The normal intracranial pressure (ICP) ranges within 7 to 15 mm Hg while in the vertical position, it does not exceed −15 mm Hg. Overnight sleep monitoring is considered the “gold standard” in conscious patients.
Typically, ICP lowering therapy initiates when ICP is greater than 20 to 25 mm Hg.
Refractory elevated ICP reduces cerebral perfusion pressure (CPP), thereby accounting for cerebral ischemia and initiating herniation syndromes that eventually lead to death.
ICP-guided therapy has been the cornerstone in managing severe traumatic brain injury.
Thus, ICP monitoring allows for the judicious use of interventions with a defined target point and thereby avoiding potentially harmful aggressive treatment.
Application of multimodal monitoring (MMM) in conjunction with adherence to Brain Trauma Foundation (BTF) guidelines during patient care bundle approaches have shown the positive outcomes as well as the minimized cost of acute care.
The guidelines (Level II recommendations) implemented by the BTF for the managing severe Traumatic Brain Injury (TBI) recommend an ICP monitor in:
ICP monitoring is also recommended (Level III recommendations) in :
Contraindications for placement of an invasive mode of ICP monitoring include cases of :
Currently, intraventricular monitor with the aid of ventriculostomy or the use of intraparenchymal strain gauge or fiber optic monitors is the recommendation for ICP monitoring. So appropriate monitoring devices should be available. There needs to be utmost care for strict adherence to aseptic conditions during these procedures. There also is paramount importance of implementing algorithmic management guidelines in all patients with invasive ICP monitors for safeguarding all monitor sets.
A composite healthcare team comprising of:
The patient and next of kin/relatives should receive a thorough explanation regarding the indication for the procedure and the risks involved before the procedure, and written consent obtained.
Strict adherence to aseptic guidelines is a cornerstone in preventing the risk of infection and prophylactic antibiotic needs to be administered just at the beginning of the procedure.
Meticulous technique is vital in minimizing procedure-related complications.
The patient should be well sedated, assuring patency of his airway, and local anesthetic administered at the allocated point of ventriculostomy or insertion of ICP monitoring devices.
The insertion of the device is aided with the placement of either a burr hole or a twist drill technique. Kocher's point is the choice for the ventriculostomy, which is 3 cm lateral of midline and 1 cm anterior to the coronal suture. Other points of ventricular puncture include Keen's point, Dandy's point, and Frazier's point.
Basic equipment sets should include the following :
Stringent analysis of the pressure and pulse amplitude of ICP waveforms is favored contrary to its assessment from the height of the CSF column.
The pulse component of the waveform shows three peaks
With decreasing brain compliance, there will be an increase in waveform amplitude, rising P2 above P1 and P3, rounding of waveform and appearance of plateau waves and Lundberg B and A waves.
Ventricular catheters represent a “global” ICP with minimal chances of drift and influence from pressure gradients between parenchyma and ventricular system.
It is the most reliable method of achieving maximum accuracy with minimal expense. There are added therapeutic benefits of cerebrospinal fluid (CSF) drainage, instilling medications like antibiotics and thrombolytic agents.
Strain gauge or fiber optic based systems inserted into the ventricles or brain parenchymas are more accurate compared to fluid-coupled or pneumatic devices.
Parenchymal monitors are easier to insert in cases of midline shift or malignant brain swelling, with no risks of blockage by hemorrhage or debris.
However, they cannot be re-calibrated in vivo, only measure a localized pressure and have drift issues in long term usage.
The current noninvasive techniques are simply not accurate enough to replace traditional invasive techniques.
CT and MRI images provide only provide a single point snapshot picture. Pulsatility index from Transcranial Doppler (TCD), Tympanic membrane displacement (otoacoustic emissions), Near-infrared spectroscopy as well as Optic nerve sheath diameter (ONSD) assessments have a study error margin of +/- 10 to 15 mm Hg with high inter-rater variability.
An underlying assumption is that an ICP reading at one point is equivocal, and the mirror reflects the global pressure throughout the brain. However, it is confounded by the pressure gradient within the ventricular system as well as the parenchyma brain interface. The accuracy and precision over time (drift), and in vivo calibration of different ICP measurement system is also a concern.
Difficulties in catheter placement in cases of severe brain edema with slit ventricles can complicate intraventricular monitoring of ICP.
