Irkutsk State Medical Academy of Postgraduate Education,

Irkutsk, Russia

 

The methods of intracranial pressure (ICP) control based on morphological functional features of extracranial organs

Ophthalmologic retinal measurements. Close morphofunctional relationship between venous and liquor systems of the brain, and also the anatomic functional features of fundus vessels, in particular for central retinal vein (CRV), make the basis for investigation of possibilities of ophthalmoretinal reactions (investigation of pulse and pressure in CRV) in estimation of intracranial hypertension (ICH). Fundus vessels are the direct reflection of the brain vascular system, and the vascular changes in disorders of venous and liquor circulation are the reasons for searching evaluation tools for present dysfunction. Owing to the fact that the space between the optic nerve and its disk is the direct continuation of subarachnoid space, then the pressure of the filling cerebrospinal fluid (CSF) is equal to the intracranial pressure (ICP) [6, 22]. ICH is characterized with increasing diameter of the optic disk (OD) and simultaneous barrier for blood flow through CRV. The disorder of venous return causes visible changes in the fundus (venostasis and OD edema). Clinicians consider this sign as increased ICP during ophthalmoscopy. The quantitative evaluation of identified changes is performed with two different techniques: measurement of OD diameter using corresponding technique (ultrasound or magnetic resonance imaging, MRI) or ophtalmodynamometry for estimating pressure in CRV, which is slightly higher (by 1-2 mm Hg) compared to ICP [7]. In patients without craniotomy CRV pressure corresponds to intracranial pressure. According to the technique patented by N.V. Zabolotsky et al. (2000), during measurement of CRV pressure in mm Hg using appropriate adjustment factor, one can get intracranial pressure in mm Hg in patients with craniotomy [58]. If CRV pressure is 10-20 mm Hg, the adjustment factor is 0.7; if CRV pressure is 21-30 mm Hg and 31-45 mm HG, the recalculation coefficient is 0.5 and 0.4 respectively. The authors believe that the method increases reliability of intracranial hypertension examination and gives an opportunity for timely definition of degree of this state and carrying out the appropriate correction. The manipulation is performed as indicated below. CRV pressure is measured with electronic ophthalmodynamometer OM-1 in horizontal position of a patient after sclera anesthesia with 0.1 % dicain solution and pupillary dilatation with 0.5 % amicil solution. In simultaneous ophthalmoscopy of OD with electric ophthalmoscope OP-2 with ophthalmodynamometer transducer the pressure onto superficial surface of eye bulb sclera is performed quickly, evenly and without jerks. Diastolic pressure in CRV is the lowest values of ophthalmodynamometer during triple assessment, with compliance with CRV maximal pulsation. Gramm values of ophthalmodynamometer scale are conversed to mm Hg with Magito-Bailliart table, with consideration of intraocular pressure. In the study by A.P. Efimov (2011) the ICP values, which were received using Neuromiometer-01 device, were associated with high correlation with micromotor activity of limbic centers and basal ganglions which were evaluated with Micromotorica-2M 03 during rehabilitation of neurology patients [10].

ICH causes changes at the cellular or axonal level, for example, edema in optical nerve fibers, which form internal layer of the retina (so called nerve fibre layer – NFL). Ophthalmoscopy, fundus examination, is used for estimating intracranial pressure. At that, OD hyperemia is observed, edema and blurring of borders, increased diameter, extrusion to corpus vitreum, arteriostenosis, venous distensibility, hyperemia and tortuosity at the fundus. The ophthalmoscopy data presents the combination of qualitative signs and is non-informative during the early phases of ICH. So, development of OD edema takes about 2-4 hours. There is a patented method using cascaded optical system tomography for measuring nerve fiber thickness and ICP calculation based on ICH-induced retina edema. However, there is no data about correlation between ICP and nerve fiber layer thickness [4].

