RF signals provide additional information on embolic events recorded during TCD monitoring

Transcranial Doppler ultrasound (TCD) is commonly used to detect embolic signals in the cerebral circulation. However, current techniques to discriminate between signals from emboli and artifacts are subjective and ambiguous. The radiofrequency (RF) signal provides an extra dimension to the information available from conventional TCD systems that may help to interpret complex events. Artifacts generated by healthy volunteers and embolic signals recorded from a flow phantom were used to characterize the appearance of the two types of event. Characteristics of events, recorded during and immediately after carotid endarterectomy surgery, were compared with those from known sources. Additional information was provided by the RF signal on events recorded during TCD monitoring thus aiding classification. The RF signal may have a role as a "gold standard" for embolus detection.     

Microemboli detection on extracorporeal bypass circuits

Numerous authors have associated gaseous microembolization with adverse cerebral outcomes during cardiopulmonary bypass (CPB). The introduction to this review provides background on the connection between microemboli and adverse cerebral outcomes. This connection is often difficult to quantify, as outcomes depend on a number of factors, including the size of the bubble, where it passes through the patient, patient comorbidities and other factors. Nonetheless, numerous studies have shown statistically significant differences in the mean number of cerebral emboli detected in patients that stroked and those that did not, as well as for patients with major cardiac complications and patients with a longer length of hospital stay. Our introduction is followed by case reports and laboratory studies showing how monitoring for gaseous microemboli (GME) can be used to reduce the embolic load delivered to the patient through the bypass circuit. These methods include improved qualification of bypass circuit design prior to surgery, modification of priming procedures to reduce air in the circuit at the start of surgery, new methods for injecting drugs into the circuit during surgery, and better detection of removal of sources of air during surgery. The review concludes with background on the ultrasonic detection of GME, comparing through-transmission gross air detectors and Doppler ultrasound technology with fixed-beam ultrasonic imaging of emboli, a new ultrasonic technique that images moving emboli in the blood using a single ultrasound transducer element in a fixed position. This overview is meant to shed light on why different ultrasonic detection technologies report widely varying counts and emboli loads, and why fixed-beam ultrasonic imaging represents an improvement in the ability to monitor, measure and quantitate embolic load during CPB.     

Neurologic dysfunctions following cardiac surgery.

This article has discussed three major categories of neurologic injury following cardiac surgery. The primary pathophysiologic mechanisms for cerebral injury are thought to be related to reperfusion phenomena and neuronal cellular changes, hypoperfusion, and microemboli while on CPB. The type of symptoms the patient manifests range from fatal cerebral injury to more commonly seen episodes of mild, transient confusion. Preoperative, intraoperative, and postoperative risk factors are discussed. The critical care nurse's role in assessing early detection of changes, offering reassurance to both the family and patient, and providing continuity of care are summarized.     

The role of asymmetry and the nature of microembolization in cognitive decline after heart valve surgery: a pilot study

Our objective was to determine the role of asymmetry and the nature of microembolization on postoperative cognitive decline in patients who had undergone heart valve surgery. Continuous transcranial Doppler ultrasound was intraoperatively used for both middle cerebral arteries in 13 right-handed heart valve surgery patients to detect microembolization. The Trail Making Test A and B, Memory with 10/30 s interference, the Digit Span Test and Phonemic Fluency were performed preoperatively, at discharge and three months after surgery. Our data suggest that early and late postoperative psychomotor and executive functions may be sensitive to microemboli in the left, but not in the right middle cerebral artery. Moreover, solid and gaseous microemboli are both similarly associated with early postoperative cognitive decline while, surprisingly, late postoperative cognitive decline is more likely to be associated with gaseous than solid microemboli.     

Transcranial Doppler Ultrasound Use in Pediatric Patients With Penetrating Traumatic Brain Injuries

The purpose of this article is to increase awareness of the usefulness of transcranial Doppler (TCD) ultrasound as a noninvasive neuromonitor and bedside ultrasound in pediatric patients who have experienced a penetrative traumatic brain injury (TBI) as a result of a firearm. To date, the use of TCD is not standard of care in pediatric TBI patients. TCD is a portable ultrasound that can be performed in any care environment. The use of TCD in pediatric TBI studies have demonstrated abnormalities in cerebral blood flow velocity, autoregulation, and embolic events; all of which have been associated with poor neurocognitive and functional outcomes. A penetrating brain injury as a result of a firearm is associated with ongoing vascular injury and thereby an increased risk for poor neurologic sequelae. We discuss two exemplars of TCD use in children who experienced a firearm-related penetrating TBI and their TCD findings. Both exemplars identified the unique insights provided by TCD that were unappreciated by clinical observation. This article provides early evidence for the use of TCD as a neuromonitor in pediatric penetrating TBI.     

