1. The role of continuous EEG in therapeutic hypothermia
Esther L. Young, D.O.
Oakland Neurology Center
September 27, 2013

2. Role of EEG
EEG has been used to assist in determining prognosis following cardiac arrest since the 1960s.
EEG rating scale can predict neurologic outcome with an accuracy of 80%
Malignant EEG patterns: myoclonus with EEG correlate, a nonreactive background, burst suppression and status epilepticus
Better prognosis: diffuse slow-wave activity

3. Therapeutic hypothermia
Therapeutic hypothermia has been shown to improve neurologic outcome after out-of-hospital cardiac arrest due to ventricular fibrillation and is the standard of care.
Protective hypothermia lowers a patient’s body temperature in order to help reduce the risk of ischemic injury to tissue following a period of insufficient blood flow

4. Seizures
Hypothermia has antiepileptic effects, yet seizures in cardiac arrest patients can occur despite therapeutic hypothermia.
The risk of seizures may increase during rewarming
Continuous EEG monitoring has been recommended during therapeutic hypothermia to provide prognostic information and monitor for subclinical seizures and nonconvulsive status epilepticus
Seizures and nonconvulsive status epilepticus have been reported at a rate of 10-12% and have been shown to be an independent risk factor for mortality

5. EEG grading system for cEEG findings following cardiac arrest
Mild (grade 1)
Excess beta, theta slowing, anesthetic pattern
Moderate (grade 2)
Diffuse or focal delta slowing, SIRPIDS, ELAE, spindle coma, interictal epileptiform discharges, generalized triphasic waves, FIRDA, TIRDA, OIRDA, PLED
Severe (grade 3)
Burst suppression pattern, low voltage outpt pattern, alpha/theta coma, focal or generalized seizures, nonreactive to stimuli, GPED, status epilepticus

6. FIRDA

7. PLED

8. Triphasic waves

9. Burst suppression

10. Alpha coma

11. GPED

12. Continuous EEG in therapeutic hypothermia after cardiac arrest
Retrospective study of all patients undergoing cEEG with hypothermia after cardiac arrest
Evaluate the prognostic significance of EEG abnormalities occurring during the course of therapeutic hypothermia and warming.
Used the EEG grading system
54 patients treated under TH protocol included
Cooled for 24 hours
cEEG monitoring initiated after hypothermia established and continued until normothermia for a minimum of 2 hours

13. EEG grade during 3 stages of therapeutic hypothermia
EEG TH rewarming normothermia
grade
1 11% 13% 26%
2 56% 57% 43%
3 33% 30% 21%

14. Results
Good neurologic outcome at hospital discharge was seen in 33 (61%) patients.
A total of 21 (39%) had a poor neurologic outcome
19 (35%) died during the hospitalization
EEG severity during TH and NT had a strong association with neurologic outcome
A grade 3 EEG during TH and NT correlated with poor neurologic outcome
Of patients with a poor neurologic outcome, the majority (16/21) showed a grade 3 pattern during TH and 16/19 patients who died had a grade 3 EEG
None of the patients with seizures or status epilepticus achieved good outcome despite treatment

15. Results
There was a trend favoring an association between the evolution of the EEG background during TH and prognosis
9 patients showed improvement in EEG severity grade after rewarming
8 had a good outcome
Of the 4 patients with worsening of the EEG, 3 had a poor outcome
The 3 showing worsening to a grade 3 EEG pattern died
The patient showing progressing to a maximum severity of grade 2 had a good recovery

16. Discussion
EEG abnormalities graded as severe based on the EEG severity grading system were associated with poor outcome
A benign EEG (grade 1) during hypothermia and NT uniformly predicted good recovery
Moderate EEG severity (grade 2) showed less predictive value
The change of cEEG findings during the course of TH-rewarming-NT tended to mirror functional outcome
¾ of patients had the same EEG grade through TH-rewarming-NT

17. Discussion
EEG findings were one of several facotrs used to estimate prognosis and were never considered in isolation
Small cohort size
Is “spot-check” EEG as good as cEEG? (majority of patients did not have a change in grade of EEG)
Clear benefit from aggressively treating identified seizures needs to be established if cEEG is to be recommended for the indication of seizure detection in this population