The clinical manifestations of anoxic brain injury

Abstract

CCerebral anoxia is typically associated with gross deterioration in brain function following disruption to, or cessation of, the brain's vascular supply. 1 There are several classifications of anoxia, which are dependent upon the nature of the anoxic event.Ischaemic anoxia occurs when there is an interruption to the brain's vascular supply, for example during a cardiac arrest. 2 Anoxic anoxia is associated with lack of oxygen in the lungs and can occur during episodes of near drowning, strangulation or anaesthetic accidents. Other types include anaemic anoxia and toxic anoxia, which involve a reduced haemoglobin concentration and a build up of toxic metabolites in the blood respectively. 3 The survival rate for ischaemic anoxia is increasing due to improved emergency care, with greater numbers of people undergoing cardiac rehabilitation with defibrillation and medication. 4 In comparison with focal brain lesions, much less is understood about the diffuse damage that occurs in cerebral anoxia, and the neurobehavioural and cognitive sequelae. Such an event is catastrophic and often fatal, as the insult occurs to both hemispheres simultaneously, thereby preventing compensation by the contralateral hemisphere. 5 Types of cerebral anoxiaThere have been relatively few studies focusing on the clinical presentations of sur vivors of anoxic brain injury. Studies investigating this condition show variable outcomes, even when the cause and severity are comparable. 6 Before exploring the specific manifestations of a typical anoxic brain injury patient, it is important to consider if it is relevant to distinguish between the different types of anoxia.A number of studies have taken place investigating dif ferent types of anoxia and their ef fects. Earlier studies suggested that the neurological signs depend more on the severity and timing of the incident, rather than the aetiology. However, a study by Garcia-Molina et al. found the type of anoxia to be important in relation to clinical manifestations. 7 It repor ted that sur vivors of anoxic anoxia performed significantly better in neuropsychological tests than the ischaemic anoxia group of patients. This is thought to be due to a certain level of compensation that is possible in anoxic anoxia, as nutrients such as glucose are still able to reach the cells. In ischaemic anoxia, however, such compensation is not possible as there is complete cessation of nutrient and oxygen supply. 7 Another study by Peskine et al. supports this theory and suggests that the different types of anoxia may produce different cerebral pathologies. 2 Neurological effects of cerebral anoxiaCerebral anoxia is known to cause diffuse brain damage. 8 Even with only several minutes of oxygen cessation there can be significant neurological and neuropsychological changes. 9 The mechanism by which cerebral anoxia causes lesions is still partially unknown but is thought to involve a complex cascade of time-dependent alterations in neuronal function, metabolism and morphology. The most significant effect on c...

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