Optical disk diameter. The first measurement of ICP, on the basis of OD diameter, was performed in 1987, when G. Cennamo and colleagues demonstrated the lineal relationship between ICP and OD diameter using transorbital ultrasonography in A-scan mode (based on time-of-the-flight technique) [6]. The original method of measurement is technically complicated and is associated with insufficient reliability, because of almost coaxial aligning of the optical nerve and the supersonic wave axis. However, accuracy of measurements became significantly better with B-scans (plain), which provide longitudinal image of cross section of the optical nerve and the disk. Since then the technique approved itself in several large studies of severe TBI, hydrocephaly, intracranial hemorrhage, stroke, liver insufficiency, and even in mountain climbers with acute altitude sickness [15, 16, 17, 23, 34, 49, 50, 54]. Some authors offered MRI for measuring OD diameter [37]. Multiple studies [15, 26, 49, 57] showed relationship between OD diameter and ICP with invasive measurements. The correlation coefficient varied within 0.59-0.73. The technique is cheap and technically simple. The examination period is 5 minutes [26].

The technologies using ultrasound or MRI for measuring OD diameter are widely used and allow measurement with accuracy within 1 mm. Almost all investigators recommend to use the technique for identification of patients with ICH requiring immediate correction (ICP > 20 mm Hg with OD diameter > 5 mm  Hg), but not for routine measurement of ICP in general clinical practice. Usually MRI is the routine practice in many specialized facilities, if suspicion of TBI or stroke is present. However, in case of OD diameter measurement MRI has no advantages in terms of accuracy compared to ultrasound measurement. The portable MRI systems, which were recently implemented into clinical practice, are used only for control of accuracy of bone reposition in multiple fractures, and now it is not clear about their use for OD diameter measurement [38].

The bedside ultrasound transducer for measurement of OD diameter allows quite accurate estimation of intracranial hypertension [42]. According to the data by V. Rajajee et al. (2011), optical nerve ultrasonography (ONUS) is the non-invasive technique for ICH control. It can identify ICP increase by 20 mm Hg [43]. According to J. Dubourg et al. (2011) ONUS allows diagnosing ICH with high accuracy (sensitivity 0.9, specificity – 0.85) and making decision about transfer of a patient to a specialized clinic or necessity of invasive monitoring, even in absent worsening neurological status [9]. OD diameter demonstrates the good level of diagnostic accuracy for intracranial hypertonia. T. Soldatos et al. (2008) compared the results of ophthalmoscopy and non-invasive control of ICP with transcranial doppler, as well as the pressure values measured with direct method with drain installation into lateral ventricle cavity. They found the high correlation [49]. T. Kirk et al. (2011) did not found any relationship between intraocular pressure and ICP measured with lumbar puncture [27].

A. Ragauskas et al. (2012) demonstrated that in case of pressure on the orbit the pressure level in ipsilateral segment of the ophthalmic artery (OA) corresponded to ICP level [40]. The non-invasive technique of transcranial doppler was used for assessing flow rate in two OA segments in 62 patients with neurologic pathology. At that, the intracranial segment was prone to ICP influence. In the extracranial segment the pressure was from outside (Pe) by means of impact on the orbit. It was found that in both segments blood flow rate indices flattened out in the case, when Pe was equal to ICP. For all patients ICP monitoring was performed with invasive and non-invasive methods. There were no statistically significant differences [40].

Ophtalmodynamometry (ODM). Ophtalmodynamometry, or measurement of venous outflow pressure (VOP), is performed by means of external pressure onto the sclera and simultaneous observation of retinal vessels with an ophthalmoscope. The pressure is increased until CRV pulsation begins. It appears when external pressure values approach VOP values. The original technique was described in 1925 by M. Baurmann and was widely used [2]. There is a range of modifications with combination of classical ODM, retinal oxymetry or ultrasound registration of blood flow in the central artery of the retina [7, 39]. Also there is an automatic evaluation technique with use of camera and the special software for registration of venous filling during sequential imaging of the fundus [13]. The clinical experiments showed the evident lineal dependence and insignificant differences (2-3 mm Hg) between VOP and ICP. The authors compared the pressure level in CRV and ICP measured with invasive techniques. As result, in 84.2 % of the cases the pressure increase in CRV corresponded to increasing pressure in the cranial cavity, but in 92.8 % of the cases the normal ICP corresponded to the normal pressure in CRV [12].

