Airway management in the patient with severe obesity for emergency medicine and critical care

INTRODUCTION — 

In patients presenting with acute respiratory or ventilatory failure, the emergency clinician's first responsibilities are to ensure oxygenation and secure the airway. Obesity-related anatomic and physiologic changes make airway management more difficult.

This topic will review emergency airway management in patients with obesity, including severe obesity, outside of the operating room. Other aspects of airway management and care of patients with obesity are discussed separately. (See "Approach to the anatomically difficult airway in adults for emergency medicine and critical care" and "Rapid sequence intubation in adults for emergency medicine and critical care" and "Overview of advanced airway management in adults for emergency medicine and critical care" and "Basic airway management in adults" and "Anesthesia for the patient with obesity" and "Obesity in adults: Overview of management".)

OBESITY'S EFFECTS ON THE AIRWAY

Definitions — The evaluation and classification of obesity is discussed in detail separately. A brief overview and aspects of obesity of particular relevance to airway management are reviewed here. (See "Obesity in adults: Prevalence, screening, and evaluation", section on 'Screening'.)

Overweight is defined as weight above the normal range. Obesity is defined as an abnormally high percentage of body weight as fat. Body mass index (BMI) is used to distinguish between the two terms and also determines the degree of excess weight.

Using the BMI, obesity is then classified as follows:

●Overweight – BMI ≥25.0 to 29.9 kg/m².

●Class I obesity – BMI of 30.0 to 34.9 kg/m².

●Class II obesity – BMI of 35.0 to 39.9 kg/m².

●Class III obesity – BMI ≥40 kg/m². This type of obesity is also referred to as severe or extreme obesity.

Physiologic and anatomic changes — The pathophysiology of obesity is discussed in detail separately. Aspects of obesity of particular relevance to emergency airway management are reviewed briefly here. (See "Obesity: Genetic contribution and pathophysiology", section on 'Physiology and pathophysiology of obesity' and "Anesthesia for the patient with obesity", section on 'Physiologic changes associated with obesity'.)

Several physiologic and anatomic changes occur in obese patients that are important for airway management (table 1). Both oxygen consumption and carbon dioxide production are increased. These increases result from metabolic activity in excess adipose tissue and from the increased work required of supportive tissues [1]. As a consequence, desaturation time and thus, the "safe apnea period" during rapid sequence intubation, are decreased. The attached figure illustrates time to desaturation for obese patients compared with others (figure 1). (See "Rapid sequence intubation in adults for emergency medicine and critical care".)

Patients with severe obesity have increased airway resistance, an abnormally elevated diaphragm, and increased work of breathing secondary to abnormal chest wall elasticity and resistance to caudal excursion of the diaphragm. In addition, the added weight of abdominal fat on inferior portions of the lung can reduce functional residual capacity. These alterations result in shallow, rapid breathing, reductions in the capacity to pre-oxygenate, and limited ventilatory capacity, all of which are more pronounced when the patient is supine [1-3].

Obesity alters upper airway anatomy. Increased fat deposition in pharyngeal tissues increases the likelihood of pharyngeal wall collapse, which can complicate the performance of rapid sequence intubation [4].

Obesity contributes to the development of many diseases and increases not only the morbidity and mortality from such diseases, but also the incidence of complications from managing them [2,5-7]. Obesity plays a significant role in atherosclerosis, hypertension, diabetes, cardiomyopathy, and arrhythmias, such as bradycardia, second-degree heart block, and ventricular arrhythmias [8]. Obese patients are also at increased risk of aspiration pneumonitis secondary to an excess volume of gastric acid and increased intraabdominal pressure [1,9]. (See "Overweight and obesity in adults: Health consequences".)

