Biomedical subjects
C S Aun
Publications and source records attributed to C S Aun.
Computer-controlled infusion of propofol for long neurosurgical procedures.
This study evaluated the performance of a computer-controlled infusion (CCI) system for propofol during long neurosurgical procedures. Anesthesia was induced and maintained in 15 patients using a CCI of propofol. The initial target concentration was set at 3 micrograms/ml, and this was then titrated according to the clinical situation. A total of 284 blood samples were taken for propofol assay. The performance of the system during anesthesia, assessed using the median performance error (MDPE), median absolute performance error (MDAPE), wobble, and divergence, were -5.3%, 20.6%, 9.0%, and 0.3%/h, respectively. MDPE and MDAPE during the first 20 min after stopping the infusion were -38.7% and 39.0%, respectively. The CCI system did not show significant changes in predictive ability, with time during anesthesia lasting up to 12 h. Changes in the measured blood concentration were in the same direction as changes in the target concentration.
Transient femoral nerve palsy after ilioinguinal block.
Explore the source record for details and available documents.
Anaesthesia for stenting tracheal stenosis.
Explore the source record for details and available documents.
A prospective evaluation of pharmacokinetic model controlled infusion of propofol in paediatric patients.
We have tested a published algorithm for pharmacokinetic model controlled infusion of propofol to supplement 67% nitrous oxide for general anaesthesia in Chinese children aged 4-10 yr. Initially we studied 10 children undergoing minor procedures with spontaneous ventilation; mean duration of surgery was 38 min and mean propofol infusion rate 497 micrograms kg-1 min-1. The precision of the model was 24.8% and bias -18.5%. The model was revised using an iterative linear least squares regression procedure and the revised model tested prospectively in another 20 children. The precision of the revised model was 21.5% (range in individuals 8.4-43.1%) and bias -0.1% (range -30 to 42%). Mean propofol infusion rate required to maintain anaesthesia was 474 micrograms kg-1 min-1 (range 125-737 micrograms kg-1 min-1). The mean blood concentration required for satisfactory anaesthesia was 6.6 micrograms ml-1 (range 3-11 micrograms ml-1) and the mean blood concentration at the time of waking, which occurred 40 min after switching off the infusion, 0.86 microgram ml-1 (range 0.40-1.45 micrograms ml-1). Our patient population required different pharmacokinetic variables from those in the previous study. Recovery was slow because of the high infusion rates required to maintain satisfactory anaesthesia and large difference between the blood concentration required for anaesthesia and that at which waking occurred.
Recovery after propofol infusion anaesthesia in children: comparison with propofol, thiopentone or halothane induction followed by halothane maintenance.
We have compared the recovery profiles of 163 healthy Chinese children after general anaesthesia for minor surgical procedures. Patients were allocated randomly to receive one of four anaesthetic techniques: propofol infusion for induction and maintenance using a pharmacokinetic model-controlled syringe pump set initially at a target concentration of 8 micrograms ml-1 and then adjusted according to clinical requirements; propofol 2.5-3.5 mg kg-1, thiopentone 4-5 mg kg-1 or 2-3% halothane for induction of anaesthesia followed by 1-2% halothane for maintenance of anaesthesia. All patients breathed a mixture of 70% nitrous oxide in oxygen through a laryngeal mask airway and received an appropriate regional anaesthetic block. Recovery was assessed using the time to achieve full Steward score, open eyes on command, orientation and the time required to complete a simple puzzle. Recovery was slowest with the propofol infusion (mean 39.8 (SD 12.9) min when eyes opened on command). The recovery times were significantly shorter with the three other techniques (propofol bolus 21.9 (9.9) min, thiopentone 23.4 (11.3) min, halothane 20.1 (8.9) min), and the choice among these three methods had no significant influence on the recovery profile.
Preoperative fasting in children.
The development of new preoperative fasting guidelines in paediatrics was reviewed in the light of present knowledge and some recent investigations. Although the proportion of healthy children with the potential risk of aspiration pneumonitis is relatively high (60-75%), the incidence of aspiration is low--1 to 8.6 in 10,000. In healthy children, there is no increase in the risk of aspiration by allowing them to drink clear fluids up to 2-3 hours before anaesthesia when compared with the conventional fasting regimen. The children are less thirsty and less irritable. The occurrence of hypoglycaemia and hypovolaemia in small infants may also be reduced. However, it is essential to identify high risk cases by clinical judgement and to treat them differently in their management. It is useful to have simple and explicit preoperative fasting instructions for parents to follow, especially in the day case setting. It is essential to note that the laryngeal mask airway (LMA) does not protect the patient's airway against the risk of regurgitation and aspiration of gastric contents in the same way as an endotracheal tube. Hence, constant vigilance is required when LMA is used in children.
