Increased intracranial pressure Notes

NOTES NOTES INCREASED INTRACRANIAL PRESSURE GENERALLY, WHAT IS IT? PATHOLOGY & CAUSES ▪ Abnormal ↑ intracranial pressure ▫ Normal: 10–15mmHg (adults); 5–20mmHg (infants) Monro-Kellie hypothesis ▪ Fixed cranial volume in skull ▪ Three main components ▫ Cerebrospinal fluid (CSF), blood, brain tissue Intracranial compliance (ICC) ▪ Changes in intracranial content volume and changes in intracranial pressure (ICP) ▪ Slight ↑ volume → compensatory mechanisms → slight ↑ ICP ▫ CSF displacement into thecal sac ▫ Venoconstriction/extracranial drainage → ↓ cerebral venous blood volume ▪ Drastic volume increase → ↓ ICC → ↑ ICP ↑ ICP ▪ → compression of blood vessels → ↓ brain perfusion → brain ischemia → edema → ↑↑ ICP ▫ Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP)−ICP ▫ ↓ CPP → ↑ systemic blood pressure/ vasodilation → ↑ cerebral blood volume → ↑ ICP → ↓ ↓ CPP Nerve compression ▪ → impaired brain function 628 OSMOSIS.ORG CAUSES ▪ Cerebral edema (e.g. acute hypoxic ischemic encephalopathy, trauma) ▪ Intracranial space occupying lesion (e.g. tumor, aneurysm, hemorrhage, etc.) ▪ ↑ CSF production ▪ Obstructive hydrocephalus ▪ ↓ CSF absorption ▪ Venous outflow obstruction ▪ Idiopathic intracranial hypertension SIGNS & SYMPTOMS ▪ Deteriorating level of consciousness (early sign) ▪ Headache ▪ Nausea ▪ Vomiting ▪ Ocular palsies ▪ Mydriasis (dilated pupils) ▪ Papilledema ▪ Dyspnea ▪ Back pain ▪ Decorticate/decerebrate posturing DIAGNOSIS DIAGNOSTIC IMAGING CT scan ▪ Mass lesions, midline shift, basilar cisterns effacement

Chapter 81 Increased Intracranial Pressure OTHER DIAGNOSTICS ▪ ICP monitoring ▫ Intraventricular catheter (gold standard) ▫ Intraparenchymal fiberoptic catheter TREATMENT MEDICATIONS ▪ Sedation (propofol), osmotic diuretics, prophylactic anticonvulsants SURGERY ▪ Surgical removal of space-occupying lesion ▪ Decompressive craniectomy ▪ Extraventricular drain (EVD) OTHER INTERVENTIONS ▪ Target → ICP < 20mmHg, MAP > 90mmHg, CPP > 65mmHg ▪ Elevate head (30°) → maximize venous outflow ▪ Airway, breathing, and circulation (ABCs), maintain adequate oxygenation ▪ Treat shock (if applicable): hypertonic saline (HTS) (e.g 7.5%) to treat edema; HTS maintains high serum osmolality → reduces cerebral edema (> 280 mOsm/L); ↑ serum osmolarity prevents intravascular fluid leakage to brain tissue; ↑ serum osmolarity draws excess water from brain tissue → ↓ ICP ▪ Hyperventilation BRAIN HERNIATION osms.it/brain-herniation site (craniectomy) → decortication of herniated gyrus PATHOLOGY & CAUSES ▪ Brain tissue displacement: through skull opening or dural fold ▪ Damages associated with herniated section TYPES Supratentorial herniation ▪ Cingulate/subfalcine ▫ Gyrus forced under falx cerebri → cerebral artery compression → cerebral ischemia then edema → ↑ ICP ▪ Uncal/transtentorial ▫ Cranial nerve (CN) compression in nerves III, IV, posterior cerebral artery → ipsilateral visual cortex ischemia → homonymous hemianopsia ▪ Central ▫ Temporal lobes squeezed through notch in tentorium cerebelli → basilar artery stretched → tearing, bleeding (Duret hemorrhage) ▪ Transcalvarial ▫ Brain herniates through fracture/surgical Infratentorial herniation ▪ Tonsillar ▫ Cerebellar tonsils herniate in foramen magnum → brainstem, spinal cord compression CAUSES ▪ ↑ ICP SIGNS & SYMPTOMS ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Decorticate/decerebrate posturing Seizures ↓ level of consciousness, coma Glasgow Coma Scale (GCS) 3–5 Mydriasis (dilated pupils) Irregular/slow pulse Respiratory/cardiac arrest Loss of brainstem reflexes (blinking, gagging, pupillary reflex) OSMOSIS.ORG 629

