Propofol is considered the drug of choice for the insertion of the laryngeal mask airway (LMA) during induction of anesthesia because of its depressant effect on airway reflexes (1). However, propofol has been associated with several adverse effects, including hypotension, apnea, pain on injection (2), and excitatory patient movement (3). Sevoflurane is a nonpungent inhaled anesthetic with a low blood gas solubility coefficient (0.69) (4) and minimal respiratory irritant characteristics that make it suitable for inhaled induction of anesthesia and insertion of the LMA (5). Furthermore, sevoflurane, as compared with propofol, has the advantage of providing better hemodynamic stability (6,7) and a smoother transition to the maintenance phase without a period of apnea (7,8). However, sevoflurane is associated with delayed jaw relaxation and a longer time for the insertion of the LMA (8–11).
Our hypothesis is that induction of anesthesia with the combination of sevoflurane and small-dose propofol may optimize the insertion conditions of the LMA and decrease the side effects that may follow either sevoflurane or propofol alone. In a prospective randomized study, we assessed the incidence of successful insertion of LMA at the first attempt in adult patients undergoing elective surgery when anesthesia was induced by the combination of sevoflurane and propofol as compared with either sevoflurane or propofol alone. Also, we compared the incidence of side effects such as coughing, gagging, and laryngospasm and the incidence and duration of apnea after LMA insertion.
Institutional ethical approval and written informed consent were obtained from all patients. Ninety-three adult ASA physical status I–II patients aged 18–65 yr undergoing elective orthopedic, plastic, or gynecologic procedures were enrolled in the study. Day surgery cases and in-patients were included. Patients with a history of difficult intubation (or likely to be difficult to intubate), gastroesophageal reflux, allergy, or sensitivity to volatile anesthetics or to propofol, those with a body mass index more than 1.5 times normal, heavy smokers (≥20 cigarettes per day), and patients taking any sedative drugs that influence the induction anesthetic were excluded from the study. After an IV access with 18-gauge indwelling cannula was established, a slow infusion of lactated Ringer’s solution was started. The patients were randomized by computer-generated numbers to one of the following three groups for induction of anesthesia: Group S, sevoflurane induction, group SP, sevoflurane induction supplemented by IV propofol, or group P, propofol IV induction. Patients allocated to groups S and SP were taught the single vital capacity breath (VCB) technique. No patients were premedicated.
For patients in the group S, a circle CO2 absorber circuit with a 3-L reservoir bag was used. The circuit was primed with sevoflurane 8% in a 2:1 ratio of nitrous oxide to oxygen at a fresh gas flow of 6 L/min for 1 min. While breathing 100% oxygen from a separate breathing system, the patients were asked to take a deep breath and then exhale to residual volume. The mask with the primed circuit was then placed firmly over the patient’s face. The patients were instructed to inhale a VCB and hold it as long as possible. If necessary, a second breath was taken. The start of induction was taken as the point at which the patients completed their VCB. While holding their breath, the patients were asked to open their eyes every 10 s. Failure to do so was taken as loss of consciousness. This was confirmed by testing for the loss of eyelash reflex. Ninety seconds after completing the VCB to achieve equilibrium between the alveolar concentration of sevoflurane and the brain, the ease of mouth opening was assessed (possible or impossible). If mouth opening was impossible, another attempt was made every 30 s up to a maximum of 4 tries. Between attempts, anesthesia was maintained with sevoflurane at a dial concentration of 8% in a 2:1 ratio of nitrous oxide to oxygen at 6 L/min.
Patients in group SP had an inhaled induction with the single VCB technique similar to that used in group S. In addition, at the loss of eyelash reflex, the patients received propofol 1.5 mg/kg premixed with lidocaine (lidocaine 2% 1 mL is mixed with each 20 mL syringe of propofol) over 15 s. Time to loss of consciousness was determined as it had been for group S. Thirty seconds after the completion of propofol induction to allow for arm-brain circulation, (i.e., 45 s after the start of propofol injection), ease of mouth opening was assessed and, if possible, LMA insertion was attempted. If impossible, repeat attempts were made every 30 s up to a maximum of 4 attempts, each time preceded by propofol boluses of 0.5 mg/kg IV. Between attempts, anesthesia was maintained with sevoflurane at a dial concentration of 8% in a 2:1 ratio of nitrous oxide to oxygen at 6 L/min.
