Physiology
Cranial Vault
- Cranial Vault Volume: 1400-1700 mL (this volume is fixed in an individual)
- Intracranial Components
- 80%: Brain
- 10%: Cerebrospinal Fluid (CSF)
- 10%: Blood
- Monro-Kellie Doctrine: intracranial pressure is a function of the compliance of each component of the intracranial compartment
- Based on Rigid Structure of the Skull and Inability of Cranial Vault Volume to Change: increased volume in any of the three intracranial components may result in intracranial hypertension
- Relationship Between Intracranial Volume and Intracranial Pressure is Exponential: with initial increase in volume, pressure rises only slightly, but when the buffering capacity of the system is exceeded, intracanial pressure rises rapidly -> this explains the rapid clinical deterioration that may occur in the setting of a traumatic intracranial hematoma
- Normal Intracranial Pressure (Adult): <15 mm Hg
- Intracranial Pressure Fluctuates with Cardiac and Respiratory Cycles
- Transient Increases in ICP May Occur During Coughing/Sneezing
- Pathologically Increased ICP is Defined as Sustained ICP >20 mm Hg
- ICP is Normally Lower in Children (and May Be Subatmospheric in Newborns)
Cerebral Blood Flow
- Hypercapnia and Hypoxia Increase Cerebral Blood Flow
Cerebral Perfusion Pressure (CPP)
- Cerebral Perfusion Pressure = MAP-ICP
Cerebrospinal Fluid (CSF) Dynamics
- Cerebrospinal Fluid is Produced in the Choroid Plexus and Other Locations Within the Central Nervous System: CSF is produced at a rate of 20 mL/hr
- Cerebrospinal Fluid is Normally Absorbed by the Arachnoid Granulations into the Venous System
Etiology of Increased Intracranial Pressure (by Predominant Mechanism)
Cerebral Edema
- Anoxic/Ischemic Encephalopathy (see Hypoxic-Ischemic Brain Injury, [[Hypoxic-Ischemic Brain Injury]])
- Physiology
- Cerebral Edema
- Physiology
- Cerebral Venous Thrombosis
- Physiology
- Altered Cerebrospinal Fluid Circulation
- Cerebral Edema
- Physiology
- During the Course of Therapy for Diabetic Ketoacidosis/Hyperosmolar Hyperglycemic State (see Diabetic Ketoacidosis and Hyperosmolar Hyperglycemic State, [[Diabetic Ketoacidosis and Hyperosmolar Hyperglycemic State]])
- Physiology
- Cerebral Edema
- Physiology
- Fulminant Hepatic Failure (FHF) (see Fulminant Hepatic Failure, [[Fulminant Hepatic Failure]])
- Etiology
- Acetaminophen Intoxication (see Acetaminophen, [[Acetaminophen]])
- Toxic Mushroom Intoxication (see Toxic Mushrooms, [[Toxic Mushrooms]])
- Physiology
- Cerebral Edema
- Cerebral Vasodilation
- Etiology
- High-Altitude Cerebral Edema (HACE) (see High-Altitude Cerebral Edema, [[High-Altitude Cerebral Edema]])
- Physiology
- Cerebral Edema
- Physiology
- Hypertensive Encephalopathy (see Hypertension, [[Hypertension]])
- Physiology
- Cerebral Edema
- Physiology
- Hyponatremia (see Hyponatremia, [[Hyponatremia]])
- Physiology
- Cerebral Edema
- Physiology
- Large Intracerebral Hemorrhage (see Intracerebral Hemorrhage, [[Intracerebral Hemorrhage]])
- Physiology
- Cerebral Edema
- Mass Effect
- Physiology
- Large Ischemic Cerebrovascular Accident (CVA) (see Ischemic Cerebrovascular Accident, [[Ischemic Cerebrovascular Accident]])
- Physiology
- Cerebral Edema
- Physiology
- Malaria (see Malaria, [[Malaria]])
- Physiology
- Cerebral Edema
- Physiology
- Meningitis (see Meningitis, [[Meningitis]])
- Physiology
- Cerebral Edema
- Physiology
- Subarachnoid Hemorrhage (SAH) (see Subarachnoid Hemorrhage, [[Subarachnoid Hemorrhage]])
- Physiology
- Altered Cerebrospinal Fluid Circulation
- Cerebral Edema
- Mass Effect
