Blog
About

8
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Transcranial Doppler ultrasound in the ICU: it is not all sunshine and rainbows

      , 1 , 2

      Critical Ultrasound Journal

      Springer Milan

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Dear Editor, We read the article about Transcranial Doppler (TCD) for intensivists [1]. Although not a novel ultrasound technique, in particular the “blind” o non-imaging TCD (bTCD), authors´ efforts to promote some basic applications of the Duplex technique (transcranial color-coded duplex sonography, TCCS) are remarkable. However, some technical points and assertions are dubious and/or incorrect, as noted below: In the first place, regarding the midline shift (MLS) measurement technique by TCCS, (A-B)/2 is well-studied and validated against CT [2]. While proposed by authors’ as an “internal standard” [1], as shown in Fig. 1 of the original article [1], measuring the distance to the contralateral cranial bone is not described in the original technique, it is unnecessary and adds complexity; thus, it should not be taken into account, as is the case with the mentioned “C and D” technique. To the authors´ knowledge, whether methodologically correct or not, there are no study validating either of them. Practitioners should be aware that the MLS measurement by TCCS is not reliable in the presence of bone defects (like decompressive craniectomy or skull fractures), temporal cephalohematoma, or changes in intracranial anatomy secondary to trauma [3], citing the most common examples observed in daily practice. Particularly in patients with a decompressive craniectomy, an alternative MLS measurement technique is well validated against CT [4]. Fig. 1 (corresponding to b and c of Fig. 2 [1]). Note the different and confusing nomenclature regarding “mean velocities”. As depicted from the trace of the envelope of the Doppler spectra (yellow arrows), time-averaged maximum velocity is recorded, namely, TAV (time-averaged velocity) in (a) and TAP (time-averaged peak velocity) in (b). There is also no doubt in a that is TAP, because pulsatility index (PI) is calculated using this value [peak systolic velocity (PSV)-end-diastolic velocity (EDV)/TAV]. Time-averaged mean velocity is not recorded in (a), but is shown in (b) as TAM, traced in the middle of the Doppler spectra (white arrow). In TCCS, time-averaged maximum or peak velocities are the “mean” velocities that should be considered. The correct Lindegaard Index (Middle cerebral artery TAP/internal carotid artery TAP) in this case is 123/58, equal to 2.1 (corresponding to hyperemia if considered independently). It is thus clearly incorrect to use different “mean velocities” when calculating the LI, such as TAP/TAMEAN. Note: the waveform in (b) is consistent with an external carotid artery flow, given its sharp systolic upstroke, high-resistance velocity profile, and early diastolic notch (another mistake that should be taken into account) Second, when moving from a bTCD technique to the Duplex technique, practitioners must be aware of the “mean velocities” recorded by the ultrasound machine: time-averaged maximum velocity, known as TAMAX or TAP and time-averaged mean velocity, also known as TAMEAN or TAMV. While both are “mean” velocities, TAMEAN is approximately half the TAMAX [5]. Since in TCCS, the velocity considered is the TAMAX [5], using TAMEAN instead of TAP leads to underestimating velocities. This is clearly evidenced in Fig. 2 [1], where in the TCCS image, TAP is correctly used, but in the transcervical insonation, TAMV is used instead of TAP. Indeed, TAP should be compared when the Lindegaard Index (LI) is used, but comparing TAMAX/TAMEAN as is performed in Fig. 2 is an obvious mistake and readers need to be cautioned from making the same error. The actual LI in this case is 2.1, which indicates hyperemia (Fig. 1). According to this now well-performed TCD ratio, the angiographic finding of vasospasm was fortuitous, at least if this index is used independently [6]. In addition, transcervical insonation should be performed with the same phased-array probe to observe the “distal” extracranial internal carotid artery (ICA)—TAP (Fig. 2a) [7]. It should be noted that this segment is not assessed with the linear probe as shown in Fig. 2c of the original article. In addition, large correction angles (60°) result when a linear transducer is used and this must be especially avoided when comparing middle cerebral artery (MCA)/ICA TAP. Thus, the Doppler correction angle should not be used [8]. As noted, transcervical insonation should be a basic part of point-of-care ultrasound (POCUS)-TCD, at least if vasospasm evaluation is considered. Fig. 2 a Transcervical window, phased-array probe. Note that the distal internal carotid artery is insonated and that angle correction is not needed in pulsed-wave Doppler. b Transforaminal window, phased- array probe. Note the inverted V configuration of the posterior circulation on color Doppler imaging (coded blue, indicating that blood is moving away from the transducer), depicted by both vertebral arteries (VA) and the basilar artery (BA), showing also the corresponding spectral Doppler on the inferior channel. F: foramen magnum; VA vertebral artery; BA basilar artery. c Transorbital window, phased-array probe. G: ocular globe Third, to the best of our knowledge, we are not aware of any guidelines that recommend TCD as a screening tool for further indication of an ancillary test to confirm the diagnosis of brain death. When determining the presence of cerebral circulatory arrest (CCA), many countries around the world accept this tool as an ancillary test to confirm the clinical diagnosis of brain death [9]. For example, there are formal TCD guidelines in Latin-American addressing this issue [10, 11]. For this indication, accepted TCD-CCA criteria for both “anterior” and “posterior” cerebral arterial circulation must be registered [12, 13]. Thus, intuitively, the transtemporal window is not enough for this indication. As a point-of-care application, transforaminal window should also be considered a basic window, at least if a CCA application is proposed (Fig. 2b). Transorbital (Fig. 2c) and transcervical (Fig. 2a) are also useful (although not fully accepted) in some actual patients to determine CCA, in particular when intracranial arterial flows are not detected on first examination, due to inadequate bone insonation windows, for example (observed in at least 25% of the patients) [13]. Regarding Doppler CCA criteria, the oscillating flow, although a biphasic flow, needs to be clearly differentiated from a high-resistance biphasic flow with a net forward flow (Fig. 3). In doubtful cases, always correlating with the clinical signs of brain death, modifications of the waveforms with interventions, such as osmotic therapy, may allow practitioners to discard the CCA diagnosis given the reversibility of the case on follow-up examinations. Fig. 3 a High-resistance biphasic flow, with a net forward flow, not compatible with cerebral circulatory arrest. b Oscillating flow, with a net flow of 0, corresponding to cerebral circulatory arrest. S systole; D diastole Finally, velocities and indices (e.g., pulsatility index) are highly variable, resulting from physiologic (arousal, for example) to pathologic conditions (e.g., raising intracranial pressure) (Tables 1 and 2). Thus, caution should be exercised when interpreting TCD findings, which should always be considered within a multimodality monitoring, and not in isolation. The phrase “trends are your friend” is highly applicable when interpreting TCD velocities and indices. Table 1 Physiologic and pathologic conditions that can modify TCCS flow velocities [3] Increase  Hyperemia  Fever, anemia, high cardiac output, arterial hypertension  Vasospasm  Intracranial arterial stenosis (for example atherosclerotic plaque)  Hypercapnia  Bacterial meningitis  Pre-eclampsia Decrease  Raised intracranial pressure  Decreased cerebral perfusion pressure  Cerebral circulatory arrest  Hypocapnia  Hypothermia  Wrong insonation angle Table 2 Physiologic and pathologic conditions that can modify TCCS Doppler indices [3] Increase  Raised intracranial pressure  Decreased cerebral perfusion pressure  Hypocapnia  Hypothermia  Cerebral circulatory arrest  Hyperviscosity  Intracranial artery occlusion  Advanced age (vessel stiffness) Decrease  Hyperemia  Anemia, fever, high cardiac output, arterial hypertension  Hypercapnia  Vasospasm  Intracranial artery stenosis  Arteriovenous malformation  Rewarming following hypothermia In conclusion, POCUS TCD is not a perfect technique. Many aspects (technical and interpretative) should be considered to obtain a reliable TCD exam. In addition, for the reasons explained above, TCCS should not be limited to transtemporal windows, since transforaminal, transcervical, and transorbital windows have a defined role in basic TCD applications. The entire TCCS exam is performed with the same phased-array probe, based on the simplicity of POCUS, without the need of formal TCD examinations or dedicated machines, as happens with most (if not all) POCUS applications in the ICU. It is clear that a TCD-training curricula is mandatory to fulfill intensivists’ needs.

