Evaluation of posttraumatic cerebral blood flow velocities by transcranial Doppler ultrasonography

Thirty-five patients were admitted to the hospital with Glasgow coma scale scores of 4 to 7 after severe, blunt head injury. Blood flow velocities of the middle cerebral artery (MCA) and the ipsilateral internal carotid artery (ICA), high in the neck, were recorded noninvasively by Doppler ultrasonography. Serial examinations were begun within 48 hours of trauma and continued until the patient either died or was discharged. Spasm of the MCA was assumed if the ratio of the velocity of blood flow in the MCA (VMCA) to the velocity of blood flow in the ICA (VICA) exceeded 3 (normal value, 1.7 +/- 0.4). In cases of severe MCA spasm, this ratio is higher because of increased flow velocity in the MCA and reduced flow in the ICA due to increased cerebrovascular resistance. Higher MCA velocities with VMCA/VICA above 3, consistent with MCA spasm, were found in 14 of the 35 patients (40%). The increase began as early as 48 hours after injury, reached a maximum between Days 5 and 7, and lasted until 2 weeks after injury. There was a significant correlation between the occurrence of vasospasm and the quantity of cisternal or intracerebral blood seen on a computed tomographic scan. No correlation was found with the age of the patients, the Glasgow coma scale score at admission, the intracranial pressure, or the functional outcome 6 months after injury. The occurrence of a secondary infarction in a patient with severe MCA spasm suggests that, at least in some cases, spasm may influence the prognosis.     

Intracranial blood velocity in head injury. A transcranial ultrasound Doppler study

We report our experience monitoring head-injured patients by means of transcranial Doppler sonography. Cerebral velocity measurements and waveforms change in a consistent pattern with the existence of intracranial pressure, and it is possible to discriminate low versus high flow states. The technique, in contrast to cerebral blood flow measurement, is reliable, atraumatic, and repeatable so that diagnostic assessments can be made and the patient can be followed for therapeutic efficacy.     

Changes in cerebral blood flow velocity after release of intraoperative tourniquets in humans: a transcranial Doppler study

The effect of release of intraoperative thigh tourniquets on velocity of blood flow in the middle cerebral artery was examined in five patients given general anesthesia with controlled ventilation for lower extremity orthopedic procedures using transcranial Doppler sonography. Middle cerebral artery blood flow velocity increased significantly from 52 +/- 6 (SEM) to 82 +/- 24 cm/s (an increase of 58% +/- 13%) within 4 +/- 1 min after tourniquet release and remained significantly elevated for 7 min. A positive linear correlation was found between middle cerebral artery blood flow velocity and PETCO2 on each occasion (0.97 greater than or equal to r greater than or equal to 0.84, 0.001 greater than P greater than 0.0001) after tourniquet deflation. Assuming a linear relationship between flow velocity and flow, these findings suggest that significant increase in cerebral blood flow can occur after intraoperative tourniquet release and that this increase appears to be mostly CO2-dependent.     

Posttraumatic cerebral arterial spasm: transcranial Doppler ultrasound, cerebral blood flow, and angiographic findings.