The metabolism and pharmacokinetics of commonly used drugs are altered by the physiologic changes of obesity. Lipophilic drugs have a larger volume of distribution (Vd), since the Vd is dependent upon the amount of adipose tissue [3]. Obese patients are known to have higher glomerular filtration rates, and renally excreted drugs may have shorter half-lives since their elimination is directly proportional to creatinine clearance. Obesity does not generally affect the clearance of drugs that are metabolized by the liver unless hepatic steatosis impairs function. Since the complexity of obesity-related pharmacokinetic changes and because detailed data are lacking for many drugs, individual drug dosing for obese patients remains controversial [10,11]. Drugs that depress the central nervous system, such as opioids, benzodiazepines, and propofol, can both depress respiratory drive and increase the tendency for collapse of the pharyngeal wall [8]. (See "Clinical manifestations and diagnosis of alcohol-associated steatosis and cirrhosis".)

AIRWAY ASSESSMENT

Obesity and airway difficulty — The goal of airway assessment is to identify clinical features that predict difficulty in any of the following areas of emergency airway management:

●Ventilation with bag mask or extraglottic device

●Laryngoscopy and endotracheal intubation

●Surgical airway performance

Obesity may complicate the performance of any of these tasks, and therefore, airway management in patients with obesity should always be considered potentially difficult [12]. However, such patients are also subject to the same risk factors for difficult airway management as those with healthy weight, and whenever possible, a careful evaluation for such factors should be conducted before undertaking airway management.

While the relationship between class I or II obesity and laryngoscopy is not entirely clear, there is a strong association between body habitus and difficult bag-mask ventilation (BMV), use of an extraglottic device, and increased risk of rapid desaturation [2,8,13-15].

After assessing the patient, the clinician must decide whether to use an awake approach or to proceed with rapid sequence intubation (RSI). This decision hinges on the number and severity of difficult airway attributes. Airway assessment and the approach to the difficult airway are discussed in detail separately (see "Approach to the anatomically difficult airway in adults for emergency medicine and critical care"). Aspects of particular relevance to obesity are reviewed below and in the table (table 1).

Bag-mask ventilation — Obesity makes BMV more difficult [2,6-8,16,17]. Redundant upper airway soft tissue coupled with increased body mass results in increased airway resistance. Higher pressures are required to ventilate effectively, and this can lead to difficulty maintaining a mask seal. Oxygen consumption is increased in patients with obesity, and target oxygen saturations may be difficult to achieve or maintain. Other predictors of difficult BMV are shown in the table (table 2) [18]. (See 'Physiologic and anatomic changes' above and "Basic airway management in adults".)

Tracheal intubation — Laryngoscopy and tracheal tube placement can be difficult in patients with obesity. Such patients may have altered upper airway anatomy resulting in a poor glottic visualization despite optimal laryngoscopic technique. In addition, short, thick necks may limit mobility and make it difficult to place the patient in the optimal sniffing position. General indicators of difficult intubation are described in the table (table 3). (See "Direct laryngoscopy and endotracheal intubation in adults".)

Studies assessing emergency airway management in obese patients are scarce. Nevertheless, a few studies in the emergency setting and multiple studies performed in the operating room report an inconsistent association between obesity and difficulty with laryngoscopy or endotracheal intubation [13-15,19-26]:

●In a cohort of more than 45,000 patients undergoing general anesthesia at an academic hospital, obese patients were found to be slightly more difficult to intubate, but the difference did not achieve statistical significance (odds ratio [OR] 1.13, 95% CI 0.96-1.33) [13]. However, patients with obesity were much more difficult to ventilate using a bag mask (OR 3.78, 95% CI 3.18-4.49).

●A large retrospective study using the Danish Anesthesia Database found that patients with a body mass index (BMI) above 35 were more likely to be difficult to intubate compared with those with a lower BMI [21]. When controlling for other risk factors, researchers found the odds ratio for patients with obesity to be 1.34 (95% CI 1.19-1.51).

●One observational study compared the incidence of difficult endotracheal intubation in consecutive obese (n = 129) and lean (n = 134) patients undergoing elective surgery using a validated difficulty score (The Intubation Difficulty Scale, or IDS) [22]. The rate of difficult intubation was 15 percent for obese patients versus 2 percent for lean patients. In patients with obesity, a Mallampati score of III or IV was the only independent risk factor for difficult intubation (odds ratio [OR] 12.51; 95% CI 2.01-77.81) (figure 2). Hypoxemia occurred more frequently in obese patients despite preoxygenation.

