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*Department of Anesthesia and Perioperative Care, University of California, San Francisco; and
Department of Anesthesiology, Texas Tech University Health Science Center, Lubbock
Address correspondence and reprint requests to Rachel Eshima, MD, University of California, San Francisco, Department of Anesthesia and Perioperative Care, 521 Parnassus Ave., Room C-450, Box 0648, San Francisco, CA 94143-0468. Address e-mail to eshimar{at}anesthesia.ucsf.edu
| Abstract |
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IMPLICATIONS: Although sevoflurane is less pungent than desflurane at larger concentrations, neither anesthetic seems to irritate the airway when administered at the smaller concentrations often used during maintenance of anesthesia. Both anesthetics may be delivered effectively via a laryngeal mask airway, with minimal evidence of airway irritation.
| Introduction |
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Mahmoud et al. (6) found no significant difference in respiratory responses between desflurane and sevoflurane given through a LMA. However, anesthesia duration equaled 18 min (1031 min) (mean [range]) after the induction of anesthesia with propofol, and therefore, this may have been a limited test of any differences between desflurane and sevoflurane. In studies that compared desflurane with another anesthetic (not sevoflurane) (7,8) or sevoflurane with another anesthetic (not desflurane) (9), all delivered through a LMA, no differences in the incidence of measures of airway irritation (e.g., coughing) were found between anesthetics or studies. We hypothesized that the absence of a difference resulted from the use of all anesthetics at the smaller concentrations often used in clinical practice. We tested this hypothesis in the present study. In addition, we took the opportunity to make comparative measurements of clinically useful variables such as the rapidity and quality of awakening.
| Methods |
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After obtaining informed consent from each patient on the day of surgery, a standard anesthetic consisting of the following was delivered: The attending anesthesiologist decided whether to premedicate each patient with midazolam or nothing. Anesthesia was induced with propofol at a dose defined by the attending anesthesiologista dose sufficient to allow insertion of a LMA. The attending anesthesiologist also could add fentanyl to the induction regimen. Once the LMA was positioned and spontaneous ventilation resumed, desflurane or sevoflurane (assigned randomly using a computer-generated scheme) was administered in a target background of approximately 50% nitrous oxide at a maintenance total gas flow of 1 L/min. Desflurane and sevoflurane concentrations to be used were at the discretion of the attending anesthesiologist, usually between 0.3 and 1.0 MAC, as revealed by end-tidal measurements of respired gases. MAC values were assumed to equal 6% desflurane and 1.85% sevoflurane (10). Additional propofol (boluses) and/or an opioid were prescribed as the attending anesthesiologist saw fit. Although the usual opioid used was fentanyl, occasional patients received morphine, Dilaudid, meperidine, or ketorolac. We assume that 10 mg of morphine, 1.5 mg of Dilaudid, 75 mg of meperidine, and 30 mg of ketorolac each were equivalent to 100 µg of fentanyl (11,12).
A blinded observer recorded the patients vital statistics (age, weight, and height), significant diseases, smoking history, duration of anesthesia, the anesthetic concentrations and drug doses delivered, and the incidence of respiratory events (specifically coughing, breath holding, and laryngospasm). Events were graded for severity. Coughing was defined as 0 if no coughing occurred, 1 if a single cough occurred and SpO2
95%, 2 if multiple coughs occurred and SpO2
95%, 3 if multiple coughs occurred and SpO2 <95%, and 4 if multiple coughs occurred, SpO2 <95%, and if coughing required an administration of IV medication. Breath holding was defined as 0 if no breath holding occurred, 1 if no breath holding occurred for 1020 s, 2 if no breath holding occurred for 2030 s, and 3 if breath holding exceeded 30 s. Laryngospasm was defined as 0 if no evidence of phonation or stridor was present, 1 if phonation or stridor appeared for <15 s and no therapy other than positive-pressure ventilation was required, 2 if phonation or stridor occurred for >15 s and no therapy was required other than positive-pressure ventilation, and 3 if phonation or stridor occurred for >15 s and IV mediation was required. SpO2 was measured as the smallest value observed during each 15-min epoch. The average, median, and largest vapor and nitrous oxide concentrations were measured. All variables were evaluated for each 15-min epoch during anesthesia and recorded for each epoch.