- Physiology
- Traumatic Brain Injury (TBI) (see Traumatic Brain Injury, [[Traumatic Brain Injury]])
- Physiology
- Cerebral Edema
- Mass Effect
- Cerebral Vasodilation
- Physiology
Cerebral Vasodilation
- Fever (see Fever, [[Fever]])
- Physiology
- Cerebral Vasodilation
- Physiology
- Hypoxemia (see Hypoxemia, [[Hypoxemia]])
- Physiology
- Cerebral Vasodilation
- Physiology
- Hypercapnia (see Hypercapnia, [[Hypercapnia]]): hypercapnia causes cerebral vasodilation
- Physiology
- Cerebral Vasodilation
- Physiology
- Hypotension (see Hypotension, [[Hypotension]])
- Physiology
- Cerebral Vasodilation
- Physiology
- Seizures (see Seizures, [[Seizures]])
- Physiology
- Cerebral Vasodilation
- Physiology
Intracranial Mass Lesion
- Brain Abscess (see Brain Abscess, [[Brain Abscess]])
- Physiology
- Cerebral Edema
- Mass Effect
- Physiology
- Brain Tumor
- Physiology
- Cerebral Edema
- Mass Effect
- Physiology
Decreased Cerebrospinal Fluid (CSF) Absorption
- Post-Bacterial Meningitis Arachnoid Granulation Adhesions (see Meningitis, [[Meningitis]])
Increased Cerebrospinal Fluid (CSF) Production
- Choroid Plexus Papilloma
Obstructive Hydrocephalus (see Hydrocephalus, [[Hydrocephalus]])
- xxxx
Increased Arterial Blood Pressure/Hypertension
- Bladder Distention
- Pain
Obstruction of Venous Outflow from Brain
- Abdominal Compartment Syndrome (see Abdominal Compartment Syndrome, [[Abdominal Compartment Syndrome]])
- Physiology: increased venous pressure
- Jugular Vein Compression
- Physiology
- Neck Position
- Restrictive Neck Dressing
- Physiology
- Neck Surgery
- Pneumothorax (see Pneumothorax, [[Pneumothorax]])
- Physiology: increased venous pressure
- Sagittal Sinus Thrombosis (see Cerebral Venous Thrombosis, [[Cerebral Venous Thrombosis]])
- Other Venous Sinus Thrombosis
- Patient-Ventilator Dyssynchrony
- Physiology: increased venous pressure
Idiopathic Intracranial Hypertension (Pseudotumor Cerebri) (see Pseudotumor Cerebri, [[Pseudotumor Cerebri]])
- Physiology
- Altered Cerebrospinal Fluid Circulation: probable mechanism
Transiently Increased Intracranial Pressure
- Coughing (see Cough, [[Cough]])
- Sneezing
- Valsalva Maneuver (see Valsalva Maneuver, [[Valsalva Maneuver]])
Other
- Craniosynostosis
- Physiology: inadequate skull growth
- Reye’s Syndrome
- Physiology: vasodilation
- Succinylcholine (see Succinylcholine, [[Succinylcholine]])
- Physiology: xxx
Diagnosis
Head CT (see Head Computed Tomography, [[Head Computed Tomography]])
- xxx
Brain MRI (see Brain Magnetic Resonance Imaging, [[Brain Magnetic Resonance Imaging]])
- xxx
External Ventricular Drain (EVD) (see External Ventricular Drain, [[External Ventricular Drain]])
- Indications for Monitoring in the Setting of Traumatic Brain Injury (Guidelines for the Management of Severe Traumatic Brain Injury, 2007) [MEDLINE]
- All Salvageable Patients with Severe TBI, GCS 3-8 After Resuscitation, and an Abnormal CT Scan (Hematoma, Contusion, Edema, Herniation, Compressed Basal Cisterns) (Level II Recommendation)
- Severe TBI with Normal CT Scan with Two or More Criteria at Admission: Age >40 y/o, Unilateral or Bilateral Motor Posturing, SBP <90 mm Hg (Level III Recommendation)
- Contraindications
- Coagulopathy (see Coagulopathy, [[Coagulopathy]]): relative contraindication
- Thrombocytopenia with Platelets <100k (see Thrombocytopenia, [[Thrombocytopenia]]): relative contraindication
- Adverse Effects/Complications
- Intracerebral Hemorrhage: rate of hemorrhage with ventricular catheter is 1-7%
- Rate of Hemorrhage for Intraparenchymal Monitor is Less Than That of Ventricular Catheter