Patients in group P received induction with propofol 3 mg/kg IV premixed with lidocaine given over 30 s. Midway through induction (at 15 s), the patients were asked if they felt any pain from the injection. Loss of consciousness was assessed as for groups S and SP. Time to loss of consciousness was calculated from the time we started injection of propofol until loss of eyelash reflex and inability to open eyes upon verbal command. Thirty seconds after the completion of propofol induction, (i.e., 60 s after the start of propofol injection), ease of mouth opening was assessed and, if possible, LMA insertion was attempted. If impossible, attempts were repeated up to 4 tries, each attempt preceded by propofol bolus 0.5 mg/kg IV.
Whenever apnea occurred in any patient of the three groups, ventilation was assisted manually between LMA insertion attempts. Apnea was evidenced by absence of chest movement and end-tidal capnography. LMA insertions were performed by the same investigator using the technique recommended in the Intavent® LMA instruction manual (Berkshire, UK). Size 3 LMA was used in women and size 4 in men. Additional propofol was given if there was any adverse response, such as movement, gagging, coughing, or laryngospasm. Failure of insertion of the LMA after four tries was rescued with succinylcholine 25 mg IV. Noninvasive arterial blood pressure, oxygen saturation, and heart rate were recorded every min for 5 min.
An independent but nonblinded observer recorded the time to loss of eyelash reflex, to jaw relaxation, and to successful LMA insertion, and the number of insertion attempts. An attempt to open the mouth was considered an attempt at insertion and inability to open the mouth was considered a failure of insertion. The presence of complications related to anesthetic induction and insertion of the LMA was noted. Also, the incidence of apnea (when time to onset of spontaneous respiration after insertion of LMA >30 s) was noted, and its duration was evaluated by end-tidal capnography as the time from completion of LMA insertion until restoration of spontaneous respiration. Once the LMA was inserted, anesthesia was continued with sevoflurane 3% in 66% nitrous oxide in oxygen. Also, all patients were given fentanyl intraoperatively as required. At the end of the operation, the LMAs were removed with the patients still anesthetized. Once fully awake, the patients were interviewed by a blinded investigator who asked whether they found the induction of anesthesia pleasant and whether they had a sore throat.
Statistical analysis involved analysis of variance test for demographic data, Mann-Whitney U-test for nonparametric data and χ2 or Fisher’s exact test for categorical data. The 5% level of probability (P < 0.05) was taken as significant. Assuming a 35% difference in the proportion of patients with successful LMA placement at the first attempt as being clinically important, we calculated that 30 patients would be required in each group to achieve 80% power at the 5% significance level to detect a true difference among the groups. Data were presented as mean ± sd, medians and ranges, or numbers and percentages of patients.
Data from 83 patients were analyzed: 26 patients in group S, 31 patients in group SP, and 26 patients in group P. Two patients from group SP were excluded because they could not tolerate the gaseous induction and refused to have a face mask induction of anesthesia. Four patients from group S and 4 patients from group P were also excluded because of protocol violation (sedative drugs were given before induction). There were no differences among the groups with respect to age, weight, sex, or smoking habits (Table 1).
As shown in Table 2, patients in groups S and SP had a longer time to loss of eyelash reflex as compared with patients in group P (P = 0.03). Also, the time to successful insertion of LMA was longer in groups S and SP as compared with group P; however, it was shorter in group SP as compared with group S (P < 0.001). The percentage of patients who had successful LMA insertion at first attempt was larger in group SP as compared to groups S and P (P < 0.001). Fewer attempts at insertion of the LMA were required in group SP as compared to groups S and P (P < 0.05). If the two patients who could not tolerate the gaseous induction were included, then the successful insertion of LMA at the first attempt would be 88% in SP group.
