Intraoperative neurophysiological monitoring

Intraoperative neurophysiological monitoring

Intraoperative neurophysiological monitoring (IONM) or intraoperative neuromonitoring is the use of electrophysiological methods to monitor the functional integrity of certain neural structures (e.g., nerves, spinal cord, and parts of the brain) during surgery. The purpose of IONM is to reduce the risk to the patient of iatrogenic damage to the nervous system, and/or to provide functional guidance to the surgeon and anesthesiologist.

see Intraoperative neurophysiological monitoring indications.

see Intraoperative neurophysiological monitoring Anesthesia.

Evoked potentials:

Somatosensory evoked potentials (SSEP)

Motor evoked potential (MEP)

Brainstem auditory evoked potentials (BAEP)

Visual evoked potentials (VEP)

Electroencephalography (EEG)

Electromyography (EMG) .


Triggered electromyography.

see Intraoperative stimulation mapping.

Intraoperative neurophysiological monitoring case series.

Seidel K, Krieg SM. Special Topic Issue: Intraoperative Neurophysiological Monitoring. J Neurol Surg A Cent Eur Neurosurg. 2021 Jul;82(4):297-298. doi: 10.1055/s-0041-1731685. Epub 2021 Jul 14. PMID: 34261154.

Noninvasive intracranial pressure monitoring

Noninvasive intracranial pressure monitoring

Intracranial pressure monitoring is necessary in many neurological and neurosurgical diseases.

There is no established method of noninvasive intracranial pressure (NI-ICP) monitoring that can serve as an alternative to the gold standards of invasive monitoring with external ventricular drainage or intraparenchymal monitoring.

To avoid lumbar puncture or intracranial ICP probes, non-invasive ICP techniques are becoming popular.

In a study a new method of NI-ICP monitoring performed using algorithms to determine ICP based on acoustic properties of the brain was applied in patients undergoing invasive ICP (I-ICP) monitoring, and the results were analyzed.

In patients with traumatic brain injury and subarachnoid hemorrhage who were undergoing treatment in a neurocritical intensive care unit, the authors recorded ICP using the gold standard method of invasive external ventricular drainage or intraparenchymal monitoring. In addition, the authors simultaneously measured the ICP noninvasively with a device (the HS-1000) that uses advanced signal analysis algorithms for acoustic signals propagating through the cranium. To assess the accuracy of the NI-ICP method, data obtained using both I-ICP and NI-ICP monitoring methods were analyzed with MATLAB to determine the statistical significance of the differences between the ICP measurements obtained using NI-ICP and I-ICP monitoring. RESULTS Data were collected in 14 patients, yielding 2543 data points of continuous parallel ICP values in recordings obtained from I-ICP and NI-ICP. Each of the 2 methods yielded the same number of data points. For measurements at the ≥ 17-mm Hg cutoff, which was arbitrarily chosen for this preliminary analysis, the sensitivity and specificity for the NI-ICP monitoring were found to be 0.7541 and 0.8887, respectively. Linear regression analysis indicated that there was a strong positive relationship between the measurements. Differential pressure between NI-ICP and I-ICP was within ± 3 mm Hg in 63% of data-paired readings and within ± 5 mm Hg in 85% of data-paired readings. The receiver operating characteristic-area under the curve analysis revealed that the area under the curve was 0.895, corresponding to the overall performance of NI-ICP monitoring in comparison with I-ICP monitoring.

This study provides the first clinical data on the accuracy of the HS-1000 NI-ICP monitor, which uses advanced signal analysis algorithms to evaluate properties of acoustic signals traveling through the brain in patients undergoing I-ICP monitoring. The findings of this study highlight the capability of this NI-ICP device to accurately measure ICP noninvasively. Further studies should focus on clinical validation for elevated ICP values 1).

Flow velocity signals from transcranial Doppler (TCD) have been used to estimate ICP; however, the relative accuracy of these methods is unclear. This study aimed to compare four previously described TCD-based methods with directly measured ICP in a prospective cohort of traumatic brain-injured patients. Noninvasive ICP (nICP) was obtained using the following methods: 1) a mathematical “black-box” model based on interaction between TCD and arterial blood pressure (nICP_BB); 2) based on diastolic flow velocity (nICP_FVd); 3) based on critical closing pressure (nICP_CrCP); and 4) based on TCD-derived pulsatility index (nICP_PI). In time domain, for recordings including spontaneous changes in ICP greater than 7 mm Hg, nICP_PI showed the best correlation with measured ICP (R = 0.61). Considering every TCD recording as an independent event, nICP_BB generally showed to be the best estimator of measured ICP (R = 0.39; p < 0.05; 95% confidence interval [CI] = 9.94 mm Hg; area under the curve [AUC] = 0.66; p < 0.05). For nICP_FVd, although it presented similar correlation coefficient to nICP_BB and marginally better AUC (0.70; p < 0.05), it demonstrated a greater 95% CI for prediction of ICP (14.62 mm Hg). nICP_CrCP presented a moderate correlation coefficient (R = 0.35; p < 0.05) and similar 95% CI to nICP_BB (9.19 mm Hg), but failed to distinguish between normal and raised ICP (AUC = 0.64; p > 0.05). nICP_PI was not related to measured ICP using any of the above statistical indicators. We also introduced a new estimator (nICP_Av) based on the average of three methods (nICP_BB, nICP_FVd, and nICP_CrCP), which overall presented improved statistical indicators (R = 0.47; p < 0.05; 95% CI = 9.17 mm Hg; AUC = 0.73; p < 0.05). nICP_PI appeared to reflect changes in ICP in time most accurately. nICP_BB was the best estimator for ICP “as a number.” nICP_Av demonstrated to improve the accuracy of measured ICP estimation 2).

