Anesth Analg 2001;93:359-362
© 2001 International Anesthesia Research Society
ANESTHETIC PHARMACOLOGY
The Use of Remifentanil to Facilitate the Insertion of the Laryngeal Mask Airway
Monica P. L. Lee, FANZCA,
Jeffrey S. W. Kua, FANZCA, FHKAM, and
Wallace K. Y. Chiu, FRCA, FHKAM, FANZCA
Department of Anaesthesia and Intensive Care, Pamela Youde Nethersole Eastern Hospital, Hong Kong Special Administrative Region, China
Address correspondence to Dr. Monica P. L. Lee, Department of Anaesthesia and Intensive Care, Pamela Youde Nethersole Eastern Hospital, 3 Lok Man Road, Hong Kong Special Administrative Region, China. Reprints will not be available.
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Abstract
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Propofol is often used as an IV induction drug for anesthesia and the insertion of a laryngeal mask airway (LMA). As a sole anesthetic, it may be associated with undesirable airway responses such as coughing and gagging. We conducted a randomized, double-blinded study to compare the conditions during insertion of the LMA in 120 patients who received normal saline (Group P), remifentanil 0.25 µg/kg (Group R1), or remifentanil 0.5 µg/kg (Group R2) before the induction of anesthesia with IV propofol. The addition of remifentanil significantly improved the conditions of insertion; in Group R1, 82.5% (33 of 40 patients), and in Group R2, 85.0% (34 of 40 patients) had excellent insertion conditions as compared with the Control group P, 32.5% (13 of 40 patients). Patients in Group P were apneic for a mean (SD) time of 85 (38) s, 186 (75) s in group R1, and 284 (130) s in group R2. There was a lesser decrease in mean arterial blood pressure in group R1. We conclude that remifentanil 0.25 µg/kg, when administered after IV propofol 2.5 mg/kg, provides excellent conditions for insertion of the LMA with minimal hemodynamic disturbances.
IMPLICATIONS: Small-dose remifentanil can provide excellent conditions for laryngeal mask airway insertion with minimal hemodynamic disturbances.
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Introduction
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Propofol is a commonly used anesthetic for the induction of anesthesia and insertion of a laryngeal mask airway (LMA). When used alone, propofol may be associated with undesirable airway responses such as coughing and gagging. The addition of a short-acting and potent opioid (e.g., alfentanil) facilitates LMA insertion after the induction of anesthesia with propofol (1). Remifentanil is a new, ultra-short acting, selective µ-receptor agonist that is 20–30 times more potent than alfentanil. Its ester linkage renders it susceptible to hydrolysis by blood and tissue nonspecific esterases with a short terminal half-life of <10 min at the site of action. Hence, the resumption of spontaneous respiration after remifentanil may be faster, making this opioid more suitable for providing ideal LMA insertion conditions when administered with propofol.
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Methods
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We conducted a double-blinded randomized study to investigate LMA insertion conditions and hemodynamic effects after the induction of anesthesia with propofol supplemented with different doses of remifentanil.
One-hundred-twenty ASA class I and II unpremedicated patients, aged 21 to 65 yr, undergoing operations during which general anesthesia with an LMA is appropriate, were recruited. Patients with a history of gastric reflux, history of allergy to any of the study drugs, or suspected difficult airway or who were taking antiepileptic medication were excluded from the study.
Approval was obtained from our local clinical research ethics committee. Informed consent was obtained from participating patients. From a resealable envelope containing coded and identically folded slips of paper (120 pieces, preshuffled), patients were randomly allocated to one of the following three groups. Group R1 received remifentanil 0.25 µg/kg followed immediately by propofol 2.5 mg/kg. Group R2 received remifentanil 0.5 µg/kg followed immediately by propofol 2.5 mg/kg, and Group P received 5 mL of 0.9% normal saline followed immediately by propofol 2.5 mg/kg. The remifentanil in Groups R1 and R2 was diluted with 0.9% normal saline to 5 mL. Each induction dose of propofol was given over 10 s and was mixed with 1 mL of 2% lidocaine to reduce the pain on injection.
