Intracranial Pressure Monitoring

Article Author:
Sunil Munakomi
Article Editor:
Joe M Das
Updated:
9/10/2019 6:14:13 PM
PubMed Link:
Intracranial Pressure Monitoring

Introduction

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.[1]

Typically, ICP lowering therapy initiates when ICP is greater than 20 to 25 mm Hg.[2]

Refractory elevated ICP reduces cerebral perfusion pressure (CPP), thereby accounting for cerebral ischemia and initiating herniation syndromes that eventually lead to death.[3]

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.[4]

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.[5][6]

Indications

The guidelines (Level II recommendations) implemented by the BTF for the managing severe Traumatic Brain Injury (TBI) recommend an ICP monitor in[7]:

  1. Patients with Glasgow Coma Scale (GCS) less than 8
  2. An abnormal computed tomogram (CT) scan of the head
  3. Two or more of the following are present:
  • Age greater than 40 years
  • Unilateral or bilateral motor posturing
  • Systolic blood pressure less than 90 mm Hg

ICP monitoring is also recommended (Level III recommendations) in [8]:

  • Patients with an initial normal CT scan or with minor changes in CT images, but later show features of neurologic worsening or progression on the repeat scan
  • Evidence of brain swelling, e.g., compressed or absent basal cisterns
  • Patients with large bifrontal contusions independent of the neurological condition
  • When sedation interruption to check neurological function is not justified, e.g., respiratory failure from lung contusions and flail chest
  • When the neurological examination is not reliable, e.g., maxillofacial trauma or spinal cord injury
  • A decompressive craniectomy performed as a last resort for intracranial hypertension refractory to medical management
  • Following craniotomy wherein there are relevant risk factors for the propagation of brain edema, e.g., confounding hypoxia, hypotension, pupil abnormalities, midline shift greater than 5 mm

Contraindications

Contraindications for placement of an invasive mode of ICP monitoring include cases of [9]:  

  1. Concurrent use of anticoagulant drugs
  2. Bleeding disorders
  3. Scalp infection
  4. Brain abscess

Equipment

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.

Personnel

A composite healthcare team comprising of:

  • A neurosurgeon
  • A qualified assistant
  • An attending nurse
  • An anesthetist
  • A general duty assistant (GDA)

Preparation

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.[9]

 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.

Technique

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 [9]:

  1. Non-sterile gloves, soap, brush, hand towel, razor, and a marker pen for parts preparation and marking of the site of placement of monitor devices.
  2. For the procedure itself, face mask, sterile gown and gloves, an antiseptic solution, a drape, a local anesthetic agent, a 5-ml syringe, a 15 or 11 number surgical blade, and an ICP-monitoring kit. A drill with a drill bit, a bolt, an ICP sensor, and a transducer as per the methods utilized.  A suture material and a sterile dressing.

Stringent analysis of the pressure and pulse amplitude of ICP waveforms is favored contrary to its assessment from the height of the CSF column.[1]

The pulse component of the waveform shows three peaks

  1. P1 (percussion wave) due to arterial pulsation
  2. P2 (tidal wave) representing brain compliance and
  3. P3 (dicrotic wave) owing to aortic valve closure.

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.

Complications

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.[2][10]

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[8]

  1. Intracranial and tract hemorrhage - 10%
  2. Infection (ventriculitis) - 20%
  3. Technical failure (failure to tap ventricle or misplacement) - 5%
  4. The cost for placing an external ventricular drain (EVD) amounting to around $200 with transducers costing an extra $400 to 600.
  5. Over drainage can lead to aneurysmal rebleed and in cases of hydrocephalus complicate the upward transtentorial herniation.
  6. Kinks and blockage by air, blood, and debris are also frequent, leading to the poor and false recording of the ICP.
  7. There can be localized elevations of ICP due to compartmentalization from mass lesions.

Clinical Significance

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.[8]

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).[1]

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.[1]

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.[8]

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.[11]

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.[12] 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.[4]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.[13] 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).

Enhancing Healthcare Team Outcomes

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:

  • Valid treatment order sheet
  • All reportable limits clearly specified
  • EVD drainage point at a prescribed level with the transducer leveled to the tragus of the ear
  • The EVD column is oscillating
  • Monitoring for normal ICP waveform
  • ICP waveform is pulsatile on the monitor
  • No soakage in the wound site or any junctions within the monitor set
  • Judicious assessment of drained CSF volume
  • Stringent evaluation of the neurological status of the patient
  • Coordination between monitoring specialty trained nurses and clinicians
  • Family education by nursing staff and clinicians; providing strong family support

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]

Nursing Actions and Interventions

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.[14] 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.[14]

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.

