Stroke prevention in sickle cell disease (STOP) study guidelines for transcranial Doppler testing

Increased cerebral blood flow velocity in children with mild sleep-disordered breathing: a possible association with abnormal neuropsychological function

OBJECTIVE

Sleep-disordered breathing describes a spectrum of upper airway obstruction in sleep from simple primary snoring, estimated to affect 10% of preschool children, to the syndrome of obstructive sleep apnea. Emerging evidence has challenged previous assumptions that primary snoring is benign. A recent report identified reduced attention and higher levels of social problems and anxiety/depressive symptoms in snoring children compared with controls. Uncertainty persists regarding clinical thresholds for medical or surgical intervention in sleep-disordered breathing, underlining the need to better understand the pathophysiology of this condition. Adults with sleep-disordered breathing have an increased risk of cerebrovascular disease independent of atherosclerotic risk factors. There has been little focus on cerebrovascular function in children with sleep-disordered breathing, although this would seem an important line of investigation, because studies have identified abnormalities of the systemic vasculature. Raised cerebral blood flow velocities on transcranial Doppler, compatible with raised blood flow and/or vascular narrowing, are associated with neuropsychological deficits in children with sickle cell disease, a condition in which sleep-disordered breathing is common. We hypothesized that there would be cerebral blood flow velocity differences in sleep-disordered breathing children without sickle cell disease that might contribute to the association with neuropsychological deficits.

DESIGN

Thirty-one snoring children aged 3 to 7 years were recruited from adenotonsillectomy waiting lists, and 17 control children were identified through a local Sunday school or as siblings of cases. Children with craniofacial abnormalities, neuromuscular disorders, moderate or severe learning disabilities, chronic respiratory/cardiac conditions, or allergic rhinitis were excluded. Severity of sleep-disordered breathing in snoring children was categorized by attended polysomnography. Weight, height, and head circumference were measured in all of the children. BMI and occipitofrontal circumference z scores were computed. Resting systolic and diastolic blood pressure were obtained. Both sleep-disordered breathing children and the age- and BMI-similar controls were assessed using the Behavior Rating Inventory of Executive Function (BRIEF), Neuropsychological Test Battery for Children (NEPSY) visual attention and visuomotor integration, and IQ assessment (Wechsler Preschool and Primary Scale of Intelligence Version III). Transcranial Doppler was performed using a TL2-64b 2-MHz pulsed Doppler device between 2 pm and 7 pm in all of the patients and the majority of controls while awake. Time-averaged mean of the maximal cerebral blood flow velocities was measured in the left and right middle cerebral artery and the higher used for analysis.

RESULTS

Twenty-one snoring children had an apnea/hypopnea index <5, consistent with mild sleep-disordered breathing below the conventional threshold for surgical intervention. Compared with 17 nonsnoring controls, these children had significantly raised middle cerebral artery blood flow velocities. There was no correlation between cerebral blood flow velocities and BMI or systolic or diastolic blood pressure indices. Exploratory analyses did not reveal any significant associations with apnea/hypopnea index, apnea index, hypopnea index, mean pulse oxygen saturation, lowest pulse oxygen saturation, accumulated time at pulse oxygen saturation <90%, or respiratory arousals when examined in separate bivariate correlations or in aggregate when entered simultaneously. Similarly, there was no significant association between cerebral blood flow velocities and parental estimation of child's exposure to sleep-disordered breathing. However, it is important to note that whereas the sleep-disordered breathing group did not exhibit significant hypoxia at the time of study, it was unclear to what extent this may have been a feature of their sleep-disordered breathing in the past. IQ measures were in the average range and comparable between groups. Measures of processing speed and visual attention were significantly lower in sleep-disordered breathing children compared with controls, although within the average range. There were similar group differences in parental-reported executive function behavior. Although there were no direct correlations, adjusting for cerebral blood flow velocities eliminated significant group differences between processing speed and visual attention and decreased the significance of differences in Behavior Rating Inventory of Executive Function scores, suggesting that cerebral hemodynamic factors contribute to the relationship between mild sleep-disordered breathing and these outcome measures.