●Another study using the IDS to assess 204 elective surgery patients found endotracheal intubation to be more difficult in obese patients [23]; a study examining 100 consecutive patients with severe obesity arrived at a similar conclusion [24]. The researchers of the latter study found that large neck circumference and high Mallampati score were the only predictors of difficult intubation in this population.

Surgical airway — Excessive soft tissue in the anterior neck limits access to the cricothyroid membrane and makes it difficult to identify the anatomic landmarks needed to perform a cricothyrotomy [27]. Therefore, surgical airways can be extremely difficult in patients with severe obesity. Other limitations to performing a cricothyrotomy are described in the accompanying table (table 4) [18]. (See "Emergency cricothyrotomy (cricothyroidotomy)".)

AIRWAY MANAGEMENT

Bag-mask ventilation — The best method for bag-mask ventilation (BMV) in any patient, especially those with obesity, is the two-person "thenar grip" technique (picture 1), with oropharyngeal and nasopharyngeal airways in place, unless these airway adjuncts are contraindicated [28]. This approach allows for better patient positioning and mask seal. In a crossover randomized trial of 81 anesthesia patients with an average body mass index (BMI) of 37, the thenar grip technique for two-person BMV was found to be more effective than the standard two-hand technique [29]. The performance of BMV, including the thenar grip two-person technique, is described separately. (See "Basic airway management in adults", section on 'Bag-mask ventilation'.)

If possible, the hospital bed is angled with the head up and foot down (reverse Trendelenburg position) to reduce pressure from the abdominal contents on the diaphragm and to shift the weight of the chest wall inferiorly, thereby improving chest wall and diaphragm excursion.

Tracheal intubation

Positioning — In preparation for intubation, the patient with obesity should be placed in an upright or semi-upright position (eg, reverse Trendelenburg), depending upon the degree of respiratory distress. An upright position improves oxygenation and respiratory function by allowing the diaphragm to fall downward and reducing the weight on the chest wall. Even in trauma patients requiring cervical spine stabilization, the stretcher can be tilted with the head elevated to improve breathing while preparations are made for intubation. (See 'Preoxygenation' below and "Direct laryngoscopy and endotracheal intubation in adults", section on 'Laryngoscopy Technique'.)

If there is no contraindication (eg, cervical spine precautions), the patient with obesity should be placed in a ramped or head-elevated position for direct laryngoscopy. In the ramped position, blankets or commercially available beds are used to elevate the head and torso such that the external auditory meatus and the sternal notch are horizontally aligned (picture 2 and figure 3) [30].

The sniffing position has traditionally been recommended to optimize glottic visualization during direct laryngoscopy, but the ramped position appears to be more effective in the patients with obesity [30-35]. Several studies have compared the positions used to optimize the glottic view and improve intubation success:

●In a blinded, randomized trial, 60 patients with severe obesity were assigned to either the ramped or to the sniffing position (7 cm head elevation) for direct laryngoscopy and endotracheal intubation prior to surgery [31]. The authors reported that the ramped position provided a significant improvement in the glottic view.

●A randomized trial of direct laryngoscopy in 40 anesthetized patients found that the glottic view improved by over 50 percent when the head-elevated position was used compared with supine positioning [32].

●In a large observational study using data from the National Emergency Airway Registry, non-supine positioning was used more frequently with obese patients and those with an anticipated difficult airway but was not associated with higher rates of successful intubation on the first attempt [36]. Non-supine positioning was associated with improved views of the larynx (ie, higher Cormack Lehane scores) when performing direct laryngoscopy but also with higher rates of adverse events during the peri-intubation period.

●A retrospective study of 528 intubations performed outside the operating room found that a backup and head elevated (ie, ramp) position was associated with significant reductions in airway complications, including hypoxia, esophageal intubation, and intubation failure, compared with supine, neutral head positioning [37].

Preoxygenation — Preoxygenation is an essential aspect of rapid sequence intubation (RSI). The significance and techniques of preoxygenation are discussed separately. (See "Rapid sequence intubation in adults for emergency medicine and critical care", section on 'Preoxygenation'.)

