The role of transcranial Doppler in confirming brain death: sensitivity, specificity, and suggestions for performance and interpretation

Utilidad clínica del Doppler transcraneal en el diagnóstico de muerte encefálica

BACKGROUND AND OBJECTIVE

The use of transcranial doppler (TD) for the assessment of critical neurological patients and brain death (BD) is steadily growing. In this study we describe the daily clinical practice around BD diagnosis and compare the usefulness of TD, including advantages and shortcomings, with that of other tests.

PATIENTS AND METHOD

A series of 100 patients diagnosed of brain death is presented including the demographic and clinical data as well as the results of ancillary tests (CE).

RESULTS

Fifty eight patients were males with a mean age of 46. The most frequent etiology of coma was spontaneous cerebral hemorrhage. Central nervous system depressants had been administered to 62 patients within a few hours prior to the diagnosis. When ancillary tests were performed, only 55% patients fulfilled the currently accepted clinical criteria for brain death. TD was performed in 44 patients and 80% of them showed a pattern supporting a brain death diagnosis. Definitive diagnostic tests were electroencephalogram (EEG) in 53% patients and TD in 35% of them. In ten cases, discrepancies were observed between the results offered by these tests.

CONCLUSIONS

Transcraneal Doppler stands out as a safe, fast, inexpensive and bloodless method of assessment of the critical neurological patient and for BD diagnosis. It is the choice test in the presence of central nervous system depressant drugs, abuse of substances or coma of unknown etiology. The main limitations of this technique are the presence of extensive craniotomies and the absence of an adequate acoustic window.

Persistence of isolated flow in the internal carotid artery in brain death

The criteria for the confirmation of brain death (BD) using transcranial Doppler ultrasonography (TCD) state that flow should not be observed in the internal carotid artery (ICA). In 94 brain-dead patients examined by TCD, 19 (20%) had flow in the ICA despite cerebral circulatory arrest. There was no difference in the clinical characteristics of patients with or without isolated flow in the ICA. Shunting of blood from the ICA into the external carotid system or the arrest of blood flow at a higher level than the carotid siphon may explain our findings. Our results show that the current TCD criteria can result in a high rate of false negatives. We suggest that the TCD criteria for the diagnosis of brain death should be reviewed.

Continuous measurement of cerebral blood flow velocity using transcranial Doppler reveals significant moment-to-moment variability of data in healthy volunteers and in patients with subarachnoid hemorrhage

OBJECTIVE

The reliability of intermittent transcranial Doppler has not been accepted widely because of problems with interobserver variability and lack of accuracy. The limitations of intermittent transcranial Doppler are thought to be overcome by continuous measurement systems. However, little published data exist on their accuracy, feasibility, and moment-to-moment variability. In this study we aimed to determine the time-related variability of continuous transcranial Doppler signal from volunteers and patients with subarachnoid hemorrhage and to examine the feasibility, ease of use, and quality of data generated from continuous transcranial Doppler for the detection of vasospasm.

DESIGN

Prospective observational study.

SETTING

Intensive care unit in a tertiary referral center.

SUBJECTS

Ten volunteers and eight patients with aneurysmal subarachnoid hemorrhage.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The middle cerebral artery blood flow velocities were recorded continuously from both patients and volunteers. The moment-to-moment variability of continuously recorded data was calculated. There was a wide range of velocity measurements in both volunteers and patients. There was a significant moment-to-moment variability in both volunteers (-31% to 58%) and in patients (-38% to 78%). There was a greater number of observations exceeding 10% moment-to-moment variability in the patient group with regard to systolic and diastolic velocities compared with volunteers (8% vs. 2%, p < .001). There was a trend toward a longer duration of good quality data in volunteers compared with patients (98 +/- 0.5% vs. 96 +/- 9%).

CONCLUSIONS

Continuous measurement of cerebral blood flow velocities revealed a significant moment-to-moment variability in both patients and in volunteers, the magnitude of which was greater in the patients. The clinical implications of these findings are discussed.

Ultrasound and other imaging technologies in the intensive care unit

As technology advances, more imaging and procedures are performed at the bedside on critically ill patients in ICUs, thereby eliminating the risks of transporting patients. These imaging techniques can serve as diagnostic and therapeutic tools in treating the acute and chronic consequences of injured, critically ill patients. One area of growth is ultrasonography. Critical care applications of ultrasonography are expanding, and the learning curve of surgeons and intensivists performing some of these studies is improving. Ultrasonography can supplement physical examination and provide useful "real-time" information on nearly every body cavity. Other imaging technology is also available in a portable form, enabling imaging directly at the bedside. Images are now becoming readily and easily available with the advancement of teleradiology. Some of the imaging modalities are still in development, and their clinical effectiveness is being studied. In the future, more uses of these various imaging technologies may become evident and cost-effective.