The equipment for ODM is light and portable. But the technique is not appropriate for ICP continuous control and it requires frequent repetitive measurements, availability of trained specialists and is operator-dependant technique. The method is not appropriate for patients with eye and orbit injuries, isolated optic nerve pathology, when OD edema is not an indicator of ICH. Finally, administration of external pressure can be a trigger for oculo-cardial reflex that is dangerous for patients with ICH because of possibility of progression to cerebral ischemia.                          

Otoacoustic methods. The histological examinations of internal ear in increased pressure found the vascular disorders: hyperemia, local congestive events, cellular infiltration, degenerative and dystrophic events of Corti's organ cells. Development of congestive structural changes in the internal ear is conditioned by the direct connection between subarachnoid space, cochlea aqueduct perilymph and scala tympani.

In the initial period of ICH the disorders of hearing function because of internal ear edema (bone conduction shortening, sound lateralization towards bad hearing ear, increased perception of deep tones) are characterized by invertibility, but continuity and increasing during development of degenerative changes in reciprocal cochlea part. Vestibular disorders are mainly manifested in view of nystagmus and different changes of experimental samples (hyporeflexia, postrotation hyperreflexia) and depend on duration of a process associated with edema. Sometimes weakening and drop out of the acute phase of optokinetic nystagmus is observed. Dizziness and statokinetic disorders are insignificant. In acute development of ICH the caloric tonic nystagmus with slow phase lengthening is observed. It is common in case of localization of process in fossa cranii posterior. These events are possible before identification of ophthalmologic and radiographic signs of hypertensive state. However, sometimes tonic character of nystagmus is observed in decreased ICP. Usually nystagmus tonicity is conditioned by not so much pathologic state of low stem mechanisms as mesocephalic mechanisms. Hypertension syndrome can be associated with positional nystagmus of large-scale or tonic character (horizontal, or more rarely vertical). It appears with most positions of the head. Sometimes declination of the outstretched arm is observed on the side of pathological process. Therefore, the pathogenetic relationship exists between ICH and vestibular apparatus disorders.

The functional state of brain stem structures in case of its dislocation is assessed by means of registration of brainstem auditory evoked potential (BSAEP). Dynamic examination of this potential allows judging about efficiency of performed treatment and dislocation syndrome course. The individual components of BSAEP corresponded to hearing impulse path. The first element reflects functional state of the distal eighth nerve, 2^nd – cochlear nucleus, 3d - superior olives and corpus trapezoideum, 4^th – lateral lemniscus, 5^th - corpora quadrigemina inferior colliculi. In case of dislocation the changes in BSAEP show both deepness and side of brainstem lesion. So, in initial forms of penetration the BSAEP changes are registered on the side of penetration (for example, hippocampus). During increasing stem dislocation it is pressed by the temporal lobe, but also forced against the opposite edge of tentorial crena. It results in BSAEP bilateral lesions.

 Tympanic membrane displace test (TMDT) was offered by R.J. Marchbanks (1989). It is based on the acoustic reflex – reflector contraction of stapedius and tensor tympani in response to sound impact [32]. Normally, eardrum vibrations are identified with acoustic stimulation and are transferred through the auditory ossicles (malleus, uncus, stapes) in the middle ear to cochlear fenestra vestibule. Incus crus vibrations are transferred to perilymph resulting in vibrations of endolymph, main membrane and Corti's cells. In this complicated mechanism the vibration transfer function is realized with two small muscles of the middle ear: tensor tympani and stapedius. Tensor tympani is the continuation of cartilage part of Eustachian tube, and its contraction influences on the handle of a hammer and strains eardrum. Stapedius, originating from the posterior wall of ear drum, prevents needless movements of stapes and separates it from fenestra vestibule. The activity of these muscles balances stapes vibrations and decreases amplitude of transferred sound up to 20 dB. Muscles contract as response to auditory stimulus. It is accompanied by non-significant, but measurable displacement of eardrum from its initial position. As CSF and perilymph are connected through cochlear window, then, in case of increased ICP, position of stapes crus changes and it will influence on the value of eardrum displacement in response to sound stimulus [51].

