A.R. Aitkenhead

Incidence of awareness with recall during general anaesthesia

One thousand patients who were anaesthetised between February and April 1990 at University Hospital, Nottingham were interviewed between 20 and 36 hours after their operation. Patients under 16 years of age, those who had undergone obstetric or intracranial surgery, those who were unable to communicate and patients who were discharged from hospital before the postoperative visit were not interviewed. A standard set of questions was used to determine the incidences of recall of events and dreams during the operation. These incidences were 0.2% and 0.9% respectively, considerably lower than reported in previous comparable studies.

COMPARISON OF PROPOFOL AND MIDAZOLAM FOR SEDATION IN CRITICALLY ILL PATIENTS

101 critically ill patients admitted to five intensive-care units were allocated randomly to receive a continuous intravenous infusion of either propofol or midazolam for sedation for up to 24 h. In addition, morphine was given to provide analgesia. The mean duration of infusion was 20.2 h (range 3.0-24.5) in the propofol group and 21.3 h (4.0-47.0) in the midazolam group and infusion rates were 1.77 mg/kg/h (range 0.40-5.00) and 0.10 mg/kg/h (0.01-0.26), respectively. The infusion rates were adjusted as necessary, and the desired level of sedation was achieved easily in most patients in both groups. There were slight falls in arterial pressure, but there were no significant differences between the groups. Heart rate was lower in patients who received propofol. Some small changes occurred in biochemical and haematological variables in both groups, but they were not clinically significant. There was no indication that either drug substantially impaired adrenal steroidogenesis. When the infusion was discontinued, there was less variability in recovery of consciousness in patients who had received propofol. In a subgroup of patients, weaning from mechanical ventilation was achieved significantly faster after discontinuation of propofol than of midazolam. Propofol proved to be a satisfactory agent for sedation of these critically ill patients and compared favourably with midazolam.

Comparison of endotracheal and peripheral intravenous adrenaline in cardiac arrest. Is the endotracheal route reliable

Twelve patients presenting to an accident and emergency department in asystolic cardiac arrest were randomly allocated to treatment with endotracheal adrenaline (five patients) or peripheral intravenous adrenaline (seven patients). Femoral-artery blood samples were taken for assay of adrenaline and noradrenaline. After intravenous adrenaline there was a good clinical and biochemical response, but after endotracheal adrenaline there was no change in serum adrenaline and no measurable clinical response. The endotracheal route of adrenaline administration is not reliable in out-of-hospital cardiac arrest.

Low‐flow anaesthesia

Although many anaesthesia machines are equipped with circle rebreathing systems, inhalational anaesthesia remains frequently performed using relatively high fresh‐gas flows. The major advantages of rebreathing techniques can be achieved only if the fresh‐gas flow is reduced to 1 l.min‐1 or less. Although there are potential risks associated with low‐flow anaesthesia, modern anaesthesia machines meet all the technical requirements for the safe use of low‐flow techniques if they are used in conjunction with equipment for monitoring inhaled and exhaled gas concentrations; these monitors are already increasingly available and, in the near future, are likely to become an obligatory safety standard in many countries. For both economic and ecological reasons, the use of new inhalational anaesthetics, with low tissue solubility and low anaesthetic potency, can be justified only if the efficiency of administration is optimised by using low‐flow anaesthetic techniques.

A comparison between propofol and desflurane anaesthesia for minor gynaecological laparoscopic surgery

Fifty‐seven healthy female patients who underwent gynaecological laparoscopic surgery received either desflurane or propofol for induction and maintenance of anaesthesia. Inhalational induction was generally well tolerated, and consciousness was lost in approximately 2 min (mean end‐tidal concentrations of desflurane were 8.3% with 60% nitrous oxide, and 7.1% with oxygen). Recovery of consciousness and orientation were more rapid in patients in whom anaesthesia was maintained with desflurane than with propofol, but there were no differences in psychomotor function test scores at 30 min. The data suggest that desflurane provides controllable anaesthesia and rapid recovery of consciousness after laparoscopic surgery.

Factors determining the onset and course of hypoxemia during apnea: an investigation using physiological modelling.

