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Biomedical subjects

M G Irwin

Publications and source records attributed to M G Irwin.

At least 37 records · Page 2Linked to original sources
PubMed2002

The ASA Physical Status Classification: inter-observer consistency. American Society of Anesthesiologists.

The American Society of Anesthesiologists (ASA) physical status classification system has previously been shown to be inconsistently applied by anaesthetists. One hundred and sixty questionnaires were sent out to all specialist anaesthetists in Hong Kong. Ten hypothetical patients, identical to those of a similar study undertaken 20 years ago, each with different types and degrees ofphysical disability were described. Respondents were asked about their country of training and type of anaesthetic practice and to assign an ASA classification status for each patient. Ninety-seven questionnaires were returned (61%) after two mailings. Agreement for each patient within groups, between groups and overall comparisons were made. Percentage of agreement was between 31 to 85%. Overall correlation was only fair in all groups (Kappa indices: 0.21-0.4). We found that the current pattern of inter-observer inconsistency of classification was similar to that 20 years ago and exaggerated between locally and overseas trained specialists (P<0.05). The validity of the ASA system, its usefulness and the need for a new, more precise scoring system is discussed.

Anesthesiology↗
PubMed2001

Incidence of diaphragmatic paralysis following supraclavicular brachial plexus block and its effect on pulmonary function.

Thirty unpremedicated ASA physical status 1-3 patients aged between 18 and 69 years, scheduled for upper limb surgery, received a conventional supraclavicular brachial plexus block using a nerve stimulator and bupivacaine 0.375% 0.5 ml.kg-1. Spirometric measurements of pulmonary function and ultrasonographic assessments of diaphragmatic function were made before the block and at 10-min intervals after injection until full motor block of the brachial plexus had developed. Complete paralysis of the ipsilateral hemidiaphragm occurred in 50% of patients. Seventeen per cent of patients had reduced diaphragmatic movement and the rest (33%) had no change in diaphragmatic movement. Those with complete paralysis all showed significant decreases in pulmonary function, whereas those with reduced or normal movement had minimal change. All patients remained asymptomatic throughout, with normal oxygen saturation on room air.

Adult↗
PubMed2001

Transoesophageal acoustic quantification for evaluation of cardiac function during laparoscopic surgery.

Pneumoperitoneum may be poorly tolerated in patients with marginal cardiopulmonary function. Transoesophageal echocardiography is a relatively non-invasive technique that can track changes in left ventricular cavity area using acoustic quantification and has been found to provide a reliable, real-time estimation of left ventricular function. We evaluated mid-papillary fractional area change during pneumoperitoneum in 17 healthy adult patients (group 1) and 17 with hypertension and/or ischaemic heart disease (group 2) undergoing laparoscopic cholecystectomy. Peritoneal insufflation led to significant (p < 0.01) decreases in fractional area change and an increase in mean blood pressure. There was no significant change in heart rate. Patients with cardiovascular disease who had a > 30% decrease in fractional area change following carbon dioxide insufflation (group 2B) were given an intravenous infusion of glyceryl trinitrate. In groups 1 and 2A, fractional area change improved slightly with head-up tilt and continued to improve over the course of surgery. Glyceryl trinitrate led to a significant increase in fractional area change and a decrease in mean blood pressure back to baseline values. We conclude that peritoneal insufflation of carbon dioxide results in a significant increase in cardiac workload that is well tolerated in patients with no cardiovascular disease. Coexisting cardiovascular disease can result in even more pronounced impairment of cardiac function, which may not be predictable by clinical assessment or adequately determined by routine monitoring. We recommend the use of transoesophageal acoustic quantification as a monitor in these patients and the administration of glyceryl trinitrate to ameliorate myocardial stress.

Adult↗
PubMed2001

Comparison of coagulation and blood loss during anaesthesia with inhaled isoflurane or intravenous propofol.

Propofol has been reported to affect blood coagulation. This prospective, randomized study compared coagulation and blood loss during anaesthetic maintenance with target-controlled intravenous propofol infusion vs. inhaled isoflurane. Thirty-eight ASA I-III patients undergoing head and neck surgery were allocated randomly to receive either inhaled isoflurane at end-tidal concentration 1-1.5% (group I, n=20) or target-controlled infusion (TCI) of propofol at target concentration 2-5 microg ml(-1) (group P, n=18). Thrombelastography on recalcified whole blood was performed pre-induction, and at 15, 30, 60, 90, 120 min post-induction and 30 min after anaesthesia in both groups. Blood loss was estimated from weighing swabs and the volume in suction bottles. Induced hypotension was not used, and perioperative body temperature was similar between groups. There were no significant differences in thrombelastographic coagulation (R-time, K-time, maximum amplitude and angle) or fibrinolytic variables (lysis index at 30 and 60 min) at all times between groups. Total blood loss was also not significantly different (median group I: 350 ml, range 20-1200 ml; group P: 200 ml, range 50-800 ml). Shortening of R-time and widening of angle developed over time in both groups (P<0.05 groups I and P, repeated measures ANOVA). We conclude that maintenance of anaesthesia with propofol TCI at 2-5 microg ml(-1) does not cause detectable coagulation changes on thrombelastography nor increase surgical blood loss when compared to inhaled isoflurane.

