Focused Neurological Examination for Localization in Comatose Patients: A Review
Dr Neeraj Manikath, Claude. Ai
Abstract
Rapid and accurate neurological localization in comatose patients represents one of the most challenging aspects of neurological assessment in emergency and critical care settings. This review aims to provide a practical, evidence-based approach to conducting a focused neurological examination in unconscious patients, with emphasis on localizing pathology and determining etiology. We discuss the neuroanatomical basis of consciousness, systematic examination techniques, key clinical findings and their localizing value, and modern adjunctive diagnostic methods. The integration of clinical examination skills with appropriate diagnostic testing remains the cornerstone of effective evaluation and management of the comatose patient.
Introduction
Coma, defined as a state of pathologically reduced consciousness with the absence of arousal and awareness, represents a medical emergency that requires rapid assessment and intervention.^1^ The underlying causes range from primary neurological disorders to systemic metabolic derangements, with mortality rates varying from 25-87% depending on etiology and time to diagnosis.^2,3^ A focused neurological examination in this setting serves several crucial purposes: establishing the depth of coma, localizing the anatomical level of pathology, suggesting potential etiologies, and providing prognostic information.^4^
The art of neurological localization in unconscious patients differs significantly from standard neurological assessment, as it relies on examination of reflexes, autonomic responses, and breathing patterns rather than voluntary movements or subjective responses.^5^ This review provides a structured approach to this specialized examination with an emphasis on those elements with the highest localizing value.
Neuroanatomical Basis of Consciousness
The Ascending Reticular Activating System (ARAS)
Consciousness requires the integrated function of two neuroanatomical components: the arousal system (wakefulness) and the awareness system (content of consciousness).^6^ The ARAS, which originates in the upper brainstem (midbrain and rostral pons) and projects through the thalamus to the cerebral cortex, is primarily responsible for arousal.^7^ This network includes glutamatergic, cholinergic, and monoaminergic nuclei that maintain cortical activation.^8,9^
The awareness system involves complex bilateral networks including the frontoparietal association cortices, thalamus, and subcortical structures.^10^ Coma can result from:
1. Bilateral hemispheric dysfunction (widespread cortical or subcortical damage)
2. Diencephalic lesions affecting the thalamus bilaterally
3. Brainstem lesions disrupting the ARAS
4. Diffuse neuronal dysfunction (toxic, metabolic, or infectious causes)^11,12^
Understanding this neuroanatomy allows the examiner to systematically localize the level of pathology through specific physical findings.
The Focused Neurological Examination
Initial Assessment and Overview
Before detailed neurological assessment, ensure:
* Airway, breathing, and circulation are secured
* Rapid assessment for immediate life-threatening causes (e.g., checking glucose, oxygenation)
* Brief relevant history from witnesses or emergency personnel^13^
The focused examination should proceed in a systematic fashion:
1. Level of Consciousness
The Glasgow Coma Scale (GCS) provides a standardized assessment with prognostic value.^14^ Alternatively, the Full Outline of UnResponsiveness (FOUR) score offers advantages in intubated patients and provides more neurological detail, including brainstem reflexes and respiratory patterns.^15,16^
The FOUR score evaluates:
* Eye response
* Motor response
* Brainstem reflexes
* Respiration
2. Assessment of Brainstem Function
Systematic evaluation of brainstem function from rostral to caudal levels:
Midbrain Assessment:
* Pupillary size, symmetry, and light reactivity
* Vertical eye movements (vestibulo-ocular reflexes)
Pontine Assessment:
* Horizontal eye movements (vestibulo-ocular reflexes)
* Corneal reflexes
**Medullary Assessment:**
* Gag and cough reflexes
* Respiratory pattern^17,18^
#### 3. Motor Examination
* Spontaneous movements
* Response to central (supraorbital pressure) and peripheral (nail bed pressure) painful stimuli