The respiratory depressant effect of morphine. A comparative study in three ethnic groups.
The respiratory response to carbon dioxide was measured in 130 ASA 1 adult male patients from three ethnic groups, European, Nepalese, and Chinese, both before and after premedication with intramuscular morphine sulphate (200 micrograms.kg-1 body weight). Satisfactory results were obtained from 125 patients. Overall, there was no ethnic difference in the effect of morphine on the respiratory response to carbon dioxide, but initially the Chinese group appeared to be more sensitive in their response to carbon dioxide than the Europeans and Nepalese. However, there was a significant correlation between respiratory response to carbon dioxide and pulse rate and on restricting analysis to those patients with a pulse rate equal to or less than 72 beat.min-1, the ethnic difference in carbon dioxide response disappeared. It was concluded that there were no ethnic differences in the respiratory response to carbon dioxide before or after morphine in male Europeans, Nepalese and Chinese but that the respiratory response to carbon dioxide may be influenced by long term physical training.
Cardiovascular effects of i.v. induction in children: comparison between propofol and thiopentone.
We have compared the haemodynamic responses to i.v. propofol 2.5 mg kg-1 with those to thiopentone 5.0 mg kg-1 in 41 healthy Chinese children at induction of anaesthesia. They were allocated to four groups according to their age and induction agent received: group 1 < 2 yr, propofol, n = 9; group II < 2 yr, thiopentone, n = 9; group III 2-12 yr, propofol, n = 12; group IV 2-12 yr, thiopentone, n = 11. Anaesthesia was maintained by spontaneous ventilation with 70% nitrous oxide and 0.5% halothane in oxygen. Arterial pressure and heart rate were monitored by automatic oscillotonometer. Stroke volume was measured by two-dimensional echocardiography and pulse Doppler. Measurements were made before induction and at 1-min intervals for 5 min after induction. The reduction in mean arterial pressure was significantly greater after propofol (28-31%) than after thiopentone (14-21%) (P = 0.001). The reduction in cardiac index (10-15%) after induction was not significantly different between the two agents (P = 0.122). Baroreflex mediated increases in heart rate and systemic vascular resistance were less after propofol than after thiopentone. The baroreceptor reflex was more attenuated in children aged less than 2 yr than in older children.
Suxamethonium myalgia: an ethnic comparison with and without pancuronium pretreatment.
The incidence of myalgia after suxamethonium was determined in 200 fit military male dental patients of European, Chinese and Nepalese descent. Half received pancuronium 1 mg and the other half received saline pretreatment on a randomised double-blind basis. The percentage incidence of postsuxamethonium myalgia after saline or pancuronium was found to be: Europeans 26%, 13%; Chinese 13%, 7%; Nepalese 20%, 14%. Although pancuronium reduced the incidence of myalgia by about 50% overall, these values were not significantly different from each other. The recovery of spontaneous ventilation following suxamethonium was quicker in the Europeans than in the Asians (p < 0.05). Pancuronium pretreatment also delayed the recovery of spontaneous ventilation and recovery from neuromuscular block (p < 0.05) but this was independent of ethnicity. The Europeans recovered from anaesthesia more quickly than the Asians. It was concluded that ethnicity affected recovery from suxamethonium and from anaesthesia but was not of clinical relevance to the incidence of myalgia in male Asians and Europeans.
Pethidine pharmacokinetics in a heroin addict: a case report.
Tolerance to some of the pharmacological actions of the opiates in drug addicts is well known. This report illustrates the effect on the pharmacokinetics of pethidine of heroin addiction compared with a well-matched control population.
Minimum alveolar concentration of halothane: an ethnic comparison.
The minimum alveolar concentration (estimate of spread) of halothane which was determined in 42 Chinese, Nepalese or European patients was found to be 0.70% (0.66-0.74%) in Chinese and 0.70% (0.65-0.76%) in Nepalese and 0.68% (0.65-0.72%) in Europeans, using the Spearman Kärber method of analysis. This preliminary trial suggests that there is no ethnic difference in the minimum alveolar concentration of halothane between Asians and Europeans.
Induction dose-response of propofol in unpremedicated children.
The induction dose requirements of propofol were compared in three age groups in 300 unpremedicated healthy Chinese children: group A, younger than 2 yr (n = 48); group B, 2-5 yr (n = 117); group C, 6-12 yr (n = 135). Patients in each group were allocated randomly to receive one of eight doses of propofol (1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4 and 2.6 mg kg-1). ED50 and ED95 for loss of eyelash reflex (LER) and acceptance of face mask (AFM) were determined using probit analysis. ED50 and ED95 for both LER and AFM were greatest in group A, less in B and smallest in C; ED95 (AFM) for groups A, B and C were 2.88 (2.55-3.36), 2.53 (2.31-2.86), and 2.20 (2.02-2.46) mg kg-1, respectively. This probably represented their effective induction dose. The incidence of apnoea was dose related, but not pain on injection.
