Biomedical subjects

W S Poon

Publications and source records attributed to W S Poon.

At least 37 records · Page 2Linked to original sources

PubMed2005

Re-defining the ischemic threshold for jugular venous oxygen saturation--a microdialysis study in patients with severe head injury.

Neurological change is more likely to occur when jugular venous oxygen saturation (SjvO2) is less than 50%. However, the value indicating cellular damage has not been clearly defined. We determined the critical SjvO2 value below which intracerebral extracellular metabolic abnormalities occurred in 25 patients with severe head injury. All patients received standard treatment with normoventilation and maintenance of intracranial pressure < 20 mmHg. SjvO2 was measured from the dominant jugular bulb using a calibrated fibreoptic catheter. Intracerebral metabolic monitoring was performed by collecting perfusate from a microdialysis probe placed in the frontal lobe anterior to the intracranial catheter. Excitotoxin (glutamate) and other extracellular metabolites (lactate, glucose and glycerol) were measured frequently using enzymatic and colorimetric methods. We observed biphasic relationships between SjvO2 and all intracerebral metabolites. Analysis of variance showed that there were rapid increases in glutamate, glycerol and lactate when SjvO2 dropped below 40, 43 and 45% respectively. Extracellular glucose decreased when SjvO2 dropped below 42%. Our findings suggested that the ischemic threshold for SjvO2 in patients with severe head injury is 45%, below which secondary brain damage occurred.

Adolescent↗

PubMed2005

Cerebral blood flow (CBF)-directed management of ventilated head-injured patients.

OBJECTIVE: Ischaemic brain damage has been shown to be an important contributing factor causing head injury fatality. Maintenance of an adequate cerebral perfusion pressure is difficult in patients with elevated intracranial pressure (ICP) and deranged cerebral vasoreactivity. Thirty-five cases of ventilated moderate-to-severe head-injured patients were prospectively studied, correlating their cerebral haemodynamic abnormalities, neurochemical disturbances (using microdialysis methodology) and clinical outcome. METHODS: Cerebral haemodynamic abnormalities were defined and classified by transcranial Doppler ultrasonography (TCD) and stable xenon-CT cerebral blood flow measurements (XeCT) into their status of CO2 reactivity, pressure autoregulation, hyperaemia or non-hyperaemia. Two-hour episodes of these abnormalities with and without haemodynamic intervention were followed in their changes in ICP, CPP, intracerebral metabolites and finally their clinical outcome. RESULTS: Loss of CO2 reactivity was associated with a significantly higher ICP, increasing intracerebral metabolites (lactate, glutamate and glycerol) and invariably a fatal outcome. Impaired pressure autoregulation was also associated with an elevated ICP, but no significant difference in intracerebral metabolites and incidence of favourable clinical outcome. Patients with intact CO2 reactivity and impaired pressure autoregulation were treated with an elevated CPP in 32 episodes, resulting in a significant reduction in ICP, intracerebral glutamate and glycerol and non-survival. In patients with intact CO2 reactivity and impaired pressure autoregulation, eleven episodes of hyperaemia were identified by XeCT. A modest 20%, blood pressure reduction resulted in a trend towards a reduction of ICP, intracerebral glutamate and glycerol and non-survival. CONCLUSIONS: The need for haemodynamic intervention in this group of ventilated patients with moderate-to-severe head inury can be made logical when these abnormalities are identified daily. The success of management was reflected by a stable or improved ICP, CPP, intracerebral metabolic deranagement and survival.

Brain Ischemia↗

PubMed2005

Effect of ischemic preconditioning on brain tissue gases and pH during temporary cerebral artery occlusion.