Adult↗
PubMed2001

A profile of anaesthesia trainees in Hong Kong.

OBJECTIVES: To examine the demographics, professional background, progress, and aspirations of anaesthesia trainees in Hong Kong. DESIGN: Anonymous questionnaire consisting of 56 items grouped into the areas of demographics, and anaesthetic and postanaesthetic training. Eight of the items were open questions. Descriptive analyses were undertaken for the closed items. SETTING: Hong Kong College of Anaesthesiologists, Hong Kong. PARTICIPANTS: All trainees. MAIN OUTCOME MEASURES: Demographic data, aspects of training, supervision, working environment, career aspirations, job satisfaction, and morale. RESULTS: The response rate was 77%. The various problems highlighted by respondents included the need for more input and feedback into individual training programmes, the lack of senior support, and the need for more relevant and examination-orientated courses and workshops. Unsatisfactory aspects of the specialty reported were the lack of control over work routines, relationships with surgeons, boredom, and the poor public image of the specialty. Eighty-four percent of respondents reported having reasonable to good job satisfaction. CONCLUSIONS: Ongoing benefits could be derived from enhancing communication between trainees and the Hong Kong College of Anaesthesiologists, through appropriate channels for trainee feedback.

Anesthesiology↗
PubMed2000

Brachial plexus infusion of ropivacaine with patient-controlled supplementation.

PURPOSE: To report the use of continuous brachial plexus analgesia to facilitate physiotherapy CLINICAL FEATURES: A 34-yr-old man had contractures of the fingers of his dominant hand following a crush injury in 1996. After several operations, he continued to experience severe pain and disability. In order to facilitate painfree active and passive physiotherapy, we performed an axillary brachial plexus block. After insertion of a brachial plexus catheter via the axilla, analgesia was continued for a period of one week using a 3 mlxhr(-1) background infusion of ropivacaine 0.2% with the facility for additional patient-controlled 1 ml boluses. Both active and passive physiotherapy was carried out daily for the entire week. CONCLUSION: This technique was successful with no major complications and resulted in a marked reduction in pain, with improved range of finger movement and general upper limb function.

Adult↗
PubMed2000

Anaesthetic management of a patient with low tracheal obstruction requiring placement of a T-Y stent.

A 60-year-old man with a history of oesophagectomy for carcinoma presented with worsening dysphagia, dyspnoea and tachypnoea secondary to oesophageal stricture and tumour invasion of the trachea causing a "ball-valve" obstruction. The patient required placement of a T-Y tracheobronchial stent to relieve the airway obstruction and was successfully managed using sevoflurane for gaseous induction followed by maintenance with propofol total intravenous anaesthesia.

Anesthesia↗
PubMed1998

Intra-articular injection of ketorolac in the rat knee joint: effect on articular cartilage and synovium.

We have investigated the effects of intra-articular (i.a.) administration of ketorolac in the rat knee joint. Thirty Sprague-Dawley rats were given 0.25 ml of a standard preparation of ketorolac trometamol (10 mg ml-1) by injection into the right knee joint and 0.25 ml of 0.9% physiological saline solution by injection into the left knee as a control. Ten rats were killed at 24 h, 10 at 48 h and 10 at 5 days after injection. The joints were prepared and sectioned for histological examination. There was significantly more inflammation in those knees that had received i.a. ketorolac at all times of examination, with the most severe changes occurring 5 days after injection. A further group of 10 rats were given 0.25 ml of 10% w/v ethanol in physiological saline (similar to the vehicle for parenteral ketorolac) injected into the knee joint, with a 0.9% saline control injected in the other knee. These rats were then killed at 5 days (as this was the time interval after which we found the maximum inflammatory response in the earlier phase of our study). The joints were prepared and examined histologically. We feel that the absence of inflammatory changes in these joints make it unlikely that ethanol was responsible for the inflammation produced by ketorolac injection.

Analgesics↗
PubMed1998

Patients' knowledge of and attitudes towards anaesthesia and anaesthetists in Hong Kong.