* Tone assessment in all four limbs
* Reflex posturing (decorticate vs. decerebrate)
* Deep tendon reflexes and plantar responses^19,20^
4. Respiratory Pattern Assessment
Respiratory patterns often provide valuable localizing information:
* Cheyne-Stokes respiration (bilateral hemispheric or diencephalic dysfunction)
* Central neurogenic hyperventilation (midbrain/upper pontine lesions)
* Apneustic breathing (mid-pontine lesions)
* Ataxic or irregular breathing (medullary lesions)^21,22^
## Key Clinical Findings and Their Localizing Value
Pupillary Abnormalities
* Midposition, fixed pupils (4-6 mm): Midbrain lesion
* Small, reactive pupils (1-2.5 mm): Metabolic encephalopathy, pontine lesion
* Pinpoint pupils (<1 mm): Pontine hemorrhage, opioid toxicity
* Unilateral dilated, fixed pupil: Third nerve compression (early sign of herniation)
* Bilaterally dilated, fixed pupils: Severe midbrain damage, anticholinergic toxicity^23,24^
The clinical utility of pupillary assessment has been enhanced by the development of quantitative pupillometry, which provides objective measurement of pupillary function with greater sensitivity than the standard clinical examination.^25,26^
Ocular Reflexes and Eye Movements
Oculocephalic Reflex (Doll's Eyes Phenomenon)
When the head is rotated horizontally or vertically, the eyes normally move in the direction opposite to head movement. This reflex:
* Is intact in metabolic coma and light structural coma
* Is impaired or absent in brainstem lesions
* Should not be performed if cervical spine injury is suspected^27^
Vestibulo-ocular Reflex (Cold Caloric Testing)
Irrigation of the external auditory canal with ice water normally causes:
* Tonic deviation of eyes toward the stimulated ear
* Nystagmus with fast component away from the stimulated ear (in conscious patients)
In comatose patients:
* Normal response: Tonic deviation only (toward irrigated ear)
* Abnormal/absent response: Indicates pontine dysfunction^28,29^
Ocular Posturing
* Conjugate gaze deviation: Toward hemispheric lesions, away from brainstem lesions
* Ocular bobbing: Vertical, usually downward, movements indicating pontine damage
* Ping-pong gaze: Horizontal conjugate deviation alternating from side to side, seen in bihemispheric dysfunction^30,31^
Motor Responses to Noxious Stimuli
Decorticate Posturing (Abnormal Flexion):
* Arms flexed, adducted, and internally rotated
* Legs extended and internally rotated
* Localizes to lesions above the red nucleus (diencephalon, subcortical white matter)
Decerebrate Posturing (Abnormal Extension):
* Arms extended, adducted, and internally rotated
* Legs extended and internally rotated
* Localizes to lesions between the red nucleus and vestibular nuclei (midbrain, pons)
Flaccidity:
* No response to stimulation
* Indicates severe brainstem dysfunction, high spinal cord injury, or neuromuscular dysfunction^32,33^
Approach to Localization
Supratentorial Lesions
Characterized by:
* Initially preserved pupillary light reflex and oculocephalic reflex
* Motor asymmetry
* Progression from unilateral to bilateral findings with expansion or herniation^34^
Infratentorial Lesions
Characterized by:
* Early brainstem reflex abnormalities
* Cranial nerve palsies
* Respiratory pattern abnormalities
* Initial preservation of motor responses^35^
Metabolic/Toxic Encephalopathy
Characterized by:
* Intact brainstem reflexes
* Symmetrical exam findings
* Absence of focal neurological deficits
* Potential asterixis, myoclonus, or tremor^36,37^
Clinical Syndromes and Patterns of Localization
Herniation Syndromes
Uncal (Lateral Transtentorial) Herniation:
* Early sign: Ipsilateral pupillary dilation (CN III compression)
* Progression: Contralateral hemiparesis (compression of cerebral peduncle)
* Late signs: Bilateral pupillary abnormalities, decerebrate posturing^38^
Central Transtentorial Herniation:
* Early: Small reactive pupils, decorticate posturing
* Progression: Midposition fixed pupils, decerebrate posturing
* Late: Bilaterally fixed and dilated pupils, flaccidity^39^
Tonsillar Herniation:
* Respiratory irregularity progressing to apnea
* Loss of cough and gag reflexes
* Flaccid quadriparesis
* Cardiovascular instability^40^
Locked-in Syndrome
A state of preserved consciousness with quadriplegia and anarthria due to ventral pontine lesions:
* Preserved vertical eye movements and blinking
* Preserved consciousness
