Which cranial nerve can be examined at the bedside in an unconscious patient?

Cranial Nerve Examination in Unconscious Patients

In unconscious patients, you can examine cranial nerves II, III, IV, VI, VII, and VIII through brainstem reflexes and pupillary responses, with the pupillary light reflex (CN II and III) and corneal reflex (CN V and VII) being the most clinically useful bedside assessments. 1

Specific Cranial Nerves Testable at the Bedside

CN II and III: Pupillary Light Response

• Assess pupillary size, symmetry, and direct/consensual light reflexes to evaluate both the optic nerve (afferent) and oculomotor nerve (efferent) pathways 1, 2
• Pupillary responses are particularly valuable because they remain testable even during deep sedation or coma 1
• Fixed, dilated pupils historically suggested irreversible brain injury, but this finding can occur after epinephrine administration during CPR and does not absolutely preclude favorable outcomes 1

CN III, IV, and VI: Oculocephalic Reflex (Doll's Eyes)

• Perform oculocephalic testing by rotating the head horizontally and vertically while observing for conjugate eye movements in the opposite direction 1
• This tests the integrity of brainstem pathways involving the oculomotor, trochlear, and abducens nerves 1
• The test is only valid when cervical spine injury has been excluded 1

CN V and VII: Corneal Reflex

• Touch the cornea with a cotton wisp to elicit blinking; the trigeminal nerve provides the afferent limb and the facial nerve provides the efferent limb 1, 2
• This reflex assesses brainstem function at the pontine level 1

CN VII: Facial Symmetry and Grimace Response

• Observe facial symmetry at rest and during noxious stimulation (e.g., supraorbital pressure) to detect facial nerve dysfunction 1, 2
• Asymmetric facial movements suggest unilateral facial nerve or upper motor neuron pathology 2

CN VIII: Oculovestibular Reflex (Cold Caloric Testing)

• Cold water irrigation of the external auditory canal produces nystagmus in intact brainstem pathways, though this requires specialized training and is typically performed by neurologists 1

Cranial Nerves NOT Testable in Unconscious Patients

• CN I (olfactory), CN IX/X (glossopharyngeal/vagus), CN XI (accessory), and CN XII (hypoglossal) require patient cooperation for smell testing, palatal elevation, shoulder shrug, and tongue protrusion, respectively 2
• Motor examination of extremities for spinal cord assessment is "very challenging" in unconscious patients on sedation and paralytics 1

Clinical Algorithm for Serial Assessment

1. Establish baseline neurological assessment immediately before and after any critical intervention (e.g., ECMO cannulation, intubation) 1
2. Perform serial bedside nursing assessments every 1-4 hours based on acute brain injury risk 1
3. Prioritize high-yield tests: pupillary reflexes, corneal reflex, oculocephalic reflex, and facial symmetry during noxious stimulation 2
4. Document "signs of life" such as pupillary light response and increased consciousness, as these correlate with improved neurological outcomes 1

Critical Pitfalls to Avoid

• Do not interpret absent brainstem reflexes as irreversible injury in the immediate post-arrest period or after epinephrine administration 1
• Sedatives and paralytics confound neurological evaluation; consider holding these agents periodically to allow meaningful assessment 1
• Cervical spine clearance is mandatory before performing oculocephalic testing in trauma patients, as forced neck rotation can cause spinal cord injury if instability exists 1
• Daily neurologist assessment improves neurological care when available, though bedside nursing evaluation remains the mainstay 1