5.1 Introduction

An intracranial pressure (ICP) monitor is any device that is utilized to measure ICP. This can be done by direct measurement of the epidural, subdural, intraparenchymal, or intraventricular pressure. The intraparenchymal monitor is the most common device utilized for this purpose and its application will be described in this chapter.

Several intraparenchymal ICP monitor devices are commercially available. The Camino (Natus, Pleasanton, CA, USA) and the Codman Microsensor (DePuy Synthes, West Chester, PA, USA) are two of the more widely used devices. The Camino probe contains a fiber-optic transducer whereas the Microsensor uses a strain gauge to detect electrical conductance. Specific procedural steps described below are most closely applicable to the Camino (Natus, Pleasanton, CA, USA) device.

All ICP monitor systems provide instantaneous measurement of pressure, graphic display of the pressure waveform, and a record of ICP trends over time. This data is typically displayed in mm Hg and is used to guide management of elevated ICP in the setting of trauma, neoplasm, craniosynostosis, liver failure, and idiopathic intracranial hypertension. ▶ Fig. 5.1 demonstrates a schematic representing an ICP monitor setup.

5.2 Relevant Anatomy and Physiology

The intracranial cavity is occupied by three substances, the brain parenchyma, cerebrospinal fluid (CSF), and blood volume. According to the Monro-Kellie Doctrine, expansion of one of these substances must be balanced by reduction in another to maintain a consistent pressure in a closed cranial cavity. ¹ When expansion of one of these substances surpasses what can be effectively displaced by the other two substances, then an increase in ICP occurs. The brain parenchyma exists throughout the cranial cavity. CSF is elaborated by the choroid plexus flows from the lateral ventricles, through the foramen of Monro, into the third ventricle, through the Sylvian aqueduct, into the fourth ventricle, through the foramina of Luschka and Magendie, and into the subarachnoid cisternal spaces around the brain, spinal cord, and spinal nerves. The CSF is reabsorbed from the subarachnoid space into the superior sagittal sinus. The blood exists in the vascular space occupied by the arteries, capillaries, veins, and sinuses. The interdependent relationship of these spaces in a closed cavity creates a continuity of pressure throughout the closed system. With a few notable exceptions in the setting of trapped ventricles, hemispheres, obstructive pathology, and the posterior fossa, the measurement of ICP at one location in the cranial vault can be assumed to represent the pressure throughout the intracranial space. ▶ Fig. 5.2 depicts the Monro-Kellie Doctrine.

5.3 Indications

Disease states in which ICP monitoring may be beneficial include, but are not limited to, trauma, neoplasm, craniosynostosis, liver failure, anoxic injury, and idiopathic intracranial hypertension. By far the most common indication for ICP monitor placement is traumatic brain injury (TBI).

5.4 Contraindications

The following are relative contraindications to insertion of an ICP monitor:

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  Coagulopathy

  
  
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  Thrombocytopenia

  
  
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  Recent antiplatelet therapy

  
  
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  Uremic platelet dysfunction

  
  
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  Recent thrombolytic therapy

  
  
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  Mass lesion obstructing catheter trajectory

  
  
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  Scalp infection

  
  
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  Hydrocephalus (ventricular catheter placement is preferred)