Serial recordings of auditory brainstem responses in severe head injury: relationship between test timing and prognostic power

Baseline, retest, and post-injury profiles of auditory neural function in collegiate football players

OBJECTIVES

Recent retrospective studies report differences in auditory neurophysiology between concussed athletes and uninjured controls using the frequency-following response (FFR). Adopting a prospective design in college football players, we compared FFRs before and after a concussion and evaluated test-retest reliability in non-concussed teammates.

DESIGN

Testing took place in a locker room. We analysed the FFR to the fundamental frequency (F0) (FFR-F0) of a speech stimulus, previously identified as a potential concussion biomarker. Baseline FFRs were obtained during the football pre-season. In athletes diagnosed with concussions during the season, FFRs were measured days after injury and compared to pre-season baseline. In uninjured controls, comparisons were made between pre- and post-season.

STUDY SAMPLE

Participants were Tulane University football athletes (n = 65).

RESULTS

In concussed athletes, there was a significant group-level decrease in FFR-F0 from baseline (26% decrease on average). By contrast, the control group's change from baseline was not statistically significant, and comparisons of pre- and post-season had good repeatability (intraclass correlation coefficient = 0.75).

CONCLUSIONS

Results converge with previous work to evince suppressed neural function to the FFR-F0 following concussion. This preliminary study paves the way for larger-scale clinical evaluation of the specificity and reliability of the FFR as a concussion diagnostic.HighlightsThis prospective study reveals suppressed neural responses to sound in concussed athletes compared to baseline.Neural responses to sound show good repeatability in uninjured athletes tested in a locker-room setting.Results support the feasibility of recording frequency-following responses in non-laboratory conditions.

Evaluation of vestibulo-ocular reflex in patients with damage to the central nervous system (GCS score 5-3)

PURPOSE

The aim of our study was to evaluate the vestibulo-ocular reflex (VOR) in patients with severe damage to the central nervous system (CNS) in the diagnosis of brain death and survival prognosis.

MATERIAL AND METHODS

The study was conducted in 20 patients with extensive primary central nervous system damage against spontaneous intracranial haemorrhage or craniocerebral trauma and secondary central nervous system damage as a result of cardiac arrest with Glasgow Coma Scale (GCS) score from 3 to 5 treated in the Intensive Care Unit, University Hospital in Bialystok. For labyrinth stimulation we used water at 30°C, recording the reactions with ENG appliance. Records were analyzed in Nathanson-Bergman four-level scale. The first assessment was performed on the second day after the trauma and subsequently the assessments were repeated at 2-day intervals.

RESULTS

Of the 20 patients studied, the reflex was recorded in nine, which accounted for 45%. In the remaining 11 (55%) patients the reflex was not reported in any test and all of them died. Among patients with recorded VOR, five died and four survived.

CONCLUSIONS

The results of our study show the usefulness of performing the vestibulo-ocular test in patients with severe brain injury to predict their survival.

Potencial evocado auditivo de tronco encefálico no prognóstico do coma superficial

O coma é a redução persistente do nível de consciência, arresponsivo a estímulos, devido à baixa atividade cerebral. Para verificar o nível de consciência, um recurso frequentemente utilizado é a Escala de Coma de Glasgow. Outro método que se destaca é o Potencial Evocado Auditivo de Tronco Encefálico, o qual avalia a atividade elétrica das vias auditivas ascendentes, desde o trajeto periférico até o mesencéfalo. O exame é simples, imune a medicamentos depressores e ambientes eletricamente carregados, sendo o mais adequado dos potenciais para a monitoração dos estados de coma. O presente estudo teve por objetivo verificar as características do Potencial Evocado Auditivo de Tronco Encefálico no estado de coma leve (Glasgow 7 - 8) e suas respectivas contribuições. Foi realizado um estudo prospectivo transversal em dois pacientes em coma (Glasgow 7), estado secundário a traumatismo cranioencefálico. Os resultados do exame evidenciaram presença de atividade elétrica em toda extensão da via estudada, em ambos os casos, com indicações de diferentes alterações, quanto à redução na latência entre os intervalos, morfologia e replicação das ondas. Tais diferenças foram contempladas com a evolução de cada caso: caso 1 evoluiu a alta hospitalar e caso 2 evoluiu a óbito. Os resultados confirmaram os achados da literatura, que descreve que a presença do Potencial Evocado Auditivo de Tronco Encefálico normal está associada à boa evolução do caso clínico, enquanto alterações no exame podem sinalizar para um mau prognóstico.