A blinded observer made the observations for the first hour after discontinuation of the anesthetic administration. The observer determined the time from discontinuation of the anesthetic administration to first appropriate response to command and to orientation to time and place. Digit symbol substitution tests were performed at 15-min intervals after discontinuation of the anesthetic administration, and the results were compared with those obtained before anesthesia. A modified Aldrete score was obtained at 15-min intervals after discontinuing the anesthetic administration (13). For each postanesthetic 15-min epoch, we recorded the incidence of nausea, vomiting, or both. In addition, postoperative nausea and vomiting (PONV) were graded 03, where 0 equaled no nausea or vomiting, 1 = mild nausea without vomiting or medical intervention, 2 = nausea without vomiting but with administration of antiemetic therapy, and 3 = vomiting. Finally, time to be fit for discharge (as defined by the ability to sit up and to ambulate with assistance) was recorded.
For ordinal data, unpaired two-tailed Students t-test were applied, and significance was accepted at P < 0.05 without correcting for multiple comparisons.
2 analysis was applied as indicated.
| Results |
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Patients at UCSF and Texas Tech did not differ except that patients at UCSF were older and had longer anesthetic durations. Similarly, the demographics, including the types of surgery, for patients given desflurane did not differ from those for patients given sevoflurane (Table 1). Coughing, breath holding, laryngospasm, and SpO2 did not differ between anesthetics (Table 2). The largest sevoflurane MAC value applied (1.06) significantly (P < 0.01) exceeded that for desflurane (0.88); the sevoflurane average MAC value (0.85) did not significantly exceed the MAC value for desflurane (0.75), and the nitrous oxide values did not differ between groups. Twenty-seven percent of patients received desflurane concentrations exceeding 6%. The incidence of coughing or breath holding in these patients did not differ from the incidence in patients not given concentrations exceeding 6%. Forty-eight percent of patients received sevoflurane concentrations exceeding 1.85%. The incidence of coughing or breath holding did not differ from the incidence in patients not given concentrations exceeding 1.85%. Smoking did not significantly increase the incidence of coughing, breath holding, or laryngospasm.
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| Discussion |
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The conditions used in this study may have influenced the finding of no difference between desflurane and sevoflurane. Anesthesia was induced with propofol and fentanyl, and the placement of the LMA proceeded in this context. Both inhaled anesthetics were delivered after insertion of the LMA, and the initial concentrations applied were less than MAC. Other studies have demonstrated that concentrations of desflurane <6% do not elicit untoward respiratory responses such as coughing or laryngospasm (14). However, as noted above, several patients received concentrations exceeding MAC for desflurane (6%) and did not have an increased incidence of coughing or breath holding.
Administration of fentanyl provided another factor that may have abolished a difference between the responses to desflurane versus sevoflurane. Administration of 1 µg/kg of fentanyl as premedication decreases the incidence of coughing on the induction of anesthesia with desflurane by 80% (15).
Smoking did not significantly increase the incidence of coughing, breath holding, or laryngospasm. However, the number of smokers in our sample was too small to provide a robust test of whether smoking would affect these variables.
As anticipated from their respective solubilities, early recovery was quicker with desflurane than sevoflurane. However, this difference also might have resulted from the slightly larger (MAC) concentration of sevoflurane used for anesthesia (Table 1). Late recovery did not differ between the two anesthetics.
The finding of increased use of postanesthesia care unit (rescue) antiemetics to treat PONV with sevoflurane than with desflurane was not expected. Most studies find no difference in PONV, and our result may be spurious. However, with one exception, it does not seem to be explained by increased administration of drugs that predispose to nausea (e.g., fentanyl or nitrous oxide; see Table 1), nor is it explained by a smaller administration of antiemetic drugs (including propofol) to patients given sevoflurane. The exception that might explain the more frequent incidence with sevoflurane is the trend to use a larger concentration of sevoflurane for anesthesia (Table 1).
Deficiencies in study design may limit interpretation of our results. As noted above, we did not impose a rigid dose scheme regarding the drugs or doses used (e.g., concentrations of the inhaled anesthetics, doses of opioids, and the choice of opioids), and bias of the anesthesiologists may have altered some of the results. This might explain, for example, the finding of increased use of postanesthesia care unit antiemetics to treat PONV with sevoflurane than with desflurane. The anesthesiologist was not blinded to the anesthetics and drugs delivered (although the person recording the data was blinded).
In summary, we find that the respiratory complications that arise during maintenance delivery of anesthesia through a LMA are minor, their incidence is small, and the incidence does not differ for desflurane versus sevoflurane. Initial recovery may be more rapid with desflurane, but time to be fit for discharge does not differ. Nausea may be slightly increased after anesthesia with sevoflurane, but this result may be because of a slightly larger MAC of sevoflurane used to maintain anesthesia rather than any inherent difference between the two anesthetics.
| Acknowledgments |
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The authors appreciate the several suggestions made by Dr Edmond I Eger II, MD, who is a paid consultant to Baxter Healthcare Corp.
| References |
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