Anesthesia for the patient with obesity

INTRODUCTION — As the prevalence of obesity increases worldwide, an increasing number of surgical patients with obesity will require anesthesia. Obesity is typically defined by body mass index (BMI), the ratio of weight (in kilograms) to the square of height (in meters) (calculator 1). In adults, the World Health Organization and the National Institute of Health define obesity as a BMI ≥30 kg/m².

This topic reviews the changes in anatomy and physiology in patients with obesity that affect anesthetic management, anesthetic drug dosing in obesity, and planning the anesthetic as it differs from patients with normal BMI. Preoperative medical evaluation of patients with obesity, the impact of obstructive sleep apnea on anesthetic management, and general principles and techniques in anesthesia are discussed separately.

●(See "Preanesthesia medical evaluation of the patient with obesity".)

●(See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea".)

●(See "Intraoperative management of adults with obstructive sleep apnea".)

●(See "Postoperative management of adults with obstructive sleep apnea".)

The choice of inpatient versus ambulatory surgery in patients with obesity is also discussed separately. (See "Preanesthesia medical evaluation of the patient with obesity", section on 'Ambulatory versus inpatient surgery'.)

PHYSIOLOGIC CHANGES ASSOCIATED WITH OBESITY — Increasing obesity leads to respiratory and cardiovascular changes that impact the delivery of anesthesia and perioperative analgesia.

Alterations in airway anatomy caused by obesity are discussed separately. (See "Preanesthesia medical evaluation of the patient with obesity", section on 'Airway assessment'.)

Respiratory physiology — Obesity-related respiratory changes occur as a consequence of physical impingement on lung volumes and chest movement as well as the increased metabolic requirements of excess tissue; these in turn lead to increased work of breathing [1], increased oxygen (O₂) consumption [2], increased carbon dioxide (CO₂) production [3,4], and disordered ventilation to perfusion matching [5].

As a consequence, respiratory rates are increased, and functional residual capacity (FRC) and expiratory reserve volume (ERV) are decreased, even in mild obesity [6]. FRC may be sufficiently reduced such that small airways and alveoli remain closed during spontaneous ventilation, leading to ventilation-perfusion mismatch and right to left shunting [7]. Lung volumes and intrapulmonary shunt worsen with the induction of general anesthesia in all patients, but to a much greater degree in patients with obesity [8,9]. The supine position and obstructive sleep apnea (OSA) increase the magnitude of these effects [10,11].

Consequences of these changes of concern to anesthesiologists include the following:

●Decreased time to desaturation during apnea [12]

●Increased O₂ requirements [2]

●Hypoventilation with supine spontaneous ventilation [11]

Modifications of airway management, patient positioning, and ventilation in response to these issues are discussed below. A general discussion of respiratory changes in obesity is found separately. (See "Chest wall diseases and restrictive physiology", section on 'Obesity'.)

Cardiovascular physiology — Cardiovascular physiologic changes in obesity include:

●Increased circulating blood volume, although it is a lower proportion of total weight (50 mL/kg as compared with 75 mL/kg) compared with patients with normal body mass index (BMI) [13].

●Decreased systemic vascular resistance [14,15].

●Increased cardiac output by 20 to 30 mL per kilogram of excess body fat.

Stroke index, cardiac index, and heart rate remain normal; the increased cardiac output occurs by means of expanded stroke volume [16].

●Left ventricular hypertrophy, related to the duration of obesity [17].

The increased cardiac output can lead to either left ventricular failure (especially when associated with hypertension) or right heart failure (especially when associated with the hypoxia and hypercapnia of OSA) (figure 1).

Hypertension and cardiovascular disease are more prevalent in patients with obesity and when present may produce additional structural and hemodynamic changes (table 1). (See "Preanesthesia medical evaluation of the patient with obesity", section on 'Cardiovascular disease' and "Obesity: Association with cardiovascular disease".)

DOSING ANESTHETIC DRUGS — The optimal method for calculating weight-based doses of many medications in patients with obesity is unclear, with limited available literature. When possible and appropriate, anesthetic medications should be titrated to effect with incremental doses or incrementally adjusted infusions. Our dosing strategy for patients with obesity is based on available pharmacokinetic and pharmacodynamic data in obesity, such data in patients without obesity, clinical experience, and the clinical use of the drug. Suggested dosing scalars for commonly used medications are shown in a table (table 2).

Modified drug dosing may be required because of obesity-related increases in lean body weight (LBW), cardiac output, and blood volume, as well as changes in regional blood flow (table 3); these can affect peak plasma concentration, clearance, and elimination half-life of many drugs [18]. Dosing is generally based on volume of distribution for bolus doses, and on clearance for infusions or repeat boluses. Some effects of obesity on pharmacokinetics are as follows:

●The volume of distribution (V_d) is the principal determinant of loading dose of drugs. The V_d of relatively lipophilic drugs is increased by obesity; less lipophilic drugs have little change in V_d in patients with obesity, as blood flow to fat tissue is lower than blood flow to vessel-rich or lean tissue [19]. V_d is largely dependent on the physiochemical attributes of a drug and varies with plasma protein binding and tissue blood flow, but changes are not consistent for all drugs within a category, and in many cases have not been determined [18].

●Drug clearance is generally higher in individuals with obesity than individuals of normal weight [18]. This is largely controlled by hepatic and renal physiology. Obesity affects hepatic metabolic pathways in different ways, with some only slightly and others significantly enhanced in obesity [19]. Renal elimination includes glomerular filtration, tubular secretion, and tubular reabsorption; changes are observed in obesity, but vary by drug and are not completely understood.

●The elimination half-life (t_1/2) impacts dosing interval and dosing of continuous infusions. The t_1/2 of a drug varies directly with V_d, and inversely with the clearance, both of which are altered in obesity. For prolonged infusion of highly lipophilic drugs, the t_1/2 and drug effect may be markedly prolonged after discontinuation of the infusion, due to increased V_d.

While somewhat difficult to predict, pharmacodynamic changes also occur in individuals with severe obesity; for example, therapeutic windows may be narrowed or side-effects exaggerated for some drugs.

Weight based drug dosing in patients with obesity can be based on actual total body weight (TBW), or one of several calculated scalars, including the following:

●Ideal body weight – Ideal body weight (IBW) is the weight associated with maximum life expectancy. It is calculated solely from the patient's height, with different equations for males and females, based on actuarial tables (calculator 2).

●Lean body weight – LBW is the difference between total body weight and fat mass. It is usually calculated with a sex-specific formula that includes both height and weight (calculator 3 and calculator 4), and accounts for the fact that as weight increases, lean body mass increases as well. Thus calculated LBW in patients with obesity is generally higher than IBW (table 4). Lean body weight calculations have not been validated for extremely patients with obesity and may be inaccurate for patients who weigh more than approximately 200 kg [20].

