B. J. Pollard

The influence of premedication on heart rate variability

Analysis of heart rate variability has been used to study the effects of midazolam, morphine and clonidine on the autonomic nervous system, when administered to patients for premedication. Ninety‐five patients were studied 60 min before and 60 min after premedication. Normal saline (n = 25), midazolam 0.08 mgkg−1 (n = 24), morphine 0.15 mgkg−1 (n = 23), or clonidine 2 μgkg−1 (n = 23) were administered intramuscularly by random allocation. A Holter device was connected to the patient during the study period. Using power spectral analysis the low‐frequency and high‐frequency components were calculated from the Holter recordings. These are markers for sympathetic and parasympathetic activity respectively; the low‐ to high‐frequency ratio was also calculated, a ratio of >1 signifying sympathetic dominance. A significant reduction was noticed in both low‐frequency and high‐frequency power in the three premedicated groups, whereas no changes were observed in the normal saline group. In the case of midazolam, both the low and high frequencies were decreased but the low‐ to high‐frequency ratio did not change significantly. Morphine and clonidine depressed the low‐frequency component more than the high‐frequency component and the low‐ to high‐frequency ratio was decreased, suggesting parasympathetic dominance. We conclude that heart rate variability may be a useful tool for investigating the effect of drugs on the autonomic nervous system.

Nasal CPAP after coronary artery surgery.

Two groups of 14 patients were compared after coronary artery bypass surgery where the left internal mammary artery had been used as a conduit. One group received nasal continuous positive airway pressure for 1 h, the other group acted as a control. Mean pulmonary shunt fraction was 16.3% before, 12.6% during and 15.7% after continuous positive airways pressure. In the control group the shunt fraction fell from 17.3% to 16.8%. The reduction in shunt fraction was significantly greater with nasal continuous positive airways pressure than in the control group (p = 0.016). There was a significant reduction (p = 0.025) in respiratory rate from 18.3 to 16.7 breath.min–1 during continuous positive airway pressure. Other measured cardiorespiratory variables did not differ significantly between the groups. Visual analogue scores showed no significant difference in chest pain or mask comfort between the groups. The ease of breathing score was, however, significantly better in the continuous positive airways pressure group, 7.5 (SD 1.8) cm and control 5.6 (SD 2.6) cm.

Bioimpedance versus thermodilution cardiac output measurement: The bomed NCCOM3 after coronary bypass surgery

Values obtained for cardiac output (CO) were compared using thermodilution (TD) with those obtained using bioimpedance (Bi) as measured using the Bomed NCCOM3 (Revision 6) in 28 consecutive patients in the first 24h after coronary artery bypass surgery (CABS). In 46 paired measurements made in the first 12 h after CABS Bi values for CO were significantly lower than TD values, the limits of agreement between the two methods were also unacceptably large (mean Bi 4.38 (SD 1.40) l/min, mean TD 5.46 (SD 1.19) l/min, limits of agreement−3.05 to +0.89). In 55 paired measurements made after 12h (all in spontaneously breathing patients) there was no significant difference between the two methods and acceptable limits of agreement, mean Bi 5.69 (SD 1.2) l/min mean TD 5.6 (SD 1.2) l/min, limits of agreement−0.99 to +1.17). The significantly lower BiCO values obtained in the first 12h after CABS show that BiCO measurement is not consistently reliable in the intensive care setting.

The effect of acutely administered phenytoin on vecuronium-induced neuromuscular blockade

Phenytoin was administered intravenously in a dose of 10 mg/kg to a group of patients in whom steady state neuromuscular blockade had been established with an infusion of vecuronium. A control group of patients were given 0.9% saline instead of phenytoin. Administration of phenytoin produced significant augmentation of neuromuscular blockade (p < 0.001). The possible mechanism of this effect is discussed.

Clinical and economic choices in anaesthesia for day surgery: a prospective randomised controlled trial.

Summary We compared the cost‐effectiveness of general anaesthetic agents in adult and paediatric day surgery populations. We randomly assigned 1063 adult and 322 paediatric elective patients to one of four (adult) or two (paediatric) anaesthesia groups. Total costs were calculated from individual patient resource use to 7 days post discharge. Incremental cost‐effectiveness ratios were expressed as cost per episode of postoperative nausea and vomiting (PONV) avoided. In adults, variable secondary care costs were higher for propofol induction and propofol maintenance (propofol/propofol; p < 0.01) than other groups and lower in propofol induction and isoflurane maintenance (propofol/isoflurane; p < 0.01). In both studies, predischarge PONV was higher if sevoflurane/sevoflurane (p < 0.01) was used compared with use of propofol for induction. In both studies, there was no difference in postdischarge outcomes at Day 7. Sevoflurane/sevoflurane was more costly with higher PONV rates in both studies. In adults, the cost per extra episode of PONV avoided was £296 (propofol/propofol vs. propofol/ sevoflurane) and £333 (propofol/sevoflurane vs. propofol/isoflurane).

