Neurotrauma: Increased Intracranial Pressure and

Brain Tissue Oxygenation - 2 Nursing CEs

Course Objectives

Upon completion of this course, the student will be able to:

·        Differentiate between an Epidural and Subdural Bleed

·        Discuss the different stages of a Diffuse Axonal Injury

·        List 2 types of intracranial monitoring devices

·        State 3 risk factors of intracranial monitoring devices

·        Describe the 3 major components of the brain

·        Be able to calculate Cerebral Perfusion Pressure

·        Describe 2 interventions to increase Brain Tissue Oxygen Delivery

·        Describe 2 interventions to decrease Brain Tissue Oxygen Consumption

Traumatic Brain Injury

Traumatic brain injury (TBI) is a non-degenerative, non-congenital insult to the brain from an external mechanical force, possibly leading to permanent or temporary impairments of cognitive, physical and psychosocial functions with an associated diminished or altered state of consciousness.

Primary vs. Secondary Brain Injury

Primary injury is immediate from bruising, bleeding or penetrating objects. Secondary injury is from either hypoxia or decreased perfusion of the brain. Major causes of secondary injury include: swelling (increased ICP), decreased oxygenation to brain tissue and/or hypotension.

Radiology for Traumatic Brain Injury

The advent of CT scanning has had a huge impact for the treatment for traumatic brain injury. It is rapid, non-invasive and allows identification of surgically treatable lesions as well as diffuse injury. The indications for CT scanning in severe head trauma are not in question unless other injuries prevent this. In most cases all patients will require a CT scan. In general, indications for CT Scan in mild/moderate head injury are:

• Neurological signs
• Decreased level of consciousness
• Mental state difficult to evaluate
  (anesthesia, drugs & alcohol, young children) 

The patient with minimal external signs of injury who is fully awake and alert (GCS of 15) with a normal neurological examination and no symptoms other than headache may not need a CT scan. However they do need close observation for the next 24 hours by reliable observers. Should they require anesthesia for treatment of other injuries they should have a CT scan prior to surgery. 

A Non-contrast CT scan is performed using continuous 5mm slices for the skull base and 10mm slices for the rest of the brain. Bone and brain tissue windows should be examined. For severe brain injury where the patient is intubated, the upper cervical spine should be included in the scan (C2), as plain films are difficult and may miss significant spine injury. 

Epidural (extradural) Hematoma

An Epidural Hematoma occurs when there is a tear in a vascular structure, usually arterial, in the potential space between the dura and the skull. The hematoma strips the dura off the skull vault and appears on CT as a biconvex lesion. Around 75% are associated with skull fractures. If there are no other brain injuries the patient may remain conscious until the hematoma expands to such a point that brain structures become compressed, which causes rapid deterioration after this point. Surgical evacuation via a craniotomy is necessary and if performed early, before damage to brain structures occurs, can have an excellent outcome. Signs and Symptoms: severe headache, drowsiness, confusion, nausea and vomiting, dizziness, enlarged pupils and weakness.

Subdural Hematoma

Subdural hematoma usually occurs due to disruption of bridging veins between the brain and the dura. Blood can track around the brain and between the leaves of the falx. The presence of a subdural hematoma is an indication of underlying brain injury. An acute subdural is associated with a worse outcome than an epidural hematoma. On CT the subdural hematoma appears as a crescentic extra-axial collection. While surgical evacuation is usually indicated, the underlying brain injury will dictate the subsequent clinical course and functional outcome. Signs and symptoms depend on acute or chronic appearance.

Cerebral Contusions

Parenchymal (cerebral) contusions are a manifestation of direct injury to brain tissue. Contusions appear as bright signals within brain tissue, usually in areas abutting the skull or in areas near the zone of impact. Contusions are more a reflection of underlying brain injury than clinically significant themselves and unless they are large, easily accessible and exert a significant mass effect surgical evacuation will not be of benefit. Multiple pinpoint contusions are a sign of diffuse brain injury. Signs and Symptoms can be from mild headache to a more severe onset of symptoms up to an including coma.

Diffuse Injury

Diffuse injury (or diffuse axonal injury) is due to acceleration and deceleration occurring at different rates across the brain as shear forces are applied during the moment of impact. There is a diffuse, non-focal pattern of injury. CT appearances vary, from a mild appearance with loss of grey-white differentiation, effaced ventricles and a small amounts of intra-ventricular blood, to a more severe picture with multiple contusions, diffuse swelling with loss of the basilar cisterns and brain stem involvement. 

