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Biomedical subjects

T G Short

Publications and source records attributed to T G Short.

At least 37 records · Page 2Linked to original sources
PubMed1996

Improvements in anaesthetic care resulting from a critical incident reporting programme.

The rôle of an anaesthetic incident reporting programme in improving anaesthetic safety was studied. The programme had been running for 4 to 5 years in three large hospitals in Hong Kong and more than 1000 incidents have been reported. The number of reports being made and frequency of the various categories of incident reported, did not alter during the study period. Sixty nine percent of incidents were considered to be preventable. Human error contributed to 76% of incidents and violations of standard practice to 30% of incidents. The programme was effective in its ability to detect latent errors in the anaesthesia system and when these were corrected, incidents did not recur. The frequency with which various contributing factors were cited did not decrease with time. With the exception of problems dealt with by specific protocol development, the study found no evidence that an increasing awareness of the problem of human error was effective in reducing this kind of problem.

Accident Prevention↗
PubMed1996

Pharmacokinetics and concentration-effect relationship after propofol infusion.

BACKGROUND: We investigated the pharmacokinetics (PK) and concentration-effect relationship after an infusion of propofol in order to obtain a model which can predict the time to eye opening. METHODS: Anaesthesia was induced and maintained with propofol in 34 patients using a Computer Controlled Infusion Pump. Arterial blood samples were taken during recovery and a new model describing the PK was derived. The model was then used to predict the concentration of propofol at the time of eye opening to command. RESULTS: The central volume of distribution was 0.228 L/kg, and the inter-compartment transfer rate constants (min-1) were: k10 0.166, K12 0.091, k13 0.124, k21 0.045, and k31 0.0098. The predicted concentration at which 50% of the patients responded to command was 0.98 microgram/ml. CONCLUSIONS: PK parameters predicting propofol concentration during anaesthesia differ from those describing recovery. The PK of propofol during recovery following an infusion are similar to those following a bolus dose. Real time estimation of blood propofol concentration serves as a useful additional monitor of recovery from anaesthesia.

Adult↗
PubMed1995

Hypotension during subarachnoid anaesthesia: haemodynamic effects of ephedrine.

We have compared the haemodynamic effects of ephedrine alone with ephedrine and colloid for the treatment of hypotension produced by subarachnoid anaesthesia in 30 patients aged 60-90 yr with fractures of the neck of femur. Group one received ephedrine as an initial bolus dose of 0.2 mg kg-1 followed by an infusion of 0.5 mg kg-1 h-1. Group two received ephedrine and colloid (polygeline, Haemaccel) 8 ml kg-1. If necessary, up to three rescue bolus doses of ephedrine (0.1 mg kg-1) and then colloid solution (8 ml kg-1) were given to maintain systolic arterial pressure (SAP) at > 75% of baseline. Arterial pressure was measured by automated oscillotonometry, central venous pressure (CVP) by a manometer and cardiac index (CI), stroke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance. Systemic vascular resistance index (SVRI) was derived. In patients receiving ephedrine only, SVRI, CVP and SI decreased and HR increased (P < 0.0001). Five patients in this group required colloid, the effect of which was to restore CVP, increase CI and SI, and decrease HR (P < 0.02). In patients receiving ephedrine and colloid solution, SVRI decreased and CI, SI and HR increased (P < 0.0001). Ephedrine was not a potent arterial vasoconstrictor and SAP was maintained mainly by increases in SI and HR.

Aged↗
PubMed1995

Additive interactions between propofol and ketamine when used for anesthesia induction in female patients.

BACKGROUND: Propofol and ketamine may be paired for anesthesia induction and for total intravenous anesthesia. The nature of any sedative interactions occurring between propofol and ketamine are unknown. The combination when used for anesthesia induction in female patients was studied. METHODS: Quantal dose-response curves were determined in 180 female patients to whom the drugs were administered individually and in combination. Two minutes after administering the drugs, two endpoints were assessed. First, loss of response to verbal command (hypnosis) and then, in those who failed to respond to this endpoint, loss of response to a 5-s transcutaneous tetanus (anesthesia). Interactions were analyzed by fitting the data to a mathematical model in which response was analyzed in terms of the doses of the two drugs and an additional term included to describe nonadditive interactions. The incidences of apnea, arterial pressure, and heart rate changes during the first 5 min were recorded. RESULTS: At the hypnotic endpoint, the ED50s were 1.10 mg/kg propofol (95% CIs 0.93-1.27), 0.39 mg/kg ketamine (95% CIs 0.27-0.46), and the combination of 0.63 mg/kg propofol and 0.21 mg/kg ketamine (95% CIs 0.53/0.18-0.73/0.24). At the anesthetic endpoint, the ED50s were 1.85 mg/kg propofol (95% CIs 1.58-2.36) 0.66 mg/kg ketamine (95% CIs 0.58-0.77), and the combination of 1.05 mg/kg propofol and 0.35 mg/kg ketamine (95% CIs 0.88/0.29-1.27/0.42). The effects were additive at both endpoints; there was no evidence of an interaction. The ED50s for apnea were 1.61 mg/kg propofol (95% CIs 1.39-1.94), greater than 0.85 mg/kg ketamine and for the combination 1.50 mg/kg propofol and 0.50 mg/kg ketamine (95% CIs 1.15/0.38-3.09/1.03). The addition of ketamine did not significantly alter the ED50 for apnea of propofol. There was a significant difference in the arterial pressures among the three groups (P < 0.001). Using the combination, the cardiostimulant effects of ketamine balanced the cardiodepressant effects of propofol. There was no change in arterial pressure or heart rate after the noxious stimulus. CONCLUSIONS: When using the combination, doses were additive at hypnotic and anesthetic endpoints. Ketamine had no influence on the incidence of apnea after propofol, and the net hemodynamic effects were minimal.

