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Anesthesiology:
doi: 10.1097/ALN.0b013e3181a9728b
Correspondence

Muscle Relaxants and Airway Management

Calder, Ian M.B., Ch.B., F.R.C.A.*; Yentis, Steve B.Sc., M.B.B.S., F.R.C.A., M.D., M.A.; Patel, Anil M.B., B.S., F.R.C.A.

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To the Editor:—

The article by Schmidt et al. and the accompanying editorial by Boylan and Kavanagh raise a very important issue, which is the place of neuromuscular blocking drugs (NMBDs) in anesthetic practice.1,2 Schmidt et al. state that “The use of muscle relaxants can cause severe hypoxia if the trachea cannot be intubated and the patient cannot be ventilated.”1 We would be grateful if they could tell us on what evidence they base this statement. With respect, we think they may be falling into the well-known medical trap of confusing subsequence with consequence.3 In our opinion a more realistic and up-to-date statement would be “If mask ventilation is impossible, the evidence suggests that an NMBD will permit ventilation or intubation.”
The large study of Kheterpal et al. has confirmed that the nonevidence-based practice of not administering an NMBD until ventilation has been demonstrated is unsound. Of the patients in whom ventilation by face mask was impossible, all but one received an NMBD to facilitate intubation.4,5 The option of waking the patient up if ventilation is impossible is often put forward as the reason for not administering an NMBD, but none of the patients with difficult or impossible mask ventilation in Kheterpal et al.'s study were woken up. In practice it seems that this is not an option anesthetists find expedient.
In their editorial, Drs. Boylan and Kavanagh refer to the use of NMBDs in Schmidt et al.'s study, writing that “The finding that their use was not associated with more complications is not surprising because they were used in the presence of the more experienced attending physicians.”2 The impression given is that NMBDs are tricky substances that might cause harm to the patient if used by an inexperienced anesthetist (in fact, Schmidt et al.'s study found a decrease (odds ratio [OR] 0.66) in complications associated with their use, albeit nonsignificant (95% CI 0.33–1.33), independent of any effect of the attending physician's presence).1 We would like to know why Boylan and Kavanagh seem to believe that the use of NMBDs by less experienced anesthetists is hazardous. As far as we can see, the evidence shows that when NMBDs are used, mask ventilation is facilitated,6 tracheal intubation is easier and less traumatic,7 more successful in less experienced hands,8 and facilitated when mask ventilation is impossible.5 We wonder whether any of the respiratory emergency patients in Schmidt et al.'s study had stridor as a result of laryngo-tracheal stenosis? Nouraei et al. have shown that these patients achieve better gas flows than they can manage while awake if they are given an NMBD.9
Schmidt et al. found that opioid use was associated with an increased risk of complications and wrote that “this is difficult to explain.”1 An obvious explanation occurs to us, which is the phenomenon of muscle rigidity associated with opioid use.10 We guess that one or other of the fentanyl-type analgesics is used in the vast majority of induction regimes in the United Kingdom, and it is our experience that the timely use of an NMBD is sometimes vital. If junior anesthetists receive messages that might inhibit their use of muscle relaxants in this not uncommon situation, we, the seniors, have failed them and their patients.
We have no problem with the proposition that tracheal intubation can be performed in an apneic patient without the use of NMBDs. However, we are alarmed by the message that we perceive (mistakenly we hope) to be implicit in Schmidt et al. and Boylan and Kavanagh's articles. They make no comment on the fact that residents did not use a NMBD to facilitate emergency intubation in 83% of patients. This makes us wonder whether the authors believe that it is in some way virtuous for residents to avoid their use. An inexperienced anesthetist could conclude that he or she might be criticized for giving an NMBD, which raises the awful prospect of a patient perishing while the anesthetist hesitates.
Of course there are patients to whom it is unwise to give an NMBD, but these are mainly those to whom it is unwise to give any sedative drug, plus those with allergies or certain neuromuscular diseases. However, when general anesthesia has been induced we believe that it is more dangerous to inhibit trainees from using NMBDs than to encourage them to use them if they think it might help.11 In airway management under general anesthesia, NMBDs are much more often the answer than the problem.
Ian Calder, M.B., Ch.B., F.R.C.A.*
Steve Yentis, B.Sc., M.B.B.S., F.R.C.A., M.D., M.A.
Anil Patel, M.B., B.S., F.R.C.A.
*The National Hospital for Neurology and Neurosurgery, London, United Kingdom. icalder@aol.com
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References

1. Schmidt UH, Kumwilaisak K, Bittner E, George E, Hess D: Effects of supervision by attending anaesthesiologists on complications of emergency tracheal intubation. Anesthesiology 2008; 109:973–7

2. Boylan JF, Kavanagh BP: Emergency airway management. Competence versus expertise? Anesthesiology 2008; 109:945–7

3. Wiltshire J: Samuel Johnson in the medical world. The Doctor and the patient. Cambridge, Cambridge University Press, 1991 :pp. 113–4

4. Kheterpal S, Han R, Tremper KK, Shanks A, Tait AR, O'Reilly M, Ludwig TA: Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006; 105:885–91

5. Calder I, Yentis SM, Kheterpal S, Tremper KK: Impossible mask ventilation. Anesthesiology 2007; 107:171–2

6. Szabo TA, Reves JG, Spinale FG, Ezri T, Warters RD: Neuromuscular blockade facilitates mask ventilation. Anesthesiology 2008; 109:A184

7. Combes X, Andriamifidy L, Dufresne E, Suen P, Sauvat S, Scherrer E, Feiss P, Marty J, Duvaldestin P: Comparison of two induction regimens using or not using muscle relaxant: Impact on postoperative upper airway discomfort. Br J Anaesth 2007; 99:276–81

8. Davis DP, Ochs M, Hoyt DB, Bailey D, Marshall LK, Rosen P: Paramedic-administered neuromuscular blockade improves prehospital intubation success in severely head-injured patients. J Trauma 2003; 55:713–9

9. Nouraei SA, Giussani DA, Howard DJ, Sandhu GS, Ferguson C, Patel A: Physiological comparison of spontaneous and positive-pressure ventilation in laryngotracheal stenosis. Br J Anaesth 2008; 101:419–23

10. Richardson SP, Egan TD: The safety of remifentanil by bolus injection. Expert Opin Drug Saf 2005; 4:643–51

11. Calder I, Yentis SM: Could “safe practice” be compromising safe practice? Should anaesthetists have to demonstrate that face mask ventilation is possible before giving a neuromuscular blocker? Anaesthesia 2008; 63:113–5

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