Effect of neuromuscular block on depth of anaesthesia as measured by the auditory evoked response.

In a double-blind, randomized, controlled, prospective study, we have investigated the effects of vecuronium and laryngoscopy on the auditory evoked response (AER) of the electroencephalogram (EEG) in 40 ASA I and II patients under steady state anaesthesia. After stable anaesthesia had been achieved with 1.0 MAC of isoflurane and nitrous oxide in oxygen, patients were allocated randomly to receive two separate doses of vecuronium 0.05 mg kg-1 or saline. The AER was recorded before and after each dose and then after 20-s laryngoscopy in each group to determine any changes in the early cortical components of the AER waveform (Pa and Nb). There were no statistically significant changes between the vecuronium and saline groups. However, there was a statistically significant increase in mean Pa amplitude of 36% (P = 0.008) and a reduction in mean Nb latency of 6% (P = 0.05) after laryngoscopy in both the paralysed and unparalysed groups, and these changes did not differ significantly between groups. There were correspondingly significant haemodynamic responses to laryngoscopy in both groups. We conclude that neuromuscular block with vecuronium does not affect depth of anaesthesia as measured by the AER in either stimulated or unstimulated patients. In addition, we have demonstrated clearly the arousal effect of laryngoscopy on the AER.

Alkalinization of local anaesthetic for intra-articular instillation during arthroscopy.

Intra-articular instillation of a local anaesthetic agent for pain relief after arthroscopy has not been shown consistently to be beneficial. Alkalinization of a local anaesthetic agent may be expected to improve onset time, quality and duration of the block. In a prospective, double-blind, randomized, placebo-controlled study, we have examined the effect of 1% prilocaine 20 ml, plain or alkalinized, or saline, instilled into the knee joint after arthroscopy. Linear analogue scale (LAS) pain scores were assessed at six times after operation and time to first request for analgesia, total analgesic consumption and times to walking unaided and normal activities were recorded. There were no differences in any of these measurements at any time between the groups, except that the group which received intraarticular saline had significantly lower pain scores 8 h after operation than the groups which had alkalinized or plain prilocaine. We conclude that prilocaine, at both pH values, is ineffective in producing postoperative analgesia but as there were patients who received no analgesic agents and who had very little pain, we may also conclude that arthroscopy is not a consistently painful procedure and is not a good model for assessing the efficacy of local anaesthetic agents.

Preoperative morphine pre-empts postoperative pain.

Postoperative analgesia is usually inadequate, perhaps because conventional approaches to pain relief do not take account of underlying mechanisms. Pre-emptive analgesia may prevent nociceptive inputs generated during surgery from sensitising central neurons and, therefore, may reduce postoperative pain. In a randomised, double-blind study, we compared the effect of parenteral morphine when given before or after total abdominal hysterectomy in 60 patients. 10 mg of morphine were given intramuscularly 1 hour before operation (im pre), intravenously at induction of anaesthesia (iv pre), or intravenously at closure of the peritoneum (iv post). Response was assessed by morphine consumption from patient-controlled analgesia machines which was found to be significantly reduced in the iv pre group for 24 hours after operation compared with the iv post group. Pain sensitivity around the wound was reduced in both preoperative treatment groups compared with the iv post group. We conclude that pre-emptive analgesia with intravenous morphine, by preventing the establishment of central sensitisation during surgery, reduces postoperative pain, analgesic requirements, and secondary hyperalgesia.

Performance and carcass quality of steers supplemented with zinc oxide or zinc methionine.

Forty-five Angus steers (avg initial wt 330 kg) were individually fed for 112 d to assess the value of supplemental Zn and source on performance and carcass quality. Steers had ad libitum access to a control diet (81 ppm Zn) of 33% whole corn, 33% ground milo, 15% cottonseed hulls and 13% cottonseed meal, or this control diet with 360 mg Zn/d added from either zinc methionine or zinc oxide. Steers were slaughtered on d 114, and carcass composition was determined by specific gravity. Average daily gain and feed efficiency were not affected by dietary treatments. Steers fed zinc methionine had a higher (P less than .05) USDA quality grade than those fed the control and zinc oxide diets. Marbling score was higher (P less than .05) for steers fed zinc methionine than for those fed control and zinc oxide treatments (4.4 vs 4.0 and 4.0, respectively, where 3 = slight, 4 = small, 5 = modest). Steers fed zinc methionine tended to have more (P less than .10) external fat (13 mm) than steers fed the control diet (10 mm); steers supplemented with zinc oxide had intermediate amounts of external fat (11 mm). Steers fed zinc methionine had 10.5 and 12.8% more (P less than .05) kidney, pelvic and heart (KPH) fat than steers fed control or zinc oxide diets, respectively. The effects of zinc methionine on carcass quality grade and marbling score may be due to Zn and (or) methionine. Regardless of the mechanism, the difference represents a potential economic benefit to producers.