In the normal situation without the presence of pathology, intracranial pressure (ICP) may undergo rises without any physiopathological effect on the brain. Abrupt increases in ICP may occur after sneezing, coughing and straining without any consequences or neurological impairment. However, in the presence of pathology, rises in ICP may become symptomatic and alter brain physiology.
Within the cranium, since the brain is enclosed in a non-expandable case of bone, any change in the volume of one component (brain tissue, blood, CSF) will necessitate compensatory changes in the volume of one or more of the other components in order for the ICP to remain constant. This is expressed as the Monroe-Kelly doctrine.
The brain uses compensatory mechanisms in order to maintain the ICP constant, which are shunting CSF to the spinal subarachnoid space, increasing CSF absorption, decreasing CSF production or shunting venous blood out of the skull. When these mechanisms are not present or exhausted, there will be a sharp rise in the ICP, leading to herniation of brain tissue downward through the Foramen Magnum. As this happens, blood will cease to flow to the brain and brain tissue hypoxia, ischaemia, infarction, necrosis and death will occur. ICP is a reflection of the relationship between alterations in the craniospinal volume and the ability of the craniospinal axis to accommodate added volume. The relationship between volume and pressure in the intracranial space may be expressed as a pressure-volume curve. Standard physiologic nomenclature defines compliance as the change in volume for a given change in pressure ΔV/ΔP), reflecting both the viscoelastic properties, or stiffness, of the intracranial content and the functioning of compensatory mechanisms available to reduce ICP at any given point on the curve.
The decision to monitor ICP is usually made on a clinical and imaging basis; the clinical situation must provide indications, and radiologic imaging studies must corroborate the indications and confirm the safety of the proposed monitor placement. Imaging techniques also provide warning of situations, such as mass lesions of the temporal lobes, in which ICP measurement may fail to reflect the progression of pathologic events.
Measuring the ICP enables to determine the interventions that are necessary to prevent secondary brain injury, which can lead to brain damage and death. If the intracranial pressure increases above 20-25 mmHg, therapeutic interventions, medical and/or surgical, should be initiated. This is because as the ICP increases, it gradually becomes more difficult for the blood to be pumped to the head to perfuse the brain tissue.
Monitoring techniques have grown safer, less expensive and more sophisticated, and our understanding of intracranial pathophysiology has improved. There are several different ways to measure the pressure within the compartment of the skull. These methods may include subdural, parenchymal or intraventricular pressure monitoring. They may be used to monitor the pressure or to drain CSF. Intraparenchymal catheters used to measure ICP are relatively precise and associated with a low complication rate.
A recent study has demonstrated that bedside insertion of an ICP monitor performed by intensive care physicians is a safe procedure, with a complication rate comparable to other series published by neurosurgeons [1-4]. The overall morbidity rate is comparable to, or even lower than, that caused by central vein catheterization. The most modern and common Cranial Access Kits available are disposable intracranial procedural kits, which contain the basic items used during each step of the cranial access procedure.
- Double edge razor, iodine, gauze sponges
Cranial access preparation
- Ruler, marking pen, fenestrated drape, tensoplast barrier
- Xylocaine (1%, 1 : 200 000 epinephrine), syringe and 25-G needle, scalpel
- Periostium scraper, drill (hand operated or battery powered), 2.7 mm drill bit with stop and wrench
- 5.8 mm drill bit with stop and wrench (for ventricolostomy), bone wax, mosquito forceps
- 2.0 silk suture, 3.0 nylon suture, needle holder, serrated, Adson forceps, Adson forceps with teeth, suture scissors
The skin is shaven and prepped with an iodine-based antiseptic solution. The right side is preferred for the insertion of the bolt screw, since the motor cortex is most commonly found on the left; however, this latter side can be used if access is not possible on the right.
Landmark for incision and bolt insertion
The landmark for the skin incision called ‘Kocher's point' should be found (Fig. 1).
The bolt should be placed in the mid-pupillary line (2-4 cm or two fingerbreadths lateral to the midline) and 2-3 cm anterior to the coronal suture (fingerbreadth in front of the coronal suture, mid-pupillary line). The coronal suture can sometimes be palpated; however, if that is not possible, its location can be estimated by following a line up midway between the lateral canthus and the external auditory meatus.
Sterile drapes should be placed to define the extent of the surgical field.
