No abstract

Summary Complications and changes in tracheal mucosa after minitracheotomy were evaluated in 28 patients. Tracheal mucosa was inspected fibreoptically after the insertion of a minitracheotomy cannula, and then at 3‐day intervals until the cannula was removed. Thereafter, assessments were made every third day until the mucosa was considered normal. Three significant complications occurred: mediastinal puncture, paratracheal entrance of the cannula and subcutaneous emphysema. Difficulties at insertion of the minitracheotomy cannula were encountered in 15 of 28 patients (54%). Air flow detected through the cannula in one patient, and lack of air flow in another patient, were misleading signs of the position of the cannula. Passing a suction catheter in three patients and a normal end‐tidal carbon dioxide tracing in one patient, were also found to be misleading. The correct position and possible complications could be verified only by fibreoptic tracheoscopy. Changes in the tracheal mucosa were independent of the duration of minitracheotomy therapy.

The doses of atracurium (by infusion) required to maintain steady-state (90-95%) neuromuscular block were assessed in 75 children aged 9 days to 17 yr during balanced anaesthesia. Following the intubating dose of atracurium 0.4 mg kg-1 and after the recovery of single twitch to 5-10% of control (monitored by evoked EMG of hypothenar muscle), an infusion of atracurium 0.5 mg kg-1 h-1 was started. In 22 of the patients this initial rate resulted in the desired steady state; 32 patients required one, and 21 required two or more adjustments in rate. The mean single twitch value at steady-state was 6.6 +/- 0.3% (SEM), which is equal to 93% neuromuscular block. The infusion requirement to maintain the steady state neuromuscular block in all paediatric patients more than 1 month old was constant (0.53 +/- 0.01 mg kg-1 h-1). The infusion requirement of neonates up to 1 month old was 25% less (0.40 +/- 0.02 mg kg-1 h-1; P = 0.003). A significant correlation (n = 75, r = 0.76, P less than 0.001) was found between the infusion rate (mg m-2 h-1) and the logarithm of the body surface area.

The effect of surface electrode positioning on the evoked compound action potential (ECAP) was studied during inhalation anaesthesia without neuromuscular blockade. The ECAP of five full-term 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 five recording electrode positions compared were: thenar (adductor pollicis) v. second finger (TD2); thenar v. second dorsal metacarpal interspace (TM2); hypothenar v. fifth finger (HD5); hypothenar v. fourth dorsal metacarpal interspace (HM4); thenar v. hypothenar (TH). The ECAP was steady at positions TD2 and HD5, but marked variation and baseline drift was found at TM2, HM4 and TH. The ECAP peak-to-peak amplitudes were twice as great in children compared with infants. The hypothenar ECAP was liable to stimulus artefact interference because of the short onset latency at HD5 (2.2(SD 0.4)ms), whereas the adductor pollicis (3.0(SD 0.5)ms) position (TD2) yielded reliable results.

The effect of surface electrode positioning on the evoked compound action potential was studied during isoflurane anaesthesia without neuromuscular block. In 20 ASA I-II patients (age 36-50 yr), the response after supramaximal ulnar nerve stimulation was analysed with a neuromuscular relaxation monitor (Relaxograph, Datex) and with a memory recorder. Seven pairs of surface recording electrodes were compared: (1) adductor pollicis muscle vs second finger; (2) adductor pollicis m. vs first finger; (3) first dorsal interosseus m. vs second finger; (4) abductor digiti minimi m. vs fifth finger; (5) adductor pollicis m. vs second dorsal metacarpal; (6) abductor digiti minimi m. vs fourth dorsal metacarpal; (7) thenar vs hypothenar. Steady biphasic response was recorded with electrode pairs 1-4. Marked variation and low amplitude existed at pairs 5-7. Peak-to-peak amplitude at pair 3 was the greatest (12.5 (SD 3.7) mV) compared with pair 4 (9.4 (SD 2.0) mV) and pair 1 (8.5 (SD 2.0) mV). A close correlation between the amplitudes and integrated areas was found. The first dorsal interosseus muscle response was optimal and the electrodes were simple to fix; this site may be recommended for clinical monitoring.