Vecuronium: an anthropometric comparison.
This study set out to determine if there was any resistance to vecuronium in Nepalese studied in Nepal compared with Nepalese, Chinese and European patients studied in Hong Kong. The four groups, each of 10 male and 10 female patients, were intubated 60 s after administration of 0.1 mg.kg-1 vecuronium. The Nepalese patients in Nepal had significantly less satisfactory intubating conditions (p = 0.002). Similarly, male patients had significantly less satisfactory conditions than female patients (p = 0.004). Some anthropometric measurements were significantly different between the patients in Nepal and those in Hong Kong. There were also sex-related anthropometric differences. It is suggested that differences in response to vecuronium could be explained by differences in distribution volume and muscle mass.
Inter-ethnic differences in postoperative pethidine requirements.
A preliminary study of 24 hours' postoperative analgesia using a patient-controlled analgesia technique was undertaken in eight European and fourteen Asian adult patients. All patients had upper abdominal surgery and received weight-related doses of pethidine postoperatively via a Cardiff Palliator. Both groups had a similar degree of analgesia as assessed by visual analogue score but the Asian patients were more sedated in the postoperative period. The Asian patients made 24% fewer demands for analgesia and had a smaller mean (SD) pethidine consumption, 7.62 (2.04) mg.kg-1, compared with the European patients, 9.97 (2.14) mg.kg-1, (P less than 0.05) during the first 24 hours. Further research is necessary to determine whether the smaller requirement for analgesia in Asian patients is a result of pharmacokinetic or pharmacodynamic differences.
Haemodynamic effects of propofol in children.
The haemodynamic effects of induction of anaesthesia with propofol in children were studied. Two hundred and sixteen children (ASA 1) were randomly allocated to receive one of six different doses of propofol, from 1.6 mg/kg to 2.6 mg/kg, in 0.2 mg/kg increments. Noninvasive measurement of blood pressure showed that mean arterial pressure was reduced by approximately 15% after 1 minute, and by 30% after 5 minutes. The reduction in pulse rate over a 5-minute period was approximately 17%. These changes were similar in each group, regardless of the dose administered. The propofol was mixed with lignocaine, 0.5 mg/ml, and the incidence of pain on injection into a vein on the dorsum of the hand was 24%. We conclude that, within the dose range of our study, the haemodynamic disturbance after induction of anaesthesia with propofol in children is not dose related.
Paediatric glucose homeostasis during anaesthesia.
The perioperative blood glucose regulatory response was compared in 20 healthy children (aged 1-5 yr) presenting for minor surgery and allocated randomly to either a fasted or a glucose group. All children received a milk feed at midnight. The fasted group received no oral intake thereafter, whereas the glucose group received 5% dextrose water 10 ml kg-1 orally about 4 h before operation. The mean plasma glucose concentrations in the two groups were similar before operation and were within normal limits. The pattern of change in the concentrations of plasma glucose, insulin, cortisol, growth hormone and glucagon were also similar between the two groups. Ten percent of patients in the fasted group and 33% in the glucose group had gastric aspirates in excess of 0.4 ml kg-1. The pH of all gastric samples was less than 2.5. The results suggest that healthy preschool children were able to maintain glucose homeostasis after 8 h of fasting. Feeding within 4-6 h before surgery may increase the risk of pulmonary aspiration.
Tubeless anaesthesia for microlaryngeal surgery.
An anaesthetic technique for laryngeal microsurgery is described and evaluated using intravenous propofol infusion and topical lignocaine with the patient breathing spontaneously without an endotracheal tube. Eighty adult patients divided into two groups according to their ASA status (Group A; 58 ASA I and II; Group B; 22 ASA III and IV) were analysed. Operating conditions were good in all but one case. Good anaesthesia was achieved in about 70% of patients. The requirement for propofol was less in Group B. Blood pressures decreased significantly following induction (P less than 0.001) but returned towards the preoperative values after ten minutes in Group A patients whereas the recovery was slower in Group B. Apnoea occurred on induction in about 40% of patients overall. PaCO2 showed a similar small increase in both groups. Oxygenation was adequate. The results show that propofol as an infusion in this simple tubeless technique is satisfactory. As the technique was considered potentially hazardous in those patients with upper airway obstruction, such patients were not included in this study.