Biomedical subjects

T G Short

Publications and source records attributed to T G Short.

At least 19 recordsLinked to original sources

PubMed2005

Dreaming during anaesthesia in patients at high risk of awareness.

Dreaming during anaesthesia is commonly reported but remains poorly understood. In this study, adult surgical patients at high risk of awareness were randomly assigned to receive bispectral index (BIS)-guided anaesthesia or routine care, and were interviewed about dreaming three times postoperatively. Dreaming patients (n = 134) were compared with all other patients who were interviewed at least once (n = 2251). Intraoperative dreaming was reported by 4.2%, 3.9% and 3.4% of patients at 2-4 h, 24-36 h and 30 days after surgery, respectively. Fewer BIS-monitored patients reported intra-operative dreaming at 2-4 h than control patients (2.7% vs. 5.7%; p = 0.004). Reports of dreaming were similar in the two groups at 24-36 h and 30 days. Dreaming patients were younger (p = 0.001); healthier (p < 0.001) and more likely to be women (p < 0.001), and were less satisfied with anaesthetic care (p = 0.004) than other patients.

Adult↗

PubMed2005

Drug error in anaesthetic practice: a review of 896 reports from the Australian Incident Monitoring Study database.

Eight hundred and ninety-six incidents relating to drug error were reported to the Australian Incident Monitoring Study. Syringe and drug preparation errors accounted for 452 (50.4%) incidents, including 169 (18.9%) involving syringe swaps where the drug was correctly labelled but given in error, and 187 (20.8%) due to selection of the wrong ampoule or drug labelling errors. The drugs most commonly involved were neuromuscular blocking agents, followed by opioids. Equipment misuse or malfunction accounted for a further 234 (26.1%) incidents; incorrect route of administration 126 (14.1%) incidents; and communication error 35 (3.9%) incidents. The outcomes of these events included minor morbidity in 105 (11.7%), major morbidity in 42 (4.7%), death in three (0.3%) and awareness under anaesthesia in 40 (4.4%) incidents. Contributing factors included inattention, haste, drug labelling error, communication failure and fatigue. Factors minimising the events were prior experience and training, rechecking equipment and monitors capable of detecting the incident. The information gained suggests areas where improved guidelines are required to reduce the incidence of drug error. Further research is required into the effectiveness of preventive strategies.

Adolescent↗

PubMed2005

Recovery from bispectral index-guided anaesthesia in a large randomized controlled trial of patients at high risk of awareness.

Electroencephalographic monitors of anaesthetic depth are reported to assist anaesthetists in reducing recovery times. We explored the effect of bispectral index (BIS) monitoring on recovery times in a double-blind, randomized controlled trial of 2,463 patients at high risk of awareness. Patients were randomized to BIS-guided anaesthesia or routine care. In the BIS group, anaesthesia was adjusted to maintain a BIS value of 40-60 from the commencement of laryngoscopy to the start of wound closure, and 55-70 during wound closure. In the routine care group, anaesthesia was adjusted according to traditional clinical signs. In multivariate models, BIS monitoring, female gender, lower American Society of Anesthesiologists' physical status and shorter duration of anaesthesia predicted faster time to eye-opening after anaesthesia, and faster time to post-anaesthesia care unit discharge. BIS monitoring did not affect times to tracheal extubation among patients admitted to the intensive care unit. We conclude that BIS monitoring has statistically significant, but clinically modest, effects on recovery times in high risk surgical patients.

Adult↗

PubMed2002

Awareness during general anaesthesia: a review of 81 cases from the Anaesthetic Incident Monitoring Study.

Because of recent studies suggesting that awareness is still a major issue in anaesthetic practice, we reviewed 8372 incidents reported to the Anaesthetic Incident Monitoring Study. There were 81 cases in which peri-operative recall was consistent with awareness. There were 50 cases of definite awareness and 31 cases with a high probability of awareness. In 13 of the 81 incidents, the patients appeared to receive adequate doses of anaesthetic drugs. Where the cause could be determined, awareness was mainly due to drug error resulting in inadvertent paralysis of an awake patient (n = 32) and failure of delivery of volatile anaesthetic (n = 16). Less common causes included prolonged attempts at intubation of the trachea (n = 5), deliberate withdrawal of volatile anaesthetic (n = 4) or muscle relaxant apnoea with inadequate administration of hypnotic (n = 3). An objective central nervous system depth of anaesthesia monitor may have prevented 42 of these incidents and an improved drug administration system may have prevented 32. On the basis of these reports, we have developed guidelines that may have prevented the majority of these incidents.

