We determined the dose-response curves and effective doses of propofol for insertion of the laryngeal mask airway (LMA) in 50 unpremedicated children and in 60 children premedicated with midazolam, aged 3-12 yr. One of several doses of propofol was administered i.v. over 15 s to groups of 10 children, and conditions for LMA insertion were assessed at 60 s. The dose-response curves were parallel (P = 0.94), but the curve for premedicated children was shifted significantly to the left of that for unpremedicated children and propofol requirements were reduced by one-third (P < 0.0001). The doses required for satisfactory LMA insertion in 50% and 90% of unpremedicated patients (ED50, ED90) (95% confidence interval) were 3.8 (3.4-4.2) mg kg-1 and 5.4 (4.7-6.8) mg kg-1, respectively; those for premedicated patients were 2.6 (2.2-2.8) mg kg-1 and 3.6 (3.2-4.3) mg kg-1, respectively.

The precision of the compact Mini-Accelograph (M-A) was compared with the Myograph 2000 (MYO). Neuromuscular block resulting from atracurium was measured simultaneously by the MYO and the M-A applied to contralateral thumbs. During onset, the M-A frequently underestimated the extent of block (maximal at approximately 50% twitch depression). The M-A control train-of-four (TOF) ratio was characteristically > 1.0 and remained greater than the MYO ratio during the onset of atracurium. During recovery, the difference between the MYO and the M-A was maximal at approximately 50% twitch depression, but the M-A frequently overestimated the extent of block. The mean differences between the MYO and the M-A were small in respect of the recovery index (RI) and the TOF. However, the limits of agreement were unacceptably wide for both TOF and RI. When the MYO TOF was 0.7, the corresponding M-A TOF varied between 0.4 and 1.0. The M-A was more susceptible to drift than the MYO.

No abstract

Summary A 5‐year‐old girl who had Patau's syndrome associated with double outlet right ventricle and pulmonary stenosis required general anaesthesia for the formation of a modified Blalock‐Taussig shunt.

Summary Key wordsNeuromuscular relaxants; doxacurium. Pharmacology. Age factors.Doxacurium is a new benzylisoquinolinium nondepolarising neuromuscular blocking agent. It is very potent (EDg5 23-33 pg.kg-l) with a duration of action similar to pancuronium [ 1-31. It has minimal cardiovascular side effects [2,4] although hypotension associated with an anaphylactoid response to doxacurium has been reported [5]. Approximately 30% of a dose of doxacurium is excreted unchanged in the urine [6] and the duration of action is prolonged in the presence of renal failure [7]. The physiological changes associated with ageing, i.e. a decrease in muscle mass, serum proteins, total body water and renal and hepatic blood flow, may affect drug disposition and elimination in the elderly. Doxacurium has been shown to have a similar potency in young and elderly patients with a slower onset in the elderly [6], but the effect of advancing age on the conditions for tracheal intubation has not been determined previously.Many workers have reported that doxacurium is antagonised relatively slowly [3, and this, together with a relatively slow rate of spontaneous recovery in patients aged over 70 years [lo], may make reversal more difficult in elderly age groups. The rate of antagonism of doxacurium in elderly patients, following a standard single dose of neostigmine, has not been previously compared with a younger group. This study was designed to compare the speed of onset of doxacurium, intubating conditions and the efficacy of neostigmine-induced antagonism in young and elderly patients during isoflurane anaesthesia. MethodsApproval for the study was granted by the Hospital Ethics Committee and written, informed consent was obtained from each patient. Thirty-eight patients were studied in two age groups: 18 to 55 years (young group) (n = 21) and over 65 years (elderly group) (n = 17). Patients were ASA 1 or 2 and underwent elective surgery of at least 1 h duration. Patients with neuromuscular disease, or receiving treatment withdrugs known to influence neuromuscular transmission, or who were more than 20% outside their ideal body weight were not studied. The majority of patients received oral premedication with temazepam 10-20 mg and droperidol 5 mg. General anaesthesia was induced with thiopentone 3-5 mg.kg-' (titrated to the loss of the eyelash reflex) and fentanyl 1-1.5 pg.kg-l, and maintained initially with 67% nitrous oxide in oxygen with increments of thiopentone as required. Ventilation was assisted manually if necessary. Skin electrodes were applied over the ulnar nerve at the wrist and supramaximal train-&-four stimuli (at 2 HZ every 20 s) were delivered by a portable electromyograph (Relaxograph, Datex). This also recorded the compound muscle action potential (CMAP) of the adductor pollicis using similar electrodes. After calibration and stabilisation of the control CMAP, a single intravenous bolus injection of doxacurium 30 pg.kg-' was administered over 5 s. Tracheal intubation was attempted after 4 min by the same investiga...