British journal of anaesthesia
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Comparative Study
Somatosensory and auditory evoked responses recorded simultaneously: differential effects of nitrous oxide and isoflurane.
Auditory (AER) and somatosensory evoked responses (SSER) were recorded simultaneously in eight patients under anaesthesia before surgery. We studied the effects of equi-MAC end-expiratory concentrations of isoflurane (0.65-0.75%) and nitrous oxide (60-65%). The anaesthetics were changed at random in three consecutive 10-min periods so that each patient received both drugs. ⋯ We were unable to demonstrate significant differences in Pa and Nb amplitude between isoflurane and nitrous oxide that we had seen previously. However, the amplitude of the SSER wave N20 was reduced significantly by nitrous oxide compared with isoflurane (P = 0.0004). This wave (N20) is thought to emanate from the thalamo-cortical radiations, and our findings may be explained by an analgesic effect of nitrous oxide mediated by endogenous opioids.
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Comparative Study
Effect of doxapram on the rate of recovery from atracurium and vecuronium neuromuscular block.
We have studied the effect of doxapram on the rates of spontaneous and neostigmine-induced recovery from neuromuscular block with atracurium and vecuronium, by measurement of the time to recovery of T1 (first twitch in the train-of-four) from 25 to 75% of control (recovery index, RI). After each neuromuscular blocking drug, RI was measured without administering either doxapram or neostigmine (control group), or after administration of doxapram 1 mg kg-1, neostigmine 50 micrograms kg-1 or a combination of doxapram and neostigmine, in groups of 10 patients. RI was significantly longer after vecuronium in the presence of doxapram compared with control (20.1 min vs 14.6 min). There was no significant difference in the RI after atracurium in the presence of doxapram compared with control (12.5 min vs 11.8 min) or when neostigmine was administered with or without doxapram (2.4 min vs 2.4 min, respectively after vecuronium; 3.3 min vs 2.9 min, respectively, after atracurium).
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We have examined in sheep the efficiency of the Hemopump during ventricular fibrillation. Circulatory arrest was induced by electrical stimulation and maintained for 30 min. ⋯ During fibrillation, the Hemopump sustained a mean arterial pressure of about 60 mm Hg with a blood flow rate of about 2.3 litre min-1. These perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but with a borderline circulatory supply to the total organism.
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Comparative Study
Voltage fields surrounding needles used in regional anaesthesia.
Using a bench model, we have studied the voltage fields surrounding both insulated and uninsulated needles used in regional anaesthesia. The findings were compared with earlier computer predictions which suggested that the fields would be markedly different for the two types of needle. The results confirm that the fields differ markedly and suggest that the use of insulated needles may not necessarily improve the accuracy of nerve location and that uninsulated needles may be more appropriate.