●Adjusted body weight – Adjusted body weight (AdjBW) is calculated by applying an adjustment factor to estimate the proportion of adipose tissue to which a drug distributes. For drug dosing in patients whose weight is >20 percent above IBW, an adjustment factor of 40 percent is usually used, as follows:

When the optimal dosing method for a specific drug is unknown, it is reasonable to base doses on AdjBW, except for highly lipophilic drugs (eg, midazolam, fentanyl, sufentanil) for which TBW should usually be used [18]. The rationale for using AdjBW is to avoid the underdosing that may occur with use of LBW, and the overdosing that may occur with use of TBW. However, because of the complexities of pharmacokinetics and pharmacodynamics introduced by obesity, the choice of the most appropriate dosing scalar for some drugs is debated.

While somewhat difficult to predict, pharmacodynamic changes also occur in individuals with severe obesity; for example, therapeutic windows may be narrowed or side-effects exaggerated for some drugs.

Dosing algorithms for target controlled infusion devices (not available in the United States) in patients with obesity have been published, though the optimal weight scalar for patients with obesity is unclear [21-23]. (See "Intravenous infusion devices for perioperative use", section on 'Target-controlled infusion systems'.)

Effects of obesity on the required concentrations of inhaled anesthetics are discussed below. (See 'Maintenance' below.)

CHOICE OF ANESTHETIC DRUGS — Due to the high prevalence of sleep apnea in patients with obesity and associated potential sensitivity to sedatives and opioids, the use of long-acting respiratory depressants should be minimized in these patients. The guiding principle should be to use shorter acting and minimally fat soluble agents whenever feasible to allow for rapid recovery of consciousness, protective reflexes, and mobility [24,25].

SPECIAL EQUIPMENT NEEDS — The ability to safely anesthetize patients with severe obesity may require additional equipment that is not typically immediately available. These include:

●Specialized or extra equipment for positioning – (See 'Patient positioning' below.)

●Large and/or high weight capacity beds and operating tables – Designated weight limits for operating tables may not remain valid if the patient is shifted on the table, the table is positioned other than level (eg, Trendelenburg, reverse Trendelenburg, lateral tilt), or the table is unlocked [26]. Additional arm supports to widen the table, or the use of two operating tables, may be necessary.

●Mechanical transfer mechanisms – Various means of mechanically assisting the transfer of patients with severe obesity between stretchers and beds have been developed (eg, inflatable lateral transfer mattress). These may improve patient safety and prevent injury to care personnel.

●Additional personnel – Assistance may be needed to transfer and position patients safely.

●Extra-long needles – Normal length epidural, spinal, and nerve block needles may be insufficient to access structures in patients who are severely obese.

●Ultrasound – Ultrasound may be used to assist in vascular access, nerve block, and neuraxial procedures [27,28]. (See "Overview of peripheral nerve blocks", section on 'Ultrasound guidance'.)

PATIENT PREPARATION FOR ANESTHESIA — Preparation for anesthesia includes measures to prevent aspiration, and application of standard American Society of Anesthesiologists (ASA) monitors.

Aspiration prophylaxis — Standard preoperative fasting guidelines should be followed for patients with obesity; for patients without additional risk factors for aspiration (eg, gastroesophageal reflux, gastroparesis, bowel obstruction), this means fasting for two hours for clear liquids, and six hours for solid food (eight hours for high protein or fatty food), prior to anesthesia (table 5). In most studies gastric emptying of both liquids and solids is not delayed in patients with obesity and may be more rapid than in patients of normal weight [29-31].

We agree with the practice guidelines of the ASA that do not recommend routine use of pharmacologic medication to decrease aspiration risk in patients without an increased risk of aspiration [32]. Severe obesity did not correlate with gastroesophageal reflux in a study of 250 patients [33], and there is no evidence that aspiration risk is increased in obesity. Patients with obesity who are at increased risk of aspiration are managed in the same manner as patients without obesity.

As point of care ultrasound is increasingly used in the operating room for a variety of purposes, gastric ultrasound has been utilized in clinical trials to assess gastric volume. In one small study in patients with severe obesity patients, gastric ultrasound estimated gastric volume correlated well with volume of gastric aspirate, with accuracy similar to that reported for gastric ultrasound in patients of normal weight [34]. However, similar to other methods for assessing gastric volume, results have not been correlated with the risk of aspiration during anesthesia.

Sedative premedication — If premedication is required for patients with obesity, sedatives should be administered incrementally, at lower doses than typically used, titrated to effect and to avoid side effects. Premedication of the patient with obesity should ideally allow anxiolysis without abolishing airway reflexes or preventing patient cooperation prior to induction of general anesthesia.

MANAGEMENT OF ANESTHESIA

Blood pressure monitoring — In patients with obesity, during general anesthesia we measure intermittent non-invasive blood pressure no less than every three minutes, and more often as needed. Accurate, frequent or continuous blood pressure measurement is important in clinical practice. (See "Hemodynamic management during anesthesia in adults", section on 'Blood pressure targets'.)

Noninvasive blood pressure measurement in patients with obesity is often complicated by the size and conical shape of their upper arms [35]. Invasive arterial blood pressure monitoring should be considered when surgical and/or patient conditions suggest a critical need for accurate blood pressure monitoring and or repeated intraoperative blood sampling.

Blood pressure cuffs must often be applied for patients with obesity in either a crisscross fashion, or with gaps at the lower end of the cuff, which may result in inaccurate measurement. Alternate cuff locations (eg, forearm or lower leg) are often used to obtain a better fit. Two small observational studies of intraoperative [36] and postoperative blood pressure measurement [37] in patients who are severely obese suggest that the lower arm may be a reasonable alternative to the upper arm. Compared with upper arm measurement, both studies reported better or acceptable agreement between the forearm mean arterial cuff pressure versus invasive mean arterial pressure. We frequently place a forearm cuff when upper arm cuff does not fit adequately, although validation of the accuracy in a large patient cohort has yet to be conducted.

The optimal size blood pressure cuff for lower arm placement has not been determined, and practice varies. In the studies mentioned above, a standard adult blood pressure cuff was used for all patients [36], and the other used cuff sizes recommended for the patients' arm circumference [37]. However, arm circumference is rarely measured in clinical practice. One retrospective study of over 100 bariatric surgical patients found that a regular size cuff fit best on the forearm in patients with BMI between 40 and 55 kg/m², and a large cuff fit best for patients with BMI >55 kg/m² [38].

A conical shaped blood pressure cuff is commercially available and may be an option for improved accuracy for noninvasive blood pressure measurement in patients with obesity. In a study including 34 non-surgical patients with a mean body mass index (BMI) of 33 kg/m², lower arm blood pressure measurements with the conical cuff were validated against a radial arterial line and determined to be acceptable, defined as an absolute average error of ≤5 mmHg, with a standard deviation of ≤8 mmHg [39]. Larger perioperative studies, including patients with higher mean BMI, are required before recommending this cuff for routine use.

The volume clamp system is a new technology that uses a finger cuff for noninvasive continuous beat to beat blood pressure measurement as well as assessment of additional hemodynamic parameters. Studies comparing this technology with arterial pressure measurement in bariatric surgical patients have reported conflicting results [36,40,41]. Two studies using the same device found good agreement with invasive arterial blood pressures with respect to trending and absolute values for mean arterial blood pressures [36,41]. Another study using a different device based on the same physiologic principle found good trending agreement, but absolute values for mean arterial pressure were not interchangeable [40]. Larger scale trials are needed to validate these reports, which included a limited number of patients and clinical circumstances. (See "Basic patient monitoring during anesthesia", section on 'Noninvasive blood pressure monitoring'.)