Displacement is measured with tympanometer for impedance audiometry. It is portable, convenient and relatively cheap. There are modern computer tympanometers with full automatic measurement. Internal displacement (negative peak pressure on an audiogram) is an indicator of increased ICP [53]. TMD value depends both on stapes initial position and many other factors associated with acoustic impedance (eardrum integrity, ear bones state, Eustachian tube patency, presence of fluid or other pathologic substances in the middle ear cavity) and acoustic reflex strength (physiological variability of cutoff value, functional integrity of cochlear and facial nerves, possible sensory deafness). Besides, the assumption of equality of perilymph pressure and intracranial pressure is incorrect, if ductus cochlearis structure is impaired (it is common for older age) [36]. The accuracy of ICP estimation with TMD is within the range of ±15 mm Hg.  It is not enough for proper quantitative estimate of ICP in clinical practice [53]. However, for qualitative estimation of ICP including three main categories (increased, normal and low ICP), TMD demonstrates quire good sensitivity and specificity in children with disresorptive hydrocephaly [45]. Test of displaced eardrum is used for sequential serial registrations of ICP [48, 49].

The great interest is associated with the technique patented by A. Ragauskas (2006). Instead of acoustic reflex estimate the author offers to use direct impact on eardrum [41]. Measurement of eardrum position is performed at null value of ICP (main position). ICP aligning with atmospheric pressure can be achieved with non-invasive means of patient’s head inclination or with neurosurgical intervention. Late ICP is measured with external pressure on eardrum, with simultaneous pressure on fenestra vestibule and the internal ear (for example, through Eustachian tube), until eardrum comes to the main position after aligning external pressure with intracranial one. Unfortunately, there is no convincing evidential basis for support of administration of this technique in clinical practice.            

S. Shimbles et al. (2005) tested the method in the group of 148 patients with intracranial pathology (hydrocephaly with initial signs of ICH) and compared the data with the results of examination of 77 control healthy persons [48]. The technique was successful in 70 % of healthy persons and only in 40 % of patients with basically increased ICP. Also it was found that perilymph features change with aging, and displacement of eardrum does not allow reliable estimation of ICP in persons at the age > 40.

In cases of comparison of invasive measurement of ICP with ICP, which was calculated on the basis of displaced eardrum, the high degree of correlation of two values was identified. However, high variability of values in intragroup regression analysis does not allow to use this technique in wide clinical practice [48].

Otoacoustic emission (OAE) is the sound which is produced with little vibrations of endo- and perilymph. It is induced by contraction of external hair cells of the internal ear in response to loud external sound impact. Sound wave is transferred to stapes, then, trough the ear bones to tympanic membrane, where it is identified with high sensitive microphone installed into the external ear canal. TMD does not provide accurate estimate of ICP, because acoustic impedance and its changes during acoustic reflex are defined with, mainly, structural and functional characteristics of the middle ear and only insignificantly with changes in ICP. Theoretically, measurement of acoustic events in the middle ear could give more precise estimation of pressure of peri- and endolymph, and, correspondingly, ICP.