Transcranial Doppler ultrasonography: year 2000 update

In this update, the main clinical applications of transcranial Doppler ultrasonography are reassessed. A specific format for technology assessment, personal experience, and an extensive review of the literature form the basis of the evaluation. The document is approved by the American Society of Neuroimaging and the Neurosonology Research Group of the World Federation of Neurology.

Non-invasive diagnosis of ischemic brain damage after cardiopulmonary resuscitation in dogs by using transcranial Doppler ultrasonography

We have attempted to identify whether it is possible to utilize transcranial Doppler ultrasonography to evaluate the brain damage that occurs after resuscitation from 3 min (control group) and 12 min (damage group) of cardiac arrest in dogs. In this study we used transcranial Doppler ultrasonography to follow the basilar arterial flow and middle cerebral arterial flow for 180 min following the induction of cardiac arrests. Two abnormal waveform patterns (the "to-and-fro" and "diastolic no-flow" patterns) were found in all dogs in the damage group whereas abnormal waveforms were not detected in the control group. Pathological diagnosis revealed that, compared with the control group, the damage group recognized ischemic alteration at the level of the hippocampus and caudate nucleus. In conclusion, this study shows that the basilar arterial flow of observed with transcranial Doppler ultrasonography may be use for the prediction of outcome and the diagnosis of brain damage in the dog.

[Current concepts in diagnosing brain death in Germany]

Diagnosis of brain death requires definite evidence of an acute CNS catastrophe and exclusion of complicating medical conditions that may confound clinical assessment. Acute CNS catastrophe may be due to direct ("primary") brain damage (e.g., intracerebral hemorrhage, severe concussion, brain tumors), or indirect ("secondary") brain damage (e.g., cerebral hypoxia following cardio-pulmonary resuscitation). The cardinal findings in brain death are coma, absence of brainstem reflexes, and apnea. Persistence of these clinical signs determines brain death. In Germany, the intervals of a repeat clinical evaluation are at least 12 hours in patients with primary, and at least 72 hours in those with secondary brain damage. Electroencephalographically documented absence of electrical activity for at least 30 minutes or by means of transcranial Doppler ultrasonography or isotope angiography documented intracranial circulatory arrest also confirm brain death. Under such conditions, a repeat clinical evaluation is unnecessary in patients with clinical brain death signs. First of all, brain death is a clinical diagnosis. Confirmatory tests are not mandatory in most situations. In Germany, confirmatory tests are required in newborns, infants below the age of 2 years, and patients with infratentorial brain damage.

Evaluating the outcome of severe head injury with transcranial Doppler ultrasonography

The authors conducted a study to determine the value of transcranial Doppler (TCD) ultrasonography in evaluating the outcome of severely head injured patients and to correlate the TCD values with those obtained from intracranial pressure (ICP) and cerebral perfusion pressure (CPP) monitoring. The authors conducted a prospective study of 125 patients with severe head injury (Glascow Coma Scale scores of less than 9) who underwent TCD ultrasonography according to the standard technique of insonating the middle cerebral artery (MCA) and measuring the mean blood flow velocity and pulsatility index within the first 24 hours of admission. The ICP and CPP values, as well as other clinical, analytical, and neuroimaging data, were also recorded. After 6 months, outcome was evaluated using the Glasgow Outcome Scale. Moderate disability and complete recovery were considered "good" outcome; death, vegetative state, and severe disability were considered "poor." In 67 patients (54%) good outcome was demonstrated whereas in 58 (46%) it was poor. The mean blood flow velocity of the MCA in patients with good outcome was 44 cm/second; in those with poor outcomes it was 36 cm/second (p < 0.003). The mean PI in cases of good outcome was 1 whereas in poor outcome was 1.56 (p < 0.0001). The correlations of ICP and CPP to PI were statistically significant (r2 = 0.6; p < 0.0001). When performed in the first 24 hours of severe head injury, TCD ultrasonography is valid in predicting the patient's outcome at 6 months and correlates significantly with ICP and CPP values.

Brain death and transcranial Doppler: experience in 130 cases of brain dead patients

BACKGROUND AND PURPOSE

Diagnosis of brain death requires confirmation of the clinical diagnosis by appropriate tests, generally electroencephalography (EEG) and angiography. The diagnostic limitations or logistical problems inherent to these tests indicate the need to develop other more appropriate methods. The results obtained with transcranial Doppler (TCD) led us to conduct this prospective study of TCD recordings in brain dead patients.

