Innovative monitoring in the neuro-ICU
Perhaps uniquely among physicians, neurologists follow a carefully scripted examination to localize and diagnose patients' problems. In critically ill patients, the neurological examination is limited but remains the most reliable tool for monitoring a patient's condition. Because of these limitations, patient monitoring systems serve a crucial role. Mayo Clinic utilizes innovative neurointensive care unit (neuro-ICU) monitoring as an essential adjunct in both patient care and research.
Cerebral oxygenation monitoring and real-time EEG
EQUANOX™ Model 7600 cerebral/somatic regional oximeter
The neuro-ICU at Mayo Clinic in Rochester, Minn., is now equipped with a monitor that can measure regional cerebral oxygen saturation. Like pulse oximeters, cerebral oxygenation monitors use near-infrared light to measure oxyhemoglobin and deoxyhemoglobin levels in blood. The noninvasive technology utilizes optode-containing pads that are attached to the patient's forehead.
Cerebral oxygenation monitoring is especially helpful for evaluating patients after aneurysmal subarachnoid hemorrhage. Those patients are at risk of developing delayed cerebral ischemia, a major contributor to poor outcome after subarachnoid hemorrhage. Near-infrared technology can detect disturbances in cerebral perfusion, which have been implicated in the development of delayed cerebral ischemia.
"Cerebral oxygenation monitoring is another tool — in addition to transcranial Doppler, which we've used for many years — that warns of early changes in cerebral perfusion in patients at risk of ischemia," says Sara E. Hocker, M.D., a neurointensivist at Mayo Clinic in Rochester, Minn. "Having this noninvasive option is a huge advantage for patients."
Mayo's commitment to innovative monitoring extends to providing continuous, real-time EEG monitoring. Neuro-ICU patients not only are monitored continuously; EEG technicians also watch the tracing around the clock. "That allows us to react quickly to seizure activity rather than waiting until the next day to find out the patient had five or six seizures overnight," Dr. Hocker says. Real-time EEG helps Mayo neurointensivists define the number, duration and nature of seizures and autonomic spells, and sometimes has implications about the patient's prognosis.
Continuous EEG is also of particular benefit to patients undergoing therapeutic hypothermia after cardiac arrest. Mayo Clinic helped pioneer the use of that therapy, which has been shown to improve neurological outcome after out-of-hospital cardiac arrest due to ventricular fibrillation.
In 2009, Mayo began continuous EEG monitoring of patients during therapeutic hypothermia and rewarming after cardiac arrest. According to an article in the January 2013 issue of Neurology, a Mayo retrospective study of the records of 54 patients treated with that protocol from 2009 to 2012 found continuous EEG to have prognostic value. EEG severity grading during both therapeutic hypothermia and rewarming — as well as incidence of seizures, nonreactive background and epileptiform discharges — correlated with treatment outcome.
In addition to improving patient treatment, innovative monitoring plays a key role in Mayo's many research efforts in the neuro-ICU. Following the study of continuous EEG in therapeutic hypothermia, researchers at Mayo are using cerebral oxygenation monitoring to learn more about cerebral oxygenation during the procedure. Issues under investigation include:
- The frequency of cerebral desaturation when peripheral oxygen appears normal
- The duration of desaturation events
- Their occurrence during the cooling versus the rewarming period
- The impact on patient outcomes, particularly cognitive outcomes
Continuous EEG monitoring is also frequently used in research on epilepsy, including a recent Mayo study characterizing the predictors of outcome in refractory status epilepticus. According to an article in the January 2013 issue of JAMA Neurology, that study documented an association between the severity of status epilepticus, and clinical course and outcome.
In addition, real-time EEG is facilitating a Mayo study of the ketogenic diet as adjunct therapy for refractory status epilepticus. The prospective study, done in collaboration with researchers at Johns Hopkins University, examines the diet's feasibility and safety and eventually will seek to determine efficacy in managing refractory status epilepticus.
"We would like to know whether we can wean study participants from anesthetic agents sooner because of the ketogenic diet. Continuous EEG monitoring will be very helpful in that setting," Dr. Hocker notes.
For more information
Crepeau AZ, et al. Continuous EEG in therapeutic hypothermia after cardiac arrest: Prognostic and clinical value. Neurology. 2013;80:339.
Hocker SE, et al. Predictors of outcome in refractory status epilepticus. JAMA Neurology. 2013;70:72.