Anesthesia, General↗

PubMed2000

The sedative and electroencephalographic effects of regional anaesthesia.

We studied sedation scores, the processed electroencephalogram and mean arterial pressure pre-operatively in patients before and after spinal (n = 15) and lumbar epidural (n = 15) anaesthesia. We compared them with changes occurring over time in a control group (n = 15), using the responsiveness component of the Observer Assessment of Alertness and Sedation rating scale. The electroencephalographic variables studied were bispectral index, 95% spectral edge frequency, median frequency and the power distribution between frequency bands alpha, beta, theta and delta. No differences were detected within groups in sedation scores before and after intervention, or between groups at either stage. No between-group differences were detected in electroencephalographic variables. In the spinal group, spinal anaesthesia caused an increase in bispectral index, 95% spectral edge frequency, median frequency and beta frequencies, and a decrease in delta frequencies and mean arterial pressure. The increase in beta frequencies is similar to that seen in patients with low plasma concentrations of midazolam and may represent subclinical sedation.

Adult↗

PubMed2000

Closed loop control of anaesthesia: an assessment of the bispectral index as the target of control.

We investigated the performance of a closed-loop system for administration of general anaesthesia, using the bispectral index as a target for control. One hundred patients undergoing gynaecological or general surgery were studied. In 60 patients, anaesthesia was maintained by intravenous infusion of a propofol/alfentanil mixture. In 40, an isoflurane/nitrous oxide based technique was used. For each technique, patients were randomly allocated to receive either closed-loop or manually controlled administration of the relevant agents (propofol/alfentanil or isoflurane), with an intra-operative target bispectral index of 50 in all cases. Closed-loop and manually controlled administration of anaesthesia resulted in similar intra-operative conditions and initial recovery characteristics. During maintenance of anaesthesia, cardiovascular and electro-encephalographic variables did not differ between closed-loop and manual control groups and deviation of bispectral index from the target value was similar. Intra-operative concentrations of propofol, alfentanil and isoflurane were within normal clinical ranges. Episodes of light anaesthesia were more common in the closed-loop group for patients receiving propofol/alfentanil anaesthesia and in the manual group for patients receiving isoflurane/nitrous oxide anaesthesia. Convenience aside, the closed-loop system showed no clinical advantage over conventional, manually adjusted techniques of anaesthetic administration.

Adult↗

PubMed2000

Response surface model for anesthetic drug interactions.

BACKGROUND: Anesthetic drug interactions traditionally have been characterized using isobolographic analysis or multiple logistic regression. Both approaches have significant limitations. The authors propose a model based on response-surface methodology. This model can characterize the entire dose-response relation between combinations of anesthetic drugs and is mathematically consistent with models of the concentration-response relation of single drugs. METHODS: The authors defined a parameter, theta, that describes the concentration ratio of two potentially interacting drugs. The classic sigmoid Emax model was extended by making the model parameters dependent on theta. A computer program was used to estimate response surfaces for the hypnotic interaction between midazolam, propofol, and alfentanil, based on previously published data. The predicted time course of effect was simulated after maximally synergistic bolus dose combinations. RESULTS: The parameters of the response surface were identifiable. With the test data, each of the paired combinations showed significant synergy. Computer simulations based on interactions at the effect site predicted that the maximally synergistic three-drug combination tripled the duration of effect compared with propofol alone. CONCLUSIONS: Response surfaces can describe anesthetic interactions, even those between agonists, partial agonists, competitive antagonists, and inverse agonists. Application of response-surface methodology permits characterization of the full concentration-response relation and therefore can be used to develop practical guidelines for optimal drug dosing.

Algorithms↗

PubMed1999

Aspiration during anaesthesia: a review of 133 cases from the Australian Anaesthetic Incident Monitoring Study (AIMS).