Thirty patients admitted after suffering closed head injuries, with Glasgow Coma Scale scores ranging from 3 to 15, were evaluated with transcranial Doppler ultrasound monitoring. Blood flow velocity was determined in the middle cerebral artery (MCA) and the intracranial portion of the internal carotid artery (ICA) in all patients. Because proximal flow in the extracranial ICA declines in velocity when arterial narrowing becomes hemodynamically significant, the extracranial ICA velocity was concurrently monitored in 19 patients. To assess cerebral perfusion, cerebral blood flow (CBF) measurements obtained with the intravenous 133Xe technique were completed in 16 patients. Vasospasm, designated as MCA velocity exceeding 120 cm/sec, was found in eight patients (26.7%). Severe vasospasm, defined as MCA velocity greater than 200 cm/sec, occurred in three patients, and was confirmed by angiography in all three. Subarachnoid hemorrhage (SAH) was documented by computerized tomography in five (62.5%) of the eight patients with vasospasm. All cases of severe vasospasm were associated with subarachnoid blood. The time course of vasospasm in patients with traumatic SAH was similar to that found in patients with aneurysmal SAH; in contrast, arterial spasm not associated with SAH demonstrated an uncharacteristically short duration (mean 1.25 days), suggesting that this may be a different type of spasm. A significant correlation (p less than 0.05) was identified between the lowest CBF and highest MCA velocity in patients during the period of vasospasm, indicating that arterial narrowing can lead to impaired CBF. Ischemic brain damage was found in one patient who had evidence of cerebral infarction in the territories supplied by the arteries affected by spasm. These findings demonstrate that delayed cerebral arterial spasm is a frequent complication of closed head injury and that the severity of spasm is, in some cases, comparable to that seen in aneurysmal SAH. This experience suggests that vasospasm is an important secondary posttraumatic insult that is potentially treatable.     

Changes in blood flow of anterior and middle cerebral arteries following carotid endarterectomy: a transcranial Doppler study

AIM: The aim of the present study was to evaluate the changes in blood flow of anterior and middle cerebral arteries following carotid endarterectomy, using transcranial Doppler (TCD) flow studies. PATIENTS AND METHODS: This study included 100 patients (72 men, mean age 65 years) who underwent carotid endarterectomy because of high-grade carotid stenosis or symptoms of ischemic stroke. Endarterectomy was performed by a distal shunt between the common carotid and internal carotid arteries. Blood flow in the anterior and middle cerebral arteries was assessed by TCD preoperatively and also in the postoperative period (1st and 4th day; 1st, 6th, and 12th month). Collateral circulation in the Willis circle was evaluated by common carotid compression. RESULTS: Patients with bilateral carotid stenosis > or =70% exhibited a significantly increased flow velocity in the ipsilateral anterior cerebral artery (ACA), middle cerebral artery (MCA), and in the contralateral ACA. Patients with entirely occluded contralateral internal carotid artery showed the most pronounced changes in cerebral hemodynamics. Blood flow velocities returned to the preoperative values at 1 to 12 months following endarterectomy. Hyperperfusion syndrome was manifested in 14 patients, who exhibited significantly higher flow velocities in the ipsilateral MCA compared with asymptomatic patients. CONCLUSIONS: A transient bilateral increase of blood flow velocity in the anterior part of the Willis circle may often occur in the immediate postoperative period following carotid endarterectomy. Although its clinical significance is not entirely understood, this increase may be associated with cerebral hyperperfusion syndrome.     

Change and clinical significance of cerebral blood flow after concussion of brain detected with three-dimensional transcranial Doppler

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Evaluation of cerebral AVM's using transcranial Doppler ultrasound

Blood flow velocities in basal cerebral arteries were recorded noninvasively in 28 patients with cerebral arteriovenous malformations (AVM's) and were correlated with the angiographic findings. In normal arteries remote from the AVM, flow velocities ranged from 44 to 94 cm/sec (median 65 cm/sec) with pulsatility indexes from 0.65 to 1.10 (median 0.87). This is consistent with findings in normal individuals. Arteries feeding the AVM's were identified by the high flow velocities (ranging from 75 to 237 cm/sec, median 124 cm/sec). The pulsatility index ranged from 0.22 to 0.74 (median 0.48). The difference of these results from findings in normal remote arteries was highly significant (p less than 0.001). Hyperventilation tests illustrated the hemodynamic difference between an AVM and normal cerebrovascular beds. Flow velocity measurements permitted noninvasive diagnosis of AVM's in 26 of the 28 patients. Furthermore, the identification of individual feeding arteries permitted good definition of the anatomical localization of individual AVM's. Flow velocity measurements combined with computerized tomography scans are useful in the diagnosis of AVM's. With the feeding artery's configuration identified on angiography, flow velocity measurements permit a new insight into the "hemodynamic dimension" of an AVM and its possible effects on adjacent normal brain-tissue perfusion in the individual patient.     