It can be difficult to achieve and maintain adequate oxygenation in patients with severe obesity as reductions in functional residual capacity (FRC) impair creation of an oxygen reserve within the lungs and lower lung zone atelectasis increases intrapulmonary shunt fractions and gas exchange. Furthermore, oxygen saturation levels fall faster in these patients during RSI [38]. Thus, it is important to preoxygenate as well as possible. Techniques to optimize preoxygenation include the following:

●Use bi-level positive airway pressure (BiPAP). Whenever possible, patients with severe obesity should be preoxygenated with noninvasive positive pressure in order to minimize intrinsic shunt fraction and ventilation/perfusion (V/Q) mismatch.

●When patients are unable to tolerate BiPAP or there is a contraindication, administer flush-flow rate oxygen (40 to 90 L/minute) by nonrebreather mask or by bag-valve mask if the need for early assisted ventilation is clear or anticipated. Gentle bag-assist can be performed if inspiratory effort is deemed to be insufficient to meet the patient's ventilatory needs.

●Place the patient in either an upright or semi-erect position whenever possible.

●Use lubricated, bilateral nasal trumpets to assist with oxygenation when needed.

Flush-flow rate (40 to 90 L/minute) oxygenation has been shown to be superior to NRB at 15L/min [39]. End-tidal oxygen (ETO₂) is significantly higher using flush-rate oxygen compared with the traditional 15 L/minute. The traditional nonrebreather mask provides about a 70 percent fraction of inspired oxygen (FiO₂) when attached to a standard wall spigot set at a flow rate of 15 L/minute. A properly configured bag-valve-mask unit can provide 90 to 100 percent oxygen during active breathing, even without bag assist.

In a multicenter randomized trial, approximately 1200 emergency department (ED) and intensive care unit (ICU) patients were randomized to either 10/5 of BiPAP or non-rebreather mask at 15 L/min for preoxygenation during emergency airway management [40]. Nearly half of all patients were intubated for hypoxemic respiratory failure. There was an overall reduction in peri-intubation hypoxemia, defined as an oxygen saturation <85 percent during or two minutes after the intubation, in the BiPAP cohort (9.1 versus 18.5 percent). This effect was magnified in patients with a BMI ≥ 30 kg/m², in whom 26 percent desaturated after using an NRB mask compared with only 9 percent in the BiPAP group. There was no difference in witnessed or delayed evidence of aspiration.

A systematic review concluded that preoxygenation in adults with severe obesity is more effective when performed with the patient in the head-up position rather than a supine position [41]. Among several studies that have investigated the effects of positioning on preoxygenation, one assessed the time necessary for desaturation to occur in 40 patients with obesity undergoing elective surgery [42]. After preoxygenation, induction, and intubation, patients were left apneic until their SpO2 dropped to 90 percent. Preoxygenation in the sitting position increased the mean time needed to desaturate to 90 percent by almost one minute. Other studies have reported similar results [43].

The angle of head elevation that enables optimal preoxygenation while still permitting a good intubating position remains unclear. One option is to preoxygenate with the patient positioned as close to 90 degrees as possible (ie, sitting upright) and then move the patient to a semi-upright position (approximately 30 degrees) for intubation once induction and paralysis are complete. (See 'Positioning' above.)

Providing oxygen by nasal cannula during the apneic phase of RSI may improve oxygenation in obese patients. In a small randomized trial, patients (n = 15) provided with oxygen at 5 L/minute by nasal cannula maintained an SpO2 above 95 percent for a mean of 5.29 minutes compared to 3.49 minutes for those not given oxygen [44]. Some advocate that the highest flow rate the patient will tolerate should be used, as this ensures a high flow of oxygen with little downside [45].

Medication dosing — Optimal dosing for many drugs in the patient with obesity remains controversial. Obesity alters the pharmacokinetics and pharmacodynamics of many medications, including some of those used for rapid sequence intubation (table 1) [1,10,11]. The mechanisms by which obesity alters the effects of drugs are described above. (See 'Physiologic and anatomic changes' above.)