Patient positioning — Particular care is required when positioning patients with obesity for surgery. The improperly positioned patient can experience physiologic derangement (eg, impaired ventilation), nerve or tissue damage, rhabdomyolysis, or injury related to falls. The risk of developing rhabdomyolysis after bariatric surgery increases with male sex, elevated BMI, and prolonged operating time [42]. Nerve and tissue injury related to patient positioning for surgery are discussed in detail separately. (See "Patient positioning for surgery and anesthesia in adults", section on 'Nerve injury' and "Patient positioning for surgery and anesthesia in adults", section on 'Skin and tissue injury'.)

Considerations related to different positions for patients with obesity include the following:

●Supine or head-down (Trendelenburg) positions – Decreased lung volumes and increased work of breathing (caused by the weight of the intra-abdominal contents on the diaphragm), and increased venous blood return (leading to increased cardiac output) occur when compared with the head-up (reverse Trendelenburg) or sitting positions. In patients with obesity, these changes can cause more rapid oxygen desaturation during apneic periods, increased pulmonary shunt, hypoventilation with spontaneous breathing, and edema of the head and neck after lengthy periods [43]. (See "Patient positioning for surgery and anesthesia in adults", section on 'Trendelenburg'.)

●Head-up position (reverse Trendelenburg, or semi-sitting/"semi-Fowler") – Upright or semi-upright positions improve respiratory function in patients with obesity by reducing pressure on the chest wall and diaphragm. (See "Patient positioning for surgery and anesthesia in adults", section on 'Reverse Trendelenburg'.)

Head up positioning is useful during preoxygenation and improves both mask ventilation and the view at laryngoscopy. (See "Airway management in the morbidly obese patient for emergency medicine and critical care", section on 'Positioning' and 'Positioning for airway management' below.)

When the entire bed is tilted, care must be taken to prevent the patient sliding down the bed, especially if arms are secured to fixed arm supports; use of a foot plate may be helpful and should be strongly considered.

●Prone – Patients with obesity who are properly positioned prone for general anesthesia may have improved respiratory function, with increased functional residual capacity (FRC), lung compliance, and oxygenation, compared with supine position [44]. (See "Prone ventilation for adult patients with acute respiratory distress syndrome".)

Patient supports should be placed under the chest and pelvis rather than the abdomen (which should be compression-free) to avoid increasing intra-abdominal pressure [45]. In selected cases, patients have been intubated awake, and then allowed to comfortably position themselves prone, prior to the induction of anesthesia; this eliminates the need for operating room personnel to turn and position the patient, and allows identification of pressure points by the patient before injury occurs [46,47]. (See "Patient positioning for surgery and anesthesia in adults", section on 'Prone'.)

●Lateral decubitus – The lateral position removes the weight of the abdomen from the diaphragm and increases the diameter of the pharyngeal airway [48]. The lateral decubitus position combined with head and upper body elevation may be helpful during recovery from general anesthesia, unless contraindicated due to the nature of the surgery.

Chest pads or rolls used to avoid axillary compression during lateral positioning may need to be larger than is standard. It can be challenging to support the head in a neutral position, as the neck is often short and wide; extra pieces of foam and rolled towels can be helpful. Standard bean-bags may be too narrow to support patients with obesity, so alternatives should be sought to maintain the patient in lateral position. Use of gel-pads may prevent injury to pressure points such as the hip. (See "Patient positioning for surgery and anesthesia in adults", section on 'Lateral decubitus'.)

●Lithotomy position – Lithotomy position decreases lung volumes by shifting abdominal contents towards the diaphragm, which may contribute to hypoxia and hypoventilation. Correct positioning and adequate padding of the legs is critical; neurologic injury or compartment syndrome may result from prolonged pressure [49,50]. Specially designed leg holders may be necessary to accommodate the size and weight of the legs. (See "Patient positioning for surgery and anesthesia in adults", section on 'Lithotomy'.)

Beds and equipment used to support patients with obesity must be constructed to support the additional weight and must provide sufficient space to avoid pressure from side-rails. Carefully padding pressure points will help to prevent pressure-related peripheral nerve injuries.

Positioning should be checked regularly during the maintenance phase of general anesthesia, as large patients are prone to shift position when the operating table is tilted and may need to be repositioned. The use of Velcro to attach the mattress to the bed can help prevent slipping.

Choice of anesthetic technique — General anesthesia, regional anesthesia, and sedation have all been employed safely in patients with obesity, and overall, no technique has been found to be superior to another with respect to important patient outcomes specifically in patients with obesity (eg, mortality, cardiopulmonary complications).

When regional anesthesia (ie, neuraxial anesthesia, peripheral nerve blocks, local anesthesia) is feasible, these techniques are often considered in patients with obesity, particularly those with obstructive sleep apnea (OSA), to reduce the potential for respiratory or airway related problems [51-53]. However, these benefits are reduced if the patient requires moderate or deep sedation to tolerate a procedure with regional anesthesia.

Neuraxial anesthesia and peripheral nerve blocks offer the advantages of improved postoperative pain control, reduced use of opioids for postoperative analgesia, and consequently decreased potential for drug-induced respiratory depression. Postoperative epidural analgesia may mitigate postoperative respiratory dysfunction in patients with obesity who undergo upper abdominal or thoracic procedures, though it has not been shown to improve outcomes [54,55]. Whereas landmarks for neuraxial anesthesia and nerve blocks may be less palpable in these patients, in most cases these techniques can be accomplished [56-58]. Ultrasound guidance and long needles may be required. (See 'Neuraxial anesthesia' below and 'Peripheral nerve blocks' below.)

When either regional anesthesia or general anesthesia would be possible for a particular procedure, the following factors should be considered, and may make general anesthesia preferable:

●Positioning – Patients with obesity have decreased respiratory tolerance for supine, lithotomy, or head-down positioning, and may require ventilatory assistance or airway control in these positions. (See "Patient positioning for surgery and anesthesia in adults", section on 'Physiologic effects of Trendelenburg positioning'.)

Patients with obesity may also be uncomfortable in the prone position due to pressure on the abdomen, and may require more sedation to tolerate this discomfort.

●Need for controlled ventilation – Spontaneous breathing in patients with prominent abdominal obesity may interfere with the need for an immobile abdominal or pelvic surgical field; these patients may require controlled ventilation under general anesthesia, with either an endotracheal tube (ETT) or supraglottic airway designed for controlled ventilation (eg, Proseal laryngeal mask airway [LMA]). (See 'Airway management' below.)

●Anticipated difficult mask ventilation or intubation – If airway difficulty is anticipated, it may be prudent to intubate in a controlled manner at the beginning of the case, rather than after problems develop. This decision should be individualized, based partly on access to the airway during surgery, and the likelihood that regional anesthesia will be effective for the duration of the procedure. (See "Preanesthesia medical evaluation of the patient with obesity", section on 'Airway assessment' and 'Airway management' below.)

