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Biomedical subjects

N D Edwards

Publications and source records attributed to N D Edwards.

At least 19 recordsLinked to original sources
PubMed2006

Relationship between perioperative troponin elevation and other indicators of myocardial injury in vascular surgery patients.

BACKGROUND: In 2000 the European Society of Cardiology and the American College of Cardiology published a consensus document revising the definition of myocardial infarction. The usefulness of this revised definition has been challenged. It has been suggested that, rather than any release of cardiac troponin being potentially diagnostic of myocardial infarction, a diagnostic threshold consistent with significant myocardial injury should be defined. METHODS: We studied 65 patients undergoing elective major vascular surgery to examine the relationship between the magnitude of cardiac troponin I (cTnI) and creatine kinase MB fraction (CK-MB) release and clinical signs or symptoms of myocardial injury. cTnI and CK-MB concentrations were measured preoperatively and on the first 4 postoperative days using the ACCESS assay (Beckmann). Patients were considered to have suffered a perioperative myocardial infarction if they had either symptoms or ECG changes consistent with this diagnosis, together with cTnI release. RESULTS: Peak postoperative cTnI concentrations above the lower detection limit of the ACCESS assay (0.06 microg litre(-1)) occurred in 26 patients. Eight of these patients displayed symptoms or ECG changes consistent with myocardial injury. A cTnI level greater than 0.68 microg litre(-1) was found to be consistent with the clinical diagnosis of myocardial infarction. The optimal cut-off for the diagnosis of MI using CK-MB was 40.4 microg litre(-1). CONCLUSIONS: These data suggest that further studies are required to define the optimal cardiac troponin diagnostic threshold for the diagnosis of myocardial infarction in the non-cardiac surgery population.

Aged↗
PubMed2001

Anaesthesia for stent graft repair of thoracic aneurysm and coarctation of the aorta.

We present the anaesthetic management of a patient for stenting of a thoracic aortic aneurysm at the site of an aortic coarctation. The specific challenges to the anaesthetist for this case are outlined. These include the specific problems of placing the graft, the obvious risk of aortic rupture and the unfamiliar environment of the separate radiological theatre. The advantages and disadvantages to the anaesthetist of the treatment of thoracic aortic aneurysms with stents are briefly discussed.

Adult↗
PubMed2001

Comparing the effects of stimulation and propofol infusion rate on implicit and explicit memory formation.

Doubt remains about the conditions under which learning persists despite anaesthesia. This study investigated the relative importance of dose of anaesthetic and stimulation for learning during propofol infusion before surgery. Thirty-six patients were randomly assigned to three groups. Group 1 received two word lists (category examples and nonsense words) during infusion of propofol to a target concentration of 2 microg ml(-1). Groups 2 and 3 received the word lists during infusion of propofol 5 microg ml(-1). Group 2 received nonsense words before tracheal intubation and category examples during intubation; Group 3 heard category examples before and nonsense words during intubation. Bispectral index was recorded as a measure of depth of sedation/anaesthesia. We assessed explicit memory on recovery using a structured interview and a recognition test. We assessed implicit memory using a category generation test and a preference rating task. To establish baseline, a control group of 12 patients completed the category generation test without receiving the category examples during anaesthesia. Overall, there was no evidence for learning during propofol infusion, though the category generation task showed a trend towards more implicit memory for words presented during intubation than during anaesthesia. We conclude that learning does not occur during anaesthesia without surgery.

Anesthetics, Intravenous↗
PubMed2000

Randomized placebo-controlled trial to assess the effect of remifentanil and propofol on bispectral index and sedation.

The effect of the combination of opiates and hypnotics on bispectral index (BIS) is unclear. This double-blind placebo-controlled trial investigated the effect on BIS and sedation of different infusion doses of remifentanil combined with a steady infusion of propofol. Forty patients initially received a target-controlled infusion of propofol 2 micrograms ml-1 for 15 min. They were then randomized to receive either placebo, 0.01, 0.05 or 0.1 microgram kg-1 min-1 remifentanil for a further 15 min. We found a significant correlation between the dose of remifentanil and the change of BIS after 15 min of infusion. The correlation between all the sedation scores and their corresponding BIS was also significant. We concluded that remifentanil, in combination with propofol, reduces BIS when used for sedation.

Adjuvants, Anesthesia↗
PubMed1999

Self-learning fuzzy control with temporal knowledge for atracurium-induced neuromuscular block during surgery.

Self-learning fuzzy logic control has the important property of accommodating uncertain, nonlinear, and time-varying process characteristics. This intelligent control scheme starts with no fuzzy control rules and learns how to control each process presented to it in real time without the need for detailed process modeling. In this study we utilize temporal knowledge of generated rules to improve control performance. A suitable medical application to investigate this control strategy is atracurium-induced neuromuscular block of patients in the operating theater where the patient response exhibits high nonlinearity and individual patient dose requirements may vary fivefold during an operating procedure. We developed a computer control system utilizing Relaxograph (Datex) measurements to assess the clinical performance of a self-learning fuzzy controller in this application. Using a T1 setpoint of 10% of baseline in 10 patients undergoing general surgery, we found a mean T1 error of 0.28% (SD = 0.39%) while accommodating a 0.25 to 0.38 mg/kg/h range in the mean atracurium infusion rate. This result compares favorably with more complex and computationally intensive model-based control strategies for atracurium infusion.

