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Transcranial Doppler Ultrasonic Monitoring Technology Update American Society of Neurophysiologic Monitoring and American Society of Neuroimaging Joint Guidelines for Transcranial Doppler Ultrasonic Monitoring Harvey L. Edmonds, Jr, PhD, FASNM (ASNM), Michael R. Isley, PhD, DABNM, FASNM (ASNM), Tod B. Sloan, MD, PhD, MBA, FASNM (ASNM), Andrei V. Alexandrov, MD, RVT (ASN), Alexander Y. Razumovsky, PhD, FAHA (ASN) From the Department of Anesthesiology, University of Louisville, Louisville, Kentucky (HLE); Intraoperative Neuromonitoring, Orlando Regional Medical Center, Orlando, Florida (MRI); Department of Anesthesiology, University of Colorado, Colorado (TBS); Department of Neurology, Division of Cerebrovascular Disease and Comprehensive Stroke Research Center, The University of Alabama at Birmingham, Birmingham, Alabama (AVA); and Sentient NeuroCare Services, Inc., Hunt Valley, Maryland (AYR). ABSTRACT The American Society of Neurophysiologic Monitoring (ASNM) and American Society of Keywords: Transcranial Doppler, mon- Neuroimaging (ASN) Guidelines Committees formed a joint task force and developed itoring, cardiothoracic surgery, vascular guidelines to assist in the use of transcranial Doppler (TCD) monitoring in the surgical surgery, intensive care. and intensive care settings. Specifically, these guidelines: Acceptance: Received May 15, 2009, (1) delineate the objectives of TCD monitoring; and in revised form October 19, 2009. Ac- (2) characterize the responsibilities and behaviors of the sonographer during monitoring; cepted for publication October 23, 2009. (3) describe methodological and ethical issues uniquely relevant to monitoring. Correspondence: Address correspon- The ASNM and ASN strongly support the positions that (1) acquisition and interpretation dence to Alexander Razumovsky, PhD, of intraoperative TCD ultrasonograms be performed by qualified individuals, (2) service FAHA, Vice-President and Director, Sen- providers define their diagnostic criteria and develop on-going self-validation programs tient NeuroCare Services, Inc. 1101 of these performance criteria in their practices. We agree with the guidelines of other McCormick Rd, Suite 200, Hunt Val- professional societies regarding the technical and professional qualifications of individ- ley, MD 21031. E-mail: arazumovsky@ sentientmedical.com. uals responsible for TCD signal acquisition and interpretation (Class III evidence, Type C recommendation). On the basis of current clinical literature and scientific evidence, J Neuroimaging 2011;21:177-183. TCD monitoring is an established monitoring modality for the: (1) assessment of cere- DOI: 10.1111/j.1552-6569.2010.00471.x bral vasomotor reactivity and autoregulation; (2) documentation of the circle of Willis functional status; (3) identification of cerebral hypo- and hyperperfusion, recanalization and re-occlusion; and (4) detection of cerebral emboli (Class II and III evidence, Type B recommendation). Introduction iologic Monitoring (ASNM) and American Society of Neu- The Intersocietal Commission on Accreditation of Vascular roimaging (ASN) formed a joint task force to develop these Laboratories (www.ICAVL.org) has established guidelines for practice guidelines for TCD monitoring in the surgical and in- the certification of laboratories making or interpreting diag- tensive care settings. The primary goals of this document are nostic ultrasonic measurements of cerebral blood flow veloc- to: ity (CBFV) with transcranial Doppler (TCD) ultrasonography. However, of the more than 950 ICAVL-approved facilities, (1) delineate the objectives of TCD monitoring; less than 2% are certified for intracranial or TCD measure- (2) characterize the responsibilities and behaviors of the sonogra- pher during monitoring; and 1 ments. Practice standards describing the performance of diag- (3) describe methodological and ethical issues uniquely relevant to nostic TCD examination were published in 2007 by the Jour- TCD monitoring. nal of Neuroimaging.2 Previously, the published evidence for diagnostic TCD applications, including peri-operative monitor- Instrumentation and Acquisition Parameters ing and sonothrombolysis, had been assessed by the American Probe Choice Academy of Neurology panel of experts.3 However, neither ICAVL nor any other recognized professional organization pro- Adequate transcranial insonation of intracranial vessels gener- vides guidelines or certification specifically for the unique skills ally requires ultrasonic probes with crystals operating at 2 MHz involved in continuous peri-operative or critical care TCD mon- or less. Monitoring services should establish local probe per- itoring in order to immediately influence patient care. Thus, formance standards and regularly document that each probe in Guideline Committees