          Related collections

          Most cited references 10

          • Record: found
          • Abstract: found
          • Article: not found

          Practice standards for transcranial Doppler ultrasound: part I--test performance.

          Indications for the clinical use of transcranial Doppler (TCD) continue to expand while scanning protocols and quality of reporting vary between institutions. Based on literature analysis and extensive personal experience, an international expert panel started the development of guidelines for TCD performance, interpretation, and competence. The first part describes complete diagnostic spectral TCD examination for patients with cerebrovascular diseases. Cranial temporal bone windows are used for the detection of the middle cerebral arteries (MCA), anterior cerebral arteries (ACA), posterior cerebral arteries (PCA), C1 segment of the internal carotid arteries (ICA), and collateralization of flow via the anterior (AComA) and posterior (PComA) communicating arteries; orbital windows-for the ophthalmic artery (OA) and ICA siphon; the foraminal window-for the terminal vertebral (VA) and basilar (BA) arteries. Although there is a significant individual variability of the circle of Willis with and without disease, the complete diagnostic TCD examination should include bilateral assessment of the M2 (arbitrarily located at 30-40 mm depth), M1 (40-65 mm) MCA [with M1 MCA mid-point at 50 mm (range 45-55 mm), average length 16 mm (range 5-24 mm), A1 ACA (60-75 mm), C1 ICA (60-70 mm), P1-P2 PCA (average depth 63 mm (range 55-75 mm), AComA (70-80 mm), PComA (58-65 mm), OA (40-50 mm), ICA siphons (55-65 mm), terminal VA (40-75 mm), proximal (75-80), mid (80-90 mm), and distal (90-110 mm) BA]. The distal ICA on the neck (40-60 mm) can be located via submandibular windows to calculate the VMCA/VICA index, or the Lindegaard ratio for vasospasm grading after subarachnoid hemorrhage. Performance goals of diagnostic TCD are to detect and optimize arterial segment-specific spectral waveforms, determine flow direction, measure cerebral blood flow velocities and flow pulsatility in the above-mentioned arteries. These practice standards will assist laboratory accreditation processes by providing a standard scanning protocol with transducer positioning and orientation, depth selection and vessel identification for ultrasound devices equipped with spectral Doppler and power motion Doppler.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: found
            Is Open Access