Previous studies have demonstrated that a brief period of ischemia protect against subsequent severe ischemic insults to the brain, i.e. preconditioning. We evaluated the effects of ischemic preconditioning, produced by 2 min proximal temporary artery occlusion, on brain tissue gases and acidity during clipping of cerebral aneurysm. Twelve patients with aneurysmal subarachnoid hemorrhage were recruited. All patients received standard anesthetics. After craniotomy, a calibrated multiparameter catheter was inserted to measure oxygen (PtO2) tension, carbon dioxide (PtCO2) tension and pH (pHt) in tissue at risk of ischemia during temporary artery occlusion. In patients assigned to the preconditioning group, proximal artery was occluded initially for 2 min and was allowed to reperfuse for 30 min. All patients underwent cerebral artery occlusion for clipping of aneurysm. The rate of change in PtO2, PtCO2 and pHt after artery occlusion were compared between groups using unpaired t test. Baseline brain tissue gases and pHt were similar between groups. Following artery occlusion, the decline in PtO2 and pHt were significantly slower in the preconditioning group compared with the routine care group. These results suggested that ischemic preconditioning attenuates tissue hypoxia during subsequent artery occlusion. Brief occlusion of the proximal artery may be a simple maneuver for brain protection during complex cerebrovascular surgery.

Adult↗

PubMed2005

Magnesium sulfate for brain protection during temporary cerebral artery occlusion.

We evaluated the effects of magnesium sulfate on brain tissue oxygen (PtO2) tension, carbon dioxide (PtCO2) tension and pH (pHt) in patients undergoing temporary artery occlusion for clipping of cerebral aneurysm. We studied 18 patients with aneurysmal subarachnoid hemorrhage. All patients received standard anesthetics using target controlled infusion of propofol (3 microg/ml) and remifentanil (10 ng/ml). After craniotomy, a calibrated multiparameter sensor (Neurotrend, Diametrics Medical, Minneapolis, MN) was inserted to measure PtO2, PtCO2 and pHt in tissue at risk of ischemia during temporary artery occlusion. Patients were then randomly allocated to receive either intravenous saline or magnesium 20 mmol over 10 min followed by an infusion 4 mmol/h. Plasma magnesium concentration, brain tissue gases and pHt were determined at baseline, 30 min after study drug infusion and 4 min after temporary clipping. Data were analyzed by factorial ANOVA with repeated measures. Intergroup difference was compared with unpaired t test. P value < 0.05 was considered significant. Patient characteristics, baseline brain tissue gases and pHt did not differ between groups. Magnesium infusion increased PtO2 by 34%. Following temporary artery occlusion, PtO2 and pHt decreased and PtCO2 increased in both groups. However, tissue hypoxia was less severe and the rate of PtO2 decline was slower in the magnesium group. Our data suggested that magnesium enhances tissue oxygenation and attenuates hypoxia during temporary artery occlusion.

Brain↗

PubMed2005

Monitoring of autoregulation using intracerebral microdialysis in patients with severe head injury.

We evaluated the performance of continuous intracerebral microdialysis to indicate the autoregulatory reserve in 36 severely head-injured patients. All patients received standard treatment with intracranial pressure (ICP) monitoring. A microdialysis probe was placed in the frontal cortex anterior to the ICP catheter. Perfusate was collected frequently and extracellular concentration of glutamate was measured online using enzymatic method. Autoregulatory index was calculated by comparing glutamate concentration with CPP using Pearson's correlation. A correlation coefficient (r) < 0.5 is considered as loss of autoregulation, whereas r values approach 0 indicate preserved autoregulation. The change of autoregulatory status over time was correlated with outcome at 6 months. Three patterns of autoregulatory profiles were identified. Patients with intact autoregulation had satisfactory outcome. Transient impairment of autoregulation may result in favorable outcome if patients responded to treatment. However, persistent loss of autoregulation was associated with poor outcome (P < 0.001). The correlation between extracellular glutamate concentration (by microdialysis) and CPP is a useful index of autoregulation in head-injured patients. It predicts clinical outcome and may be used to guide therapy.

Adolescent↗

PubMed2005

Intravenous magnesium sulfate to improve outcome after aneurysmal subarachnoid hemorrhage: interim report from a pilot study.