METHODS

130 patients, aged 2-88 years were diagnosed as brain dead between July 1987 and June 1993. Clinical criteria were confirmed in all cases by EEG (n=88) and or angiography (n=64). Intracranial anterior circulation was insonated via temporal windows or, when impossible, via a transorbital approach. The posterior circulation was studied only in more recent patients. Examinations were made as soon as possible after brain death diagnosis and repeated for about 30 min. Vital parameters and treatments were taken into account.

RESULTS

There was only one false negative result, in a patient with an extended skull defect, who retained TCD and angiographic intracranial circulation despite confirmed irreversible brain death. All other patients displayed typical ultrasonic patterns of cerebral circulation arrest: an oscillating signal (n= 190, 73%), a systolic spike (n=62, 24%) or a unilateral absence of signal (n=5). Despite a total correlation for positive diagnosis, TCD and angiography may differ as to the level of circulation arrest. TCD is useful for patients under sedative drugs. No false positive result was encountered but we were unable to insonate any intracranial artery in 5 patients.

CONCLUSION

Data from previous studies and the results of this study indicate that TCD is a very sensitive and safe method for diagnosing cerebral circulatory arrest. TCD may be used as a confirmatory test alongside EEG and angiography. TCD is more widely applicable than EEG and may be earlier and safer than angiography.

99mTc-HMPAO SPECT in the diagnosis of brain death

OBJECTIVE

To evaluate the effectiveness of single proton emission tomography (SPECT) with 99mTc-HMPAO in the diagnosis of brain death (BD).

DESIGN

Prospective study in comatose and brain-dead patients.

SETTING

Neurologic ICU.

PATIENTS AND METHODS

Fifty 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.

INTERVENTIONS

Brain SPECT following i.v. injection of 99mTc-HMPAO (300-1100 MBq), using a 4-headed gamma-camera (20 min, 360 degrees, 88 images).

MEASUREMENTS AND RESULTS

All 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.

CONCLUSIONS

Our 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.

Consensus opinion on diagnosis of cerebral circulatory arrest using Doppler-sonography: Task Force Group on cerebral death of the Neurosonology Research Group of the World Federation of Neurology

BACKGROUND AND PURPOSE

Oscillating flow or systolic spikes are typical Doppler-sonographic flow signals found in the presence of cerebral circulatory arrest, which if irreversible, results in brain death. The Neurosonology Research Group (NSRG) of the World Federation of Neurology (WFN) created a Task Force Group in order to evaluate the role of Doppler-sonography as a confirmatory test for determining brain death.

METHODS

The available evidence from the literature has been reviewed and discussed by a group of experts, the members of the Task Force Group on cerebral death of the NSRG.

RESULTS AND CONCLUSIONS

Extra- and intracranial Doppler-sonography is a useful confirmatory test to establish irreversibility of cerebral circulatory arrest as optional part of a brain death protocol. Doppler-sonography is of special value when the therapeutic use of sedative drugs renders electroencephalography unreliable. Doppler-sonographic criteria are defined and guidelines for the use of Doppler-sonography in this setting are presented.

[The use of EEG in the diagnosis of brain death in France]

Scientific and modern conception of brain-death is rather recent, thus making possible organ transplantations. During the past three decades clinical criteria for brain-death have been defined. Electroencephalography (EEG) appears to be a complementary tool as it permits brain-death assessment. In France laws enforced respectively in 1968, 1978, 1991 and 1996 provide a framework for brain-death evaluation before organ transplantation and include EEG recording. Advantages and pitfalls of EEG in the diagnosis of brain-death are considered as this technique may be unreliable. Only evoked potential recordings can allow assessment and confirmation of brain stem death, which is a mandatory criterion. We recommend simultaneous EEG and either brain stem auditory or somatosensory evoked potential recordings to strengthen clinical criteria of brain-death and definitely prove it using objective electrophysiological criteria.

Correlation between transcranial Doppler ultrasonography and regional cerebral blood flow in experimental intracranial hypertension

BACKGROUND AND PURPOSE

Transcranial Doppler ultrasonography (TCD) provides useful information on cerebral circulation even under raised intracranial pressure. This study was designed to evaluate the correlation between cerebral blood flow (CBF) and TCD parameters under conditions of boundary intracranial hypertension that can cause brain death.

METHODS

Intracranial pressure was raised by inflation of a supratentorial epidural balloon in cats. Blood flow velocity of the middle cerebral artery was measured transorbitally with microvascular Doppler sonography, and intracranial pressure and CBF were evaluated.