Two-hundred and forty incidents of vomiting/regurgitation and aspiration were reported to the Anaesthetic Incident Monitoring Study database consisting of 5000 reports. Of these, 133 cases of aspiration were recorded. Passive regurgitation occurred three times more commonly than active vomiting. Aspiration was reported twice as often in elective compared with emergency surgery, with 56% of incidents taking place during induction of anaesthesia. Anti-aspiration prophylaxis was prescribed in 14% of patients who subsequently aspirated; however, the majority of cases had at least one predisposing factor for regurgitation, vomiting or aspiration evident peri-operatively. While a major immediate physiological disturbance was common, long-term morbidity was not. Death ensued in five cases, all of whom had significant co-morbidities. Factors reported as contributing to the incident included error of judgement and fault of technique, while clinical experience and anaesthetic assistance tended to minimise the incident. Aspiration remains an important anaesthetic-related morbidity. The application of simple guidelines may have prevented the incident in 60% of all cases of aspiration. Ensuring airway security may be as important as chemoprophylaxis in its prevention.

Adolescent↗

PubMed1999

Long-term outcome and functional health status following intensive care in Hong Kong.

OBJECTIVES: To assess mortality and functional health status of patients at 1 yr following admission to a multidisciplinary intensive care unit (ICU) in Hong Kong. To determine which factors are associated with a poor long-term outcome. DESIGN: Prospective data collection and review. SETTING: A 14-bed multidisciplinary ICU in a 1,400-bed tertiary care university hospital. PATIENTS: Data from 2,268 consecutive patients admitted over a 2.5-yr period was analyzed, including follow-up at 1 yr in 853 adult survivors. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The patients' clinical details and Acute Physiology and Chronic Health Evaluation (APACHE) II scores were recorded on day 2 of admission and reviewed at time of discharge or death. The mean APACHE II score on admission was 18. Survival status at 1 yr was ascertained and the sickness impact profile (SIP) scored as a measure of functional health status for survivors. Sixty-five percent of patients survived to discharge from hospital and 44% of patients were known to survive to 1 yr; 6% of patients could not be traced at 1 yr. Functional health status was assessed in 85% of eligible adult patients. Survivors to 1 yr were younger than nonsurvivors and had lower APACHE II scores. The median SIP score was 5.1, (25th and 75th percentiles: 0 to 15), and 76% of patients had SIP scores < or = 15, i.e., normal health to moderate disability. Five percent of the patients were not working or had retired for health-related reasons. Stepwise logistic regression to identify factors associated with poor functional health status defined as a SIP score >15 at 1 yr found increasing age, cardiac/ respiratory arrest, intracranial hemorrhage, and trauma to be associated with poor outcomes. A correlation was found between APACHE II scores and SIP scores (Spearman's correlation coefficient = 0.13, p < .001). CONCLUSIONS: The SIP scores indicated that the majority of patients who survived to 1 yr after ICU admission enjoyed reasonable functional health status. A poor functional health status at 1 yr did not relate to the severity of the acute illness suffered, but appeared to relate to the prognosis of the underlying disease process.

APACHE↗

PubMed1999

The use of propofol infusions in paediatric anaesthesia: a practical guide.

Children require higher infusion rates of propofol than adults to maintain clinical anaesthesia. We aimed to produce a manual infusion regimen capable of maintaining a steady-state blood concentration of 3 microg ml(-1) in children aged 3-11 years. Pharmacokinetic parameter estimates were taken from published studies of infusion data in children and used in a pharmacokinetic simulation programme to predict likely propofol blood concentrations during infusions. A variability of 5% was allowed about the target concentration of 3 microg ml(-1). A loading dose of 2.5 mg x kg(-1) followed by an infusion rate of 15 mg x kg(-1) x h(-1) for the first 15 min, 13 mg x kg(-1) x h(-1) from 15 to 30 min, 11 mg x kg(-1) x h(-1) from 30 to 60 min, 10 mg x kg(-1) x h(-1) from 1 to 2 h and 9 mg x kg(-1) x h(-1) from 2 to 4 h resulted in a pseudo-steady state target concentration of 3 microg x ml(-1) in children 3-11 years. We were unable to predict similar rates by applying size models to adult data. The context sensitive half-time in children was longer than in adults, rising from 10.4 min at 1 h to 19.6 min at 4 h compared to adult estimates of 6.7 min and 9.5 min, respectively. Children require higher infusion rates than adults to maintain steady state concentrations of 3 microg x ml(-1) and have longer context sensitive half-times than adults. These differences can be attributed to altered pharmacokinetics in this age group.