Adult↗
PubMed1995

An adaptation of the objective structured clinical examination to a final year medical student course in anaesthesia and intensive care.

The Department of Anaesthesia and Intensive Care at the Chinese University of Hong Kong provides a 4 week course in our specialty for final year medical students. Our curriculum covers basic concepts in anaesthesia and intensive care, management of common medical emergencies and the safe performance of basic practical skills. For the last 4 years we have used an adaptation of the Objective Structured Clinical Examination to assess learning. Question stations included the use of manikins to assess practical skills, such as cardiopulmonary resuscitation and airway management, identification and description of the use of equipment and interpretation of clinical scenarios and investigations. We believe that our adaptation of the Objective Structural Clinical Examination is better than traditional methods of examination and it has allowed us to identify deficiencies in our teaching methods. The Objective Structured Clinical Examination has been well received by our students and is perceived by them to be a fair reflection of their level of knowledge and skill attainment during the course.

Anesthesiology↗
PubMed1994

Pharmacokinetic interactions between midazolam and propofol: an infusion study.

We have tested the hypothesis that the synergistic interaction which occurs when midazolam and propofol are combined for i.v. sedation is caused by an increase in the free plasma concentration of one of the drugs. Six patients undergoing general anaesthesia received an infusion of propofol with the addition of an infusion of midazolam commenced 30 min later. Another six patients received an infusion of midazolam with the addition of an infusion of propofol 30 min later. All infusions were administered via pharmacokinetic model-controlled syringe pumps programmed to maintain a constant plasma concentration. Venous blood samples were taken before and after introduction of the second infusion for later analysis. Free plasma concentration of midazolam increased from 2.0 (SD 1.5) ng ml-1 to 2.2 (1.9) ng ml-1 after introduction of the propofol infusion (P = 0.32). Free propofol plasma concentration was unchanged at 18.5 (5.3) ng ml-1 before and 18.7 (7.8) ng ml-1 after introduction of the midazolam infusion (P = 0.94). It was concluded that the observed synergism with this combination cannot be explained solely by alteration in free plasma concentration of either of these drugs when they are administered together.

Adolescent↗
PubMed1994

Hypotension during subarachnoid anaesthesia: haemodynamic analysis of three treatments.

We have compared three methods of preventing hypotension during subarachnoid anaesthesia. We attempted to maintain systolic arterial pressure (SAP) greater than 75% of baseline by use of i.v. fluids (preloading with normal saline 16 ml kg-1 and, if necessary, three subsequent boluses of 2.5 ml kg-1), an infusion of metaraminol titrated as necessary between 0 and 5 mg h-1 and an infusion of ephedrine titrated as necessary between 0 and 120 mg h-1. SAP and mean arterial pressure (MAP) were measured by automated oscillotonometry, central venous pressure (CVP) by a manometer and cardiac index (CI), stroke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance. Systemic vascular resistance index (SVRI) was derived. Fluids alone failed to maintain SAP in five of 10 patients. Although CI and CVP were maintained, SVRI decreased (25 (SD 15)%; P = 0.02). Metaraminol maintained SAP in all 12 patients. The main cardiovascular change was decreased HR (15 (8)%; P = 0.0001). Ephedrine failed to maintain SAP in two of 12 patients and was accompanied by several cardiovascular changes: HR (21 (12)%; P = 0.001) increased and SI (16 (10)%; P = 0.0001), CVP (3.8 (1.5) cm H2O; P = 0.0001) and SVRI (24 (6)%; P = 0.0001) decreased. Treatment failures resulted from failures to maintain SVRI in the fluid group and CVP and SVRI in the ephedrine group.

Aged↗
PubMed1994

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.

Algorithms↗
PubMed1994

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.

Anesthesia Recovery Period↗
PubMed1994

Haemodynamic effects of subarachnoid block in elderly patients.