Effect of sevoflurane on cerebral blood flow and cerebrovascular resistance at surgical level of anaesthesia: a transcranial Doppler study

BACKGROUND AND OBJECTIVE: It is widely accepted that sevoflurane affects cerebral circulation, but there are uncertainities regarding the magnitude of its effect. The aim of the present work was to assess the effect of sevoflurane on the cerebral circulation at surgical levels of anaesthesia. METHODS: Twenty patients undergoing elective lumbar discectomies were investigated. Anaesthesia was induced with propofol and maintained with sevoflurane. The level of surgical anaesthesia was determined by bispectral index, the target level was 45-55. Transcranial Doppler (TCD) measurement was performed before induction and after reaching the surgical level of anaesthesia. Besides routine parameters (middle cerebral artery mean blood flow velocity (MCAV) and pulsatility index (PI)) derived parameters (estimated cerebral perfusion pressure (eCPP), cerebral blood flow index (CBFI) and resistance area product (RAP)) were calculated by taking changes of mean arterial pressure also into account. RESULTS: MCAV decreased from 54.1 +/- 13.3 to 43.7 +/- 18.5 cm s-1, P < 0.01 and PI increased from 0.79 +/- 0.2 to 0.92 +/- 0.2, P < 0.01 after reaching the surgical level of anaesthesia. As a result eCPP decreased by 18.2%, CBFI by 25.5% and RAP increased by 15% respectively. CONCLUSIONS: Our data indicate a vasodilatory effect of sevoflurane at surgical level of anaesthesia on large cerebral vessels or a vasoconstriction of the resistance arterioles likely caused by decreased brain metabolism.     

Evaluating middle cerebral artery collateral blood flow reserve using acetazolamide transcranial Doppler ultrasound in patients with carotid occlusive disease

BACKGROUND: The objective of this study is to examine the utility of acetazolamide TCD ultrasound in the evaluation of MCA collateral blood flow reserve in patients with carotid occlusive disease. METHODS: Acetazolamide TCD and cerebral angiography were performed for 28 carotid territories in 14 patients with carotid occlusive disease. The percentage change in mean blood flow velocity and PI in the MCA was measured before and after 1 g of acetazolamide was administered. The carotid territories were divided into groups according their angiographic findings: (1) mild/moderate (<70%) vs severe (> or =70%) extracranial carotid artery stenosis, and (2) active collateral blood flow to the MCA territory vs no collateral blood flow to the MCA. RESULTS: After acetazolamide injection, the percentage increase in mean MCA velocity for mild/moderate vs severe carotid artery stenosis was 43% +/- 10% and 19% +/- 6%, respectively, indicating less collateral blood flow reserve in patients with severe stenosis (P = .04). The percentage decrease in the PI for MCA territories with vs without angiographic evidence of collateral blood flow was 4.6% +/- 4% and 16% +/- 3%, respectively (P = .04), indicating an exhausted vascular reserve in patients with evidence of active collateral blood flow on angiography. CONCLUSIONS: A decrease in the PI after acetazolamide administration represents a safe and noninvasive indicator of limited collateral blood flow reserve to the MCA territory ipsilateral to an extracranial carotid stenosis. Further study into the role acetazolamide TCD has in the preoperative evaluation of these patients, including threshold values, is warranted.     

Pulsatile flow pattern in cerebral arteries during cardiopulmonary bypass. An evaluation based on transcranial Doppler ultrasound

Pulsatile wave patterns in basal cerebral arteries were studied by means of transcranial Doppler ultrasound (TCD) in 11 patients undergoing cardiopulmonary bypass (CPB) surgery. Different physiological states and technical parameters were demonstrated influencing wave forms delivered from a pulsatile CPB roller pump. The results gave evidence of the variability of pulsatile perfusion which may explain the inconsistency in the literature concerning its effectiveness in preserving tissue function. TCD proved to be a useful approach to define pulsatility of cerebral blood flow during CPB.     

