J. G. Whitwam

The haemodynamic effects of intravenous induction. Comparison of the effects of thiopentone and propofol.

The haemodynamic changes following induction of anaesthesia with equipotent doses of propofol and thiopentone have been compared. Propofol caused a significant fall in arterial blood pressure and total peripheral resistance, with a slight fall in cardiac output. There were no changes in heart rate. Apart from an initial, but statistically insignificant increase in heart rate, similar changes were produced by thiopentone, but to a lesser degree. It is concluded that induction of anaesthesia with propofol results in acceptable haemodynamic changes, but that the agent is more depressant to the cardiovascular system than thiopentone.

Magnetic resonance for the anaesthetist. Part I: Physical principles, applications, safety aspects.

Anaesthetists are being increasingly involved in magnetic resonance (MR) procedures, both in patient care and as a research tool. This paper outlines the physical basis of nuclear magnetic resonance and describes its application in magnetic resonance imaging and spectroscopy. Principles of magnet design and safety relevant to anaesthetic practice in a magnetic resonance environment are discussed and guidelines for anaesthetic practice suggested. Some recent clinical magnetic resonance studies of anaesthetic interest are reviewed.

The current status of pulse oximetry. Clinical value of continuous noninvasive oxygen saturation monitoring.

The history of the development of pulse oximetry is outlined and the principle of how the apparatus works is described. The instrument detects hypoxic hypoxia and the shape of the oxygen dissociation curve means that the minimum saturation alarm should be set at 94% in anaesthetic usage. It is accurate to within 2% and is usually unaffected by racial pigmentation, but accuracy can be aflected in low perfusion states, hypotherrnia and in the presence of abnormal forms of haemoglobin and pigments in the blood. Its clinical evaluation in the operating theatre and intensive care unit is reported. It was found to be useful and reliable and would appear to have logistical and other advantages over current methods of detecting hypoxia. Pulse oximetry may make a signijcant contribution to the safety of anaesthetic practice.

True patient‐controlled sedation

A modified patient‐controlled analgesia pump provided doses ofpropofol 3 mg or midazolam 0.1 mg in 0.3 ml, over 5.4 s, with no lockout, during transvaginal oocyte retrieval. Alfentanil 0.2 mg was administered at three points during the procedure, and on request. Patients were randomly assigned to receive either propofol (25 patients) or midazolam (22 patients). The mean age, weight, duration of procedure and dose ofalfentanil were similar in both groups. Onset of sedation with propofol or midazolam took 70.6 (SD 22.4) and 106.3 (50.7) s respectively. Mean doses over the first 5 min were midazolam 2.7 (1.2) mg, and propofol 54 (18) mg. Thereafter requirements decreased: midazolam 0.065 (0.065) mg.min−1, propofol 2.1 (1.3) mg.min−1. All patients successfully completed the procedure; none required additional sedation. P‐deletion, reaction time, and critical flicker fusion tests revealed similar depression in both groups immediately postoperatively. After 30 min the p‐deletion and critical flicker fusion scores were still impaired in the midazolam, but not in the propofol, group.

Magnetic resonance for the anaesthetist. Part II: Anaesthesia and monitoring in MR units.

Anaesthetists are increasingly involved in patient care during magnetic resonance imaging and spectroscopy. This paper describes a system which has been developed for the management of critically ill patients and the conduct of anaesthesia in a magnetic resonance unit with a 1.6 tesla whole body magnet. Difficulties which arise from working in a confined space in a high magnetic field are highlighted. Different approaches to anaesthesia, sedation and the modification of equipment for use in this environment are reviewed. The problems associated with patient monitoring within a magnetic field are discussed and some solutions are suggested. A transport system for critically ill patients is described and a protocol for management is outlined.