CONCLUSIONS

Cerebral blood flow velocities measured by noninvasive transcranial Doppler provide evidence for increased cerebral blood flow and/or vascular narrowing in childhood sleep-disordered breathing; the relationship with neuropsychological deficits requires further exploration. A number of physiologic changes might alter cerebral blood flow and/or vessel diameter and, therefore, affect cerebral blood flow velocities. We were able to explore potential confounding influences of obesity and hypertension, neither of which explained our findings. Second, although cerebral blood flow velocities increase with increasing partial pressure of carbon dioxide and hypoxia, it is unlikely that the observed differences could be accounted for by arterial blood gas tensions, because all of the children in the study were healthy, with no cardiorespiratory disease, other than sleep-disordered breathing in the snoring group. Although arterial partial pressure of oxygen and partial pressure of carbon dioxide were not monitored during cerebral blood flow velocity measurement, assessment was undertaken during the afternoon/early evening when the child was awake, and all of the sleep-disordered breathing children had normal resting oxyhemoglobin saturation at the outset of their subsequent sleep studies that day. Finally, there is an inverse linear relationship between cerebral blood flow and hematocrit in adults, and it is known that iron-deficient erythropoiesis is associated with chronic infection, such as recurrent tonsillitis, a clinical feature of many of the snoring children in the study. Preoperative full blood counts were not performed routinely in these children, and, therefore, it was not possible to exclude anemia as a cause of increased cerebral blood flow velocity in the sleep-disordered breathing group. However, hemoglobin levels were obtained in 4 children, 2 of whom had borderline low levels (10.9 and 10.2 g/dL). Although there was no apparent relationship with cerebral blood flow velocity in these children (cerebral blood flow velocity values of 131 and 130 cm/second compared with 130 and 137 cm/second in the 2 children with normal hemoglobin levels), this requires verification. It is of particular interest that our data suggest a relationship among snoring, increased cerebral blood flow velocities and indices of cognition (processing speed and visual attention) and perhaps behavioral (Behavior Rating Inventory of Executive Function) function. This finding is preliminary: a causal relationship is not established, and the physiologic mechanisms underlying such a relationship are not clear. Prospective studies that quantify cumulative exposure to the physiologic consequences of sleep-disordered breathing, such as hypoxia, would be informative.

Elevated blood flow velocity in the anterior cerebral artery and stroke risk in sickle cell disease: extended analysis from the STOP trial

Elevated velocity in the internal carotid artery (ICA) or middle cerebral artery (MCA), detected by transcranial Doppler (TCD) ultrasonography, predicts an increased risk of stroke in children with sickle cell disease (SCD). Although strokes also occur in an anterior cerebral artery (ACA) distribution, the significance of elevated velocity in this vessel has not been determined previously. We assessed the effect of elevated ACA velocity on stroke risk using the results of the first adequate TCD study performed on 1975 children as part of The Stroke Prevention Trial in Sickle Cell Anemia (STOP). Elevated ACA velocity (> or =170 cm/s) was associated with an increased risk of stroke (P = 0.0013) after adjusting for the ICA/MCA classification. Among subjects with normal ICA/MCA velocity, the risk of stroke was more than 10-fold greater in those with elevated compared with normal ACA velocity (2.13 and 0.20 per 100 patient-years, respectively, P < 0.001); risk more than doubled with elevated compared with normal ACA velocity in those already at high risk due to abnormal ICA/MCA findings (7.56 vs. 3.22 per 100 patient-years, P = 0.042). Few of the strokes in those with elevated ACA velocity occurred in an ACA distribution, suggesting changes in blood flow velocity in anterior vessels may be associated with diffuse arterial disease or, alternatively, manifest collateral flow from compromised middle cerebral vessels.

A web-based interactive database system for a transcranial Doppler ultrasound laboratory

BACKGROUND

Variations in transcranial Doppler (TCD) examination performance techniques and interpretive paradigms between individual laboratories are a common challenge in the practice of TCD. Demand for rapid access to patient ultrasound examination data and report for use in intensive care settings has necessitated a more flexible approach to data management. Both of these issues may benefit from a computerized approach.

METHODS

We describe the application of a World Wide Web-based database system for use in an ultrasound laboratory. Results. Databasing information while generating a TCD report is efficient. Web accessibility allows rapid and flexible communication of time-sensitive report information and interpretation for more expeditious clinical decision making.

CONCLUSIONS

Web-based applications can extend the reach and efficiency of traditionally structured medical laboratories.

