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Biomedical subjects

S Midgley

Publications and source records attributed to S Midgley.

13 recordsLinked to original sources
PubMed2005

Patient perceptions of "awake" brain tumour surgery.

BACKGROUND: Awake brain tumour surgery allows intraoperative patient assessment and is done to optimise safe tumour removal. It is an established technique but little is known about patient perceptions of the procedure. METHOD: Fifteen adult patients filled out a dedicated questionnaire to assess 10 aspects of patient perceptions of the procedure. FINDINGS: All patients, who were awake for a median of 45 minutes (range 10-105), stated they were adequately prepared for the operation. Most recollected various aspects of the procedure, although 3 patients (20%) had little memory of actually being awake during the surgery despite being cooperative. A minority reported more than minor discomfort (20%), fear (15%) or anxiety (29%), and most felt they coped with the cortical stimulations and functional testing well. Sources of discomfort and pain were the cranial pin holding device, operative position, inadequate infiltration of the cranial wound with local anesthetic, a full bladder causing a desire to micturate and a hard and uncomfortable operating table. CONCLUSIONS: These results, are very similar to a previous American report using a different anesthetic technique, in that most patients tolerate awake craniotomy remarkably well if the procedure is explained to them and some simple precautions are taken. Additionally between 8%-37% of patients (95% Confidence Interval, summing data from the two studies, n = 35) will have no recollection of being awake. Ways of minimising discomfort and problems of anxiety in this patient cohort are discussed.

Adaptation, Psychological↗
PubMed2003

Quantum dynamics under the influence of external magnetic fields.

In this paper, we describe a very versatile numerical model, which can be applied to study the quantum dynamics of an electron wave packet in the presence of external electric and magnetic fields. Detailed numerical analysis is carried out in the paper on the validity of such a model, including (1). comparison with analytical solution in the case of uniform magnetic field, and (2). stringent numerical tests in the case of both electric and magnetic fields. The algorithm presented here is found to be highly accurate, computationally efficient, and numerically stable. It also has the advantage of being able to accommodate arbitrarily complex magnetic field profiles as well as time-varying external fields.

Journal Article↗
PubMed2000

Complex absorbing potential and chebyshev propagation scheme

This work presents a detailed analysis of complex absorbing potentials employed to eliminate reflection or wrap-around of wave packets at numerical grid boundaries. In particular, a limiting value for the maximum propagation time step is derived, beyond which the complex potential may introduce massive errors and the Chebyshev propagation scheme is found to fail.

Journal Article↗
PubMed1998

A feasibility study for megavoltage cone beam CT using a commercial EPID.

This study used a standard commercial electronic portal imaging device (EPID) area detector attached to an isocentric linear accelerator and the Feldkamp algorithm to produce cone beam tomographic reconstructions. The EPID has a active area of 32.5 x 32.5 cm2, and can record 12-bit images using two monitor units (MU), with a resolution of 2.1 x 2.0 mm2 FWHM. Since the EPID was not large enough to record the full patient projection at about 1.5 geometric magnification, it was necessary to offset the detector to collect half-cone projections. Corrections are required to convert pixel values into units of exit dose and to realign the projections to overcome the +/- 4 mm support arm sag. With a geometric magnification of 1.5 the sensitive volume is a cylinder of radius 21 cm and length 17 cm. Unfortunately, the patient couch contains metal bed support rails that lie just outside this cylinder, and produce streak artefacts in the reconstruction. Using 90 views the system delivers a central dose of 90 cGy, and has a density resolution of 4%.

Algorithms↗
PubMed1996

What do general practitioners and community mental health teams talk about? Descriptive analysis of liaison meetings in general practice.