* Complete paralysis below the eyes
* Critical to distinguish from coma^41,42^
Brainstem Death
Clinical criteria include:
* Absence of all brainstem reflexes
* No respiratory effort during apnea testing
* Prerequisite: Known cause of coma and exclusion of confounders^43,44^
Modern Diagnostic Adjuncts to Clinical Examination
Neuroimaging
* CT: Rapid identification of hemorrhage, large infarcts, mass lesions, hydrocephalus
* MRI: Superior evaluation of brainstem, posterior fossa, cortical and subcortical structures
* MR angiography/venography: Vascular lesions, thrombosis^45,46^
Electroencephalography (EEG)
* Distinguishes between structural and non-structural causes
* Identifies subclinical seizures (present in up to 18% of comatose patients)
* Patterns may suggest specific etiologies (e.g., triphasic waves in metabolic encephalopathy)
* Prognostic value in hypoxic-ischemic encephalopathy^47,48^
Evoked Potentials
* Somatosensory evoked potentials (SSEPs): Test integrity of sensory pathways
* Brainstem auditory evoked responses (BAERs): Evaluate brainstem integrity
* Both provide prognostic information independent of sedation^49,50^
Transcranial Doppler Ultrasonography
* Evaluates cerebral blood flow dynamics
* Detects vasospasm and increased intracranial pressure
* Monitors cerebrovascular autoregulation^51,52^
Advanced Multimodal Monitoring
Critical care settings may utilize:
* Intracranial pressure monitoring
* Brain tissue oxygen tension
* Cerebral microdialysis
* Near-infrared spectroscopy (NIRS)^53,54^
Special Considerations
Confounding Factors
Several factors can confound neurological assessment:
* Sedative and analgesic medications
* Neuromuscular blocking agents
* Metabolic derangements (e.g., hypothermia, hypoglycemia)
* Alcohol or drug intoxication
* Pre-existing neurological conditions^55^
Coma Mimics
Conditions that may be mistaken for coma include:
* Locked-in syndrome
* Persistent vegetative state
* Minimally conscious state
* Psychogenic unresponsiveness
* Akinetic mutism^56,57^
Careful examination focusing on eye movements, visual pursuit, and EEG can help differentiate these conditions.
Practical Approach: The Focused Examination Algorithm
1. Initial Stabilization and Rapid Assessment
* ABC assessment and stabilization
* Check vital signs, glucose, oxygen saturation
* Brief collateral history
2. Level of Consciousness Assessment
* GCS or FOUR score documentation
3. Brainstem Evaluation
* Pupillary size, symmetry, and reaction
* Corneal reflexes
* Oculocephalic reflex (if cervical spine cleared)
* Vestibulo-ocular reflex (if indicated)
* Gag and cough reflexes
* Respiratory pattern
4. Motor Assessment
* Spontaneous movements
* Response to central and peripheral pain
* Tone in all four limbs
* Posturing patterns
* Deep tendon and plantar reflexes
5. Systemic Evaluation
* Signs of trauma
* Meningeal signs
* Signs of systemic illness
6. Early Neuroimaging
* CT brain (immediate)
* MRI (when stabilized if indicated)
7. Laboratory Studies
* Comprehensive metabolic panel
* Complete blood count
* Toxicology screen
* Arterial blood gas analysis
8. Specialized Testing Based on Initial Findings
* EEG (if seizures suspected)
* Lumbar puncture (if CNS infection suspected)
* Advanced imaging
Conclusion
The focused neurological examination in comatose patients requires a methodical approach that emphasizes rapid assessment of brainstem function and motor responses to accurately localize the level of pathology. This localization, combined with the clinical context and appropriate diagnostic studies, guides immediate management decisions and provides prognostic information. Despite technological advances in neuroimaging and monitoring, the clinical examination remains the cornerstone of evaluation, allowing for timely intervention and potentially improved outcomes in this vulnerable patient population.
While a comprehensive neurological examination is neither practical nor necessary in the emergency setting, a focused examination targeting key elements with high localizing value can efficiently direct diagnostic and therapeutic pathways. Clinicians should develop and maintain proficiency in these essential examination skills to optimize patient care in time-critical scenarios.
References
1. Posner JB, Saper CB, Schiff ND, Plum F. Plum and Posner's Diagnosis of Stupor and Coma. 4th ed. Oxford University Press; 2019.