Determination of cerebral blood flow dynamics during retrograde cerebral perfusion using power M-mode transcranial Doppler

BACKGROUND: Retrograde cerebral perfusion (RCP) during profound hypothermic circulatory arrest has been used as an adjunct for cerebral protection for repairs of the ascending and transverse aortic arch. Transcranial Doppler ultrasound has been used to monitor cerebral blood flow during RCP with varying success. The purpose of this study was to characterize cerebral blood flow dynamics during RCP using a new mode of monitoring known as transcranial power motion-mode (M-mode) Doppler ultrasound. METHODS: Data on pump-flow characteristics and patient outcomes were collected prospectively for patients undergoing ascending and transverse aortic arch repair. Retrograde cerebral perfusion during profound hypothermic circulatory arrest was used for all operations. Intraoperative cerebral blood flow dynamics were monitored and recorded using transcranial power M-mode Doppler ultrasound. RESULTS: Between August 2001 and March 2002, we used transcranial power M-mode Doppler ultrasound monitoring for 40 ascending and transverse aortic arch repairs during RCP. Mean RCP time was 32.2 +/- 13.8 minutes. Mean RCP pump flow and RCP peak pressure for identification of cerebral blood flow were 0.66 +/- 0.11 L/min and 31.8 +/- 9.7 mm Hg, respectively. Retrograde cerebral blood flow during RCP was detected in 97.5% of cases (39 of 40 patients) with a mean transcranial power M-mode Doppler ultrasound flow velocity of 15.5 +/- 12.3 cm/s. In the study group, 30-day mortality was 10.0% (4 of 40 patients). The incidence of stroke was 7.6% (3 of 40 patients); the incidence of temporary neurologic deficit was 35.0% (14 of 40 patients). CONCLUSIONS: Transcranial power M-mode Doppler ultrasound consistently demonstrated retrograde middle cerebral artery blood flow during RCP. Transcranial power M-mode Doppler ultrasound can provide optimal RCP with individualized settings of pump flow.     

Hyperventilation after tourniquet deflation prevents an increase in cerebral blood flow velocity

PURPOSE: In this study we examined whether normocapnia maintained by hyperventilation after lower limb tourniquet deflation prevents an increase in cerebral blood flow velocity. METHODS: Thirteen patients, undergoing elective orthopedic surgery, requiring a pneumatic tourniquet around the lower extremity, were divided into two groups. In group 1, ventilation was controlled at tidal volume of 10 mL x kg(-1) and respiratory rate of eight per minute after tourniquet release. In group 2, ventilation was controlled to maintain P(ET)CO2 between 30 and 35 mmHg after tourniquet release. Arterial blood pressure, heart rate, peak and mean middle cerebral artery (MCA) flow velocity, and arterial blood gas were measured every minute for ten minutes after tourniquet release. The MCA blood flow velocity was measured using Transcranial Doppler ultrasonography (TCD). RESULTS: In group 1, the maximum peak MCA flow velocity was 53+/-6 cm x sec(-1) (50%+/-6% increase compared with pre- release value), and achieved 3+/-0.4 min after tourniquet release. In group 2, there was no increase either in mean or peak MCA velocity after tourniquet release. CONCLUSIONS: Normocapnia maintained by hyperventilation after tourniquet deflation prevents an increase in cerebral blood flow velocity.     

Brain function and blood flow velocity in the middle cerebral artery in subarachnoid hemorrhage: evaluation with multimodality evoked potentials (MEPs) and transcranial Doppler (TCD) ultrasound