A technology uses Two Depth Transcranial Doppler to compare arterial pulsations in the intra- and extra-cranial segments of the ophthalmic artery for non-invasive estimation of ICP 3).

Numerous techniques have been described with several novel advances. While none of the currently available techniques appear independently accurate enough to quantify raised ICP, there is some promising work being undertaken 4).

see Optic nerve sheath diameter ultrasonography.

Flanders et al. compared non-invasive and invasive ICP measurements in infants with hydrocephalus. Infants born term and preterm were eligible for inclusion if clinically determined to require cerebrospinal fluid (CSF) diversion. The ventricular size was assessed preoperatively via ultrasound measurement of the fronto-occipital (FOR) and fronto-temporal (FTHR) horn ratios. Invasive ICP was obtained at the time of surgical intervention with a manometer. Intracranial hypertension was defined as invasive ICP ≥15 mmHg. Diffuse optical measurements of cerebral perfusionoxygen extraction, and non-invasive ICP were performed preoperatively, intraoperatively, and postoperatively. Optical and ultrasound measures were compared with invasive ICP measurements, and their change in values after CSF diversion was obtained.

They included 39 infants; 23 had intracranial hypertension. No group difference in ventricular size was found by FOR (p=0.93) or FTHR (p=0.76). Infants with intracranial hypertension had significantly higher non-invasive ICP (p=0.02) and oxygen extraction fraction (p=0.01) compared with infants without intracranial hypertension. Increased cerebral blood flow (p=0.005) and improved oxygen extraction fraction (P < .001) after CSF diversion were only observed in infants with intracranial hypertension.

Noninvasive diffuse optical measures (including a non-invasive ICP index) were associated with intracranial hypertension. The findings suggest impaired perfusion from intracranial hypertension was independent of ventricular size. Hemodynamic evidence of the benefits of cerebrospinal fluid diversion was seen in infants with intracranial hypertension. Non-invasive optical techniques hold promise for aiding the assessment of CSF diversion timing 5).


Ganslandt O, Mourtzoukos S, Stadlbauer A, Sommer B, Rammensee R. Evaluation of a novel noninvasive ICP monitoring device in patients undergoing invasive ICP monitoring: preliminary results. J Neurosurg. 2018 Jun;128(6):1653-1660. doi: 10.3171/2016.11.JNS152268. Epub 2017 Aug 8. PubMed PMID: 28784032.

Cardim D, Robba C, Donnelly J, Bohdanowicz M, Schmidt B, Damian M, Varsos GV, Liu X, Cabeleira M, Frigieri G, Cabella B, Smielewski P, Mascarenhas S, Czosnyka M. Prospective Study on Noninvasive Assessment of Intracranial Pressure in Traumatic Brain-Injured Patients: Comparison of Four Methods. J Neurotrauma. 2016 Apr 15;33(8):792-802. doi: 10.1089/neu.2015.4134. Epub 2015 Dec 17. PubMed PMID: 26414916; PubMed Central PMCID: PMC4841086.

Koskinen LD, Malm J, Zakelis R, Bartusis L, Ragauskas A, Eklund A. Can intracranial pressure be measured non-invasively bedside using a two-depth Doppler-technique? J Clin Monit Comput. 2016 Mar 14. [Epub ahead of print] PubMed PMID: 26971794.

Padayachy LC. Non-invasive intracranial pressure assessment. Childs Nerv Syst. 2016 Sep;32(9):1587-97. doi: 10.1007/s00381-016-3159-2. Review. PubMed PMID: 27444289.

Flanders TM, Lang SS, Ko TS, Andersen KN, Jahnavi J, Flibotte JJ, Licht DJ, Tasian GE, Sotardi ST, Yodh AG, Lynch JM, Kennedy BC, Storm PB, White BR, Heuer GG, Baker WB. Optical Detection of Intracranial Pressure and Perfusion Changes in Neonates With Hydrocephalus. J Pediatr. 2021 May 15:S0022-3476(21)00447-9. doi: 10.1016/j.jpeds.2021.05.024. Epub ahead of print. PMID: 34004191.

Intracranial pressure monitoring in children

Intracranial pressure monitoring in children

Protocols for treatment of children with severe traumatic brain injury incorporate intracranial pressure monitoring as part of a comprehensive plan to minimize secondary injuries, using either ICP and/or cerebral perfusion pressure (CPP) as the therapeutic target 1).