A prospective clinical study of cerebral microemboli and neuropsychological outcome comparing vent-line and auto-venting arterial line filters: both filters are equally safe

INTRODUCTION: Microemboli are the main implicated cause of neuropsychological (NP) impairment after cardiac surgery. This prospective clinical trial compared the effect of an auto-venting arterial line filter on intraoperative cerebral microemboli and NP outcome compared to an arterial line filter with a vent line, in patients undergoing elective coronary artery bypass graft (CABG) surgery. METHODS: One hundred and ten patients received either an Avecor Affinity (n =73) or Pall AV-6 (n =37) control filter. Cerebral microemboli during cardiopulmonary bypass were recorded by transcranial Doppler monitoring of the right middle cerebral artery. Evidence of cerebral impairment was obtained by comparing patients' performance in a NP test battery (nine tests) administered 6-8 weeks postoperatively with their preoperative scores. RESULTS: During cardiopulmonary bypass, the median number and range of microemboli were 67 (5-846) and 55 (2-773) for the Avecor and AV-6 groups, respectively (p = 0.47). There was no difference in NP outcome. CONCLUSION: There is no difference in the filtering ability of vent-line and auto-vent filters as assessed by cerebral microemboli. This, together with the similar NP outcome, suggests that both types of filter are equally safe for clinical use.     

急性脑梗死合并2型糖尿病患者微栓子与血清基质金属蛋白酶-9的关系

目的探讨急性脑梗死合并2型糖尿病患者脑动脉微栓子与血清基质金属蛋白酶-9含量的关系。方法前瞻性地纳入颈动脉系统急性脑梗死患者118例,分为糖尿病急性脑梗死组60例、非糖尿病急性脑梗死组58例。收集一般临床资料,采用EMS-9型经颅多普勒超声检测仪及酶联免疫吸附测定法(ELISA)分别检测所有入组患者大脑中动脉微栓子信号及血清基质金属蛋白酶-9浓度,并进行相关分析。结果糖尿病并急性脑梗死患者微栓子信号阳性率高于非糖尿病急性脑梗死患者(P<0.05);糖尿病并急性脑梗死患者的血清基质金属蛋白酶-9含量明显高于非糖尿病急性脑梗死患者(P<0.01);Logistic回归提示,血清基质金属蛋白酶-9是微栓子信号阳性的危险因素(OR=1.013,P<0.01)。结论糖尿病并急性脑梗死患者微栓子信号阳性率与血清基质金属蛋白酶-9含量更高,基质金属蛋白酶-9的高表达可能促进微栓子的产生。     

Evaluation of an alternative S100b assay for use in cardiac surgery: relationship with microemboli and neuropsychological outcome

INTRODUCTION: The aim of the study was to investigate the relationship between S100b release, neuropsychological outcome and cerebral microemboli. Peri-operative assay of the astroglial cell protein S100b has been used as a marker of cerebral damage after cardiac surgery but potential assay cross-reactivity has limited its specificity. The present study uses an alternative enzyme-linked immunoabsorbant assay (ELISA) for serum S100b that has documented sensitivity and specificity data in patients undergoing coronary artery bypass grafting (CABG). METHODS: Fifty-five consecutive patients undergoing routine CABG surgery received serial venous S100b sampling at five time points: i) Pre-operative, ii) At the end of cardiopulmonary bypass (CPB), iii) 6 hrs, iv) 24 hrs and v) 48 hrs post skin closure. A previously described sandwich ELISA with monoclonal anti- S100b was used. This assay has a lower limit of detection of 0.04 microg/L and < 0.006% reactivity with S100a at a concentration of 100 microg/L S100a. Cerebral microemboli during surgery were recorded by transcranial Doppler monitor over the right middle cerebral artery. Evidence of cerebral impairment was obtained by comparing patients' performance in a neuropsychological battery of 9 tests administered 6-8 weeks post-operatively with their pre-operative scores. RESULTS: There was a significant increase in S100b only at the end of bypass (mean 0.30 microg/L, SD +/- 0.33 and range .00 to 1.57). S100b levels at the end of bypass did not correlate with neuropsychological outcome or microemboli counts. CONCLUSIONS: The low levels of S100b detected using the present assay, despite its high sensitivity and despite the routine use of cardiotomy suction, suggest that the assay may have higher specificity for cerebral S100b than previously used assays. There was no evidence that this assay is related to neuropsychological change or cerebral microemboli in cardiac surgery.     

