Transcranial Doppler and anesthetics

Middle Cerebral Artery Blood Flow Velocity During Normal Pregnancy

BACKGROUND

The present study aimed to evaluate resting middle cerebral artery (MCA) blood flow velocities using transcranial Doppler ultrasound (TCD) in healthy women at different stages of pregnancy, and to compare these velocities with those of normal controls.

METHODS

A total of 105 healthy normotensive pregnant women and 25 non-pregnant healthy controls were included in the study. We formed 3 groups according to gestational age: first trimester (7 to 13 wk pregnant), second trimester (14 to 28 wk pregnant), and third trimester (29 to 42 wk pregnant). Age, body mass index, heart rate, arterial blood pressure, and hematological data were recorded and TCD was performed on the subjects. Regarding TCD, we evaluated the mean cerebral blood flow velocity, the peak systolic velocity, the end-diastolic flow velocity, S/D ratio, the pulsatility Index (PI) and the resistance Index (RI).

RESULTS

The MCA mean blood flow velocities differed significantly among the groups ( P <0.001) and were higher in the controls than those of the first trimester, second trimester, and third trimester groups ( P <0.01, P <0.001, P <0.001 respectively). The MCA mean and peak blood flow velocities, and the PI and RI decreased significantly with advancing gestation.

CONCLUSIONS

TCD is a noninvasive and non-toxic method of monitoring the adaptation of the maternal cerebral blood flow in pregnancy. The progressive decreases in the MCA mean and peak blood flow velocities, PI, and RI during gestation may be the result of chemical and neuronal factors. This study supports the need for additional studies using TCD to establish normative cerebral blood flow volumes throughout pregnancy.

Pre- and Post-Hemodialysis Cerebral Blood Flow Velocity in Patients With End-Stage Renal Disease

BACKGROUND

This study assessed the consequences of hemodialysis (HD) on hemodynamic parameters of cerebral circulation by measuring middle cerebral artery blood flow velocities using transcranial Doppler ultrasound before and after a single dialysis session in patients with end-stage renal disease (ESRD).

MATERIALS AND METHODS

Fifty clinically stable patients with ESRD undergoing HD and 40 healthy controls were recruited for the study. Blood pressure, heart rate, and body weight were measured. Transcranial Doppler ultrasound evaluations and blood analyses were performed immediately before and after a single dialysis session.

RESULTS

The mean cerebral blood flow velocities (CBFVs) in the ESRD patients before HD was 65 ± 17 cm/second and did not differ from that of the normal controls (64 ± 14 cm/s) ( P = 0.735). The postdialysis CBFV also did not differ from that of the controls ( P = 0.054).

CONCLUSION

Compensatory cerebral autoregulation and chronic adjustment to therapy may be the reason for the nondeviation of the CBFV values from normality observed in both sessions.

Assessing rheoencephalography dynamics through analysis of the interactions among brain and cardiac networks during general anesthesia

Cerebral blood flow (CBF) reflects the rate of delivery of arterial blood to the brain. Since no nutrients, oxygen or water can be stored in the cranial cavity due to space and pressure restrictions, a continuous perfusion of the brain is critical for survival. Anesthetic procedures are known to affect cerebral hemodynamics, but CBF is only monitored in critical patients due, among others, to the lack of a continuous and affordable bedside monitor for this purpose. A potential solution through bioelectrical impedance technology, also known as rheoencephalography (REG), is proposed, that could fill the existing gap for a low-cost and effective CBF monitoring tool. The underlying hypothesis is that REG signals carry information on CBF that might be recovered by means of the application of advanced signal processing techniques, allowing to track CBF alterations during anesthetic procedures. The analysis of REG signals was based on geometric features extracted from the time domain in the first place, since this is the standard processing strategy for this type of physiological data. Geometric features were tested to distinguish between different anesthetic depths, and they proved to be capable of tracking cerebral hemodynamic changes during anesthesia. Furthermore, an approach based on Poincaré plot features was proposed, where the reconstructed attractors form REG signals showed significant differences between different anesthetic states. This was a key finding, providing an alternative to standard processing of REG signals and supporting the hypothesis that REG signals do carry CBF information. Furthermore, the analysis of cerebral hemodynamics during anesthetic procedures was performed by means of studying causal relationships between global hemodynamics, cerebral hemodynamics and electroencephalogram (EEG) based-parameters. Interactions were detected during anesthetic drug infusion and patient positioning (Trendelenburg positioning and passive leg raise), providing evidence of the causal coupling between hemodynamics and brain activity. The provided alternative of REG signal processing confirmed the hypothesis that REG signals carry information on CBF. The simplicity of the technology, together with its low cost and easily interpretable outcomes, should provide a new opportunity for REG to reach standard clinical practice. Moreover, causal relationships among the hemodynamic physiological signals and brain activity were assessed, suggesting that the inclusion of REG information in depth of anesthesia monitors could be of valuable use to prevent unwanted CBF alterations during anesthetic procedures.