- Hemorrhages Rarely Require Surgical Evacuation
- Infection/Ventriculitis (see Central Nervous System Device Infection, [[Central Nervous System Device Infection]])
- Culture of Tip of External Ventricular Drains May Demonstrate Bacterial Colonization: however, the rate of invasive infection is lower
- Risk of Infection is Higher with Ventricular Catheter (1-27%) Than with Parenchymal Monitor
- Risk Factors for Infection
- Leakage Around the Ventriculostomy Site
- Longer Duration of Catheter Placement
- Presence of Open Skull Fracture with Leakage of Cerebrospinal Fluid
- Intracerebral Hemorrhage: rate of hemorrhage with ventricular catheter is 1-7%
Clinical Manifestations
Neurologic Manifestations
Coma (see Obtundation-Coma, [[Obtundation-Coma]])
- xxx
Brain Herniation
- Routes of Brain Herniation
- Hemisphere is Displaced Medially Against the Falx, Resulting in Falcine Herniation
- Unilateral Pressure Gradient Pushes the Medial Edge of the Temporal Lobe (Uncus) Through the Tentorial Foramen, Resulting in Uncal Herniation
- Third Cranial Nerve and Posterior Cerebral Artery are Compressed -> Unilateral Pupillary Dilation, Lack of Response to Light, and Infarction
- Brainstem is Distorted and Compressed with Early Impairment of Consciousness
- Bilateral Homogeneous Increase in Intracranial Pressure in the Supratentorial SPace Displaces the Brain Downward Through the Tentorial Foramen, Resulting in Transtentorial Herniation
- Brainstem is Compressed and Displaced Downward without Signs of Lateralization -> Bilateral Pupillary Abnormalities
Other Manifestations
- xxx
Management of Increased Intracranial Pressure (ICP)
General Measures
- Avoid Increases in ICP >20-25 cm H2O
- Body Position: keep head at 30 degree elevation
Sedation
Barbiturates (see Barbiturates, [[Barbiturates]])
-
Pharmacology
- Decrease Cerebral Blood Flow: decreasing intracranial pressure
- Decrease Cerebral Metabolism
Propofol (Diprivan) (see Propofol, [[Propofol]])
-
Pharmacology
- Onset: rapid
- Half-Life (with Infusion): 30-60 min
- Longer Half-Life is Observed After Prolonged Infusion, Due to Redistribution from Fat Stores
- However, the Duration of the Clinical Effect is Typically Minutes, as Propofol is Rapidly Distributed into Peripheral Tissues
- Properties
- Amnestic Effect (see Amnesia, [[Amnesia]])
- Anti-Emetic Effect
- Anxiolytic Effect
- Decreases Intracranial Pressure (see Increased Intracranial Pressure, [[Increased Intracranial Pressure]])
- Increases Seizure Threshold
- Sedative Effect
- No Analgesic Effect
- Large Lipid Load: requiring adjustment of enteral/parenteral nutritional support
- Administration
- Dose: 10-60 μg/kg/min
- Decrease Dose in Elderly by 20%
- Slow Administration in Elderly
Other Pharmacologic Interventions
Mannitol (see Mannitol, [[Mannitol]]): indicated for
- Indications
- xxxx
- Pharmacology: osmotic diuretic
- Adverse Effects
- xxxx
Hyperosmolar Fluids
- Hypertonic Saline (see Hypertonic Saline, [[Hypertonic Saline]])
Corticosteroids (see Corticosteroids, [[Corticosteroids]])
- Indications
- xxxx
Respiratory Support
- Mechanical Ventilation (see General Ventilator Management, [[General Ventilator Management]])
- Avoid Hypoxemia (see Hypoxemia, [[Hypoxemia]]): hypoxemia causes cerebral vasodilation
- Avoid Hypercapnia (see Hypercapnia, [[Hypercapnia]]): hypercapnia causes cerebral vasodilation
- Avoid Patient-Ventilator Dyssynchrony
- Treat Airway Obstruction: airway clearance, intubation, etc
Treatment of Cerebral Vasodilation
- Treat Fever (see Fever, [[Fever]])