伴有大脑中动脉狭窄急性脑梗死患者扩容治疗及微栓子监测的研究

目的通过对伴有大脑中动脉（MCA）狭窄的急性脑梗死患者进行扩容治疗,来评价患者的预后。方法选取伴有病灶侧大脑中动脉狭窄急性脑梗死患者180例,其中扩容组89例,对照组91例。扩容组进行扩容治疗,对照组常规治疗,分别于人院时、第3天、第7天、第14天进行TCD检测狭窄MCA的微栓子的数量。14d后给予临床神经功能缺损评分,进行临床疗效比较。结果扩容组患者的显效率及总有效率均高于对照组,差异有统计学意义（P〈0．01）;扩容组的微栓子数量较对照组增多,但无统计学意义。结论扩容治疗可以改善伴有大脑中动脉狭窄急性脑梗死患者的预后。     

经颅多普勒超声对经皮颈动脉血管成形术和血管内支架术的脑血流及栓子的监测

目的⑶应用经颅多普勒超声⒉ Ｔ Ｃ Ｄ⒕动态监测脑血流动力学的变化及微栓子信号的产生⒚方法⑶经股动脉插管将缚有球囊及支架的导管输送至病侧颈动脉⒚采用 Ｔ Ｃ Ｄ 对 ３ 例成功实施 Ｐ Ｔ Ｃ Ａ 加 Ｓ Ｔ Ｅ Ｎ Ｔ 的患者⒙检测术前、术后双侧半球中、前、后及眼动脉血流⒙术中持续监测双侧中动脉流速及微栓子信号的变化⒚结果⑶术前 ３ 例患者双侧半球血流不对称⒙狭窄侧低流速、低搏动性血流⒙术后脑血流明显改善⒙双侧流速对称⒚术中均发现微栓子信号⒚结论⑶采用 Ｔ Ｃ Ｄ 可以有效地监测脑血流的变化及栓子信号的产生⒙评价 Ｐ Ｔ Ｃ Ａ 加 Ｓ Ｔ Ｅ Ｎ Ｔ 对颈动脉狭窄的治疗效果⒚     

Power M-mode Doppler (PMD) for observing cerebral blood flow and tracking emboli

Difficulties in location of transcranial ultrasound (US) windows and blood flow in cerebral vessels, and unambiguous detection of microemboli, have limited expansion of transcranial Doppler US. We developed a new transcranial Doppler modality, power M-mode Doppler (PMD), for addressing these issues. A 2-MHz digital Doppler (Spencer Technologies TCD100M) having 33 sample gates placed with 2-mm spacing was configured to display Doppler signal power, colored red and blue for directionality, in an M-mode format. The spectrogram from a user-selected depth was displayed simultaneously. This system was then explored on healthy subjects and patients presenting with varying cerebrovascular pathology. PMD facilitated window location and alignment of the US beam to view blood flow from multiple vessels simultaneously, without sound or spectral clues. Microemboli appeared as characteristic sloping high-power tracks in the PMD image. Power M-mode Doppler is a new paradigm facilitating vessel location, diagnosis, monitoring and microembolus detection.     

Detection of Cerebral High-Intensity Transient Signals by NeoDoppler during Cardiac Catheterization and Cardiac Surgery in Infants

There is a risk of gaseous and solid micro-embolus formation during transcatheter cardiac interventions and surgery in children with congenital heart disease (CHD). Our aim was to study the burden of high-intensity transient signals (HITS) during these procedures in infants. We used a novel color M-mode Doppler (CMD) technique by NeoDoppler, a non-invasive ultrasound system based on plane wave transmissions for transfontanellar continuous monitoring of cerebral blood flow in infants. The system displays CMD with 24 sample volumes and a Doppler spectrogram. Infants with CHD undergoing transcatheter interventions (n = 15) and surgery (n = 13) were included. HITS were manually detected based on an “embolic signature” in the CMD with corresponding intensity increase in the Doppler spectrogram. Embolus-to-blood ratio (EBR) defined HITS size. A total of 1169 HITS with a median EBR of 9.74 dB (interquartile range [IQR]: 5.10–15.80 dB) were detected. The median number of HITS in the surgery group was 45 (IQR: 11–150), while in the transcatheter group the median number was 12 (IQR: 7–24). During cardiac surgery, the highest number of HITS per hour was seen from initiation of cardiopulmonary bypass to aortic X-clamp. In this study we detected frequent HITS and determined the feasibility of using NeoDoppler monitoring for HITS detection.     

