In clinical anaesthesia, which nerve is the most popular site, and commonly used for monitoring neuromuscular response during anaesthesia & in intensive care units?
(A) Ulnar nerve[Miller's Anaesthesia6-1557,1559,1559f)[?]Neuromuscular function is monitored by evaluating the muscular response to Supramaximal Stimulation of a Peripheral Motor Nerve.Two types of stimulation can be used: 1. Electrical & 2. Magnetic.Electrical nerve stimulation is by far the most commonly used method in clinical practice.[?]Patterns of Nerve Stimulation:For evaluation of neuromuscular function, the most commonly used patterns of electrical nerve stimulation are Single-Twitch, TOF, Tetanic, Post-Tetanic Count (PTC), & Double-Burst Stimulation (DBS).Advantages of Train-of-Four (TOF) stimulation are greatest during nondepolarizing blockade because the degree of block can be read directly from the TOF response even though a preoperative value is lacking.TOF stimulation has some advantages over tetanic stimulation: It is less painful &, unlike tetanic stimulation, doesnot generally affect the degree of neuromuscular blockade.Sites of Nerve Stimulation & Different Muscle Responses:Any superficially located peripheral motor nerve may be stimulated.In clinical anesthesia, the ulnar nerve is the most popular site.Median, posterior tibial, common peroneal, & facial nerves are also sometimes used.For stimulation of the ulnar nerve, the electrodes are best applied to the volar side of the wrist.Distal electrode should be placed about 1 cm proximal to the point at which the proximal flexion crease of the wrist crosses the radial side of the tendon to the flexor carpi ulnaris muscle.Proximal electrode should preferably be placed so that the distance between the centers of the two electrodes is 3 to 6 cm.Electrical stimulation normally elicits only finger flexion & thumb adductionIf one electrode is placed over the ulnar groove at the elbow, thumb adduction is often pronounced because of stimulation of the flexor carpi ulnaris muscle.Ulnar groove placement of electrodes (sometimes preferred in small children) is used, the active negative electrode should be at the wrist to ensure maximal response.Polarity of the electrodes is less crucial, placement of the negative electrode distally normally elicits the greatest neuromuscular response.Because different muscle groups have different sensitivities to neuromuscular blocking agents, results obtained for one muscle cannot be automatically extrapolated to other muscles.Diaphragm is among the most resistant of all muscles to both depolarizing and nondepolarizing neuromuscular blocking drugs.Clinical significance is that onset time is normally shorter for the diaphragm than for the adductor pollicis muscle and the diaphragm recovers from paralysis more quickly than the peripheral muscles do.Other respiratory muscles are less resistant than the diaphragm, as are the larynx & the corrugator supercilii muscles.Most sensitive are the abdominal muscles, the orbicularis oculi muscle, the peripheral muscles of the limbs, & the geniohyoid, masseter, & upper airway muscles.From a practical clinical point of view, it is worth noting that:Response of the corrugator supercilii to facial nerve stimulation reflects the extent of neuromuscular blockade of the laryngeal adductor muscles & abdominal muscles better than the response of the adductor pollicis to ulnar nerve stimulation does.Upper airway muscles seem to be more sensitive than the peripheral muscles.Although three investigations using acceleromyography have indicated small differences in the response to TOF nerve stimulation in the arm (adductor pollicis muscle) & the leg (flexor hallucis brevis muscle), these differences are probably of little clinical significance.Remember: In assessing neuromuscular function, use of a relatively sensitive muscle such as the adductor pollicis of the hand has both disadvantages & advantages.During surgery it is a disadvantage that even total elimination of the response to single-twitch & TOF stimulation does not exclude the possibility of movement of the diaphragm, such as hiccuping & coughing.
Ulnar nerve
Fascial nerve
Posterior tibial nerve
Median nerve
Fundamental Concepts