OBJECTIVES: Magnesium sulfate (MgSO4) may be useful in preventing neurological injury after subarachnoid haemorrhage (SAH). In this randomized, double-blind study we evaluated the safety and efficacy of MgSO4 infusion to improve clinical outcome after aneurysmal SAH. METHODS: With ethics committee approval and informed consents, 45 patients with SAH were randomly allocated to receive either MgSO4 80 mmol/day or saline infusion for 14 days. All patients also received intravenous nimodipine. Episodes of vasospasm were treated with hypertensive, hypervolemic therapy. Neurological status was assessed 3 months after haemorrhage using Barthel index and Glasgow outcome scale (GOS). Incidences of cardiac and pulmonary complications were also recorded. Data were compared between groups using Mann-Whitney or Fisher exact tests as appropriate. P < 0.05 was considered significant. RESULTS: Patient characteristics, severity of SAH and surgical treatment did not differ between groups. Although the number of episodes was not reduced, MgSO4 shortened the duration of vasospasm. Patients receiving MgSO4 tended to have fewer neurological deficits, better functional recovery and an improved score in GOS. However, none of these outcome variables reached statistical significance. The incidence of cardiac and pulmonary complications in the MgSO4 group (43%) was also similar to that in the saline group (59%), P = 0.14. CONCLUSIONS: MgSO4 infusion after aneurysmal SAH is well tolerated and may be useful in producing better outcome. A larger study is required to confirm the neuroprotective effect of MgSO4.

Comorbidity↗

PubMed2005

Cerebral haemodynamic assessment in patients with thalamic haemorrhage: a pilot study with continuous compliance monitoring.

OBJECTIVE: Thalamic brain haemorrhage is a common disabling and potentially fatal condition. However, management is mainly supportive, very rarely do neurosurgeons resort to evacuation of the haematoma. We hypothesised that cerebral haemodynamic abnormalities in the forms of lost pressure autoregulatory response (PAR) and/or impaired cerebral vasoreactivity (CVR) to carbon dioxide may indicate the haematoma should be aspirated to prevent further brain damage. MATERIAL AND METHODS: Patients with thalamic haemorrhage were selected on clinical ground for intracranial pressure (ICP) monitoring and intensive care management. Spiegelberg double lumen intraventricular balloon catheter was inserted as any other fluid-filled ICP monitoring technique, on the side of the haematoma. Data of ICP, arterial blood pressure (ABP), cerebral perfusion pressure (CPP) and intracranial compliance were collected on a minute basis. Hourly averages were used for analysis. To assess PAR and CVR, blood flow velocity (BFV) in both middle cerebral arteries were measured continuously by transcranial Doppler (TCD) ultrasonography. RESULTS: Six patients with medium (15-25 ml) to large (>25 ml) haematoma volume were subjected to ultrasoud-guided aspiration. 51 CVR and 53 PAR tests were performed. 80820 sets of data were prospectively collected. Progressive reduction in ICP and sustained improvement in compliance and BFV were observed after aspiration. Impairment in PAR and/or CVR was consistent with clinical deterioration in four patients. Such disturbance was normalised after aspiration. Increments in BFV and improvement in compliance were demonstrated. CONCLUSIONS: Cerebral haemodynamic abnormalities in thalamic haematomas can be demonstrated by the non-invasive TCD ultrasonograpy. These abnormalities can be corrected by aspiration of the haematoma, and hence improve intracranial compliance.

Aged↗

PubMed2005

The correlation of midline shifts of human brain with large brain haematoma using a finite element approach.

OBJECTIVES: We report on using a computational (finite element) model to simulate a human skull-brain structure to quantify the distortion of brain. METHODS: We simulated various effects of brain haematoma causing the distortion of brain. Midline shifts of the human brain in relation to size and location of haematoma were compared with the theoretical prediction. RESULTS: Prediction of midline shifts in lobar space-occupying lesions was more accurate that in deep-seated ones (such as thalamic lesions). DISCUSSION: More accurate boundary conditions of space-occupying lesions and better knowledge of physical materials properties of brain tissues can improve predictions of brain deformation using mathematical models.

Brain↗

PubMed2005

Aneurysm recurrence after treatment of paraclinoid/ophthalmic segment aneurysms--a treatment-modality assessment.