●Need for sedation – When sedation is offered to patients with obesity, they should understand that the sedation level may be light. Patients who are particularly anxious, or who would require deeper levels of sedation to tolerate longer procedures (particularly in uncomfortable positions), may not be good candidates for regional anesthesia, due to potential for sedatives or opioids to cause airway obstruction or hypoventilation. Hypercapnia may be especially problematic in patients with pulmonary hypertension due to OSA or obesity hypoventilation syndrome.

General anesthesia — Modifications of the approach to general anesthesia in patients with obesity center largely on respiratory issues. Patients with obesity have a higher incidence of hypoxia and respiratory events in the perioperative period than patients with normal BMI [59,60]. Because these patients desaturate more quickly during apneic periods, the anticipation and management of respiratory problems is critical.

Obesity is a risk factor for accidental awareness during general anesthesia, particularly during the dynamic phase of induction with intravenous agents, possibly due to rapid redistribution of the drug [61-63]. (See 'Induction' below.)

Airway management

Choice of airway device — Patients with obesity are seldom managed with mask ventilation alone; mask ventilation is generally restricted to brief anesthetics (eg, an examination under anesthesia, knee manipulation, or electroconvulsive therapy). Face mask ventilation can be technically challenging in these patients because of difficulty with mask fit and handling, or obstruction related to abundant oropharyngeal tissue or a large tongue.

Patients with obesity are more likely to require intubation rather than a supraglottic airway (SGA; eg, LMA). They are more likely to require controlled ventilation to prevent hypoventilation, and during positive pressure ventilation, an SGA may not maintain a seal at the higher airway pressures needed in patients with obesity. Use of a pressure support ventilation mode in the presence of an SGA may be a feasible alternative in some cases. Obesity-specific criteria for the use of a supraglottic airway have not been established, and practice varies. However, we consider the degree and distribution of obesity, type and length of surgery, patient position, and intraoperative accessibility to the head and neck to determine whether an SGA is appropriate. We prefer to control ventilation with an endotracheal tube in any of the following circumstances:

●Patients with BMI >45 kg/m²

●Patients with primarily abdominal obesity

●Major abdominal or thoracic surgery

●Most surgery lasting >2 hours

●Head down or lithotomy positioning

In addition to the above considerations, some experts advocate using an endotracheal tube for airway management in patients who have undergone sleeve gastrectomy weight loss procedures, due to a high incidence of reflux of gastric contents, regardless of symptoms. (See "Laparoscopic sleeve gastrectomy", section on 'GERD'.)

For patients with obesity in whom we use an SGA, we usually use second generation SGAs which are designed for controlled ventilation, allow higher seal pressures, and provide a gastric vent. (See "Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults", section on 'Choice of supraglottic airway'.)

Difficulty with airway management — Obesity is associated with risk factors for potential difficulty with all aspects of airway management (ie, mask ventilation, use of SGA, endotracheal intubation, extubation). These issues are discussed separately. (See "Airway management for induction of general anesthesia", section on 'Obesity as a risk factor'.)

The plans for airway management during anesthesia follow from assessment of risk factors for difficulty with airway management, the history of prior attempts at airway management, and the risk factors for aspiration. Airway assessment, creation of a strategy for airway management, and management of the difficult airway are discussed in detail separately. Algorithms for difficult airway management are also provided (algorithm 1 and algorithm 2). (See "Airway management for induction of general anesthesia" and "Management of the difficult airway for general anesthesia in adults".)

Positioning for airway management — Preoxygenation is ideally performed in head-up (reverse Trendelenburg) position to maintain oxygenation, as both the supine position and the induction of anesthesia decrease lung volumes in the patient with obesity [64-66]. In addition, patients positioned with the back up and head elevated are easier to mask ventilate [67], and there is a better view of the airway during direct laryngoscopy compared with those in the flat horizontal supine position. (See "Airway management in the morbidly obese patient for emergency medicine and critical care", section on 'Positioning'.)

For preoxygenation and intubation in patients with obesity, we routinely tilt the operating table head up, and in addition place the patient in a ramped position with the back up and the head elevated [68]. The goal for this position is to align the external auditory meatus and the sternal notch in a horizontal plane (figure 2). The bed can be placed in the semi-Fowler's position, or a stack of blankets or a pre-formed or inflatable ramp can be used to achieve a ramped position. When supports are added to the bed to raise the upper trunk, it is important to provide sufficient support to the arms in order to maintain a neutral position and prevent nerve injury from excessive tissue stretch at the shoulders.

Preoxygenation and apneic oxygenation — Preoxygenation is used to increase oxygen reserves in order to prevent hypoxemia during apnea. Preoxygenation and apneic oxygenation are particularly beneficial for patients with obesity, who are expected to desaturate rapidly during apnea related to attempts at airway management. There is less time to rescue the patient with obesity in a failed airway situation (cannot ventilate, cannot intubate) due to rapid apneic desaturation. (See "Preoxygenation and apneic oxygenation for airway management for anesthesia".)

Preoxygenation can be performed via a tight-fitting facemask using 100 percent oxygen (O₂) at a flow rate high enough to prevent rebreathing (10 to 12 L/min), aiming for an end-tidal concentration of O₂ greater than 90 percent to maximize safe apnea time. Patients should be preoxygenated with either three minutes of tidal volume (TV) breathing or eight vital-capacity breaths over 60 seconds. These two techniques have been shown to be equally effective at preventing desaturation and are more effective than four vital-capacity breaths over 30 seconds [69-71].

Preoxygenation with manually-applied positive end-expiratory pressure (PEEP), or the use of noninvasive ventilation (NIV), will improve oxygenation in patients with obesity who tolerate it [72]. (See "Preoxygenation and apneic oxygenation for airway management for anesthesia", section on 'Positive airway pressure techniques during preoxygenation'.)

The use of nasal cannula for passive apneic oxygenation during laryngoscopy can prolong the time to desaturation in high-risk patients during airway management [73-76]. We suggest the administration of oxygen by nasal cannula at 10 L as tolerated by the patient in addition to facemask oxygen in those patients who are at high risk for difficult laryngoscopy and intubation. Where available, heated humidified high flow nasal oxygen can significantly delay apneic desaturation, including in patients with obesity [77]. As an example, in a randomized trial including 40 patients with BMI ≥ 40 kg/m², preoxygenation and apneic oxygenation with high flow nasal oxygen prolonged time to desaturation to ≤95 percent by a mean of 76 seconds (95% CI 33-118 seconds), absolute difference 261 versus 156 seconds [78].

When high concentration oxygen is used during induction of anesthesia, resorption atelectasis may occur, particularly in patients with obesity [79-81]. Decreasing the fraction of inspired oxygen (FiO₂) during preoxygenation prevents atelectasis but reduces the duration of safe apnea. Thus, the relative risk of atelectasis versus the risk of rapid desaturation must be assessed by the clinician when deciding whether to use 100 percent oxygen for preoxygenation, or a lower FiO₂. Use of a recruitment maneuver and prompt application of PEEP after intubation may prevent or reverse resorption atelectasis. (See 'Ventilation management' below and "Preoxygenation and apneic oxygenation for airway management for anesthesia", section on 'Complications of preoxygenation'.)