of the American Society of Neurophys- current use meets these criteria. The crowded surgical/critical Copyright ◦C 2010 by the American Society of Neuroimaging 177 care environment often requires TCD probe cables to have a Safety Considerations minimum length of at least 4 m. Exposure to Ultrasound Microvascular probes are now available for intracranial ap- Prolonged high-intensity ultrasonic insonation presents a risk plication in the assessment of cerebral hemodynamics during of thermal injury because tissue dissipation of ultrasonic energy cerebral aneurysm4 and arteriovenous malformation surgeries.5 results in local warming.7 Since all the energy studies have been These probes have a diameter of 1.5 mm or less and employ performed in vitro, the potential intracranial heating effect as- a carrier frequency of 16 or 20 MHz. The probes are placed sociated with tissue perfusion is unknown. Consequently, there on the vessel of interest using either a malleable wand or rigid are as yet no internationally established maximum ultrasound suction cannula. Insonation depth and angle are typically .6-1.2 ◦ intensity output standards for TCD devices and the effects of mm and <30 , respectively. long-term exposure are not well understood. Due to these con- cerns, transorbital insonation is currently not recommended for Probe Fixation intraoperative or continuous critical care monitoring. 2 Continuous TCD monitoring requires probe fixation to the in- The maximum output of 100 mW/cm recommended by sonation site. The probe holder should: the American Institute of Ultrasound in Medicine has been adopted by all manufacturers of devices cleared for use by the U.S. Food and Drug Administration (FDA). In addition, (1) prevent probe movement relative to the insonation site; the lowest pulse repetition frequency should be used which (2) avoid traumatic compression of cranial or facial tissues; (3) permit access to critical cranial or neck regions. just permits measurement of the highest CBFV. However, the effects of continuous long-term exposure, such as may occur in the surgical/critical care environments, are not fully un- Equipment Selection for TCD Monitoring derstood. Therefore, the acoustic power and pulse amplitude should be kept to a minimum commensurate with the pro- TCD low-profile and microvascular Doppler probes used in duction of waveforms that can be accurately measured. Sono- the critical care and peri-operative environments require capa- graphers and monitoring technologists should adhere to the bilities that are often unnecessary in the diagnostic laboratory. universally accepted ALARA (as low as reasonably achievable) However, three new TCD diagnostic applications approved output principle. This is particularly important with transor- by the Center for Medicare Services in January of 2005 do bital insonation, which places the ultrasonic probe over to the also require probe fixation. These new applications that bridge unprotected eye. Transorbital insonation is not recommended the gap between diagnosis and monitoring are (1) evaluation for intraoperative or continuous critical care monitoring at this of cerebrovascular reactivity, (2) emboli quantification, and (3) time. emboli detection with air microbubble injection. In addition to a low profile, monitoring probes should be Probe Contamination relatively immune to radio-frequency contamination. Audio squelching should attenuate acoustic signals of an intensity Non-sterile ultrasonic probes and gel may expose the eye >110 dB acoustic signals. TCD software should permit trending or scalp wound margins to infectious material. Thus, probes of CBFV and embolization for at least 8 hours. should be carefully cleaned and decontaminated prior to use in these circumstances and sterile aquasonic gel must be used if Filter Settings applying a probe on or near wound margins. High-pass filtering of TCD signals is necessary to minimize the impact of vessel wall motion artifact. During surgery, very low Documentation of TCD Monitoring CBFV signals may be encountered. Thus, filter settings as low CBFV Monitoring as 50 Hz may be required to visualize these low CBFV. In some cases, it may become necessary to totally deactivate the filter. The details of the Fast Fourier Transform (FFT) analysis used to display Doppler shift spectra, including windowing and other CBFV Measurement digital filtering techniques, should be fully described by the manufacturer. Interpreters of TCD signals should understand Although the peak CBFV is the preferred trended parameter by the impact of variations in these display techniques on CBFV some sonographers because of a favorable signal-to-noise ratio, and pulsatility indices. others rely primarily on the intensity-weighted mean CBFV Each TCD monitoring recording should, at
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