OBJECT: The treatment of 21 paraclinoid/ophthalmic segment internal carotid artery aneurysms (PCOSAs) over a seven year period in a regional neurosurgical center was reviewed to assess the degree of obliteration and recurrence rate of these aneurysms after treatment by surgical and endovascular methods. METHOD AND RESULT: An assessment of the clinical notes, operation records and cerebral angiograms was made to evaluate the rate of residual and recurrent aneurysms after treatment and at follow-up. In the coiling group, the aneurysm recurrence rate was eight out of fifteen aneurysms (53%). Four recurrences were from previously totally occluded aneurysms. Out of the six surgical cases, five had follow-up angiography performed. All had stable occlusions of their aneurysms including one with subtotal occlusion. Two clipping procedures after previous coiling achieved total occlusion of aneurysm on follow-up angiography. CONCLUSION: Based on our case series we conclude that PCOSAs frequently recur after primary treatment. GDC coiling was associated with a higher rate of recurrent aneurysms when compared with surgical treatment. A review of the literature on the surgical and endovascular treatment of PCOSAs support this observation.

Adult↗

PubMed2005

Differential role of hydrogen peroxide and staurosporine in induction of cell death in glioblastoma cells lacking DNA-dependent protein kinase.

Various DNA double-strand break repair mechanisms, in which DNA-dependent protein kinase (DNA-PK) has a major role, are involved both in the development and treatment of glioblastoma. The aim of the present study was to investigate how glioblastoma cells responded to hydrogen peroxide and staurosporine (STS) and how such a response is related to DNA-PK. Two human glioblastoma cell lines, M059J cells that lack DNA-PK activity, and M059K cells that express a normal level of DNA-PK, were exposed to hydrogen peroxide or STS. The response of the cells to hydrogen peroxide or STS was recorded by measuring cell death, which was detected by three different methods-MTT, annexin-V and propidium iodide staining, and JC-1 mitochondrial probe. The result showed that both hydrogen peroxide and STS were able to induce cell death of the glioblastoma cells and that the former was mainly associated with necrosis and the latter with apoptosis. Glioblastoma cells lacking DNA-PK were less sensitive to STS treatment than those containing DNA-PK. However, DNA-PK had no significant influence on hydrogen peroxide treatment. We further found that catalase, an antioxidant enzyme, could prevent cell death induced by hydrogen peroxide but not by STS, suggesting that the pathways leading to cell death by hydrogen peroxide and STS are different. We conclude that hydrogen peroxide and STS have differential effects on cell death of glioblastoma cells lacking DNA-dependent protein kinase. Such differential roles in the induction of glioblastoma cell death can be of significant value in selecting and/or optimizing the treatment for this malignant brain tumor.

Apoptosis↗

PubMed2005

Non-surgical primary treatment of chronic subdural haematoma: Preliminary results of using dexamethasone.

From a series of 112 cases (64 men and 48 women, aged 37 - 91 years) of chronic subdural haematoma (CSDH) in a 2-year period from January 1998 to December 1999, we have prospectively studied a group of 30 patients, who were managed non-operatively: 26 patients were treated with dexamethasone (Group 1) and four patients expectantly (Group 4). Nineteen patients (73%) from Group 1 were confused or had focal neurological deficits on admission. The mean maximum thickness of the CSDH was 12 mm. Only one of these cases (4%) required surgical drainage 6 weeks after steroid therapy. One patient died of an unrelated stroke (mortality = 4%). Two patients (8%) were left severely disabled. No significant complication from steroid therapy was documented. Out of the 85 surgically treated patients, 69 patients underwent surgical drainage in addition to steroid therapy (Group 2). Thirteen patients were treated with burr-hole drainage only (Group 3). The mean maximum thickness of the CSDH for these two groups were both 16 mm. Comparing with group 1, the redrainage rate of Group 2 [4% (3/69, p = 1)] and that of Group 3 [15% (2/13, p = 0.253)] were not significantly different. 50% of patients in Group 4 (2/4, p = 0.039) required delayed surgical drainage. The mortality rates of Groups 2, 3 and 4 were 3% (2/69, p = 1), 15% (2/13, p = 0.253) and 50% (2/4, p = 0.039), respectively. Our results suggest that steroid treatment in a selected group of patients is a good option, particularly in patients with co-morbidity.

Adult↗

PubMed2005

Early computed tomography features in extensive middle cerebral artery territory infarct: prediction of survival.

