Disease riska relative to normal weight and waist circumference
Men 102 cm (40 in) or less
Women 88 cm (35 in) or less
Men > 102 cm (40 in)
Women > 88 cm (35 in)
While providing an anesthetic in a familiar operating room (OR) environment to morbidly obese patients is challenging enough, we are now increasingly required to anesthetize these patients outside of the OR for various procedures. Large portions of these cases are done under monitored anesthesia care, and the patients can range from clinically stable to critically ill . Common out of OR locations are shown in Table 27.2. Performing procedures outside the traditional OR environment provides the benefit of quicker turn over time at a lower overhead cost. In other instances, these procedures are performed off-site due to specialized equipment, or patient needs. Surgeons, other proceduralists and post anesthesia care unit nurses alike, depend on the use of agents with quick onset, and offset in order to best utilize limited resources. Furthermore, this out of traditional OR model is less than optimized to handle any clinical crisis given limited support staff. This chapter will aim to present an in depth review of various challenges that can be anticipated, and prepared for, in order to ensure a safe anesthetic delivery to morbidly obese patients undergoing various procedures.
Common locations for procedures outside the OR
Neurointerventional and vascular
Tracheostomy, percutaneous gastrostomy
Various other procedural sedation
Patient selection takes into consideration the extent of surgical stress, anesthetic concerns , and post-operative recovery. The procedure should have nominal expectant blood loss and minimal derangements in physiology. The American Society of Anesthesia (ASA) patient stratification score is often used when selecting patients for elective procedures in remote settings. ASA class 1 and 2 are considered safe to be performed, while class 3 is relatively safe if comorbid systemic diseases are well controlled. If at all possible, performing procedures on ASA classification four and five patients should be done in a well-equipped environment such as the OR. Unfortunately, the clinical decision-making is not always that simple. Clinical judgment must be exercised as the patient may require an urgent procedure in and out of OR setting. For example, you are asked to perform a bedside Esophagogastroduodenoscopy (EGD), and Colonoscopy in the Critical Care Unit for a patient with a BMI of 56 kg/m2. Of note, his past medical history includes ischemic cardiomyopathy and he is status post a biventricular assist device 8 years ago. He now presents with hematochezia and hemoglobin of 6.4 g/dl. At the time of his BiVAD placement his BMI was 42 kg/m2, meeting inclusion criteria. There are numerous challenges in this anesthetic. Is it safe to perform this bedside, outside of the operating room given associated risks with his obesity, and comorbidities? Should this patient receive a general anesthetic with an assisted airway in order to avoid obstruction, and hypoxemia? If over sedated bedside, are resources available to treat the expected drop in systemic vascular resistance and subsequent reduced pulse index on his BiVAD? There are numerous ways to perform this anesthetic, but it’s important to identify such concerns in this high-risk patient population. Although obesity alone is not this patient’s most concerning medical problem; the physiologic differences in this patient, compared to the normal BMI patient make him more susceptible to anesthetic induced morbidity.
The basic requirements of equipment and personnel resources, as defined by the ASA practice guidelines  for out of operating room anesthesia must be met for every procedure. The position of the patient should allow for quick access to the patient, have adequate lighting, sufficient power sources (and back up sources), gas supply, oxygen cylinders and hand resuscitation bags capable of 90 % oxygen delivery. Access to emergency drugs and more personnel should be readily available. Monitoring should at minimum include oxygenation, ventilation, circulation and temperature. Airway equipment, suction, and emergency drugs should be readily available. Trained staff under the supervision of an Anesthesiologist should provide post anesthesia management.