All insertions of the LMA were successful in the three groups. However, more patients required additional propofol for successful insertion in group P as compared with group S and group SP (P < 0.01). Succinylcholine was never given. The duration of apnea was longer in group P as compared with groups S and SP (P < 0.001), and the incidence of apnea was more frequent in group P as compared with groups S and SP (P < 0.001) (Table 2). None of the patients suffered oxygen desaturation.
The overall incidence of complications related to induction of anesthesia, such as excitatory movement, cough, laryngospasm, and hiccup, was comparable among the 3 groups (Table 3). Eighteen patients (69%) in group P had pain on injection. During insertion of LMA, more patients had movements in group P (P < 0.05) (Table 3). The 3 groups exhibited a stable hemodynamic profile (Table 4). Our patients found the induction techniques pleasant and would have the same induction again. The incidence of postoperative nausea and vomiting (PONV) was more frequent in group S and SP as compared with group P. The difference was statistically significant between group P and group S (P < 0.05) (Table 5).
The present report shows that single VCB induction of anesthesia with sevoflurane 8% or IV propofol 3 mg/kg alone resulted in successful LMA insertion at the first attempt in 46% and 61.5% of patients, respectively. Our results are comparable to those achieved by Ti et al. (8), who compared LMA insertion after induction of anesthesia with either single VCB of sevoflurane 8% or IV propofol 3 mg/kg; they reported an incidence of successful initial mouth opening in 55.2% and 78.9% of patients in the sevoflurane and propofol groups, respectively. As shown by our report, the coinduction of anesthesia using sevoflurane 8% supplemented with propofol 1.5 mg/kg significantly increased the incidence of successful LMA insertion at the first attempt to 93.5%. Also, the time to optimum jaw relaxation and completion of successful LMA insertion was shortened in group SP as compared with group S. Another benefit from the supplementation of sevoflurane with a small dose of propofol was the absence of apnea in most of the patients as compared with group P.
In our patients, induction of anesthesia with sevoflurane alone was associated with a prolonged time to jaw relaxation and a delay in insertion of the LMA as compared with induction of anesthesia with propofol or with sevoflurane and propofol. Also, more attempts at insertion were required in group S. Several previous reports support our findings and show that anesthetic induction with sevoflurane results in a longer time to jaw relaxation and even jaw tightness that may result in delay or failure to insert the LMA (8–11).
Induction of anesthesia with propofol allows the fastest insertion of the LMA among the three induction modalities. Propofol has a relaxant effect on jaw muscles (12), whereas inhaled anesthetics may cause increased muscle tone (13); therefore for a similar depth of anesthesia, there may be more jaw relaxation with propofol (8). However, this advantage of propofol was offset in our patients by the frequent incidence of pain on injection (69%) despite the addition of lidocaine and the occurrence of movements during insertion of the LMA (50%). In Ti et al.’s study (8), frequent involuntary movement during LMA insertion occurred in the propofol group (52.9%), an incidence that is similar to that noted in our propofol group. Also, propofol induction was associated with frequent and more prolonged time of apnea. Apnea occurred in 84% of patients in group P as compared with 16% in group SP and 7% in group S. Similar to Molloy et al.’s results (9), we found that the need for additional propofol was increased in group P as compared with group S and group SP, which may have contributed to the increased duration and incidence of apnea in group P. Apnea requires intermittent positive pressure ventilation, which may result in gastric distension. However, a previous report has shown that the incidence of pulmonary aspiration of gastric contents was not different between patients whose lungs were ventilated with positive pressure and patients breathing spontaneously (14).
One limitation of our report is that the study was randomized but not blinded; therefore there is a possibility of observer bias. Also, the times at which LMA insertion was attempted are not defined the same way in all three groups. However, the significant and marked difference in the incidence of successful LMA insertion at the first attempt between group SP versus groups S or P and the more frequent and prolonged time of apnea in group P cannot be explained only by the observer bias or by the various time definitions.
