Summary At present in the UK there is no consensus regarding the parameters anaesthetists use to indicate adequacy of reversal from neuromuscular blockade. In an attempt to determine current practice, we carried out a survey covering 12 anaesthetic departments throughout the UK. Individuals were asked to give details regarding their usage of available monitors or, alternatively, to list those clinical parameters which they felt offered the best guidance as to the adequacy of recovery from neuromuscular blockade. There was no consensus among anaesthetists as to the most reliable clinical signs of recovery from neuromuscular blockade. There was an apparent lack of understanding of the limitations of some clinical signs used to determine recovery, as well as inappropriate application of others. In all departments where monitors (quantitative or qualitative) were available, there was limited knowledge regarding the current minimum recommended train‐of‐four ratio which should be observed prior to extubation. There is an apparent overall confusion among clinicians as to the best method to confirm recovery from neuromuscular blockade. This is probably due to the lack of a single reliable clinical test which can be applied in the immediate postoperative period. Insufficient reliance is placed upon the use of quantitative monitors. There is a lack of clarity in national anaesthetic guidelines with respect to monitoring of neuromuscular function. Current standards need to be re‐assessed in the light of recent improvements in nerve stimulators.

Recent breakthroughs in molecular biology have enabled a reclassification of drug metabolising enzymes based on their amino acid sequence. This has led to a better understanding of drug metabolism and drug interactions. The majority of these drug metabolising enzymes may be either induced or inhibited by drugs or by extraneous substances including foodstuffs, cigarette smoke and environmental pollutants. Virtually all drugs used in anaesthesia are metabolised by either hepatic phase 1 or phase II enzymes. This review considers the classification of drug metabolising enzymes, explains the mechanisms of enzyme induction and inhibition, and also considers how the action of drugs commonly used by anaesthetists, including opioids and neuromuscular blocking drugs, may be altered by this mechanism. Factors that affect the metabolism of foreign substances (collectively called xenobiotics) include age, sex, hereditary and genetic factors, disease states, dietary and nutritional status, hormonal changes in the body and the activity of liver enzymes. Humans are exposed to a number of environmental substances that are known to affect the activity of liver enzymes. These substances include foodstuffs, medications, recreational substances such as alcohol and tobacco, and pollutants found in the household and in the atmosphere. Recently, our improved understanding of the classification of liver enzymes has enabled us to predict with considerable precision how these substances will affect enzyme function , thus altering drug metabolism. Xenobiotics are broken down by drug metabolising enzymes (DMEs), which are found mainly in the liver and which act by making these substances more water-soluble. Traditionally, these enzymes are designated as being either Phase 1 or Phase II enzymes. Phase I enzymes consist of cytochrome P450 enzymes, previously known as mixed function oxidase enzymes and are responsible for reactions (mainly oxidation and hydroxylation) that alter the existing functional groups to increase water solubility. The cytochrome P450 (CYP) isoenzymes (the name derives from the enzymes' absorption peak at 450 nm; the p signifies pigment) are a family of haemoproteins that are the terminal oxidases of the mixed function oxidase system found on the membranes of the endoplasmic reticulum [1]. The present system of nomenclature for the various CYP isoenzymes employs a three-tiered classification based on the conventions of molecular biology: a numeral and a capital letter designate the amino-acid sequence, with a final number indicating the individual enzyme, e.g. CYP3A4 [2]. Italicised lettering signifies the gene that encodes the enzyme. At present, more than 270 different CYP families have been described across the animal kingdom, with 18 recorded in mammals [3]. In man there are 43 subfamilies and 57 individual enzymes, each of which is encoded by an individual gene. Phase II reactions involve conjugation reactions occurring primarily in the cytosolic (that part of the cytoplasm outside the organelles) fraction of cell...

The morphology of the bone marrow of 21 dentists who habitually used nitrous oxide in their surgeries was investigated. Exposure to nitrous oxide was measured with an atmospheric sampling device, and each dentist was invited to fill in a questionnaire giving details of medical history, diet, and intake of alcohol. During the trial a full neurological and haematological investigation was carried out and a bone marrow aspirate was examined both morphologically and by the deoxyuridine suppression test. Mean exposures to nitrous oxide ranged from 159 to 4600 parts per million. In all subjects serum vitamin B12 and folate concentrations were within normal limits. Abnormal results of deoxyuridine suppression tests were obtained in three of the 20 dentists tested; two of these three had abnormal white cells in their peripheral blood films.This study provides direct evidence that occupational exposure to nitrous oxide may cause depression of vitamin B12 activity resulting in measurable changes in bone marrow secondary to impaired synthesis of deoxyribonucleic acid.

SummaryIn an attempt to quantify the postoperative effects of smoking, 327 consecutive patients undergoing arthroscopic day case knee surgery were given a standard anaesthetic consisting of an intravenous induction with propofol and fentanyl followed by inhalational maintenance using isoflurane in an oxygen and nitrous oxide mixture. Pre-operatively, patients were asked inter alia to give details of social smoking habits. Postoperatively, patients were given standard analgesic and anti-emetic drugs. Prior to discharge patients were asked to give details of postoperative nausea and vomiting together with details of the severity of postoperative pain. There were 85 smokers and 242 nonsmokers. Of the 327 patients, a total of 42 (13%) complained of postoperative nausea and vomiting. Of the smokers, only 6% complained of postoperative nausea and vomiting in contrast to 15% of the nonsmokers (p , 0.05). It is postulated that enzyme induction is the most likely reason for this anti-emetic effect. Possible ways in which this clinically beneficial mechanism can be utilised to improve outcome after anaesthesia are discussed.

SummaryIn a double‐blind study, the effects of positive intra‐operative suggestions on the incidence and severity of postoperative nausea and vomiting were studied in 60 patients randomly selected to undergo routine major gynaecological surgery. Patients who received positive suggestions suffered significantly less nausea and vomiting in the 24 h after surgery.