Physiology in the Morbidly Obese
It is well established that excess adipose tissue increases the risk of metabolic syndrome (MetS), diabetes, cardiovascular disease, cancer, and premature death [12–16]. The presence of metabolic syndrome is implicated in the increased all-cause mortality seen in morbidly obese patients . Broadly, MetS is characterized by an imbalance between glucose and insulin homeostasis, dyslipidemia, obesity (in particular abdominal fat distribution), and hypertension. The postulated pathogenesis of this condition takes into account possible genetic susceptibility, however living a sedentary lifestyle and obesity is widely accepted as the predominant contributing factors [18, 19]. Studies have identified a direct correlation between waist size and incidence of coronary artery disease, independent of morbid obesity. That is to say, a male that has a BMI of <30, with a waist of greater than 40 in. also is at risk of coronary artery disease (CAD). Body fat content, not BMI, is the primary determinant that leads to the cascade of physiologic changes commonly present in the morbidly obese population . The high vascularity of fat creates an elevation in both cardiovascular and metabolic demand. Adipose tissue also serves as a powerhouse for numerous endocrine and paracrine cytokines that trigger physiologic change [21, 22]. Accelerated atherosclerosis, insulin resistance, alterations in lipid levels, coagulation, and elevation c-reactive protein (CRP) is all seen secondary to the various bioactive markers present in adipose tissue [23–25]. Many of these processes are reversible with optimization of diet, and weight loss. Given the physiologic changes that result from an elevated body fat content in combination with the limited mobility owing to an increase in musculoskeletal disorders , surgical intervention is often explored by these patients for weight loss.
As with any good anesthetic, it is crucial to obtain an in depth history and focused physical examination. If available, it is helpful to review past anesthetic records, as any concerning information gathered may lead to an alteration in the planned anesthetic. A detailed history must include an assessment of obstructive sleep apnea, cardiopulmonary and other common systemic diseased associated with morbid obesity (Table 27.3).
Table showing system based comorbidies associated with morbid obesity
Congestive heart failure, ischemic heart disease, atrial fibrillation, dysrhythmias
Diabetes Type II, metabolic syndrome, hypothyroidism
Pulmonary hypertension, OSA
Endometrial cancer, esophageal adenocarcinoma
Obstructive Sleep Apnea
Morbid obesity has a direct correlation with obstructive sleep apnea (OSA) [27, 28], however this is often undiagnosed . The diagnosis is made on polysomnography by measuring the apnea- hypopnea index (AHI)- a measure of complete cessation and partial obstructions during an hour of sleep. Each event must be at least 10 s in duration and accompanied by a desaturation as measured by pulse oximetry. OSA is considered to be mild with an AHI of 5–15, moderate if 15–30, and severe when >30. There is data to suggest that having moderate to severe OSA increases all cause mortality [3, 30]. It is prudent to have a high level of clinical suspicion when conducting the pre-anesthetic evaluation. When inquired, patients will report fatigue, daytime sleepiness, loud snoring and possibly witnessed apnea episodes by their family. Screening for OSA can quickly be performed using one of the many existing questionnaires including STOP-BANG [31, 32]. Non-invasive therapy for diagnosed patients consists of providing continuous positive airway pressure (CPAP) at night during sleep . Current data available on the correlation between OSA and the rate of perioperative complication shows varying results [34–38]. It is still useful to know if the patient is being treated at home, and their settings for CPAP, which can be made available for the post operative course if needed. Once identified, it is important to strategize a plan that will optimize ventilation and oxygenation [39, 40].
Furthermore, the diagnosis of OSA carries with it additional criteria that must me met prior to discharge. The ASA practice guidelines on the perioperative management of patients with OSA, has set forth supplementary guidelines for discharge. They recommend that OSA patients should be:
Monitored for 3 h longer compared to healthy patients
Not have hypoxemic episodes or airway obstruction when left alone
Return to their baseline oxygen saturation on room air
Monitored for an additional 7 h after an episode of airway obstruction or hypoxemia while breathing room air in an un-stimulating environment.
Morbidly obese patients have a lower threshold for desaturation due to dramatic changes in their physiologic reserves, increased oxygen consumption, and anatomical obstruction. Positioning the head of the bed at a 30° elevation helps maintain functional residual capacity (FRC) and limits redundant tissue from obstructing the airway . If the patient is to be supine for the procedure, it is helpful to construct a ramp elevating the chest and allowing for better alignment of the oropharyngeal and laryngeal axis’. This is accomplished when the external auditory meatus is parallel with the level of the chest. It is advantageous to have the patient in lateral or prone position, as these positions are less associated with airway obstruction when compared to being supine .