            Transcranial Doppler Ultrasound: A Review of the Physical Principles and Major Applications in Critical Care

            Transcranial Doppler (TCD) is a noninvasive ultrasound (US) study used to measure cerebral blood flow velocity (CBF-V) in the major intracranial arteries. It involves use of low-frequency (≤2 MHz) US waves to insonate the basal cerebral arteries through relatively thin bone windows. TCD allows dynamic monitoring of CBF-V and vessel pulsatility, with a high temporal resolution. It is relatively inexpensive, repeatable, and portable. However, the performance of TCD is highly operator dependent and can be difficult, with approximately 10–20% of patients having inadequate transtemporal acoustic windows. Current applications of TCD include vasospasm in sickle cell disease, subarachnoid haemorrhage (SAH), and intra- and extracranial arterial stenosis and occlusion. TCD is also used in brain stem death, head injury, raised intracranial pressure (ICP), intraoperative monitoring, cerebral microembolism, and autoregulatory testing.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Vasospasm probability index: a combination of transcranial doppler velocities, cerebral blood flow, and clinical risk factors to predict cerebral vasospasm after aneurysmal subarachnoid hemorrhage.

              The goal in this study was to create an index (vasospasm probability index [VPI]) to improve diagnostic accuracy for vasospasm after subarachnoid hemorrhage (SAH). Seven hundred ninety-five patients in whom aneurysmal SAH was demonstrated by computed tomography, and in whom one or more intracranial aneurysms had been diagnosed, underwent transcranial Doppler (TCD) studies between April 1998 and January 2000. In 154 patients angiography was performed within 24 hours of the TCD examination, and in 75 133Xe cerebral blood flow (CBF) studies were obtained the same day. Seven cases were excluded because of a limited sonographic window. Forty-one women (60.3%) and 27 men (39.7%) between the ages of 35 and 84 years (58.0 +/- 13.2 years [mean +/- standard deviation]) were included. Clinical characteristics analyzed included age, sex, Hunt and Hess grade, Fisher grade, days after SAH, day of treatment, type of treatment (coil embolization, surgical clip occlusion, or conservative treatment), smoking history, and hypertension history. Lindegaard ratios and spasm indexes (TCD velocities/hemispheric CBF) were calculated bilaterally. Digital subtraction angiography images were measured at specific points of interest. Sensitivity, specificity, predictive values, and global accuracy of the different tests were calculated. Logistic regression was used to evaluate the possible predictive factors, and the coefficients of the logistic regression were integrated to create the VPI. In 18 patients (26.5%) symptomatic vasospasm was diagnosed, and 33 (48.5%) had angiographic evidence of vasospasm. For TCD velocities above 120 cm/second at the middle cerebral artery, the global accuracy was 81.1% for the diagnosis of clinical vasospasm and 77.2% for angiographic vasospasm. For a Lindegaard ratio higher than 3.0, the accuracy was 85% for clinical vasospasm and 83.2% for angiographic vasospasm. A spasm index higher than 3.5 had an accuracy of 82.0% for the diagnosis of clinical vasospasm and 81.6% for angiographic vasospasm. The selected model for estimation of clinical vasospasm included Fisher grade, Hunt and Hess grade, and spasm index. The VPI had a global accuracy of 92.9% for clinical vasospasm detection. For diagnosis of angiographic vasospasm, the model included Fisher grade, Hunt and Hess grade, and Lindegaard ratio. The VPI achieved a global accuracy of 89.9% for angiographic vasospasm detection. The use of TCD velocities, Lindegaard ratio, and spasm index independently is of limited value for the diagnosis of clinical and angiographic vasospasm. The combination of predictive factors associated with the development of vasospasm in the new index reported here has a significantly superior accuracy compared with the independent tests and may become a valuable tool for the clinician to evaluate the individual probability of cerebral vasospasm after aneurysmal SAH.
                Bookmark

                Author and article information

                Contributors
                ohtusabes@gmail.com
                aaabdo@infomed.sld.cu
                Journal
                Crit Ultrasound J
                Crit Ultrasound J
                Critical Ultrasound Journal
                Springer Milan (Milan )
                2036-3176
                2036-7902
                16 January 2018
                16 January 2018
                2018
                : 10
                Affiliations
                [1 ]Ecodiagnóstico-Centro de Diagnóstico por Imágenes, 3272, 50 St., Necochea, 7630 Argentina
                [2 ]Centro de Investigaciones Médico-Quirúrgicas, 11-13 and 216 St., Siboney, La Habana, 12100 Cuba
                Article
                85
                10.1186/s13089-018-0085-4
                5770348
                29340797
                © The Author(s) 2018

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                Categories
                Letter to the Editor
                Custom metadata
                © The Author(s) 2018

                Radiology & Imaging

                Comments

                Comment on this article