Optimal peri-operative management of neuromuscular block or more of the same?

Neuromuscular block (NMB) is an essential part of anesthetic management of many types of modern surgery. It allows for tracheal intubation to take place atraumatically, surgery to take place at lighter levels of anesthesia with added safety, and ensures absolute immobility when necessary. However, the management of NMB in routine clinical practice is performed intuitionally more often rather than based on monitoring. It is well known that the use of NMB monitoring is not very common when it is known that the use of monitoring can optimize the use of neuromuscular blocking agents (NMBAs). [1] It is also known that the use of NMBAs is associated with a considerable incidence of residual block. [2] This could be avoided by optimum use of NMBAs and reversal agents which in turn could be guided by monitoring.

Can an automated system of monitored administration of NMBA improve practice? Such systems in theory could have advantages for optimum drug delivery, reduced workload for the anesthesiologist and reduction of drug administration errors. Closed loop methods of administering NMBAs have been described previously but have not made it into clinical practice remaining the preserve of the research groups. [3,4] The systems need to be easy to use and relatively quick to set up.

The current issue of AnesthesiaNow contains the description and use of an automated computer controlled method of administering NMBAs. [5] Neuromuscular Blockade Advisory System (NMBAS) guides the anesthesiologist about the timing and dosage of the NMBA, using the electromyography (EMG) to assess the responses. The system is a partial closed-loop controller with the anesthesiologist administering the drug in contrast to the previous closed loop systems where the drug administration was automated. The patient model was built on the back of pilot data and EMG measurements obtained from the patient. The degree of block was fixed at a train-of-four (TOF) ratio of 0.1.

The results from the limited study in 30 patients each in the control and the NMBAS groups showed that inadequate surgical relaxation and breathing against the ventilator were less frequent in the NMBAS group. A higher TOF ratio at the end of surgery was also observed in this group although the dosage of rocuronium used and the duration of surgery were identical in the two groups.

Although the authors concluded that the NMBAS is superior to the conventional administration method, it depends upon the anesthetist carrying out the instruction. The method is constrained by stipulating the administration to be every 20 minutes. It is not known how easy it is to change the desired depth of block and it still requires the attention of the anesthesiologist. Whether the latter is a distraction or resting of the control with the anesthesiologist needs to be determined. Could what has been achieved using the NMBAS system not have been attained simply by the attention of the anesthesiologist to the patient response?

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Kind regards

Rajinder Mirakhur, MD.

References

1. Dascalu A, Geller E, Moalem Y, et al. Acoustic monitoring of neuromuscular block. Br J Anaesth 1999;83:405-409.

2. Hayes AH, Mirakhur RK, Breslin DS, Reid JE, McCourt KC. Postoperative residual block after intermediate-acting neuromuscular blocking drugs. Anaesthesia 2001;56:312-318.

3. Wait CM, Goat VA, Blogg CE.Feedback control of neuromuscular blockade. A simple system for infusion of atracurium. Anaesthesia 1987;42:1212-1217.

4. MacLeod AD, Asbury AJ, Gray WM, Linkens DA. Automatic control of neuromuscular block with atracurium. Br J Anaesth 1989;63:31-35.

5. Gilhuly TJ, MacLeod BA, Dumont GA, Bouzane AM, Schwarz SKW. Improved neuromuscular blockade using a novel neuromuscular blockade advisory system: A randomized controlled, clinical trial. Anesth Analg 2008;107:1609-1617.

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