Starting an intravenous line (IV) can be a laborious task in this patient population. Redundant adipose tissue often impairs direct visualization on commonly sought after cannulation sites such as the hands, forearms, and antecubital fossa. Tactile sensation sometimes used to find veins is also diminished for the same reason. Unfortunately, there is no secret strategy to better identifying veins. The method of applying heat using a warm towel to facilitate vasodilation of the vessel in question is helpful. If available, ultrasound can facilitate cannulation in the antecubital fossa, however its success is dependent on user proficiency. It is important to realize that when encountering this problem in a situation where image guidance is not available, more unconventional sites for IVs can be explored. A small 22–24-guage in the volar surface of the hand, fingers, abdomen and chest wall may suffice. Larger peripheral access is more easily obtained with the resultant vasodilatory effects of anesthetic agents. If an adequately functional peripheral IV cannot be obtained for the procedure, central access, with ultra sound guidance should be considered.
The airway assessment should focus on both the predictors of difficult mask ventilation and intubation. Morbidly obese patients by definition meet at least one of the predetermined risks for difficult ventilation, a BMI > 26 Kg/m2. Other factors that are known to impede ventilation include age >55 years, edentulous, presence of a beard, and a history of snoring . The sensitivity and specificity, if two factors are present is 72 % and 73 % respectively. Predictors of having a challenging laryngoscopy include having a history of difficult intubation, Mallampati 3–4 classification, short thyromental distance, inter-incisor gap of less than 3 cm, limited Atlanto-Occipital extension, limited mandibular protrusion, prominent incisors, or a high arched palate . There is conflicting data regarding the correlation amongst elevated BMI and difficult/failed intubation [45, 46]. Traditionally, it has been taught to control a difficult or questionable airway at the start of the case in order to avoid complications during the procedure. When performing out of OR anesthesia, invariably all morbidly obese patients present with numerous risk factors identified above. The length of the procedure, need for paralysis, and patient specific concerns are often the driving variables whether to perform sedation or general anesthesia with a supraglottic or endotracheal airway.
Appropriate pre-oxygenation is of the utmost importance in these patients. It should be conducted in head up position (reverse Trendelenburg) to minimize the profound reduction in functional residual capacity that occurs in the supine position. Owning to a higher metabolic demand, obese patients have increased oxygen consumption per kg of body weight at approximately 4–6 ml/kg. An increase in airway resistance also makes these patients prone to quickly becoming hypoxemic. There may be some benefit in using low pressure CPAP while pre-oxygenating in effort to further reduce atelectasis . Routine airway equipment such as oropharyngeal airways, and nasal trumpets must be available to assist with ventilation. Although an elevated BMI in itself is not a determinant of difficult laryngoscopy, it is advisable to have access to an intubating bougie, and video laryngoscopes should an unanticipated airway be encountered. While on mechanical ventilation, the use of vital capacity maneuvers in addition to positive end-expiratory pressure (PEEP) helps to improve oxygenation .
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When providing sedation in an out of OR setting, the guidelines for monitoring must be adhered to as outlined earlier. The depth of unconsciousness required varies by the procedure being performed. The patient should be kept spontaneously breathing, as entering deep sedation or general anesthesia without a protected airway increases the risk of complications resulting from hypoxia. The spectrum of sedation to general anesthesia is best examined by assessing patient response to verbal or painful stimuli, need for assistance with airway, ability to ventilate, and cardiovascular stability (Table 27.4).
Spectrum of Sedation
Table showing spectrum of increasing sedation (Adapted from Practice Guidelines for Sedation and Analgesia by Non-Anesthesiologist, developed by American Society of Anesthesiologists)
Minimal sedation (anxiolysis)
Moderate sedation/analgesia (conscious sedation)
Normal response to verbal stimulation
Purposefula response to verbal or tactile stimulation
Purposefula response after repeated or painful stimulation
Unarousable, even with painful stimulus
No intervention required
Intervention may be required
Intervention often required
May be inadequate
May be impaired