Evidence supporting the use of any particular calculation of body weight to determine the dosing of induction or neuromuscular blocking agents (NMBAs) is limited and our approach is based primarily upon clinical experience and pharmacologic considerations, although there is stronger evidence in the case of succinylcholine. In summary, we suggest using dosing based upon lean body weight (LBW) for most induction agents, ideal body weight (IBW) for propofol, given its propensity to cause hypotension, and total body weight (TBW) for neuromuscular blocking agents.

Commonly used formulas to calculate LBW that rely on height and sex underestimate actual non-adipose tissue mass in the severely obese (class II or III) and may be difficult to use in emergencies [11,46]. Clinicians can use the attached table or calculators to rapidly estimate LBW and calculate emergent drug doses in the severely obese (table 5) (calculator 1 and calculator 2). Another calculator is provided to help clinicians determine IBW (calculator 3).

We believe the use of LBW for induction agents provides the best trade-off between insufficient sedation, which may occur with dosing based upon IBW, and hemodynamic compromise, which may occur with dosing based upon TBW. Furthermore, in emergency circumstances, it can be difficult to recall which drugs should be dosed according to which body weight. For this reason as well, we suggest using LBW for all induction agents, unless there is time available to determine the best approach for a particular drug.

The characteristics of particular induction agents may also affect dosing [6]. Benzodiazepines may have prolonged effects in patients with obesity due to their lipophilicity and large volumes of distribution. Dosing for propofol and opioids is generally similar for patients with and without obesity. Data evaluating etomidate dosing in patients with obesity is scant.

Both depolarizing and nondepolarizing NMBAs have been used successfully for the intubation of patients with severe obesity. When dosed appropriately, succinylcholine and rocuronium provide identical intubating conditions [47]. Particularly in patients with obesity, dosing succinylcholine by TBW appears to give better results. NMBAs are hydrophilic drugs, and theoretically, dosing based on adjusted body weight (AdjBW) or IBW is preferred. However, pseudocholinesterase activity increases with increasing obesity, and unless TBW is used to determine NMBA dosing, insufficient drug may reach the motor endplate, resulting in inconsistent or incomplete paralysis. In one randomized trial, excellent intubating conditions and full paralysis were achieved in all patients with obesity dosed by TBW, while poor intubating conditions were found in one-third of those dosed by IBW [48]. The results of an observational operating room study suggest that succinylcholine demonstrates equivalent activity in adolescents with and without obesity when dosed by TBW [49].

Several trials have evaluated rocuronium use in patients with severe obesity, but none have been performed in the emergency department setting. The duration of action is prolonged in patients with obesity who receive larger than IBW-based doses [50-55]. A small randomized trial found that recovery time (ie, time to muscle twitch recovery) was doubled in patients dosed according to TBW compared with IBW, while the time to onset of muscle relaxation was not significantly different (TBW group 77 seconds and IBW group 87 seconds) [52]. Several small trials in the operating room setting suggest that AdjBW dosing provides good intubating conditions, but these results do not extrapolate exactly to the emergency department setting where the desired time of onset for complete relaxation is shorter than in the operating room [53,54]. The AdjBW often cannot be rapidly calculated since an accurate height and weight are unknown in a patient in extremis.

Given the importance of ensuring rapid and complete paralysis for RSI in emergency circumstances, the risks associated with inadequate paralysis, and less concern about a slightly longer duration of neuromuscular blockade (ie, extubation typically does not happen in the emergency department), we suggest TBW dosing in such circumstances (although, in our experience, doses >250 mg should rarely, if ever, be needed). In addition, regardless of the calculation used for dosing, the duration of effect is sufficiently long that definitive airway management must be accomplished before the effects of rocuronium have worn off. Administration of sugammadex (after successful tracheal intubation) is an option in the rare circumstance where reversal of paralysis is needed before the potentially prolonged rocuronium effects have worn off [56].

