EEG Pharmacological and Metabolic Effects on EEG — Questions and Answers
Question 1: A patient on high-dose phenobarbital for status epilepticus shows a burst-suppression pattern on EEG. Which feature is most characteristic of drug-induced burst suppression compared to anoxic burst suppression?
- Bursts are consistently asymmetric between hemispheres
- Burst suppression is dose-dependent and reverses as the drug is metabolized (Correct answer)
- Suppression periods are always longer than 10 seconds
- Delta activity is absent during burst periods
Correct answer: Burst suppression is dose-dependent and reverses as the drug is metabolized
Drug-induced burst suppression (from barbiturates, propofol, or benzodiazepines) is dose-dependent and will improve as serum drug levels fall. Anoxic burst suppression following cardiac arrest is not dose-dependent and carries a far worse prognosis. This distinction is clinically critical for EEG interpretation in the ICU.
Question 2: Benzodiazepine administration typically produces which EEG change that a technologist should recognize and document?
- Prominent generalized theta slowing without faster activity
- Increase in frontocentral beta activity (14–30 Hz) (Correct answer)
- Appearance of triphasic waves over frontal regions
- Suppression of all activity below 1 Hz
Correct answer: Increase in frontocentral beta activity (14–30 Hz)
Benzodiazepines (and other GABA-A agonists such as barbiturates at sub-anesthetic doses) characteristically increase fast-frequency beta activity, most prominent over frontocentral regions. Recognizing drug-induced beta prevents misinterpretation as normal or abnormal endogenous activity.
Question 3: Triphasic waves with anterior-to-posterior phase lag are most classically associated with which metabolic condition?
- Hypoglycemia
- Hyponatremia
- Hepatic encephalopathy (Correct answer)
- Hyperthyroidism
Correct answer: Hepatic encephalopathy
Triphasic waves — high-amplitude, anteriorly dominant complexes with three phases and an anterior-to-posterior time lag — are the classic EEG hallmark of hepatic (portosystemic) encephalopathy, though they can also appear in renal failure and other toxic-metabolic states. Recognizing this pattern and its metabolic context is essential for accurate reporting.
Question 4: A critically ill patient is being actively cooled to 33°C for targeted temperature management after cardiac arrest. How does this temperature affect the EEG?
- Produces diffuse high-amplitude delta without affecting frequency
- Has no effect on EEG background until temperature drops below 20°C
- Progressively slows and suppresses EEG activity; may produce burst suppression or ECI at very low temperatures (Correct answer)
- Selectively abolishes sleep spindles while preserving alpha activity
Correct answer: Progressively slows and suppresses EEG activity; may produce burst suppression or ECI at very low temperatures
Hypothermia is a potent EEG suppressant. At 33°C, background slowing and decreased amplitude are expected. As temperature falls further (below ~20°C), burst suppression and eventually ECI can occur — all reversible with rewarming. Failure to account for hypothermia when interpreting EEGs leads to false prognostication.
Question 5: An EEG technologist notes that a patient's EEG shows generalized high-amplitude rhythmic delta with superimposed faster frequencies. The patient's chart indicates a blood glucose of 28 mg/dL. The MOST likely explanation for this EEG pattern is:
- Nonconvulsive status epilepticus
- Hypoglycemic encephalopathy producing diffuse metabolic slowing (Correct answer)
- Subcortical ischemia from a posterior circulation stroke
- Benzodiazepine overdose
Correct answer: Hypoglycemic encephalopathy producing diffuse metabolic slowing
Severe hypoglycemia deprives neurons of their primary energy substrate, producing diffuse encephalopathy with EEG slowing ranging from theta to delta frequencies, often with high amplitude. This metabolic encephalopathy reverses rapidly with glucose correction. The clinical context (blood glucose 28 mg/dL) makes this the most parsimonious explanation.
Question 6: Which antiepileptic drug effect on the EEG may be mistaken for a pathological finding if the technologist is unaware of the patient's medication list?
- Carbamazepine causing bifrontal spike-and-wave discharges
- Phenytoin toxicity causing rhythmic beta activity indistinguishable from normal
- Lamotrigine causing prominent mu rhythm enhancement
- Valproate at therapeutic levels causing diffuse slowing that mimics metabolic encephalopathy (Correct answer)
Correct answer: Valproate at therapeutic levels causing diffuse slowing that mimics metabolic encephalopathy
Valproate, even at therapeutic serum levels, can produce diffuse background slowing that resembles a mild encephalopathy. Without knowing the patient is on valproate, the EEG reader could incorrectly diagnose a metabolic or structural abnormality. This is a common source of interpretation error and underscores the importance of obtaining a complete medication history before interpreting any EEG.
EEG Pharmacological and Metabolic Effects on EEG
A patient on high-dose phenobarbital for status epilepticus shows a burst-suppression pattern on EEG.
Which feature is most characteristic of drug-induced burst suppression compared to anoxic burst suppression?