Algorithms↗
PubMed1999

Perioperative myocardial ischaemia, heart rate and arrhythmia in patients undergoing thoracotomy: an observational study.

We have studied myocardial ischaemia, heart rate and arrhythmia in 82 patients undergoing elective thoracotomy. Myocardial ischaemia was detected using a microprocessor-based surveillance system programmed to record leads V2 and V5. Patients were monitored on the day before and for up to 72 h after surgery. The total monitoring time was 5158 h. The incidence of silent myocardial ischaemia before operation was 11% (nine of 82). This increased to 24% (20 of 82) after operation. Postoperative myocardial ischaemia was associated with preoperative myocardial ischaemia in six patients. Before operation, the mean duration of myocardial ischaemia was 0.31 min per hour of monitoring. After operation, this increased to 1.36 min per hour of monitoring (P < 0.05). For the whole population, mean heart rate before operation was 74 beat min-1 and increased to 84 beat min-1 after operation (P < 0.01). Patients with ischaemia had a mean heart rate of 92.8 beat min-1 after operation compared with those with no ischaemia whose mean heart rate was unchanged at 81.8 beat min-1 (P < 0.05). The incidence of atrial tachyarrhythmia increased from one patient before operation to 12 patients after operation (P < 0.01). Atrial tachyarrhythmia was not associated with postoperative myocardial ischaemia. Nine patients had an adverse operative outcome; two had non-fatal myocardial infarction and seven died. Postoperative myocardial ischaemia was associated with adverse outcomes (P < 0.05).

Adult↗
PubMed1998

A portable self-learning fuzzy logic control system for muscle relaxation.

We have assessed the practicality and performance of the Vital Signs Paragraph neuromuscular blockade monitor as part of a 'self-learning' fuzzy logic control feedback system used to administer atracurium to a required depth of neuromuscular blockade. Fifteen patients undergoing surgery expected to last longer than 90 min entered the study. A Vital Signs Paragraph was used to measure the degree of neuromuscular blockade and control it such that the first twitch of the train-of-four was kept at 10% of its baseline value. The controller instructed a Graseby Medical 3400 infusion pump to administer an atracurium infusion to maintain this level of blockade. Five patients (33%) were withdrawn from the study due to inadequate piezo-electric sensor function. In the remaining 10 patients, the system achieved stable control of neuromuscular blockade with a mean (range) error for the first twitch of the train-of-four of -0.45 (-1.06 to 0.13)%. The mean atracurium infusion rate ranged from 0.13 to 0.67 mg.kg-1.h-1. These results compare reasonably well with previous results using the Datex Relaxograph, whilst the system itself was portable and easy to use. However, the reliability of the system was limited due to variability in the sensitivity of piezoelectric sensors.

Adult↗
PubMed1997

Self-learning fuzzy control of atracurium-induced neuromuscular block during surgery.

Self-learning fuzzy logic control has the important property of accommodating uncertain, non-linear and time-varying process characteristics. This intelligent control scheme starts with no fuzzy control rules and learns how to control each process presented to it in real time, without the need for detailed process modelling. A suitable medical application to investigate this control strategy is atracurium-induced neuromuscular block (NMB) of patients in the operating theatre. Here, the patient response exhibits high non-linearity, and individual patient dose requirements can vary five-fold during an operating procedure. A portable control system was developed to assess the clinical performance of a simplified self-learning fuzzy controller in this application. A Paragraph (Vital Signs) NMB device monitored T1, the height of the first twitch in a train-of-four nerve stimulation mode. Using a T1 setpoint = 10% of baseline in ten patients undergoing general surgery, a mean T1 error of 0.45% (SD = 0.44%) is found while a 0.13-0.70 mg k-1 h-1 range in the mean atracurium infusion rate is accommodated. The result compares favourably with more complex and computationally-intensive model-based control strategies for the infusion of atracurium.

Atracurium↗
PubMed1997

Self-learning fuzzy logic control of neuromuscular block.

We have assessed the performance of a "self-learning" fuzzy logic controller to administer atracurium to a required depth of neuromuscular block. We studied 20 ASA I and II patients undergoing surgery anticipated to last longer than 90 min. A Datex Relaxograph was used to measure the degree of neuromuscular block, and control to a T1 twitch height set point of 10% of baseline neuromuscular function was selected. The controller commenced with a blank rule-base and instructed a Graseby 3400 infusion pump to administer an atracurium infusion to maintain this level of block. The system achieved stable control of neuromuscular block with a mean T1 error of -0.52% (SD 0.55%) accommodating a range in mean atracurium infusion rate of 0.25-0.44 mg kg-1 h-1. These results compare favourably with the more computationally intensive and unwieldy adaptive control strategies for atracurium infusion used previously. There was less variation in infusion rates than in our previously studied fixed rules fuzzy controller.

