Transient analysis of M/M/1 queuing theory: an overview

Queuing is a common phenomenon in our daily life. Mathematical study on waiting line or queues is called queuing theory. Generally, queuing theory has been used extensively by service industry in order to optimize the service effectiveness and improve the customer satisfaction since it helps an organization to understand how a system operates while reviewing the efficiency of the system. Most of queuing theory deals with system performance in steady-state condition. That is, most queuing models assume that the system has been operating with the same arrival rate, service rate and other characteristics for a sufficiently long time that the probabilistic behavior of performance measures such as queue length is independent of initial condition. However, in many situations, the parameters defining the queuing system may vary over time. Under such circumstances, it is most unlikely that such systems are in equilibrium. This paper reviews the transient behavior (no assumption of statistical equilibrium) of the queuing model. The aim is to provide sufficient information to analysts who are interested in studying queuing theory with this special characteristic

An outcome analysis of children who underwent repair of spinal dysraphism Hospital Universiti Sains Malaysia

An outcome analysis of children who underwent spinal dysraphism repair in Hospital Universiti Sains Malaysia. Objective: To evaluate the impact of multiple factors and outcome (ambulatory function, and control of bowel and bladder) associated with spinal dysraphism following surgical repair. Methodology: A retrospective chart review of children operated for spinal dysraphism in Hospital Universiti Sains Malaysia from 1 January 1990 to 31 December 2004 was conducted. Children who were solely operated before age 12 years old and who had been followed-up for at least 18 months post repair were included in the study. Results: A total of 53 children with spinal dysraphism were included in the study. Open spinal dyraphism was 79.2% and closed spinal dysraphism 20.8%. 77.4% of patients with spinal dysraphism were ambulatory after two years following repair. Univariate analysis of the association of predictors with ambulatory status revealed that hydrocephalus, presence of shunt, motor and reflex score of SBNS, and status of difference between functional and anatomical level were significant factors of ambulatory status. By using multiple logistic regression, none of the significant predictors from the univariate analysis for ambulation function remained significant. The significant predictors from the univariate analysis of poor bladder control in this study were related to the type of spina bifida, presence of hydrocephalus, presence of sensation at 81 and below, and functional level below LS and above. From multivariate analysis, type of spinal dysraphism and functional level at L5 were found to be the significant predictors for poor bladder control. Conclusion: Open spinal dysraphism was the more common operated spinal dysraphism in Hospital Universiti Sains Malaysia. This study has demonstrated various factors that can affect the ambulatory function, and control of bowel and bladder in children with spinal dysraphism

Factors Affecting the Outcomes in Children Post-Myelomeningocoele Repair in Northeastern Peninsular Malaysia

Background: The present study aimed to evaluate the impact of multiple factors and outcomes (ambulatory function and sphincter function) on children with myelomeningocoele (MMC) following surgical repair. Methods: A retrospective chart review of children that underwent surgery for MMC in the Hospital Universiti Sains Malaysia from 1 January 1990 to 31 December 2004 was conducted. Only those children who were followed-up for at least 18 months after the operation were included in the study. Results: A total of 42 children with MMC were included in the study. Approximately 79% of the MMC were located in the lumbosacral and sacral regions. Thirty (71.4%) of the children had hydrocephalus, and 28 (67.7%) had a cerebrospinal fluid (CSF) shunt inserted. An analysis of the association between the predictors of ambulatory status revealed that hydrocephalus (P = 0.013), the presence of a CSF shunt (P = 0.005), intact motor function at L3 and below (P < 0.001), and the presence of deep tendon reflexes (P < 0.001) were good factors of ambulatory status. Only 16.7% of the children did not have urinary or faecal incontinence. Hydrocephalus (P = 0.049) and low-level MMC (P = 0.028) were significantly associated with sphincter control. Conclusion: Multiple factors contributed to the outcomes in post-MMC repair children in terms of ambulation and sphincter function following a repair of MMC. The Spina Bifida Neurological Scale (SBNS) should be applied during the management of these children to identify neurological deterioration

Neuronavigation-guided endoscopic management of a pineal region tumour with obscured floor of the third ventricle: case report