We used the Nottingham Physiology Simulator to examine the onset and course of hypoxemia during apnea after pulmonary denitrogenation. The following factors, as possible determinants of the hypoxemia profile, were varied to examine their effect: functional residual capacity, oxygen consumption, respiratory quotient, hemoglobin concentration, ventilatory minute volume, duration of denitrogenation, pulmonary venous admixture, and state of the airway (closed versus open). Airway obstruction significantly reduced the time to 50% oxyhemoglobin saturation (8 vs 11 min). Provision of 100% oxygen rather than air to the open, apneic patient model greatly prolonged time to 50% oxyhemoglobin saturation (66 vs 11 min). Hemoglobin concentration, venous admixture, and respiratory quotient had small, insignificant effects on the time to desaturation. Reduced functional residual capacity, short duration of denitrogenation, hypoventilation, and increased oxygen consumption significantly shortened the time to 50% oxyhemoglobin saturation during apnea. Implications: Reduction in oxygen levels during cessation of breathing is dangerous and common in anesthetic practice. We used validated, mathematical, physiological models to reveal the impact of physiological factors on the deterioration of oxygen levels. This study could not be performed on patients and reveals important information.

Simple method for the determination of morphine and its active glucuronide metabolite in human plasma by high-performance liquid chromatography with electrochemical detection

A simple method for the simultaneous determination of morphine and its pharmacologically active metabolite morphine-6-glucuronide in 0.5 ml human plasma is described. It is based on the method of Svensson [J. Chromatogr., 230 (1982) 427 and 375 (1986) 174], but uses only one solid-phase extraction cartridge prior to chromatography and only a 20-microliter injection volume. Mean recoveries of 90 and 85% for morphine and morphine-6-glucuronide, respectively, were obtained, the limit of detection being 2 nmol/l (at a signal-to-noise ratio of 3.0).

Effect of morphine on gastric emptying

expiratory valve closed and the reservoir bag inflated. Pressure on the bag will then test the integrity of the whole system (Fig. 2a). The obturator is then reversed and both limbs are thus occluded. With the expiratory valve open there should be no gas escape on applying pressure to the inflated reservoir bag (Fig. 2b). However, if the inner limb is defective the bag collapses and gas escapes through the expiratory valve (Fig. 2c).

A comparison of droperidol and cyclizine in the prevention of postoperative nausea and vomiting associated with patient-controlled analgesia

Fifty ASA 1 or 2 patients scheduled to undergo major gynaecological surgery were allocated randomly to one of two groups. All patients received a standard anaesthetic regimen. Patients in group 1 received droperidol 1.25 mg given intravenously 20min prior to the end of surgery and a patient‐controlled analgesia infusion containing morphine 1 mg.ml‐1 and droperidol 0.05 mg.ml‐1. Patients in group 2 received cyclizine 50 mg by slow intravenous injection 20 min prior to the end of surgery and a patient‐controlled analgesia infusion containing morphine 1 mg.ml‐1 and cyclizine 2 mg. ml‐1. Fifteen of 25 patients (60%) in group 1 and 18 (72%) of 25 in group 2 suffered no nausea or vomiting postoperatively. Two patients (8%) in group 1 and three (12%) in group 2 suffered severe postoperative nausea or vomiting. We conclude that cyclizine is as effective as droperidol in the prevention of postoperative nausea and vomiting when included in a patient‐controlled analgesia infusion using morphine.

Survey of intrathecal opioid usage in the UK

Background and objective: Intrathecal opioids are now used routinely in the UK for intra‐ and postoperative analgesia. The opioids of choice have altered over recent years and the dosage regimens used can vary between institutions. Concerns over safety have been reduced probably because much lower doses of opioids are now being used. This survey explored the practice of intrathecal opioid usage in the UK. Methods: We sent a questionnaire survey to 270 anaesthetic departments and received 199 replies, a response rate of 73.7%. Results: Intrathecal opioids were used in 175 (88.4%) departments. Of these departments, 107 (61.1%) had local guidelines or protocols in place. Opioids such as diamorphine (used in 136 (78.2%) of departments) and fentanyl (129 (74.1%)) with a shorter duration of action are now more commonly used than morphine (37 (21.3%)) for intrathecal analgesia. In 96 (54.5%) departments, patients were nursed on regular surgical wards following administration of spinal opioids. Conclusions: The use of low‐dose lipophilic intrathecal opioids for postoperative analgesia is widespread in the UK. Patients are commonly nursed in low‐dependency post‐anaesthetic care areas. The low incidence of adverse events reported by the respondents along with the popularity of the technique suggests that low‐dose spinal opioid administration is safe.