Anaesthetic agents in adult day case surgery.

This study reports a review of all comparative published studies of adult day case anaesthesia in the English language up to December 2000. Ten databases were searched using appropriate keywords and data were extracted in a standardized fashion. One hundred-and-one published studies were examined. Recovery measurements were grouped as early, intermediate, late, psychomotor and adverse effects. With respect to induction of anaesthesia, propofol was superior to methohexital, etomidate and thiopental, but equal to sevoflurane and desflurane. Desflurane and sevoflurane were both superior to thiopental. There was no detectable difference between sevoflurane and isoflurane. With respect to the maintenance of anaesthesia, isoflurane and halothane were the worst. There were no significant differences between propofol, desflurane, sevoflurane and enflurane. Propofol is the induction agent of choice in day case patients. The use of a propofol infusion and avoidance of nitrous oxide may help to reduce postoperative nausea and vomiting.

The use of propofol for sedation of critically ill patients undergoing haemodiafiltration

ObjectiveTo assess the requirement for propofol to provide sedation in critically ill patients in established renal failure during the commencement of haemodiafiltration.DesignProspective clinical study.SettingICU, University Hospital.Patients10 adult patients. All were mechanically ventilated, had acute oliguric renal failure which necessitated continuous veno-venous haemodiafiltration and were receiving a continuous intravenous infusion of propofol for sedation. Sedation was assessed using a scoring system.InterventionVeno-venous haemodiafiltration.Measurements and resultsConnection of the extracorporeal circuit produced a reduction in plasma propofol concentration in 7 out of 9 patients (one sample misplaced) with subsequent awakening in 3 of these 7 patients. The commencement of haemodiafiltration itself did not significantly influence the requirement for propofol (8 out of 10 patients).ConclusionHaemodiafiltration does not substantially influence the requirement for propofol but the initial introduction of the extracorporeal circuit will reduce plasma concentrations in the majority of patients. This may be due to haemodilution alone or absorption of plasma albumin (with propofol) onto the membrane.

Perturbation of heart rate variability in cattle fed BSE-infected material

The brainstem is the region of the brain of cattle with the highest concentration of the abnormal prion protein associated with bovine spongiform encephalopathy (BSE), and specific nuclei in the medulla oblongata of the brainstem, which exhibit changes as a result of the disease, are involved in the modulation of heart rate variability (HRV). The low- and high-frequency components of the HRV of 48 control cattle, 43 cattle fed 1 g of brain homogenate from BSE field cases and 42 cattle fed 100 g of brain homogenate from BSE field cases were analysed repeatedly for a year. There was a significant difference (P<0.001) between the level of high-frequency HRV observed in the control cattle and in both groups of cattle exposed to BSE. There was also a significant difference (P<0.01) between the low-frequency HRV of the cattle given the high dose and the other two groups.

Obstructive sleep apnoea.

A patient with obstructive sleep apnoea is described, who required admission to an intensive care unit on two separate occasions within 2 months. The first admission was after anaesthesia for operation on the upper airway. The second occurred after a relative overdose of an opioid analgesic was administered. The diagnosis, treatment and anaesthetic management of patients with this syndrome are discussed.

The effect of anaesthetic agents on induction, recovery and patient preferences in adult day case surgery: a 7-day follow-up randomized controlled trial.

Background and objective: To compare induction, pre‐ and post‐discharge recovery characteristics and patient preferences between four anaesthetic regimens in adult day‐surgery. Methods: Randomized controlled trial. In all, 1158 adults assigned to: propofol induction and maintenance, propofol induction with isoflurane/N2O, or sevoflurane/N2O maintenance, or sevoflurane/N2O alone. We prospectively recorded induction and pre‐discharge recovery characteristics, collected 7‐day post‐discharge recovery characteristics using patient diaries and patient preferences by telephone follow‐up. Results: Recruitment rate was 73% ‐ of the 425 refusals, 226 were not willing to risk a volatile induction. During induction, excitatory movements and breath holding were more common with sevoflurane only (P < 0.01). Injection pain and hiccup were more common with propofol induction (P < 0.01). In the recovery room and the postoperative ward, both nausea and vomiting were more common with sevoflurane only (P < 0.01). This difference disappeared within 48 h. There was no difference between groups in the mental state on awakening, recovery time, time to discharge or overnight admissions; then was also no difference in pain between the four groups for each of the seven postoperative days (P < 0.01), nor any differences in concentration or forgetfulness. Patients took 6.5 days (95% CI: 6.0‐7.0, n = 693) to resume normal activities. Patients who received sevoflurane only were more likely to recall an unpleasant induction and least likely to want the same induction method again (P < 0.01). Conclusion: Differences in outcome between the four regimens are transient; sevoflurane is not an ideal sole agent for adult day case anaesthesia and, in this setting, patients base their preferences for future anaesthetics on the method of induction.