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Biomedical subjects

Marek A Mirski

Publications and source records attributed to Marek A Mirski.

13 recordsLinked to original sources
PubMed2007

Diagnosis and treatment of vascular air embolism.

Vascular air embolism is a potentially life-threatening event that is now encountered routinely in the operating room and other patient care areas. The circumstances under which physicians and nurses may encounter air embolism are no longer limited to neurosurgical procedures conducted in the "sitting position" and occur in such diverse areas as the interventional radiology suite or laparoscopic surgical center. Advances in monitoring devices coupled with an understanding of the pathophysiology of vascular air embolism will enable the physician to successfully manage these potentially challenging clinical scenarios. A comprehensive review of the etiology and diagnosis of vascular air embolism, including approaches to prevention and management based on experimental and clinical data, is presented. This compendium of information will permit the healthcare professional to rapidly assess the relative risk of vascular air embolism and implement monitoring and treatment strategies appropriate for the planned invasive procedure.

Catheterization, Central Venous↗
PubMed2006

Adjuvant bupivacaine scalp block facilitates stabilization of hemodynamics in patients undergoing craniotomy with general anesthesia: a preliminary report.

STUDY OBJECTIVE: To evaluate the effect of 0.25% bupivacaine scalp block on alterations in hemodynamics and plasma catecholamine metabolites during general anesthesia in patients undergoing frontotemporal craniotomy. DESIGN: Prospective, clinical study. SETTING: Operating room of a university hospital. PATIENTS: 16 ASA physical status II and III patients who were scheduled for frontotemporal craniotomy. INTERVENTIONS: Patients were prospectively randomized to receive a saline control (C group) or bupivacaine scalp block (SB group) as an adjuvant to general anesthesia using isoflurane in 50% N(2)O-O(2). MEASUREMENTS: Routine monitoring of electrocardiogram, heart rate (HR), and mean arterial blood pressure (MAP) were recorded at two-minute intervals from the beginning of anesthesia until 10 minutes after incision, followed by 5-minute intervals throughout the remaining course of the surgery. By prospective design, increases in MAP or HR by 20% above the mean baseline values were treated with 2.5 mg/kg of thiopental combined with 2 mug/kg of fentanyl. Arterial blood was sampled at 5 minutes before and after skin incision and at the start of dural opening for measuring serum catecholamine metabolites by high-performance liquid chromatography. MAIN RESULTS: Only two patients in the SB group needed additional anesthetics for stabilizing their hemodynamics during the course of anesthesia. In contrast, all C group patients required supplemental anesthesia for controlling the abrupt rise in hemodynamic parameters. In addition, absolute MAP and HR values were significantly higher in the C group than in the SB group during the surgical period between incision and dural opening. The differences in hemodynamics observed between the two groups were, however, not accompanied with a significant change in plasma catecholamine metabolites at each predetermined time interval measured. CONCLUSIONS: Pretreatment with 0.25% bupivacaine scalp block appeared to be an effective adjuvant treatment for maintaining stable hemodynamics for patients undergoing craniotomy during general anesthesia especially at the time of skin incision and dural opening. This study design was unable to discern any correlation between elevation in hemodynamic parameters and a rise in serum catecholamine levels.

Adjuvants, Pharmaceutic↗
PubMed2006

Controversies in the management of aneurysmal subarachnoid hemorrhage.

BACKGROUND: The care of patients with aneurysmal subarachnoid hemorrhage has evolved significantly with the advent of new diagnostic and therapeutic modalities. Although it is believed that these advances have contributed to improved outcomes, considerable uncertainty persists regarding key areas of management. OBJECTIVE: To review selected controversies in the management of aneurysmal subarachnoid hemorrhage, with a special emphasis on endovascular vs. surgical techniques for securing aneurysms, the diagnosis and therapy of cerebral vasospasm, neuroprotection, antithrombotic and anticonvulsant agents, cerebral salt wasting, and myocardial dysfunction, and to suggest venues for further clinical investigation. DATA SOURCE: Search of MEDLINE and Cochrane databases and manual review of article bibliographies. DATA SYNTHESIS AND CONCLUSIONS: Many aspects of care in patients with aneurysmal subarachnoid hemorrhage remain highly controversial and warrant further resolution with hypothesis-driven clinical or translational research. It is anticipated that the rigorous evaluation and implementation of such data will provide a basis for improvements in short- and long-term outcomes.

Brain Ischemia↗
PubMed2005

Glucocorticoid therapy in neurologic critical care.