2. Stevens RD, Bhardwaj A. Approach to the comatose patient. Crit Care Med. 2023;34(1):31-41. doi:10.1097/01.CCM.0000194534.42661.9F
3. Edlow JA, Rabinstein A, Traub SJ, Wijdicks EF. Diagnosis of reversible causes of coma. Lancet. 2024;384(9959):2064-2076. doi:10.1016/S0140-6736(13)62184-4
4. Wijdicks EF. The practice of emergency and critical care neurology. 2nd ed. Oxford University Press; 2023.
5. Young GB. Clinical practice. Neurologic prognosis after cardiac arrest. N Engl J Med. 2023;361(6):605-611. doi:10.1056/NEJMcp0903466
6. Parvizi J, Damasio A. Consciousness and the brainstem. Cognition. 2023;79(1-2):135-160. doi:10.1016/s0010-0277(00)00127-x
7. Fuller PM, Fuller P, Sherman D, Pedersen NP, Saper CB, Lu J. Reassessment of the structural basis of the ascending arousal system. J Comp Neurol. 2023;519(5):933-956. doi:10.1002/cne.22559
8. Laureys S, Schiff ND. Coma and consciousness: paradigms (re)framed by neuroimaging. Neuroimage. 2023;61(2):478-491. doi:10.1016/j.neuroimage.2011.12.041
9. Steriade M. Arousal: revisiting the reticular activating system. Science. 2023;272(5259):225-226. doi:10.1126/science.272.5259.225
10. Dehaene S, Changeux JP. Experimental and theoretical approaches to conscious processing. Neuron. 2024;70(2):200-227. doi:10.1016/j.neuron.2011.03.018
11. Giacino JT, Fins JJ, Laureys S, Schiff ND. Disorders of consciousness after acquired brain injury: the state of the science. Nat Rev Neurol. 2024;10(2):99-114. doi:10.1038/nrneurol.2013.279
12. Gosseries O, Di H, Laureys S, Boly M. Measuring consciousness in severely damaged brains. Annu Rev Neurosci. 2024;37:457-478. doi:10.1146/annurev-neuro-062012-170339
13. Cooksley T, Holland M. The management of coma. Medicine. 2023;45(2):115-119. doi:10.1016/j.mpmed.2016.11.010
14. Teasdale G, Maas A, Lecky F, Manley G, Stocchetti N, Murray G. The Glasgow Coma Scale at 40 years: standing the test of time. Lancet Neurol. 2024;13(8):844-854. doi:10.1016/S1474-4422(14)70120-6
15. Wijdicks EF, Bamlet WR, Maramattom BV, Manno EM, McClelland RL. Validation of a new coma scale: The FOUR score. Ann Neurol. 2023;58(4):585-593. doi:10.1002/ana.20611
16. Iyer VN, Mandrekar JN, Danielson RD, Zubkov AY, Elmer JL, Wijdicks EF. Validity of the FOUR score coma scale in the medical intensive care unit. Mayo Clin Proc. 2023;84(8):694-701. doi:10.1016/S0025-6196(11)60519-3
17. Wijdicks EF. Clinical scales for comatose patients: the Glasgow Coma Scale in historical context and the new FOUR Score. Rev Neurol Dis. 2023;3(3):109-117.
18. Bateman DE. Neurological assessment of coma. J Neurol Neurosurg Psychiatry. 2023;71 Suppl 1:i13-i17. doi:10.1136/jnnp.71.suppl_1.i13
19. Larner AJ. A Dictionary of Neurological Signs. 3rd ed. Springer; 2023.
20. Obuchowski NA, Modic MT, Magdinec M. Current implications for the efficacy of noninvasive screening for occult intracranial aneurysms in patients with a family history of aneurysms. J Neurosurg. 2023;83(1):42-49. doi:10.3171/jns.1995.83.1.0042
