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Anesth Analg 2005;100:697-700 © 2005 International Anesthesia Research Society doi: 10.1213/01.ANE.0000146514.65070.AE
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Abstract |
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Patients given a more soluble inhaled anesthetic usually take longer to awaken from anesthesia than do patients given a less soluble anesthetic. In the present study, we tested whether such a delay in awakening was also associated with a delay in restoration of protective airway reflexes. Patients were randomly assigned to receive desflurane (n = 31) or sevoflurane (n = 33) via a laryngeal mask airway. Demographics did not differ between groups. The average minimum alveolar anesthetic concentration fraction for both groups was 0.62, and the mean (±sd) minimum alveolar anesthetic concentration hours was 1.00 ± 0.68 for desflurane versus 0.95 ± 0.57 for sevoflurane, although more patients given sevoflurane also received regional anesthesia (17 for sevoflurane and 8 for desflurane). The time from stopping anesthetic administration to appropriate response to command was longer after sevoflurane (5.5 ± 3.1 versus 3.4 ± 1.9 min; P < 0.01). In addition, the time from first response to command to ability to swallow 20 mL of water without coughing or drooling was longer after sevoflurane. At 2 min after responding to command, all patients given desflurane were able to swallow without coughing or drooling, whereas 55% of patients given sevoflurane coughed and/or drooled (P < 0.001). At 6 min after responding to command, 18% of patients given sevoflurane still could not swallow without coughing or drooling (P < 0.05). We conclude that desflurane allows an earlier return of protective airway reflexes.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Numerous studies demonstrate more rapid awakening after desflurane versus sevoflurane anesthesia, as determined by the time to eye opening, regaining of orientation, and ability to follow commands (1–5). We hypothesized: 1) that it would take longer for patients to restore their protective airway reflexes than for recovery of responsiveness to commands, and 2) that recovery of airway reflexes would be more rapid with desflurane than with sevoflurane. In support of this hypothesis, De Baerdermaeker et al. (5) found that obese patients who received desflurane recovered the ability to breathe in an unobstructed manner without the help of airway devices or external maneuvers more rapidly than those who had received sevoflurane.
We tested this hypothesis in the present study, using the patient’s ability to swallow 20 mL of water without coughing or drooling to indicate recovery of protective airway reflexes. We performed our tests at predetermined time intervals after the first appropriate response to command, independent of the time required to awaken and follow commands after anesthesia. In addition, we took the opportunity to make comparative measurements of clinically useful variables such as the rapidity of awakening.
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Methods |
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The study was approved by our IRB. ASA physical status I–II male (n = 23) and female (n = 41) patients aged 18–70 yr scheduled to have general anesthesia for surgical procedures were given a written description of the study at their visit to the presurgical clinic. Inclusion criteria included selection by the attending anesthesiologist of general anesthesia via a laryngeal mask airway. We excluded any patient with difficulty in swallowing, neuromuscular disease, or diabetes. We also excluded patients who would receive a supraclavicular or interscalene brachial plexus block.
Informed consent was obtained from each patient on the day of surgery. Before anesthesia, each patient was given 20 mL of water to swallow approximately 30 min before induction of anesthesia; all could swallow this volume without coughing or drooling. The attending anesthesiologist determined premedication (midazolam), propofol, and fentanyl doses for induction of anesthesia. Once the laryngeal mask airway was positioned and spontaneous ventilation resumed, desflurane or sevoflurane (assigned randomly) 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 0.3–1.0 minimum alveolar anesthetic concentration (MAC), as revealed by end-tidal measurements of respired gases. MAC values were assumed to be 6% desflurane and 1.85% sevoflurane (6). Additional propofol (boluses) and/or opioid (usually fentanyl) were prescribed as determined by the attending anesthesiologist. Although the usual opioid used was fentanyl, one patient received morphine (desflurane group) and one received meperidine (sevoflurane group). We assumed that 10 mg of morphine and 75 mg of meperidine were equivalent to 100 µg of fentanyl (7). Some patients (n = 25) also received regional blockade (10 lumbar plexus, 4 fascia iliaca, 4 femoral/sciatic, 5 axillary, and 2 ankle blocks). All patients received 12.5 mg of dolasetron and 4 mg of dexamethasone after induction of anesthesia.
