The role of continuous EEG in therapeutic hypothermia

Esther L. Young, D.O.Oakland Neurology Center

September 27, 2013

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

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

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

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

FIRDA

PLED

Triphasic waves

Burst suppression

Alpha coma

GPED

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

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%

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

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

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

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