BACKGROUND: To assess the predictive value of prognosis of different computed tomography (CT) features and National Institutes of Health Stroke Scale score (NIHSS) in acute extensive middle cerebral artery (MCA) infarct. METHODS: Fifty five patients with acute extensive MCA infarct had the CT performed within 24 hours of the onset of symptoms. A total of 11 CT features were analysed. The age distribution, presence of risk factors, presence of individual CT feature, the total CT score, and the NIHSS were correlated with the 30 day mortality. RESULTS: Single explanatory variable analysis showed NIHSS, presence of midline shift, midline shift of more than 1 cm, extent of infarct, presence of hydrocephalus, effacement of subarachnoid space/cella media, attenuation of corticomedullary differentiation, and total CT score were associated with the 30 day mortality. Both extent of infarct >67% and attenuation of corticomedullary differentiation gave a sensitivity and specificity of 93% and 95%, respectively, for the prediction of survival. Logistic regression analysis showed that the extent of infarct and NIHSS were the only independent predictors. CONCLUSIONS: CT features and admission NIHSS are important parameters for prediction of survival in extensive MCA infarct.

Aged↗

PubMed2005

Cerebral vasoreactivity: a comparison of color velocity imaging quantification and stable xenon-enhanced CT.

OBJECTIVE: Compromised cerebral vasoreactivity increases the risk of stroke. In this study, we sought to determine whether extracranial arterial blood flow volume measured on color velocity imaging quantification could be predictive of cerebral vasoreactivity after the administration of acetazolamide. SUBJECTS AND METHODS: Cerebral blood flow and extracranial arterial blood flow volume of 35 patients with symptomatic carotid occlusive disease were measured before and after the administration of acetazolamide on stable xenon CT and color velocity imaging quantification, respectively. The changes in unilateral extracranial arterial blood flow volume and respective hemispheric cerebral blood flow were compared. The mean difference in the percentage of change in flow volume, the 95% limit of agreement, and Cohen's kappa coefficient were calculated. RESULTS: A total of 64 unilateral extracranial arterial blood flow volume changes were successfully compared with the changes in the ipsilateral hemispheric cerebral blood flow. The mean difference in percentage of change in flow volume between the two techniques was 4.7%, with the 95% limit of agreement ranging from -90.2% to 99.7%. Cohen's kappa coefficient was 0.41 (95% confidence interval, 0.13-0.68; p = 0.001). CONCLUSION: The performance of color velocity imaging quantification for evaluating cerebral vasoreactivity is comparable to that of transcranial Doppler sonography. Because color velocity imaging quantification is not as limited as transcranial Doppler sonography, it could be an ideal complementary tool to transcranial Doppler sonography. More studies are required to define its clinical value.

Aged↗

PubMed2005

Cervical meningocele with tethered cervical cord in a Chinese infant.

Cervical meningocele and myelomeningocele are rare spinal dysraphic lesions. Unlike lumbosacral dysraphic lesions, there is often no neurological deficit in infants with cervical lesions, thus the subtle features of cervical cord tethering may be overlooked on imaging. We report a case of cervical meningocele in an 8-month-old girl. The tethering band, confirmed intra-operatively, was not evident on imaging. Untethering of the cord was performed together with resection of the sac and repair of the dura. Tethered cord should be suspected in the presence of cervical meningocele and intact neurology. It should be carefully looked for using high-resolution magnetic resonance imaging or computed tomography. Treatment aims to prevent future neurological deterioration, and should include careful intradural exploration with untethering of the cord.

Cervical Vertebrae↗

PubMed2005

Temozolomide in the treatment of recurrent malignant glioma in Chinese patients.