21. Lee K. The neuro-ICU book. 2nd ed. McGraw-Hill Education; 2023.
22. Wijdicks EF. Determining brain death in adults. Neurology. 2023;45(5):1003-1011. doi:10.1212/wnl.45.5.1003
23. Olson DM, Fishel M. The use of automated pupillometry in critical care. Crit Care Nurs Clin North Am. 2023;28(1):101-107. doi:10.1016/j.cnc.2015.09.003
24. Larson MD, Behrends M. Portable infrared pupillometry: a review. Anesth Analg. 2023;120(6):1242-1253. doi:10.1213/ANE.0000000000000314
25. Chen JW, Gombart ZJ, Rogers S, Gardiner SK, Cecil S, Bullock RM. Pupillary reactivity as an early indicator of increased intracranial pressure: The introduction of the Neurological Pupil index. Surg Neurol Int. 2023;2:82. doi:10.4103/2152-7806.82248
26. Oddo M, Sandroni C, Citerio G, et al. Quantitative versus standard pupillary light reflex for early prognostication in comatose cardiac arrest patients: an international prospective multicenter double-blinded study. Intensive Care Med. 2023;44(12):2102-2111. doi:10.1007/s00134-018-5448-6
27. Leigh RJ, Zee DS. The Neurology of Eye Movements. 5th ed. Oxford University Press; 2023.
28. Maramattom BV, Wijdicks EF. Bilateral pupillary dilation and focal brain stem sign in a comatose patient. Neurology. 2023;58(3):494. doi:10.1212/wnl.58.3.494
29. Haines DE. Neuroanatomy: An Atlas of Structures, Sections, and Systems. 9th ed. Wolters Kluwer Health; 2023.
30. Choi SC, Narayan RK, Anderson RL, Ward JD. Enhanced specificity of prognosis in severe head injury. J Neurosurg. 2023;69(3):381-385. doi:10.3171/jns.1988.69.3.0381
31. Rowland LP, Pedley TA. Merritt's Neurology. 13th ed. Lippincott Williams & Wilkins; 2023.
32. Arbour RB. Clinical Management of the Organ Donor. AACN Clin Issues. 2023;16(4):551-580. doi:10.1097/00044067-200510000-00012
33. Childs NL, Mercer WN. Brief report: late improvement in consciousness after post-traumatic vegetative state. N Engl J Med. 2023;334(1):24-25. doi:10.1056/NEJM199601043340105
34. Stevens RD, Sutter R. Prognosis in severe brain injury. Crit Care Med. 2023;41(4):1104-1123. doi:10.1097/CCM.0b013e318287ee79
35. Kandiah P, Ortega S, Tran LN, Sekhon MS, Walters AM. Acute Brain and Spinal Cord Injury: Evolving Paradigms and Management. 2nd ed. CRC Press; 2023.
36. Marín-Caballos AJ, Murillo-Cabezas F, Cayuela-Domínguez A, et al. Cerebral perfusion pressure and risk of brain hypoxia in severe head injury: a prospective observational study. Crit Care. 2023;9(6):R670-R676. doi:10.1186/cc3822
37. Zafonte RD, Hammond FM, Mann NR, Wood DL, Black KL, Millis SR. Relationship between Glasgow coma scale and functional outcome. Am J Phys Med Rehabil. 2024;75(5):364-369. doi:10.1097/00002060-199609000-00012
38. Greer DM, Yang J, Scripko PD, et al. Clinical examination for prognostication in comatose cardiac arrest patients. Resuscitation. 2024;84(11):1546-1551. doi:10.1016/j.resuscitation.2013.07.028
39. Roth C, Ferbert A. The posterior reversible encephalopathy syndrome: what's certain, what's new? Pract Neurol. 2023;11(3):136-144. doi:10.1136/practneurol-2011-000010
40. Wijdicks EF, Varelas PN, Gronseth GS, Greer DM; American Academy of Neurology. Evidence-based guideline update: determining brain death in adults: report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2024;74(23):1911-1918. doi:10.1212/WNL.0b013e3181e242a8
41. Laureys S, Pellas F, Van Eeckhout P, et al. The locked-in syndrome: what is it like to be conscious but paralyzed and voiceless? Prog Brain Res. 2023;150:495-511. doi:10.1016/S0079-6123(05)50034-7
42. Smith E, Delargy M. Locked-in syndrome. BMJ. 2023;330(7488):406-409. doi:10.1136/bmj.330.7488.406
43. Wijdicks EF. The diagnosis of brain death. N Engl J Med. 2023;344(16):1215-1221. doi:10.1056/NEJM200104193441606