Age-Related Changes in Cerebral Hemodynamics in Children Undergoing Congenital Cardiac Surgery: A Prospective Observational Study

OBJECTIVE

To explore age-related cerebral hemodynamic characteristics before and after pediatric cardiac surgery.

DESIGN

Prospective observational study.

SETTING

Single-center study based at a tertiary care center in Shanghai, China.

PATIENTS

Fifty-three children with congenital heart disease (CHD) aged zero-to-six years undergoing cardiac surgery with cardiopulmonary bypass were enrolled, and 44 children finally were analyzed.

INTERVENTION

Cerebral hemodynamics were measured by transcranial color-coded duplex sonography in the right temporal window before and after surgery. The resistance index (RI), pulsatility index (PI), and cerebral blood flow velocity (CBFV), including time average maximum flow velocity (V_tamax), mean blood flow velocity (V_mean), and the peak systolic flow velocity (V_peak), of the right middle cerebral artery (MCA) and regional cerebral oxygen saturation (rScO₂) of the right frontal lobe were measured and analyzed. Heart rate and mean arterial pressure were also recorded during ultrasound.

MEASUREMENTS AND MAIN RESULTS

RI and PI decreased exponentially with age before and after cardiac surgery. While PI remained unchanged after cardiac surgery, RI was significantly reduced. Furthermore, RI reduction after cardiac surgery was more significant in children >18 months compared to those ≤18 months. CBFV of the right MCA also showed exponential increase with age, but rScO₂ linearly increased. Cardiac surgery significantly changed the cerebral hemodynamics, but it did not affect rScO₂ in children regardless of age.

CONCLUSIONS

Age-related cerebral hemodynamic changes exist in children with CHD. Cardiopulmonary bypass surgery led to greater cerebrovascular dilation in children aged ≤18 months than those >18 months.

Cerebral blood flow velocity in migraine and chronic tension-type headache patients

Introduction

The present study seeks to use transcranial Doppler ultrasound to evaluate cerebral blood flow velocities in anterior and posterior circulation arteries, during an attack-free episode in migraine patients, with and without aura, as well as in chronic tension-type headache patients who were not receiving prophylactic medication.

Methods

A total of 50 patients (35 female, 15 male) were evaluated during a headache-free episode: 30 migraine patients without aura (mean age: 32±8 years), 10 migraine patients with aura (mean age: 34±4 years), and 10 patients with chronic tension-type headache (mean age: 34±5 years).

Results

No significant difference was present between anterior, middle, and posterior cerebral and vertebral arteries' blood flow velocities between migraine patients, with and without aura, or in patients with a tension-type headache, and normal controls (p>0.05). However, a significant increase in basilar artery cerebral blood flow velocities relative to controls was present in patients with a tension-type headache (p>0.001).

Conclusion

It is difficult to predict the main reason for the significant increase in basilar artery blood flow velocities in patients with chronic tension-type headache. It may be due to constriction of conductance or the dilatation of the resistance vessels.

Whole blood viscosity and cerebral blood flow velocities in obese hypertensive or obese normotensive adolescents

BACKGROUND

Obesity affects all major organ systems and leads to increased morbidity and mortality. Whole blood viscosity is an important independent regulator of cerebral blood flow. The aim of the present study was to evaluate the effect of whole blood viscosity on cerebral artery blood flow velocities using transcranial Doppler ultrasound in pediatric patients with obesity compared to healthy controls and analyze the effect of whole blood viscosity and blood pressure status to the cerebral artery blood flow velocities.

METHODS

Sixty patients with obesity diagnosed according to their body mass index (BMI) percentiles aged 13-18 years old were prospectively enrolled. They were grouped as hypertensive or normotensive according to their ambulatory blood pressure monitoring. Whole blood viscosity and middle cerebral artery velocities by transcranial Doppler ultrasound were studied and compared to 20 healthy same aged controls.

RESULTS

Whole blood viscosity values in hypertensive (0.0619±0.0077 poise) and normotensive (0.0607±0.0071 poise) groups were higher than controls (0.0616±0.0064 poise), with no significance. Middle cerebral artery blood flow velocities were higher in the obese hypertensive (73.9±15.0 cm/s) and obese normotensive groups (75.2±13.5 cm/s) than controls (66.4±11.5 cm/s), but with no statistical significance.

