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,§,||
Department of Anesthesia and General Intensive Care (
*A) and (
B), and
Outcomes ResearchTM, University of Vienna;
§Apotheus Laboratories, Ltd., Lubbock, Texas;
||Department of Anesthesia, University of California-San Francisco, San Francisco, California; and
||Ludwig Boltzmann Institute for Clinical Anesthesia and Intensive Care, Vienna, Austria
Address correspondence to Dr. Ozan Akça, Department of Anesthesia and General Intensive Care (A), University of Vienna, Währinger-Gürtel 18–20, A-1090 Vienna, Austria. Address e-mail to 73674.63{at}CompuServe.com
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Abstract |
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Implications: Anesthetic induction techniques influence awakening time, recovery duration, and drug costs. We tested two IV methods and two inhaled techniques. However, none of the four tested methods was clearly superior to the others.
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Introduction |
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Sevoflurane and desflurane share a short duration of action. Desflurane, however, is pungent, and rapid concentration increases provoke autonomic nervous system hyperactivity and hemodynamic instability (1). In contrast, sevoflurane is suitable for inhaled inductions and is used extensively for this purpose in pediatric patients (2). A limitation of sevoflurane is that the drug is relatively expensive. This expense can be reduced somewhat during maintenance anesthesia by reducing the fresh gas flow to 2 L/min, which is currently the lowest recommended rate in the United States and several other countries. During induction, however, flows near 10 L/min are required to rapidly fill the circle system and to compensate for absorption of the anesthetic into the patient’s lungs and circulation. The result is that an inhaled induction with sevoflurane can contribute substantially to the total cost of anesthetic drugs, especially during short procedures.
The cost and time required for an inhaled induction with sevoflurane can potentially be reduced by avoiding the circle system with its large (approximately 7 L) intrinsic volume. As an alternative, we considered a 5-L bag prefilled with sevoflurane 7% in nitrous oxide 60%. This bag was connected to a valve inserted between the circle system and the face mask. Depressing the spring-loaded valve disconnected the circle system so that the patient was directly connected to the bag. Anesthesia then resulted from breathing and rebreathing from this bag (Fig. 1). We tested two conventional induction techniques (thiopental and propofol), an inhaled induction with sevoflurane using a circle system, and the rebreathing method described above. Our purpose was to evaluate the effects of induction technique on induction time, recovery characteristics, and drug cost.
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Methods |
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Patients who were seriously obese, claimed allergy to any of the study drugs, were pregnant or nursing, or used opioids or sedatives were excluded. We also excluded patients who refused either IV or inhaled induction and those at risk of regurgitation.
None of the patients was premedicated. Each was preoxygenated for 1 min with 100% oxygen, and then given 1 µg/kg IV fentanyl. One of the following randomly assigned anesthetic induction techniques (n = 20 each) was then started at elapsed time zero:
Lung ventilation was initially spontaneous in each case, then assisted at a rate of approximately 10 breaths/min when apnea prevailed. The specified induction method was continued until eyelid reflexes were lost, and an additional minute. A lubricated laryngeal mask was then inserted using standard technique (the cuff was slightly inflated to facilitate insertion). Additional propofol or thiopental was given if required clinically in the patients assigned to IV induction. Fresh gas flow was discontinued during laryngeal mask insertion.
Anesthesia was subsequently maintained with sevoflurane (1.2%–1.4% end-tidal concentration) in nitrous oxide 60%, using a 6-L/min fresh gas flow via a circle circuit. Patients breathed spontaneously, their breathing was assisted as necessary to maintain a PETCO2 near 35 mm Hg. Minimal peak airway pressures were used, consistent with maintaining physiological PETCO2 concentrations with a respiratory rate of 10 breaths/min. Additional fentanyl (50 µg IV) was given when it was clinically indicated.
Sevoflurane and nitrous oxide concentrations were not reduced toward the end of surgery; instead, both were abruptly discontinued when the operation was complete. After spontaneous breathing resumed and airway reflexes were reestablished, the laryngeal mask was removed. Patients were observed until they responded to command and were then transferred to the postanesthesia care unit. Postoperatively, patients were given IV boluses of the opioid piritramid as necessary for treatment of pain. Postoperative nausea and vomiting was treated by the IV administration of ondansetron (4–8 mg). Antiemetic treatment was determined by the patient’s reported sensation of nausea or when emesis or retching was observed. The treating anesthesiologists, who were blinded to group assignment and intraoperative management, based their treatments on direct patient observation and their 5-min queries (see below).