In a meta-analysis comparing anesthetic induction between sevoflurane and propofol, Joo and Perks (15) found that sevoflurane induction was associated with a trend toward more frequent patient dissatisfaction and more frequent PONV. Smith and Thwaites (16) compared target-controlled infusion propofol with large initial concentration of sevoflurane reduced after LMA insertion. Inhaled anesthetic was associated with more PONV (30% versus 3%) with delayed discharge; however, patient satisfaction was high (≥90%) with both techniques. Our report shows that the three groups of patients demonstrated a similar degree of satisfaction with the anesthesia technique. However, two patients in the sevoflurane groups did not accept the VCB technique of induction and were excluded from analysis. Also, patients in groups S and SP had more frequent PONV than patients in group P. One explanation is that propofol has antiemetic properties (17). Another explanation may be that sevoflurane causes frequent PONV. The PONV may be a function of the initial large concentration of sevoflurane or it may be caused by air and gases swallowed into the stomach during anesthetic induction (15).
In conclusion, our results showed that induction of anesthesia using the combination of sevoflurane and propofol resulted in the most frequent successful LMA insertion at first attempt as compared with induction of anesthesia with either sevoflurane or propofol alone. Also, the sevoflurane-propofol combination was associated with a significant decrease in apnea as compared with the propofol group.
1. Mc Keating K, Bali IM, Dundee W. The effects of thiopentone and propofol on upper airway integrity. Anaesthesia 1988;43:638–40.
2. Sebel PS, Lowdon JD. Propofol: a new intravenous anesthetic. Anesthesiology 1989;71:260–77.
3. Ho KM, Chui PT. The use of mini-dose suxamethonium to facilitate the insertion of a laryngeal mask airway. Anaesthesia 1999;54:683–702.
4. Strum DP, Eger EI II. Partition coefficients for sevoflurane in human blood, saline, and olive oil. Anesth Analg 1987;66:654–6.
5. Ganatra SB, D’Mello J, Butani M, Jhamnani P. Conditions for insertion of the laryngeal mask airway: comparisons between sevoflurane and propofol using fentanyl as a co-induction agent. Eur J Anaesth 2002;19:371–5.
6. Yurino M, Kimura H. Induction of anesthesia with sevoflurane, nitrous oxide, and oxygen: a comparison of spontaneous ventilation and vital capacity rapid inhalation induction (VCRI) techniques. Anesth Analg 1993;76:598–601.
7. Thwaites A, Edmends S, Smith I. Inhalation induction with sevoflurane: a double-blind comparison with propofol. Br J Anaesth 1997;78:356–61.
8. Ti LK, Chow MYH, Lee TL. Comparison of sevoflurane with propofol for laryngeal mask airway insertion in adults. Anesth Analg 1999;88:908–12.
9. Molloy M, Buggy D, Scanlon P. Propofol or sevoflurane for laryngeal mask airway insertion. Can J Anaesth 1999;46:322–6.
10. Muzi M, Robinson BJ, Ebert TJ, O’Brien TJ. Induction of anesthesia and tracheal intubation with sevoflurane in adults. Anesthesiology 1996;85:536–43.
11. Hall JE, Stewart JIM, Harmer M. Single-breath inhalation induction of sevoflurane anesthesia with and without nitrous oxide: a feasibility study in adults and comparison with an intravenous bolus of propofol. Anesthesia 1997;52:410–5.
12. Ummenhofer WC, Kindler C, Tschaler G, et al. Propofol reduces succinylcholine induced increase of masseter muscle tone. Can J Anaesth 1998;45:417–23.
13. Rosenberg H, Clofine R, Bialik O. Neurologic changes during awakening from anesthesia. Anesthesiology 1981;54:123–30.
14. Keller C, Sparr HJ, Luger TJ, Brimacombe J. Patient outcomes with positive pressure versus spontaneous ventilation in non-paralyzed adults with the laryngeal mask. Can J Anaesth 1998;45:564–7.
15. Joo HS, Perks WJ. Sevoflurane versus propofol for anesthetic induction: Meta-analysis. Anesth Analg 2000;91:213–9.
16. Smith I, Thwaites AJ. Target-controlled propofol vs. sevoflurane: a double-blind, randomized comparison in day-case anaesthesia. Anaesthesia 1999;54:745–52.
17. Borggeat A, Stirnemann HR. Antimetic effect of propofol. Anaesthetist 1998;47:918–24.