Adult↗

PubMed1998

The application of a modified proportional-derivative control algorithm to arterial pressure alarms in anesthesiology.

OBJECTIVE: We have developed an arterial pressure alarm system based on a modified proportional-derivative (PD) controller algorithm, and prospectively tested its ability to predict significant hypotensive episodes, defined as systolic arterial pressure < 80 mmHg, in comparison to conventional limit alarms. METHODS: The alarm algorithm was tuned to detect hypotension using selected invasive arterial pressure traces taken from ten patients who had large intra-operative arterial pressure changes. The algorithm's performance was then tested prospectively in comparison to conventional limit alarms and median filtered limit alarms, set at 85 mmHg and 90 mmHg, for its ability to predict hypotensive episodes in a further 100 patients who required invasive arterial pressure monitoring. RESULTS: For the PD alarm algorithm, onset times for significant hypotensive episodes were between those of limit alarms set at 85 mmHg and 90 mmHg. Offset times were similar to the 85 mmHg limit alarms. The false positive rate was 34% compared with 45-64% for the other alarms (p < 0.01). Using our definitions, there was one false negative in the PD group, being a 15 second drop in observed arterial pressure, when a non invasive blood pressure cuff was inflated above the arterial line. CONCLUSIONS: An arterial pressure alarm system design based on a closed loop control algorithm offered improved perform ance over conventional limit alarms and in addition provided a graded output of severity of the hypotension.

Adolescent↗

PubMed1998

With what certainty can post-anaesthetic outcome be predicted?

Prediction of outcome is an important aspect of anaesthetic practice. In populations prediction systems are well developed, but systems capable of identifying individuals at risk are still lacking. Importantly, anaesthesia outcome cannot be considered in isolation and must include patient, surgical, and social factors.

Journal Article↗

PubMed1998

Translation and calibration of a Chinese version of the Sickness Impact Profile for use in Hong Kong.

Because of the lack of suitable generic health status measures in Hong Kong that reflect the value structure and culture of the society, we have translated and calibrated the Sickness Impact Profile, which was originally developed in the United States. Translation consisted of a sequence of forward translations into Chinese, back translations into English and, when there was a loss of meaning or conceptual equivalence, retranslation into Chinese. Sixty Hong Kong Chinese people, including health professionals, patients, and members of the public were then recruited to determine item and dimension weights for the Hong Kong population. Individual ratings were averaged to obtain a consensus value for each item. Within-category reliability analysis for scores varied from 0.70 to 0.92 (Cronbach's alpha values) and overall internal consistency was 0.98. There were only small differences between this version and the original American English version in the ratings given to individual questions (Pearson's product moment correlation coefficient, r=0.8). We have developed a Chinese translation of the Sickness Impact Profile, which can now be used to evaluate health outcomes in Hong Kong and to compare outcomes with studies in other populations where the Sickness Impact Profile was used.

Journal Article↗

PubMed1997

Decreased thiopental requirements in early pregnancy.