We have studied the haemodynamic effects of subarachnoid block in elderly patients. Thirty patients were undergoing elective transurethral surgery and 18 non-elective orthopaedic surgery, predominantly fractured neck of femur. Systolic arterial pressure (SAP) was measured by automated oscillotonometry, central venous pressure (CVP) by manometer and cardiac index (CI), stroke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance. Systemic vascular resistance index (SVRI) was derived. SAP decreased by more than 25% in 33 patients and SVRI showed similar decreases (P = 0.0001). CVP decreased (2.5 (SD 1.5) cm H2O) in all patients. CI was unaffected because a decrease in SI in some patients (13 (19)%; P = 0.01) was compensated for by an increase in HR (13 (13)%; P = 0.01). Decreases in SAP of 25% were treated initially with colloid solution 8 ml kg-1, which restored SAP in 19 patients. CVP, SI and HR were all restored to baseline values, however, SVRI was decreased further (P < 0.05). Fourteen patients required additional treatment with metaraminol which restored SVRI to baseline values. Patients with systolic hypertension were more likely to require treatment with metaraminol (P = 0.04).

Aged↗
PubMed1994

Midazolam and flumazenil pharmacokinetics and pharmacodynamics following simultaneous administration to human volunteers.

Resedation after antagonism of midazolam sedation with flumazenil may occur because some individuals have rapid elimination of flumazenil but slow elimination of midazolam. To determine whether there are parallel or divergent rates of elimination of the two drugs between individuals, the pharmacokinetic profiles of midazolam and flumazenil were studied simultaneously in 12 adult male volunteers. Free drug concentration data for the two drugs were incorporated into a receptor occupancy model and psychomotor testing was performed and correlated with receptor occupancy. Variation was found between individuals in the pharmacokinetics of the two drugs. There were significant correlations between Cltot (P < 0.01) but not in t1/2 alpha, t1/2 beta, Vc, or VDss. In individuals, midazolam elimination half-life ranged from less than half that of flumazenil to more than three times that of flumazenil. There was a relatively poor, although statistically significant linear correlation found between calculated receptor occupancy and critical flicker fusion frequency, r = 0.50, P < 0.01, and linear analogue scales of sedation r = 0.56, P < 0.005; and anxiolysis, r = 0.54, P < 0.005. There is divergence in the disposition and elimination of midazolam and flumazenil in some individuals. A benzodiazepine receptor occupancy model is useful for predicting the consequent differences in clinical effect when the drugs are given together.

Adult↗
PubMed1993

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.

Anesthesia, Inhalation↗
PubMed1993

Hypnotic and anesthetic interactions between ketamine and midazolam in female patients.

BACKGROUND: Midazolam, if used with ketamine for induction and maintenance of anesthesia, may attenuate hyperdynamic circulatory effects and prevent undesirable emergenic reactions. The nature of the interaction between midazolam and ketamine used for anesthesia induction was studied in female patients. METHODS: Quantal dose-response curves were determined in 170 female patients for the drugs, individually and in combination. Two endpoints were assessed, loss of response to verbal command (hypnosis) and loss of response to a 5-s transcutaneous tetanus (anesthesia). At the hypnotic endpoint, interactions were analyzed by fitting the data to a mathematical model in which the response was analyzed in terms of the doses of the two drugs, and an additional term was included to describe nonadditive interactions. At the anesthetic endpoint, the decrease in ED50 of ketamine in the presence of midazolam was assessed because dose-related effects could not be demonstrated for midazolam alone. RESULTS: At the hypnotic endpoint, the ED50s were: 0.15 mg/kg midazolam (95% CIs 0.11-0.38 mg/kg), 0.37 mg/kg ketamine (95% CIs 0.08-0.44 mg/kg), and the combination of 0.086 mg/kg midazolam and 0.27 mg/kg ketamine (95% CIs 0.07/0.22-0.10/0.31 mg/kg), respectively. The hypnotic effects were found to be additive, and there was no evidence of an interaction. At the anesthetic endpoint, the ED50 of ketamine alone was 0.57 mg/kg (95% CIs 0.47-0.69) and the ED50 for ketamine in the presence of midazolam was also 0.57 mg/kg (95% CIs 0.48-0.79); 0.18 mg/kg midazolam was given at this point. Midazolam had no influence on the anesthetic dose of ketamine. CONCLUSIONS: When using the combination, doses employed should be adjusted according to the depth of central nervous system depression that is required.

Adolescent↗
PubMed1993

Critical incident reporting in an anaesthetic department quality assurance programme.

The critical incident technique was introduced as an additional form of quality assurance to an anaesthetic department of a major Hong Kong teaching hospital. In one year, 125 critical incidents were reported from over 16,000 anaesthetics. The most common incidents reported concerned the airway, breathing systems, and drug administration, with inadequate checking of equipment a frequent associated factor. Human error was a factor in 80% of incidents. Critical incidents were reported for the time during which the patient was under the anaesthetist's care. The majority occurred at induction or during anaesthesia, and were reported for all surgical subspecialties. Half of the incidents were detected by the anaesthetist and one third by monitoring equipment. Although there were improvements in anaesthetic care as a consequence of increased vigilance, critical incidents still occurred. Critical incident reporting highlighted problems not otherwise covered by case and peer reviews, and complemented our quality assurance programme.

Adolescent↗