Comparison of integrated evoked EMG between the hypothenar and facial muscle groups following atracurium and vecuronium administration

Electromyographic response of facial nerve stimulation under different levels of neuromuscular blockade during middle-ear surgery

OBJECTIVE

To investigate facial nerve monitoring in patients receiving the partial nondepolarizing neuromuscular blocking agents (NMBAs), remifentanil and propofol.

METHODS

Patients with normal facial function and advanced middle-ear disease were enrolled. For total intravenous anaesthesia (TIVA), propofol and remifentanil were infused as induction/maintenance anaesthesia. Stimulation thresholds and amplitudes were recorded at each train-of-four (TOF) nerve stimulation level. Time differences between start of TOF and electromyographic (EMG) amplitude decreases (Ti), and between complete recovery of TOF and EMG amplitudes (Tr), were calculated.

RESULTS

Fifteen patients were enrolled. Mean ± SD Ti was 3.4 ± 1.28 min; Tr was 18.7 ± 4.41 min. Amplitude of stimulation was apparent mostly at TOF level 1. In most cases, no or a weak response (<100 µV) was observed at TOF 0. Mean ± SD threshold of electrical stimulation was 0.31 ± 0.10 mA at TOF 1. At TOF > 2, all cases showed EMG response on electrical stimulation.

CONCLUSIONS

Induction of TIVA using propofol and remifentanil provided reliable conditions for delicate microsurgery. Minimal NMBA use, considered as producing TOF levels >1, was sufficient for facial nerve monitoring in neuro-otological surgery.

Apparatus and simple method of monitoring neuromuscular function

The use of muscle relaxant is an integral part of anesthetic management in present-day practice. Clinically, the neuromuscular blockade is evaluated by determining the thumb twitching to train-of-four (TOF) ulnar nerve stimulation at elbow.(1-3) There are many ways for the assessment of twitch response, such as the use of electromyography(4,5); force displacement transducer techniques(2,6-9); and most recently, the acceleration transducer-based system of neuromuscular monitoring.(10-15) These equipments are, however, bulky, cumbersome, expensive, or time consuming for operation. Because of these limitations, the routine use of such monitors is impractical. The evaluation of neuromuscular blockade, at the present time, relies on either visual or manual (tactile) thumb twitch responses to the TOF nerve stimulation. Visual or tactile evaluation of neuromuscular blockade is subjective and involves uncertainty, especially in the recovery phase. Furthermore, in certain surgical procedures, such as those on the head and neck, both hands are tucked in the sides of the table and become inaccessible, rendering visual or tactile evaluation of the thumb twitch impossible. In such situation, muscle relaxant is often given in the light of guessing rather than on objective basis. Clearly, there is a need for a simple and practical way of measuring the twitch responses to TOF stimulation during anesthesia. Based on the current method of stimulation of the ulnar nerve over the ulnar groove at the elbow, which elicits a string thumb adduction (because of stimulation of the flexor carpi ulnaris muscle), a simple method that can objectively monitor and record the thumb twitch is developed. The unique features of the method or device are its simplicity and its ability to adapt to any pressure transducer to display the twitch response to TOF simultaneously with electrocardiogram, arterial, or central venous pressure.

Acceleromyography of the orbicularis oculi muscle II: comparing the orbicularis oculi and adductor pollicis muscles

BACKGROUND

The orbicularis oculi (OO) muscle has been recommended for neuromuscular monitoring when the adductor pollicis (AP) muscle is not available. We investigated whether neuromuscular block could be measured reliably from the orbital part of the OO muscle by the use of acceleromyography.

METHODS

During propofol, fentanyl, and alfentanil anaesthesia two TOF-Guards (Organon Teknika NV, Boxtel, the Netherlands) with acceleration transducers placed on the distal phalanx of the thumb and over the middle of the eyebrow, respectively, were used to measure neuromuscular block simultaneously in 23 patients during vecuronium-induced and neostigmine-antagonized neuromuscular block. For both muscles, the simultaneously recorded first response (T1) in the train-of-four (TOF) and TOF-ratio were measured both during onset and recovery of the block. Furthermore, both the AP muscle T1 and TOF-ratio responses were plotted against 10% intervals of the OO muscle responses during onset and recovery, respectively.

RESULTS

The orbicularis oculi muscle had a shorter latency and a faster recovery to TOF-ratio 0.80 compared with the AP muscle. During onset and recovery, pronounced variations of the AP muscle T1 and TOF-ratio responses were observed when compared with the OO muscle.

CONCLUSION

A significant clinical disagreement exists between the degree of paralysis measured at the OO and the AP muscles. It is impossible to obtain a reasonable estimate of the degree of block at the AP muscle when the block is measured from the OO muscle with acceleromyography. If used, there is substantial risk of overlooking a residual block, and adequate recovery of the block should be confirmed by a final AP muscle measurement.

The use of muscle relaxants in the intensive care unit

Neuromuscular blocking agents are frequently used in the Intensive Care Unit to facilitate tracheal intubation and the application of continuous paralysis. This review will focus on various conditions of the critically ill patient such as multi-organ dysfunction, acid-base and electrolyte imbalance, prolonged immobility, multiple drug interactions and specific disease/injury processes that may affect the pharmacokinetic and pharmacodynamic behaviour of muscle relaxants. As such, due to the complex nature of the critically ill patients, the effects of neuromuscular blocking agents are unpredictable. Therefore, guidelines regarding their administration and the methodology and requirement for continuous bedside monitoring of neuromuscular function will be presented.