Adult↗
PubMed1997

Current practice in the pre-operative assessment of patients for elective repair of abdominal aortic aneurysm. A survey of UK hospitals.

A postal survey of 100 hospitals throughout the United Kingdom and Ireland was conducted to assess current practice in the pre-operative assessment and use of pulmonary artery catheters in patients undergoing elective abdominal aortic aneurysm repair. Seventy-four completed questionnaires were received. The survey revealed that 53% of respondents hold designated preoperative assessment clinics, attended by anaesthetists in 54% and cardiologists in 26%. However, only 4% of respondents have a written protocol for stratifying patients and assessing peri-operative risk. By far the commonest investigation of choice for further cardiological assessment is transthoracic echocardiography (67%). Other investigations of choice are multiple update gated acquisition (MUGA) scan (13%), dipyridamole thallium imaging (9%), exercise ECG (6%), stress echocardiography (1%) and stress MUGA (1%). Two units (3%) never undertook further investigation. Pulmonary artery flotation catheters are used as a routine by 9% of respondents, dependent upon left ventricular ejection fraction by 65%, dependent on other factors by 7% and not used at all by 19%. The survey reveals widespread variation in pre-operative assessment of patients undergoing elective repair of abdominal aortic aneurysm.

Aortic Aneurysm, Abdominal↗
PubMed1996

Development of a portable closed-loop atracurium infusion system: systems methodology and safety issues.

Safety of closed-loop drug infusion systems is an issue often raised as a matter of concern. As a result, many closed-loop control systems are reported in the literature merely as computer simulation studies and few ever reach the stage of physical realisation and formal clinical evaluation. We address the safety issues involved with such systems by describing the development of a portable closed-loop control system for atracurium-induced muscle relaxation. This is a safety-critical system particularly when applied to brain and eye surgery where movement could have serious deleterious effects. The benefits of closed-loop muscle relaxation in providing stable surgical operating conditions over a wide range of patient sensitivities while infusing the minimum amount of drug makes this a worthwhile aim and serves to demonstrate safety issues which are generally applicable to other closed-loop drug infusion systems. It is hoped that the described methodology will facilitate and encourage the clinical application of closed-loop drug infusion systems so that clinical staff and patients may receive the benefits of closed-loop drug therapy.

Atracurium↗
PubMed1996

Performance assessment of a fuzzy controller for atracurium-induced neuromuscular block.

The performance of a fuzzy controller for atracurium-induced neuromuscular block was assessed. Ten ASA I or II patients undergoing surgery anticipated to last at least 120 min were studied. A Datex Relaxograph was used to monitor neuromuscular block. Initially the T1 set point was set at 10% of baseline for at least 30 min (phase I). The T1 set point was then increased to 20% and then returned to 10% for two further periods of at least 30 min duration (phases II and III). The mean (SD) of the mean T1 error in 10 patients for phases I, II and III were 1.1 (1.4)%, -0.43 (1.2)% and 0.28 (0.94)%, respectively. The results show that a simple fuzzy logic controller can provide good accuracy with insensitivity to set point changes despite the considerable inter-individual variation in infusion rate required.

Adult↗
PubMed1995

Perioperative myocardial ischaemia in patients undergoing transurethral surgery: a pilot study comparing general with spinal anaesthesia.

We have studied the incidence and duration of perioperative myocardial ischaemia using ambulatory ECG monitoring in 100 patients undergoing transurethral surgery, who were allocated randomly to receive either general or spinal anaesthesia. The overall incidence of myocardial ischaemia increased from 18% to 26% between the preoperative and postoperative periods. Patients with ischaemic heart disease had a significantly greater incidence of myocardial ischaemia after operation than patients without known ischaemic heart disease (P < 0.05). There was an increase in both the incidence and duration of myocardial ischaemia after operation with both anaesthetic techniques, but no significant difference between the two.

Aged↗
PubMed1995

Early detection and treatment of myocardial ischaemia after operation using continual ambulatory arterial pressure monitoring and ECG ST segment analysis.

We report a case in which the use of continual ambulatory arterial pressure monitoring and ECG ST-segment analysis allowed early detection and treatment of myocardial ischaemia in the postoperative period. We believe that this case illustrates the potential value of ambulatory monitoring in the early postoperative period in high-risk patients.

Blood Pressure Monitoring, Ambulatory↗
PubMed1995

Utilisation of the pre-operative ECG.

The utilisation of the pre-operative ECG in patients undergoing routine surgery was investigated in 354 adult patients over a 2-week period. Sixty-four percent of patients had an ECG pre-operatively. An ECG was not performed in 17% of patients who, current hospital policy suggests, should have had one. In contrast, an ECG was performed in 33% of patients who, hospital policy suggests, have no need of one (all of which were normal), which represented 18% of the total number of pre-operative ECGs performed. In 62% of patients with known cardiac disease, and 44% of patients with strong risk factors for ischaemic heart disease (in the absence of known disease) the ECG was abnormal. This compares with only 7% of patients aged over 50 with no risk factors in whom the ECG was abnormal. These findings suggest that there is room for improvement in the utilisation of the pre-operative ECG, which may have cost implications.

Adolescent↗