OBJECTIVE: To determine the anti-tumour efficacy and safety profile of temozolomide in local Chinese patients with recurrent malignant glioma. DESIGN. Open-label trial. SETTING: University teaching hospital, Hong Kong. PATIENTS: Twenty-two patients had been enrolled in the study since 2001. Patients had to show unequivocal evidence of tumour recurrence or progression on gadolinium-enhanced magnetic resonance imaging after failing conventional radiotherapy and surgery for initial disease. Histology reviewed by a neuropathologist was required to show anaplastic glioma (anaplastic astrocytoma, anaplastic oligodendroglioma, or mixed anaplastic oligoastrocytoma) or glioblastoma multiforme. INTERVENTIONS: Patients were treated with temozolomide (200 mg/m(2) per day for the first 5 days of a 28-day cycle for four cycles) and monitored clinically every month and radiologically (gadolinium magnetic resonance imaging) at 6 months. MAIN OUTCOME MEASURES: Six-month progression-free survival and objective response rate. RESULTS: Twenty-two patients with recurrent malignant glioma were recruited between January 2001 and July 2004. Progression-free survival at 6 months was 54.5%. The mean progression-free survival for all patients was 7.2 months. The objective response rate, determined by gadolinium magnetic resonance imaging, was 9% for patients demonstrating a complete or partial response and a further 45% for patients demonstrating stable disease. Temozolomide was well tolerated orally with minimal adverse events. CONCLUSION. Preliminary results showed that temozolomide had an acceptable safety profile and anti-tumour activity in recurrent malignant glioma in local Chinese population. The results were comparable with those of western studies.

Adolescent↗

PubMed2004

Identification of two contiguous minimally deleted regions on chromosome 1p36.31-p36.32 in oligodendroglial tumours.

Loss of the short arm of chromosome 1 is a hallmark of oligodendroglial tumours (OTs). Deletion mapping studies in OTs have revealed multiple commonly deleted regions on chromosome 1p, suggesting that there are more than one tumour suppressor gene. To map critical deletion regions on 1p, a series of 25 OTs were examined for loss of heterozygosity (LOH) on 19 polymorphic markers across the 1p arm using microsatellite analysis. Our study revealed that 60% of tumours had LOH of all informative markers on 1p and identified one tumour showing LOH at telomeric markers only. Since this deletion region lies in one of the critical deletion intervals defined previously, we then screened another series of 27 OTs specifically at 1p36.3 for LOH using nine polymorphic markers. A total of 12% (six out of 52) of tumours were found to carry interstitial deletions. The allelic status and the deletion breakpoints in these tumours with interstitial deletion were further verified by fluorescent in situ hybridisation. The small overlapping intervals facilitated the delineation of two contiguous minimally deleted regions of 0.76 Mb, defined by D1S468 and D1S2845, and of 0.41 Mb, bound by D1S2893 and D1S1608, on 1p36.31-36.32. Based on current reference human genome sequence these deletion regions have been sequenced almost to entirety and contain eight annotated genes. TP73, DFFB and SHREW1 are the only known genes located in these deletion regions, while the others are uncharacterised novel genes. In conclusion, our study has narrowed down the critical tumour suppressor loci on 1p36.3, in which two minimally deleted regions are mapped, and markedly reduced the number of candidate genes to be screened for their involvement in OT development.

Brain Neoplasms↗

PubMed2004

Spinal shock in spontaneous cervical spinal epidural haematoma.

A young man presented with quadriparesis and spinal shock because of a spontaneous cervical spinal epidural haematoma was reported. Immediate MRI diagnosis followed by emergency decompression with six hours of presentation resulted in complete recovery.

Adult↗

PubMed2004

A review of isolated third nerve palsy without subarachnoid hemorrhage using computed tomographic angiography as the first line of investigation.

INTRODUCTION: Digital subtraction angiography is recognized as the standard investigation for isolated third nerve palsy thought to be caused by an expanding aneurysm. We reviewed our experience in using computed tomographic angiography (CTA) as the first line investigation for patients presenting with isolated third nerve palsy without subarachnoid hemorrhage. METHOD: We retrieved the medical records of 34 patients who had presented with isolated third nerve palsy without associated subarachnoid hemorrhage to our institution between January 1998 and July 2001. The clinical history, course and outcome as well as the radiological data was reviewed. RESULTS: A total of nine structural lesions (26%) were noted as the etiology of the third nerve palsy. All of the five posterior communicating artery aneurysms were picked up by the CTA. Neither the presence nor the absence of painful complete third nerve palsy was of diagnostic value for intracranial aneurysm. CONCLUSION: A good quality CTA is sufficient to detect a compressive aneurysm and may detect other structural lesions. This allows neurosurgeons to plan the management of patients with isolated third nerve palsy. Patients in whom CTA results are inconclusive should be further investigated with catheter angiography.

Adolescent↗