An evaluation of factors influencing the assessment time in a nurse practitioner-led anaesthetic pre-operative assessment clinic.

Elective patients undergoing anaesthetic pre-operative assessment are usually allocated the same period of time with a nurse practitioner, leading to potential inefficiencies in patient flow through the clinic. We prospectively collected data on 8519 patients attending a pre-operative assessment clinic. The data set were split into derivation and validation cohorts. Standard multiple regressions were used to construct a model in the derivation cohort, which was then tested in the validation cohort. Due to missing data, 2457 patients were not studied, leaving 5892 for analysis (3870 in the derivation cohort and 2022 in the validation cohort). The mean (SD) pre-operative assessment time was 46 (12) min. Age, ASA physical status, nurse practitioner and surgical specialty all influenced the time spent in pre-operative assessment. The predictive equations calculated using the derivation cohort, based on age and ASA physical status, correctly estimated duration of consultation to within 20% of the maximum predicted time in 74.2% of the validation cohort. We conclude that if age and ASA physical status are known before the pre-operative assessment consultation, it could allow appointment times to be allocated more accurately.

Adverse effects of general anaesthetics.

This review deals with the adverse reactions associated with general anaesthetic agents in current use. These reactions fall into 2 categories; those which are more common, predictable and often closely related, and those which are rare, unpredictable and carry a high mortality. Both inhalational and intravenous anaesthetic agents affect the central nervous and cardio-respiratory systems in a dose-related manner. Neuronal inhibition results in decreasing levels of consciousness and depression of the medullary vital centres which can lead to cardiorespiratory failure. Both groups of agents have some depressant effect on the myocardium and vascular smooth muscle leading to a fall in cardiac output and hypotension. Centrally-mediated respiratory depression is common to both groups and the inhalational agents have a direct effect on lung physiology. The most important idiosyncratic reactions to the volatile agents are malignant hyperpyrexia and 'halothane hepatitis'. Malignant hyperpyrexia has an incidence of 1:12,000 with a mortality of about 24%. It is triggered most often by halothane together with suxamethonium. Post halothane hepatic necrosis is rare. Evidence points to 2 distinct syndromes; direct toxicity from the products of reductive metabolism, and a more serious illness, immunologically mediated via haptens formed by liver proteins and the products of oxidative metabolism. Prolonged nitrous oxide exposure can cause bone marrow depression and life-threatening pressure effects by expansion of air-filled spaces within the body. The idiosyncratic reactions to the intravenous agents include anaphylactoid reactions (which are rare) and triggering of acute porphyria. Etomidate is immunologically 'clean', but it inhibits cortisol synthesis.

Effectiveness of preoxygenation in morbidly obese patients.

The time taken for the oxygen saturation (SpO2) to decrease to 90% after preoxygenation was studied in six morbidly obese patients and six matched controls of normal weight. During apnoea the obese patients maintained Spo2 greater than 90% for 196 (SD 80) s (range 55-208 s), compared with 595 (SD 142) s (range 430-825 s) in the control group (P less than 0.001). One patient in the obese group had desaturation before the onset of complete relaxation and tracheal intubation, without complications. Bedside lung function tests were not significantly different between groups and cannot be used as a predictor of the effectiveness of preoxygenation.

Effectiveness of continuous positive airway pressure to enhance pre-oxygenation in morbidly obese women.

Morbid obesity is associated with a reduction in time to desaturate during apnoea following standard pre-oxygenation and induction of anaesthesia. We have compared the effects of using 7.5 cmH2O of continuous positive airway pressure (CPAP) for pre-oxygenation with a standard technique using a Mapleson A breathing system, in 20 morbidly obese women. In a prospective, open, randomised trial, we measured the time taken to desaturate to 90% from time of giving a succinylcholine bolus as part of a rapid induction of anaesthesia. All patients received 3 min pre-oxygenation prior to induction. Tracheal intubation was confirmed and all patients kept apnoeic until oxygen saturation decreased to 90%. No statistically significant difference in mean time to desaturate to 90% could be demonstrated in the CPAP group compared to the Mapleson A group (240 s and 203 s, respectively). A brief period of lower mean heart rate in the CPAP group was the only statistically significant difference in cardiovascular parameters. There was no significant difference in the volume of gastric gas after induction between groups.

Comparison of infusion rates of three i.v. anaesthetic agents for induction in elderly patients.

We have compared the effect of different rates of injection of 2.5% thiopentone, 0.5% methohexitone and 0.2% etomidate for induction of anaesthesia in 90 premedicated, elderly patients. The agents were administered by infusion pump at rates of 1200 ml h-1, 600 ml h-1 and 300 ml h-1, respectively until anaesthesia was induced as judged by loss of verbal contact with the patient. The times for induction were significantly greater with the slower infusion rates (thiopentone 41 s, 57 s and 91 s (P < 0.001); methohexitone 44 s, 62 s and 84 s (P < 0.01); etomidate 48 s, 59 s and 87 s (P < 0.001)). The doses were significantly smaller (P < 0.001) with the slower infusion rates for all three agents (thiopentone 5.0, 3.7 and 2.8 mg kg-1; methohexitone 1.00, 0.75 and 0.56 mg kg-1; etomidate 0.26, 0.15 and 0.11 mg kg-1). For each drug there was no significant difference in induction characteristics, oxygen saturation, heart rate or mean arterial pressure, at the different infusion rates.