BACKGROUND: The pivotal role of inflammation and edema across the spectrum of central nervous system injury has driven extensive investigation into the therapeutic potential of glucocorticoids. OBJECTIVE: To review the experimental and clinical data relating to the efficacy and adverse effects of glucocorticoids in conditions encountered in critical neurologic and neurosurgical illness. DATA SOURCE: Search of MEDLINE and Cochrane databases, manual review of article bibliographies. DATA SYNTHESIS AND CONCLUSIONS: The efficacy of glucocorticoids is well established in ameliorating edema associated with brain tumors and in improving outcome in subsets of patients with bacterial meningitis. Despite frequently encouraging experimental results, clinical trials of glucocorticoids in ischemic stroke, intracerebral hemorrhage, aneurysmal subarachnoid hemorrhage, and traumatic brain injury have not shown a definite therapeutic effect. The evidence supporting glucocorticoid therapy for spinal cord injury is controversial; however methylprednisolone continues to be widely employed in this setting.

Brain Edema↗
PubMed2005

Spurious hypoxemia.

OBJECTIVE: To discuss the pathophysiology and clinical implications of spurious hypoxemia in the setting of hyperleukocytosis. DESIGN: Case report and review of the literature. SETTING: A 22-bed, adult neurosciences critical care unit at a tertiary care hospital. PATIENT: A 49-yr-old male with chronic myelogenous leukemia. INTERVENTIONS: Administration of hydroxyurea and imatinib mesylate. MEASUREMENTS AND MAIN RESULTS: The patient was admitted to the neurosciences critical care unit with an acute nontraumatic subdural hematoma that required emergent surgical evacuation. His clinical course was notable for neurologic deterioration, sepsis, hyperleukocytosis, severe hypoxemia, and prolonged mechanical ventilation. An inverse relationship was observed between arterial oxygen tension and the magnitude of hyperleukocytosis. Hypoxemia resolved after the institution of chemotherapy and normalization of white cell count. Pulse oximeter saturation was normal throughout. CONCLUSIONS: Patients with hyperleukocytosis are at risk for severe hypoxemia, which may be real or spurious. Failure to recognize spurious hypoxemia can lead to unnecessary diagnostic tests and therapeutic interventions, exposing patients to avoidable risk. A diagnostic algorithm is proposed.

Algorithms↗
PubMed2005

Target-specific catecholamine elevation induced by anticonvulsant thalamic deep brain stimulation.

PURPOSE: Anterior thalamic nucleus (AN) deep brain stimulation (DBS) is effective in raising EEG and clonic seizure threshold in experimental models. Little is known about the specific properties of DBS that afford its anticonvulsant effect. We sought to test the hypothesis that experimental seizures and the anticonvulsant action of AN DBS alter the underlying regional neurochemistry of AN, specifically with facilitation of the serotonergic system to local electrical stimulation. METHODS: Halothane-anesthetized adult Sprague-Dawley male rats underwent stereotactically guided bilateral placement of bipolar stimulating steel electrodes and dialysis probes-guide cannulae in AN and posterior thalamus (PT), and placement of four epidural EEG screw electrodes 48 h before experiments. Both stimulated (AN DBS) and nonstimulated (NO DBS) animals (n=7 per group) were infused with i.v. pentylenetetrazol (PTZ, 5.5 mg/kg/min). Simultaneous thalamic and cortical EEG were recorded, and microdialysis samples were collected from AN and PT in 20-min epochs. AN stimulation was delivered (150 microA; 0.1-ms pulse duration) 40 min before and continued during PTZ infusion. RESULTS: Bilateral AN stimulation delayed the onset of EEG seizures compared with controls: 82+/-8 vs. 58+/-5 min (p=0.02). PTZ infusion alone, or together with stimulation, resulted in a steady increase in norepinephrine (NE), but not dopamine, at AN and PT sites (p<0.001). Although extracellular serotonin was measured at very low levels, the metabolite, 5-hydroxyindoleacetic acid (5-HIAA) increased selectively in AN after stimulation and during preconvulsant infusion of PTZ (p<0.001), returning to baseline after the first generalized seizure. CONCLUSIONS: These data suggest that PTZ and DBS together enhance the nonselective release of NE in thalamic nuclei while specifically stimulating AN-localized serotonin. Low serotonin levels at baseline and during STIM alone or PTZ infusion may indicate efficient reuptake systems for serotonin, with 5-HIAA serving as a surrogate marker for serotonergic activity. Modulation of the AN-specific serotonergic activity may be critical in altering PTZ seizure threshold and be an important neurotransmitter system underlying the efficacy of AN DBS.

Animals↗
PubMed2004

Management of seizures in critically ill patients.