Rapid sequence intubation — Airway management is always potentially difficult in patients with obesity [12]. Based upon an assessment of the patient's airway, the clinician may decide it is prudent to take a spontaneously breathing intubation or an awake evaluation of the airway to determine if intubation is feasible and rapid sequence intubation (RSI) is appropriate. The clinician can proceed with RSI if the vocal cords are well visualized during the awake look [57]. If the patient is combative or otherwise uncooperative due to respiratory distress and hypoxia, an awake look may not be possible without dissociative doses of ketamine, and RSI may provide the best approach for securing the airway [35,58]. Assessment of the airway for signs of potential difficulty, the performance of rapid sequence intubation, and the awake look are all discussed in greater detail separately (see "Approach to the anatomically difficult airway in adults for emergency medicine and critical care" and "Rapid sequence intubation in adults for emergency medicine and critical care"). Awake intubation in the patient with obesity is discussed below. (See 'Awake intubation' below.)

If RSI is performed in a patient with obesity, the clinician should anticipate rapid oxygen desaturation. This may be due to incomplete preoxygenation coupled with high peripheral oxygen extraction from metabolically active adipose tissue. BiPAP should be used to preoxygenate, whenever possible. Flush-rate oxygen (40 to 90 L/minute through a nonrebreather mask) is an alternative method when patient intolerance or contraindications preclude use of noninvasive ventilation. If available, ETO₂ should be measured to assess the effectiveness of preoxygenation efforts before sedative agents are administered [59]. Judiciously applied, gentle bag-mask ventilation can be performed during the induction phase of RSI to mitigate the risk of desaturation, provided that the risk of aspiration is not high (eg, patient with active hemoptysis or emesis). (See 'Preoxygenation' above and "Rapid sequence intubation in adults for emergency medicine and critical care", section on 'Adjunct strategies to maximize preoxygenation'.)

We recommend using video laryngoscopy whenever possible for emergency airway management; however, when direct laryngoscopy must be performed, specific pieces of equipment may make management easier in obese patients. A short laryngoscope handle may be easier to insert. Larger width laryngoscope blades, such as a size four Macintosh or Grandview, can help to control excess soft tissue and improve the glottic view. An endotracheal tube introducer may be extremely helpful in cases of a limited view despite optimal technique. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

Devices for airway management — Below is a brief description of airway adjuncts that can be employed when managing a difficult airway in a patient with obesity, particularly a "can't intubate, can ventilate" scenario, in which BMV is successful, but the vocal cords cannot be adequately visualized using direct laryngoscopy to place an endotracheal tube. These devices are discussed in greater detail separately; techniques and evidence concerning their use in patients with obesity are described here. (See "Devices for difficult airway management in adults for emergency medicine and critical care".)

●Optical and video laryngoscopes – Preliminary studies suggest that optical and video laryngoscopes are useful for intubating the patient with severe obesity and have advantages over standard laryngoscopes (picture 3) [60-63]. These devices can also be used for awake intubation [64]. (See 'Awake intubation' below and "Devices for difficult airway management in adults for emergency medicine and critical care", section on 'Video laryngoscopes' and "Videolaryngoscopes and optical stylets for airway management for anesthesia in adults".)

In several small randomized trials performed in the operating room with patients with obesity, video laryngoscopes have consistently provided a superior view of the glottis and led to fewer difficult intubations compared with direct laryngoscopy [60,65,66].

In two randomized trials performed in bariatric surgery patients, the Airtraq, an optical laryngoscope (picture 4), provided a better view of the glottis and allowed for more successful and faster tracheal intubation than a standard Macintosh laryngoscope [67,68]. Differences in the glottic view and speed of intubation achieved statistical significance in both studies.

●Laryngeal mask airway (LMA) and laryngeal tubes – LMAs and laryngeal tubes are supraglottic devices, placed blindly, for use in difficult airways and in failed airways as a temporizing measure before cricothyrotomy. They are easy to place, have high ventilation success rates, and have been used effectively in patients with obesity [69]. They are not definitive airways and provide only partial protection against aspiration (picture 5). (See "Extraglottic devices for emergency airway management in adults".)

When using the LMA, patient positioning may be important as excessive resistance to ventilation in patients with obesity may overcome the seal pressure of the LMA cuff, reducing the effectiveness of ventilation. Proper positioning is identical to that used for BMV. (See 'Bag-mask ventilation' above.)

