Best practice & research. Clinical anaesthesiology
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Best Pract Res Clin Anaesthesiol · Dec 2007
ReviewPrevention and treatment of intracranial hypertension.
Intracranial pressure (ICP) is the pressure exerted by cranial contents on the dural envelope. It comprises the partial pressures of brain, blood and cerebrospinal fluid (CSF). Normal intracranial pressure is somewhere below 10 mmHg; it may increase as a result of traumatic brain injury, stroke, neoplasm, Reye's syndrome, hepatic coma, or other pathologies. ⋯ When intracranial hypertension persists, second-tier treatments may be indicated. These include 'forced hyperventilation' (paCO2 < 25 mmHg), barbiturate coma or experimental protocols such as tris buffer, indomethacin or induced hypothermia. The last resort is emergent bilateral decompressive craniectomy; once taken into consideration, it should be performed without undue delay.
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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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Increased attention in recent years in both the academic literature and general media on awareness during general anaesthesia has raised the spectre of an increase in the liability burden of anaesthesia awareness. Liability will be different around the world, largely influenced by factors such as the presence of no-fault compensation systems for medical complications in some countries and the characteristics of the common law tort systems in others, such as the United States. A review of the largest single source for liability data, the American Society of Anesthesiologists' Closed Claims database, found the proportion of anaesthesia malpractice claims and claim payment amounts for awareness did not increase during the 1990s. However, due to the time lag to settlement of claims, this data predates recent attention to awareness and electroencephalographic monitoring, factors that may increase liability for awareness in the future.
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Do patients form memories of intra-operative events when they are adequately anaesthetized? Studies of memory priming during anaesthesia with depth or awareness monitoring provide some evidence that they do, although only the most basic form of memory function, perceptual priming, persists when patients are unconscious. The probability of memory encoding increases as depth of anaesthesia decreases. There is a theoretical possibility that patients can be adversely affected, through memory priming, by comments made in the operating theatre, and some evidence that positive intra-operative suggestions can benefit patients.