EFFECT OF SURFACE ELECTRODE POSITIONING ON THE COMPOUND ACTION POTENTIAL EVOKED BY ULNAR NERVE STIMULATION IN ANAESTHETIZED INFANTS AND CHILDREN

The effect of surface electrode positioning on the evoked compoundaction potential (ECAP) was studied during inhalation anaesthesiawithout neuromuscular blockade. The ECAP of five fullterm infants(aged 2–20 weeks) and five children (age 1–10 yr)was recorded with a neuromuscular relaxation monitor (Relaxograph,Datex) after supramaximal ulnar nerve stimulation. The fiverecording electrode positions compared were: thenar (adductorpollicis) v. second finger (TD2); thenar v. second dorsal metacarpalinterspace (TM2); hypothenar v. fifth finger (HD5); hypothenarv. fourth dorsal metacarpal interspace (HM4); thenar v. hypothenar(TH). The ECAP was steady at positions TD2 and HD5, but markedvariation and baseline drift was found at TM2, HM4 and TH. TheECAP peak-to-peak amplitudes were twice as great in childrencompared with infants. The hypothenar ECAP was liable to stimulusartefact interference because of the short onset latency atHD5 (2.2(SD 0.4)ms), whereas the adductor pollicis (3.0 (SD0.5)ms) position (TD2) yielded reliable results. Address for Correspondence: Helsinki University, Surgical Hospital,Department of Anaesthesia, SF-00130 Helsinki, Finland.