An experienced anesthesiologist [who had successfully inserted the LMA in more than 200 patients with the technique described by Brain (2)] inserted the LMA in all the patients in the study 1 min after the administration of propofol. This anesthesiologist was also blinded to the induction drugs used. After successful LMA insertion, anesthesia was maintained with end-tidal 0.5% isoflurane and 70% nitrous oxide in oxygen. The position of the LMA was checked by observing chest movement and capnography. Apneic patients were manually ventilated to maintain a pulse oximetry reading of >95% and an end-tidal carbon dioxide level of 35 to 40 mm Hg. Bradycardia, <50 bpm, was treated with IV atropine 0.3 to 0.6 mg. If there were airway reflexes preventing LMA insertion, inability to ventilate after insertion of the LMA, or limb and head movement requiring restraint in the patient, another dose of propofol 0.5 mg/kg bolus was given, followed by another attempt at LMA insertion 30 s later. This cycle was repeated until the LMA was successfully inserted.
An investigator blinded to the patient group collected the following data:
- Demographic data: age, body weight, sex, and ASA status.
- Noninvasive blood pressure, heart rate, and pulse oximetry were recorded before and every 1 min for 3 min after LMA insertion.
- Any episode of bradycardia requiring atropine.
- Ease of insertion of LMA graded by the following three-point scale: Grade 1, excellent, no response to LMA insertion; Grade 2, acceptable, gagging or swallowing with insertion of LMA; Grade 3, poor, unable to open mouth or biting upon insertion of LMA.
- Duration of apnea (the time from induction until the first spontaneous breath).
- Airway quality at the first attempt of LMA insertion was graded as either good (easy ventilation) or poor (partial or complete obstruction).
- The number of attempts at LMA insertion.
To detect a difference in the proportion of patients with excellent insertion in the Remifentanil group (90%) compared with the Control group (60%) and allowing for 10% dropouts, 40 patients in each group were required to achieve 80% power with an 
error of 5%. StatView software (SAS, Cary, NC) was used in the statistical analysis. Nonparametric data were analyzed by using the 
2 test, and parametric data were analyzed by using analysis of variance.
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Results
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The demographic data were comparable among the three groups in terms of age, weight, and gender ratio (Table 1). A larger number of patients in Groups R1 and R2 had excellent insertion conditions (Fig. 1) as compared with patients in Group P (33 and 34 vs 13 of 40, P < 0.0001). There was however, no difference between Groups R1 and R2. There were two patients in each group in whom we failed to insert the LMA at the first attempt. There was no difference in the number of attempts among the three groups (Table 2).
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Figure 1. Percentage with excellent insertion condition (95% confidence interval). Group P = normal saline; Group R1 = remifentanil 0.25 µg/kg; Group R2 = remifentanil 0.5 µg/kg.
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Additional propofol was required for successful insertion of the LMA in 35% of patients in Group P, but in only 15% and 7.5% in Groups R1 and R2, respectively (Fig. 2). The difference among them was statistically significant (P < 0.005).
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Figure 2. Percentage requiring additional propofol (95% confidence interval). Group P = normal saline; Group R1 = remifentanil 0.25 µg/kg; Group R2 = remifentanil 0.5 µg/kg.
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The resumption of spontaneous respiration from induction was significantly different among the three groups (F2,117 = 49.19, P < 0.0001) (Fig. 3). The apnea time was defined as the time from the end of propofol injection to the resumption of a spontaneous breath. The values are reported as mean (SD). The mean duration of apnea in Group P was 85 (38) s, which was significantly shorter when compared with 186 (75) s and 284 (130) s in Groups R1 and R2, respectively. Also, the duration of apnea in Group R2 was significantly longer than in Group R1. The level of significance was set at P < 0.05. These were confirmed by the post hoc test (Table 3). The airway quality was similar among the three study groups (Table 4).
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Figure 3. Box plot of apnea time (s). P < 0.0001. Group P = normal saline; Group R1 = remifentanil 0.25 µg/kg; Group R2 = remifentanil 0.5 µg/kg.
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Baseline hemodynamics did not differ among the three groups. Repeated-measures analyses of variance were performed (Fig. 4). All three groups demonstrated a decrease in the mean arterial blood pressure (12% in Group P, 19% in Group R1, and 25% in Group R2), which was still within clinically acceptable limits. The post hoc Bonferroni test showed a statistically significant difference between the Propofol group and the Remifentanil group, but not within Groups R1 and R2. None of the patients studied required atropine as a rescue therapy for bradycardia (heart rate <50 bpm). Repeated-measures analyses of variance showed that there was a significant variation in heart rate after induction among the three groups (Fig. 5). There was an increase in heart rate in Group P, whereas the heart rate decreased in Groups R1 and R2. The post hoc Bonferroni test showed that the differences occurred between the Remifentanil and Control groups. Again, these were all clinically insignificant. None of the patients experienced a significant decrease in SpO2 during the study.
