Outline the techniques  you would use to determine the prognosis in a comatose survivor of a cardiac arrest.

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College Answer

The major determinants of survival after a cardiac arrest are cardiac (arrhythymias and myocardial function) and neurological. Accuracy of assessment of prognosis of both factors increases with time. No techniques have 100% positive predictive value, or more importantly 100% negative predictive value.

•    Cardiovascular techniques of most value are the response to therapy (including thrombolysis or angioplasty) and echocardiography.
•    Neurological survival is best predicted by neurologic examination (again increasing certainty with time). Early poor prognostic signs (eg at 24 hours post-arrest) are fixed,unreactive pupils and extensor or absent motor response to painful stimuli (if not paralysed or deeply sedated). Brain death criteria are rarely met. Further refinement of prognosis may be achieved with investigations such as Somato-Sensory Evoked Potentials or EEG. CT is notoriously unreliable. MRI will detect more abnormalities, as it is a more sensitive test (though studies relating appearance to outcome are lacking).

Discussion

This question closely resembles Question 4 from the second paper of 2013: "Describe the clinical signs and investigations available to predict poor neurological outcome in comatose survivors of cardiac arrest. Include in your answer the factors that may confound the interpretation of these signs and investigations."