The initial CT scan appearance often underestimates the actual brain injury and the patients clinical condition may be much worse than the CT scan would suggest. Diffuse injury evolves and becomes more prominent on CT during the next 48-72 hours after injury. A diffuse injury grading system has been developed based on compression of the basal cisterns and the degree of midline shift. 

 ICP/CPP and Brain Tissue Oxygenation

Increased intracranial pressure is a condition in which the pressure of the cerebrospinal fluid or brain matter within the skull exceeds the upper limits for normal pressure. Increased intracranial pressure is almost always indicative of severe medical problems. The pressure itself can be responsible for further damage to the central nervous system by decreasing blood flow to the brain or by causing the brain to herniate (push through) the opening in the back of the skull where the spinal cord is attached. Sudden herniation through the foramen magnum (back of the skull) is fatal. Components found with in the rigid skull include: 

Parenchyma - The essential tissue (Brain in this case) of an organ distinct from its surrounding connective tissue. This is the largest intracranial volume (80%). 

Blood vessel - The volume of blood in the cerebral arteries is an important determinant of intracranial pressure (10%). 

Cerebral Spinal Fluid - CSF is comprised of fluid in the ventricles and subarachnoid spaces and is produced by the choroid plexus.  Approximately 500 ml’s are produced daily (10%). 

The Monroe-Kellie Doctrine simply states that in a non-expandable, non-contractable, freely communicating space, the pressure of the fluid contents and the brain itself, must be directly porportional to eachother in order to maintain a constant pressure. If one of these pressures increases, another must decrease in order to compensate. 

Intracranial Pressure Monitoring

An intracranial pressure monitor is a sensing device placed inside the head that senses the pressure intracranially and sends its measurements to a recording device. 

There are three ways of monitoring intracranial pressure:

1. Intraventricular catheter (a catheter threaded into one of the lateral ventricles of the brain)
2. A subarachnoid screw or bolt (a screw or bolt placed just through the skull in the space between the arachnoid and cerebral cortex)
3. Epidural sensor (a sensor placed into the epidural space beneath the skull) 

The intraventricular catheter is thought to be the most accurate, but if immediate access is necessary, a subarachnoid bolt will probably be used. If there is not a qualified neurosurgeon to place a bolt, then a epidural sensor will probably be used.

To insert an intraventricular catheter a burr hole is drilled through the skull and the catheter is inserted through the brain matter into the lateral ventricle which normally contains cerebrospinal fluid. Not only can the intracranial pressure (ICP) be monitored, but it can be lowered by draining cerebral spinal fluid (CSF) out through the catheter. This catheter may be difficult to place with increased intracranial pressure, since the ventricles change shape under increased pressure and are often quite small secondary to brain expanding around them from injury and swelling. 

A subarachnoid screw or bolt is a hollow screw that is inserted through a hole drilled in the skull and through a hole cut in the dura mater. This is a monitoring device only.

The epidural sensor is placed through a burr hole drilled in the skull, just over the epidural covering. Since the epidural lining is not perforated this procedure is less invasive but it has the disadvantage of not being able to withdraw excess CSF

Note: Normally, the ICP ranges from 1 to 15 mm Hg (millimeters of mercury).

When placing any type of Intracranial Pressure Monitoring System, nursing documentation both pre and post insertion is essential and should include the following:

• Pre-procedure neurological assessment
• Medications given to patient prior to and during procedure
• Conditions under which ICP catheter is inserted
• Type of procedure/catheter placed (reference number, if applicable)
• Catheter location (i.e. right or left, frontal, parietal, or occipital)
• Post-procedure neurological assessment
• Opening pressures
• Calculation of cerebral perfusion pressure (CPP)
• Characteristics of CSF (color, clarity, flow and quantity)/Specimens sent
• If ICP elevated or CPP < 60, what treatment was ordered by MD
• Waveform
• Level of the transducer – foramen of Monro (outer canthus of eye, top of ear, or tragus of ear)
• Condition of the dressing
• HOB position

Risk Factors of Intracranial Pressure Monitoring

• Infection
• Bleeding
• Damage to the brain tissue with residual neurologic effects
• Risks of general anesthesia
• Inability to locate ventricle and accurately place catheter 

