Comparison of intubating conditions following propofol and succinylcholine with propofol and remifentanil 2 µg kg–1 or 4 µg kg–1

I. A. McNeil, B. Culbert and I. Russell

Department of Anaesthesia, Hull Royal Infirmary, Anlaby Road, Hull HU3 2JZ, UK

Accepted for publication: May 18, 2000


    Abstract
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
We evaluated the intubating conditions, haemodynamic responses and duration of apnoea in 60 healthy adult patients after propofol 2 mg kg–1 combined with either a bolus of remifentanil 2 µg kg–1 or 4 µg kg–1, or succinylcholine 1 mg kg–1. Patients intubated following remifentanil showed dose-dependent intubating conditions, similar at 4 µg kg–1 to the conditions produced with succinylcholine. Post-induction mean arterial pressure decreased from baseline values by 21% (P<0.0001), 28% (P<0.0001) and 8% (P>0.05) in the remifentanil 2 µg kg–1, remifentanil 4 µg kg–1 and succinylcholine 1 mg kg–1 groups, respectively. The mean (SD) duration of apnoea following induction was 9.3 (2.6) min and 12.8 (2.9) min in the remifentanil 2 µg kg–1 and 4 µg kg–1 groups, and 6.0 (0.9) min in the succinylcholine group (P<0.001 between groups).

Br J Anaesth 2000; 85: 623--5

Keywords: analgesics opioid, remifentanil; anaesthetics i.v., propofol; neuromuscular block, succinylcholine; intubation tracheal


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Neuromuscular blocking drugs, particularly succinylcholine, may cause serious side effects but remain in clinical use to facilitate tracheal intubation due to a lack of suitable alternatives.1 A combination of propofol and alfentanil has been demonstrated to reliably facilitate intubation without the use of neuromuscular blocking agents.2 3 Remifentanil is a new potent fentanyl derivative with a unique metabolic profile and plasma clearance considerably faster than alfentanil.4 These properties make remifentanil the opioid of choice to facilitate tracheal intubation, and subsequently allow a rapid return of spontaneous respiration and airway reflexes. In this study, we have compared the intubating conditions, haemodynamic changes and duration of apnoea in healthy adults following induction of anaesthesia with propofol in combination with either succinylcholine or varying doses of remifentanil.


    Methods and results
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
With Ethics Committee approval and written informed consent, 60 ASA 1 and 2 non-obese, elective surgical patients, aged between 18 and 65 yr who required intubation for their proposed surgery were studied. Those on obstetric, neurosurgical or ophthalmic lists, those with Mallampati scores greater than 2 or with gastro-oesophageal reflux were excluded. Patients were randomized into three groups by opening unmarked envelopes indicating the induction regime as follows: PS=propofol 2 mg kg–1 and succinylcholine 1 mg kg–1; PR 2=propofol 2 mg kg–1 and remifentanil 2 µg kg–1; and PR 4=propofol 2 mg kg–1 and remifentanil 4 µg kg–1. No patients were prescribed sedative premedication.

Intravenous access was established, but no fluids were given. Mean arterial pressure (MAP), heart rate (HR), oxygen saturation and end-tidal carbon dioxide (FE'CO2) were monitored during induction using the Datex Cardiocap. Patients were not preoxygenated, but received oxygen from the end of a Bain system held 5–10 cm caudal to the chin. In group PS, propofol 2 mg kg–1 was given over 60 s followed immediately by succinylcholine 1 mg kg–1. In groups PR 2 and PR 4, propofol 2 mg kg–1 was followed immediately by remifentanil 2 or 4 µg kg–1, with each drug administered over 30 s. After induction, mask ventilation was initiated with 2% sevoflurane in 50% nitrous oxide in oxygen at a total flow of 8 litres min–1 and continued in group PS until fasciculation had ceased, and for 30 s in both remifentanil groups. At this point an experienced, blinded anaesthetist took over airway control and attempted tracheal intubation of the patient. During laryngoscopy, each patient was assessed for five variables: jaw mobility; mask ventilation; vocal cord visibility; vocal cord position; and patient movement during intubation. The criteria used for ranking these variables are shown in Table 1.


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Table 1 Intubating conditions scoring system
 
Following intubation, patients were hand ventilated with a Bain breathing system at five breaths per minute. If FE'CO2 levels reached 8 kPa in any patient, ventilation was increased to prevent any further rise. Duration of apnoea was recorded in patients as the period from the beginning of the propofol injection until the first recognizable breath. If spontaneous respiration had not resumed within 15 min (so as not to delay operating time), this time was recorded as the duration of apnoea.

Data were analysed using one-way analysis of variance with Tukey’s multiple comparisons (age, weight, duration of apnoea and MAP changes between groups), the paired t-test (MAP and HR changes within groups) and the Kruskal–Wallis test with Dunn’s multiple comparisons (intubation scores). A value of P<0.05 was considered statistically significant.

We studied 17 patients in group PS, 20 in group PR 4 and 23 in group PR 2. One patient in group PR 4 was an unexpected difficult intubation and was withdrawn from the study. Patients in all three groups were similar in age and weight. Mean (SD, range) patient age in groups PS, PR 4 and PR 2 were 44 (15, 18–65) yr, 40 (13, 18–61) yr and 39 (11, 18–62) yr, respectively. Mean patient weight in groups PS, PR 4 and PR 2 were 75 (10, 49–92) kg, 71 (12, 50–94) kg and 76 (15, 55–100) kg, respectively. All subjects in the study were successfully intubated except for two, both in group PR2. In one of these patients vocal cord relaxation was insufficient to allow passage of a tracheal tube, and purposeful movement continued following induction in another. Subsequently, both patients were intubated following the administration of atracurium 0.5 mg kg–1. Scores in the three groups, for each of the five intubation characteristics graded in the study are shown in Fig. 1.