Skin infiltration using 0.5% lidocaine with 1 : 200 000 epinephrine from a syringe with a 25-G needle.
The surgeon should stand at the head of the bed and should wear a face mask and cap as well as sterile gloves and a gown.
Supine with head facing directly forward and held in place with tape. The head of the bed can be elevated as desired.
The patient should be sufficiently sedated prior to beginning the insertion.
Should help hold the head of the patient during drilling. The assistant is not sterile during the procedure although he/she is required to put on sterile gloves to help the surgeon in the surgical (draped) field.
The skin and subcutaneous tissues should be incised (antero-posterior for roughly 2-3 cm in length) until reaching the periosteum. After the incision and retraction of the skin and subcutaneous tissue, the periosteum should be scraped off with an appropriate tool in order expose the skull.
- Divaricate with the mosquito forceps.
- Select the appropriate drill bit. Use the 2.7 mm drill bit for subdural, intraparenchymal and bolt procedures (the 5.8 mm drill bit for ventriculostomy procedures).
- Place the drill bit into the chuck.
While holding the drill handle in place, tighten the drill bit by turning the chuck anticlockwise. Loosen the drill guide using the appropriate hex wrench. Carefully slide the drill guide towards the tip of the drill bit until the determined skull depth is reached.
Warning: The drill guide will not stop the drill. The guide is designed only to provide the neurosurgeon with a marker for drilling depth. The guide must be adjusted to the proper position prior to drilling. Tighten the drill guide in place with the hex wrench. Begin the drilling procedure.
Cranial tissue layers
Several layers of soft and bony tissue must be crossed to reach the intracranial space from the skin surface. The layers, from superficial to deep, are the scalp (skin, connective tissue-dense, aponeurosis, loose connective tissue pericranium), bone, dura, arachnoid, pia and brain.
After stripping away the periosteum, a hole is drilled. The hole is then irrigated with sterile saline and an 18-G spinal needle is used to open the dura in a cruciate fashion. The drilling procedure must be performed with the drill held within 10° of the perpendicular position to the incision site. Exercise caution when perforating the dura so as to avoid damage to the underlying structures (Fig. 2).
Following opening of the dura, the bolt is screwed manually into the skull. This will be approximately 2-3 mm for the neonatal age group, 3-5 mm for the paediatric age group and 5 mm to 1 cm for adults. If desired, the spacer can be used as a guide. The stylet provided in the kit is inserted through the bolt and dura to clear the passage for the transducer-tipped catheter. Screwing in the skull bolt at an angle may result in a fracture of the device. The stylet is then removed after the bolt has been screwed in, after which the bolt should be filled with saline. It may be important to check if CSF leaks out of the bolt and, if so, at what pressure.
Zeroing the catheter transducer tip
The most commonly used ICP monitoring devices are provided with catheters that have the transducer at one extremity (must remain sterile), and the socket that is to be attached to the monitor itself at the other. The zeroing is performed by simply holding the transducer tip in air zeroing on the monitor, after which the transducer is inserted inside the bolt and the screw tightened. The ICP value can then be read. Again, it is important to note the first ICP reading after the catheter is inserted. A few seconds may be necessary until this first value can be read with accuracy.
After the bolt is secured in place, the intracranial pressure bolt site is covered with a sterile Kerlex and the patient is observed in the ICU so as to avoid accidental pulling of the bolt.
Bleeding may occur at the site of the drill hole, originating from the scalp, bone, dural or cerebral areas.
It is essential to maintain strict aseptic technique during craniotomy procedures. Care should be exercised when applying sutures to ventricular catheters and over-tightening of bolt screws could result in catheter occlusion or breakage.
As mentioned previously, in the literature complications have been found to be extremely rare, and in some reports they were less in % than those encountered when inserting a central venous line. The most clinically relevant complications were meningitis, local infection, intracranial haematoma and device failure.
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monitoring performed by intensive care physicians. A 5-year experience. Intensive Care Med
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monitors by non-neurosurgeons. Am Surg
3. Ko KM, Conforti A. Training protocol for intracranial pressure
monitor placement by non neurosurgeons: 5-Year experience. J Trauma Injury Infect Crit Care
4. Latronico N, Marino R, Rasulo FA, Stefini R, Schembari M, Chandiani A. Bedside burr hole for intracranial pressure
monitoring performed by anaesthetist intensive-care physicians: extending the practice to the entire team. Minerva Anestesiol