7 Invasive Neuromonitoring Techniques



10.1055/b-0035-121753

7 Invasive Neuromonitoring Techniques

Mathieu Laroche, Michael C. Huang, and Geoffrey T. Manley

Introduction


Invasive neuromonitoring assists the diagnosis and treatment of patients presenting with—or at risk for—intracranial hypertension, defined as intracranial pressure (ICP) greater than 20 mm Hg. A variety of intracranial pathologies such as traumatic brain injury, subarachnoid hemorrhage, intracerebral hemorrhage, and ischemic stroke (associated with malignant edema) may contribute to an altered level of consciousness and, therefore, an unreliable neurologic exam. Further decline in neurologic status may be difficult to detect based on serial clinical evaluation alone. Invasive neuromonitoring can point to signs of deterioration and trigger appropriate interventions. Although ICP monitoring is most common, additional advanced modalities for the monitoring of brain tissue oxygen tension, microdialysis, cerebral blood flow, and jugular venous saturation can help the practitioner achieve a more comprehensive understanding of pathologic cerebral physiology and, in turn, provide individualized treatment with targeted therapies.



Indications



Monitoring of ICP by External Ventricular Drain or Intraparenchymal Pressure Probe 1




  • Diagnosis and treatment of intracranial hypertension




    • An external ventricular drain (EVD) is considered the gold standard for ICP measurement. Placement of an EVD allows both for diagnostic monitoring of ICP and therapeutic drainage of cerebrospinal fluid (CSF).



    • An intraparenchymal pressure monitor (fiberoptic or micro strain gauge device) allows for monitoring of ICP alone. The intraparenchymal probe may be coupled with other neuromonitoring modalities in a multiport bolt apparatus or used in isolation.



  • As per published guidelines, indications for ICP monitoring in the setting of severe traumatic brain injury (TBI) 2




    • Glasgow Coma Scale (GCS) score ≤ 8 after resuscitation, in combination with an abnormal head computed tomography (CT; hematoma, contusions, swelling, herniation, compressed basal cisterns) (Level II recommendation)



    • GCS ≤ 8 after resuscitation, with a normal head CT, and associated with two or more of the following on admission (Level III recommendation):




      • Age > 40 years



      • Unilateral or bilateral motor posturing



      • Systolic blood pressure < 90 mm Hg



Monitoring of Brain Tissue Oxygen Tension, Jugular Venous Saturation, and/or Cerebral Blood Flow 3




  • Ancillary monitoring of cerebral physiology may facilitate cerebral perfusion pressure (CPP) management in severe TBI with loss of autoregulation (Level III recommendation).



  • The brain tissue oxygen tension probe usually is placed in the less injured cerebral hemisphere for more consistent measurement and early detection of secondary brain injury.



Microdialysis 4




  • Ancillary monitoring of cerebral metabolic parameters may facilitate CPP and brain-specific management in severe TBI (Level III recommendation).



  • Placement of the microdialysis catheter is dictated by the specific pathology:




    • In the right frontal lobe of patients with diffuse brain injury.



    • In the pericontusional tissue (penumbra) in patients with a focal mass lesion; a second probe may be placed in uninjured or “normal” tissue for comparison.



    • In the region of the brain at risk of vasospasm following severe subarachnoid hemorrhage. 4



Preprocedure Considerations



Radiographic Imaging




  • Noncontrast head CT should be reviewed for:




    • Size of the ventricular system



    • Intraventricular hemorrhage



    • Mass effect or focal lesion



    • Skull fractures



    • Distance from the bone to the frontal horn (for EVD placement)



Coagulation Parameters




  • International normalized ratio (INR), partial thromboplastin time (PTT), and platelets should be in normal range.



  • In the coagulopathic patient, consider transfusion of platelets, fresh frozen plasma (FFP), and/or prothrombin complex concentrate—as appropriate—before the procedure.



Availablity of All Necessary Equipment




  • Placement can be performed either in the operating room or at the bedside (most commonly).



Medication




  • Lidocaine 1% with epinephrine 1:100,000 for local anesthesia



  • Midazolam or propofol for sedation



  • Fentanyl for analgesia



Operative Field Preparation for Intracranial Neuromonitoring




  • Position the head in the neutral position (a rigid C-collar, bean bag, or fixation with tape are effective ways to achieve this at the bedside).



