The role of new anesthetic agents.

The three anesthetic drugs introduced most recently to the market are sevoflurane, desflurane, and ropivacaine. Sevoflurane and desflurane are both inhalational anesthetic agents and ropivacaine is a local anesthetic agent. Sevoflurane provides a rapid onset and offset of action; it is well tolerated with little airway irritation. It is hemodynamically stable, with low potential for toxicity. Concerns about its interaction with soda lime during low-flow anesthesia with the production of Compound A have not proved to be a clinical problem. While desflurane also provides rapid onset and recovery from anesthesia, it is not as hemodynamically stable as sevoflurane, and also causes airway irritation. Ropivacaine is a unique local anesthetic in that it is supplied as the pure S-enantiomer. It is at least as effective as bupivacaine, with lower toxicity and less motor block for the same degree of sensory block.

The effect on the rat isolated atria of amiodarone in the presence of either ouabain or verapamil.

Amiodarone causes a decrease in the rate of contraction of the rat isolated atria and has a negative inotropic action in the paced preparation. Interactions occur between amiodarone and ouabain and amiodarone and verapamil. It is possible that the clinically reported drug interaction with amiodarone may have a component of direct interactions on the myocardium rather than solely changes in plasma protein binding.

Anaesthesia for laparoscopy: alfentanil and fentanyl compared.

A double blind comparison was made between alfentanil and fentanyl as analgesic components of anaesthesia. Sixty-six women undergoing laparoscopy received methohexitone, alcuronium, nitrous oxide and oxygen, with either alfentanil 0.75 mg or fentanyl 0.25 mg. Ten of the patients who received alfentanil and 1 patient who received fentanyl required supplementation of anaesthesia by enflurane. Recovery from anaesthesia was similar in the two groups of patients though the onset of spontaneous breathing occurred more quickly after alfentanil (P less than 0.002). The injection of fentanyl was followed by a fall in BP (P less than 0.05) and the mean minimum value for pulse rate occurring after fentanyl was slower than after alfentanil (P less than 0.05).

Postoperative nausea and vomiting: a comparison of anti-emetic drugs used alone or in combination.

Drugs with anti-emetic properties can exert their actions at more than one receptor site, histamine H1, muscarinic cholinergic or dopaminergic D2 receptors. This study was designed to test the hypothesis that a combination of drugs acting at different receptor sites in lower than standard doses would be at least as effective as a standard therapeutic dose of a single anti-emetic agent. A combination of droperidol, hyoscine and metoclopramide in subtherapeutic doses has been shown to be at least as effective as droperidol (1.25 mg) alone. In both groups there was a low incidence of emetic sequelae in the first 3 hours postoperatively.

Propofol ('Diprivan') for outpatient cystoscopy. Efficacy and recovery compared with althesin and methohexitone.

In two non-concurrent investigations, propofol was compared with methohexitone and with Althesin as an intravenous anaesthetic for cystoscopy in outpatients. In the comparison between propofol and methohexitone the 60 patients also received alfentanil in similar dosage; in comparison with Althesin (43 patients) the Cremophor formulation of propofol was used. During induction of anaesthesia propofol caused fewer excitatory effects than either methohexitone or Althesin, and less pain than methohexitone. There was no difference in the incidence of apnoea caused by propofol 1.5 mg/kg and Althesin 0.05 ml/kg, or propofol 2 mg/kg and methohexitone 1.5 mg/kg. Induction of anaesthesia by propofol was faster than that by Althesin. The use of alfentanil 7 micrograms/kg at induction of anaesthesia apparently increases the incidence of apnoea seen at that time and during maintenance of anaesthesia, but an overall dose of approximately 1 mg reduces the mean dose of propofol required from 0.459 mg/kg/min to 0.192 mg/kg/min and improves the quality of anaesthesia. During maintenance of anaesthesia propofol produced less myoclonia and movement than Althesin, and fewer hiccups than methohexitone, but the mean minimum systolic arterial pressure observed in the propofol group was less than that seen in the methohexitone group. Immediate recovery of consciousness was faster and better after propofol than methohexitone, and fewer complications were seen after propofol than Althesin. Recovery of coordination and perception, tested by the digit substitution test, was faster after propofol than methohexitone. Exact comparisons of recovery of ocular tone (Maddox Wing test) between the anaesthetics were not possible as both Althesin and methohexitone rendered some patients incapable of taking the tests in the early post-operative period. In response to a take-home questionnaire, patients stated that they were drowsy for a shorter time, and ate earlier after propofol than after methohexitone. No patient who received propofol vomited or was nauseated and all would wish to receive the same anaesthesia again. The studies suggest that propofol is preferable to both Althesin and methohexitone for intravenous anaesthesia for cystoscopy in outpatients.