●Intubating LMAs – The intubating LMA (ILMA) is a laryngeal mask modified to facilitate intubation directly through the mask. Prospective trials suggest it is effective for intubating patients with severe obesity [33,70].

●Endotracheal tube introducer – The endotracheal tube introducer (often referred to as a gum elastic bougie or bougie) is a plastic, semirigid stylet that can be useful for tracheal tube placement (picture 6 and picture 7). Regardless of whether laryngoscopy is anticipated to be challenging, an introducer should be available at the bedside during any attempt to intubate a patient with obesity. In the event of a grade III view of the glottis, the clinician may be able to place the introducer into the trachea and then insert the endotracheal tube over it (movie 1). Use of the introducer is described separately. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

●Flexible endoscopic laryngoscopes – Flexible video or fiberoptic laryngoscopy with light sedation and topical anesthesia is the mainstay of "awake" intubation for the patient with obesity. (See 'Awake intubation' below.)

Awake intubation — The use of an awake approach to intubation is prudent when traits associated with rapid desaturation and challenges with reoxygenation are identified in the patient with severe obesity. The awake approach is described separately; issues related to its performance in patients with obesity are reviewed here. (See "Awake tracheal intubation".)

In patients considered poor candidates for rapid sequence intubation (RSI) because of difficult airway attributes (including obesity itself), awake intubation, using a video laryngoscope or a flexible endoscopic laryngoscope via the nasal or oral route, often is the best approach, provided that time and the necessary equipment and expertise are available. Awake intubation offers superior visualization without the time pressure inherent in the use of neuromuscular blockade, and intubation can be accomplished while the patient continues to maintain respiratory drive and protective airway reflexes.

An awake approach usually requires sedation and topical anesthesia [71]. If time permits, topical anesthesia is preceded (by 10 to 15 minutes) by administration of a mucosal drying agent, such as glycopyrrolate (0.005 mg/kg IM or IV; usual adult dose 0.4 mg), to reduce mucosal moisture, enhance effectiveness of topical anesthetics, and minimize blockage of the fiberoptic lens by secretions. Light to moderate systemic sedation is then given, followed by inspection of the airway using video or direct laryngoscopy or fiberoptic instruments.

Failure to obtain an adequate view of the glottis using direct or video laryngoscopy despite excellent technique and effective sedation and topical anesthesia argues against RSI and in favor of switching to a flexible endoscopic method if possible [19]. When a flexible endoscopic laryngoscope is used, the procedure continues until the glottis is traversed, the scope is advanced to the carina, and the endotracheal tube is introduced over the endoscope into the trachea. If the vocal cords are adequately visualized during the "awake look," the operator may opt to proceed with intubation during awake laryngoscopy or to perform RSI. Immediate intubation may be best in dynamic situations where the airway may degenerate quickly (eg, neck trauma, thermal burns, anaphylaxis).

Awake intubation requires careful use of medications because patients with obesity, particularly those with obstructive sleep apnea, have an increased risk of upper airway obstruction precipitated by opioids or sedatives, particularly when these are used in combination [8]. When performing awake intubation in these patients, physicians should use medications with which they are familiar and titrate them to achieve a level of sedation similar to that needed for a painful procedure. The medication chosen should be given in reduced doses, typically 25 to 50 percent of the normal dose (based upon lean body weight), and titrated to the desired effect using small aliquots. Commonly used drugs include ketamine, propofol, midazolam, or etomidate [72,73]. These are often accompanied by fentanyl for analgesia.

In more urgent circumstances when time is short or the airway of a combative patient must be assessed, haloperidol (doses of 2 to 10 mg IV) or ketamine (0.5 mg/kg IV) may enable the physician to take an awake look while the patient maintains airway reflexes.

Limited evidence suggests that the awake approach is effective in patients with obesity requiring intubation. In a study of 64 patients with severe obesity being intubated awake in preparation for bariatric surgery, both video laryngoscopy (Glidescope) and fiberoptic bronchoscopy allowed for excellent glottic views in nearly all cases and rapid, successful intubation during the first attempt during the preponderance of cases [74].

