Best practice & research. Clinical anaesthesiology
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Osmolality is the primary determinant of water movement across the intact blood-brain barrier (BBB), and we can predict that reducing serum osmolality would increase cerebral oedema and intracranial pressure. Brain injury affects the integrity of the BBB to varying degrees. With a complete breakdown of the BBB, there will be no osmotic/oncotic gradient, and water accumulates (brain oedema) consequentially to the pathological process. ⋯ In patients with brain pathology, volume depletion and/or hypotension greatly increase morbidity and mortality. In addition to management of intravascular volume, fluid therapy must often be modified for water and electrolyte (mainly sodium) disturbances. These are common in patients with neurological disease and need to be adequately treated.
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Best Pract Res Clin Anaesthesiol · Dec 2007
ReviewCardiovascular therapy of neurosurgical patients.
The causes of postoperative cardiovascular disturbances in neurosurgical patients include direct cardiac neurogenic effects, clinical situations where brain tissue is underperfused, and hyperdynamic states. EKG and echographic abnormalities are common in subarachnoid hemorrhage where cardiac troponin I is the most useful predictor of cardiac risk after SAH. Neurogenic pulmonary edema is short lived and often resolves with resolution of the neurologic problem. ⋯ Induced hypertension improves blood flow through vessels compromised by cerebral stenting, angioplasty, microcatheters, thrombolysis, carotid clamping, intracranial bypass and cerebral vasospasm. Hyperdynamic lesions include vascular breakthrough after elimination of cerebral arteriovenous malformations, but also emergence hypertension and hyperemia. Pharmacologic agents and adjunctive measures are effective in controlling both the systemic and the cerebral circulation.
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Dreaming during anaesthesia is defined as any recalled experience (excluding awareness) that occurred between induction of anaesthesia and the first moment of consciousness upon emergence. Dreaming is a commonly-reported side-effect of anaesthesia. The incidence is higher in patients who are interviewed immediately after anaesthesia (approximately 22%) than in those who are interviewed later (approximately 6%). ⋯ Most dreaming however, occurs in younger, fitter patients, who have high home dream recall, who receive propofol-based anaesthesia and who emerge rapidly from anaesthesia. Their dreams are usually short and pleasant, are related to work, family and recreation, are not related to inadequate anaesthesia and probably occur during recovery. Dreaming is a common, fascinating, usually pleasant and harmless phenomenon.
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Inadequate anaesthesia may lead to awareness. A properly trained anaesthetist, administering anaesthesia according to their knowledge of pharmacology and patient and surgical characteristics, assisted by clinical signs and monitoring, can minimize this risk. Relying upon volatile-based anaesthesia delivered at a concentration of at least 0.5 MAC may be effective, but this precludes the use of total intravenous anaesthesia techniques and in any case may lead to unwanted hypotension. ⋯ The development of electroencephalographic monitors of anaesthetic depth provides an opportunity to prevent awareness. Two large scale studies, one of which was a randomized trial, have identified a 5-fold reduction in risk of awareness when depth of anaesthesia using bispectral index monitoring was used. The incidence of awareness can be further reduced with currently available techniques used more widely.