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Fig 1 Percentage of patients in groups and the scores attained for each of five intubation characteristics. Groups: PS=propofol 2 mg kg–1 and succinylcholine 1 mg kg–1; PR4=propofol 2 mg kg–1 and remifentanil 4 µg kg–1; and PR2=propofol 2 mg kg–1 and remifentanil 2 µg kg–1. Intubation characteristics: JM, jaw mobility; MV, mask ventilation; CV, vocal cord visibility; CP, vocal cord position; PM, patient movement.

 
While there were no differences between groups for the intubation characteristic scores of jaw mobility (P>0.05), ease of mask ventilation (P>0.05) or vocal cord visibility (P>0.05), significant differences were found between groups for the characteristics of vocal cord position (P<0.05) and movement during intubation (P<0.001). Although multiple comparisons demonstrated no significant differences between pairs of groups for vocal cord position (P>0.05), movement during intubation was found to be significantly more likely in group PR 2 than in either of the other groups (P<0.05). Mask ventilation was described as ‘difficult’ in one patient in group PR 2 and ‘impossible’ in one patient in group PR 4, but neither subject experienced oxygen desaturation, and both were successfully intubated.

Baseline preinduction values of MAP and HR were similar in all three groups (P>0.05). Postinduction MAP values decreased from baseline in groups PR 2, PR 4 and PS by 21% (P<0.0001), 28% (P<0.0001) and 8% (P>0.05), respectively. While the difference in post-induction MAP values between groups PR2 and PR4 was not significant (P>0.05), post-induction MAP values were significantly lower in both remifentanil groups compared with group PS (P<0.001). Values of post-induction HR decreased from baseline in groups PR 2 and PR 4 by 14% (P<0.01) and 19% (P<0.001), and increased in group PS by 15% (P<0.01). One patient in group PR 4, whose heart rate fell to 35 beats min–1, was treated with glycopyrrolate 500 µg. The mean (SD) times, recorded from the beginning of the propofol injection until the first recognizable breath, were 6.0 (0.9) min in group PS, 9.3 (2.6) min in group PR 2 and 12.8 (2.9) min in group PR 4 (P<0.001 between all groups).


    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Our study has demonstrated that in healthy adults, with normal airway anatomy, a combination of propofol 2 mg kg–1 and remifentanil 2 or 4 µg kg–1 produces dose-dependent intubating conditions which at the higher remifentanil dose are similar to those produced with succinylcholine 1 mg kg–1. Unfortunately, using a sufficiently high dose of remifentanil to consistently ensure optimum intubating conditions is not without problem. We found significant, dose-related cardiovascular depression associated with the use of a large dose of remifentanil. These levels of hypotension were well tolerated by the subjects in our study, but how they might be tolerated in those less healthy is unproven. High doses of potent opioids are also well recognized to cause muscle rigidity, and in this respect remifentanil is no exception.5 In our study, two patients receiving remifentanil were difficult to hand ventilate, and this difficulty may well have been due to opioid-induced rigidity.

For an opioid to replace succinylcholine in a rapid sequence induction it should provide optimum intubating conditions, and also allow a rapid return of spontaneous respiration and airway reflexes. Although we demonstrated that patients intubated following remifentanil 4 µg kg–1 and succinylcholine 1 mg kg–1 had similar intubating conditions, the mean duration of apnoea was more than twice as long in the remifentanil group (12.8 vs 6.0 min in the succinylcholine group). The period of apnoea, following a sufficient dose of remifentanil to ensure optimum intubating conditions, would be unacceptable in rapid sequence induction should intubation fail. Although the opioid antagonist, naloxone, could be administered in these circumstances, the degree to which it might lessen apnoea is as yet undetermined.

Our study indicates a role for remifentanil and propofol as an effective method of tracheal intubation. We hope our described technique will be considered an alternative to the use of neuromuscular blocking drugs for procedures requiring tracheal intubation but not muscle relaxation during surgery, and in situations where the use of neuromuscular blocking agents is contraindicated.


    References
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Robinson AL, Jerwood DC, Stokes MA. Routine suxamethonium in children. A regional survey of current usage. Anaesthesia 1996; 51: 874–8[ISI][Medline]

2 Scheller MS, Zornow MH, Saidman LJ. Tracheal intubation without the use of muscle relaxants: a technique using propofol and varying doses of alfentanil. Anesth Analg 1992; 75: 788–93[Abstract]

3 Beck GN, Masterson GR, Richards J, Bunting P. Comparison of intubation following propofol and alfentanil with intubation following thiopentone and suxamethonium. Anaesthesia 1993; 48: 876–80[Abstract/Free Full Text]

4 Kapila A, Glass PSA, Jacobs JR, et al. Measured context sensitive half times of remifentanil and alfentanil. Anesthesiology 1995; 83: 968–75[ISI][Medline]

5 Jhaveri R, Joshi P, Batenhorst R, Baughman V, Glass PS. Dose comparison of remifentanil and alfentanil for loss of consciousness. Anesthesiology 1997; 87: 253–9[ISI][Medline]