In clinical practice OAE is used for testing hearing disorders in newborn and children. The equipment is portable and relatively convenient. For decreasing background interference and simplifying extraction of waveforms two systems of derivates are used in OAE, which estimate signal provoking otoacoustic emission (TEOAE) and signal of reflection of otoacoustic emission (DPOAE). TEOAE system includes wide range of audio signals and analyzes reflected sound, which appears after 4-20 ms. Signal-noise ratio (SNR) is neutralized with the system using averaging great amount (about 1000) of reflected synchronized stimuli, which are similar with accidentally provoked EEG potentials. DPOAE system, conversely, independently reproduces two primary tones of f₁ and f₂ (f₁ < f₂) and analyzes reflected sound in the frequency range of primary tones, main of which is cubic derivative of distortion f_cdt = 2f₁ - f₂. The recent American patent by S.C. Meyerson and colleagues (2003) offers using TEOAE and DPOAE for measurement of ICP [33]. TEOAE is used at the start for estimation of OAE optimal response rate. Later, the pair of clean tones sweep in DPOAE paradigm in such way that cubic derivate of distortion (2f₁-f₂) is equal to optimal response rate, where f₂/f₁ ratio is equal to 5:4, but I₂/I₁ frequency intensity is in 6:5 ratio. Also the authors offered the formulae, which allow relating ICP with intensity or duration of measured OAE signal, and described influence of different physiologic states on ICP. Small ICP oscillations are observed in cardiac cycle, respiratory act or in changing position and can be used as control of measurements. For example, absence of modulation of measure OAE phase during respiratory cycle can indicate cochlea occlusion. In this case OAE for ICP control is not informative. The rare modern studies showed efficacy of AOE for assessing ICP. So, the pilot study by A.M. Frank and colleagues (2006) analyzed different OAE techniques in 12 healthy individuals and 5 patients with ventricular drains. It showed that physiologic increase in ICP (in body position change, coughing, sneezing) correlated with decreasing intensity of evoked OAE potentials (from -2.1 to -7.9 SPL) [14]. However, all results were presented in view of means, without statistically reliable analysis.

Jugular blood flow changes. The method by J.A. Allocca (1980) is based on the temporary forcipressure of the jugular vein (about 5 seconds) and non-invasive measurement with Hall transducer or ultrasound transducer at the level above the occlusion place [1]. The study is presented in view of patent document: the experiment included cats and demonstrated lineal relationship between ICP level and changing jugular blood flow. Despite of technical simplicity, the clinical administration of the technique is limited with two serious problems: measurements are not considered as reliable, because jugular vein cross-clamping provokes ICP increase; even short term disorder of cerebral circulation can result in dangerous complications in patients with basic ICH or impaired cerebral perfusion.

Perspectives. Despite of relatively long history of presence of many interesting approaches for non-invasive ICP measurement, many techniques are still in the phase of development. The main reason is that no method is sufficiently precise and simultaneously convenient for usage. According to D. Popovic one can see that most projects are not compliant with AAMI standards, because of too wide range of errors in measurements (table) [38]. The non-invasive techniques clearly identify low or extremely high ICP, without reliable results of measurements in patients with ICP of 15-30 mm Hg.

Table
Comparison of methods for non-invasive ICP monitoring [38]

In most cases errors in measurements are associated with physiologic or anatomic characteristics of surveillance objects and with dependence of studied parameters on both ICP level and other factors, for example, arterial pressure, preservation of cerebral blood flow autoregulation (for transcranial doppler, multidimensional ultrasound investigations), functional features of individual brain structures (EEG, TMD), presence of additional volume in cranial cavity (time of the  flight ultrasound, ocular technique), integrity of internal ear structures etc. [29, 30, 35, 52].

Near-infrared spectroscopy (NIRS) is a non-invasive technique of ICP measurement based on detection of changes in cerebral tissue oxygenation, volemic and velocity values of cerebral blood flow, and changing levels of oxyhemoglobin and deoxyhemoglobin. Cerebrovascular activity monitoring (PRx) is the diagnostic and predictive criterion for patients with severe TBI, but for adequate estimate the non-invasive ICP monitoring is necessary.  C.I. Zweifel et al. (2010) used NIRS data for development of technique for cerebrovascular reactivity index calculation (THx) in dependence on hemoglobin contents in circulating blood [59]. R.A. Weerakkody et al. (2012) used NIRO 200 device for examination of patients with idiopathic ICH and TBI [55]. The received results were compared to ICP values which were received during external ventricular draining. The correlation was found between change in ICP and change in levels of oxyhemoglobin and deoxyhemoglobin during infusion test (introduction of Hartman's solution into ventricular catheter, 15 ml/min, ICP increased from 10.7 to 18.9). The direct relationship was observed: oxyhemoglobin and deoxyhemoglobin increased simultaneously with ICP increase.

