1 Department of Anesthesiology, Advocate Illinois Masonic Medical Center, Chicago, IL, USA. 2 Department of Anesthesiology, University of Illinois College of Medicine, Chicago, IL, USA
* Corresponding author: Department of Anesthesiology, Advocate Illinois Masonic Medical Center, 836 W. Wellington Avenue, Chicago, IL 60657, USA. E-mail: mohammad.el-orbany-md{at}advocatehealth.com
Accepted for publication August 23, 2005.
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Abstract |
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Methods. One hundred and seventy-five ASA I and II adult patients scheduled to undergo surgical procedures requiring general anaesthesia and tracheal intubation were allocated to one of five groups according to i.v. anaesthetic induction drug used. General anaesthesia was induced by i.v. administration of lidocaine 30 mg and propofol 2.5 mg kg1 (Group 1), thiopental 5 mg kg1 (Group 2), lidocaine 30 mg and thiopental 5 mg kg1 (Group 3), etomidate 0.3 mg kg1 (Group 4), or lidocaine 30 mg and etomidate 0.3 mg kg1 (Group 5). After loss of consciousness, succinylcholine 0.6 mg kg1 was given i.v. followed by direct laryngoscopy and tracheal intubation after 60 s. Measurements included intubation conditions recorded during laryngoscopy 60 s after succinylcholine administration, and apnoea time.
Results. Overall, clinically acceptable intubation conditions were met in 168 out of the 175 patients studied (96%). They were met in 35/35 patients in Group 1, 33/35 patients in Group 2, 34/35 patients in Group 3, 33/35 patients in Group 4, and 33/35 patients in Group 5. Mean (SD) apnoea time was 4.0 (0.4), 4.2 (0.3), 4.2 (0.6), 4.1 (0.2) and 4.1 (0.2) min respectively in Groups 15. There were no differences in the intubation conditions or apnoea times between the groups.
Conclusions. The use of succinylcholine 0.6 mg kg1 produced the same favourable intubation conditions and a short apnoea time regardless of the induction drug used.
Keywords: intubation, endotracheal ; neuromuscular block, succinylcholine ; small-dose succinylcholine
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Introduction |
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The objective of this study was to examine whether the administration of different i.v. induction drugs can affect the 1-min intubation conditions and the apnoea time resulting when small-dose succinylcholine (0.6 mg kg1) is used to facilitate tracheal intubation.
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Methods |
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If tracheal intubation proved impossible, an additional dose of succinylcholine 0.5 mg kg1 could be given and the patient was ventilated by the face-mask for 1 min, after which tracheal intubation would be re-attempted. Patients requiring additional doses of succinylcholine were excluded from the study. In all patients, ventilation was gently and intermittently assisted as needed to keep the oxygen saturation above 96%.
Statistical analysis
Sample size estimation was based on previous studies that examined the influence of various i.v. anaesthetics on tracheal intubation conditions during laryngoscopy using rocuronium or succinylcholine.4 9 A power analysis revealed that approximately 35 patients in each group would be required to identify a statistically significant difference between the intubation conditions with 80% power and P=0.05 and correction for multiple (four) comparisons. One-way analysis of variance and the StudentNeumanKeuls (for continuous variables) and Kruskal-Wallis (for discrete variables) tests were used to identify statistically significant differences between the five groups. Statistical significance was accepted when P<0.05. Data are given as mean (SD).
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Results |
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Discussion |
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The addition or omission of a small dose of i.v. lidocaine to the i.v. induction drug that we used during induction did not result in any significant differences in intubation conditions. In contrast to our findings, however, lidocaine was found to improve intubation conditions when intubation was attempted 1 min after rocuronium 0.6 mg kg1.10 Others could not demonstrate such a salutary effect.11 The discrepancy between these different reports may be due to the difference in the dose of lidocaine given and the timing of its administration in relation to the time of tracheal intubation. We used a small dose of lidocaine (30 mg) immediately before i.v. drug injection only for the purpose of preventing injection pain during i.v. propofol administration. We chose this dose based on earlier recommendations.12 Since we preferred not to administer propofol without lidocaine, we evaluated the contribution of lidocaine to intubation conditions in patients induced with thiopental (Group 3) and etomidate (Group 5). Whether increasing the lidocaine dose or the timing of its administration could have resulted in different results was not investigated in our study.
Our results indicate that the tracheal intubation conditions 1 min after administering succinylcholine 0.6 mg kg1 were similar, regardless of the induction drug used. Fuchs-Buder and colleagues,7 in agreement with our results, did not find a significant difference between the intubation conditions produced when either thiopental or etomidate was used with rocuronium for rapid sequence induction. Similar findings were reported when either propofol or thiopental was used for induction with rocuronium.13 Although propofol was found to produce better jaw and pharyngeal muscle relaxation than thiopental in one study,14 the authors intentionally did not use any neuromuscular blocking drug during induction. In addition, since their objective was only to assess ease of laryngoscopy, no tracheal intubation was attempted in that study. When propofol was compared with thiopental for tracheal intubation with no muscle relaxant in another study,15 neither drug ensured acceptable conditions. Adding a neuromuscular blocking drug to facilitate tracheal intubation during induction, however, minimizes the role played by induction drug choice on intubation conditions. It also explains our results as well as those of other workers that are in agreement with our results.
The doses of propofol, thiopental and etomidate that were used in our study were reported to be equipotent16 and the adequacy of depth of anaesthesia produced by the induction dose was always assessed before succinylcholine administration. In this way, we avoided discrepancies in the depth of anaesthesia which may result from inter-individual variability in the response to the same drug.
Our results also showed that the apnoea time resulting after succinylcholine 0.6 mg kg1 was not significantly affected by choice of induction drug. Although it has been demonstrated that etomidate has minimal effect on respiratory functions,17 in contrast to propofol or thiopental,18 the apnoea resulting when equipotent doses of propofol, thiopental or etomidate were given was not found to be statistically different.19 The central apnoea that may occur when either propofol or thiopental is used is usually short-lived20 and is outlasted by the peripheral apnoea produced by the neuromuscular blockade. This might explain the lack of any effect on the duration of the succinylcholine-induced apnoea in our study. The apnoea time reported in our study is similar to earlier findings.3 21 It should be noted that although small doses of succinylcholine are associated with a short apnoea time in most patients, individual variations in the response to succinylcholine do exist, and in some patients in our study the duration of apnoea was as long as 6 min. However, in most patients the duration of apnoea was short, and it seems likely that the period of time for which favourable conditions for intubation was obtained was shorter than would be expected with higher-dose succinylcholine. Thus, the trade-off might be a short duration of apnoea vs a short window for intubation.
We considered both excellent and good intubating conditions to be clinically acceptable. In clinical situations where intense paralysis is desired at the time of intubation, small-dose succinylcholine may not be ideal. The dose must always be individualized according to the clinical situation. However, we must keep in mind that succinylcholine doses as high as 1.5 mg kg1 do not guarantee excellent conditions in all patients.22
In conclusion, we found that the choice of induction drug had no effect on intubation conditions or apnoea time when succinylcholine 0.6 mg kg1 i.v. was used to facilitate tracheal intubation.
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References |
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