Fully automated, real-time, calibration-free, continuous noninvasive estimation of intracranial pressure in children

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>In the search for a reliable, cooperation-independent, noninvasive alternative to invasive intracranial pressure (ICP) monitoring in children, various approaches have been proposed, but at the present time none are capable of providing fully automated, real-time, calibration-free, continuous and accurate ICP estimates. The authors investigated the feasibility and validity of simultaneously monitored arterial blood pressure (ABP) and middle cerebral artery (MCA) cerebral blood flow velocity (CBFV) waveforms to derive noninvasive ICP (nICP) estimates.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Invasive ICP and ABP recordings were collected from 12 pediatric and young adult patients (aged 2–25 years) undergoing such monitoring as part of routine clinical care. Additionally, simultaneous transcranial Doppler (TCD) ultrasonography–based MCA CBFV waveform measurements were performed at the bedside in dedicated data collection sessions. The ABP and MCA CBFV waveforms were analyzed in the context of a mathematical model, linking them to the cerebral vasculature’s biophysical properties and ICP. The authors developed and automated a waveform preprocessing, signal-quality evaluation, and waveform-synchronization “pipeline” in order to test and objectively validate the algorithm’s performance. To generate one nICP estimate, 60 beats of ABP and MCA CBFV waveform data were analyzed. Moving the 60-beat data window forward by one beat at a time (overlapping data windows) resulted in 39,480 ICP-to-nICP comparisons across a total of 44 data-collection sessions (studies). Moving the 60-beat data window forward by 60 beats at a time (nonoverlapping data windows) resulted in 722 paired ICP-to-nICP comparisons.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Greater than 80% of all nICP estimates fell within ± 7 mm Hg of the reference measurement. Overall performance in the nonoverlapping data window approach gave a mean error (bias) of 1.0 mm Hg, standard deviation of the error (precision) of 5.1 mm Hg, and root-mean-square error of 5.2 mm Hg. The associated mean and median absolute errors were 4.2 mm Hg and 3.3 mm Hg, respectively. These results were contingent on ensuring adequate ABP and CBFV signal quality and required accurate hydrostatic pressure correction of the measured ABP waveform in relation to the elevation of the external auditory meatus. Notably, the procedure had no failed attempts at data collection, and all patients had adequate TCD data from at least one hemisphere. Last, an analysis of using study-by-study averaged nICP estimates to detect a measured ICP &gt; 15 mm Hg resulted in an area under the receiver operating characteristic curve of 0.83, with a sensitivity of 71% and specificity of 86% for a detection threshold of nICP = 15 mm Hg.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>This nICP estimation algorithm, based on ABP and bedside TCD CBFV waveform measurements, performs in a manner comparable to invasive ICP monitoring. These findings open the possibility for rational, point-of-care treatment decisions in pediatric patients with suspected raised ICP undergoing intensive care.</jats:p></jats:sec>

Adaptive Maximal Blood Flow Velocity Estimation From Transcranial Doppler Echos

“…Irrespective of the employed algorithm, the difficulty in finding the maximal flow velocity in Doppler spectrograms has implications on derived indices such as the pulsatility index and other derived quantities such as ICP [8], [9], [11]. This uncertainty in the blood flow velocity waveform and the associated need for visual review and manual annotation of the waveforms to flag regions of sufficiently high signal quality is one of a series of challenges that need to be overcome in the translational effort to bring non-invasive ICP monitoring to the bedside.…”

“…Since we had no information on the insonation angle, we set α = 0 • for all recordings, which is commonly a reasonable assumption for the middle cerebral artery (MCA) and internal carotid artery (ICA). In addition, many applications such as the non-invasive estimation of ICP [8], [11] require only a scaled version of the maximal cerebral blood flow velocity. In the following, we describe the algorithm used to obtain maximal blood flow velocity estimates from the Doppler spectrogram.…”

“…Recent work also suggests that TCD ultrasonography, combined with minimally-invasive blood pressure measurements, can be used for monitoring cerebral autoregulation [6], [7] This work was supported in part by the PhD student stipend of ETH Zurich and a grant by Philips Healthcare. and for obtaining non-invasive estimates of intracranial pressure (ICP) [8]- [11]. In most neuromonitoring applications, the quantity of interest is the maximal blood flow velocity waveform, which together with measurements or assumptions on the vessel geometry, can be used to estimate volumetric blood flow.…”

Review: pathophysiology of intracranial hypertension and noninvasive intracranial pressure monitoring

“…Abbreviations used: TCD (Transcranial Doppler), TDTD (twodepth transorbital doppler), NIRS (near-infrared spectroscopy), TMD (tympanic membrane displacement), OAE (otoacoustic emissions), SVP (spontaneous venous pulsations), ONSD (optic nerve sheath diameter), OCT (optical coherence tomography), VEP (visual evoked potentials), EEG (electroencephalography) Though not necessarily universally positive, evidence is generally more consistent and substantial than for rank 2 and method is likely to be useful as a supplement to invasive measurement in at least some clinical situations in the absence of technical hurdles to adoption rankings of 4 or 5 could theoretically exist for methods that have demonstrated the requisite accuracy, precision, standards of evidence, and feasibility of use to achieve widespread adoption in clinical care settings, it is the authors' opinion that none of the current proposed noninvasive ICP monitoring methods approach this level of efficacy. This review primarily focuses on noninvasive ICP monitoring in adults, though other work has also been devoted to monitoring in children [45].…”

A Spectral Approach to Model-Based Noninvasive Intracranial Pressure Estimation

“…To guard against inclusion of stretches of data with unphysiological signatures or excessive noise, we have previously developed an automated signal waveform pre-processing pipeline, consisting of ABP and CBFV signal quality assessment, waveform synchronization, and beat-onset alignment [28]. Additionally, the mean ABP was adjusted to account for the fact that the model requires ABP measurements at the level of the MCA but clinically, the ABP waveform is commonly calibrated to the level of the heart [28]. During each recording session, we therefore measured the vertical heights of the ABP and ICP transducers and calculated the hydrostatic pressure difference to be expected due to the difference in vertical locations of the pressure measurements.…”