Pharmacology of flumazenil

Flumazenil, an imidazobenzodiazpine, is the first benzodiazepine antagonist available for clinical use. It is a specific competitive antagonist at benzodiazepine receptors, which are associated with receptors for gammaaminobutyric acid, the most important inhibitory neurotransmitter in the central nervous system. Administered orally, it has a low bioavailability and the preferred route is intravenous. Its usual clinical role is to reverse the effects of benzodiazepine sedation; however, administered before, or with, other benzodiazepines, it modifies their effects, the extent of such modification depending on the dose, duration of effect and relative receptor affinity of the agonist. Flumazenil also reverses adverse physiological effects of benzodiazepines. Its indications include reversal of benzodiazepine‐induced sedation, termination of benzodiazepine‐induced anaesthesia, return of spontaneous respiration and consciousness in intensive care patients and the treatment of paradoxical reactions to benzodiazepines. Other potential indications include its use in hepatic encephalopathy, alcohol intoxication and coma; however, these claims still require substantiation. Following sedation reversed with flumazenil, minimal residual effects of the agonist can sometimes be detected using psychomotor tests and are due to the relatively short half‐life of flumazenil, but are of no clinical consequence. There is concern that flumazenil could precipitate an acute withdrawal syndrome following long‐term benzodiazepine administration; however, the available evidence suggests otherwise and that it could be useful in the treatment of benzodiazepine tolerance. The existence of flumazenil is important, with implications for future research and the development of minimally invasive therapy and day‐case surgery. With increasing pressures on non‐anaesthetically trained practitioners to perform sedation, flumazenil has important implications for safety.

Midazolam and diazepam for gastroscopy

Midazolam 0.1 mg/kg was compared with diazepam 0.15 mg/kg intravenously in patients undergoing gastroscopy. The patients receiving midazolam were more sedated at the end of the procedure. The mean discharge times from the clinic for diazepam and midazolam patients were 85 and 102 minutes, respectively. The principal differences between the two drugs were that midazolam had a faster rate of onset, was virtually free from venous complications, provided much better amnesia (90% compared with 50%), and although the recovery time was longer with midazolam, the rate of recovery during the period of observation was faster. Neither drug caused any significant cardiorespiratory depression.

C‐reactive protein in patients undergoing cardiac surgery

Among 25 patients undergoing cardiac surgery with the aid of cardiopulmonary bypass, 13 who recovered uneventfully all had normal (< 2 mg/litre) levels of serum C‐reactive protein pre‐operatively. In contrast, 10 of the 12 patients who suffered from various postoperative complications, including two who died, had abnormally raised levels of C‐reactive protein pre‐operatively. AN patients showed a major acute phase response to surgery with peak C‐reactive protein levels at about 46 hours but, whereas the uncomplicated cases showed a characteristic smooth biphasic pattern of declining levels thereafter, the complicated cases all exhibited significant alterations of this pattern. The occurrence during the postoperative period of a secondary rise in C‐reactive protein or the failure of the level to continue falling, generally preceded clinical evidence of intercurrent infection. Pre‐operative measurement of serum C‐reactive protein may thus make a valuable contribution to the assessment of patients requiring elective cardiac surgery; regular postoperative monitoring can provide early warning of serious complications.

Acute cardiovascular changes following disoprofol. Effects in heavily sedated patients with coronary artery disease.

The acute cardiovascular changes following induction of anaesthesia with disoprofol 2 mg/kg have been studied in eight heavily premedicated patients with coronary artery disease. There was a significant increase in heart rate (+ 19%) and significant falls in mean arterial blood pressure (− 23%), peripheral vascular resistance (− 19%) and stroke volume (− 26%). Cardiac output did not change significantly. The extent and pattern of these changes are very similar to those seen after other intravenous induction agents.

Crystalloid versus colloid for circulatory preload for epidural Caesarean section

Sixty mothers were randomly allocated to receive either 2 litres of crystalloid or 1 litre of colloid solution (hydroxyethyl starch) in order to preload the circulation prior to elective Caesarean section under epidural anaesthesia. There were no differences in the incidence of hypotension, degree of haemodilution, umbilical cord blood gas tensions or umbilical blood osmolalities between the two groups.