1Department of Neurosurgery, Keimyung University School of Medicine, Daegu, Korea
2Department of Neurosurgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
© 2026 The Korean Society of Critical Care Medicine
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
FUNDING
None.
ACKNOWLEDGMENTS
None.
AUTHOR CONTRIBUTIONS
Conceptualization: JHK, SL. Data curation: CHK. Visualization: HJ. Writing - original draft: JHK, SL. Writing - review & editing: JHK, CHK, SL. All authors read and agreed to the published version of the manuscript.
| Modality | Principle | Advantage | Limitation | Clinical application |
|---|---|---|---|---|
| Quantitative pupillometry | Measures pupil light reflex parameters (size, velocity, latency, NPi) using an automated device | Noninvasive and portable | May be falsely low in optic nerve/midbrain lesions | Monitoring in patients with unreliable exams |
| Provides objective, standardized assessments | Cannot fully replace direct ICP monitoring | Early detection of neurologic decline | ||
| Useful in sedated/paralyzed patients | Indirect ICP estimation | |||
| Optic nerve sheath diameter | Ultrasound-based measurement of optic nerve sheath dilation in response to raised ICP | Quick and safe bedside tool | Inter-operator variability | ICP screening and follow-up |
| Noninvasive and repeatable | Lack of universal standardization | Alternative when invasive monitoring is contraindicated | ||
| Good sensitivity for elevated ICP | Affected by anatomical variability | |||
| Transcranial Doppler | Doppler ultrasound to assess blood flow velocity in intracranial arteries | Real-time hemodynamic monitoring | Poor acoustic windows in 10%–15% of patients | Vasospasm monitoring after a SAH |
| Bedside and repeatable | Operator-dependent | Blood pressure titration | ||
| Applicable to various neurovascular conditions | Limited continuous monitoring capability | Real-time cerebral blood flow assessment | ||
| Near-infrared spectroscopy | Measures regional cerebral oxygen saturation (rSO₂) using near-infrared light | Continuous oxygenation monitoring | Signal contamination from extracranial tissue | Early ischemia detection |
| Useful in deeply sedated or unstable patients | Limited depth resolution | Intraoperative and acute stroke care | ||
| Early warning for hypoxia | Values must be interpreted contextually | Part of multimodal neuromonitoring | ||
| Electroencephalography | Measures cortical electrical activity; continuous electroencephalography enables real-time monitoring | Functional brain monitoring | Requires trained personnel and interpretation | Seizure/NCSE detection |
| Detects non-convulsive seizures | Affected by sedation/paralytics | Prognostication after brain injury or cardiac arrest | ||
| Prognostic value in comatose patients | Resource-intensive | Monitoring cerebral ischemia |
NPi: Neurological Pupil Index; ICP: intracranial pressure; SAH: subarachnoid hemorrhage; NCSE: nonconvulsive status epilepticus.