Brain dysfunction and blood flow velocity changes in the middle cerebral artery (MCAFV) were studied in 59 patients with ruptured cerebral aneurysms presenting subarachnoid hemorrhage. Brain function and blood flow velocity were evaluated by multimodality evoked potentials (MEPs) consisting of ABR, SEP and VEP as reported, and transcranial Doppler (TCD) ultrasound. The abnormality on MEPs were graded into 4 grades. Nearly normal, mildly abnormal, moderately abnormal and severely abnormal. The results on MEP study were compared with clinical Hunt and Hess (H. H) grade or Fisher's CT group of subarachnoid hemorrhage in 44 patients. MCAFV was measured in 15 patients and mean velocity as well as CO2 reactivity and effect of head elevation were studied. Control value of MCAFV was 64 +/- 13 cm/sec in 50 healthy adults. CO2 reactivity was determined by K values obtained from the modified formula of cerebral blood flow by Olesen et al. MEP grade in H. H grade III and IV patients showed, on admission, variations in their grades in comparison with those in H. H grade I II and V patients. There was no definite correlation between the abnormality in MEPs and the degree of subarachnoid hemorrhage in Fisher's group 3 and 4 patients. When the surgical results in early and late operation in H. H grade III and IV patients were compared, it was shown that the outcome was favourable in early operated patients of H. H grade III if initial MEP grades were between I-III.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperventilation reverses the nitrous oxide-induced increase cerebral blood flow velocity in human volunteers

Because hypocapnia is routine during general anaesthesia forintracranial procedures, we have compared, in 1 3 healthy volunteers,the effect of normocapnia (PE'_CO2 5.3 kPa) and hypocapnia (PE'_CO23.3 kPa) on mean blood flow velocity in the middle cerebralartery (Vmca) during normoventilation and hyperventilation withair and with 50% nitrous oxide in oxygen. After replacementof air with 50% nitrous oxide in oxygen, there was an increasein mean Vmca during normoventilation (air: mean 68.23 (SD 16.98)cm s^–1 vs nitrous oxide in oxygen: 90.69 (20.41) cm s^–1;P < 0.01), whereas during hyperventilation mean Vmca valueswere similar regardless of the inhaled gas mixture (air: 43.46(9.97) cm s^–1 vs nitrous oxide in oxygen: 41.69 (8.08)cm s^–1 Our data suggest that the nitrous oxide-inducedincrease in mean Vmca can be blocked by hyperventilation. (Br.J. Anaesth. 1995; 74: 616–618)     

Transcranial Doppler sonography: halothane increases average blood flow velocity in the middle cerebral artery

Transcranial Doppler sonography (TCD) can non-invasively measure the blood flow velocity of basal cerebral arteries, especially of the middle cerebral artery (MCA). TCD has been used for monitoring the cerebral circulation during cardiopulmonary bypass or cross-clamping of the carotid artery. To date, systemic investigation of the effects of anesthetic agents on mean blood flow velocity in the MCA (vMCA) has been neglected, although their effects on cerebral blood flow are well known. Two groups of 10 patients each with minor surgical or gynecological operations were studied using TC2-64 (EME) TCD equipment. Constant artificial ventilation with N2O:O2 = 2:1 was controlled by capnometry; capillary pCO2 ranged from 35 to 40 mmHg in both groups. In group I, patients underwent general anaesthesia with approximately 0.8 vol% halothane. vMCA, blood pressure, and heart rate were determined before and during anesthesia as well as after skin incision. Group II patients received fentanyl and droperidol. Measurements were performed at time points comparable to those in group I. Halothane caused an increase in vMCA by more than one third of the preanesthetic value (from 54.4 +/- 12.2. to 84.2 +/- 23.9 (P less than 0.01]. In group II (neuroleptanesthesia), no significant alterations of vMCA or hemodynamic parameters were observed. These results show that anesthetic agents can influence vMCA as well as cerebral blood flow. Therefore, these data should be taken into account while monitoring vMCA during operative procedures. However it has to be considered that TCD only permits measurement of blood flow velocity, while the diameter of the investigated vessel remains unknown. Clinical applications of this fascinating noninvasive monitoring device are discussed.     

