Some anesthetic aspects of morbid obesity Ashish C. Sinha

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1 Some anesthetic aspects of morbid obesity Ashish C. Sinha University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA Correspondence to Ashish C. Sinha, MD, PhD, DABA, Assistant Professor of Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, 680 Dulles Building, 3400 Spruce Street, Philadelphia, PA , USA Tel: ; fax: ; Current Opinion in Anaesthesiology 2009, 22: Purpose of review Obese, morbidly obese and ultra-obese patients have multiple surgical procedures. Although they can have an acute abdomen, obstetric procedures, trauma-related procedures and many others, morbidly obese patients are most consistently cared for in the bariatric surgery operating room. The lessons from that group of patients can, could and, usually, should be applied in all patients who are morbidly obese and present for anesthetic care. Recent findings There is a paucity of recent evidence-based studies that investigate this patient population. Many recommendations in this review are based on experience of the bariatric anesthesia group at this university hospital. The current review period shows an impressive study that indicates the possibility of predicting sleep apnea fairly accurately by using a few easily answered questions instead of the gold standard polysomnography. Another study showed that, in the morbidly obese, nasal ventilation might be advantageous over oronasal ventilation prior to induction. Summary The number of patients with obesity and morbid obesity continues to increase. Following certain guidelines will ease the management and improve outcomes of the morbidly obese patient presenting for any surgery. Keywords airway challenges, morbid obesity, obstructive sleep apnea, ultra-obese Curr Opin Anaesthesiol 22: ß 2009 Wolters Kluwer Health Lippincott Williams & Wilkins Introduction Obesity as a disease is a relatively recent phenomenon, appearing in the mid-20th century, when it stopped being a rarity. Across the United States, almost 200 million people are overweight or obese. Today, across the globe, more people are overweight than malnourished, though one could argue that obesity is a form of malnourishment as well. Obesity is one of the top two causes of preventable mortality in the United States, the other being smoking, though obesity may achieve the dubious distinction of being number 1 soon enough. The increasing BMI of the United States population is reflected in the patients presenting for surgical care. Using a rough estimate of population distribution in the United States, the morbidly obese have a potential to be a large part of the patients who not only present for medical care in the United States hospitals but also correspondingly in the operating rooms. Distribution of BMI in the operating rooms of a tertiary care medical center at the University of Pennsylvania in Philadelphia showed that of the nearly individual patient presenting for surgery, with height weight data available in the year 2007, nearly 8% had a BMI over 40 kg/m 2. The distribution indicated that 1.8% (349 patients) had a BMI over 50 kg/m 2, and 50 patients were ultra-obese [BMI >70 kg/m 2 or weight >200 kg (or >440 pounds)] (see Fig. 1). In other words, almost every day we have somebody in the operating room with a BMI of more than 50 kg/m 2, and almost every week we anesthetize somebody who is ultra-obese, with a BMI of more than 70 kg/m 2. We recently anesthetized a man with a BMI of 112 kg/m 2 for an incision and drainage of the lower extremity for fasciitis, and a colleague recently intubated a 500-pound gravid woman for Cesarean section for twins due to failure of placement of an epidural. With almost one in 12 patients being morbidly obese, the challenges of anesthesia in this group will have to be met by all practitioners, not just those specializing in bariatric surgery. This is an increasingly international problem and definitely not limited to one hospital, region or country. Even though BMI (kg/m 2 ) is a good estimate of obesity and generally a good definition of the problem, other factors such as hip:waist ratio, which is a reflection of truncal obesity, may provide more useful information of risks associated with increasing weight ß 2009 Wolters Kluwer Health Lippincott Williams & Wilkins DOI: /ACO.0b013e32832b6807

