Sequential changes of auditory brain stem responses in relation to intracranial and cerebral perfusion pressure and initiation of secondary brain stem damage

Modified brain stem auditory evoked potentials in patients with intracranial mass lesions

The authors report their experience utilizing a recently described rapid rate, binaural click and 1000-Hz tone burst modification of the brain stem auditory evoked potentials (BAEP), modified (MBP), in 27 symptomatic patients with non-brain stem compressive space-taking cerebral lesions (22), hydrocephalus (4), and pseudotumor cerebri (1).  Many presented with clinical signs suggestive of increased intracranial pressure (ICP) and focal neurological deficits. The cerebral lesions, mostly large tumors with edema, had very substantial radiological signs of mass effect. Fourteen patients were also studied following surgical decompression. A number of significant changes in the wave V and Vn latency/intensity and less so amplitude/intensity function was found in the 27 patients, compared to normal volunteers, as well as those studied pre- and postoperatively. Similar MBP changes had been noted in normal volunteers placed in a dependent head position. Possible mechanisms to explain these findings are discussed.  The MBP methodology shows promise and further development could make neuro-intensive care unit monitoring practical.

Cerebral perfusion pressure and intracranial pressure in relation to neuropsychological outcome

OBJECTIVE

The study attempted to examine the relationship between neuropsychological functioning and reduced cerebral perfusion pressure (CPP), raised intracranial pressure (ICP), and reduced mean arterial pressure (MAP), monitored during intensive care treatment.

DESIGN

This prospective follow-up study included consecutive patients and evaluated outcome at 6 months postinjury by the administration of a neuropsychological test battery.

SETTING

The study was conducted at the University Hospital of Gent, Belgium.

PATIENTS AND PARTICIPANTS

Over a 30-month period, 43 patients were included. Inclusion criteria were the following: hospital admission following closed head injury. ICP monitoring, no medical history of central nervous system disease or mental retardation, survival for at least 6 months, and informed consent for participation.

INTERVENTIONS

All patients received the hospital's standard treatment for head injury, which remained unchanged during the study period.

MEASUREMENTS AND RESULTS

Reduced CPP was analyzed using the number of observed values below 70 mmhg, raised ICP using the number of values above 20 mmHg, and MAP using the number of values below 80 mmHg. The neuropsychological test battery included 11 measures of attention, information processing, motor reaction time, memory, learning, visuoconstruction, verbal fluency, and mental flexibility. No linear relationships were found between overall neuropsychological impairment and episodes of reduced CPP, raised ICP, or reduced MAP.

CONCLUSIONS

Although reduced CPP and raised ICP are frequent, often fatal, complications of head injury, in survivors they do not seem to be related to later neuropsychological functioning.

Hemicraniectomy for massive cerebral infarction: Evoked potentials as presurgical prognostic factors

In patients with massive hemispheric infarctions, mortality exceeds 80% with medical therapy alone. In certain conditions hemicraniectomy may result in meaningful survival. We studied presurgical clinical and electrophysiological parameters that may serve as prognostic factors to assess efficacy of decompressive surgery. We evaluated 26 consecutive patients with severe focal neurological deficit, deterioration of consciousness, and massive hemispheric infarction by cranial computerized tomography who underwent hemicraniectomy. Clinical examination included pupillary size and reaction, and determination of level of consciousness on an hourly basis. Median nerve somatosensory evoked potentials and brainstem auditory evoked potentials were obtained before and after hemicraniectomy. Outcome was assessed by using the Barthel Index. Clinical and evoked potential data were correlated with the outcome. Fisher's Exact Test was applied to establish statistical significance. With surgery 18 of 26 patients survived on an average intensive care treatment of 29.6 (+/-27.5) days. Barthel Index at discharge was 61.7 (+/-24.4) in survivors. Presurgical pupillary reaction, level of consciousness, and somatosensory evoked potentials were not found to correlate with outcome. In contrast, presurgical brainstem auditory evoked potentials showed a significant correlation with survival (P<.05). All patients with good outcomes (Barthel Index >/=60: n=12, 46.1%) had normal brainstem auditory evoked potentials before surgery. Clinical parameters did not reliably forecast prognosis in patients with massive cerebral infarction treated with hemicraniectomy.

Serial somatosensory and brainstem auditory evoked potentials in monitoring of acute supratentorial mass lesions

OBJECTIVE

To determine the relevance of serial evoked potentials (brainstem auditory evoked potentials and somatosensory evoked potentials) and clinical parameters (pupillary response and intracranial pressure) in patients with acute supratentorial mass lesions.

