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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.56 no.2 Campinas Mar/Apr. 2006
LETTERS TO THE EDITOR
Prolonged neuromuscular block after mivacu-rium. Case report
It was with interest that I read the article mencioned, and I would like to do some considerations, which were not clear to the reader, as well as others, of a practical order.
- The main one concerns is the needing a regular use of neuromuscular transmission monitors in daily practice. The present case well illustrated this need, because if that monitor were already installed, one could have conjectured earlier about the change of the cholinesterase, when the patient would have then presented a quite enlarged onset action, even considering the small dose given.
- It is always interesting to describe which current was used for gauging the sequence of 4 stimuli (SQE) when there is no research on the basal supramaximal response. This point is quite important, because currents of very low intensity tend to not show this relation, thus confusing the involvement diagnosis of the neuromuscular blocker in extended apnea. The most current apparatus of accelerometry, the TOF Watch, which presents a basic current of 50 mA as soon as the apparatus is turned on, although the same does not happen with TOF Guard.
- Taking into consideration how it was described in the article, that is, even in the absence of some muscular response, the authors opted for administering neostigmine. This conduct is very questionable, and it is recommended that the reversion with the anticholinesterasic should be initiated with at least some motor response, or if monitoring is used, with about 10% of T1. The little efficient response that the patient presented to the administration of neostigmine corroborates the knowledge that deep blockades do not significantly benefit from the adminis-tration of neostigmine and the injection of such medication can, besides, deepen the muscular relaxation.
- Another concept that must not be taken into account as criterion of satisfactory reversion is the maintenance of a good current volume, since this value can be normal and the patient can still present expressive degrees of residue of neuromuscular blocker. Likewise, other criteria as capno-graphy and normal values of blood gases do not exclude the residual curarization.
- Finally, it was not described which value of SQE was conside-red satisfactory when choosing to remove the larynx mask and waking up the patient. This concern with the use of accele-rometry must always be present, because it is known that this method tends to underestimate the blockade degree. In this particular case the concern is even redoubled, because the diagnostic procedure involved the air pathways.
Maria Cristina Simões de Almeida, TSA, M.D.
Member of RBA Editorial Council
Thank you for the opportunity to send this message. I would like to thank the careful and enriching comments. There is little to add, but I consider them all pertinent.
I would like to answer, as an explanation, the following observations:
- The need for the routine use of neuromuscular transmission monitors in daily practice is a reality, but unfortunately not all hospitals have this type of monitoring and when they have it, its availability is not enough to supply all surgical rooms. In the case in question, it was made available after the appearance of this complication.
- The neuromuscular transmission monitor used was S/5 module - Anesthetic Monitor Datex-Ohmeda (M-NMT), mechano-sensor, which automatically begins sending a supramaximal stimulus current of 50 mA, stimulus of square pulse wave, constant current, pulse length varying from 100 up to 300 µs, at a 20 second interval, frequency of 2 HZ.
- In the first dose of neostigmine, despite of the patient not presenting response to SQE, she presented a clinical criterion represented by the capacity presence for generating a low current volume with high frequency, thus suggesting residual curarization and, having at this time, disagreement between the monitoring and the clinic. Probably due to a bad positioning of the monitor electrodes.
- As already mentioned, due to the lack of availability of the neuromuscular transmission monitor, for all surgical rooms and the existence of hospital units without it, this important monitoring for the patient's safety regarding the clinical criteria is still regularly applied for the evaluation of residual curarization. Remembering that the presence of a value of T4/T1 > 0,8 the patient does not present significant breathing difficulty, thus being able to keep the head up for 5 seconds, adequate average volume, adequate inspiratory and expiratory flow. Yet being possible to have the swallowing jeopardized and the glottis closing as a protection against aspiration with this ratio.
- In order to conclude, as it concerns the SQE value for removal of the larynx mask was T4/T1 > 0.9. It is worth to stand out that due the fact that the diagnostic procedure involves the air pathways and the availability of the neuromuscular transmission monitor is irregular, the neuromuscular blocker chosen has a short duration (from 15 up to 30 min) due to its fast hydrolysis by means of the plasmatic cholinesterase.
I hope to have answered in a coherent way the relevant questionings.
Karina Bernardi Pimenta,TSA, M.D.