Nursing Monitoring

The nurses involved in patient care should monitor the following-

  • Monitor hourly CSF drainage
  • Ensure CSF oscillation inside the tubes
  • Confer no soakage of the wound
  • Ensure the correct height of EVD
  • Zeroing of the EVD height at the level of the foramen of Monro or tragus of the ear
  • Stringent neurological monitoring of the patient
  • Monitor hourly ICP

References

[1] Czosnyka M,Pickard JD, Monitoring and interpretation of intracranial pressure. Journal of neurology, neurosurgery, and psychiatry. 2004 Jun;     [PubMed PMID: 15145991]
[2] Zacchetti L,Magnoni S,Di Corte F,Zanier ER,Stocchetti N, Accuracy of intracranial pressure monitoring: systematic review and meta-analysis. Critical care (London, England). 2015 Dec 2;     [PubMed PMID: 26627204]
[3] Bullock R,Chesnut RM,Clifton G,Ghajar J,Marion DW,Narayan RK,Newell DW,Pitts LH,Rosner MJ,Wilberger JW, Guidelines for the management of severe head injury. Brain Trauma Foundation. European journal of emergency medicine : official journal of the European Society for Emergency Medicine. 1996 Jun;     [PubMed PMID: 9028756]
[4] Su SH,Wang F,Hai J,Liu NT,Yu F,Wu YF,Zhu YH, The effects of intracranial pressure monitoring in patients with traumatic brain injury. PloS one. 2014;     [PubMed PMID: 24586276]
[5] Fakhry SM,Trask AL,Waller MA,Watts DD, Management of brain-injured patients by an evidence-based medicine protocol improves outcomes and decreases hospital charges. The Journal of trauma. 2004 Mar;     [PubMed PMID: 15128118]
[6] Gerber LM,Chiu YL,Carney N,Härtl R,Ghajar J, Marked reduction in mortality in patients with severe traumatic brain injury. Journal of neurosurgery. 2013 Dec;     [PubMed PMID: 24098983]
[7] Bratton SL,Chestnut RM,Ghajar J,McConnell Hammond FF,Harris OA,Hartl R,Manley GT,Nemecek A,Newell DW,Rosenthal G,Schouten J,Shutter L,Timmons SD,Ullman JS,Videtta W,Wilberger JE,Wright DW, Guidelines for the management of severe traumatic brain injury. VI. Indications for intracranial pressure monitoring. Journal of neurotrauma. 2007;     [PubMed PMID: 17511544]
[8] Le Roux P, Intracranial Pressure Monitoring and Management 2016;     [PubMed PMID: 26583172]
[9] Marcus HJ,Wilson MH, VIDEOS IN CLINICAL MEDICINE. Insertion of an Intracranial-Pressure Monitor. The New England journal of medicine. 2015 Nov 26;     [PubMed PMID: 26605942]
[10] Tavakoli S,Peitz G,Ares W,Hafeez S,Grandhi R, Complications of invasive intracranial pressure monitoring devices in neurocritical care. Neurosurgical focus. 2017 Nov;     [PubMed PMID: 29088962]
[11] Tasneem N,Samaniego EA,Pieper C,Leira EC,Adams HP,Hasan D,Ortega-Gutierrez S, Brain Multimodality Monitoring: A New Tool in Neurocritical Care of Comatose Patients. Critical care research and practice. 2017;     [PubMed PMID: 28555164]
[12] Chesnut RM,Temkin N,Carney N,Dikmen S,Rondina C,Videtta W,Petroni G,Lujan S,Pridgeon J,Barber J,Machamer J,Chaddock K,Celix JM,Cherner M,Hendrix T, A trial of intracranial-pressure monitoring in traumatic brain injury. The New England journal of medicine. 2012 Dec 27;     [PubMed PMID: 23234472]
[13] Sahuquillo J,Biestro A, Is intracranial pressure monitoring still required in the management of severe traumatic brain injury? Ethical and methodological considerations on conducting clinical research in poor and low-income countries. Surgical neurology international. 2014;     [PubMed PMID: 25024886]
[14] Exo J,Kochanek PM,Adelson PD,Greene S,Clark RS,Bayir H,Wisniewski SR,Bell MJ, Intracranial pressure-monitoring systems in children with traumatic brain injury: combining therapeutic and diagnostic tools. Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. 2011 Sep     [PubMed PMID: 20625341]