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Figure 4. Changes in mean blood pressure (mean ± SD). LMA = laryngeal mask airway; Group P = normal saline; Group R1 = remifentanil 0.25 µg/kg; Group R2 = remifentanil 0.5 µg/kg.
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Figure 5. Changes in heart rate (mean ± SD). LMA = laryngeal mask airway; Group P = normal saline; Group R1 = remifentanil 0.25 µg/kg; Group R2 = remifentanil 0.5 µg/kg.
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Discussion
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We have demonstrated that remifentanil 0.25 or 0.5 µg/kg before propofol 2.5 mg/kg reliably provided excellent conditions for insertion of an LMA (82.5% and 85% in Groups R1 and R2, respectively, as compared with 32.5% in Group P). The decreased success rate in our Group P as compared with another study (3) was probably because our patients were not premedicated. Our success rate in the Remifentanil group is slightly less frequent than in other studies of a similar nature advocating the use of muscle relaxants to facilitate the insertion of LMA (4,5). Patient groups were comparable, but the timing and sequence of drug administration and LMA insertion differ in view of the difference in onset of action of the studied drug. With suxamethonium, myalgia was a concern, and masseter spasm can certainly prevent the successful insertion of an LMA. Although prolonged apnea is a concern with nondepolarizing muscle relaxants, there was no clinically significant problem when small-dose mivacurium was used to facilitate the insertion of an LMA (5). Nonetheless, the duration of apnea may be much longer in patients with hereditary plasma cholinesterase deficiency, and hence suxamethonium and mivacurium should be avoided in these individuals. These drugs are also contraindicated in patients with neuromuscular disorders.
Remifentanil (3 to 5 µg/kg) has been used together with propofol, with considerable success, to facilitate tracheal intubation without muscle relaxants (6,7). Thus, it is not surprising that the combination would also improve the ease of insertion of LMA when compared with propofol alone. The more frequent success rate of the combination of the two drugs is probably because of the apneic, analgesic, and antitussive effects of the opioid.
Because of rapid metabolism, remifentanil should not prolong the duration of apnea as compared with equipotent doses of other opioids, such as fentanyl or alfentanil. This is an important consideration in spontaneously breathing patients to avoid hypoventilation and the development of hypercarbia. In one study (1), the average apnea time for equipotent doses of alfentanil 5 µg/kg and 10 µg/kg were reported as 282.6 and 439.2 s, respectively.
Remifentanil attenuates the hemodynamic response to tracheal intubation (8). However, bradycardia (<50 bpm)—which is a potential complication associated with the use of remifentanil (>1 µg/kg)—was not reported. In our study, both doses of remifentanil prevented the increase in heart rate related to the insertion of the LMA that was present in the Control group. LMA insertion is less stimulating when compared with tracheal intubation, but clinically significant bradycardia did not occur in our study. This may be because we were using a smaller dose of remifentanil and our patients were all ASA I or II. The decrease in the mean arterial pressure relative to baseline was not unexpected in patients maintained under volatile-based anesthesia without surgical stimulation. This was more prominent in Group R2 (25%). The decrease, however, was transient, and there were no adverse consequences in healthy patients.
Our results show that the addition of remifentanil during the propofol induction of anesthesia significantly improves the conditions for LMA insertion. We recommend remifentanil 0.25 µg/kg, because it is associated with a shorter duration of apnea and fewer hemodynamic disturbances.
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References
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Ang S, Cheong KF, Ng TI. Alfentanil co-induction for laryngeal mask insertion. Anaesth Intensive Care 1999; 27: 175–8.[Web of Science][Medline]
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Brain AIJ. The laryngeal mask instruction manual. Henley, UK: Intravent, 1995.
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Alexander R, Booth J, Olufolabi AJ, et al. Comparison of remifentanil with alfentanil or suxamethonium following propofol anaesthesia for tracheal intubation. Anaesthesia 1999; 54: 1032–6.[Web of Science][Medline]
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Thompson JP, Hall AP, Russell J, Cagney B. Effect of remifentanil on the haemodynamic response to orotracheal intubation. Br J Anaesth 1997; 80: 467–9.
Accepted for publication April 10, 2001.
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Abstract
Introduction