DESIGN

Prospective case series of comatose patients with acute supratentorial mass lesions.

SETTING

Neurocritical care unit of a tertiary care center.

PATIENTS

Thirty consecutive patients with the following study inclusion criteria: a) clinical and computed tomography evidence of an acute supratentorial mass lesion; b) implantation of an intracranial pressure monitoring device; and c) a persistent comatose state during the observation period.

INTERVENTIONS

Brainstem auditory evoked potentials, somatosensory evoked potentials, intracranial pressure, and pupillary responses were recorded at the time of three particular events: a) immediately after implantation of an epidural intracranial pressure monitoring device; b) during intracranial pressure therapy; and c) at termination of intracranial pressure therapy. Evoked potential results were ranked into three categories: a) normal on both sides; b) abnormal or absent on one side; and c) evoked potentials on both sides abnormal or absent. Spearman's rank correlation was performed to analyze serial recordings. Cross tables were generated to determine the prognostic value of evoked potentials and clinical parameters. Fisher's exact test was applied to calculate statistical significance.

MEASUREMENTS AND MAIN RESULTS

Intracranial pressure values correlated with pupillary responses and brainstem auditory evoked potentials during and at the termination of intracranial pressure therapy. Pupillary findings correlated with brainstem auditory evoked potentials only at the time of termination of intracranial pressure therapy. There was no correlation between somatosensory evoked potentials and clinical parameters. Pupillary responses indicated a good or poor recovery during and at the termination of intracranial pressure therapy. Brainstem auditory evoked potentials and intracranial pressure values distinguished between good and poor outcome only at termination of intracranial pressure therapy. Somatosensory evoked potential results did not predict outcome.

CONCLUSIONS

Shortly after manifestation of supratentorial mass lesions, the results of evoked potentials and clinical parameters indicate increased intracranial pressure and incipient transtentorial herniation but do not predict sequelae. Our results indicate that after institution of effective therapy, pupillary abnormalities and brainstem auditory evoked potentials serve as valuable prognostic predictors. In contrast, somatosensory evoked potentials reflect neither therapeutic efficacy nor outcome in our patient population.

Brain-stem auditory evoked responses to hypercarbia in preterm infants

To determine the effect of acute hypercarbia on brain-stem function in preterm neonates, we compared brain-stem auditory evoked responses (BAERs) during 8% CO2 breathing to those elicited during room air breathing in 12 healthy preterm infants during the first week of life. End-tidal CO2 (ETpCO2), respiratory rate and depth were monitored throughout the protocol. Absolute wave latencies and interpeak intervals of the BAERs were analyzed from duplicate trials. During 8% CO2 breathing, ETpCO2, respiratory rate and depth of respiration increased significantly (P < 0.05). The absolute latency of wave V was prolonged (P < 0.025) in the hypercarbic state as compared to baseline. Interpeak interval III-V was also prolonged (P < 0.025). Values of absolute peak latencies I and III were unaffected by the hypercarbic state. These data demonstrate that elevations in pCO2 which elicit ventilatory responses also effect the BAER. The specific effects on ventilatory pattern, peak V latency and interpeak interval III-V indicate brain-stem responsiveness and alterations in the more central components of the auditory pathway. These findings raise important considerations regarding the influence of hypercarbia on brain-stem function in preterm infants and the clinical management of such infants with abnormalities of gas exchange.

The combined monitoring of brain stem auditory evoked potentials and intracranial pressure in coma. A study of 57 patients

Continuous monitoring of brainstem auditory evoked potentials (BAEPs) was carried out in 57 comatose patients for periods ranging from 5 hours to 13 days. In 53 cases intracranial pressure (ICP) was also simultaneously monitored. The study of relative changes of evoked potentials over time proved more relevant to prognosis than the mere consideration of "statistical normality" of waveforms; thus progressive degradation of the BAEPs was associated with a bad outcome even if the responses remained within normal limits. Contrary to previous reports, a normal BAEP obtained during the second week of coma did not necessarily indicate a good vital outcome; it could, however, do so in cases with a low probability of secondary insults. The simultaneous study of BAEPs and ICP showed that apparently significant (greater than 40 mm Hg) acute rises in ICP were not always followed by BAEP changes. The stability of BAEP's despite "significant" ICP rises was associated in our patients with a high probability of survival, while prolongation of central latency of BAEPs in response to ICP modifications was almost invariably followed by brain death. Continuous monitoring of brainstem responses provided a useful physiological counterpart to physical parameters such as ICP. Serial recording of cortical EPs should be added to BAEP monitoring to permit the early detection of rostrocaudal deterioration.