Monitoring Neurological Injury by qEEG - Quantitative EEG Analysis Methods and Clinical Applications - page 187

7.6 Discussion of the Results

Cardiac arrest results in global ischemic brain injury leading to low survival and
very poor neurological outcome in the majority of patients. Comatose CA survivors
are typically cared for by nurses and physicians in general or cardiac intensive care
units who may have little specialized training in neurological examination. Cur-
rently, the ability to monitor and detect even major or outcome-modifying changes
in brain function in comatose patients is limited. Recent clinical studies have shown
that hypothermia treatment, involving cooling the brain and the whole body, is able
to ameliorate the neurological injury of global ischemia, leading to better survival
and neurological function in CA survivors. At the present time, therapeutic hypo-
thermia is provided within an empirically determined range of temperatures. How-
ever, a real-time method of tracking the effects of temperature on neurological
recovery after CA has not been developed. Neurological monitoring may provide
the means to evaluate the brain's response to global ischemic injury and to titrate
the effects of hypothermic therapy.
The experimental studies of global ischemic brain injury following CA and the
utility of the qEEG analysis based on the entropy measure IQ have been presented.
The results show that the entropy measure IQ is an early marker of injury and neu-
rological recovery after asphyxial CA. IQ accurately predicted the impact of tem-
perature on recovery of cortical electrical activity, functional outcomes, and
mortality soon after resuscitation. With the use of sham animals, we also demon-
strated that it is not the temperature itself that alters the EEG, but the response of
the injured brain to hypothermia or hyperthermia as manifested in the qEEG
results. This review further validates the value of the IQ measure for predicting
72-hour NDS. Essentially, as early as 30-minute post-ROSC, a sufficient indication
of the long-term outcome—as measured by NDS—is evident in the EEG signals.
The most significant observations occurred within the first 2 hours while rats
remain unresponsive and when clinical evaluation would be least reliable.
Based on ROC analysis, the optimal IQ cutoff point may be used as a threshold
to predict the eventual good neurological outcomes. These studies demonstrate that
IQ thresholds can be determined as early as 60 minutes after ROSC with the goal of
reliably predicting the downstream neurological outcomes. From a neurological
monitoring perspective, this review highlights the importance of the immediate
postresuscitation period when brain injury may be most amenable to therapeutic
interventions [72]. Recording the brain's electrical response and its rapid analysis
by qEEG during the first 2 hours postresuscitation may thus prove to be clinically
useful. Such monitoring during the early hours, coupled with hypothermia therapy,
may help with efforts to protect the brain.
Hypothermia treatment in the studies reported led to better functional out-
comes and EEG recovery quantified by IQ. IQ levels are significantly greater in rats
treated with hypothermia compared to normothermic controls. The separation of
IQ values between the treatment and control groups is noticeable within 1 hour of
ROSC and persists throughout the 72-hour experiment. Better IQ values are associ-
ated with significant improvements in neurological function as measured by NDS
throughout the experiment. IQ measure is able to detect the acceleration of neuro-