BACKGROUND: Liaison meetings between psychiatrists and general practitioners are now well established. Much has been written about their purpose and structure but little about their content. AIM: A study aimed to describe the clinical focus of meetings between a community mental health team and general practitioners and the nature of the professionals' interactions. METHOD: Audiotapes of six consecutive monthly meetings between a community mental health team and general practitioners in two general practices were analysed. RESULTS: Attendance rates among professionals were over 70%. Over 90% of discussion time was focused on patient-centred clinical matters. Almost two thirds of interactions were focused on patients receiving ongoing joint care; few interactions were devoted to new referrals or to patients who had not been assessed. Psychotic patients, although accounting for 15% of referrals, occupied 54% of patient-centred discussion time. Most interactions consisted of reciprocal information exchange between members of the community mental health team and general practitioners. CONCLUSION: The high attendance rates indicate that both general practitioners and community mental health team members considered these meetings as high priority. The steady move towards management of severely ill psychiatric patients in the community rather than in hospital requires close collaboration between primary and secondary care teams. The meetings described in this paper appear to be a simple, manageable and sustainable response to this need.

Communication↗
PubMed1994

Role of intracranial pressure monitoring in severely head-injured patients without signs of intracranial hypertension on initial computerized tomography.

Previous studies have suggested that only a small proportion (< 15%) of comatose head-injured patients whose initial computerized tomography (CT) scan was normal or did not show a mass lesion, midline shift, or abnormal basal cisterns develop intracranial hypertension. The aim of the present study was to re-examine this finding against a background of more intensive monitoring and data acquisition. Eight severely head-injured patients with a Glasgow Coma Scale score of 8 or less, whose admission CT scan did not show a mass lesion, midline shift, or effaced basal cisterns, underwent minute-to-minute recordings of arterial blood pressure, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) derived from blood pressure minus ICP. Intracranial hypertension (ICP > or = 20 mm Hg lasting longer than 5 minutes) was recorded in seven of the eight patients; in five cases the rise was pronounced in terms of both magnitude (ICP > or = 30 mm Hg) and duration. Reduced CPP (< or = 60 mm Hg lasting longer than 5 minutes) was recorded in five patients. Severely head-injured (comatose) patients whose initial CT scan is normal or does not show a mass lesion, midline shift, or abnormal cisterns nevertheless remain at substantial risk of developing significant secondary cerebral insults due to elevated ICP and reduced CPP. The authors recommend continuous ICP and blood pressure monitoring with derivation of CPP in all comatose head-injured patients.

Adolescent↗
PubMed1994

Measuring the burden of secondary insults in head-injured patients during intensive care.

Primary traumatic brain damage may be compounded by secondary pathophysiological insults that can occur soon after trauma, during transfer to hospital or subsequent treatment of the head-injured patient. The aim of this prospective study was to quantify the burden of a wide range of secondary insults occurring after head injury and to relate these to 12-month outcome. In 124 adult head-injured patients studied during intensive care using a computerized data collection system, < or = 14 clinically indicated physiological variables were measured minute-by-minute. Verified values falling outside threshold limits for > or = 5 min, as defined by the Edinburgh University Secondary Insult Grading scheme, were analysed by insult grade and duration. A greater incidence of secondary insults was detected than previous studies have indicated. Insults were found in 91% of patients and occurred in all severities of head trauma, at all ages, and at every level of Injury Severity Score (ISS). The cumulative durations were much greater than previously recorded although 85% of the total time was at the least severe grade. Short duration insults were common. In 71 patients, in whom 8 insults could be assessed (intracranial pressure, arterial hypo- and hypertension, cerebral perfusion pressure, hypoxemia, pyrexia, brady- and tachycardia), outcome at 12 months was analysed using logistic regression to determine the relative influence of age, admission Glasgow Coma Sumscore, ISS, pupil response on admission, and insult duration on both mortality and morbidity. The most significant predictors of mortality in this patient set were durations of hypotensive (p = .0064), pyrexic (p = .0137), and hypoxemic (p = .0244) insults. When good versus poor outcome was considered, hypotensive insults (p = .0118) and pupil response on admission (p = .0226) were significant.

Adult↗
PubMed1993

Technical considerations in continuous jugular venous oxygen saturation measurement.

Fibreoptic reflection oximetry allows continuous in-vivo estimation of jugular venous oxygen saturation. In combination with pulse oximetry the oxygen extraction ratio SaO2-SjO2/SaO2 can be derived enabling identification of states of global luxury perfusion, normal coupling of global cerebral blood flow with global cerebral metabolism, global cerebral hypoperfusion and global cerebral ischemia. Several technical difficulties may arise affecting the accuracy of SjO2 recordings which must be recognised by the clinician before medical intervention is contemplated.

