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Biomedical subjects

R G Hicks

Publications and source records attributed to R G Hicks.

At least 19 recordsLinked to original sources
PubMed1992

Some effects of isoflurane on I waves of the motor evoked potential.

We have investigated the effects of isoflurane anaesthesia on the motor evoked potential recorded in the extradural space during corrective spinal surgery in 15 patients. Isoflurane was added to a nitrous oxide in oxygen mixture supplemented with fentanyl and a neuromuscular blocking agent. Isoflurane was administered to achieve end-tidal concentrations of 2%, 1% and 0% in all patients, and also of 1.5% and 0.5% in nine patients. Transcranial electrical stimulation of the motor cortex was used to elicit descending volleys in corticospinal axons (the motor evoked potential). With stimuli of 450-750 V and no isoflurane, multiple I waves were always seen following the D wave. In all patients the number of I waves decreased and individual I waves became smaller in amplitude the greater the isoflurane concentration, but there were only minor changes in the D wave. The greatest depressant effect on I waves occurred at an end-tidal concentration of 0.5%. Given that I waves are an index of synaptic transmission, anaesthetic-induced changes in I waves may provide a useful model for the neuronal events underlying anaesthesia-induced unconsciousness.

Adolescent↗
PubMed1992

Reoperation for recurrent coronary artery disease--a ten year experience.

The need for reoperation caused by recurrence of coronary artery disease is becoming increasingly common. Although reoperation is more difficult and time-consuming, with careful surgical technique it can be carried out with the same mortality as that described by many units for primary coronary artery bypass grafting (1.2-2.0%). In the 172 patients described here, who had coronary artery reoperations between 1981 and 1990, there were two in-hospital deaths (1.2%). There were three postoperative bleeds which required return to theatre. No patient suffered a postoperative neurological deficit or postoperative myocardial infarction. These reoperations comprised 6.9% of the 2497 coronary artery operations carried out in the same period. Follow-up disclosed eight late deaths, from five-62 months after operation; all survivors claim to be symptomatically improved. Consideration should be given to the potential problems of reoperation when carrying out primary myocardial revascularisation.

Adult↗
PubMed1991

Monitoring spinal cord function during scoliosis surgery with Cotrel-Dubousset instrumentation.

Cotrel-Dubousset instrumentation has been a major advance in spinal surgery but, at least theoretically, it carries a higher risk of spinal cord damage. This paper describes our experience in monitoring the function of either ascending sensory pathways or both ascending sensory and descending motor pathways in the spinal cord during such procedures. Seventy-nine juvenile and adult patients are presented in whom either somatosensory recording (n = 39) or simultaneous corticospinal and somatosensory monitoring (n = 40) was attempted by means of epidural electrodes during corrective surgery with Cotrel-Dubousset instrumentation. Abnormal evoked responses were seen in two cases but these resolved in both before the operation was completed. No new neurological deficits occurred nor were any pre-existing deficits increased.

Adolescent↗
PubMed1990

Corticospinal volleys evoked by anodal and cathodal stimulation of the human motor cortex.

1. In fifteen neurologically normal subjects, corticospinal volleys evoked by transcranial stimulation of the motor cortex were recorded from the spinal cord using epidural electrodes in the high-thoracic and low-thoracic regions during surgery to correct scoliosis. 2. Anodal stimulation at the vertex produced complex corticospinal volleys that could be recorded at both sites, with multiple waves analogous to the D and I waves documented in animal experiments. These volleys were of higher amplitude when the cathode was 7 cm lateral to the vertex rather than 7 cm anterior. There were no differences in conduction time between the two recording sites for D and I waves, when these waves could be identified at the low-thoracic site. 3. Anodal stimuli of 150 V commonly produced a descending volley containing a single peak at both recording sites. Modest increases in stimulus intensity to 225-375 V produced a peak 0.8 ms in advance of the wave of lowest threshold in thirteen subjects and, in seven subjects, further increases produced an additional peak 1.7 ms in advance of the first-recruited wave. The early peaks increased in size with stimulus intensity, replacing the first-recruited wave. These results suggest that the site of impulse initiation with electrical stimulation of the motor cortex shifts from superficial cortex to deep structures, approximately 5 and 10-11 cm below the cortex. These sites are probably the internal capsule and the cerebral peduncle. 4. With cathode at the vertex and anode over the 'hand area' the response of lowest threshold occurred at the latency of the anodal D wave but could not be recorded at the low-thoracic site, suggesting that it was generated by the anode over the 'hand area'. Slightly higher intensities induced a 'cathodal D wave' and still higher intensities produced late peaks at latencies of anodal I waves. These cathodal D and I waves involved axons innervating lumbar segments. There was no evidence that cathodal stimulation preferentially produced I waves. Cathodal stimulation at the vertex with the anode 7 cm anteriorly produced similar results: D waves were produced at relatively low intensities, but I waves appeared at relatively high stimulus intensities if at all.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1988

Combined carotid and coronary artery surgery: a review of the literature.

This article reviews 41 different reports that describe various means of surgical management of coexistent carotid and coronary artery disease in almost 1,500 patients. Stroke is the major risk for patients undergoing myocardial revascularization in the presence of symptomatic carotid artery disease or an asymptomatic carotid bruit that reflects an ulcerative lesion or stenosis exceeding 75%. However, patients with asymptomatic carotid stenosis should not routinely undergo prophylactic carotid endarterectomy. Myocardial infarction is the major hazard in patients undergoing carotid endarterectomy who have coronary artery disease. This risk is magnified when the disease is silent. A high level of awareness and rigorous screening are essential in all patients suspected of having coexistent disease. Although a protocol for the management of these patients is important, individual assessment is essential.