Induction — Anesthetic induction agents (ie, propofol, ketamine, etomidate, methohexital) should be chosen based on patient factors other than obesity (see "General anesthesia: Intravenous induction agents"). Dose of induction agents may require modification for obesity (table 2).

Rapid redistribution of IV induction agents is thought to contribute to the risk of awareness during induction in patients with obesity [62]. If induction is prolonged for any reason, additional doses of induction agents should be administered. Some experts recommend using processed electroencephalograph (EEG) monitors (eg, BIS) during induction in patients with obesity, though it is unclear to what extent these monitors can reliably prevent awareness during induction. (See "Accidental awareness during general anesthesia".)

Obesity itself is not an indication for rapid sequence induction and intubation (RSII). However, it is reasonable to use a rapid acting neuromuscular blocking agent (ie, succinylcholine or high dose rocuronium) for endotracheal intubation in patients with obesity, to shorten the interval during which mask ventilation (which may be a struggle) may be needed.

If RSII is indicated for reasons other than obesity, low pressure mask ventilation may be required to prevent or treat oxygen desaturation. (See "Rapid sequence induction and intubation (RSII) for anesthesia", section on 'Modified RSII'.)

Maintenance — Maintenance intravenous and inhaled anesthetic agents should be chosen based on patient factors other than obesity. (See "Maintenance of general anesthesia: Overview".)

The literature on the use of inhaled and intravenous anesthetics in patients with severe obesity is conflicting regarding anesthesia relevant endpoints and outcomes. Several studies have reported more rapid emergence and recovery from anesthesia with the use of desflurane, compared with sevoflurane, isoflurane, or propofol [82-84], whereas other studies have reported no differences in recovery or other outcomes [85-88].

In a study of adult patients with severe obesity, the end-tidal sevoflurane concentration required to maintain 50 percent of patients at a bispectral index (BIS) of <50 was 1.6 percent [89], higher than that reported in a separate study of adults of normal weight (0.97 percent) [90].

Nitrous oxide (N₂O) may be used to supplement either volatile anesthetics or propofol in patients with obesity, though the concentration of N₂O may have to be limited to allow an adequate FiO₂. Use of N₂O during laparoscopic surgery is controversial and is discussed separately. (See "Anesthesia for laparoscopic and abdominal robotic surgery in adults", section on 'Use of nitrous oxide'.)

Ventilation management — When patients are managed with spontaneous respiration (either with an SGA or an ETT), minute ventilation and end-tidal carbon dioxide (CO₂) should be closely monitored to assure adequate ventilation. We use continuous positive airway pressure (CPAP) during spontaneous respiration to improve oxygenation. When patients are unable to maintain sufficient volumes, ventilation should be assisted or controlled. The addition of pressure support assistance to PEEP may result in adequate ventilation; otherwise, ventilation should be controlled with either pressure or volume control. (See "Mechanical ventilation during anesthesia in adults", section on 'Modes of intraoperative mechanical ventilation'.)

When patients with obesity are managed with controlled ventilation, we recommend using a lung protective ventilation strategy to avoid lung damage, based on the available evidence and expert opinion, including this author [91,92]. This consists of low TVs, low levels of oxygen (as tolerated), PEEP, and perhaps recruitment maneuvers, as follows (see "Overview of initiating invasive mechanical ventilation in adults in the intensive care unit", section on 'Settings' and "Mechanical ventilation during anesthesia in adults", section on 'Lung protective ventilation during anesthesia' and "Acute respiratory distress syndrome: Ventilator management strategies for adults", section on 'Recruitment maneuvers'):

●Set TV of 6 to 8 mL/kg ideal body weight (IBW) (calculator 2).

●Adjust respiratory rate to maintain normocapnia (permissive hypercapnia is acceptable in patients without pulmonary hypertension).

●Limit FiO₂ to the level required to maintain peripheral arterial oxygen saturation (SpO₂) >92 percent (ideally, FiO₂ below 0.5 to 0.8), to prevent resorption atelectasis and oxygen toxicity.

●Employ individualized PEEP to optimize plateau and driving pressure as well as lung compliance so as to follow an "open lung" concept. (See "Mechanical ventilation during anesthesia in adults", section on 'Individualized PEEP' and "Acute respiratory distress syndrome: Ventilator management strategies for adults", section on 'Open lung ventilation'.)

●Use recruitment maneuvers judiciously during anesthesia (ideally delivered by a stepwise increase/decrease in PEEP and TV respectively to a plateau pressure >40 but <55 cm H₂O) to improve oxygenation and optimize plateau pressure as needed (see "Mechanical ventilation during anesthesia in adults", section on 'Our approach'). Recruitment maneuvers should not be performed unless patients are hemodynamically stable and euvolemic, as they may lead to a transient decrease in preload and hypotension [93-95]. (See "Mechanical ventilation during anesthesia in adults", section on 'Recruitment maneuvers'.)

●Maintain head-up (reverse Trendelenburg) position, whenever feasible.

As in patients with normal weight, the relative importance of low TVs, PEEP, and recruitment maneuvers is unclear, as these strategies are often bundled together in studies of lung protective ventilation. We recommend protective ventilation based on the effectiveness of various elements of this strategy in patients with obesity and evidence from studies of patients with normal weight. Examples of relevant studies include the following:

●In a trial of 400 adults with normal weight having major abdominal surgery, patients were randomized to lung-protective ventilation (TV 6 to 8 mL/kg IBW, PEEP 6 to 8 cm H₂O, recruitment maneuvers after intubation and every 30 minutes) or traditional ventilator settings (TV 10 to 12 mL/kg IBW, no PEEP, no recruitment maneuvers); both groups received FiO₂ <50 percent, as tolerated [96]. Protective ventilation led to:

•Decreased incidence of major pulmonary and extrapulmonary complications in the first week (10.5 versus 27.5 percent, relative risk [RR] 0.40 [95% CI 0.24-0.68])

•Lower incidence of acute respiratory failure requiring noninvasive ventilation or intubation (5 versus 17 percent, RR 0.29 [95% CI 0.14-0.61])

•Shorter median hospital stay (11 versus 13 days, between-group difference 2.45 days [95% CI 0.72-4.17 days])

●In a 2012 meta-analysis of studies of ventilation strategies (pressure- or volume-controlled ventilation, tidal volumes, PEEP, or recruitment maneuvers) in patients with BMI >30 kg/m², recruitment maneuvers added to PEEP improved intraoperative oxygenation and compliance, compared with PEEP alone; the incidence of adverse effects was similar between groups, and there was no significant difference between pressure-controlled and volume-controlled ventilation [97].