Shunt surgery is frequently chosen to manage periventricular metastasis of pineal region tumors which obscured the floor of the third ventricle. However, this procedure falls short due to distant metastasis. Neuronavigation-guided endoscopic surgery offers a viable alternative. A 17 years old man became symptomatic from widespread periventricular metastasis of a pineal region tumor which conmpletely obscured the floor of the third ventricle. Endoscopic tumor biopsy followed by neuronavigation-guided endoscopic third ventriculostomy was performed successfully.This case report emphasizes the value of neuronavigation-guided endoscopic third ventriculostomy as a feasible surgical alternative for pineal region tumors with widespread periventricular metastasis that obscure the third ventricular floo

Post traumatic cerebral oedema in severe head injury is related to intracranial pressure and cerebral perfusion pressure but not to cerebral compliance

This was a prospective cohort study, carried out in the Neuro Intensive Care Unit, Department of Neurosciences, Hospital Universiti Sains Malaysia, Kubang Kerian Kelantan. The study was approved by the local ethics committee and was conducted between November 2005 and September 2007 with a total of 30 patients included in the study. In our study, univariate analysis showed a statistically significant relationship between mean intracranial pressure (ICP) as well as cerebral perfusion pressure (CPP) with both states of basal cistern and the degree of diffuse injury and oedema based on the Marshall classification system. The ICP was higher while CPP and compliance were lower whenever the basal cisterns were effaced in cases of cerebral oedema with Marshall III and IV. In comparison, the study revealed lower ICP, higher mean CPP and better mean cerebral compliance if the basal cisterns were opened or the post operative CT brain scan showed Marshall I and II. These findings suggested the surgical evacuation of clots to reduce the mass volume and restoration of brain anatomy may reduce vascular engorgement and cerebral oedema, therefore preventing intracranial hypertension, and improving cerebral perfusion pressure and cerebral compliance. Nevertheless the study did not find any significant relationship between midline shifts and mean ICP, CPP or cerebral compliance even though lower ICP, higher CPP and compliance were frequently observed when the midline shift was less than 0.5 cm. As the majority of our patients had multiple and diffuse brain injuries, the absence of midline shift did not necessarily mean lower ICP as the pathology was bilateral and even when after excluding the multiple lesions, the result remained insignificant. We assumed that the CT brain scan obtained after evacuation of the mass lesion to assess the state basal cistern and classify the diffuse oedema may prognosticate the intracranial pressure and cerebral perfusion pressure thus assisting in the acute post operative management of severely head injured patients. Hence post operative CT brain scans may be done to verify the ICP and CPP readings postoperatively. Subsequently, withdrawal of sedation for neurological assessment after surgery could be done if the CT brain scan showed an opened basal cistern and Marshall I and II coupled with ICP of less than 20 mmHg. [Asian J Surg 2009;32(3):157–62

Pleomorphic xanthoastrocytoma in a case of tuberous sclerosis

Tuberous sclerosis is a known phakomatosis and the associated finding of a subependymal giant cell astrocytoma is common with this disorder. A case of tuberous sclerosis with a finding not previously reported, i.e. that of a pleomorphic xanthoastrocytoma, is presented here

Role of High Augmentation Index in Spontaneous Intracerebral Haemorrhage

Intracerebral haemorrhage (ICH) is the most disabling and least treatable form of stroke. Its risk factors include old age, hypertension, diabetes mellitus, hypercholesterolaemia, smoking and high alcohol intake, which are also associated with arterial stiffness. The aim of the present study was to determine the prognostic value of high augmentation index (AI), which is a surrogate marker of arterial stiffness, in patients with spontaneous ICH. Methods: A prospective study of 60 patients with spontaneous supratentorial ICH was conducted. Outcome was assessed using the Modified Rankin Scale at 3 months follow-up. Data were collected on age and sex, risk factors for ICH, clinical parameters, laboratory parameters, radiological findings and hospital management. Logistic regression analysis was carried out to identify independent predictors of 3-month outcome and mortality. Results: Admission Glasgow Coma Scale score (OR, 0.7; 95% CI, 0.450–0.971; p = 0.035), total leukocyte count (OR,1.2; 95% CI, 1.028–1.453; p = 0.023) and haematoma volume (OR, 1.1; 95% CI, 1.024–1.204; p = 0.011) were found to be statistically significant in multivariate analysis of 3-month poor outcome. Factors independently associated with mortality were high AI (OR, 8.6; 95%CI, 1.748–40.940; p = 0.007) and midline shift (OR, 7.5; 95%CI, 1.809–31.004; p = 0.005). Conclusion: Admission Glasgow Coma Scale score, total leukocyte count and haematoma volume were significant predictors for 3-month poor outcome; high AI and midline shift were significant predictors for 3-month mortality