Anoxic brain injury
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Associate Editors-In-Chief: Varun Kumar, M.B.B.S.; Lakshmi Gopalakrishnan, M.B.B.S.
Overview
Anoxic or hypoxic brain injury is often seen after cardiac arrest. Major efforts are underway to improve "The Chain of Survival" and prognosis based upon early access to medical care, early defibrillation, early CPR and early hospital care. Therapeutic hypothermia may improve outcomes. Steroids and hyperventilation have not improved outcomes.
Predictors of Survival
Improved Prognosis with In-Hospital versus Out-of-Hospital Cardiac Arrest
Out-of-hospital cardiac arrest (OHCA) has a worse survival rate (8-22% on admission resulting in 2-8% at hospital discharge) than in-hospital cardiac arrest (15% at discharge).
Improved Prognosis with VT/VF versus PEA or Asystole
A major determining factor in survival is the initially documented rhythm. Patients with ventricular fibrilation (VF) or ventricual tachycardia (VT) (aka VT/VF) have a 10-15 fold greater chance of survival than patients with pulseless electrical activity (PEA) or asystole. VT/VF are sensitive to defibrillation, whereas asystole and PEA are not.
Rapid Defibrillation is Associated with Imporved Survival
Rapid intervention with a defibrillator increases survival rates.[1][2]
Role of Pre-Hospital Ambulance Care
Cobbe et al (1996) conducted a study into survival rates from out of hospital cardiac arrest. 14.6% of those who had received resuscitation by ambulance staff survived as far as admission to an acute hospital ward. Of these, 59.3% died during that admission, half of these within the first 24 hours. 46.1% survived to hospital discharge (this is 6.75% of those who had been resuscitated by ambulance staff), however 97.5% suffered a mild to moderate neurological disability, and 2% suffered a major neurological disability. Of those who were successfully discharged from hospital, 70% were still alive 4 years after their discharge.[3][4]
Incidence and Predictors of Entering Into a Vegetative State versus Making a Full Recovery
Cardiac arrest is the third leading cause of coma. Approximately 80% of patients who suffered a cardiac arrest who survived to be admitted to the hospital will be in coma for varying lengths of time. Of these patients, approximately 40% will enter into a persistent vegetative state and 80% die within 1 year. in contrast, if a patient survives until discharge without significant neurological impairment, he/she can expect a fair to good quality of life.
The duration of hypoxia/ischemia determines the extent of neuronal injury i.e. in patients who suffer hypoxia for less than 5 minutes, are less likely to have permanent neurologic deficits, while with prolonged, global hypoxia, patients may develop myoclonus or a persistent vegetative state.[5]
Thomassen A and Wernberg M conducted a study into prevalence and prognostic significance of coma after cardiac arrest outside intensive care and coronary units where 181 patients resuscitated from cardiac arrest were reviewed. In patients who suffered cardiac arrest outside hospital, 84% were comatose for more than 1hour and 56% for more than 24 hours. There was no significant neuronal damage if coma lasted less than 24hours. However, in patients who were comatose for more than 24 hours, had a bad prognosis. Of the patients reviewed, 85 remained comatose for more than 24hours and only 7 of them were discharged alive, but with severe neurological impairment with severity increasing with duration of coma. Of the patients who were in coma for more than 7days, none regained consciousness and 80 patients died in coma.[6]
Ballew (1997) performed a review of 68 earlier studies into prognosis following in-hospital cardiac arrest. They found a survival to discharge rate of 14% (this roughly double the rate for out of hospital arrest found by Cobbe et al (see above)), although there was a wide range (0-28%).[7]
Systematic Efforts to Improve Survival Following Cardiac Arrest: The Chain of Survival
Multiple organizations now promote the "Chain of Survival" as a way to maximise prognosis following cardiac arrest. The Chain of Survival is made up of 4 links:
- Early Access - Early identification of patients at risk of cardiac arrest early is an effective way of improving prognosis, as it is often possible to prevent the cardiac arrest. Similarly, if the arrest is witnessed there is a much greater chance of survival, as treatment can be innitiated immediately.
- Early CPR - Cardiopulmonary resuscitation (CPR) buys time by maintaining a limited circulation until it is possible to defibrillate the patient. Effective CPR may minimize the risk of cerebral hypoxia (which can lead to neurological impairment following restoration of circulation).
- Early defibrillation - The earlier defibrillation of VT/VF is performed, the better the prognosis. Untreated VF/VT often degenerates into asystole which is poorly responsive to defibrillation.
- Early hospital care - Many patients suffer recurrent cardiac arrest within the first 24 hours of admission, and outcomes are improved with inpatient care in a monitored setting that allows early defibrillation.
References
- ↑ Eisenberg MS, Mengert TJ (2001). "Cardiac resuscitation". N. Engl. J. Med. 344 (17): 1304–13. PMID 11320390. Unknown parameter
|month=ignored (help) - ↑ Bunch TJ, White RD, Gersh BJ; et al. (2003). "Long-term outcomes of out-of-hospital cardiac arrest after successful early defibrillation". N. Engl. J. Med. 348 (26): 2626–33. doi:10.1056/NEJMoa023053. PMID 12826637. Unknown parameter
|month=ignored (help) - ↑ Lyon RM, Cobbe SM, Bradley JM, Grubb NR (2004). "Surviving out of hospital cardiac arrest at home: a postcode lottery?". Emerg Med J. 21 (5): 619–24. doi:10.1136/emj.2003.010363. PMC 1726412. PMID 15333549. Unknown parameter
|month=ignored (help) - ↑ Cobbe SM, Dalziel K, Ford I, Marsden AK (1996). "Survival of 1476 patients initially resuscitated from out of hospital cardiac arrest". BMJ. 312 (7047): 1633–7. PMC 2351362. PMID 8664715. Unknown parameter
|month=ignored (help) - ↑ Mellion ML (2005). "Neurologic consequences of cardiac arrest and preventive strategies". Medicine and Health, Rhode Island. 88 (11): 382–5. PMID 16363390. Unknown parameter
|month=ignored (help) - ↑ Thomassen A, Wernberg M (1979). "Prevalence and prognostic significance of coma after cardiac arrest outside intensive care and coronary units". Acta Anaesthesiologica Scandinavica. 23 (2): 143–8. PMID 442945. Unknown parameter
|month=ignored (help) - ↑ Ballew KA (1997). "Cardiopulmonary resuscitation". BMJ. 314 (7092): 1462–5. PMC 2126720. PMID 9167565. Unknown parameter
|month=ignored (help)