Standard morphometric and demographic characteristics of the participating patients were recorded, along with their ASA physical status and Mallampati airway scores.
During induction, we recorded the number of breath-holding episodes (
15 s). The time required for the eyelid reflex to disappear was recorded at 15-s intervals. Saturation from a pulse oximeter and concentrations of sevoflurane, oxygen, and carbon dioxide in the rebreathing bag were determined at 30-s intervals by using a Hewlett Packard M1026A gas monitor (Hewlett Packard, Boeblingen, Germany). The number of attempts at laryngeal mask insertion was recorded, along with the time elapsed since the beginning of induction. Induction time thus included the time to loss of lid reflex, 1 min additional ventilation per protocol, and the time required for laryngeal mask insertion per se.
Movement in response to laryngeal mask insertion was qualitatively graded as none, little, or major. During the maintenance phase of anesthesia, we recorded saturation from a pulse oximeter, hemodynamic responses, vaporizer setting, and end-tidal sevoflurane and carbon dioxide concentrations at 1-min intervals. Return of consciousness was determined by asking patients to open their eyes at 30-s intervals. The time elapsed between discontinuation of anesthesia and eye opening was defined as the awakening time.
Postoperative pain was evaluated at 5-min intervals using a conventional 100-mm visual analog scale (0 = no pain; 100 = most severe pain). Pain scores >50 were treated with 3 mg of IV piritramid. Fitness for discharge was evaluated using a modification (5) of the Aldrete and Kroulik (6) scoring system (Table 1). The time elapsed between discontinuation of anesthesia and a recovery score of 13 was considered the recovery duration. All postoperative measurements were performed by an investigator blinded to group assignment and anesthetic induction details.
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Sevoflurane use (in milliliters of liquid) was calculated by integrating the vaporizer settings and fresh gas flows over the duration of the study. Only the administered drug volumes were used in the analysis; that is, any amount wasted in unused syringes was not considered. Nitrous oxide was not included in the analysis because it is inexpensive and the total amount used was similar in each group.
Normally distributed data were compared by using one-way analysis of variance and Scheffé’s F-tests. Nominal data were compared by using 
2. Results are presented as means ± SD. P < 0.05 was considered statistically significant.
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Results |
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The cost of induction drugs was lowest with the Sevo/Bag technique and thiopental, intermediate with Sevo/Circle, and highest with propofol. The cost of maintenance sevoflurane was comparable in the four groups. When the cost of postoperative ondansetron was added to induction and maintenance drug costs, the Sevo/Circle method proved significantly more expensive than thiopental. Costs were intermediate and similar with Sevo/Bag and propofol (Table 3).
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Discussion |
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Induction of anesthesia was rapid and facile with each of the four tested methods, and there were no clinically important or statistically significant differences among them. This is consistent with a previous study, which indicated that laryngeal mask insertion characteristics were comparable with thiopental (4 mg/kg), propofol (2 mg/kg), and 6% sevoflurane (8). Postoperative awakening, however, was fastest in patients given sevoflurane. Prolonged awakening with thiopental was expected based on the drug’s pharmacokinetics (9). However, it was surprising that awakening after propofol induction required nearly the same amount of time (10,11). Our data indicate that induction times are comparable with each tested method but that awakening after sevoflurane is faster. Recovery duration was significantly longer in patients given thiopental than in those given sevoflurane, which again is consistent with the drugs’ pharmacokinetics.
As expected, the cost of induction drugs differed significantly among the tested methods, with sevoflurane from the rebreathing bag and thiopental being the least expensive and propofol being the most expensive. However, we did not anticipate the high incidence of nausea and vomiting after sevoflurane administration and the consequent need for antiemetic therapy. Because ondansetron is so expensive, total drug cost was actually greater with sevoflurane than propofol. Thiopental, which was associated with little nausea and vomiting, was the least expensive method overall.