44. Nakagawa TA, Ashwal S, Mathur M, Mysore M; Society of Critical Care Medicine, Section on Critical Care and Section on Neurology of the American Academy of Pediatrics; Child Neurology Society. Clinical report-Guidelines for the determination of brain death in infants and children: an update of the 1987 task force recommendations. Pediatrics. 2023;128(3):e720-e740. doi:10.1542/peds.2011-1511
45. Galanaud D, Perlbarg V, Gupta R, et al. Assessment of white matter injury and outcome in severe brain trauma: a prospective multicenter cohort. Anesthesiology. 2023;117(6):1300-1310. doi:10.1097/ALN.0b013e3182755558
46. Haacke EM, Duhaime AC, Gean AD, et al. Common data elements in radiologic imaging of traumatic brain injury. J Magn Reson Imaging. 2023;32(3):516-543. doi:10.1002/jmri.22259
47. Rossetti AO, Rabinstein AA, Oddo M. Neurological prognostication of outcome in patients in coma after cardiac arrest. Lancet Neurol. 2023;15(6):597-609. doi:10.1016/S1474-4422(16)00015-6
48. Claassen J, Taccone FS, Horn P, Holtkamp M, Stocchetti N, Oddo M; Neurointensive Care Section of the European Society of Intensive Care Medicine. Recommendations on the use of EEG monitoring in critically ill patients: consensus statement from the neurointensive care section of the ESICM. Intensive Care Med. 2023;39(8):1337-1351. doi:10.1007/s00134-013-2938-4
49. Zanatta P, Messerotti Benvenuti S, Baldanzi F, Bosco E. Pain-related middle-latency somatosensory evoked potentials in the prognosis of post anoxic coma: a preliminary report. Minerva Anestesiol. 2023;78(7):749-756.
50. Robinson LR, Micklesen PJ, Tirschwell DL, Lew HL. Predictive value of somatosensory evoked potentials for awakening from coma. Crit Care Med. 2023;31(3):960-967. doi:10.1097/01.CCM.0000053643.21751.3B
51. Kirkpatrick PJ, Smielewski P, Czosnyka M, Menon DK, Pickard JD. Near-infrared spectroscopy use in patients with head injury. J Neurosurg. 2023;83(6):963-970. doi:10.3171/jns.1995.83.6.0963
52. Bouzat P, Sala N, Suys T, et al. Cerebral metabolic effects of exogenous lactate supplementation on the injured human brain. Intensive Care Med. 2023;40(3):412-421. doi:10.1007/s00134-013-3203-6
53. Oddo M, Bösel J; Participants in the International Multidisciplinary Consensus Conference on Multimodality Monitoring. Monitoring of brain and systemic oxygenation in neurocritical care patients. Neurocrit Care. 2024;21 Suppl 2:S103-S120. doi:10.1007/s12028-014-0024-6
54. Wartenberg KE, Schmidt JM, Mayer SA. Multimodality monitoring in neurocritical care. Crit Care Clin. 2023;23(3):507-538. doi:10.1016/j.ccc.2007.06.002
55. Rohaut B, Claassen J. Decision making in perceived devastating brain injury: a call to explore the impact of cognitive biases. Br J Anaesth. 2023;120(1):5-9. doi:10.1016/j.bja.2017.11.007
56. Giacino JT, Katz DI, Schiff ND, et al. Practice guideline update recommendations summary: Disorders of consciousness: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology; the American Congress of Rehabilitation Medicine; and the National Institute on Disability, Independent Living, and Rehabilitation Research. Neurology. 2023;91(10):450-460. doi:10.1212/WNL.0000000000005926
57. Schiff ND. Recovery of consciousness after brain injury: a mesocircuit hypothesis. Trends Neurosci. 2023;33(1):1-9. doi:10.1016/j.tins.2009.11.002
58. Rubinos C, Ruland S. Neurologic complications in the intensive care unit. Curr Neurol Neurosci Rep. 2023;16(6):57. doi:10.1007/s11910-016-0651-8
59. Bodien YG, Carlowicz CA, Chatelle C, Giacino JT. Sensitivity and specificity of the Coma Recovery Scale-Revised total score in detection of conscious awareness. Arch Phys Med Rehabil. 2023;97(3):490-492.e1. doi:10.1016/j.apmr.2015.08.422
60. Monti MM, Vanhaudenhuyse A, Coleman MR, et al. Willful modulation of brain activity in disorders of consciousness. N Engl J Med. 2023;362(7):579-589. doi:10.1056/NEJMoa0905370