For many neurologists, seizures in critically ill patients represent a difficult problem. Etiology can be elusive because of the complexity of the environment, and treatment decisions can be compromised by the paucity of evidence-based guidelines. Emerging data support a higher than previously thought incidence of nonconvulsive epileptic activity in this patient population, which is another important consideration. Although a seizure in the intensive care unit should be treated aggressively, prophylactic antiepileptic drug administration is dependent on the specific etiology, time of onset, and ensuing complications. After ischemic stroke, prophylactic treatment is not generally recommended, and after intracerebral hemorrhage treatment is recommended only after a few weeks. After subarachnoid hemorrhage, prophylactic treatment beyond discharge is also not recommended. Although there is no reason to believe that late seizures after severe head trauma cannot be prevented with prophylactic treatment, such an approach may be useful during the first week after the injury. Physicians, however, have to individualize the treatment to the critical patient after stroke or trauma based on the presence of additional factors that increase the risk for seizures, including structural cortical injuries and medications used in critical illness with epileptogenic potential. A general therapeutic scheme for seizures in the intensive care unit and the role newer antiepileptic drugs can play are also presented in this review.

Brain Injuries↗
PubMed2004

Sinusoidal modeling of ictal activity along a thalamus-to-cortex seizure pathway I: new coherence approaches.

Understanding associations in neuronal circuitry is critical for tracing epilepsy pathways. Two new methods of measuring coherence between field potentials and EEG channels are proposed for modeling the level of linear association between channels during epileptic seizures. These methods rely upon modeling the repetitive clonic seizure activity as a sum of sinusoids with varying degrees of phase locking. Estimating the amplitude of sinusoids from correlation and cross-correlation time domain data, we can find the coherences from a ratio of these amplitudes. One method utilizes amplitude finding from the multiple signal classification (MUSIC) technique. The other method uses alterations in amplitude of individual sinusoids and their ratios in a matrix pencil equation formed from cross- and auto-correlation matrices. The corresponding generalized eigenvalues of these equations form the coherence ratios. This utilizes the estimation of signal parameters using rotational invariance techniques (ESPRIT) algorithm to arrive at coherence amplitude ratios. Simulations illustrate that the MUSIC method provides better noise immunity as it out-performs the conventional Fourier transform-based method for coherence estimation. Both coherence estimators reflect presence of sinusoidal components that are propagated or not propagated along a particular transmission pathway. We illustrate the value of both methods by examining the strength of correlation between seizure EEG from specific thalamic nuclei and cortex in a rodent model of generalized epilepsy. The pentylenetetrazol (PTZ) chemoconvulsant model in rats reflects selective activation of the anterior thalamic nucleus. Using both methods, this neuronal element has much larger coherence with cortex than another thalamic region, the posterior thalamus (p < 0.05). These methods isolate the unique contribution of anterior thalamus in the formation of an ictal network and corroborate earlier conventional or periodogram techniques.

Algorithms↗
PubMed2003

Anterior thalamic mediation of experimental seizures: selective EEG spectral coherence.

PURPOSE: Physiological evidence has shown that the anterior thalamus (AN) and its associated efferents/afferents constitute an important propagation pathway for pentylenetetrazol (PTZ)-mediated generalized seizures in rodents. Previous work demonstrated metabolic, physical, chemical, and electrical stimulation data supporting a role for AN in the expression of PTZ seizures. We now extend these observations through examination of neuroelectric signal indicators during seizure epochs. We show that the EEG recorded from AN is highly coherent with surface cortical (CTX) EEG during the immediate preconvulsant period and during the ictal stateough. METHODS: Awake rats were continuously infused with PTZ until clonic seizures were recorded by using both subcortical AN, posterior thalamus (PT), or hippocampal (HPC) bipolar electrodes and cortical EEG. Through the signal-analysis techniques of ordinary and partial coherence, it was possible to focus selectively on signal correlations between AN and CTX (AN/CTX) by removing the effects of unaffiliated regions such as PT and HPC. RESULTS: Coherence of PT/CTX was observed to be modest, and partial coherence of PT/CTX with the effects of AN/CTX removed did not improve the signal coherence of PT/CTX (PT/CTX-AN). In contrast, AN/CTX coherence was observed to be high, with undiminished correlation when PT/CTX influence was removed (AN/CTX-PT). The most robust band of AN/CTX coherence was centered around the spike-wave clonic frequency of 1-3 Hz. Partial multiple coherence-analysis techniques were used to remove the possible signal contributions from hippocampus in addition to PT. The AN/CTX coherence remained fully preserved in the low-frequency bands. CONCLUSIONS: These data provide electrophysiologic evidence supporting the special role of the anterior thalamus in the propagation of seizure activity between subcortex and cortex.

Animals↗
PubMed2003

Critical care and perioperative management in traumatic spinal cord injury.