2 Some anesthetic aspects of morbid obesity Sinha 443 Figure 1 Distribution of the 1499 morbidly obese patients presenting for surgery at the hospital of the University of Pennsylvania in cm may also predict difficult intubation. Prior anesthetic care may provide useful information for successful airway management as well as information regarding how the patient reacted to anesthesia. One study [1] showed that morbidly obese patients, with or without OSA, experience frequent oxygen desaturation postoperatively, despite supplemental oxygen therapy, and perioperative management should incorporate plans to prevent postoperative hypoxemia. Bariatric surgery refers to the surgical alteration of the small intestine or the stomach with a view towards producing weight loss. The surgical goal of weight loss surgery in morbid obesity is to reduce the patient s capacity to ingest food. This subsequently results in weight loss, and perhaps more importantly decreases comorbidities. These procedures may be restrictive, such as vertical-banded gastroplasty, though this has largely been replaced by a laparoscopic gastric-banding procedure. Alternately, the procedures may be malabsorptive and restrictive such as the Roux-en-Y gastric bypass or the biliary pancreatic bypass. Approximately, weight loss procedures were performed in Owing to space constraints, this commentary is restricted to some common aspects in the anesthetic care of the morbidly obese: obstructive sleep apnea (OSA), intubation, ventilation, positioning and extubation. (For a thorough review of the subject, the reader is referred to chapter 64 in Miller s Anesthesia, 7th ed. Amsterdam: Elsevier.) Obstructive sleep apnea Preoperative preparation of these patients includes common problems of hypertension, diabetes and OSA. This group of patients has unique challenges secondary to the sleep apnea. Up to a quarter of the general population may have sleep apnea, with it being present in almost three-quarters of the patients presenting for bariatric surgery. An apnea hypopnea index (AHI), as done in an overnight sleep study, polysomnography, provides classification of patients. A score of 5-15 is considered mild disease, as moderate, and severe if over 30. When greater than 30, it can be a predictor of rapid severe desaturation with induction. This combined with a continuous positive airway pressure (CPAP) requirement during sleep greater than 10 cm H 2 O implies potentially difficult mask ventilation. Neck size larger than Screening tool for obstructive sleep apnea The STOP questionnaire [2 ] has four questions with yes/no answers: snoring, tiredness during daytime, observed apnea and high blood pressure. This was validated with the AHI obtained with monitored polysomnography. The authors demonstrated that the sensitivities of the STOP questionnaire with AHI with more than five, more than 15 and more than 30 as cut-offs were 65.3, 74.3 and 79.5%, respectively. To further improve the sensitivity of the STOP questionnaire, the same authors [2 ] incorporated BMI (>35 kg/m 2 ), age (>50 years), neck circumference (>40 cm) and sex (male, yes) and enhanced the sensitivity and the negative predictive value (NPV) of this screening tool, the STOP-Bang scoring model. The sensitivities at an AHI of more than five, more than 15 and more than 30 were 83.6, 92.9 and 100%, respectively. The corresponding NPVs were 60.8, 90.2 and 100%. A very thorough review of OSA and its implications for anesthesiologists was published by Chung et al. [3 ] in Intubation Even though exact agreement varies, a difficult intubation has been practically described as one in which a conventionally trained anesthesiologist has problematic mask ventilation, intubation or both. The morbidly obese may present with a potentially difficult airway due to an abnormal anatomy, secondary to excess soft tissue. The large tongue can affect accessibility to the larynx at laryngoscopy. The redundant palatal and pharyngeal tissues may make mask ventilation, laryngoscopy and intubation more challenging. Overall, difficulty of intubation and ventilation is unknown but was estimated at almost 7% in the 1980s and 1990s [4,5]. With the development and widespread use of modern technology such as fiberoptic bronchoscopes and video laryngoscopes in the last 20 years, it is difficult to imagine that the percentage is still that high. More probably, the number quoted by Brodsky et al. [6] of approximately 1% for difficult intubation and about 10% for difficult ventilation is closer to the estimate in the morbidly obese. In the nonmorbidly obese, BMI of less than 40 kg/m 2, the number is probably similar. It is also difficult to get