Heart rhythm variability. It is known that increasing intracranial pressure leads to impaired vegetative status associated with cerebrocardial influence. It is supported by well-known Cushing triad, which is characterized with vegetative disbalance in view of arterial hypertension, respiratory disorders and bradycardia which develop in brain stem ischemia. Earlier manifestations of vegetative disbalance and, first of all, heart rhythm changes are identified with heart rhythm variability (HRV) analysis. The long term studies showed that the classical effect of Kocher-Cushing (increasing arterial pressure and pulse slowdown in intracranial pressure increase) is conditioned by compression and ischemia of limited pressor region under the 4th ventricle bottom. HRV examination is adequate and relatively simple method of estimation of sympathetic parasympathetic balance and neurohumoral regulation background.

For the first time the technique for mathematic estimation of heart rhythm was used by A. Fleisen and P. Beckman who offered R-R interval mean square deviation for estimation of rhythm oscillation [3].  In study of fetal lesions E.H. Íîn and S.T. Lee (1965) noted that rhythm changes came before significant disorders of heart rhythm [24]. B. Sayers et al. (1973) described physiologic variations of heart rhythm [48]. In 80s D.J. Ewing et al. offered several simple bed-side tests which used short term changes in R-R intervals for identification of vegetative neuropathy in patients with diabetes mellitus [11].

In our country the greatest contribution to HRV research and its clinical significance was made by D.I. Zhemaytite (the studies of rhythmogram classes) and R.M. Baevsky (variation pulsometry, evaluation of rates of strain of regulatory systems in different states) [3].

HRV reflects complex picture of different directing influences on circulation system with interference of periodical components of different frequency and amplitude with non-lineal character of interaction of different control levels. According to M. Katz-Leurer (2005) who studied the parameters of timing and spectral analysis two weeks after stroke, the direct relationship exists between motor functions and BPC values [25]. According to their opinion, BPC is used for predictive evaluation of motor functions in long term period. N. Lakusic (2005), D. Mahovic (2003) assessed expression of heart rhythm vegetative regulation and its restoration dynamics during 6 months after acute ischemic stroke [28]. The significant reduction of all BPC values (except for LF/HF) was found, as well as strong increase in the mean values of BPC (SDNN and total spectrum yield) between the second and sixth months after acute stroke. The results of the study supported the hypothesis about incremental recovery of heart rhythm vegetative regulation during the first months after acute phase.

The studies by A.R. Gujjar (2004) were dedicated to comparative investigation of clinical course and BPC values in survivors and died patients in acute period of stroke [21]. There was a relationship between two components of spectral analysis (low frequency and very low frequency) and mortality. It was supported even after prescription of vasopressors. According to the results of regression analysis, transfer to ALV, eye opening according to GCS and BPC-LF are the factors for reliable prediction of lethal outcome. A.M. Makikalio (2004) investigated predictive significance of BPC values in patients who suffered a stroke for the first time [31]. After adjustment for age the multivariative analysis showed that the single independent and objective predictive factor of sudden death risk was associated with pathological changes in long term (24 hours) beat-to-beat ratemetry. The results of traditional (5 minutes) BPC examination are not reliable for prediction [31]. I.A. Golovin (2004) studied disorders in vegetative regulation functions in acute period of traumatic brain injury (TBI). The out-of-limit disorders of vegetative balance were resistant to pharmacological correction and were accompanied by maximal mortality [18]. At rest the ANS parasympathetic tone dominates, and heart rhythm variability corresponds to vagal influence. The activity of the ANS sympathetic part increases during stress reaction. The combination of heart rhythm variability values demonstrates prevailing sympathicotonia. BPC reaction to activity of ANS different parts correlates with cardiovascular system function and effectively demonstrates the course of body adaptive reaction to non-standard influences.