Carotid Artery Diseases↗
PubMed1986

Operative mortality after coronary artery surgery. A seven-year experience of 1500 consecutive operations.

Between January 1978 and August 1985, 1500 patients underwent coronary artery bypass grafting by one surgical team, with a total mortality of 0.46% (seven patients). All these patients were suffering from class 3 or class 4 angina and more than half (54%) had evidence of preoperative infarction. The achievement of minimal mortality and morbidity is the immediate aim of surgery; a continuing long-term improvement in symptoms and life expectancy is the ultimate goal. Every physician should be aware of the risks of the invasive treatment of coronary artery disease either by bypass grafting or by angioplasty.

Adult↗
PubMed1986

Thiopentone cerebral protection under EEG control during carotid endarterectomy.

Seventy patients who underwent a total of 77 consecutive carotid endarterectomies were given thiopentone (mean dose 19 mg/kg) under EEG control for cerebral protection during the period of carotid clamping. This technique was used instead of elective insertion of a temporary bypass shunt in response to adverse EEG changes occurring after clamping. The EEG was monitored continuously throughout operation. The EEG burst-suppression pattern with electrically inactive periods of 30-60 seconds was taken as indicating a depth of barbiturate anaesthesia adequate to provide brain protection. Patients exhibited a drop in blood pressure during barbiturate administration: in most the pressure recovered spontaneously but in twenty operations metaraminol was needed to re-establish an adequate pressure before clamping. No adverse cardiological effects were associated with the administration of thiopentone or metaraminol. There was no mortality and no neurological morbidity in this series.

Aged↗
PubMed1979

The vestibulo-ocular (caloric) reflex in the diagnosis of cerebral death.

Correlation between vestibulo-ocular (caloric) reflex and the electroencephalogram was examined in 25 apparently brain-dead and 17 severely brain-injured patients. Among the apparently cerebrally dead, 3 patients still had some EEG activity and in 2, there was some response to caloric testing. In the control group of patients some EEG activity was present in all, and the caloric response was absent in 1. It is concluded that absence of caloric response has similar power to the electroencephalogram in confirming cerebral death. The diagnosis, however, must be made on the total information available, including history and examination of the patient. The policy of the Intensive Care Unit of Prince Henry Hospital in this regard is outlined.

Brain Death↗
PubMed1979

Case report: althesin in status epilepticus.

A case of status epilepticus, resistant to conventional anti-epileptic treatment is described. Althesin rapidly abolished the epileptic activity, and control was achieved by a continuous infusion of Althesin.

Aged↗
PubMed1979

Deep hypothermic arrest: observations on later development in children.

Thirty-two children were reviewed following closure of ventricular septal defect in infancy. Fifteen had undergone continuous perfusion and 17 had been subjected to core cooling followed by deep hypothermic arrest. Parental and professional evaluations of intellectual and motor development, at periods between 7 and 72 months following operation, suggest that there is a higher incidence of developmental abnormality in the subgroup treated with deep hypothermic arrest.

Cardiopulmonary Bypass↗
PubMed1976

The influence of duration of circulatory arrest at 20 degrees C on cerebral changes.

In infants and piglets subjected to periods of circulatory arrest at 20 degrees C there was close correlation between duration of arrest and delay in return of electroencephalographic activity. Post mortem studies demonstrated histological evidence of brain damage in patients after circulatory arrest at 20 degrees C. Similar histological changes were demonstrated in piglets, including some who had complete E.E.G. and clinical recovery from circulatory arrest.

Animals↗
PubMed1975

Some advantages of the membrane oxygenator for open-heart surgery.

The Lande'-Edwards oxygenator has been used for clinical perfusions on 283 patients. Among these patients we have encountered the full range of congenital and acquired defects and a variance in age from 1 day to adulthood. Data are presented concerning the means and methods of perfusion, the defects involved, and the results of treatment. A comparison has been made between two groups of 20 adults each, one group perfused with a bubble oxygenator (Bently) and the other with the Lande'-Edwards membrane lung. This study showed that platelet function is better preserved by the membrane lung, that hemolysis is less severe, and that postoperative bleeding is reduced. Indirect evidence has been accumulated to suggest that pulmonary, cerebral, and renal function is also better preserved when the membrane lung is employed.

Adolescent↗
PubMed1975

The surgical management of extracranial cerebrovascular occlusive disease: a review of 200 consecutive surgical cases.

The role of surgery in the treatment of extracranial cerebrovascular disease is essentially a prophylactic one but it should be borne in mind that apart from preventing stroke, such procedures will or should eliminate symptoms. The authors believe that every patient suffering from cerebrovascular insufficiency should be thoroughly evaluated for extracranial cerebrovascular occlusive disease and that arteriograms should be performed on all patients who could be expected to be candidates for surgery. The various indications for surgery have been discussed. The authors believe that people who have severe bilateral disease and who are of an advanced age are probably in a higher risk group. They also believe that surgery should not be offered to people who have a complete stroke and who are in semi-coma or coma, no matter how rapidly they may be transferred to the operating theatre. The authors firmly believe that intra-operative E.E.G. monitoring is an important adjunct to the safe surgical treatment of lesions of the carotid bifurcation, not only to indicate when shunting is necessary but also to indicate how well that shunt is functioning. In spite of the frequent presence of associated heart disease, hypertension and other vascular lesions, operation can be offered with confidence to suitable candidates. Elimination of symptoms can be expected in over 90% of cases. Only one patient has suffered a stroke since leaving hospital and this occurred because of occlusion in his internal carotid artery which was not operated on. Apart from patient selection, the factors which have contributed to the authors' low morbidity and mortality have been the use of intra-operative E.E.G. monitoring, intra-operative heparinisation and the availability of excellent angiographic studies.

Aged↗