient or procedure selection. Factors important to safely perform surgical procedures at freestanding ambulatory facilities include the immediate availability of emergency difficult airway equipment, advanced respiratory care equipment, access to laboratory and radiology facilities, and transfer agreements for patient transfer to an external facility. The establishment of clinical pathways for the care of obese patients undergoing a variety of other procedures, and particularly for those procedures performed in the day surgery setting, may reduce morbidity. (See ‘Ambulatory versus inpatient surgery’ above.)
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