●In a large international multicenter trial (Protective Intraoperative Ventilation With Higher Versus Lower Levels of Positive End-Expiratory Pressure in Obese Patients [PROBESE]), over 2000 patients with obesity (BMI >35 kg/m²) undergoing open or laparoscopic surgery lasting >2 hours were randomly assigned to receive PEEP at 4 cm H₂O without recruitment maneuvers or PEEP at 12 cm H₂O with hourly recruitment maneuvers [98]. All patients received a TV of 7 mL/kg predicted body weight. There was no significant difference in the primary outcome, a composite of postoperative pulmonary complications within the first five days after surgery (21.3 percent of the high PEEP group versus 23.6 percent of low PEEP group, RR 0.93, 95% CI 0.83-1.04). Intraoperative hypoxemia was more frequent in the low PEEP group, while intraoperative hypotension and bradycardia were more frequent in the high PEEP group. In a follow-up sub-study, individualized PEEP resulted in better oxygenation, lower driving pressures, and redistribution of ventilation toward dependent lung areas determined by electrical impedance tomography. However, effects on postoperative outcomes are not clear [99].

●PEEP of 15 cm H₂O is effective in maintaining FRC and improving oxygenation during laparoscopic surgery in patients with severe obesity [94,100].

In addition to a lung protective ventilation strategy, inverse inspiratory:expiratory (I:E) ratio volume or pressure-controlled ventilation may improve intraoperative oxygenation and respiratory mechanics, and possibly reduce lung injury. In several small trials of patients with obesity undergoing laparoscopic surgery, use of I:E ratios of 2:1 or 1.5:1 resulted in improved oxygenation, pulmonary mechanics, and reduced inflammatory markers, compared with standard ratio ventilation. [101-103].

Fluid management — There is very little evidence addressing perioperative fluid management specifically in patients with obesity, and euvolemia in this population is poorly defined; consequently clinical judgment based upon available measures of volume status and tissue perfusion should be used to guide fluid administration. (See "Intraoperative fluid management".)

The use of dynamic indices to guide intravascular fluid administration has not been well studied in patients with obesity. However, in a prospective study of 50 bariatric surgery patients with mean BMI over 50 kg/cm², fluid therapy guided by stroke volume variation (derived from arterial pressure waveform analysis) maintained all hemodynamic parameters within 10 percent of baseline values [104]. (See "Intraoperative fluid management", section on 'Dynamic parameters to assess volume responsiveness'.)

Reversal of neuromuscular blockade — Neuromuscular blockade may be reversed using either sugammadex or neostigmine, depending on the neuromuscular blocking agent used. Sugammadex is a slightly lipophilic reversal agent for steroidal non-depolarizing neuromuscular blockers, used mainly to reverse rocuronium and vecuronium. In a trial of patients with obesity receiving sugammadex 2 mg/kg versus neostigmine 0.05 mg/kg, both given according to adjusted body weight (AdjBW; IBW + 0.4 [total body weight (TBW) – IBW]), the sugammadex group had a significantly faster recovery from neuromuscular blockade (2.7 versus 9.6 minutes) and a significantly better train-of-four (TOF) ratio in the recovery room (110 versus 85 percent) [105]. Anecdotal evidence suggests that sugammadex may offer additional benefits over neostigmine in certain clinical circumstances including fatty liver disease and recurarization of those with obesity [106,107].

Although some authors advocate sugammadex dosing based on TBW in patients with obesity [108], in a dose finding study (100 patients at a TOF recovery between 1 and 2) sugammadex 2 mg/kg IBW resulted in adequate reversal, with no residual neuromuscular blockade. However, reversal was achieved more quickly at a dose adjusted to IBW + 40 percent, slightly above lean body weight (LBW) [109]. There is limited information regarding dose adjustments of neostigmine for obesity. We administer neostigmine based on AdjBW (table 2). (See "Clinical use of neuromuscular blocking agents in anesthesia", section on 'Reversal of neuromuscular block'.)

Extubation — The trunk and head-up position is ideal at emergence, to improve oxygenation and decrease work of breathing. Some patients with obesity may be slow to emerge from anesthesia and should remain intubated until they are awake and meet standard extubation criteria. Avoiding premature extubation is particularly important in the patient with obesity, as interim airway swelling and edema following a procedure can further complicate an already challenging intubation. Extubation should be planned as carefully as intubation; emergency airway equipment (table 6) and personnel to assist in airway management must be available to manage potential difficulties. (See "Extubation following anesthesia".)

Neuraxial anesthesia — In general, neuraxial anesthetic techniques with local anesthetic (ie, without opioids) minimally affect respiratory drive, and are safe and appropriate choices for patients with obesity. Spinal and epidural anesthesia at higher dermatomal levels (ie, thoracic levels) may lead to respiratory difficulty; in one study, the onset of spinal anesthesia decreased spirometric lung volumes, to a greater extent in patients who were more severely obese [110]. Neuraxial medication should be given incrementally whenever possible, to avoid excessively high blockade; the same dose of spinal and epidural local anesthetics can spread to higher levels in patients with obesity compared with patients with normal weight [111-113]. When planning a neuraxial technique at higher levels, it is prudent to use a technique that allows control of the amount and interval of dosing, such as an epidural or spinal catheter, or a low dose, sequential combined spinal epidural, rather than a "single shot" block (table 7). (See "Overview of neuraxial anesthesia" and "Overview of neuraxial anesthesia", section on 'Use of neuraxial anesthesia'.)

Although landmarks tend to be more difficult to identify inpatients with obesity and a greater number of attempts are required to place spinal and epidural anesthetics, the success rate of placement in individuals with obesity is equivalent to that in normal weight patients [56-58]. Preprocedure ultrasound determination of spinal anatomy may improve identification of the needle insertion site and successful placement for selected patients, and this approach is under active investigation. (See "Spinal anesthesia: Technique", section on 'Preprocedure ultrasonography' and "Epidural and combined spinal-epidural anesthesia: Techniques", section on 'Preprocedure ultrasonography'.)

Peripheral nerve blocks — Peripheral nerve blocks with ultrasound guidance appear to be safe in patients with obesity, with relatively high block success rates, when expertise and appropriate equipment are available. However, obesity may make peripheral nerve block more difficult to perform, and may be associated with higher block failure rates [27]. As an example, in a retrospective study of combined ultrasound guidance and nerve stimulation for single shot interscalene blocks, a higher BMI was associated with prolonged, more difficult placement and less successful blocks [114]. In contrast, in a retrospective review of ultrasound guided perineural catheter placement for continuous peripheral nerve block, there were no differences in catheter insertion time or success rates in patients with obesity, compared with patients with normal weight [115].

Similar to patients without obesity, ultrasound guidance for peripheral nerve blocks may be beneficial in patients with obesity, compared with nerve stimulator or landmark based approaches. (See "Overview of peripheral nerve blocks", section on 'Ultrasound guidance'.)

In one small randomized study involving patients with obesity who underwent lateral popliteal sciatic block, ultrasound guidance was associated with faster and less painful block placement and higher patient satisfaction, compared with nerve stimulation [116].

Obesity may be a risk factor for catheter related infection. In a large retrospective analysis, obesity was an independent risk factor for peripheral, but not neuraxial, catheter related infections [117].