A blinded observer recorded the patient’s vital statistics (age/weight/height), significant diseases, smoking history, and duration of anesthesia. The observer was blinded to the drug the patient received (the vaporizers were covered by a towel and were visible only by the attending anesthesiologist). The blinded observer determined the time to first appropriate response to command, asking the patient to "open his/her eyes" every 30 s after discontinuation of anesthetic administration. Exactly 2 min after the patient responded appropriately to command, he or she was asked to swallow 20 mL of water. Successful swallowing was defined as ingestion of the 20 mL without coughing or drooling. If swallowing was successful, this ended the patient’s participation in the study. If it was unsuccessful, the patient was asked to swallow at 6, 14, 22, and 30 min, with termination of participation after successful swallowing.
For ordinal data, unpaired two-tailed Student’s t-tests were applied, and significance was accepted at P < 0.05 without correcting for multiple comparisons. 
2 analysis was applied as indicated.
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Results |
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A total of 64 patients were enrolled in the study: 31 patients received desflurane and 33 patients received sevoflurane. All completed the study.
The demographics, including the types of surgery, did not differ between the groups, except that fewer patients in the desflurane group received regional block, and more patients in the sevoflurane group underwent orthopedic surgery (Table 1).
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After discontinuation of anesthetic administration, patients given desflurane responded to command in 3.4 ± 1.9 (mean ± sd) min, whereas those given sevoflurane took significantly longer (5.3 ± 3.1 min, P < 0.01). All 31 patients given desflurane drank the 20 mL of water without coughing or drooling 2 min after responding to command; 16 of 33 patients given sevoflurane were able to swallow the 20 mL of water without coughing or drooling (Fig. 1; P < 0.001). The patient given morphine and the patient given meperidine both successfully swallowed at 2 min. At 6 min, 27 of 33 patients given sevoflurane were able to swallow without coughing or drooling (P < 0.05). One patient given sevoflurane repeatedly failed the test of swallowing (out to 30 min; not significant).
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Sevoflurane anesthesia was associated with a longer, and more variable, time from discontinuation of anesthetic administration to an ability to swallow 20 mL of water without coughing or drooling (Fig. 2) than was desflurane (9.2 [7.0, 12.2] min [median, quartiles] versus 4.9 [4.0, 6.4] min; P < 0.01).
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The use of regional anesthesia did not affect the time between discontinuation of anesthetic administration and the time until patients could respond to commands. For patients receiving desflurane plus a regional anesthetic (n = 8), the time to respond to commands was 3.2 ± 1.9 versus 3.4 ± 1.9 min in those not given regional anesthesia (n = 23). Patients in the sevoflurane group with a regional anesthetic (n = 17) required 6.2 ± 3.7 min to respond to commands versus 4.7 ± 2.6 min for those without a regional block (n = 16). A regional anesthetic also did not delay the return of airway reflexes. Among the patients in the sevoflurane group, 7 of 17 (41%) receiving regional anesthesia swallowed successfully 2 min after following commands whereas 8 of 16 (50%) who did not receive regional anesthesia successfully swallowed at 2 min (P = 0.73); by 6 min, 13 of 17 (76%) receiving regional anesthesia swallowed successfully whereas 14 of 16 (88%) without regional anesthesia swallowed successfully (P = 0.66).
Finally, the weight of the patient did not correlate with time to respond to command or the time to recovery of protective airway reflexes (Figs. 3 and 4).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The results of the present study confirm our hypothesis: desflurane anesthesia allowed both a more rapid awakening than sevoflurane and a more rapid return of protective airway reflexes. Our results thus demonstrate that return of consciousness is not necessarily accompanied by restoration of protective airway reflexes, and that the choice of anesthetic can influence the time to restoration of such reflexes.
Why might desflurane allow a more rapid return of protective reflexes? The lower solubility of desflurane in blood and tissues (8–10), and the consequent kinetics supplies one explanation. It is also possible that a pharmacodynamic explanation would apply—that desflurane is inherently less depressant to protective airway reflexes, but this speculation is unproven.
