• A fundamental understanding of neuroanatomy and physiology is needed.

• Knowledge of aseptic and sterile technique is necessary.

• Proper equipment assembly and setup specific to fiberoptic intracranial pressure monitoring device should be understood.

• Intracranial pressure (ICP) is the pressure exerted by the intracranial contents, brain tissue, blood, and cerebrospinal fluid (CSF) within the cranium. Increased ICP occurs when the intracranial volume exceeds the brain’s ability to compensate for increased volume.^16,18 Increased ICP contributes to secondary neuronal injury.

• The ventricular catheter with external strain gauge transducer is considered the gold standard for ICP monitoring.^3,4 The external ventricular drain (EVD) is considered the most accurate and reliable method of monitoring ICP and ICP waveform and allows for CSF drainage.³ However, the fluid-filled system of the external ventricular catheter has the greatest infection rate^1,2 and hemorrhage rate and requires repeated zeroing and leveling with the anatomic reference point for the foramen of Monro.³

• The parenchymal fiberoptic catheter provides quality ICP monitoring but cannot be rezeroed once inserted, cannot be used for CSF drainage, and is subject to drift, particularly after 5 days.^3,14

• The combination catheter has some of the advantages and disadvantages of both the ventricular catheter with an external strain gauge transducer and the fiberoptic transducer tipped catheter. The combination catheter can only be zeroed before insertion. However, because the transducer is in the tip of the fiberoptic catheter, there is no external strain gauge transducer and therefore no repetitive zeroing and leveling of a transducer with the anatomic reference point for the foramen of Monro. In addition, the combination catheter allows for CSF drainage but still requires attention to the level of the reference point of the drip chamber to the anatomic reference point for the foramen of Monro and setting of the pressure level at the top of the graduated burette (drip chamber) to prevent underdrainage or overdrainage of CSF.¹²

• The anatomic reference point for the foramen of Monro is the external auditory canal.¹¹

• Normal ICP ranges from 0 to 15 mm Hg; sustained ICPs of greater than 20 mm Hg are generally considered neurologic emergencies.¹⁷

• The normal ICP waveform has three or four peaks, with P₁ being of greater amplitude than P₂ and P₂ of greater amplitude than P₃. P₁ is thought to reflect arterial pressure; P₂, P₃, and P₄ (if present) have been described as choroid plexus or venous in origin (see Fig. 88-2).¹⁸ The amplitude of P₂ may exceed P₁ with increased ICP or decreased intracranial compliance (see Fig. 88-3).

• ICP waveform trends include a, b, and c waves. The a waves, also referred to as plateau waves, are associated with ICP values of 50 to 100 mm Hg and last 5 to 20 minutes. The a waves (see Fig. 88-4) are associated with abrupt neurologic deterioration and herniation. The b waves (see Fig. 88-5) with ICP values of 20 to 50 mm Hg, lasting 30 seconds to 2 minutes, may become a waves. The c waves (see Fig. 88-6) may coincide with ICPs as high as 20 mm Hg but are short lasting and without clinical significance.^3,10,18

• Cerebral perfusion pressure (CPP) is a derived mathematic calculation that indirectly reflects the adequacy of cerebral blood flow. The CPP is calculated by subtracting the ICP from the mean arterial pressure (MAP); thus CPP = MAP – ICP. The normal CPP range for adults is approximately 60 to 100 mm Hg, or a mean of 80 mm Hg. The optimal CPP for a given patient and clinical condition is not entirely known. ICP and CPP should be managed concomitantly. According to the Brain Trauma Foundation Guides, an acceptable CPP for an adult with a severe traumatic brain injury (Glasgow Coma Scale [GCS] score of equal to or less than 8) lies between 50 and 70 mm Hg.⁴ Patients with aneurysmal subarachnoid hemorrhage vasospasm may need higher CPPs to maintain adequate perfusion through vasospastic cerebral blood vessels. Patients with strokes, aneurysmal subarachnoid hemorrhage, or other neurologic injuries may require higher or individualized CPP parameters reflective of the neuropathology and brain perfusion needs. Research continues regarding the relationship between cerebral blood flow and CPP.

• ICP and CPP must be considered together in management of the patient.

• Cerebral autoregulation is the intrinsic ability of the cerebral vessels to constrict and dilate as needed to maintain adequate cerebral perfusion. Cerebral autoregulation is impaired with brain injury, and the cerebral blood flow becomes passively dependent on the systemic blood flow. The cerebral blood vessels are no longer able to react to maintain CPP in response to a change in blood pressure.

• Sustained ICP elevations of 20 mm Hg or greater necessitate immediate reporting and intervention. ICP waveform changes that indicate loss of cerebral compliance or cerebral autoregulation should be reported immediately.^11,16

• ICP monitoring is indicated for the following:

 Traumatic brain injury with a GCS score less than 8 and abnormal computed tomographic (CT) scan or normal CT scan with two of the following: hypotension, age more than 40 years, and posturing⁴

 Intracranial hemorrhage¹⁸

 Aneurysmal subarachnoid hemorrhage¹⁸

 Hydrocephalus¹⁸

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