Artifacts↗
PubMed1993

Multimodality monitoring as a guide to treatment of intracranial hypertension after severe brain injury.

Transcranial doppler measurements of blood flow velocity in the middle cerebral artery were made during treatment of raised intracranial pressure (ICP) in 22 patients with severe brain injury. Twenty patients also had continuous measurement of arterial and jugular bulb venous oxygen saturation (SJO2). The transcranial Doppler parameters studied included both mean flow velocity and pulsatility index (PI). Successful treatment was defined as a reduction of ICP to less than 20 mm Hg with improvement or preservation of cerebral perfusion pressure (CPP) above 60 mm Hg. Successful therapy was associated with a significant rise in SJO2 and reduction of cerebral arteriovenous oxygen content difference (AVDO2) and PI only when the pretreatment CPP was less than 60 mm Hg. An increase in CPP beyond 70 mm Hg did not further improve cerebral oxygen delivery and PI, suggesting that autoregulation became a factor above this CPP threshold. Treatment failure during administration of hypnotic drugs resulted in a reduction in arterial pressure, CPP, SJO2, and mean velocity and in an increase in PI and AVDO2, despite a decrease in ICP. CPP is the most important parameter to monitor during ICP therapy. It should be maintained above 70 mm Hg in patients with severe brain injury.

Adolescent↗
PubMed1992

Transcranial Doppler waveform differences in hyperemic and nonhyperemic patients after severe head injury.

Although increased cerebral blood flow velocity is readily measured by transcranial doppler ultrasonography (TCD), the causes of the velocity elevation may differ. After severe head injury, increased blood flow velocity can develop both in patients with global hyperemia (suggestive of vasodilation) and in those without hyperemia (suggestive of vasospasm). The present study attempts to determine whether TCD can differentiate these two mechanisms of velocity increase. Fourteen severely brain-injured patients who developed increased middle cerebral artery blood flow velocity (time-averaged mean velocity > 100 cm/s) were studied. Eight cases were nonhyperemic and six were hyperemic as defined by arterial-jugular venous oxygen content differences of more than 4 mL/dL and less than 4 mL/dL, respectively. The TCD waveform of all eight nonhyperemic cases showed a diastolic notch, which was absent in all six hyperemic patients (p = 0.00066). TCD waveform profile appears to provide a noninvasive means of differentiating at the bedside the two causes of increased flow velocity. If associated with raised intracranial pressure, these require different treatment.

Adolescent↗
PubMed1992

The effect of changes in cerebral perfusion pressure upon middle cerebral artery blood flow velocity and jugular bulb venous oxygen saturation after severe brain injury.

Middle cerebral artery blood flow velocity and jugular bulb venous oxygen saturation (SJO2) were measured by transcranial Doppler (TCD) ultrasonography and continuous venous oximetry, respectively, in 41 severely brain-injured patients. The purpose of the study was to examine the relationships between TCD flow velocity, SJO2, and alterations in blood pressure (BP), intracranial pressure (ICP), and cerebral perfusion pressure (CPP). In these patients, CPP was reduced either by rising ICP or by falling BP. Both forms of reduction of CPP resulted in a greater fall in diastolic flow velocity than other flow parameters. As CPP decreased below a critical value of 70 mm Hg, a progressive increase in TCD pulsatility index (PI) was observed (r = -0.942, p less than 0.0001), accompanied by a fall in SJO2 (r = 0.78, p less than 0.0001). At pressures above 70 mm Hg, there was no correlation of either PI or SJO2 with CPP. The relationship between PI and CPP held true in patients with both focal and diffuse pathologies and was the same whether changes in CPP resulted from alterations in ICP or BP. The PI and SJO2 correlated better with CPP than with ICP or BP. Transcranial Doppler ultrasonography can identify states of reduced CPP. Decreases in SJO2 with falling CPP suggested progressive failure of cerebral blood flow to meet metabolic demands. Monitoring of TCD and SJO2 may be used to define the optimum CPP level for management of severely brain-injured patients.

Adolescent↗