We studied patients undergoing extremely brief operations to maximize the effects of induction technique on induction speed, awakening time, recovery duration, and cost. The four techniques we studied were associated with statistically significant differences in some of these factors, and some of the differences were also clinically important. Nonetheless, no one technique was obviously superior; each had advantages and disadvantages. Our data thus suggest that the anesthetic induction technique for individual patients may best be chosen based on the relative importance of awakening time, recovery duration, cost, and the avoidance of nausea and vomiting.
The major limitation of our protocol is that recovery characteristics depend strongly on the type and duration of surgery. Our operations were all short; induction technique will have progressively less influence on postanesthetic recovery as the duration of surgery increases. Our thiopental and propofol results are specific for the doses we used, which were typical and have been used in numerous previous studies. However, we can assume that larger thiopental and propofol doses would produce faster and smoother inductions but slower recoveries.
An important limitation of our cost calculations is that total costs would differ substantially had we used a less expensive and equally effective (12) antiemetic such as droperidol. Because droperidol is so inexpensive, total cost would then roughly equal the sum of induction and maintenance costs. Our estimates were based on average United States wholesale pharmacy costs; costs in individual hospitals and in other countries may vary, and the variation in some cases may be substantial. Actual costs in a given hospital can be calculated by applying the appropriate ratios of actual cost to estimated cost to Table 3. Drug expenses are a relatively small fraction of the costs associated with anesthetic administration and an even smaller fraction of total surgical cost. Nonetheless, it is reasonable to use inexpensive drugs when there seems to be little benefit from more expensive ones. We also did not include the cost of the 5-L rebreathing bag in our calculation; using a disposable bag would add a small cost to the Sevo/Bag method.
In summary, induction times were similar with each of the four techniques. Recovery duration was shortest with sevoflurane, intermediate with propofol, and longest with thiopental. Induction drug costs were lowest with Sevo/Bag and thiopental, intermediate with Sevo/Circle, and highest with propofol. However, sevoflurane by either method caused the most nausea and vomiting that required treatment with ondansetron. Consequently, total drug cost was least with thiopental, intermediate with Sevo/Bag and propofol, and greatest with Sevo/Circle. No single technique was obviously superior, which suggests that the anesthetic induction technique for individual patients may best be chosen based on the relative importance of recovery duration, cost, and avoidance of nausea and vomiting.
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Acknowledgments |
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The authors gratefully acknowledge the support and generous assistance of the gynecological anesthesia and surgical nurses in Operation Group 8C.
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Footnotes |
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References |
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This article has been cited by other articles:
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  M. C. Lewis, R. I. Gerenstein, and G. Chidiac Onset time for sevoflurane/nitrous oxide induction in adults is prolonged with increasing age. Anesth. Analg., June 1, 2006; 102(6): 1699 - 1702. [Abstract] [Full Text] [PDF]
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A. A. van den Berg, D. A. Chitty, R. D. Jones, M. S. Sohel, and A. Shahen Intravenous or Inhaled Induction of Anesthesia in Adults? An Audit of Preoperative Patient Preferences Anesth. Analg., May 1, 2005; 100(5): 1422 - 1424. [Abstract] [Full Text] [PDF]
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 H. Yang, P. T.-L. Choi, J. McChesney, and N. Buckley Induction with sevoflurane-remifentanil is comparable to propofol-fentanyl-rocuronium in PONV after laparoscopic surgery: [L'induction avec sevoflurane-remifentanil ou propofol-fentanyl rocuronium est similaire quant aux NVPO en chirurgie laparoscopique] Can J Anesth, August 1, 2004; 51(7): 660 - 667. [Abstract] [Full Text] [PDF]
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H. S. Joo and W. J. Perks Sevoflurane Versus Propofol for Anesthetic Induction: A Meta-Analysis Anesth. Analg., July 1, 2000; 91(1): 213 - 219. [Abstract] [Full Text] [PDF]
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K. H. Hoerauf, T. Wallner, O. Akca, R. Taslimi, and D. I. Sessler Exposure to Sevoflurane and Nitrous Oxide During Four Different Methods of Anesthetic Induction Anesth. Analg., April 1, 1999; 88(4): 925 - 925. [Abstract] [Full Text] [PDF]
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