Bariatric Times - January 2009 - (Page 24)

24 Anesthesiology Perspective Bariatric Times • January 2009 Regional Anesthesia and Obesity by Pedro P. Tanaka, MD, PhD, and Jay B. Brodsky, MD Both from the Department of Anesthesia, Stanford University Medical Center, Stanford, California. INTRODUCTION One consequence of the worldwide obesity epidemic is that every day in operating rooms and ambulatory treatment centers, obese patients present for all types of surgical procedures. Many of the same concerns that the anesthesia team has when anesthetizing a morbidly obese patient for a bariatric procedure are valid for these other operations as well. The challenge of managing a patient with significant medical comorbidities and the potential for airway complications is always present. In addition, many morbidly obese patients have obstructive sleep apnea (OSA) and are extremely sensitive to the respiratory depressant effects of sedatives, opioids, and general anesthetics. DISCUSSION A successful regional anesthetic technique can offer distinct advantages over general anesthesia for an obese patient. As illustrated in Table 1, benefits include minimal airway intervention, a reduction or even complete avoidance of cardiopulmonary depressant agents, and the possibility of improved postoperative analgesia. If complications from over-sedation are reduced, post-anesthesia care unit (PACU) and overall hospital stays should also be decreased. Unfortunately there have been very few studies describing regional anesthesia in obese patients, and even fewer reports for extremely obese patients. We do not know the actual risks and benefits of regional anesthesia for these patients. What are the safe and effective doses of local anesthetics in obesity and are they similar or different from those needed for normal weight patients? There are additional considerations that are unique to the obese patient as seen in Table 2. These include the technical challenge of identifying the appropriate nerve, or the epidural or intrathecal space in a patient whose anatomic landmarks may be obscured. Special equipment, such as longer needles, may be required. Obese patients can be difficult to move and position for a regional block, and an inadequate block may necessitate establishing an airway and performing general anesthesia in less than ideal conditions. The most extensive experience with regional anesthetic techniques in obesity is with neuraxial (spinal and epidural) anesthesia. The majority of information we have on neuraxial anesthesia and obesity comes from obstetrics, so any relevance to the obese non-obstetric population must be inferred.1-2 Obese patients require less epidural local anesthetic than normal weight patients to achieve a similar level of anesthetic block. Following administration of 20ml of 0.75% bupivacaine in the L3-L4 interspace, there was a direct correlation between cephalad spread of analgesia and body mass index (BMI).3 Obese parturients (BMI>30kg/m2) in labor have significantly reduced epidural analgesic requirements, and have higher sensory blocks with a similar dose of local anesthetic than normal weight patients.4 Thus, it would seem prudent to administer local anesthetics in smaller volumes or in divided doses until an appropriate sensory block is achieved for any obese patient undergoing epidural anesthesia. Not surprisingly, location of the epidural space is often technically more difficult in large patients. In one study of obstetrical patients, 74 percent of those weighing greater than 300 pounds (136.4kg) needed more than one attempt to place an epidural, and 14 percent required more than three attempts.5 In another study, the initial epidural catheter “failed” in 42 percent of morbidly obese parturients, but in only six percent of control patients. Misidentification of appropriate landmarks and anatomic distortion were implicated for the high initial anesthetic failure rate in the obese group.6 Similar results have been reported by others.7 Increasing weight is significantly correlated with the depth of placement of an epidural at all epidural sites (lumbar, lower, and upper thoracic) and with all approaches (midline, paramedian).8 After the epidural catheter is inserted, usually with the patient in the sitting position, and after the catheter is securely fixed to the skin, catheter position can change and actually be withdrawn from epidural space during repositioning to the lateral decubitus or supine positions. The magnitude of catheter movement is greatest with obese patients. Multi-orificed epidural catheters should be inserted a minimum of 4cm into the epidural space in obese patients since unrecognized catheter migration with position change can result in loss of anesthetic agent and an inadequate block.9 A high level of overall satisfaction in the obese group clearly demonstrated that REGIONAL ANESTHESIA TECHNIQUES WERE WELL ACCEPTED among patients with increased BMI.

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Bariatric Times - January 2009

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