3 444 Anesthesia and medical disease accurate estimates, as intubation skill can vary even among trained anesthesiologists. At our hospital, about 400 patients have weight loss surgery every year, and the difficult intubation number is less than 1%. Partly by good planning, consistent practice and some luck, we have not experienced any cannot intubate, cannot ventilate scenarios in the last 4 years. Does every elective fiberoptic intubation indicate an impossible or even difficult laryngoscopic intubation? Probably not, but in the field of anesthesia, good preparation predicates good outcomes. Some practitioners feel that if I thought about it, maybe I should just go ahead and do it (fiberoptic intubation). That is definitely a reasonable approach, and in a specialty that is all about safety, there is little to criticize in that approach except that some patients may get labeled difficult intubation or can (only) be intubated with a fiberoptic bronchoscope. According to Brodsky et al. [6], patients with a BMI of more than 35 kg/m 2 have a six-fold higher risk for difficult laryngoscopy, but many studies have since refuted that BMI alone is a predictor of difficult laryngoscopy or failure to intubate. Mashour et al. [7], looking at 346 patients, showed that in patients with BMI at least 40 kg/m 2 versus less than 40 kg/m 2, there was no difference in difficult laryngoscopy or intubation. Some studies have looked at neck circumference and shown a positive association with difficulty in intubation. Intubation difficulty scale (IDS) as described by Adnet et al. [8], over 10 years ago, is probably an often underused scale that allows for comparison in different facets among diverse patients. The study by Gonzalez et al. [9 ] of 131 patients showed that difficult tracheal intubation is more frequent in obese rather than lean patients. They also showed that IDS scores more than 5, thyromental distance, BMI, large neck circumference and higher Mallampati score were the only predictors of potential intubation problems. Many authors have identified neck circumference as a risk factor for difficult intubation. Brodsky et al. [6] showed that, when neck size increases past 40 cm, the odds ratio of difficulty in intubation increases by 1.13 with each increasing centimeter. Risk of aspiration Nearly 35 years ago, Vaughan et al. [10] had claimed that larger patients had more gastric juice with lower ph, but this has since been refuted as well [11]. It still seems prudent to do a rapid sequence induction with cricoid pressure. Postbariatric surgery patients may pose a different challenge due to altered gastric and esophageal anatomy and physiology. A study from France [12] showed that risk of aspiration is significant in this group, versus the morbidly obese who have not undergone weight loss surgery. Positioning At our institution, we induce all of these patients in a 308 head up position. This improves laryngoscopic view, increases well tolerated apneic time by relieving pressure on the diaphragm from abdominal contents and is usually more comfortable for the patient as well. Even though evidence-based studies are sorely lacking, it seems intuitive that these patients require extra care for intraoperative positioning. Even when in a supine position, these patients can suffer severe complications such as renal failure [13] and death [14] that have both been reported. The prone position requires use of cushioning gel pads and rolls. Pressure points must be checked frequently and readjusted as needed. The excess axillary tissue may make an axillary role redundant or impossible to place appropriately. An Italian study [15] showed that the beach chair position and positive end-expiratory pressure (PEEP), when used together, prevented some of the adverse effects of anesthesia and paralysis during pneumoperitoneum in morbidly obese patients undergoing gastric banding. Liang et al. [16 ] make a fairly convincing argument for nasal ventilation instead of the usual oronasal method used prior to induction. Their noteworthy findings include a lower peak inspiratory pressure (16.7 versus 24.5 cm H 2 O) and a larger expired volume (264.5 versus 65.6 ml). Additionally, the median CO 2 removal nasally was 5.0 versus 0 ml by the oronasal route. The explanation accorded was soft-tissue obstruction in the oropharynx. I wonder whether similar results are achievable by using a regular mask and asking our patients to breathe just through the nose. Another study [17] showed that nasopharyngeal supplementation of preoxygenation in morbidly obese patients leads to an increased period of apnea, with a fall in SaO 2 from 100 to 95%. In this study, the authors also provide a nice short reminder on apneic oxygenation and its underlying principles. Dhonneur et al. [18] show the efficacy of using an Airtraq laryngoscope (King Systems, Noblesville, Indiana, USA) in morbidly obese parturients having emergency cesarean delivery. There seems to be an increasing role of video laryngoscopes in airway management in the morbidly obese. A study in the European Journal of Anaesthesiology [19] demonstrated that video laryngoscopy, in patients with BMI more than 35 kg/m 2, had a better grade of Cormack Lehane view, and the lowest SpO 2 achieved in the laryngoscope patient was clinically better but could