Cricothyrotomy — Cricothyrotomy is the technique of choice to secure a failed airway. Cricothyrotomy must be performed quickly under stressful circumstances making it a difficult procedure, but it can be even more difficult in a patient with severe obesity, in whom landmarks such as the cricothyroid membrane can be difficult to identify [75]. If the clinician must perform a cricothyrotomy in an obese patient, it may be necessary to have an assistant retract redundant soft tissue. The scalpel-finger-bougie technique is our preferred technique in all patients, including those with obesity. Due to the difficulty in confirming anterior neck landmarks in patients with severe obesity, we avoid using the Seldinger-style percutaneous cricothyrotomy.

When performing the procedure, the clinician should be prepared to make a generous vertical midline incision [18], and may need to place an endotracheal tube rather than a standard cricothyrotomy tube, if the latter is too short. Bedside ultrasound can be a helpful adjunct and has been shown to help with identification of the cricothyroid membrane in both patients and cadaveric models with poor external landmarks [76,77]. The performance of cricothyrotomy is described separately. (See "Emergency cricothyrotomy (cricothyroidotomy)".)

Mechanical ventilation — Providing adequate ventilation and oxygenation to the intubated patient with obesity can be difficult. Tidal volumes are calculated based upon the patient's IBW (obesity does not change underlying lung volumes) and then adjusted according to the clinical response, using airway pressures, oxygen saturation, and blood gas results. Oxygenation and ventilation can be improved in patients with severe obesity by placing them in a more upright position (eg, reverse Trendelenburg). Management of mechanical ventilation in the emergency department is reviewed separately. (See "Mechanical ventilation of adults in the emergency department".)

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: Airway management in adults".)

SUMMARY AND RECOMMENDATIONS

●Obesity and airway difficulty – Obesity leads to a number of anatomic and physiologic changes that increase the difficulty of airway management and alter the pharmacology of many medications used for rapid sequence intubation (RSI) and awake intubation. Of note, patients with obesity desaturate quickly. Bag-mask ventilation (BMV), laryngoscopy and intubation, and cricothyrotomy are all more likely to be difficult in patients with obesity. Important aspects of emergency airway management in patients with obesity are summarized in the table (table 1). (See 'Physiologic and anatomic changes' above and 'Airway assessment' above.)

●Bag-mask ventilation – The best method for BMV in patients with obesity is the two-person technique with oropharyngeal and nasopharyngeal airways in place using a thenar grip on the mask. (See "Basic airway management in adults", section on 'Bag-mask ventilation'.)

●Preoxygenation – Bi-level positive airway pressure (BiPAP) is the primary method for preoxygenation. Flush-flow rate oxygen (40 to 90 L/minute by nonrebreather mask or by bag-valve mask) is an alternative when BiPAP is contraindicated. Patients should be in the upright position whenever feasible. Placing the patient in the ramped position (align the external auditory meatus and sternal notch) improves intubation success and should be used if cervical spine precautions are not necessary (picture 2). (See 'Preoxygenation' above and 'Positioning' above.)

During RSI, gentle ventilation using a bag mask may be performed during induction to mitigate oxygen desaturation, provided that the patient is not at high risk for aspiration. (See 'Rapid sequence intubation' above.)

●Tracheal intubation – Video laryngoscopes provide advantages over direct laryngoscopy in patients with obesity. A tracheal tube introducer (bougie) should be available at the bedside whenever a patient with obesity is to be intubated. A number of airway adjuncts can be employed when managing a difficult airway in the patient with obesity. These are described in the text. (See 'Devices for airway management' above.)

●Medications for RSI – When performing RSI in the patient with obesity, we use the following approach to medication dosing: We suggest using the lean body weight (LBW) to determine the dose of the induction agent (Grade 2C); we suggest using the total body weight (TBW) to determine the dose of succinylcholine (Grade 2B) and the dose of rocuronium (Grade 2C). (See 'Medication dosing' above.)

●Awake intubation – Based upon the clinical circumstances and the characteristics of the airway, the clinician may decide it is prudent to manage the airway of a patient with obesity using an "awake approach." This approach is described in the text. (See 'Rapid sequence intubation' above and 'Awake intubation' above.)