CONCLUSIONS

Physiological changes in blood viscosity and changes in blood pressure did not seem to have any direct effect on cerebral blood flow velocities, the reason might be that the cerebral circulation is capable of adaptively modulating itself to changes to maintain a uniform cerebral blood flow.

Comparison of phase-contrast MR imaging and endovascular sonography for intracranial blood flow velocity measurements

BACKGROUND AND PURPOSE

Local hemodynamic information may help to stratify rupture risk of cerebral aneurysms. Patient-specific modeling of cerebral hemodynamics requires accurate data on BFV in perianeurysmal arteries as boundary conditions for CFD. The aim was to compare the BFV measured with PC-MR imaging with that obtained by using intra-arterial Doppler sonography and to determine interpatient variation in intracranial BFV.

MATERIALS AND METHODS

In 10 patients with unruptured intracranial aneurysms, BFV was measured in the cavernous ICA with PC-MR imaging in conscious patients before treatment, and measured by using an intra-arterial Doppler sonography wire when the patient was anesthetized with either propofol (6 patients) or sevoflurane (4 patients).

RESULTS

Both techniques identified a pulsatile blood flow pattern in cerebral arteries. PSV differed >50 cm/s between patients. A mean velocity of 41.3 cm/s (95% CI, 39.3-43.3) was measured with PC-MR imaging. With intra-arterial Doppler sonography, a mean velocity of 29.3 cm/s (95% CI, 25.8-32.8) was measured with the patient under propofol-based intravenous anesthesia. In patients under sevoflurane-based inhaled anesthesia, a mean velocity of 44.9 cm/s (95% CI, 40.6-49.3) was measured.

CONCLUSIONS

We showed large differences in BFV between patients, emphasizing the importance of using patient-specific hemodynamic boundary conditions in CFD. PC-MR imaging measurements of BFV in conscious patients were comparable with those obtained with the intra-arterial Doppler sonography when the patient was anesthetized with a sevoflurane-based inhaled anesthetic.

Ultrasonography of the optic nerve in neurocritically ill patients

The rapid diagnosis of intracranial hypertension is urgently needed for therapeutic reasons in various clinical settings. This can rarely be achieved without invasive procedures such as intracranial pressure (ICP) monitoring or neuroimaging. The optic nerve is surrounded by cerebrospinal fluid (CSF) and dura mater, which forms the optic nerve sheath (ONS). Because of the connection with the intracranial subarachnoid space, ONS diameter (ONSD) is influenced by CSF pressure variations. Bedside ultrasonographic measurement of ONSD has been proposed as a non-invasive and reliable means to detect raised ICP in neurocritically ill patients. In several studies, it proves to have a good correlation with the direct measurement of ICP and a low interobserver variability. However, no general consensus exists over the upper normal ONSD limit. We performed a review of the literature on the use of the ultrasonography of the optic nerve in the evaluation of patients with suspected intracranial hypertension. The aim of this review is to describe the technique and to assess the validity of this diagnostic method.

Evaluation of cerebrovascular carbon dioxide reactivity in patients with diabetes mellitus under sedative doses of propofol

The present study compared cerebrovascular CO2 reactivity in diabetic patients on different treatment modalities under sedative doses of propofol. Fifteen patients with diabetes mellitus (on three different antidiabetic treatment modalities) who required mechanical ventilation during intensive care therapy were studied, sedation during mechanical ventilation being maintained using propofol. As controls, 6 patients without diabetes were monitored. A 2.5-MHz pulsed transcranial Doppler probe was attached to the head of the patient at the right temporal window for continuous measurement of mean blood flow velocity in the middle cerebral artery (Vmca). After establishing baseline values of Vmca and cardiovascular hemodynamics, end-tidal CO2 was decreased by increasing ventilatory frequency by 5-8 breaths.min(-1). Values for absolute and relative CO2 reactivity in insulintreated patients were lower than those in the other three groups (absolute CO2 reactivity [means +/- SD]: control, 3.1 +/- 0.6 cm.s(-1).mmHg(-1), diet, 3.8 +/- 1.4 cm.s(-1) x mmHg(-1); oral antidiabetic drug 3.2 +/- 0.9 cm x s(-1) x mmHg(-1); insulin, 1.1 +/- 0.6 cm x s(-1) x mmHg(-1); P = 0.002).The present study shows that insulin-treated diabetic patients probably have lower cerebrovascular CO2 reactivity under propofol anesthesia than control patients or diabetics treated with dietary therapy or oral hypoglycemics.