Cerebral Perfusion Pressure

Cerebral perfusion pressure (CPP) is defined as the difference between mean arterial and intracranial pressures. Mean arterial pressure is the diastolic pressure plus one third of the pulse pressure (difference between the systolic and diastolic). MAP is thus between systolic and diastolic pressures, nearer diastolic. It is used, as it is the best value to estimate the "amount of pressure" perfusing in the brain:

CPP = MAP – ICP 

Normal cerebral perfusion pressure is 80 mmHg, but when reduced to less than 50 mmHg there is metabolic evidence of ischemia and reduced electrical activity. There have been a number of studies on patients with severe head injuries, which have shown an increase in mortality and poor outcome when CPP falls to less than 70 mmHg for a sustained period. 

In addition to calculating CPP from the ICP and MAP, Jugular Venous Bulb Saturation (SjO2) is another tool that can be used to monitor the adequacy of the cerebral circulation. SjO2 is the oxygen saturation of venous blood in the jugular bulb, which is at the base of the skull. Normal SjO2 =’s 65%-75%. If blood flow to the brain is reduced below a critical point there is a fall in venous saturation. As the flow of blood and delivery of oxygen is reduced, the brain, maintains its oxygen supply by extracting more oxygen from the blood, leading to a fall in venous oxygen saturation. 

Brain Tissue Oxygenation

Cerebral Oxygen Delivery – is the amount of oxygen delivered to the tissue each minute and is a product of flow (Cardiac Output) and arterial oxygen content (CaO2 and Hemoglobin). 

Cerebral Oxygen Consumption – is the amount of oxygen used by the brain. It is the difference between arterial oxygen content (CaO2) perfusing the brain, minus venous oxygen content (CvO2) draining from the brain. 

Note: Normal CaO2 is 20 and normal CvO2 is 13.5 with Hemoglobin of 15g/dl. 

 In order to maintain adequate brain tissue oxygenation, (PbtiO2 > 20 or SjO2 > 55) it is necessary to assure that the proper mechanisms are functioning at optimal levels. These include:

• Adequate oxygenation (Increase FiO2 if necessary
• Hemoglobin (Give PRBC for Hgb/Hct < 30/10)
•  CPP > 70 (Use vasopressors and or fluid if necessary) 

In addition to optimizing the body’s ability to mobilize oxygen, measures must be taken to decrease excessive O2 consumption. These measures include:

• Minimize Stimulation (Avoid vigorous bathing and activity
• Temperature Control (Hyperthermia increase metabolic activity)
• Pain/Sedation Medications (BIS Monitoring)
• Barbituate Coma (Continuous Bedside EEG Monitoring) 

Current Brain Tissue Oxygenation can be monitored using a Licox catheter, which is a multi-lumen catheter system that allows for brain oxygenation and temperature measurement.

References

Bader, M., Littlejohns, L., & March, K. (2003). Brain tissue oxygenation monitoring in severe brain injury II. Critical Care Nurse. 2003. Aug. 23(4), 29-43. Retrieved on December 5, 2006 at:

http://ccn.aacnjournals.org/cgi/content/full/23/4/29

 

Finn, S., RN, BSN, (2003). Traumatic brain injury. Dynamic Nursing Education. Orange California.

 

Hickey, J., V., (2002). The Clinical Practice of Neurological and Neurosurgical Nursing. (5^th ed.) Lippencott. Philadelphia

 

Lynn-McHale Wiegand, D., & Carlson, K. (Ed.). (2005).  AACN Procedure Manual for Critical Care,(5th ed). Philadelphia: Elsevier Saunders, 756-767. Retrieved on December 5, 2006 at:

unchealthcare.org/site/Nursing/nurspractice/protocols/protocols_pdf/protocoli7.pdf

 

Medline Plus Medical encyclopedia: Intracranial pressure monitoring. Retrieved on December 5, 2006 at:

www.nlm.nih.gov

 

National Institute of Neurological Disorders and Stroke. (2008). Traumatic brain injury: hope through research. Retrieved on March 10, 2009 at:

http://www.ninds.nih.gov/disorders/tbi/detail_tbi.htm

 

Seidel, H., M., Ball, J., W., Dains, J., E., & Benedict, G., W., (1999). Mosby’s Guide to Physical Examination (4^th ed.). Mosby. St. Louis MO.

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