Patients who receive therapeutic hypothermia after resuscitation from cardiac arrest have favorable chances of surviving the event and recovering good functional status; however, the role of neuron-specific enolase is not clear, according to a study in the December 2010 issue of Annals of Neurology.
In therapeutic hypothermia, a patient's body temperature is cooled to 33° Celsius following resuscitation from cardiac arrest to slow the brain's metabolism and protect the brain against the damage initiated by the lack of blood flow and oxygenation.
Alejandro Rabinstein, MD, a neurologist at the Mayo Clinic in Rochester, Minn., and colleagues identified 192 patients, more than 100 of whom were treated with therapeutic hypothermia. Detailed neurologic exams were performed, including electroencephalograms, brain CT scans and measurement of blood neuron-specific enolase (NSE), which provides information about the extent of brain damage.
High NSE level in the blood had been shown to reliably predict poor outcome after cardiac arrest in patients not treated with hypothermia. However, less is known about the value of this marker in patients who are cooled after the cardiac arrest.
Although in this study the presence of elevated levels of NSE was statistically associated with worse outcomes in patients treated with hypothermia, the researchers concluded that the NSE level was not sufficiently reliable to estimate the prognosis in this group of patients because elevated levels were also seen in some patients who recovered well.
Therefore, the NSE level should not be used in isolation to define prognosis in patients treated with hypothermia. "That was a remarkable finding of our study that deserves more attention," Rabinstein said.
"For a number of years, we have collected information about what determines whether or not a patient is going to wake up after resuscitated cardiac arrest. However, most of this information comes from the time when patients were not treated with therapeutic hypothermia, which now has become the standard of care for many cases of cardiac arrest. We wanted to know whether hypothermia therapy changed what we knew before about how to estimate neurological prognosis in these patients," he said.
"It's important for people to know that among patients treated with therapeutic hypothermia following resuscitated cardiac arrest, up to two-thirds of them may go home with good function," said Rabinstein. "We are still examining how these patients recover in terms of higher intellectual faculties, but certainly these are results that were not even conceivable prior to the application of therapeutic hypothermia."