- Rationale: fever causes cerebral vasodilation
- Standard Therapy
- Treat Hypotension (see Hypotension, [[Hypotension]])
- Standard Therapy
- Treat Seizures (see Seizures, [[Seizures]])
- Rationale: seizures result in cerebral vasodilation
- Agents
- Levatiracetam (Keppra) (see Levatiracetam, [[Levatiracetam]])
Treatment of Increased Arterial Blood Pressure/Hypertension (see Hypertension, [[Hypertension]])
- Treat Bladder Distention
- Foley Catheter (see Foley Catheter, [[Foley Catheter]])
- Treat Pain
- Analgesics
Treatment Increased Venous Pressure
- Neck Repositioning/Removal of Restrictive Neck Dressings
- Treat Abdominal Compartment Syndrome (see Abdominal Compartment Syndrome, [[Abdominal Compartment Syndrome]])
- Exploratory Laparotomy with Decompression
- Treat Abdominal Distention/Ileus
- Nasogastric Tube (see Nasogastric Tube, [[Nasogastric Tube]])
- Treat Pneumothorax (see Pneumothorax, [[Pneumothorax]])
- Chest Tube (see Chest Tube, [[Chest Tube]])
Treatment of Hydrocephalus/Disturbance in Cerebrospinal Fluid Flow (see Hydrocephalus, [[Hydrocephalus]])
- External Ventricular Drain (EVD) (see External Ventricular Drain, [[External Ventricular Drain]])
- Ventriculoperitoneal Shunt (see Ventriculoperitoneal Shunt, [[Ventriculoperitoneal Shunt]])
Treatment of Hyponatremia (see Hyponatremia, [[Hyponatremia]])
- Rationale: hyponatremia causes cerebral edema
- Standard Therapy
Renal Management
- Choice of Intermittent Hemodialysis vs Continuous Venovenous Hemodialysis (CVVHD)
- If Hemodialysis is Required, CVVHD is Preferred Over Intermittent HD, Due to Rapid Solute Changes and Potential for Hypotension with Intermittent HD (Which May Exacerbate Cerebral Ischemia) (see Hemodialysis, [[Hemodialysis]])
Decompressive Craniectomy (see Decompressive Craniectomy, [[Decompressive Craniectomy]])
- Indications
- Cerebral Contusion/Traumatic Brain Injury (see Traumatic Brain Injury, [[Traumatic Brain Injury]])
- Epidural Hematoma (see Epidural Hematoma, [[Epidural Hematoma]])
- Intracerebral Hemorrhage (see Intracerebral Hemorrhage, [[Intracerebral Hemorrhage]])
- Subdural Hematoma (SDH) (see Subdural Hematoma, [[Subdural Hematoma]])
References
- Hypertonic saline solutions in brain injury. Curr Opin Crit Care. 2004;10:126-131
- A comparision of albumin and saline for fluid resuscitation in the intensive care unit. N Engl J Med. 2004;350:2247-2256
- Injury to the cranium. In: Moore EE, Feliciano DV, Mattox KL, eds. Trauma. 5th ed. New York, NY: McGraw-Hill; 2004:385-404
- Effects of 23.4% sodium chloride solution in reducing intracranial pressure in patients with traumatic brain injury: a preliminary study. Neurosurgery. 2005;57(4):727 [MEDLINE]
- The use of hypertonic saline for treating intracranial hypertension after traumatic brain injury. Anesth Analg. 2006;102:1836-1846
- Guidelines for the management of severe traumatic brain injury. J Neurotrauma. 2007;24 Suppl 1:S1-106 [MEDLINE]
- Refractory intracranial hypertension and “second-tier” therapies in traumatic brain injury. Intensive Care Med. 2008;34:461–467 [MEDLINE]
- Sedation for critically ill adults with severe traumatic brain injury: a systematic review of randomized controlled trials. Crit Care Med. 2011 Dec;39(12):2743-51 [MEDLINE]
- Decompressive craniectomy in diffuse traumatic brain injury. N Engl J Med. 2011;364(16):1493 [MEDLINE]
- Hyperosmolar therapy for raised intracranial pressure. N Engl J Med. 2012;367:746–752 [MEDLINE]
- Traumatic intracranial hypertension. N Engl J Med. 2014;370:2121–2130. doi: 10.1056/NEJMra1208708 [MEDLINE]