RESULTS

In this study, four characteristic flow patterns were observed, appearing in the following order with progressive increases in intracranial pressure: sharp wave, systolic flow, systolic spike, and no flow. These flow patterns showed a significant correlation with flow velocity, CBF, the pulsatility index, and cerebral perfusion pressure. The systolic-spike and no-flow patterns and pulsatility index over 4.0 indicated decreased CBF, under 10% of control values.

CONCLUSIONS

The critical level of brain circulation can be detected by Doppler sonography, indicating that TCD is available as a tool for the assessment of cerebral circulatory arrest in brain death.

Transcranial Doppler ultrasonography in the neurocritical care unit

TCD ultrasonography is a noninvasive means to study the cerebral vasculature. By varying the depth and angle of insonation of a pulsed sound wave, the direction and velocity profile of the cerebral arteries can be ascertained. This can be used to identify areas of focal stenosis and increased resistance and to estimate the adequacy of cerebral flow. TCD ultrasonography commonly is used in SAH to detect cerebral vasospasm. Many centers interpret rising velocities as increasing vessel narrowing and initiate medical strategies based on these values. TCD use in head trauma is less clearly defined. TCD ultrasonography is considered an acceptable confirmatory test for the determination of brain death. TCD ultrasonography is capable of studying dynamic cerebrovascular processes. By being able to determine vessel patency, TCD may become a useful adjuvant to thrombolytic therapy. Continuous monitoring of flow velocities and profiles along with testing to cerebrovascular reserve promises to be a future active area of research.

Influence of the intra-aortic balloon pump on the transcranial Doppler flow pattern in a brain-dead patient

BACKGROUND

Confirmation of clinical brain death with transcranial Doppler (TCD) has been described. With the introduction of mechanical assist devices, it is important to know how these devices influence TCD measurements.

CASE DESCRIPTION

A patient who fulfilled the clinical criteria for brain death after cardiac arrest is described. An intra-aortic balloon pump (IABP) was necessary to maintain hemodynamic stability. A TCD examination was performed as an adjunct to the clinical diagnosis of brain death. A pattern of reversal of blood velocity typical of brain death was observed. With the IABP functioning, an increase of mean forward flow velocity without appreciable increase in the net flow velocities was seen. The results of the TCD measurements with the IABP functioning are not in concordance with values reported in the literature that confirm the clinical diagnosis of brain death.

CONCLUSIONS

Application of TCD in a patient with an IABP could lead to false interpretation of results if the TCD mean velocities are not registered with the IABP on standby or if the net flow velocities are not calculated.

Reliability in diagnosis of brain death

OBJECTIVE

To compare some of the confirmatory investigations of brain death with clinical criteria in order to achieve the most sensitive and accurate diagnosis of brain death.

DESIGN

All patients with isolated brain lesions and Glasgow Coma Scale (GCS) = 3 were subjected to neurological examination after ruling out hypothermia, metabolic disorders and drug intoxications and diagnosed as clinically brain-dead when the brainstem reflexes were absent and the apnea test positive.

PATIENTS

15 patients with clinical diagnosis of brain death entered this study.

MEASUREMENTS AND RESULTS

The patients were submitted to the following investigations: electroencephalogram (EEG), transcranial Doppler (TCD) of the middle cerebral arteries (MCA), cerebral blood flow measurements with the i.v. Xe-133 method (CBF) and selective cerebral angiography (CA). EEG was isoelectric in 8 patients while the remaining 7 patients showed persistence of electrical activity. TCD was compatible with intracranial circulatory arrest in 18 MCA districts, compatible with normal flow in 2 and undetectable in 10 out of 30 districts insonated. In CBF examinations, however, all the patients showed a characteristic "plateau" of the desaturation curves lasting through the whole investigation and suggestive of absent cortical flow. CA showed circulatory arrest in both carotid and vertebral arteries.

CONCLUSIONS

Our study suggests that cerebral angiography and CBF studies are the most reliable investigations whereas the role of EEG and TCD remains to be determined because of the presence of false negatives and positives.