Complications of ventricular catheter-based ICP monitoring
ICP rather than being a simple numeric value or a mere threshold is an epiphenomenon of multispectral interlinking brain processes such as its compliance, hemodynamic strain, metabolic dysfunction, etc.
ICP management based on the stair step-type linear algorithmic protocol has significant flaws. Assumptions that patterns and sequelae of ICP increment are the same; the only pivotal difference being their pattern of response or their resistance to them is rather empirical.
Therefore a tiered system approach has been formulated in managing refractory ICP through the implementation of “individualized ICP threshold” aided by waveform analysis through correlation coefficient (R) between the pulse pulsation amplitude and mean ICP (RAP) or pressure-volume index (PVI).
Higher RAP (correlation coefficient (R) between the pulse pulsation amplitude and mean ICP) values indicate less compliance.
As the brain ICP increases, RAP gradually falls below zero signifying exhaustion of autoregulatory capacity. There will be a right shift of the pressure-volume curve and thereby further increase in cerebral perfusion pressure leads to the paradoxical passive collapse of the arterioles.
Pressure-volume index (PVI) or the apparent volume implementing a ten-fold ICP increase is 25 to 30 ml. ICP waveform analysis also reveals a gradual increase in the amplitude of P2 becoming greater than P1.
Similarly, pathological Lundberg waves also appear.
Among various armamentarium to calculate autoregulation (AR) such as brain tissue oxygen (PbtO), near-infrared spectroscopy (NIRS), thermal dilution regional CBF (td-rCBF), microdialysis, PbtO2 has the greatest evidence base for signifying the same.
Benchmark Evidence from South American Trials: Treatment of Intracranial Pressure (BEST TRIP) trial concluded that ICP-based management showed no significant favorable outcome compared with patients management under the guidance with serial CTs and clinical examination. There were various limitations of the study, foremost being a lack of specific recommendations regarding diagnosis, inclusion criteria, and governing of patterns of interventions. There was also methodological heterogeneity as well as the bias relating to missing data.There were also issues on clinical equipoise and concerns regarding the generalized validity of the results, which also provoked concerns regarding the ethical standards of the study. There are deleterious effects of the ICP-reducing therapy itself such prolonged hyperventilation reducing cerebral blood flow (CBF) and might propagating cerebral ischemia. Similarly, fluids and vasopressors for maintaining CPP greater than or equal to 70 mm Hg carry the risk of acute lung injury (ALI).
To ensure better clinical outcome and to prioritize patient safety by minimizing complications, there need to be mandatory patient safety checklists to be implemented by the health care team involved in the process. Following guidelines has to be adhered to:
Monitoring of intracranial pressure requires an interprofessional team approach, including physicians, specialists, and specialty-trained nurses, all collaborating across disciplines to achieve optimal patient results. [Level V]
The advantage of the ventricular monitoring device is the facility for egress of CSF in cases of a sustained rise in ICP (greater than or equal to 20 mm Hg for 5 minutes or longer), but the disadvantage is that simultaneous monitoring, as well as CSF drainage, is not possible. The amount of CSF to be drained can be guided as per the recommended target ICP (commonly set as 10 mm Hg) or can be aided with the visual guidance in the improvement in the ICP waveform analysis obtained from the concurrent application of intraparenchymal monitors or through clinical neurological examination. Care always needs to be taken in preventing paradoxical upward transtentorial herniation due to over jealous drainage of CSF.
Surgical decompression is the usual recommendation there is a refractory rise in ICP and clinical deterioration despite the stepwise escalation in the management tiers aimed to counteract the same such as sedation, neuromuscular blockade, mild hyperventilation, hyperosmolar therapies, and barbiturate coma.
The ICP monitoring devices get removed once the ICP is normalized with sustained or improved clinical neurology (motor score at least 5) for at least 48 to 72 hours without the use of any interventions. In cases of ventricular devices, the EVD can undergo clamping, or more ideally gradual increment in its height (training of the EVD) is attained to watch for any clinical deterioration in the patient for at least 48 hours.
Strict aseptic precautions and care also need to be implemented during its removal as well. The head end should be lowered down to prevent the risk of pneumocephalus and pneumoventricle. The tip of the catheter can be sent for bacteriological analysis in cases of persisting fever with features of meningitis. The wound is closed in layers to minimize the risk of CSF leak and infection. The patient should be strictly monitored for any signs of clinical deterioration for at least 24 hours with all preparations made for emergency placement of a new EVD or ICP monitor devices.
The nurses involved in patient care should monitor the following-
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