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Correspondence

Tracheal intubation with and without muscular relaxation

Mencke, T.*; Kleinschmidt, S.; Fuchs-Buder, T.

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European Journal of Anaesthesiology: April 2006 - Volume 23 - Issue 4 - p 354-355
doi: 10.1017/S0265021506240584

EDITOR:

We have read with interest the article by Baillard and colleagues [1]. The authors argued that the use of a technique avoiding muscle relaxants did not appear to be associated with poor conditions for tracheal intubation, nor altered postoperative laryngeal symptoms [1]. Moreover, they proposed a more flexible approach to the issue of the need for neuromuscular blockade prior to intubation. They referred to our study which showed that adding atracurium to a propofol–fentanyl induction sequence significantly improved the intubating conditions and decreased postoperative hoarseness and vocal cord injuries [2]. Due to the fact that our results are in contrary to the results of the study of Baillard and colleagues we would like to comment.

First, the study by Baillard and colleagues was an observational, not a controlled, study without randomization and patients designed to the relaxant-free group were younger, had a better ASA physical status (at least before intubation), and were undergoing different types of surgery (mainly abdominal surgery in the relaxant group compared to orthopaedic and ear surgery in the relaxant-free group). Thus, both groups were not comparable, and therefore should not be compared.

Moreover, a muscle relaxant could be used (even in the group without muscle relaxant!) at the anaesthesiologist’s discretion to improve intubating conditions if at least one unacceptable variable was present. Second, the intubating conditions were not evaluated according to the consensus conference of good clinical practice [3], movement of limbs as a variable was omitted by the authors. This might have improved the overall intubating conditions because especially without muscle relaxation movement of limbs after tube insertion or cuff inflation occurred in nearly 20% of all patients of the muscle relaxant-free group [2]. Thus, the authors found better intubating conditions as there actually were. Third, all patients in our study were examined by stroboscopy the day before surgery and were not included into the study when pre-existing pathologic findings of the larynx were observed [2]. Of these not included patients with oedema, erythema or even granuloma of the vocal folds 30% had no hoarseness.

Finally, to support their relaxant-free technique, significantly higher doses of propofol (2.74 [2.27–3.33]) vs. (3.64 [2.94 – 4.52]mg kg−1) were required and topical lidocaine (lidocaine 5%, two sprays per 10 kg body weight) was systematically applied in the relaxant-free group. In addition, the authors reported induction-related hypotension in 14% of patients with no difference between the two groups. However, intervention criteria were not defined and absolute values were not shown, moreover, both groups were not comparable regarding age and ASA physical status (patients in the relaxant-free group were younger and in a better ASA physical status).

Thus, we suppose that in comparable patient populations the significantly higher induction dose of propofol would lead to significant differences in induction-related haemodynamic changes. Moreover, two sprays of lidocaine 5% per 10 kg body weight, as recommended by the authors corresponds to 135 mg topical lidocaine for a 75 kg patient (9 mg lidocaine per spray according to the manufacturer). Especially after surgery of short duration, this may lead to persistent pharmacodynamic effects in the postoperative period, such as vocal cord incompetence and swallowing difficulties, both risk factors for postoperative pulmonary aspiration. It would be useful if the authors could indicate a safe interval for the offset of these pharmacodynamic effects of high dose topical lidocaine.

Thus, the proposed technique is associated with less optimal intubating conditions, increased haemodynamic consequences as well as an increased risk of postoperative aspiration. We worry about the consequences of the implementation of the results of the published study [1] into clinical routine practice. This approach should be limited to patients with a known contraindication to neuromuscular blocking agents, and should not be recommended to large groups of elective patients.

References

1. Baillard C, Adnet F, Borron SW et al. Tracheal intubation in routine practice with and without muscular relaxation: an observational study. Eur J Anaesth 2005; 22: 672–677.
2. Mencke T, Echternach M, Kleinschmidt S et al. Laryngeal morbidity and quality of tracheal intubation. A randomized controlled trial. Anesthesiology 2003; 98: 1049–1056.
3. Viby-Mogensen J, Engbaek J, Eriksson LI et al. Good clinical research practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents. Acta Anaesth Scand 1996; 40: 59–74.
© 2006 European Society of Anaesthesiology