Role of short latency evoked potentials in the diagnosis of brain death

OBJECTIVE

The aim of this study is to confirm the effectiveness of auditory brain-stem responses (ABRs) and somatosensory evoked potentials (SEPs) in the diagnosis of brain death (BD).

METHODS

ABRs and SEPs were recorded at the same session in 130 BD patients (age range 8-77 years, 81 male and 49 female). Twenty-four cases were submitted to serial recordings from preterminal conditions through BD.

RESULTS

ABRs were absent in 92 cases (70.8%), only waves I or I-II were present in 32 cases (24.6%), while in the remaining 6 patients (4.6%) waves V and/or III were still present, excluding the death of the brain-stem. In 4 cases (3.1%) SEPs showed the absence of all components following the cervical N9, preventing the diagnosis of BD. Among 126 cases (96.9%) with preserved cervical N9-N13 SEPs confirmed the absence of brain-stem activity in 122 cases (93.7%), in whom no waves following P11 or P13 were recordable. SEPs excluded the diagnosis of BD in the remaining 4 cases (3.2%) showing preserved P14 and/or N18. In all pre terminal patients the far-field P14-N18 were present, and their disappearance was closely related to the onset of BD.

CONCLUSIONS

The combined us of ABRs and SEPs was able to confirm BD in almost all patients, providing an objective confirmation of the diagnosis, and to exclude it in 7 cases, thus improving the reliability of diagnosis.

[General anesthesia with remifentanil in a case of "sleep apnea syndrome"]

The authors report the case of a patient suffering from central sleep apnea (CSA) who underwent neurosurgery for ventriculo-peritoneal derivation under general anesthesia. Given the risk of postoperative hypoventilation in CSA, intraoperative anesthesia was induced using remifentanyl, an opiate with a plasma half-life of less than 5 minutes. Propofol (2 mg/kg) and remifentanyl at a dose of 0.5 microgram/kg was used during induction. The patient was curarised with vecuronium bromide, intubated and ventilated with a mixture of O2/N2O. During the operation, remifentanyl was administered as a continuous infusion at a starting dose of 0.2 microgram/kg/min, subsequently modified according to changes in arterial pressure and heart rate. At the end of surgery, which lasted approximately 120", decurarisation was carried out using prostigmin, and the infusion of remifentanyl was suspended, together with N2O. Reawakening times were recorded. Extubation took place 8' and 30" after the suspension of remifentanyl. Postoperative monitoring of SpO2 continued for 1 h and blood-gas analysis was satisfactory. No hypoventilation episodes were reported throughout the postoperative period and the patient was discharged from hospital after 7 days. The authors consider that remifentanyl should be the drug of choice to guarantee intraoperative analgesia in patients suffering from CSA requiring general anesthesia.

Auditory and somatosensory evoked potentials in coma following spontaneous cerebral hemorrhage: early prognosis and outcome

The aim of this study was to check the prognostic power of auditory brain-stem responses (ABRs) and somatosensory evoked potentials (SEPs) in coma following spontaneous cerebral hemorrhage. Seventy patients comatose following subarachnoidal or hypertensive hemorrhage were submitted to ABR and SEP recordings during the acute phase of clinical course. Twenty-one patients survived (30%), two remained vegetative (2.9%) and 47 died (68.1%). The Glasgow Coma Score (GCS) was significantly related to the outcome (P < 0.001), but showed a low sensitivity, since about 50% of patients with GCS = 5-8 died or remained vegetative. ABRs and SEPs showed a much closer correlation with outcome (P < 0.001): their combined use allowed there to be a sensitivity of 96%, a specificity of 90% and a predictive power of 96%; the relative risk of poor outcome in patients with at least one abnormal modality was equal to 223 times the one for patients with normal evoked potentials. Moreover, in surviving patients a significant relationship appeared to exist between abnormalities of SEPs during the acute phase and the severity of disability. Our results confirm the prognostic effectiveness of short latency evoked potentials in cerebral hemorrhage: they are far superior to clinical data, being able to yield a marked decrease of falsely optimistic predictions.