|
July 1998
Update From the 13th Annual Meeting of the Society of Ambulatory Anesthesia
Conference Coverage by Dr. Beverly Philip
The 13th Annual Meeting of the Society of Ambulatory Anesthesia was held in Scottsdale, Arizona on April 23-26, 1998. The general sessions of the meeting began with a Point-Counterpoint program, in which presenters compared and contrasted new or controversial issues. Other didactic sessions covered the topics of Fast-Tracking in Ambulatory Surgery, Office Based Anesthesia, New Innovations, Medical Malpractice Issues and Clinical Updates. There was also a panel discussion entitled "Challenging Cases from the Real World." In addition, there were four poster presentation sessions, and research awards were given for outstanding resident and anesthesiologist research poster submissions. The meeting was preceded by a workshop on Airway Management Techniques. Additional workshops were given on Computers in Anesthesia, Procedures Outside the Operating Room, Administrative and Quality of Care Management, Operating Room Management, and Regional Anesthetic Techniques. The Meeting's Point-Counterpoint lectures are reviewed below.
Dr. Martin Bogetz compared the laryngeal mask airway (LMA) and the cuffed oropharyngeal airway (COPA). The LMA has several advantages over the face mask, primarily in that it frees the hands and permits remote use. It also may be useful in managing patients with difficult airways. The LMA has advantages over an endotracheal tube as well, including less potential for airway trauma, avoidance of muscle relaxants, less hemodynamic effect and less increase in intraocular pressure when inserted, and reduced incidence of laryngospasm, sore throat or voice changes. Short comings of the LMA include that it does not protect the airway of a patient at increased risked for regurgitation or aspiration, it functions best with spontaneous rather than controlled ventilation, it may not be effective when respiratory mechanics are abnormal, and it is ineffective for glottic and subglottic obstruction. Furthermore, the acquisition cost of the reusable LMA is high, approximately $220 per unit; and care is required to avoid loss, theft or accidental discard.
The COPA is a modified Guedel-type oral airway with an inflatable cuff mounted at the distal end, and is intended for single use. Advantages are similar to those of the LMA when compared to both the face mask and the endotracheal tube. The dose of anesthetic needed to insert and maintain the COPA may be less than that for the LMA. Proper size selection seems to be the most crucial factor in successful use of the device. To select the correct size, the distal tip can be placed at the angle of the mandible and the transition between the proximal colored and clear portions of the airway should be at the teeth. Head and neck position is also important with this device. A jaw thrust or increased head tilt may be necessary to achieve a patient airway.
A Point-Counterpoint lecture on Fentanyl vs Remifentanil was presented by Phillip Scuderi, MD. He began with a discussion of the pharmacodynamic properties of fentanyl and remifentanil, and with a pharmacokinetic approach to opioid selection and use. One major difference between the two opioids is pharmacokinetic. Remifentanil has an extremely rapid onset of action after IV administration, and has a faster equilibration between plasma and effect site as well as a higher effect site concentration for a given dose of drug, compared to fentanyl. These differences account for the apparent differences in potency between these agents. Another major difference between the opioids is cost, with fentanyl being considerably less expensive. However, using remifentanil in situations where these pharmacokinetic advantages will provide clinical benefit can support the choice of that drug.
Beverly Philip, MD presented a Point-Counterpoint lecture on Desflurane vs Sevoflurane. A review of available studies shows that anesthesia maintenance with either of these two agents provides faster early recovery than isoflurane, and comparable (or faster) recovery than propofol. There has been one randomized double-blinded study comparing desflurane vs sevoflurane directly for procedures lasting approximately 40 minutes, which showed no differences in recovery times for the two agents. There are two major areas of difference between desflurane and sevoflurane. Sevoflurane undergoes metabolism and degradation to a much greater extent. The Compound A controversy continues to be debated in published articles, although injury in surgery patients has not been reported. The other major area of difference between desflurane and sevoflurane concerns the agents' tolerability. Desflurane is more irritating to the airway, and stimulates sympathetic nervous system discharge and resultant increases in blood pressure and heart rate. Again, however, the clinical implications of these findings are less certain, since these hemodynamic changes can be pharmacologically controlled. For both agents, the choice for clinical use depends on a balance of patient-specific advantages and disadvantages.
Dr. Dan Kopacz presented a comparison of bupivacaine vs ropivacaine. Ropivacaine differs chemically from bupivacaine in two ways. Ropivacaine is produced as the isolated S-isomer which has the potential for fewer cardiotoxic effects. Second, its chemical structure conveys a lower molecular weight and less lipid solubility. Multiple toxicity studies in animals show that at equal doses ropivacaine produces less cardiotoxicity than bupivacaine. In clinical studies, there were no differences in anesthesia duration when the two drugs were compared for brachial plexus anesthesia. When used for infiltration anesthesia, ropivacaine produced dermal anesthesia of longer duration than equivalent amounts of bupivacaine. However, the addition of epinephrine significantly increased the duration of the effects of both drugs. In situations where epinephrine is to be avoided, ropivacaine may be the preferable alternative. In a study comparing the drugs for infiltration anesthesia for inguinal herniorrhaphy, they were equivalent in efficacy and duration. Epidural studies suggest that both of these drugs produce sensory and motor anesthesia of sufficient duration to preclude their use in most outpatient procedures. The dosing and side effects of ropivacaine vs bupivacaine for spinal anesthesia have also not yet been adequately investigated.
A presentation on Ondansetron vs Dolasetron was given by John Lesley, MD. Dr. Lesley began with an overview of the size and scope of the postoperative nausea and vomiting (PONV) problem. PONV is well understood to have multiple causes, with numerous patient and surgical, as well as anesthetic, factors. Ondansetron and dolasetron are the two 5HT3 antagonists approved by the FDA for prevention or rescue of PONV. As a group, these drugs are effective. The emesis-free response rate for 4 mg ondansetron was 76%, vs 46% for placebo. Comparable response rates for 12.5 mg dolasetron were 50%, vs 31% for placebo. For both drugs, the timing of dose will affect efficacy; a lower dose is needed when given near the end of the surgical procedure. At this time it is not clear whether the recommended doses (ondansetron 4 mg and dolasetron 12.5 mg) are in fact equivalent in efficacy because of differences in the studies. Cost again is an issue with this entire class of drugs, and it is important to develop an antiemetic "strategy" based on the specific patient and procedure risk as well as cost.
Return to the Current Literature Review Front Page
|