We have performed a prospective, questionnaire-based survey on patients' knowledge of and attitudes towards anaesthetists in Hong Kong. Before their preoperative anaesthetic visit, 120 patients completed a three-section questionnaire. The first section consisted of questions designed to assess patients' knowledge about anaesthetists and their practice. The second section was designed to elicit their attitudes to anaesthetists and the third was a set of demographic questions. Seventy percent of patients recognised that anaesthetists are medical doctors and most realised that they provide anaesthesia for surgical procedures. However, there was scant knowledge of anaesthetists' perioperative role or their role in other aspects of patients care such as pain management, intensive care, resuscitation, research, and teaching. Patients felt it was important to be fully informed about the anaesthetic, and were keen to see their anaesthetist both preoperatively and postoperatively.

Journal Article↗
PubMed1997

Prevention of hypotension during spinal anaesthesia for caesarean section: ephedrine infusion versus fluid preload.

We compared the efficacy of prophylactic ephedrine infusion over fluid preloading in prevention of maternal hypotension during spinal anaesthesia for Caesarean section. Forty-six women undergoing elective Caesarean section at term were allocated randomly to receive either intravenous fluid preloading with Hartmann's solution 20 ml.kg-1 (fluid group) or prophylactic intravenous ephedrine 0.25 mg.kg-1 (ephedrine group). Moderate hypotension was defined as > or = 20% reduction in systolic blood pressure and severe hypotension as > or = 30% reduction in systolic blood pressure. Maternal uterine circulation was measured using Doppler ultrasound in 11 parturients before and after spinal anaesthesia. There was a lower incidence of severe hypotension in the ephedrine group compared with the fluid group (35% vs. 65%, p = 0.04), although the incidence of moderate hypotension was similar. Mean umbilical venous pH was higher in the ephedrine group than in the fluid group (7.33 vs. 7.29, p = 0.02) and the number of patients shivering was lower in the ephedrine group (2 vs. 9, p = 0.02). No difference was found between pre- and postspinal uterine artery pulsatility indices in either group. We conclude that prophylactic ephedrine infusion alone is at least as good as fluid preload alone in combating the hypotension associated with spinal anaesthesia for Caesarean section.

Anesthesia, Obstetrical↗
PubMed1997

An audit of the safety of an acute pain service.

We audited and analysed the adverse effects and safety of postoperative pain management on 2509 consecutive patients under care of the Acute Pain Service at a tertiary referral teaching hospital over a 32-month period. Our standard respiratory monitoring consisted of continuous pulse oximetry, hourly respiratory rate counting, sedation scoring and intermittent arterial blood gas sampling. This protocol was reliable and detected six episodes of bradypnoea, 13 of hypercapnia and 23 of oxygen desaturation occurring in 39 patients (1.8% of all spontaneously breathing patients). Two patients required naloxone injection and none had long-term sequelae. Hypotension due to epidural bupivacaine 0.0625% and fentanyl 3.3 micrograms.ml-1 infusion occurred in four patients (1.2%), all with a sensory block higher than T5. They readily responded to fluid infusion and ephedrine (two patients). Postoperative nausea or vomiting occurred in 723 (28.8%) and 380 (15.1%) patients, respectively. Odds ratio analysis showed that the risk factors for postoperative nausea and vomiting were: female gender, gynaecological operations, nongeriatric patients and systemic analgesia. Postoperative nausea and vomiting decreased analgesic efficacy by discouraging the use of patient-controlled analgesia and was regarded as equally distressing as pain. Other side-effects included: pruritus in 182 patients; dizziness in 333 and lower limb weakness in 73 (21.2% of patients receiving epidural local anaesthetics). It is concluded that a standard monitoring and management protocol, an experienced nursing team and reliable Acute Pain Service coverage is mandatory for the safe use of modern analgesic techniques.

Aged↗
PubMed1997

An unusual complication of emergency tracheal intubation.

A 68-year-old woman presented with dyspnoea having undergone a short period of tracheal intubation during an episode of congestive cardiac failure 10 days earlier. On the fourth day of admission, she suddenly developed acute respiratory distress followed by a cardiac arrest and was found to have an enlarging neck mass. Following intubation and resuscitation, computerised tomography was carried out and surgical exploration revealed a retropharyngeal abscess and a pseudo-aneurysm of the common carotid artery resulting from pharyngeal rupture which most probably occurred as a complication of the original tracheal intubation.

Aged↗
PubMed1997

Patient-maintained propofol sedation. Assessment of a target-controlled infusion system.

We have developed a system which allows patients to operate a target-controlled infusion of propofol to provide sedation and we have studied its use in 36 unpremedicated patients undergoing local and regional anaesthetic procedures lasting 10-280 min. An intravenous propofol infusion was started at a target plasma level of 1 microgram.ml-1. The patient was able to increase the target propofol concentration in 0.2- microgram.ml-1 increments by pressing a demand button. There was a lockout interval of 2 min and a maximum permissible target concentration of 3 micrograms.ml-1. There was considerable interindividual variability in propofol consumption (mean 39.3 micrograms.kg-1.min-1, range 3-131 micrograms.kg-1.min-1), no cardiovascular instability and little oversedation. Eight patients required supplementary oxygen. Optimal sedation was provided at median target concentrations of 0.8-0.9 microgram.ml-1. The target-controlled infusion system bias was-47% and the inaccuracy was 48%. Patient satisfaction was high and 89% said that they would definitely use the technique again. This technique combines the benefits of target-controlled infusion with patient-controlled feedback and produces safe intra-operative sedation.