The results of the study by V.I. Gorbachev et al. (2011) showed that values of variational beat-to-beat ratemetry and spectral analysis significantly differed between survivors and non-survivors [8, 19, 20]. During the first 24 hours of follow up the maximal differences are identified with strain index, range, R-R interval standard deviation and vagosympathetic balance coefficient. On days 3-5 maximal recognition is associated with mode amplitude, strain index, R-R interval variation coefficient, HR and theoretical average. On days 6-7 the maximal differences are identified only with HR, on days 8-10 – with range, R-R interval standard deviation, variation coefficient and values of normalized power within the limits of high and low frequency. Therefore, on the basis of changes in BPC values it is possible to predict TBI outcomes.

Summarizing the above mentioned facts, the literature data show that variational beat-to-beat ratemetry is a reliable and sensitive technique for assessing brain functions. BCP registration and interpretation reliably show sympathetic vagal balance in any pathologic process, particularly in intracranial hypertension [8, 19, 20].

Combined models for ICP calculations. B. Schmidt et al. (2012) developed the mathematic model for invasive calculation of ICP according to cerebral blood flow velocity and arterial pressure [47]. The hemodynamic parameters were calculated on the basis of AP curve shapes and cerebral blood flow velocity. The lineal relationship was found between input and output parameters of ICP and AP. The data reliability was tested with different methods: assessment of ICP plateau wave shapes, cerebral flow autoregulation parameters, endolumbar infusion of solutions. All tests showed high correlation (r 0.9-0.98) between ICP values, which were received with invasive and non-invasive techniques.

Based on lineal relationships between systemic AP, ICP and cerebral blood flow velocity, the non-lineal model of regression for ICP calculation was developed based on Kernel’s spectral regress (KSR) and vector modeling (SVM) [56].

Budohoski et al. (2012) registered blood flow velocity, ICP and AP in the middle cerebral artery [5]. Non-invasive calculation of ICP was performed with mathematic model. Other parameters were evaluated with ICP monitoring: ICP pulse amplitude, respiratory component amplitude, ICP slow wave amplitude and compensatory reserve index (RAP). The analysis and interpretation of the results were carried out after distribution of the patients into the groups of survivors and non-survivors. The significant correlation was found between ICP values obtained with invasive and non-invasive techniques. The strongest correlation was found in comparison of respiratory component amplitude (r = 0.66), the lowest one – for ICP pulse amplitude (r = 0.41).

ICH is the general manifestation of severe traumatic brain injury. It requires rapid diagnostics, therapeutic and surgical correction. Intraventricular catheter installation is a standard technique for ICH diagnostics, but this manipulation is not always possible, because of contraindications, particularly, consumption coagulopathy or thrombocytopenia, or because of absence of neurosurgery department in a facility. At the present time the specialists’ attention is related to the studies of ICP measured with invasive and non-invasive techniques. The different techniques for non-invasive control of intracranial hypertension were offered: X-ray methods, CT, MRI, transcranial doppler, EEG analysis, audiologic and ophthalmoscopic methods. Unfortunately, each technique has its own limitations. Computer tomography is cost, time-consuming and often riskful, because of transportation and relocation of critically ill patients [41]. Ophthalmoscopy is performed only by an experienced specialist. It allows identifying ICH after some time after initial ICP increase. Finally, transcranial doppler can identify blood flow changes associated with ICP increase, but it also requires availability of experienced specialist. Non-evident temporal echo-windows make this technique impossible in almost 5 % of cases. Non-invasive techniques have a lot of advantages, but lower precision compared to direct measurement of ICP. No available non-invasive technique is appropriate for continuous control. However, they can provide reliable measurement of ICP and can be irreplaceable in case of contraindications or impossibility of invasive control of ICP [44].

CONCLUSION

At the present time the different techniques for non-invasive control of intracranial pressure are available. Each technique has advantages and limitations. However, neither technique has sufficient accuracy and usability. That’s why the actual purpose is development of a technique for ICP estimate which would be simple, precise, relatively inexpensive and with possibility of multiple repetitive examinations.