Intermittent drop in blood flow velocity in the internal carotid artery and its branches

Extracranial Doppler sonography and transcranial Doppler sonography (TCD) allow the assessment and monitoring of hemodynamic and embolic events in cerebrovascular diseases. We describe an unusual hemodynamic phenomenon in a patient with intracranial carotid siphon stenosis and no clinical symptoms of stenosis. TCD examination suggested and angiography confirmed stenosis of the left internal carotid artery siphon. TCD examination revealed a sudden, intermittent drop in blood flow velocity in both the prestenotic and poststenotic segments of the internal carotid artery, whereas cardiac hemodynamic parameters were unaffected. Embolic signals were detected in the poststenotic vessels only. We speculate that such sonographic findings may be caused by intermittent vessel occlusions due to the reversible displacement of an intraluminal thrombus in relation to the cardiac cycle.     

Transcranial Doppler monitoring of middle cerebral flow velocity in a patient with a ventriculoperitoneal shunt undergoing laparoscopy

Laparoscopic surgery is possibly associated with a risk of intracranial pressure (ICP) increase due to pneumoperitoneum in patients with ventriculoperitoneal shunts (VPS). Invasive techniques for shunt pressure monitoring are not routinely used because of the possible complications. Transcranial Doppler (TCD) is a non-invasive, safe method which gives accurate information about blood-flow velocities in basal cerebral arteries and indirectly about the ICP. Moreover it is inexpensive and simple in use. We report the use of TCD for middle cerebral flow velocity monitoring in a patient with a VPS who underwent laparoscopic surgery. In the case we present, during 60?min of pneumoperitoneum, TCD showed a sustained, but not clinically significant increase of the Pulsatility Index, with a recorded maximum change of 31?%. We consider that the use of TCD may increase the safety of laparoscopic procedures in patients with preexisting VPS.     

Measurement of blood flow velocity in the basal cerebral circulation: Advantages of transcranial color-coded sonography over conventional transcranial doppler

Unlike conventional transcranial Doppler (TCD), transcranial color-coded sonography (TCCS) enables imaging of the basal cerebral arteries using color-flow ultrasonography and correction for the angle of insonation when determining blood flow velocities. We present hemodynamic data from 20 normal subjects, each studied with TCD and TCCS. Velocities derived using TCCS with angle correction were significantly greater than those derived using TCD in all vessels (mean velocities [cm/sec; mean with 95% confidence intervals])—anterior cerebral artery: TCD 48 (45–50), TCCS 62 (58–66), p < .0001; middle cerebral artery: TCD 61 (58–64), TCCS 70 (66–74), p < .0001; posterior cerebral artery: TCD 43 (41–46), TCCS 54 (50–57), p < .0001; basilar artery: TCD 40 (34–45), TCCS 45 (38–52), p <.01. Pulsatility index values were significantly greater in all arteries when determined by TCCS, and resistance index values were significantly greater except in the basilar artery. Correcting for the angle of insonation using TCCS may enable estimation of blood flow velocities closer to the “true” values than those derived using conventional TCD. © 1995 John Wiley & Sons, Inc.     

Distribution of artificially-produced microembolic signals into the cerebral circulation