DIAGNOSIS DIAGNOSTIC IMAGING Head CT scan/MRI ▪ Depending on the cause, results show mass lesions (e.g. tumor, aneurysm, infarction, hemorrhage etc.) and subsequent displacement of the brain away from the mass, depending on localization TREATMENT MEDICATIONS Osmotic diuretics Paracetamol (manage fever) Sedation/paralytic agents ↓ metabolism → ↓ O2 consumption + ↓ CO2 production → no systemic vasodilation → ↓ cerebral blood volume → ↓ ICP ▪ Prophylactic anticonvulsants ▪ ▪ ▪ ▪ Figure 81.1 An MRI scan of the head in the coronal plane demonstrating herniation of the cerebellar tonsils secondary to hypoxic brain injury. SURGERY ▪ Decompressive craniectomy OTHER INTERVENTIONS ▪ HTS boluses → support circulation ▫ HTS → ↑ serum osmolarity → draw excess water from brain tissue → ↓ ICP ▪ Hyperventilation ▫ Helps avoid ↑ PaCO2 or hypoxemia → systemic vasodilation → ↑ ↑ cerebral blood volume → ↑ ICP Figure 81.2 A CT scan of the head in the axial plane demonstrating a right sided acute subdural hemorrhage. The pressure effect has pushed the medial aspect of the right cerebral hemisphere underneath the falx cerebri, known as sub-falcine herniation. 630 OSMOSIS.ORG

Chapter 81 Increased Intracranial Pressure IDIOPATHIC INTRACRANIAL HYPERTENSION (IIH) osms.it/idiopathic-intracranial-hypertension TREATMENT PATHOLOGY & CAUSES ▪ AKA pseudotumor cerebri ▪ Chronic ↑ ICP, no obvious cause CAUSES ▪ ↑ ICP → CN II compression → visual impairment RISK FACTORS ▪ Overweight, biologically female, fertile individuals SIGNS & SYMPTOMS ▪ Papilledema ▪ Visual field loss ▪ CN palsies, typically CN VI (long intracranial course) ▪ Headache ▪ Pulsatile tinnitus ▪ Photopsia (seeing flashes of light) ▪ Diplopia (double vision) ▪ Temporary visual disturbance ▪ Retrobulbar pain ▪ Back pain ▪ Goal: treat symptoms/preserve vision MEDICATIONS ▪ Carbonic anhydrase inhibitor (acetazolamide) → ↓ CSF production ▫ Contraindication: pregnancy ▪ Loop diuretics (furosemide) → ↓ papilledema and ↓ mean CSF pressure ▫ Contraindication: pregnancy SURGERY ▪ Optic nerve sheath fenestration (ONSF) OTHER INTERVENTIONS ▪ Weight loss DIAGNOSIS OTHER DIAGNOSTICS ▪ Headache & papilledema with ▫ No secondary cause of ↑ ICP: normal neuroimaging (MRI, contrast CT scan), normal CSF composition ▫ No malignant hypertension: mimics IIH ▫ Lumbar puncture: ↑ opening pressure Figure 81.3 A retinal photograph demonstrating an expanded optic disc caused by intracranial hypertension. OSMOSIS.ORG 631