Our results are consistent with the work of Sundman et al. (11) who demonstrated that pharyngeal dysfunction could occur at 25% of MACawake for sevoflurane or isoflurane (and, presumably, desflurane). That is, the cerebral partial pressure of inhaled anesthetics must decrease to <8% of MAC to restore protective airway reflexes. Such a decrease requires a longer period of time with more soluble anesthetics.
Although the observer was blinded to the identity of the anesthetic delivered, we cannot exclude the possibility that the observer guessed whether the patient received desflurane or sevoflurane. Guessing the anesthetic identity on the basis of awakening might seem reasonable, but the "minutes to follow command" were 3.35 ± 1.92 for desflurane and 5.49 ± 3.13 for sevoflurane. That is, some patients took longer to awaken after desflurane anesthesia than the average patient given sevoflurane, and some patients awoke after sevoflurane anesthesia more rapidly than the average patient given desflurane. Yet all patients could swallow without aspiration two minutes after desflurane, but less than half the patients given sevoflurane could swallow without aspiration. Further to this point, we evaluated the time to respond to command after sevoflurane anesthesia for those who aspirated at two minutes and those who did not. The times did not differ between groups (328 ± 169 [n = 15] versus 334 ± 215 seconds [n = 18]), again indirectly suggesting that the observer remained blinded/objective.
The results have clinical implications. Patients at risk of pulmonary aspiration need to be guarded more closely after awakening, particularly when a more soluble anesthetic is used. Perhaps patients given more soluble anesthetics should be turned to the lateral position for transport. The need to closely guard the patient is notable because the time at which such extra care is needed is the time often used to transport the patient from the operating room to the postanesthesia care unit, a time when monitoring equipment and suction may not be available and the anesthesiologist may be distracted by tasks related to transportation.
The authors appreciate the several suggestions made by Dr. Edmond I Eger II, MD, who is a paid consultant to Baxter Healthcare Corp.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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- Larsen B, Seitz A, Larsen R. Recovery of cognitive function after remifentanil-propofol anesthesia: a comparison with desflurane and sevoflurane anesthesia. Anesth Analg 2000;90:168–74.
[Abstract/Free Full Text] - Eshima RW, Maurer A, King T, et al. Comparison of airway responses during desflurane and sevoflurane administration via a laryngeal mask airway (LMA) for maintenance of anesthesia. Anesth Analg 2003;96:701–5.
[Abstract/Free Full Text] - Chen X, Zhao M, White PF, et al. The recovery of cognitive function after general anesthesia in elderly patients: a comparison of desflurane and sevoflurane. Anesth Analg 2001;93:1489–94.
[Abstract/Free Full Text] - Mahmoud NA, Rose DJA, Laurence AS. Desflurane or sevoflurane for gynaecological day-case anaesthesia with spontaneous respiration? Anaesthesia 2001;56:171–82.[Web of Science][Medline]
- De Baerdemaeker LEC, Struys MMRF, Jacobs S, et al. Optimization of desflurane administration in morbidly obese patients: a comparison with sevoflurane using an ‘inhalation bolus’ technique. Br J Anaesth 2003;91:638–50.
[Abstract/Free Full Text] - Eger EI II. Age, minimum alveolar anesthetic concentration, and minimum alveolar anesthetic concentration-awake. Anesth Analg 2001;93:947–53.
[Abstract/Free Full Text] - Drugs for pain. Med Lett Drugs Ther 2000;42:73–8.[Web of Science][Medline]
- Eger EI II. Partition coefficients of I-653 in human blood, saline, and olive oil. Anesth Analg 1987;66:971–3.
[Abstract/Free Full Text] - Lockwood GG, Sapsed-Byrne SM, Smith MA. Effect of temperature on the solubility of desflurane, sevoflurane, enflurane and halothane in blood. Br J Anaesth 1997;79:517–20.
[Abstract/Free Full Text] - Zhou J-X, Liu J. The effect of temperature on solubility of volatile anesthetics in human tissues. Anesth Analg 2001;93:234–8.
[Abstract/Free Full Text] - Sundman E, Witt H, Sandin R, et al. Pharyngeal function and airway protection during subhypnotic concentrations of propofol, isoflurane, and sevoflurane: volunteers examined by pharyngeal videoradiography and simultaneous manometry. Anesthesiology 2001;95:1125–32.[Web of Science][Medline]
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