According to clinical observations, cardiogenic embolism occurs more often in the anterior than in the posterior cerebral circulation. An ultrasound (US) contrast agent was used to artificially produce microembolic signals (MES) to imitate the intracranial distribution of systemic emboli. Systemic microemboli were simulated by IV administered US agent (Levovist(R) 300 mg/mL as bolus). A total of 20 patients were monitored by means of transcranial Doppler sonography (TCD), 3 min after the injection, with a 2-MHz transducer simultaneously at 50 mm (middle cerebral artery, MCA, on one side) and 90 mm (basilar artery, BA). Four 3-min recordings were done (two of the right MCA, two of the left MCA, with the BA, respectively). Three observers and an automatic detection system independently performed an off-line analysis. A total of 160 recordings were analyzed. The mean numbers of detected high-intensity transient signals (HITS) were 34.5 +/- 28.2 in the right MCA (simultaneously registered HITS in the BA: 9.4 +/- 16.8) and 39.1 +/- 34.2 in the left MCA (simultaneously registered HITS in the BA: 12.2 +/- 14.5). Only 21.4 to 23.7% of all HITS were recorded in the BA. Microembolic signals artificially produced by means of US contrast agent made it possible to mimic the physiologic distribution of small embolic particles. In future, these might help to investigate the distribution of systemic emboli in different vascular territories in various pathologic conditions of the cerebral blood flow.     

A model for cardiopulmonary bypass redesign

INTRODUCTION: A portion of patients undergoing cardiac surgery may develop focal and/or subtle brain injuries secondary to cardiac surgery. There is evidence that, in some cases, these injuries may be related to cardiopulmonary bypass (CPB). Embolism and hypoperfusion are the dominant mechanisms for focal neurologic injuries among coronary artery bypass graft (CABG) surgery patients. Recent studies suggest that these mechanisms may also produce the more prevalent subtle neurological deficits. The aim of our current work is to obtain a thorough understanding of the processes of care associated with the production of embolic activity, cerebral hypoperfusion, and hemodynamic aberrations that often occur during CPB. METHODS: We developed a system for simultaneous recording of physiologic parameters, embolic activity in the CPB circuit and in the cerebral arteries, and near infrared regional cerebral oxyhemoglobin saturation (NIRS) during cardiac surgery. All data were synchronized with a video recording of the surgical procedure. Periods of embolic activity and NIRS were subsequently related to surgical and CPB processes of care through a systematic review of the patient's surgical case video. RESULTS: To date, we have enrolled 47 patients undergoing coronary and/or valvular procedures. We have observed wide variation across patients in detected cerebral embolic counts, NIRS and physiologic parameters. We have identified increased embolic counts in the CPB circuit related to specific processes and events such as the method of venous drainage, the entrainment of air in the venous line, the injection of medications into the CPB circuit and blood sampling from the CPB circuit. A portion of detected changes in NIRS were related to periods of hypotension and positioning of the heart during the construction of distal coronary artery grafts on the posterior coronary artery vessels. SUMMARY: Use of this model provides the surgical team with detailed information regarding the contribution of CPB to the creation of precursors of neurological injury. This system provides meaningful data to guide the surgical team in the redesign of the CPB system and associated techniques.     

Vertebral artery compression as an adjunct to transcutaneous Doppler ultrasound examination

Transcranial Doppler (TCD) evaluation is dependent on the accurate identification of intracranial vessels. Manual extracranial vertebral artery compression was used to modulate blood flow in vessels of the vertebrobasilar system in 118 patients examined by TCD. Two examples of its utility are presented in detail. Complete examination by TCD should include evaluation of the posterior cerebral circulation and its collaterals; vertebral artery compression is a new and important adjunct to the complete evaluation of intracranial vascular anatomy and cerebral collateralization.     

经颅多普勒诊断颅内动脉瘤术后脑血管痉挛

目的探讨经颅多普勒检查在颅内动脉瘤术后脑血管痉挛诊断中的价值。方法采用临床病例分析统计方法,归纳、分析颅内动脉瘤术后患者的经颅多普勒检查资料。结果33例患者中,有15例在术后出现不同程度的脑血管痉挛症状,比较有、无症状患者MCA和eICA流速变化,发现有症状性血管痉挛的患者,MCA血流速度增加值明显大于无症状组。结论经颅多普勒可以在患者出现临床症状以前,早期发现颅内动脉的血流速度增高,指导临床医生及时调整治疗方案,避免造成严重并发症。     

Doppler assessment of the cerebral circulation in pediatric intensive care.

This article gives an interim overview of the potentials of TCD as a monitoring instrument in pediatric intensive care. In the near future, typical TCD flow patterns associated with adverse neurologic outcomes must be defined so they can promptly be recognized during intensive care surveillance or intraoperatively, before permanent damage occurs. Further applications of monitoring will deliver new and exciting insights into the physiology and pathophysiology of cerebral circulation in the critically ill child. Continuous recording of the Doppler waveforms and ICP may make it possible to determine the critical CPP and to improve the control of the therapy of cerebral edema.