4 Some anesthetic aspects of morbid obesity Sinha 445 not achieve statistical significance. Their conclusions were that in morbidly obese patients the use of video laryngoscope significantly improves the visualization of the larynx, and thereby facilitates intubation. My personal experience would endorse this statement completely and also the fact that video laryngoscopes have a steep learning curve and practitioners can very quickly achieve confidence and good results with these devices. The commonly used one is the Glidescope (Verathon, Bothwell, Washington, USA), which was introduced in Others are McGrath (Aircraft Medical Ltd, Edinburgh, UK), Berci Kaplan DCI (Karl Storz Endoscopy, Culver City, California, USA), Weiss angulated video-intubating laryngoscope (Volpi AG, Schlieren, Switzerland), Pentax Airway scope (Pentax Corporation, Tokyo, Japan), Airtraq, Truview Premier (Truphatek, Netanya, Israel) and the laryngeal mask airway (LMA) CTrach (LMA North America, San Diego, California, USA). The common advantages are larger image, ease of instruction and demonstration to multiple viewers, storing image, confirming position and speed of controlling the airway. The biggest disadvantage is cost, other potential drawbacks are that the lenses in some units may fog up, some units are relatively large and a few units require electric power from a wall plug, making them less useful in certain situations. The decrease in price and increasing popularity of these can only lead to increased usage of these devices. It has even been predicted by some that video laryngoscopy will almost eliminate direct laryngoscopy in the next few decades, if not sooner, at least in the developed world. Extubation Some commonsense recommendations are to only extubate when the patient is fully conscious and responsive. Others are to use supplemental oxygen, monitor saturationandconsiderpromptcpapuseespeciallyinthose with a diagnosis of OSA and if they already have a CPAP mask. Using nonnarcotic analgesia as an adjunct to minimize respiratory depression is another intuitive decision. It is probably beneficial to keep the patient in a slightly head up position postoperatively rather than supine. Postoperative care It has been our experience that, when these patients are cared for in the same location within the hospital, the outcomes are better, as the caregivers are used to the special challenges that are associated with their care. This practice allows a high quality skilled nursing and ancillary care to be provided to these patients on a consistent basis. At this location, patients are kept on their CPAP or bilevel positive airway pressure (BiPAP) machine as appropriate and with pulse oximetry for monitoring of SpO 2 recommended. Also the potential bias faced by the very large patients is much decreased in such a location. If the patient is found to have a difficult intubation, at our hospital, the anesthesia department places a color-coded band on their wrist to identify them as such. At the head of these patients bed is placed a note to that effect, as well as the means utilized to secure the airway successfully. In case of an emergency reintubation, we feel that this information is extremely useful to the resuscitation team. Conclusion Obesity is a risk factor which when handled appropriately has become less of a challenge than it used to be in the past. There is no increase in unanticipated admissions after ambulatory surgery based on obesity alone [20 ]. An interesting study [21] from a department of surgery at a level I trauma center in New Jersey showed that morbid obesity was not a risk factor for failed intubations in the field or in the emergency department (ED), postintubation airway complications or death. At this center, all trauma intubations are considered difficult intubation. Interestingly, in this study, 92% of all intubations in the ED were performed by the anesthesia team. Does this mean that we, anesthesia providers, have the skill set to safely and rapidly intubate most if not all patients? The short answer to that is probably so. Some of this is based on better understanding of the altered physiology and pharmacology of these patients, some on the newer tools available, especially the laryngoscopes, and much is based on better training and teaching of the specialty. Dexmedetomidine, a highly selective a 2 -adrenoceptor agonist, is a drug with hypnotic, sedative, sympatholytic and analgesic properties, but at the same time it has no significant respiratory depression. A case for weight loss surgery with an infusion was described [22] for a patient with OSA, pulmonary hypertension and BMI of 110 kg/m 2, using it as a sole infusion in the absence of narcotics. Another trial of dexmedetomidine [23] showed advantages in laparoscopic gastric bypass, in which it was used as an adjunct infusion that decreased narcotic use, antiemetic therapy and length of stay in the postanesthesia care unit (PACU). As experience with it increases, its many advantages may make it a more frequently used drug in the morbidly obese in the future. Much work remains to be done in optimizing anesthesia in the obese, and evidence-based recommendations are sorely lacking. Some of the data in the current literature contradict each other, and prospective randomized trials

