NEAR DEATH EXPERIENCES DURING CARDIAC ARREST RESEARCH - Background

SPECIFIC RESEARCH STUDIES:

Perhaps the biggest challenge facing neuroscience at the dawn of the 21st century is understanding the relationship between mind, consciousness and the brain. Editorials in recent years, including in 'Scientific American' and 'Nature Neuroscience' have highlighted the difficulties faced by cognitive neuroscience in attempting to answer questions regarding the nature, as well as the mechanism by which subjective experiences and our sense of consciousness may arise through neuronal processes.

Recent research has indicated that studying the human mind and consciousness during cardiac arrest may hold the key to understanding this enigma. At least four independent studies carried out respectively in the UK, Holland and the USA, have indicated that up to 10% of cardiac arrest survivors report some continuation of consciousness and activity of the mind despite a lack of global brain activity. Due to the fact that all three clinical criteria of death (no pulse, no respiration and no brainstem activity) are invariably reached during a cardiac arrest, this is the closest clinical model to studying the human mind and consciousness at the end of life.

Cardiac arrest survivors have described lucid, well structured, thought processes together with reasoning and memory formation, as well as an ability to 'see' and recall their own resuscitation from the time of cardiac arrest (sometimes confirmed by resuscitation staff). The features of the recalled experiences are compatible with the previously described 'near death experience', which has traditionally been thought to occur in response to a cerebral chemical derangement or a psychological response to the perceived threat of death. Interestingly an eight year follow up study has shown that those with this experience also develop a positive transformational change in behaviour by two years, as characterised by greater empathy and understanding for others, involvement in the family and less fear of death compared with those without the experience.

During a cardiac arrest and advanced cardiac life support (ACLS) global brain function ceases due to the fact that maximal mean arterial blood pressure (MAP), reaches approximately 30 -40 mmHg, which is inadequate to maintain adequate cerebral perfusion. EEG studies have demonstrated that electrical activity of the brain ceases by approximately 10 seconds, leading to an isoelectric (flat) line, which may continue for up to two hours after the restoration of cardiac output. Other studies have shown a correlation between an isoelecteric (flat) EEG and a lack of electrical activity in the deep brain structures. Clinically, there is also a loss of brainstem reflexes such as the gag reflex, indicating a lack of brainstem function.

The occurrence of consciousness during cardiac arrest has widespread implications. Firstly although paradoxical, it suggests that mind or consciousness may continue even though brain function, is at best severely impaired and at worst, non-functional. In a recent editorial in The Lancet, this possibility together with the alternative explanation that the period of consciousness may be occurring as the patients' rapidly enter or gradually recover from the state of flat EEG and absent brain function were analysed. The need for further prospective research aimed at testing the reports of veridical perception was also emphasised. The second significant implication is that having the experience is associated with a positive behavioural change, which leads to a 'happier' and more positive outlook on life. The neural correlates for this change in behaviour are not understood but if discovered could hold the key to further understanding the neural mediators of 'happiness''.