Adult↗
PubMed1996

Patient maintained alfentanil target-controlled infusion for analgesia during extracorporeal shock wave lithotripsy.

PURPOSE: The purpose of this study was to determine whether alfentanil given by a pharmacokinetic-based target controlled infusion (TCI) system under patient control is a suitable analgesic technique for extracorporeal shock wave lithotripsy (ESWL). METHODS: The design was an open, unblinded, noncomparative, prospective study. Forty outpatients undergoing ESWL were given patient maintained alfentanil TCI. Pain, nausea and sedation were assessed every 300 shocks. Vital signs were recorded every three minutes, pulse oximetry and electrocardiography being monitored continuously. Blood alfentanil concentration was measured for comparison with the predicted value. RESULTS: Alfentanil consumption (median 1.34 mg, range 0.8-3.6) and measured levels following treatment (median 60 ng.ml-1, range 15.6-134.3) varied widely. The precision of the TCI system and the median prediction error (bias) were both 49%. The median of pain scores recorded during treatment was 4 (range 0-8). The median respiration rate was 15 bpm (range 10-23), three patients required oxygen (SaO2 < 92%) cardiovascular measurements were stable and there was no excessive sedation. The incidence of nausea was 15%. All patients were ready for hospital discharge within one hour following treatment. CONCLUSIONS: Patient maintained alfentanil TCI provides good analgesia for ESWL in the majority of patients with little sedation. Respiratory depression is uncommon but supplementary oxygen should be given prophylactically. There is considerable interindividual variation in demand for alfentanil indicating the usefulness of the patient control method. The TCI system underestimated alfentanil blood concentrations but this did not affect its clinical usefulness.

Adult↗
PubMed1996

Patient-controlled alfentanil. Target-controlled infusion for postoperative analgesia.

We have compared the opioid effects of a patient-demand, target-controlled infusion of alfentanil (n = 10), with patient-controlled bolus administration of morphine (n = 10) following major spinal surgery in Chinese patients aged from 11 to 67 years. The same general anaesthesia regimen was used in all patients. One group of patients were given intra-operative morphine analgesia followed by postoperative intravenous morphine patient-controlled analgesia, while the other group received an intra-operative target-controlled infusion of alfentanil. Following surgery, the alfentanil group were given control of a handset and were able to increase the target alfentanil plasma level in 5 ng.ml-1 increments with a 2-min lockout interval. If analgesia was not demanded within a 15-min period, the computer reduced the target concentration by 5 ng.ml-1. All patients had continuous pulse oximetry monitoring and hourly recording of pain, sedation, nausea scores and respiratory rate. Patients receiving alfentanil had the target concentration noted hourly and four blood samples taken during the first 24 h for measurement of plasma alfentanil concentrations by high performance liquid chromatography. The alfentanil infusion system was equally effective as an analgesic technique when compared with morphine patient-controlled analgesia. There were no hypoxaemic episodes (oxygen saturation < 94%), no difference in sedation scores and the incidence of nausea (30%) was the same in both groups. There was a significantly (p < 0.001) lower respiratory rate in the alfentanil group compared with patients receiving morphine at, clinically assessed, equianalgesia. The predicted plasma alfentanil concentrations increased rapidly from about 30 ng.ml-1 during the first 4 h to around 100 ng.ml-1 at the end of the 24-h study period. The precision of the target-controlled infusion system was 75.4% and the mean prediction error (bias) 58.1%, suggesting an underestimation of the measured alfentanil concentrations by the alfentanil infusion system in these Chinese patients.

Adolescent↗
PubMed1996

Pre-operative parental anxiety.

This study attempts to identify the incidence and specific sources of anxiety in the parents of children admitted to hospital for elective surgery, to isolate factors associated with increased anxiety and to identify useful ameliorative measures. One hundred parents were interviewed and completed a questionnaire before their child's surgery. Parental anxiety levels were measured using the Leeds scale for self-assessment of anxiety. Anxiety-related illness was identified in 47% of parents, who were significantly more concerned than others about all aspects of their children's hospitalisation. No factors were identified which could predict which parents were at high risk of developing an anxiety state. When questioned about educational and interventional measures which they felt would be reassuring, the same factors were identified by 'anxious' and 'non-anxious' parents. As all parents agree on useful ameliorative factors, a general advice and education programme would be appropriate.

Adult↗