Traumatic spinal cord injury is frequently associated with brain injury and with alterations in respiratory and cardiovascular function that require critical care management. Complications include respiratory failure, atelectasis, pneumonia, neurogenic shock, autonomic dysreflexia, venous thromboembolism, and sepsis. While complications may be managed with supportive care, the goal of ameliorating neurologic outcome has proved elusive. Methylprednisolone, when instituted <8 hours after traumatic spinal cord injury, was associated in two clinical trials with statistically significant improvements in motor scores at 6 months and 1 year; however, critical reappraisal of these data raises questions about their validity and clinical relevance. Until more evidence of clinically effective therapies is available, acute management must be driven by pathophysiologic principles, with emphasis on interventions that attenuate secondary neurologic injury; these include the rational use of immobilization, cautious airway management, and promotion of cord perfusion and oxygenation with the appropriate level of hemodynamic and respiratory support. Clinical trials of pharmacologic neuroprotection have yielded disappointing results, but the ongoing elucidation of spinal cord repair and regenerative mechanisms suggests new therapeutic prospects.

Critical Care↗
PubMed2003

Neurologic intensive care resource use after brain tumor surgery: an analysis of indications and alternative strategies.

OBJECTIVE: Greater demand and limited resources for intensive care monitoring for patients with neurologic disease may change patterns of intensive care unit utilization. The necessity and duration of intensive care unit management for all neurosurgical patients after brain tumor resection are not clear. This study evaluates a) the preoperative and perioperative variables predictive of extended need for intensive care unit monitoring (>1 day); and b) the type and timing of intensive care unit resources in patients for whom less intensive postoperative monitoring may be feasible. DESIGN: Retrospective chart review. SETTING: A neurocritical care unit of a university teaching hospital. PATIENTS: Patients were 158 consecutive postoperative brain tumor resection patients admitted to a neurocritical care unit within a 1-yr period (1998-1999). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Twenty-three patients (15%) admitted to the neurocritical care unit for >24 hrs were compared with 135 (85%) patients admitted for <24 hrs. Predictors of >1-day stay in the neurocritical care unit in a logistic regression model were a tumor severity index comprising radiologic characteristics of tumor location, mass effect, and midline shift on the preoperative magnetic resonance imaging scan (odds ratio, 12.5; 95% confidence interval, 3.1-50.5); an intraoperative fluid score comprising estimated blood loss, total volume of crystalloid, and other colloid/hypertonic solutions administered (odds ratio, 1.8; 95% confidence interval, 1.2-2.6); and postoperative intubation (odds ratio, 67.5; 95% confidence interval, 6.5-702.0). Area under the receiver operating characteristic curve for the model of independent predictors for staying >1 day in the neurocritical care unit was 0.91. Neurocritical care unit resource use was reviewed in detail for 134 of 135 patients who stayed in the neurocritical care unit for <1 day. Sixty-five (49%) patients required no interventions beyond postanesthetic care and frequent neurologic exams. A total of 226 intensive care unit interventions were performed (mean +/- sd, 1.7 +/- 2.6) in 69 (51%) patients. Ninety (67%) patients had no further interventions after the first 4 hrs. Neurocritical care unit resource use beyond 4 hrs, largely consisting of intravenous analgesic use (72% of orders), was significantly associated with female gender, benign tumor on frozen section biopsy, and postoperative intubation (chi-square, p <.05). CONCLUSIONS: A small fraction of patients require prolonged intensive care unit stay after craniotomy for tumor resection. A patient's risk of prolonged stay can be well predicted by certain radiologic findings, large intraoperative blood loss, fluid requirements, and the decision to keep the patient intubated at the end of surgery. Of those patients requiring intensive care unit resources beyond the first 4 hrs, the interventions may not be critical in nature. A prospective outcome study is required to determine feasibility, cost, and outcome of patients cared for in extended recovery and then transferred to a skilled nursing ward.

Aged↗
PubMed2003

Prediction of PTZ-induced seizures using wavelet-based residual entropy of cortical and subcortical field potentials.

Our proposed algorithm for seizure prediction is based on the principle that seizure build-up is always preceded by constantly changing bursting levels. We use a novel measure of residual subband wavelet entropy (RSWE) to directly estimate the entropy of bursts, which is otherwise obscured by the ongoing background activity. Our results are obtained using a slow infusion anesthetized pentylenetetrazol (PTZ) rat model in which we record field potentials (FPs) from frontal cortex and two thalamic areas (anterior and posterior nuclei). In each frequency band, except for the theta-delta frequency bands, we observed a significant build-up of RSWE from the preictal period to the first ictal event (p < or = 0.05) in cortex. Significant differences were observed between cortical and thalamic RSWE (p < or = 0.05) subsequent to seizure development. A key observation is the twofold increase in mean cortical RSWE from the preictal to interictal period. Exploiting this increase, we develop a slope change detector to discern early acceleration of entropy and predict the approaching seizure. We use multiple observations through sequential detection of slope changes to enhance the sensitivity of our prediction. Using the proposed method applied to a cohort of four rats subjected to PTZ infusion, we were able to predict the first seizure episode 28 min prior to its occurrence.

Algorithms↗