BACKGROUND: Anesthetic requirements for inhalational agents are decreased during pregnancy, but there are no data regarding requirements for intravenous agents. The quantal dose-response curves for thiopental were calculated for 70 nonpregnant women having gynecologic surgery and for 70 pregnant women of 7-13 weeks' gestation having elective abortions. METHODS: Groups of 10 patients were given 2, 2.4, 2.8, 3.3, 3.8, 4.5, or 5.3 mg/kg thiopental as a bolus dose during a period of 10 s. Two minutes later, patients were asked to open their eyes as a test for hypnosis. Patients who did not open their eyes were given a 10-s, 50-Hz, 80-mA transcutaneous tetanic electrical stimulus to the ulnar nerve as a test for anesthesia. Purposeful movement indicated that there was no anesthesia. Log dose-response curves for hypnosis and anesthesia were calculated after logit transformation. RESULTS: In the nonpregnant women, the median effective doses (ED50s) (95% confidence interval) for hypnosis and anesthesia were 3.1 (2.8-3.4) mg/kg and 4.9 (4.5-5.4) mg/kg, whereas in the pregnant women the corresponding ED50s were 2.6 (2.3-2.8) mg/kg and 4 (3.7-4.4) mg/kg. In the non-pregnant women, the ED95s (95% CI) for hypnosis and anesthesia were 4.4 (3.9-5.4) mg/kg and 6.4 (5.7-7.9) mg/kg, whereas in the pregnant women the corresponding ED95s were 3.7 (3.3-4.5) mg/kg and 5.2 (4.7-6.3) mg/kg. The pregnant to nonpregnant relative median potency (95% CI) ratio for hypnosis was 0.83 (0.67-0.96) and for anesthesia it was 0.82 (0.62-0.94). CONCLUSIONS: The dose of thiopental for hypnosis was 17% less and that for anesthesia was 18% less in pregnant women of 7-13 weeks' gestation compared with that in nonpregnant women.

Adult↗

PubMed1997

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.

Adolescent↗

PubMed1997

Critical incident reporting in the intensive care unit.

Critical incident reporting was introduced into the intensive care unit (ICU) as part of the development of a quality assurance programme within our department. Over a 3-year period 281 critical incidents were reported. Factors relating to causation, detection and prevention of critical incidents were sought. Detection of a critical incident in over 50% of cases resulted from direct observation of the patient while monitoring systems accounted for a further 27%. No physiological changes were observed in 54% of critical incidents. The most common incidents reported concerned airway management and invasive lines, tubes and drains. Human error was a factor in 55% of incidents while violations of standard practice contributed to 28%. Critical incident reporting was effective in revealing latent errors in our "system' and clarifying the role of human error in the generation of incidents. It has proven to be a useful technique to highlight problems previously undetected in our quality assurance programme. Improvements in quality of care following implementation of preventative strategies await further assessment.

Adolescent↗

PubMed1996

Abdominal surgery alters the calibration of bioimpedance cardiac output measurement.

The performance of impedance cardiography (TEBco), using the BoMed NCCOM3-R7S, and thermodilution (TDco) were compared in eight patients during major abdominal surgery. An opioid, volatile and relaxant anaesthetic technique was employed. This was supplemented with an epidural in five cases. Sets of three cardiac output readings, for both methods, were made at 10-20 min intervals throughout surgery. Data were compared using the Bland and Altman method, regression analysis and a nested model to measure variance components at different stages of surgery. Data from 157 sets of readings are presented. Agreement between the two devices was poor, with a ratio of TDco/TEBco of 115% and limits of agreement of 51-193%. The regression line was TDco = (0.98) x TEBco-0.95 with r = 0.60. A more detailed analysis, using nested data, showed good repeatability with coefficients of variation of 5.4% for TDco and 4.8% for TEBco. During surgery shifts in the bias between the two devices occurred, which were related to changes in surgical conditions. Between shifts both devices showed good repeatability over time. Variance components were 0.27 within nested data and 0.082 between bias shifts, with a significantly greater overall component of 1.2 (ANOVA; P = 0.0001). Shifts could be explained by deficiencies in the algorithm used to calculate TEBco. Current TEBco technology is too inaccurate for intra-operative use. However, under stable operating conditions TEBco and TDco showed good repeatability.

Abdomen↗

PubMed1996

Prospective evaluation of pharmacokinetic model-controlled infusion of propofol in adult patients.

We have tested prospectively the algorithm of White and Kenny for pharmacokinetic model-controlled infusion of propofol in 40 healthy Oriental adults. Anaesthesia consisted of a target-controlled infusion of propofol, 70% nitrous oxide and an infusion of alfentanil. For the first 20 patients studied, median performance error was -5%, median absolute performance error 19%, divergence -9% and wobble 6%. The model was revised to minimize the prediction error of the variable set and tested prospectively in another 20 patients. There was a deterioration in performance of the revised model. Performance statistics for the original model in all 40 patients were: median performance error 2% (range -34 to 69%), median absolute performance error 21% (6-69%), divergence -17% (-92 to 49%) and wobble 7% (2-34%). The algorithm was found to perform adequately in our Oriental patient population.

Adult↗