The reproducibility of transcranial Doppler middle cerebral artery velocity measurements: implications for clinical practice

Use of transcranial Doppler (TCD) to diagnose vasospasm has been criticised. We examined reproducibility of TCD middle cerebral artery (MCA) velocity measurements. Thirty-six healthy adult volunteers were recruited. Four operators, two experienced and two inexperienced, participated. MCA velocity was measured twice by one operator and once by a second operator. Mean (95% limits of agreement) interoperator agreement was 2.4(+/-36.7) cm/s. Experienced vs. inexperienced, inexperienced vs. inexperienced, and experienced vs. experienced operators were -2.8(+/-39.3), -5.6(+/-40.1), 1.8(+/-22.1) cm/s, respectively. Intraoperator agreement across all operators, experienced and inexperienced were -0.5(+/-16.9), -1.6(+/-19.3), 0.7(+/-13.7) cm/s, respectively. Interoperator limits of agreement for experienced operators were almost half that of inexperienced operators. Intraoperator reproducibility was much better, regardless of level of experience, but aberrant results did occur even with experienced operators. If TCD measurements are used to guide management it is essential that operators are adequately trained, and readings repeated before potentially harmful treatments are instituted.     

Changes in middle cerebral artery blood flow after carotid endarterectomy as monitored by transcranial Doppler

OBJECTIVE: By using transcranial Doppler (TCD) it is possible to measure blood flow velocities within the circle of Willis. In this study, TCD was performed before and after carotid endarterectomy (CEA) with the aim to describe cerebral hemodynamics after normalization of the carotid artery blood flow. METHODS: Thirty CEA patients were consecutively entered into the TCD study, whereas 15 patients were referred for postoperative TCD for various clinical reasons. All 45 patients were investigated by using TCD: first preoperatively, then during the first few days after CEA before discharge from the hospital, and finally 3 to 12 months later. In addition, all patients underwent duplex investigation of the internal carotid artery the day before surgery and 3 months postoperatively. For the analysis, the patients were divided into two groups, one with (S-group), suspected postoperative neurologic complications/symptoms and another one without (C-group). Six patients were assigned to the S-group and 37 to the C-group, the latter including two patients who underwent bilateral CEAs. RESULTS: In the whole study group,a significant postoperative increase in systolic flow velocity was recorded bilaterally in the middle cerebral artery (MCA) as measured some days after surgery. The patients in the S-group showed high blood flow velocities mainly in the MCA on the ipsilateral side. A contralateral flow velocity increase did not occur in patients with very severe contralateral stenosis or occlusion (n = 9) if the late follow-up investigation was chosen as a reference value. Twenty patients in the C-group formed a subgroup with high blood pressure and/or headache postoperatively (CB-group) The other 19 patients were referred to as the CA-group. The CB- and S-groups showed more pronounced vessel disease in internal carotid artery on the contralateral side combined with lower collateral capacity in the circle of Willis compared to the CA-group. In the S-group the mean +/- standard deviation peak systolic velocity in ipsilateral MCA increased from a preoperative value of 0.71 +/- 0.22 m/sec to 2.23 +/- 0.72 m/sec (P <.005). In the CB-group, we observed a bilateral MCA blood flow velocity increase from 0.72 +/- 0.18 to 1.35 +/- 0.56 m/sec (P <.0001) on the ipsilateral side and from 0.82 +/- 0.37 to 1.28 +/- 0.66 m/sec (P < 0.001) on the contralateral side. In the CA-group, we observed minor bilateral blood flow velocity increases in the MCA, from 0.79 +/- 0.25 m/sec to 1.03 +/- 0.33 m/sec on the ipsilateral (P <.001) and from 0.70 +/- 0.17 m/sec to 0.93 +/- 0.26 m/sec on the contralateral side (P <.005). At the follow-up 3 to 12 months after surgery, the MCA flow velocities had returned to normal. CONCLUSIONS: Soon after surgery, blood flow velocity increases often bilaterally in the MCA. However a contralateral flow velocity increase did not occur in patients with very severe contralateral stenosis or occlusion if the late follow-up investigation was chosen as a reference value. The clinical significance of bilateral flow velocity increases is uncertain, but very high blood flow velocities might be a signal for cerebrovascular hyperperfusion. In those patients, increased postoperative surveillance is recommended.