Noninvasive ICP measurement methods

Measuring Elevated Intracranial Pressure through Noninvasive Methods: A Review of the Literature

Authors: Kristiansson H, Nissborg E, Bartek J Jr, Andresen M, Reinstrup P, Romner B.

Elevated intracranial pressure (ICP) is an important cause of secondary brain injury, and a measurement of ICP is often of crucial value in neurosurgical and neurological patients. The gold standard for ICP monitoring is through an intraventricular catheter, but this invasive technique is associated with certain risks. Intraparenchymal ICP monitoring methods are considered to be a safer alternative but can, in certain conditions, be imprecise due to zero drift and still require an invasive procedure. An accurate noninvasive method to measure elevated ICP would therefore be desirable. This article is a review of the current literature on noninvasive methods for measuring and evaluating elevated ICP. The main focus is on studies that compare noninvasively measured ICP with invasively measured ICP. The aim is to provide an overview of the current state of the most common noninvasive techniques available. Several methods for noninvasive measuring of elevated ICP have been proposed: radiologic methods including computed tomography and magnetic resonance imaging, transcranial Doppler, electroencephalography power spectrum analysis, and the audiological and ophthalmological techniques. The noninvasive methods have many advantages, but remain less accurate compared with the invasive techniques. None of the noninvasive techniques available today are suitable for continuous monitoring, and they cannot be used as a substitute for invasive monitoring. They can, however, provide a reliable measurement of the ICP and be useful as screening methods in select patients, especially when invasive monitoring is contraindicated or unavailable.

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Clinical assessment of noninvasive intracranial pressure absolute value measurement method

Authors: David S, Marcinkevicius E, Pranevicius M, Pranevicius O, Ragauskas A, Matijosaitis V, Zakelis R, Petrikonis K, Rastenyte D, Piper I, Daubaris G, Miller MM, Chang T, Keating R, Sable C, Ragauskas A, Matijosaitis V, Zakelis R, Petrikonis K, Rastenyte D, Piper I, Daubaris G.

Ragauskas et al.(1) demonstrated that when external pressure is applied, the orbit tends to equilibrate flow in the ipsilateral ophthalmic artery (OA) when its level approaches intracranial pressure (ICP). The authors detected this relationship by making the OA into a "natural pair of scales, in which the intracranial segment of the OA is compressed by extracranial pressure (Pe) applied to the orbit."

Non-invasive evaluation of intracranial pressure: How and for whom?

Authors: Dubost C, Motuel J, Geeraerts T.

The invasive monitoring of intracranial pressure is useful in circumstances associated with high-risk of raised intracranial pressure. However the placement of intracranial probe is not always possible and non-invasive assessment of intracranial pressure may be useful, particularly in case of emergencies. Transcranial Doppler measurements allow the estimation of perfusion pressure with the pulsatility index. Recently, new ultrasonographic methods of cerebral monitoring have been developed: the diameter of the optic nerve sheath diameter, a surrogate marker of raised intracranial pressure and the estimation of median shift line deviation.

Clinical assessment of noninvasive intracranial pressure absolute value measurement method

Authors: Ragauskas A, Matijosaitis V, Zakelis R, Petrikonis K, Rastenyte D, Piper I, Daubaris G.

OBJECTIVE: To assess prospectively the accuracy and precision of a method for noninvasive intracranial pressure (ICP) measurement compared with invasive gold standard CSF pressure measurement.
METHODS: Included were 62 neurologic patients (37 idiopathic intracranial hypertension, 20 multiple sclerosis, 1 Guillain-Barré syndrome, 1 polyneuropathy, and 3 hydrocephalus). The average age was 40 ± 12 years. All patients had lumbar puncture indicated as a diagnostic procedure. ICP was measured using a noninvasive ICP measurement method, which is based on a two-depth high-resolution transcranial Doppler insonation of the ophthalmic artery (OA). The OA is being used as a natural pair of scales, in which the intracranial segment of the OA is compressed by ICP and the extracranial segment of the OA is compressed by extracranial pressure (Pe) applied to the orbit. The blood flow parameters in both OA segments are approximately the same in the scales balance case when Pe = ICP. All patients had simultaneous recording of noninvasive ICP values and invasive gold standard CSF pressure values.
RESULTS: Analysis of the 72 simultaneous paired recordings of noninvasive ICP and the gold standard CSF pressure showed good accuracy for the noninvasive method as indicated by the low mean systematic error (0.12 mm Hg; confidence level 0.98). The method also showed high precision as indicated by the low SD of the paired recordings (2.19 mm Hg; CL 0.98). The method does not need calibration.
CONCLUSION: The proposed noninvasive ICP measurement method is precise and accurate compared with gold standard CSF pressure measured via lumbar puncture.

Model-based noninvasive estimation of intracranial pressure from cerebral blood flow velocity and arterial pressure

Authors: Kashif FM, Verghese GC, Novak V, Czosnyka M, Heldt T.

Intracranial pressure (ICP) is affected in many neurological conditions. Clinical measurement of pressure on the brain currently requires placing a probe in the cerebrospinal fluid compartment, the brain tissue, or other intracranial space. This invasiveness limits the measurement to critically ill patients. Because ICP is also clinically important in conditions ranging from brain tumors and hydrocephalus to concussions, noninvasive determination of ICP would be desirable. Our model-based approach to continuous estimation and tracking of ICP uses routinely obtainable time-synchronized, noninvasive (or minimally invasive) measurements of peripheral arterial blood pressure and blood flow velocity in the middle cerebral artery (MCA), both at intra-heartbeat resolution. A physiological model of cerebrovascular dynamics provides mathematical constraints that relate the measured waveforms to ICP. Our algorithm produces patient-specific ICP estimates with no calibration or training. Using 35 hours of data from 37 patients with traumatic brain injury, we generated ICP estimates on 2665 nonoverlapping 60-beat data windows. Referenced against concurrently recorded invasive parenchymal ICP that varied over 100 millimeters of mercury (mmHg) across all records, our estimates achieved a mean error (bias) of 1.6 mmHg and SD of error (SDE) of 7.6 mmHg. For the 1673 data windows over 22 hours in which blood flow velocity recordings were available from both the left and the right MCA, averaging the resulting bilateral ICP estimates reduced the bias to 1.5 mmHg and SDE to 5.9 mmHg. This accuracy is already comparable to that of some invasive ICP measurement methods in current clinical use.

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