MANAGEMENT OF POSTOPERATIVE PAIN — A multimodal, opioid sparing approach to analgesia should be used for all patients, including those with obesity [118,119]. Multimodal opioid sparing analgesic strategies may include nonopioid analgesics (eg, acetaminophen, nonsteroidal antiinflammatory drugs [NSAIDs]), regional anesthesia techniques (eg, local anesthetic wound infiltration, neuraxial analgesia, peripheral nerve blocks), adjunctive medication (eg, systemic lidocaine, ketamine, alpha-2 agonists), and nonpharmacologic therapy. (See "Approach to the management of acute pain in adults", section on 'Use multimodal analgesia'.)

Several studies have reported that protocols including local anesthetic wound infiltration and NSAIDs improved postoperative pain scores and reduced postoperative opioid use after weight loss surgery [120-123].

Examples of studies involving perioperative pain management in patients with obesity include the following:

●In a few small trials, patients with obesity who received alpha-2 agonists (preoperative oral clonidine, or intraoperative intravenous dexmedetomidine infusion) had lower opioid use than patients who did not, and in some cases had decreased need for antiemetic drugs and shorter post-anesthesia care unit (PACU) stays [124-127]. Similarly, a small study reported that preoperative infusion of ketamine with clonidine during induction of anesthesia decreased opioid consumption after open gastric bypass surgery [128].

●In a small study, 30 patients were randomly assigned to receive fentanyl or a combination of nonopioid analgesics (ie, ketorolac, clonidine, lidocaine, ketamine, magnesium sulfate, and methylprednisolone) for gastric bypass surgery [129]. The nonopioid analgesics resulted in comparable analgesia and less sedation, compared with fentanyl.

●In one study involving 50 patients who underwent laparoscopic gastric reduction surgery, patients randomly assigned to an intraoperative lidocaine infusion had modestly reduced postoperative morphine consumption, and improved quality of recovery, compared with controls who received saline [130].

General considerations for the management of postoperative pain and aspects of analgesic management specific to patients with obstructive sleep apnea (OSA) are discussed separately. (See "Postoperative management of adults with obstructive sleep apnea", section on 'Pain control'.)

Enhanced recovery after surgery (ERAS) — The ERAS protocols that are increasingly used for many types of surgery typically include elements for pain control, including preoperative education and the use of multimodal opioid sparing analgesic techniques. Literature on which to base obesity specific ERAS protocols is scant, and in general, such protocols must be extrapolated from those that are used for patients with normal weight. An exception may be the ERAS protocols specific to patients undergoing bariatric surgical procedures that have been established early and are frequently updated [131]. Anesthetic concerns regarding ERAS are discussed separately. (See "Anesthetic management for enhanced recovery after major noncardiac surgery (ERAS)".)

POST-ANESTHESIA CARE UNIT MANAGEMENT — Issues specific to the patient with obesity in the post-anesthesia care unit (PACU) are largely respiratory and ventilatory. General care in the PACU, issues specific to patients with obstructive sleep apnea (OSA), and postoperative care of the critically ill patient with obesity are discussed elsewhere. (See "Overview of post-anesthetic care for adult patients" and "Postoperative management of adults with obstructive sleep apnea" and "Intensive care unit management of patients with obesity".)

●Respiratory monitoring – Patients should have continuous pulse oximetry in the PACU until they have demonstrated that they can maintain adequate oxygenation when left unstimulated. If patients do not meet this standard when otherwise ready to be discharged from the PACU, pulse oximetry monitoring should continue when transferred to the hospital ward. Patients who cannot maintain adequate oxygenation when left undisturbed should not be discharged from the hospital.

An arterial blood gas measurement is the best assessment for suspected hypoventilation, such as in patients who are unable to maintain acceptable oxygen saturation despite supplementation, possibly with a sustained decrease in level of consciousness. (See "Arterial blood gases".)

Although adequacy of ventilation is not routinely measured in the PACU, a high level of suspicion for hypoventilation should be maintained in patients who remain sedated or become hypoxic despite administration of oxygen. Hypoventilation due to sedative medication should be ruled out; pharmacologic reversal of benzodiazepines or opioids may be used as clinically indicated. Often simply arousing a drowsy patient with a reminder to breathe deeply is sufficient, but this may need to be repeated frequently. When upper airway obstruction occurs, an oropharyngeal airway (if the patient is sedated), a nasopharyngeal airway, or both, may open the airway and permit adequate ventilation. When these maneuvers are insufficient, it is reasonable to assist these patients with noninvasive ventilation (NIV), which may keep them from requiring reintubation. (See "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)

Newer monitors for objective assessment of ventilation in spontaneously breathing patients have been developed. Examples include impedance-based respiratory volume monitoring devices and acoustic respiratory rate monitors. However, the role for these newer technologies in routine perioperative care is yet to be determined.

●Maintaining adequate oxygenation – Patients with obesity are at greater risk for hypoxia in the postoperative period, compared with patients with normal weight, due to physiologic changes. (See 'Respiratory physiology' above.)

Following extubation, we use the following measures to maintain adequate oxygenation in patients with obesity:

•For all patients

-Supplemental oxygen by facemask or nasal cannula, titrated to keep oxygen saturation at >90 percent.

-Positioning patient in head-up (sitting or semi-sitting) or lateral position (if surgically acceptable).

-Use of incentive spirometry or chest physiotherapy. (See "Strategies to reduce postoperative pulmonary complications in adults", section on 'Lung expansion'.)

We suggest providing incentive spirometry devices to patients with obesity in the PACU, with instruction to use the device every 15 minutes. Incentive spirometry is noninvasive and inexpensive, but it may be labor intensive to monitor and ensure patient use in a busy PACU.

The literature on the benefits of postoperative incentive spirometry or chest physiotherapy in patients with obesity is conflicting, and results may depend on the surgical procedure and the protocol for incentive spirometry. In a trial that included 60 patients with body mass index (BMI) 30 to 40 kg/cm² who underwent minor surgery with general anesthesia, patients were randomly assigned to incentive spirometry administered by a respiratory therapist every 10 to 15 minutes, starting 15 minutes after extubation, for the first two hours after surgery, versus standard PACU care without incentive spirometry [132]. Patients who received incentive spirometry had improved oxygen saturation and spirometric measures of lung function in the PACU and during the first 24 postoperative hours.

In contrast, in a randomized trial including approximately 200 patients who underwent bariatric surgery, there were no differences in postoperative hypoxemia or pulmonary complications between patients who received self-administered incentive spirometry when awake and those who had no incentive spirometry [133].

•Patients with postextubation airway obstruction – For patients with intermittent post-extubation airway obstruction despite meeting extubation criteria, especially for those with suspected or severe OSA, we insert a nasopharyngeal airway (NPA) in the operating room prior to transfer to the PACU. If opioid analgesia is required immediately postoperatively, the NPA may mitigate potential opioid induced airway obstruction. The NPA also provides an option to escalate non-invasive airway support using an endotracheal tube connector and an ambu bag or breathing circuit [134].