5 446 Anesthesia and medical disease with appropriate statistical power would go a long way in settling some of these debates. References and recommended reading Papers of particular interest, published within the annual period of review, have been highlighted as: of special interest of outstanding interest Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 456). 1 Ahmad S, Nagle A, McCarthy RJ, et al. Postoperative hypoxemia in morbidly obese patients with and without obstructive sleep apnea undergoing laparoscopic bariatric surgery. Anesth Analg 2008; 107: Chung F, Yegneswaran B, Liao P, et al. STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology 2008; 108: An excellent study of a screening tool for sleep apnea. 3 Chung SA, Yuan H, Chung F. A systemic review of obstructive sleep apnea and its implications for anesthesiologists. Anesth Analg 2008; 107: An excellent review on sleep apnea. 4 Wilson ME, Spiegelhalter D, Robertson JA, Lesser P. Predicting difficult intubation. Br J Anaesth 1988; 61: Jacobsen J, Jensen E, Waldau T, Poulsen TD. Preoperative evaluation of intubation conditions in patients scheduled for elective surgery. Acta Anaesthesiol Scand 1996; 40: Brodsky JB, Lemmens HJ, Brock-Utne JG, et al. Morbid obesity and tracheal intubation. Anesth Analg 2002; 94: Mashour GA, Kheterpal S, Vanaharam V, et al. The extended Mallampati score and a diagnosis of diabetes mellitus are predictors of difficult laryngoscopy in the morbidly obese. Anesth Analg 2008; 107: Adnet F, Borron SW, Racine SX, et al. The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997; 87: Gonzalez H, Minville V, Delanoue K, et al. The importance of increased neck circumference to intubation difficulties in obese patients. Anesth Analg 2008; 106: This study addresses the relationship between neck circumference and difficult intubation. 10 Vaughan RW, Bauer S, Wise L. Volume and ph of gastric juice in obese patients. Anesthesiology 1975; 43: Juvin P, Fevre G, Merouche M, et al. Gastric residue is not more copious in obese patients. Anesth Analg 2001; 93: Jean J, Compere V, Fourdrinier V, et al. The risk of pulmonary aspiration in patients after weight loss due to bariatric surgery. Anesth Analg 2008; 107: Bostanjian D, Anthone GJ, Hamoui N, Crookes PF. Rhabdomyolysis of gluteal muscles leading to renal failure: a potentially fatal complication of surgery in the morbidly obese. Obes Surg 2003; 13: Collier B, Goreja MA, Duke BE 3rd. Postoperative rhabdomyolysis with bariatric surgery. Obes Surg 2003; 13: Valenza F, Vagginelli F, Tiby A, et al. Effects of the beach chair position, positive end-expiratory pressure, and pneumoperitoneum on respiratory function in morbidly obese patients during anesthesia and paralysis. Anesthesiology 2007; 107: Liang Y, Kimball WR, Kacmarek RM, et al. Nasal ventilation is more effective than combined oronasal ventilation during induction of general anesthesia in adult subjects. Anesthesiology 2008; 108: This study addresses nasal versus oronasal ventilation prior to intubation. 17 Baraka AS, Taha SK, Siddik-Sayyid SM, et al. Supplementation of preoxygenation in morbidly obese patients using nasopharyngeal oxygen insufflation. Anaesthesia 2007; 62: Dhonneur G, Ndoko S, Amathieu R, et al. Tracheal intubation using the Airtraq in morbid obese patients undergoing emergency cesarean delivery. Anesthesiology 2007; 106: Marrel J, Blanc C, Frascarolo P, Magnusson L. Videolaryngoscopy improves intubation condition in morbidly obese patients. Eur J Anaesthesiol 2007; 24: Hofer RE, Kai T, Decker PA, Warner DO. Obesity as a risk factor for unanticipated admissions after ambulatory surgery. Mayo Clin Proc 2008; 83: This study addresses perceptions about impact of obesity in unanticipated admissions after ambulatory surgery. 21 Sifri ZC, Kim H, Lavery R, et al. The impact of obesity on the outcome of emergency intubation in trauma patients. J Trauma 2008; 65: Hofer RE, Sprung J, Sarr MG, Wedel DJ. Anesthesia for a patient with morbid obesity using dexmedetomidine without narcotics. Can J Anaesth 2005; 52: Tufanogullari B, White PF, Peixoto MP, et al. Dexmedetomidine infusion during laparoscopic bariatric surgery: the effect on recovery outcome variables. Anesth Analg 2008; 106: