Anesthesia for thoracic surgery in morbidly obese patients Jens Lohser, Vivek Kulkarni and Jay B. Brodsky
Purpose of review This review considers the anesthetic management of obese patients undergoing thoracic surgery. Extremely or morbidly obese patients differ from patients of normal weight in several ways. Obese patients have altered anatomy and physiology, and usually have associated comorbid medical conditions that may complicate their operative course and increase their risks for postoperative complications. Recent findings During anesthetic induction and laryngoscopy for tracheal intubation the morbidly obese patient should be in the reverse Trendelenburg position with the head and neck elevated above the table. Placement of a double-lumen tube should be no more difficult in an obese patient than in a normal-weight patient. There are no clear advantages for any of the commonly available inhalational anesthetic agents and each can be used for general anesthesia. Summary With proper attention to their special needs, the morbidly obese patient can safely undergo thoracic surgery and onelung ventilation. Keywords body mass index, morbid obesity, obesity, one-lung ventilation, ventilation Curr Opin Anaesthesiol 20:10–14. ß 2007 Lippincott Williams & Wilkins. Department of Anesthesiology, Stanford University School of Medicine, Stanford, California, USA Correspondence to Dr Jay Brodsky, MD, Department of Anesthesia, H-3580, Stanford University Medical Center, Stanford, CA 94305, USA Tel: +1 650 725 5869; fax: +1 650 725 8544; e-mail:
[email protected] Current Opinion in Anaesthesiology 2007, 20:10–14 Abbreviations DLT OLV OSA PEEP
double lumen tube one-lung ventilation obstructive sleep apnea positive end-expiratory pressure
ß 2007 Lippincott Williams & Wilkins 0952-7907
Introduction More than one-third of American adults are obese (body mass index > 30 kg/m2) and almost 5% are severely or morbidly obese (body mass index > 40 kg/m2) [1]. As a result, increasing numbers of obese patients are scheduled for every type of surgical procedure, including thoracic operations. Obese patients often have altered airway anatomy and changes in their pulmonary mechanics and pulmonary circulation. Many have serious comorbidities associated with obesity. Since even normal-weight patients experience some decrease in pulmonary function following thoracotomy, a morbidly obese patient is probably at increased risk of pulmonary complications. In this review we will consider the perioperative anesthetic management of the morbidly obese patient undergoing thoracic surgery.
Preoperative assessment A thorough preoperative assessment should precede any scheduled anesthetic. For a morbidly obese patient the anesthesiologist must consider the many associated comorbid conditions [including hypertension and cardiovascular disease, type II diabetes, obstructive sleep apnea (OSA) and osteoarthritis] in addition to the medical problem that necessitates surgery [2]. Obstructive sleep apnea
Moderate to severe OSA may be present in more than half the morbidly obese population. OSA has important implications for airway management and the use of sedatives and opiates in the perioperative period [3]. Unfortunately most morbidly obese surgical patients have not had a polysomnographic study to confirm the diagnosis [4]. The anesthesiologist performing the preoperative assessment of a morbidly obese patient may be the first person to suspect OSA. Symptoms include a history of day-time drowsiness, snoring, frequent awakenings, and periods of apnea during sleep. This suspicion is further increased if the patient has a large neck (circumference > 40 cm) and/or a history of hypertension. A complete sleep study, although indicated, may not be practical depending on the urgency of surgery. All morbidly obese patients should be presumed to have OSA and managed within that context. Airway assessment
Available previous anesthesia records should be reviewed for evidence of difficulty with tracheal intubation. A morbidly obese patient, especially with a history or symptoms suggestive of OSA, may have a diminution of 10
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Anesthesia for thoracic surgery in morbidly obese patients Lohser et al. 11
the pharyngeal space secondary to fat deposition in the pharyngeal wall [5], which can make airway access and mask ventilation difficult. The best preoperative predictors of potential difficulty with tracheal intubation in a morbidly obese patient are a Mallampatti score of III or IV and increased neck circumference [6]. Pulmonary function
Pulmonary mechanics are significantly altered by excess body fat, which reduces chest wall compliance. The diaphragm is affected by mass loading resulting in reduction of total pulmonary compliance. Airway resistance is usually increased, and the work of breathing is increased in the spontaneously breathing morbidly obese patient. Spirometry usually reveals a restrictive defect with decreases in expiratory reserve volume and functional residual volume with associated small-airway collapse during tidal breathing. These changes result in ventilation/perfusion (V/Q) mismatch, an elevated shunt fraction, and relative hypoxemia [7]. Preoperative pulmonary function testing can help predict which patient can safely undergo lung resection [8]. However, published minimum postoperative predicted values of at least 40% FEV1 (forced expiratory volume in 1 s) and 40% DLCO (the diffusion capacity of the lung for CO) are likely to be inappropriate in the obese patient since they are not indexed to weight. No similar studies to establish predictive baseline spirometry for obese patients undergoing lung resection have been published, but it has been shown that postoperative values for FEV1 and forced vital capacity decrease proportionally as body mass index increases [9]. Following abdominal surgery, when compared with normal-weight patients morbidly obese patients experience more atelectasis, greater decreases in functional residual volume, and lower PaO2 values [10]. Therefore, it is likely that morbidly obese patients experience greater reductions in pulmonary function following thoracic operations. Predictive spirometric values are not indexed to weight so they may be inappropriate in obese patients. Cardiovascular function
A larger blood volume and higher cardiac output in extreme obesity, in addition to concomitant OSA, results in a greater risk of pulmonary and systemic hypertension. When long standing these lead to eccentric rightventricular hypertrophy, left-ventricular hypertrophy, and development of right and left heart failure (obesity cardiomyopathy) [11]. A routine electrocardiogram is adequate for most morbidly obese patients, even those with hypertension. However, even in asymptomatic obese patients some degree of right-ventricular dysfunction can be demonstrated be echocardiography [12]. The presence of angina or other cardiac symptoms requires a more thorough cardiac evaluation. Longstanding or
severe OSA should alert one to the possibility of pulmonary hypertension and right-ventricular failure and prompt an echocardiographic evaluation [13].
Management of anesthesia There are several considerations in the management of anesthesia for the morbidly obese patient, including premedication, positioning of the patient, successful double lumen tube (DLT) placement and one-lung ventilation (OLV), tracheal extubation, and the choice of anesthetic agent. Premedication
Benzodiazepines and opiates, even given preoperatively, can have prolonged effects, and in a patient with OSA they can increase the risk of respiratory depression into the postoperative period. Sedative premedication should be used with caution or avoided completely. Positioning
An awake morbidly obese patient should never be allowed to lie supine. In this position there is a further reduction in functional residual volume resulting in dangerous hypoxemia, as well as decreased venous return from compression of the inferior vena cava. Preoxygenation with the patient in the reverse Trendelenburg position will prolong the duration of safe apnea time after muscle relaxation for tracheal intubation [14]. The semi-Fowler position with the patient’s upper body elevated 25–308 also extends safe apnea time [15]. In both positions the panniculus drops down and unloads the diaphragm, increasing the functional residual volume. The ramped head-elevated laryngoscopy position (H.E.L.P.), with the operating room table in the reverse Trendelenburg position, maximizes functional residual volume while improving view during direct laryngoscopy [16]. Changing to the lateral position requires additional physical help and equipment. Axillary rolls have to be proportionally larger to protect the brachial plexus. Beanbags to support the patient in the lateral decubitus position may not sufficiently wrap around the patient due to their excessive girth and patients may need to be restrained with belts or tape across the pelvis. Supporting the head in the lateral, flexed position can be difficult due to a proportionally short neck, which requires creative placement of towels and blankets to ensure that the head is positioned on a horizontal line extending through the spine of the patient, in a neutral position. Placement of the double lumen tube
Although there are no studies comparing ease and success of DLT placement in morbidly obese patients with normal-weight patients, tube placement should be no more difficult in the majority of morbidly obese patients
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12 Thoracic anaesthesia
providing that the patient is appropriately positioned for tracheal intubation [17]. As always, in the event of difficult tracheal intubation, placement of a single-lumen endotracheal tube by direct laryngoscopy, with a ProSeal or Fastrach intubating laryngeal mask airway [18], or with another adjunct such as a bougie, an Aintree intubating catheter, or awake fiberoptic intubation, allows subsequent tube exchange for a DLT. If tube exchange is not practical, lung isolation can be achieved with a bronchial blocker through the endotracheal tube. Unlike chronic obstructive lung disease, which results in a dilation of trachea and bronchi, a similar effect does not occur for the restrictive lung disease associated with obesity. Relatively small tracheas are often found in very large patients. We select a DLT by examining the patient’s chest radiographs or computer tomographs preoperatively to determine tracheobronchial anatomy and airway diameters [19]. A large DLT should be chosen to minimize airflow resistance during OLV [20]. One-lung ventilation
Successful OLV in morbidly obese patients is technically possible in the lateral position if the panniculus falls away from the body and unloads the dependent diaphragm [21]. A single clinical report of morbidly obese patients undergoing gastric stapling through a thoracotomy incision, published almost 25 years ago, found that all patients tolerated the procedure with adequate oxygenation during OLV [22]. Morbidly obese patients benefit from lung-recruitment maneuvers following induction of anesthesia, particularly prior to the institution of OLV [23]. For most patients, maintaining intraoperative oxygenation during OLV can be accomplished with large tidal volume ventilation, intermittent alveolar recruitment, continuous positive airway pressure to the collapsed lung, or may occasionally require positive end-expiratory pressure (PEEP) to the ventilated lung. Basilar atelectasis is present in supine morbidly obese patients preoperatively, and worsens following induction of general anesthesia. In morbidly obese patients ventilation with tidal volumes greater than 13 ml/kg (ideal weight) does not improve oxygenation, and can result in excessively high peak pressures during OLV. High peak inspiratory pressures secondary to restriction of chest wall and diaphragmatic excursion and the narrow single lumen of a DLT can further limit volume-controlled mechanical ventilation during OLV. Pressure-controlled ventilation during OLV can improve oxygenation and decrease peak pressures in normalweight patients [24]. Pressure-limited OLV may have an application in the morbidly obese population, but if too low a tidal volume is delivered to patients with an already low functional residual volume then hypoxemia may worsen.
PEEP is beneficial during two-lung ventilation in morbidly obese patients. During OLV the benefits of PEEP to the single ventilated dependent lung are less clear as any pressure above the lower inflection point of the alveolar pressure-volume loop results in increased pulmonary vascular resistance, thereby increasing shunt fraction and worsening hypoxemia [25]. Tracheal extubation
Tracheal extubation immediately following completion of a pulmonary resection lowers the risk of bronchial stump disruption and pulmonary air leaks secondary to positivepressure ventilation. In normal-weight patients our practice is to extubate the trachea early, with the patient in the lateral position, followed by assisted mask ventilation until the patient is fully awake. In the morbidly obese patient mask ventilation can be difficult, especially if there is a history of OSA. Tracheal extubation in a morbidly obese patient should be performed in the reverse Trendelenburg position to optimize ventilation and access to the airway if re-intubation becomes necessary. Two strategies can be employed to ensure that a morbidly obese patient is sufficiently awake and has established a regular respiratory pattern before the trachea is extubated. The DLT can be replaced with an endotracheal tube via a tube exchanger. Alternatively, after deflating both cuffs and withdrawing the endobronchial segment into the trachea, the tracheal cuff can be reinflated and the DLT can be used as a single-lumen tube. A DLT completely in the trachea is less stimulating than when in the mainstem bronchus and with both lumens patent flow resistance is comparable with that of a regular endotracheal tube. Anesthetic agents
Short-acting anesthetic and analgesic agents are appropriate choices in the morbidly obese patient. Some anesthesiologists advocate a total intravenous anesthesia technique with remifentanil, whereas most find an inhalational technique combined with epidural analgesia more suitable. Despite claims to the contrary, there is no clear advantage to any inhalational anesthetic in morbidly obese patients [26,27].
Postoperative analgesia Postthoracotomy analgesia is important to maximize lung function. Epidural analgesia has proven advantages and can be delivered in either the lumbar or thoracic area, depending on operator comfort and anatomic ease. Paravertebral blockade can be as effective as epidural blockade and can be performed during the procedure under direct visualization of the thoracic cavity by the surgeon [28]. Rescue techniques include intrapleural analgesia with local anesthetics or parenteral nonsteroidal analgesic agents like ketorolac. Large doses of epidural opioids are
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Anesthesia for thoracic surgery in morbidly obese patients Lohser et al. 13
best avoided in patients with proven or suspected OSA to avoid delayed respiratory depression. The a-2 agonist dexmedetomidine has been used successfully as an intravenous adjunct to epidural local anesthetics for postthoracotomy analgesia [29]. Dexmedetomidine may be useful for morbidly obese patients because of its minimal effects on respiration [30].
Complications Extremely obese patients undergoing cardiac procedures have a longer recovery time and a greater incidence of postoperative complications than normal-weight patients [31]. The risk of postoperative thromboembolism, atelectasis and pneumonia are believed to be greater in morbidly obese patients [32], but outcome studies on obese thoracic surgical patients have not been performed.
Surgical issues Operative exposure in a morbidly obese patient may be less than optimal as the usual lateral decubitus position with extreme table flexion may not result in an adequate opening of the chest wall. Exposure is further compromised by increased thickness of the chest wall. Soft-tissue thickness also becomes important during video-assisted thoracic surgical procedures since longer instruments are needed and the range of motion may be limited. Unsatisfactory conditions for video-assisted thoracic surgery can lead to conversion to thoracotomy, but once again, it remains unknown whether this complication occurs more often in morbidly obese patients. This has important implications since it raises issues as to whether an epidural catheter should be placed preoperatively in a technically difficult video-assisted thoracic surgical patient when there is a high likelihood of proceeding to thoracotomy. Preemptive epidural analgesia reduces the level and duration of postthoracotomy pain [33].
Conclusion Although obese patients comprise an ever-increasing percentage of thoracic surgical patients, current anesthetic management is based on experience with morbidly obese patients undergoing other surgical procedures. Morbid obesity in itself is not a contraindication to thoracic surgery. Given the potential problems of extreme obesity, there is a need for clinical studies to develop anesthetic management strategies for morbidly obese thoracic surgical patients.
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. 84). 1
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2
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14 Thoracic anaesthesia 19 Brodsky JB, Lemmens HJ. Tracheal width and left double-lumen tube size: a formula to estimate left-bronchial width. J Clin Anesth 2005; 17:267–270. A large DLT is usually preferred, particularly to minimize airway resistance in morbidly obese patients undergoing OLV. Direct airway measurement is the most accurate way of selecting a DLT. Tube selection based solely on patient gender, height and/or weight is less accurate than airway measurements and may lead to selection of a DLT that is too small for the patient. 20 Slinger PD, Lesiuk L. Flow resistances of disposable double-lumen, singlelumen, and Univent tubes. J Cardiothorac Vasc Anesth 1998; 12:142–144. 21 Aono J, Ueda K, Ueda W, Manabe M. Induction of anaesthesia in the lateral decubitus position in morbidly obese patients. Br J Anaesth 1999; 83:356. 22 Brodsky JB, Wyner J, Ehrenwerth J, et al. One-lung anesthesia in morbidly obese patients. Anesthesiology 1982; 57:132–134. 23 Henzler D, Rossaint R, Kuhlen R. Is there a need for a recruiting strategy in morbidly obese patients undergoing laparoscopic surgery? Anesth Analg 2004; 98:268. 24 Senturk NM, Dilek A, Camci E, et al. Effects of positive end-expiratory pressure on ventilatory and oxygenation parameters during pressurecontrolled one-lung ventilation. J Cardiothorac Vasc Anesth 2005; 19:71–75. 25 Michelet P, Roch A, Brousse D, et al. Effects of PEEP on oxygenation and respiratory mechanics during one-lung ventilation. Br J Anesth 2005; 95:267–273. 26 Brodsky JB, Lemmens HJ, Saidman LJ. Obesity, surgery, and inhalation anesthetics – is there a ‘‘drug of choice’’? Obes Surg 2006; 16:734. Despite claims to the contrary, none of the commonly used inhalation anesthetic agents (isoflurane, desflurane, sevoflurane) can be considered as the drug of choice for morbidly obese surgical patients. 27 Arain SR, Barth CD, Shankar H, Ebert TJ. Choice of volatile anesthetic for the morbidly obese patient: sevoflurane or desflurane. J Clin Anesth 2005; 17:413–419. This study demonstrated that in the immediate postoperative period there are no differences in emergence and recovery profiles in morbidly obese patients receiving desflurane and sevoflurane when anesthetic concentration was carefully titrated.
28 Davies RG, Myles PS, Graham JM. A comparison of the analgesic efficacy and side-effects of paravertebral vs epidural blockade for thoracotomy – a systematic review and meta-analysis of randomized trials. Br J Anaesth 2006; 96:418–426. Following thoracotomy, paravertebral block and epidural analgesia can provide comparable pain relief. In this study paravertebral blocks were associated with fewer side effects and with a reduction in pulmonary complications. 29 Wahlander S, Frumento RJ, Wagener G, et al. A prospective, double-blind, randomized, placebo-controlled study of dexmedetomidine as an adjunct to epidural analgesia after thoracic surgery. J Cardiothorac Vasc Anesth 2005; 19:630–635. Following thoracotomy, dexmedetomidine is a potentially effective analgesic adjunct to epidural local anesthesia since it reduces opioid requirements, thus reducing their potential for respiratory depression. Although this would be greatly advantageous for morbidly obese patients, published experience with dexmedetomidine and obesity is currently limited to anecdotal case reports. 30 Hofer RE, Sprung J, Sarr MG, Wedel DJ. Anesthesia for a patient with morbid obesity using dexmedetomidine without narcotics. Can J Anaesth 2005; 52:176–180. A case report supporting the potential benefit of dexmedetomidine in the management of postoperative pain in extremely obese patients. 31 Wigfield CH, Lindsey JD, Munoz A, et al. Is extreme obesity a risk factor for cardiac surgery? An analysis of patients with a BMI 40. Eur J Cardiothorac Surg 2006; 9:34–40. 32 Flier S, Knape JT. How to inform a morbidly obese patient on the specific risk to develop postoperative pulmonary complications using evidence-based methodology. Eur J Anaesthesiol 2006; 23:154–159. 33 Bong CL, Samuel M, Ng JM, Ip-Yam C. Effects of preemptive epidural analgesia on postthoracotomy pain. J Cardiothorac Vasc Anesth 2005; 19:786–793. Preemptive thoracic epidural anesthesia reduced the severity of acute pain but had no effect on the incidence of chronic pain after thoracotomy.
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