Premedication by controlled-release morphine.

In a double-blind investigation the effect of oral controlled-release morphine (MST 30 mg) on pre-operative anxiety was assessed in 50 patients undergoing cholecystectomy. The effects on anaesthetic requirements and recovery, and postoperative pain were also studied. The patients who received morphine treatment were more sedated than those who received the placebo; however there was no significant difference in the anxiety scores for both groups of patients. During anaesthesia there were no significant differences between the groups, although the group of patients who received morphine required less anaesthetic supplement, and appeared to recover more slowly than the placebo group. One hour postoperatively, the morphine group had significantly less pain and were more sedated than the placebo group; the time to the administration of a postoperative analgesic was also significantly longer in the morphine group than the placebo group.

The Mancunian way.

The authors have examined early records of the administration of ether anaesthesia in Manchester and the lives of several medical men involved in these events. Charles Strange, a dentist and chemist, in a letter to the Manchester Guardian published on 14 January 1847, described a self-administration of ether for dental extraction, but George Bowring, a surgeon, subsequently claimed the first anaesthetic administered by a doctor in Manchester. The merits of these claims are discussed in the light of the circumstances surrounding these events.

The additional work of breathing through Portex Polar 'Blue-Line' pre-formed paediatric tracheal tubes.

The work of breathing through north- and south-facing Portex Polar 'Blue-Line' paediatric tracheal tubes of sizes 3.0-7.0 mm ID has been measured using sinusoidal flow at equivalent ventilatory rates of 10-50 breaths min-1 with tidal volumes of 10-500 ml. North-facing tubes are designed to sit with the connection on the forehead after intubation, whilst south-facing ones are designed so that the connection sits on the chin of the patient. It was found that the total work of breathing through north-facing tubes is approximately 8% higher than the total work of breathing through south-facing tubes of the same size, irrespective of tidal volume or respiration rate. The total work of breathing was dependent on total tube length but independent of tube design. The endotracheal connectors themselves were found to contribute a significant proportion of the total work of breathing but there was no significant difference between the inspiratory and expiratory performance of the tubes.

Aminoglycoside antibiotics and sympathetic ganglionic transmission.

The effects of streptomycin, gentamicin, tobramycin and amikacin on transmission in sympathetic ganglia have been studied using the guinea pig isolated hypogastric nerve-vas deferens preparation. These aminoglycoside antibiotics produce dose-related sympathetic blockade at concentrations greater than the common therapeutically effective antibiotic concentrations.

A comparison of the antibacterial properties of six local analgesic agents.

The effect of six local analgesic drugs on bacterial growth is reported. Amethocaine proved to be the only effective antibacterial agent.

Tobramycin and neuromuscular transmission in the rat isolated phrenic nerve-diaphragm preparation.

The effects of different concentrations of tobramycin, streptomycin, neomycin and gentamicin on the rat isolated phrenic nerve-diaphragm preparation are reported. Streptomycin, neomycin and gentamicin produced dose-dependent neuromuscular blockade. Tobramycin increased the muscle response at high concentrations (6.4 X 10(-4) - 2.6 X 10(-2) mol litre-1, but had no detectable effect when used in therapeutically recommended concentrations.

Muscle fibrillation following thiopentone and pancuronium bromide. An association with metachromatic leucodystrophy.

A case is reported of muscle 'gibrillation' following the administration of thiopentone and pancuronium to a patient suffering from metachromic leucodystrophy and possible mechanisms are discussed.

In vitro comparison between the neuromuscular and ganglion blocking potency ratios of atracurium and tubocurarine.

Results from in vitro experiments, using the hypogastric nerve--vas deferens preparation, and the phrenic nerve--hemidiaphragm preparation of the guineapig, have been used to determine the separation between the neuromuscular and ganglionic blocking effects of atracurium and tubocurarine. Regression lines were used to calculate the concentrations of each drug (99% confidence limits) which would produce a 50% blockade (EC50) of ganglionic and neuromuscular transmission. The equipotent molar ratio, using EC50 values, for ganglionic/neuromuscular blockade was 48 for atracurium and 9.4 for tubocurarine.

Anaesthesia and demyelinating disease.

The demyelinating diseases are classified and the current concepts of the aetiology and pathophysiology of the most common of these diseases, multiple sclerosis, are described. The effects of the impaired function, local responses and known complications of the disease on the choice of anaesthetic, drugs and techniques are discussed.