Koma

BACKGROUND

The prognosis after traumatic coma is often unclear. We investigated the prognostic value of somatosensory (SSEP) and early acoustic (EAEP) evoked potentials on comatose patients in the intensive care unit regarding long-term outcome. Different evaluation systems were investigated.

METHODS

This was a retrospective analysis of 100 patients. SSEP and EAEP were examined at different times and analysed according to the Riffel score. Combinations of the different types of potentials were evaluated regarding possible improvement of outcome prediction.

RESULTS

The positive predictive value of at least one missing peak V of the EAEP regarding a fatal prognosis was 83%. The negative predictive value of the EAEP was 96%. A good outcome (GOS 4+5) could be predicted by bilateral normal SSEP and EAEP with a positive predictive value of 98%.

CONCLUSIONS

Early evaluation of SSEP and EAEP allows reliable prognostic predictions regarding a later outcome in patients with severe traumatic brain injury and should therefore be used more often for intensive care patients.

Multimodality evoked potentials (auditory, somatosensory and motor) in coma

Auditory brainstem responses (ABRs) have proved to be significantly related to outcome, both in severe head injury and brain hemorrhage. Nevertheless, the usefulness of ABR is limited by the anatomic extent of the investigated pathways. The combined use of ABRs and somatosensory evoked potentials (SEPs) improves the outcome prediction in comparison to the use of only one modality. It mainly decreases the rate of false negatives, since patients with severe hemispheric damage sparing the brain stem may have a poor outcome despite normal ABRs. The use of motor evoked potentials (MEPs) from magnetic transcranial stimulation is also significantly related to outcome: it appears to be far superior to the clinical evaluation of motor responses, while the combined use of MEPs and SEPs gives a new opportunity of checking sensorimotor dysfunction. ABRs and SEPs may also be useful tools in the confirmation of brain death, the kernel of which is the assessment of brainstem death: they allow to check lemniscal pathways, which cannot be properly evaluated by clinical examination, and provide an objective confirmation of absence of brain stem activity.

Brainstem auditory evoked potentials during procaine toxicity in dogs

Although the toxic effect of local anaesthetics on the activity of cerebral cortex has been extensively studied, little is known about their toxic effect on brainstem. Accordingly, the influence of procaine on brainstem auditory evoked potentials (BAEPs) and on the electroencephalogram (EEG) was observed in 15 dogs. After the administration of procaine (15 mg.kg-1, i.v.), the amplitudes of wave I (1.88 +/- 0.56 vs 2.06 +/- 0.61 microV, mean +/- SD) and wave II (1.91 +/- 0.41 vs 2.06 +/- 0.46 microV) in BAEPs increased (P less than 0.05), while the amplitudes of wave III (0.97 +/- 0.27 vs 0.81 +/- 0.24 microV), wave IV (1.15 +/- 0.43 vs 0.85 +/- 0.29 microV) and wave V (1.04 +/- 0.46 vs 0.92 +/- 0.41 microV) were decreased (P less than 0.05), and both the I-III inter-peak latency (1.57 +/- 0.04 vs 1.70 +/- 0.07 msec) and III-V inter-peak latency (2.15 +/- 0.09 vs 2.35 +/- 0.12 msec) were prolonged (P less than 0.01). The EEG changed from an awake pattern to seizure activity. These results suggest that the electrical activity of the brainstem auditory pathway is suppressed even when the cerebral cortex is in an excitatory state at the convulsive stage of procaine toxicity.

Short latency evoked potentials: new criteria for brain death?

The aim of this study was to evaluate whether the auditory brain stem responses (ABR) and short latency somatosensory potentials (SEP) from median nerve stimulation are effective tools in the confirmation of brain death. Thirty six brain dead patients were submitted to ABR and 24 to SEP in the same session. All waves of the ABR were absent in 28 (77.8 per cent) patients, while only wave I was present in the others (22.2 per cent). In SEP recordings the components later than P13 were absent in 17 (70.8 per cent) of cases; in the remaining seven patients (29.2 per cent) a N13/P13 dissociation (namely, retention of the cervical N13 and absence of the far-field P13) was found. The results suggest that SEP and ABR are reliable tools in the diagnosis of brain death and should be included in the criteria: they enable the functional status of two pathways in the brainstem to be checked, which cannot be explored by the clinical examination.