Transcranial Doppler validation pilot study

The use of transcranial Doppler sonography (TCD) for the evaluation of patients with ischemic cerebrovascular disease remains controversial. This study was organized to gather preliminary data regarding the sensitivity and specificity of TCD when compared to cerebral angiography in detecting stenosing lesions and collateral flow patterns of the anterior cerebral circulation. Forty-two patients from six medical centers were prospectively enrolled. Each received cerebral angiography and TCD testing within 24 hours of each other. Based on TCD criteria established a priori, the results were first analyzed by a blinded investigator and then by computer. Computerized analyses were then repeated with modified criteria. Collateral flow through the anterior communicating and ophthalmic arteries was detected with sensitivities of 62% and 100%, and specificities of 98% and 92%, respectively. Internal carotid artery proximal and distal severe ( greater than 70%) stenoses were detected with sensitivities of 79% and 100% and specificities of 88% and 97%. Middle and anterior cerebral artery stenoses and middle cerebral artery occlusion were detected with specificities exceeding 98%; however, the data were insufficient to determine sensitivity. Computerized analyses did not permit improvement of sensitivity and specificity of the baseline criteria. The selected TCD criteria are highly specific in detecting intracranial stenoses and collateral flow patterns of the anterior circulation. The criteria have limited but acceptable sensitivity and specificity in detecting internal carotid artery origin severe stenoses, and are highly sensitive in detecting ophthalmic artery retrograde flow. A study with a larger sample is necessary to provide definitive guidelines for diagnosis.

The function of the hypothalamo-pituitary axis in brain dead patients

In order to find out the function of the hypothalamo-pituitary axis in brain dead patients, pituitary and hypothalamic hormone concentrations were measured and several anterior pituitary releasing tests were carried out in 39 brain dead patients. In addition, cerebral blood flow measurements were simultaneously performed. In almost all cases, the blood concentration of pituitary and hypothalamic hormones were above the sensitivity of the assay. Anterior pituitary releasing tests indicated that efficient functions of the hypothalamus were severely suppressed, while the normal secretory mechanism of the anterior pituitary was partially preserved in brain dead patients. Histological changes of hypothalamic neurons varied from barely detectable ghost cells to nearly normal cells even in the same case. Although, the remaining circulation seemed not to be sufficient enough to maintain integrated hypothalamo-pituitary function, as shown by the examinations of cerebral blood flow, the presence of hypothalamic hormones in the systemic circulation suggests that these hormones were released and carried from the hypothalamus by minimal flow which is preserved even after the diagnosis of brain death.

Management of intracranial hypertension

Intracranial hypertension is the final common denominator of morbidity and mortality for diverse neurologic problems, and its proper treatment requires the heuristic application of the available therapeutic alternatives when the clinical situation and patient's prognosis warrants treatment. The initial therapeutic focus for ICP reduction should be control of factors that may aggravate intracranial hypertension such as inappropriate head and body position, elevated body temperature, pain, noxious stimuli, elevated airway pressure, elevated blood pressure, seizures, and hypotonic intravenous fluids. The appropriate conventional therapies (e.g., hyperventilation, osmotic agents, sedatives, barbiturates, and cerebrospinal fluid removal) should be selected based on the details of each individual case. Surgical removal of intracranial mass lesions may be indicated in some circumstances, particularly for intractable intracranial hypertension and progressive, severe brain tissue shifts.

Reverse flow in the intracranial arteries--the possible significance of comparative flow in the anterior cerebral and the basilar arteries

Four infants with reverse flow patterns of the intracranial arteries are reported. Two with severe brain damage, had a reverse flow pattern in the anterior cerebral artery, which was recorded during the recovery stage from cardiac arrest. The other two patients showed a reverse flow pattern in the basilar artery and had a good prognosis. Reverse flow in the anterior cerebral artery suggests severe brain damage, but that in the basilar artery does not.

Transcranial Doppler sonographic monitoring in the intensive care unit

Transcranial Doppler sonography noninvasively measures flow velocities within the basal cerebral arteries. It has been used for the management of patients with ischemic cerebrovascular disease and subarachnoid hemorrhage, as well as in the determination of brain death. Its role and technical limitations in the intensive care unit are reviewed.

Transcranial Doppler ultrasonography: clinical applications in cerebrovascular disease

Transcranial Doppler ultrasonography was introduced in 1982 as a noninvasive procedure for assessment of the intracranial cerebral circulation. The lightweight and portable equipment used for transcranial Doppler examination facilitates its use in the bedside assessment of critically ill hospitalized patients and outpatients. Clinical applications include the diagnosis of vasospasm in patients with subarachnoid hemorrhage, assessment of intracranial collateral flow in patients with extracranial arterial occlusive disease, detection of intracranial arterial stenosis, identification of the feeding arteries of arteriovenous malformations and monitoring the hemodynamic effects of their treatment, confirmation of the clinical diagnosis of brain death, intensive-care unit monitoring of brain-injured patients, and intraoperative and postoperative monitoring of neurosurgical patients. Transcranial Doppler technology is also providing new insights into the pathophysiologic mechanisms of a variety of cerebrovascular conditions. Clinicians will find transcranial Doppler technology most helpful if they have a specific question about the status of the intracranial circulation. Further investigations may expand the clinical and research utility of this technology.