At least 500 children enrolled in 9 studies have demonstrated at least some association between ICP and outcome 2) 3) 4) 5) 6) 7) 8) 9) 10).

As a result, most centers adopted ICP monitoring years ago, while some have argued against the need for such an approach 11).

Data suggest that there is a small, yet statistically significant, survival advantage in patients who have ICP monitors and a GCS score of 3. However, all patients with ICP monitors experienced longer hospital length of stay, longer intensive care unit stay, and more ventilator days compared with those without ICP monitors. A prospective observational study would be helpful to accurately define the population for whom ICP monitoring is advantageous 12).

EVD and IP measurements of ICP were highly correlated, although intermittent EVD ICP measurements may fail to identify ICP events when continuously draining cerebrospinal fluid. In institutions that use continuous cerebrospinal fluid diversion as a therapy, a two-monitor system may be valuable for accomplishing monitoring and therapeutic goals 13).

In the search for a reliable, cooperation-independent, noninvasive alternative to invasive intracranial pressure 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 intracranial pressure estimates. Fanelli et al. 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.

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.

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 > 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.

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 14).

Noninvasive quantitative measures of the peripapillary retinal structure by SD-OCT were correlated with invasively measured intracranial pressure. Optical coherence tomographic parameters showed promise as surrogate, noninvasive measures of intracranial pressure, outperforming other conventional clinical measures. Spectral-domain OCT of the peripapillary region has the potential to advance current treatment paradigms for elevated intracranial pressure in children 15).



Adelson PD, Bratton SL, Carney NA, Chesnut RM, du Coudray HE, Goldstein B, Kochanek PM, Miller HC, Partington MP, Selden NR, Warden CR, Wright DW; American Association for Surgery of Trauma; Child Neurology Society; International Society for Pediatric Neurosurgery; International Trauma Anesthesia and Critical Care Society; Society of Critical Care Medicine; World Federation of Pediatric Intensive and Critical Care Societies. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents. Chapter 19. The role of anti-seizure prophylaxis following severe pediatric traumatic brain injury. Pediatr Crit Care Med. 2003 Jul;4(3 Suppl):S72-5. PubMed PMID: 12847355.

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Barzilay Z, Augarten A, Sagy M, Shahar E, Yahav Y, Boichis H. Variables affecting outcome from severe brain injury in children. Intensive Care Med. 1988;14(4):417–421.

Chambers IR, Treadwell L, Mendelow AD. Determination of threshold levels of cerebral perfusion pressure and intracranial pressure in severe head injury by using receiver-operating characteristic curves: an observational study in 291 patients. J Neurosurg. 2001;94(3):412–416.

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Kasoff SS, Lansen TA, Holder D, Filippo JS. Aggressive physiologic monitoring of pediatric head trauma patients with elevated intracranial pressure. Pediatr Neurosci. 1988;14(5):241–249.

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Salim A, Hannon M, Brown C, Hadjizacharia P, Backhus L, Teixeira PG, Chan LS, Ford H. Intracranial pressure monitoring in severe isolated pediatric blunt head trauma. Am Surg. 2008 Nov;74(11):1088-93. PubMed PMID: 19062667.

Alkhoury F, Kyriakides TC. Intracranial Pressure Monitoring in Children With Severe Traumatic Brain Injury: National Trauma Data Bank-Based Review of Outcomes. JAMA Surg. 2014 Jun;149(6):544-8. doi: 10.1001/jamasurg.2013.4329. PubMed PMID: 24789426.

Exo J, Kochanek PM, Adelson PD, Greene S, Clark RS, Bayir H, Wisniewski SR, Bell MJ. Intracranial pressure-monitoring systems in children with traumatic brain injury: combining therapeutic and diagnostic tools. Pediatr Crit Care Med. 2011 Sep;12(5):560-5. doi: 10.1097/PCC.0b013e3181e8b3ee. PubMed PMID: 20625341; PubMed Central PMCID: PMC3670608.

Fanelli A, Vonberg FW, LaRovere KL, Walsh BK, Smith ER, Robinson S, Tasker RC, Heldt T. Fully automated, real-time, calibration-free, continuous noninvasive estimation of intracranial pressure in children. J Neurosurg Pediatr. 2019 Aug 23:1-11. doi: 10.3171/2019.5.PEDS19178. [Epub ahead of print] PubMed PMID: 31443086.

Swanson JW, Aleman TS, Xu W, Ying GS, Pan W, Liu GT, Lang SS, Heuer GG, Storm PB, Bartlett SP, Katowitz WR, Taylor JA. Evaluation of Optical Coherence Tomography to Detect Elevated Intracranial Pressure in Children. JAMA Ophthalmol. 2017 Apr 1;135(4):320-328. doi: 10.1001/jamaophthalmol.2017.0025. PubMed PMID: 28241164; PubMed Central PMCID: PMC5470406.
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