Increased incidence and impact of nonconvulsive and convulsive seizures after traumatic brain injury as detected by continuous electroencephalographic monitoring

Abstract

Object: The early pathophysiological features of traumatic brain injury observed in the intensive care unit (ICU) have been described in terms of altered cerebral blood flow, altered brain metabolism, and neurochemical excitotoxicity. Seizures occur in animal models of brain injury and in human brain injury. Previous studies of posttraumatic seizures in humans have been based principally on clinical observations without a systematic approach to electroencephalographic (EEG) recording of seizures. The purpose of this study was to determine prospectively the incidence of convulsive and nonconvulsive seizures by using continuous EEG monitoring in patients in the ICU during the initial 14 days post-injury.

Methods: Ninety-four patients with moderate-to-severe brain injuries underwent continuous EEG monitoring begin-ning at admission to the ICU (mean delay 9.6+/-5.4 hours) and extending up to 14 days postinjury. Convulsive and nonconvulsive seizures occurred in 21 (22%) of the 94 patients, with six of them displaying status epilepticus. In more than half of the patients (52%) the seizures were nonconvulsive and were diagnosed on the basis of EEG studies alone. All six patients with status epilepticus died, compared with a mortality rate of 24% (18 of 73) in the nonseizure group (p<0.001). The patients with status epilepticus had a shorter mean length of stay (9.14+/-5.9 days compared with 14+/-9 days [t-test, p<0.031). Seizures occurred despite initiation of prophylactic phenytoin on admission to the emergency room, with maintenance at mean levels of 16.6+/-2.8 mg/dl. No differences in key prognostic factors (such as the Glasgow Coma Scale score, early hypoxemia, early hypotension, or 1-month Glasgow Outcome Scale score) were found between the patients with seizures and those without.

Conclusions: Seizures occur in more than one in five patients during the 1st week after moderate-to-severe brain injury and may play a role in the pathobiological conditions associated with brain injury.

Fig. 1

Electroencephalographic tracings showing total power trend of 15 hours duration (upper) with the electrode derivations shown at the left. The arrows show an increase in total power that corresponds to generalized seizure activity (lower) that was accompanied by subtle facial twitching. The remainder of the trend demonstrates reduced total power that results from induction of pentobarbital burst-suppression coma.

Fig. 2

Upper: Segment of an EEG tracing demonstrating a focal nonconvulsive seizure emanating from the right frontal area, predominant over the F4 electrode. Lower: The corresponding total power trend demonstrating repeated bursts of total power (arrows) over a 12-hour epoch.

Fig. 3

Tracings showing an example of a generalized electroencephalographically detected seizure that evolves over time. The EEG study demonstrates polyspike and wave discharges, repetitive spike discharges, and an eventual decrease in amplitude with rhythmic low-amplitude activity that gradually abates. No clinically observed activity accompanied the electroencephalographically defined seizure.

Fig. 4

Tracings showing paroxysmal discharges that occurred in patients in whom seizure criteria were not fulfilled. This demonstrates an example of a patient who at baseline has low-amplitude beta and theta frequencies (upper) and suddenly develops rhythmic bilateral temporal epileptiform discharges (lower). The discharges have a few features of sharp waves (arrows) but do not evolve over time and gradually fade back into the previous background activity. These were not considered to be seizures in this study.

Fig. 5

Bar graphs showing comparison of the overall means of ICP (upper) and CPP (lower) in the seizure and the nonseizure group. Data from a total of 13,659 hours of continuous recording of ICP and CPP were analyzed by comparing overall means of the nonseizure and seizure subgroups across all days of monitoring. As indicated, significant differences in ICP (p < 0.001) and CPP (p < 0.03) were found between the two groups, with the seizure group demonstrating overall lower mean ICP and higher CPP than the nonseizure group. The magnitude of the differences may not be clinically significant.