unari M

99mTc-HMPAO SPECT in the diagnosis of brain death

ObjectiveTo evaluate the effectiveness of single proton emission tomography (SPECT) with 99mTc-HMPAO in the diagnosis of brain death (BD).DesignProspective study in comatose and brain-dead patients.SettingNeurologic ICU.Patients and methodsFifty comatose patients (age range: 10 days-75 years) were submitted to SPECT study. In 21 of them (42%) reversible factors (e.g., influence of drugs affecting the central nervous system) were present. Thirty-eight patients were clinically brain-dead, while the remaining 12 were tested both in pre-terminal conditions and after the clinical onset of BD.]InterventionsBrain SPECT following i.v. injection of 99mTc-HMPAO (300–1100 MBq), using a 4-headed gamma-camera (20 min, 360 °, 88 images).Measurements and resultsAll patients tested in pre-terminal conditions showed preserved brain perfusion. Two of them had flat EEGs despite the absence of any reversible cause of coma; three patients survived, but remained in persistent vegetative states. SPECT confirmed the diagnosis of BD in 45 out of 47 patients (95.7 %), clearly showing the arrest of brain perfusion (picture of “empty skull”); in two clinically brain-dead children (aged 10 days and 12 months, respectively) weak perfusion of the basal ganglia, thalamus and/or brain stem was still present, precluding the diagnosis of BD; both of them died a few days later.ConclusionsOur results confirm the reliability of SPECT in the diagnosis of BD. A problem arises about its effectiveness in brain-dead children, but this seems to be a matter of definition of BD and cerebral viability, rather than a limit of SPECT.

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.

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.

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.

Sensorimotor central conduction time in comatose patients

Motor evoked potentials (MEPs) following magnetic stimulation were recorded in 22 patients comatose as a result of head injury (13 cases), stroke (7 cases) or anoxia (2 cases). Somatosensory evoked potentials (SEPs) from median nerve were recorded as well in 19 cases in the same session. Thirteen patients died or remained vegetative (59.1%), 3 were severely disabled (13.6%) and 6 showed a good recovery (27.3%). MEPs were significantly related to the outcome; they appeared to be a more accurate prognostic indicator than the Glasgow Coma Scale (GCS). However, 1 out of 6 patients with bilaterally absent MEPs (16.7%) showed a good recovery. SEPs were significantly related to the outcome as well, but the combined use of SEP and MEP improved the outcome prediction, decreasing the rate of false negatives. Two patients had normal sensorimotor function, 13 a combined sensorimotor dysfunction, while 4 had a pure motor dysfunction. Our results suggest that SEPs and MEPs may improve the assessment of sensorimotor dysfunction in comatose patients. A significant relationship between MEPs and outcome appears to exist, but the assessment of MEP reliability requires further study.

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.

EEG monitoring of carotid endarterectomy with routine patch-graft angioplasty : an experience in a large series

Four hundred and thirty-nine carotid endarterectomies (CEAs) with routine use of patchgraft angioplasty were performed in 375 patients; the indwelling shunt was used only in patients showing clamp-related EEG abnormalities. Five patients showed EEG abnormalities just after head positioning, which reversed after removal of head hyperextension; three cases suffered EEG flattening due to severe bradycardia or cardiac arrest before carotid clamping, which promptly reversed after treatment. Clamp-related EEG abnormalities appeared in 106 operations (24.2%) and all reversed after the insertion of the indwelling shunt; patients with occlusion of the contralateral internal carotid artery showed a 68.8% rate of EEG clamp-related changes. The short term follow-up (one month after the operation) showed six minor strokes with complete recovery (1.37%), one intraoperative stroke (0.23%), three delayed major strokes (0.69%) and three neurological deaths (0.69%). The long-term follow-up over an average of 42 months showed a 3.7% rate of relevant neurological complications (ie permanent deficits + death) and a 3.16% rate significant restenosis or occlusion of the operated carotid artery. Our results show that the routine use of EEG monitoring and patch-graft angioplasty allow to perform CEAs with a very high degree of safety, improving the clinical course of the disease.

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

ABRs have proved to be very accurate prognostic indicators in severe head injury, even when predictions are based on single ABR recordings. In this study we submitted 30 severely head-injured patients to serial ABR recordings (during the clinical course of posttraumatic coma) in order to verify whether the ABR prognostic power may depend on test timing in relation to the injury. 15 patients (50%) died, 5 (16.7%) remained vegetative, 2 (6.6%) severely disabled and 8 (26.7%) recovered. All recovered patients had normal ABR throughout clinical course, while severely disabled and vegetative patients showed at least transently ABR abnormalites (namely, an interpeak latency of waves V-I>4.48 ms).Among dead patients, 8 showed steady and 3 transient ABR abnormalities during the clinical course, while 2 of 3 patients with normal ABR dead from extracranial complications.ABRs were significantly related to the outcome at any time, but gave more accurate prognostic indications on days 3–6 after the injury. The use of serial ABR recordings appeared to improve the outcome predictions in comparison with single ABR tests. Finally our result confirm the previously reported existance of a breakpoint between reversible brainstem dysfunction and irreversible brainstem damage defined by an IPL V-I of about 4.50 ms.

Intracranial pressure monitoring

Brain injury is the result of both primary and secondary damage, yielded by a complex range of factors including ischemia, biochemical changes and inflammatory cascade. Secondary brain injury may be caused by systemic or intracranial mechanisms including oligaemia due to low cerebral perfusion pressure (CPP) or increased cerebral vascular resistance (vascular distortion or cerebro-vascular narrowing), hypoxemia (airway obstruction, pulmonary pathology or anaemia), intracranial hypertension and changes of brain metabolic rate. Furthermore, secondary insults cause tissue damage according to their nature, severity and duration, making their early detection and correction an essential step of management. Several neuroprotective agents have been introduced in the past two decades, but, despite their potential effectiveness, the results have been disappointing; therefore, the current basis for prevention of secondary brain damage remains prevention and correction of secondary insults. While nowadays several techniques are available for monitoring severely head-injured patients, monitoring intracranial pressure (ICP) still plays a key role, providing essential information for further decision making.