Doppler transcraniano na prática neurológica

O Doppler transcraniano (DTC) é um método relativamente novo, descrito em 1982 por Rune Aaslid e introduzido no Brasil em 1992 por Roberto Hirsch, na Universidade de São Paulo. O serviço de Neurologia do Hospital de Clínicas da Universidade Federal do Paraná (HC-UFPR) disponibilizou esse exame em 2001, com divulgação das principais vantagens do método no diagnóstico, seguimento e manejo terapêutico de pacientes com suspeita ou portadores de doença cerebrovascular. O objetivo deste trabalho é demonstrar como o DTC vem sendo utilizado em nosso meio e quais são as especialidades médicas que vêm absorvendo o auxílio do método. Embora diretrizes como a publicada pela Academia Americana de Neurologia em 2004 validem as indicações do DTC, estabelecendo especificidade e sensibilidade do método, verificamos que a solicitação do exame em nosso meio depende da divulgação do serviço, da implementação de linhas de pesquisa e, finalmente, do reconhecimento de sua utilidade na prática diária.

Defining stroke risk in children with sickle cell anaemia

Sickle cell anaemia (SCA) is the most common cause of childhood stroke, occurring with the highest frequency before the age of 6 years. Despite the relative frequency of stroke in SCA, few predictors of risk exist. Anaemia, leucocytosis, hypertension, silent infarction, and history of acute chest syndrome are well-documented risk factors for ischaemic stroke in SCA. Recent data suggest that other environmental and genetic factors, many unrelated to SCA, influence the development of cerebrovascular disease. Non-invasive assessment of individual stroke risk using transcranial Doppler ultrasonography has provided a means of selecting and prophylactically treating SCA children at highest risk. With the ultimate goal of preventing stroke, the information gained from the studies reviewed here may lead to improved prediction of stroke so that clinical trials to assess risk-based therapy may be carried out on selected children with SCA.

Screening children for sickle cell vasculopathy: guidelines for transcranial Doppler evaluation

Cerebral infarction is a major cause of morbidity and mortality in children with sickle cell disease. Prevention of primary stroke might be feasible with a way to identify children at greatest risk. Transcranial Doppler (TCD) has been shown to be a noninvasive, reliable, inexpensive method of identifying children at highest risk for cerebral infarction. The pros and cons of imaging and non-imaging TCD techniques are discussed. The protocol for the stroke prevention trial in sickle cell anemia (STOP), including data acquisition and interpretation, is reviewed. Providing TCD to sickle cell patients can be a valuable service that results in a significant decrease in first stroke rates.

Genetics of cerebrovascular disorders

Physicians must be able to recognize stroke caused by a mendelian or mitochondrial disorder. Some genetic disorders such as sickle cell anemia and Fabry disease have proven disease-specific treatments, whereas others have no effective treatment, including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Proper diagnosis of a genetic disorder has prognostic value and prevents patient exposure to unnecessary and potentially harmful therapeutic agents and diagnostic tests. This article reviews the clinical and genetic features of some mendellan and mitochondrial disorders associated with ischemic stroke, hemorrhagic stroke, and cerebrovascular malformations.

Can peak systolic velocities be used for prediction of stroke in sickle cell anemia?

BACKGROUND AND PURPOSE

Ischemic stroke occurs in at least 11% of patients with homozygous sickle cell anemia (SCD) by the time they turn 20 years old. High risk associated with distal intracranial internal carotid (ICA) and proximal middle cerebral artery (MCA) stenosis can be detected by transcranial Doppler (TCD). TCD screening offers the possibility of reducing the risk of first stroke significantly based on a paradigm tested and proven to be effective in a stroke prevention trial in sickle cell anemia (STOP). Children with high flow velocity in the ICA and MCA of 200 cm/s time average mean of the maximum (TAMM) or higher had a 10% per year risk of first stroke that was reduced to <1% with regular red cell transfusion (reduction of hemoglobin S <30%). The clinical application of the STOP results could be enhanced if criteria for treatment could be found that are based on peak systolic velocity (PSV), the measure more commonly used in vascular ultrasound practice.

OBJECTIVE

To compare PSV and end diastolic velocity (EDV) with TAMM for prediction of stroke and to derive PSV cutpoints for STOP protocol definitions of conditional and abnormal TCD. Using the STOP TCD and stroke outcome data to compare PSV and TAMM in terms of stroke prediction, PSV cutpoints comparable to those based on TAMM and used in STOP were derived. Because of their familiarity to the vascular ultrasound community, PSV cutpoints should be an important alternative to TAMM and may increase availability of screening and risk stratification for children with this disease.

