Emergent electroencephalogram in the intensive care unit: indications and diagnostic yield

Our aim was to study the frequency and reasons an emergent electroencephalogram (EmEEG) is ordered in the ICUs compared to the hospital ward, examine its usefulness and find predictive variables for its results. We retrospectively identified all electroencephalograms ordered between December 1997 and March 2002 and performed within 1 hour. The tests ordered from four ICUs were compared with those ordered from the Ward beds, and predictive models were developed for the results based on clinical variables. We also compared the EmEEGs ordered by the Neuro-ICU to those from the other Units. The ICUs ordered 129 (49.4%) of all EmEEGs during the study period. The NICU ordered 32 tests. The most frequent reason for obtaining the test was to rule out status epilepticus (68.2%). The NICU ordered more frequently the test to exclude non-convulsive status than the other ICUs. Compared to non-ICU, ICU patients with head trauma or post cardiopulmonary arrest had more tests and patients with stroke fewer. Convulsive status epilepticus and generalized slowing were found more frequently in the ICUs, and normal EEG, interictal epileptiform activity or focal non-epileptic slowing were more frequent in the non-ICU cases. In at least 12.4% of ICU patients, the test was expected to lead to an anti-epileptic management change. Cardiopulmonary arrest and age were predictive of any epileptic activity on the EEG in ICU patients. In conclusion, in our institution EmEEG is ordered by the ICUs in two thirds of the cases to exclude status epilepticus. Although status epilepticus is confirmed more frequently in the ICUs than on the Ward, the most frequent finding remains generalized slowing, which is found in half of the ICU-ordered EmEEGs. A conservative estimation is that EmEEG will lead to medication change in at least 1 out of 8 ICU patients. Cardioopulmonary arrest is predictive of epileptic activity and a prolonged EmEEG may also increase the yield.