•Patients with hypoxia unresponsive to incentive spirometry and conventional oxygen – For these patients we suggest using noninvasive ventilation (NIV; continuous positive airway pressure [CPAP] or bilevel positive airway pressure [BiPAP]) or high flow nasal oxygen (HFNO) in the PACU, with intubation for refractory patients.

The use of NIV is feasible in patients with no previous experience with NIV, when applied by a trained respiratory therapist [135].(See "Postoperative management of adults with obstructive sleep apnea", section on 'Positive airway pressure therapy'.)

In a 2023 network meta-analysis of randomized trials that compared various noninvasive postoperative ventilatory strategies in patients with severe obesity, high flow nasal oxygen (HFNO) or bilevel positive airway pressure [BiPAP] reduced atelectasis, HFNO, BiPAP, or CPAP reduced postoperative pneumonia, and HFNO reduced length of stay, compared with conventional oxygen therapy [136]. The timing, duration, and settings used for NIV varied among the included studies. (See "Strategies to reduce postoperative pulmonary complications in adults", section on 'Lung expansion'.)

Despite concern that aspiration of air during CPAP treatment might cause disruption of fresh anastomotic suture lines following intestinal surgery, studies of gastric bypass patients receiving CPAP or other forms of NIV in the PACU have not shown an increased risk for anastomotic leak [137-139]. Following gastrointestinal surgery such as gastric bypass, we prefer early joint decision making between anesthesiologist, surgeon, respiratory technician, and nurse to determine CPAP or other NIV use in selected patients, emphasizing the team concept for the perioperative care of these patients [120].

DISCHARGE CRITERIA — Evidence regarding the optimal duration of postoperative monitoring for patients with severe obesity is lacking. We follow the standard considerations for the discharge of surgical patients, such as those published by the American Society of Anesthesiologists (ASA) [140]. Prior to transfer of the patient to an unmonitored setting, oxygen saturation on room air should return to preoperative baseline, and when left undisturbed the patient should not develop clinical hypoxemia or airway obstruction [141]. We extend use of these recommendations to all patients with severe obesity, with a low threshold for prolonged recovery room monitoring based upon the individual patient's course. The decision to discharge patients with diagnosed or likely OSA should take into account the ability to use CPAP, the need for opioid medication, and comorbid medical conditions [142]. Postoperative management of OSA is discussed elsewhere. (See "Postoperative management of adults with obstructive sleep apnea".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Sleep-related breathing disorders in adults".)

SUMMARY AND RECOMMENDATIONS

●Physiologic changes of obesity (See 'Physiologic changes associated with obesity' above.)

•Respiratory physiologic changes in patients with obesity include an increase in oxygen consumption and a decreased functional residual capacity, leading to a rapid decrease in oxygen saturation during apneic periods.

•Increased blood volume, decreased systemic vascular resistance, and increased cardiac output may lead to either left or right heart failure or both.

●Drug dosing – Drug doses in patients with obesity depend on the pharmacokinetic and pharmacodynamic parameters of the specific drug (table 2); when specific recommendations are not available, it is reasonable to base drug doses on adjusted body weight (AdjBW). (See 'Dosing anesthetic drugs' above.)

●Choice of anesthetic techniques

•Although no anesthetic technique has been found to be superior to another with respect to important patient outcomes (eg, mortality, cardiopulmonary complications) in patients with obesity, the requirement for general anesthesia should be carefully examined and alternatives chosen when possible, to minimize airway and drug-related respiratory problems. (See 'Choice of anesthetic drugs' above.)

•No specific induction or maintenance agent has been shown to result in improved clinical outcomes when compared with others. (See 'Induction' above and 'Maintenance' above.)

•Opioid and sedative administration should be minimized to decrease the risk of respiratory depression, particularly in patients with obstructive sleep apnea. In patients with severe obesity, opioid-sparing multimodal analgesia may reduce the risk of respiratory depression and other opioid- and sedative-related side effects. This may include the use of local or regional anesthesia, nonsteroidal anti-inflammatory drugs, acetaminophen, alpha-2 agonists, and other medications, in addition to preoperative education and setting expectations for postoperative recovery. (See 'Management of postoperative pain' above.)

●Airway management

•When general anesthesia is used for patients with obesity, similar to patients without obesity, we recommend adequate pre-oxygenation (with continuous positive airway pressure [CPAP] if tolerated) and induction in a trunk and head-up (preferably reversed Trendelenburg) position to improve oxygenation and tolerance for apneic periods without desaturation. (See 'Respiratory physiology' above and 'Positioning for airway management' above.)

•Mask ventilation may be more difficult, and intubation may be more challenging in patients with obesity. When difficulty with both is anticipated, it may be prudent to perform awake intubation. Equipment and skilled personnel to assist with a difficult or failed airway should be readily available. (See 'Airway management' above.)

●Blood pressure monitoring – During general anesthesia we measure and respond to intermittent non-invasive blood pressure no less than every three minutes, and more often as needed. A standard blood pressure cuff may not fit the conical shape of the upper arm in the patient with obesity; a forearm cuff is a reasonable alternative. Invasive arterial blood pressure monitoring should be considered when surgical and/or patient conditions suggest a critical need for accurate blood pressure monitoring (See 'Blood pressure monitoring' above.)

●Ventilation – Similar to patients without obesity, we suggest the use of lung protective ventilation for patients with obesity who require mechanical ventilation. (See "Mechanical ventilation during anesthesia in adults", section on 'Lung protective ventilation during anesthesia'.)

Our strategy includes the following (see 'Ventilation management' above):

•Tidal volume (TV) of 6 to 8 mL/kg ideal body weight (IBW) (calculator 2)

•Respiratory rate to maintain normocapnia (permissive hypercapnia is acceptable in patients without pulmonary hypertension)

•Fraction of inspired oxygen (FiO₂) to maintain peripheral arterial oxygen saturation (SpO₂) >92 percent (ideally below 0.5 to 0.8), to prevent resorption atelectasis and oxygen toxicity

•Individualized positive end-expiratory pressure (PEEP) to optimize driving pressure and lung compliance so as to follow an "open lung" concept

•Recruitment maneuvers judiciously during anesthesia (ideally delivered by a stepwise increase/decrease in PEEP and TV respectively to a plateau pressure >40 but <55 cm H₂O) to improve oxygenation when needed

•Head-up (reverse Trendelenburg) position, whenever feasible

●Postoperative care – Postoperative oxygenation should be monitored until patients can maintain adequate oxygenation when left unstimulated.

•For all patients we maintain a head-up position with oxygen by face mask and use incentive spirometry.

•For patients with hypoxia unresponsive to incentive spirometry, we suggest using continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), or high flow nasal oxygen as well rather than proceeding directly to intubation (Grade 2C). We reserve intubation for refractory patients. (See 'Post-anesthesia care unit management' above.)

Prior to transfer to an unmonitored setting, oxygen saturation on room air should return to preoperative baseline, and when left undisturbed, the patient should not develop clinical hypoxemia or airway obstruction. (See 'Discharge criteria' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Roman Schumann, MD, who contributed to earlier versions of this topic review.