MATERIALS AND METHODS

Data from 1,937 baseline TCD studies from STOP were correlated with stroke outcome in those not treated with transfusion. Stroke prediction was assessed with survival analysis using TAMM, PSV and EDV as continuous variables individually and then pair-wise in the same model, which contained 53 stroke events.

RESULTS

PSV and EDV were highly correlated to the TAMM velocity (r=0.94). The multivariate model for prediction indicated that TAMM velocity was a better predictor than EDV, and PSV and TAMM were approximately equivalent. PSV cutpoints defining the two relevant STOP risk categories--"conditional," which should lead to increased TCD surveillance, and "abnormal," which should lead to strong consideration for treatment according to STOP--were derived taking into consideration known differences in measurements between the dedicated Doppler systems (TCD) used in STOP and the transcranial Doppler imaging (TCDI) systems commonly used in clinical practice. The recommended PSV cutpoint for conditional TCD is 200 cm/s, and for abnormal TCD triggering consideration for treatment is 250 cm/s.

CONCLUSION

Assuming TCDI equipment is used and the STOP protocol is applied, a PSV cutpoint of 200 cm/s is recommended as the threshold for increased TCD surveillance (comparable to a TCD TAMM of 170 cm/s in STOP); a PSV of 250 cm/s is recommended as the cutpoint at which, if confirmed in a second examination, chronic transfusion should be considered. Assuming the STOP scanning protocol is used, PSV is at least as good as TAMM and can be used to select children with SCD for treatment or increased surveillance to prevent first stroke.

Sickle cell disease and stroke in a pediatric population

Cerebrovascular complications are common in SCD and constitute a major source of concern to the pediatric hematologist. These complications can be either clinically overt or covert. The authors' review of the diagnostic tests does not offer absolute indications for neuroimaging because most of the evidence is based on studies that are not randomized controlled trials. Imaging guidelines for children have emerged based on the available level 2 and 3 literature, however, CT and MR imaging remain the initial tests of choice for stroke assessment, and TCD is the imaging tool of choice for stroke prevention. Based on guidelines handed down from the NIH, TCD has become a part of routine continuing care of children with SCD.

Blood transfusion for preventing stroke in people with sickle cell disease

BACKGROUND

Sickle cell disease is a common inherited haemoglobin disorder. The abnormal haemoglobin causes distortion of red blood cells, anaemia, vaso-occlusion and dysfunction in virtually any organ system in the body. Stroke occurs in around 10% of children with sickle cell anaemia, and recurrences after a first stroke are likely. Chronic blood transfusion regimes are often used in an attempt to dilute the sickled red blood cells, thus reducing the risk of vaso-occlusion and stroke. However, the side-effects of such regimens can be severe.

OBJECTIVES

To assess the relative risks and benefits of chronic blood transfusion regimes in patients with sickle cell disease to prevent a first stroke or further strokes.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group specialist register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Date of the most recent search of the Group's specialised register: July 2001

SELECTION CRITERIA

All those randomised or quasi-randomised controlled trials in which blood transfusion as a preventative measure for stroke in patients with sickle cell disease are compared to an alternative treatment or to no treatment.

DATA COLLECTION AND ANALYSIS

Both reviewers independently assessed trial quality and extracted data from the study included.

MAIN RESULTS

One trial was identified by the initial search and this met the inclusion criteria for the review. The trial compared a chronic transfusion regime to maintain sickle haemoglobin at less than 30% with standard care in 130 children with sickle cell disease who were judged to be at high risk of a first stroke through transcranial doppler ultrasonography. Eleven children in the standard care group suffered a stroke during the trial, compared to only one in the transfusion group. Because of this 92% relative risk reduction, the trial was terminated 16 months early. It had been planned that all patients would be treated for 30 months, but median follow-up only 21.1 months. However, a high rate of complications such as iron overload, alloimmunisation and transfusion reactions were seen in the children who were receiving transfusions. No randomised controlled trials were identified which investigated use of transfusion for preventing recurrence of stroke.

REVIEWER'S CONCLUSIONS

While the included study demonstrated a significantly reduced risk of stroke in patients receiving regular blood transfusions, the degree of risk must be balanced against the burden of a chronic transfusion regime. Further research is required to establish the use of transfusion in preventing secondary stroke, the age, or length of time after an event, at which transfusion can safely be stopped, and to further define risk factors for stroke in order to reduce the chance of unnecessarily putting children onto a chronic transfusion regime.