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R A Boas

Publications and source records attributed to R A Boas.

22 records · Page 2Linked to original sources
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Epidural space as a Starling resistor and elevation of inflow resistance in a diseased epidural space.

BACKGROUND AND OBJECTIVES: The origin and the presence of negative pressure in the epidural space as well as the relationship of the extent of epidural anesthesia to epidural pressure has long been a subject of controversy. To further elucidate epidural pressure and its time course, the pressure at the needle tip was continuously measured as it traversed the interspinous ligament and the ligamentum flavum. METHODS: In a group of 22 patients, fluid was infused under gravity, and in a second group of 25 patients, boluses of fluid were administered at controlled infusion rates and under gravity. The volume-pressure-flow relationship was thus measured in one of two ways, either with a manual syringe and pressure transducer or with a pressure-monitoring-computer-controlled volumetric infusion pump. RESULTS: Natural pressure, (i.e., pressure in the epidural space before instrumentation is applied) could be approached when the space was first entered before fluid was infused (initial pressure); or after fluid had been infused (residual pressure). Epidural pressure could be extrapolated from the upsweep of the volume-pressure-flow relationship by projecting it back to just before the first injection. The extrapolated pressure lay between the initial and residual pressures. Medicinal solution placed in the barrel of the syringe did not infuse under gravity until the syringe barrel was lifted to a certain height, at which flow began and continued at a perceptible rate, with very little or no further increase in height required to maintain flow. The pressure at which flow began was the critical opening pressure, a characteristic of a Starling resistor. Furthermore, resistance to inflow of fluid was related to the presence or absence of natural or surgical disease in the epidural space. Resistance was significantly higher in the diseased than in the surgical group, at 114 (range, 22-226) mm Hg/L/h versus 46 (range, 8-86) mm Hg/L/h. Three phases were seen in the pressure-time recordings. CONCLUSIONS: Volume-pressure-flow relationships in the epidural space can be explained by a model in which epidural and subarachnoid pressures are inextricably related with the Starling pressure, dependent on the subarachnoid pressure. This model suggests reasons why spread of anesthetics might be difficult to predict.

Adult↗
PubMedDate not supplied

Sympathetic nerve blocks: in search of a role.

OBJECTIVE: The role of sympathetic blocks in pain therapy is examined in the light of changing concepts of pain pathophysiology. A critical review of the literature also sought to develop an evidence-based analysis of outcome studies to provide recommendations for appropriate applications of sympathetic blocks, together with ideas for further clinically based research. METHODS: A focus on the pathophysiology of neuropathic and inflammatory pain disorders was used to help redefine what contribution, if any, was provided by the sympathetic system, to chronic pain states. Validation of nerve block therapies based on historical practices and these newer concepts and outcome determinations has then been used to present an overview of clinical nerve block therapies as applied to the sympathetic nervous system. RESULTS: 1. Pain Diagnosis: A reclassification of reflex sympathetic dystrophy (RSD) to the new taxonomy of complex regional pain syndromes (CRPS) is supported, with evidence that only a questionable sympathetic contribution at the dorsal root ganglion level can be ascribed etiologically to this group of disorders. Sympathetic blocks can establish whether pains may be nonresponsive or variably responsive to such blocks, but are considered inappropriate in determining a clinical diagnosis. 2. Neuropathic Pain Therapy: (a) A critical review of the literature regarding the use of sympathetic blocks in the treatment of acute herpes zoster pain and in the treatment of postherpetic neuralgia found little support for the widely held view that sympathetic blocks reduced either the incidence of long-term reduction of pain in these disorders. Further attempts to reduce PHN by the combination of blocks with aggressive drug therapies during acute herpes infection are suggested. (b) CRPS (RSD) treatments are seen as evolutionary at present, with the role of sympathetic blocks being only part of a balanced pain treatment strategy aimed at getting patients activated under cover of good analgesia and improved function. These proposals come as consensus recommendations but are not substantiated by outcome studies. 3. Ischemic Pain: Permanent sympathetic block with neurolytic or thermocoagulation techniques provides up to 50% long-term improved blood flow and reduction of pain and ulceration for patients with advanced peripheral vascular disease. This is particularly appropriate at lumbar levels in which percutaneous techniques are safe when conducted with real time imaging control. CONCLUSIONS: Changes in the understanding of CRPS disorders and the role of the sympathetic nervous system in neuropathic pain has changed both the diagnostic and management strategies for these pain states. The sensitivity and specificity of response to sympathetic blocks in establishing their value at diagnostic aids will not be fully established without further clinical study. Further use of intravenous regional blocks or diagnostic intravenous infusions remains questionable. Preventive and therapeutic use of sympathetic blocks in herpes zoster pain remains open to well-controlled study.

Animals↗