  • Elevate the head of the bed approximately 30 degrees.



  • Clip hair overlying the frontal quadrant using an electric razor.



  • Identify important anatomic landmarks:




    • Midline



    • Nasion



    • Mid-pupillary line



    • External auditory canal



    • Coronal suture (by palpation)



  • Identify the approximate location of Kocher′s point by one of the following strategies:




    • 11 cm posterior to the nasion and 3 cm lateral to midline



    • 1 cm anterior coronal suture and 3 cm lateral to midline



    • Intersection of the midpupillary line with a perpendicular line extending from the midpoint of an imaginary line connecting the external canthus to the tragus



  • Infiltrate the skin at the planned incision site with 1% lidocaine with epinephrine 1:100,000.



  • Prepare the skin with alcohol before application of proviodine iodine or chorhexidine.



  • Anatomic landmarks for placement of EVD (Fig. 7.1).

Fig. 7.1a–c Multiple measurement strategies have been proposed to determine the optimal entry point for insertion of an EVD (or comparable invasive monitor): (a) 11 cm posterior to the nasion and 3 cm lateral to midline, (b) 1 cm anterior to coronal suture and 3 cm lateral to midline, and (c) intersection of the midpupillary line with a perpendicular line extending from the midpoint of an imaginary line connecting the external canthus to the tragus.


Operative Procedure



Placement of Intracranial Monitors



Positioning (Fig. 7.2)
Figure Fig. 7.2 Procedural Steps The head is maintained in the neutral position with the head of bed at 30 degrees. Pearls • The operator stands behind the patient. • A C-collar or bean bag is useful to maintain the head in the neutral position. • EKG electrodes can be placed on the nasion and tragus for easier palpation of the landmarks after draping.


Skin Incision (Fig. 7.3)
Figure Fig. 7.3 Procedural Steps A small stab incision is made at the planned entry site and extended through the scalp to the level of bone. Pearls • For EVD: at Kocher′s point. • For brain tissue oxygen: 1 to 2 cm behind Kocher′s point. • For cerebral blood flow: 1 to 2 cm in front of Kocher′s point. • If advanced neuromonitoring probes are too close to the EVD, or each other, they may not provide accurate and reliable information.


Twist Drill Craniostomy (Fig. 7.4)
Figure Fig. 7.4 Procedural Steps Using the twist drill, a small craniostomy is performed, followed by copious irrigation to remove blood and bone debris. Pearls • An assistant is helpful to stabilize the head during drilling to maintain neutral positioning. As a general rule, each cannulation system comes equipped with a proprietary drill bit. For an EVD, a 5.3-mm drill bit is provided. If available, a drill safety stop should be used. • It is important to perform the craniostomy absolutely perpendicular to the plane of the skull. The trajectory may be assisted by aiming at the ipsilateral inner canthus in the coronal plane and just anterior to the tragus in the sagittal plane or with the use of a tripod device. • The operator is able to feel a change in the resistance as the drill travels through the outer cortex (hard), diploe (soft), and inner cortex (hard). The operator should slow down as more resistance is felt while the drill penetrates into the inner cortex to avoid plunging into the brain tissue. After removing the twist drill, the dura can be palpated using a spinal needle or a small blunt instrument.


Variation for Bolt-type Monitors (Fig. 7.5)
Figure Fig. 7.5 Procedural Steps If a bolt-based system is being used, the bolt should be screwed into the craniostomy site to finger tightness. Pearls • The dura then is punctured by passage of the central stylet. The fiberoptic pressure monitor or EVD catheter is threaded through the central opening in the bolt to the desired depth. The cuff is tightened and the locking sheath pulled over top to secure the system.


Opening of Dura and Leptomeninges (Fig. 7.6)
Figure Fig. 7.6 Procedural Steps The dura is punctured using a 18-gauge spinal needle or a 14-gauge needle. The pia is perforated using the spinal needle or a no. 11 blade. Pearls • A loss of resistance will be felt when the dura is perforated using the needle. Multiple punctures might be necessary to open the dura completely. • For brain tissue oxygen monitors: The dura must be opened completely beneath the craniostomy to avoid damaging the electrode tip. To achieve a better result, a no. 11 blade is used to open the dura in a cruciate manner, under direct visualization. A slighty larger skin incision may be necessary. • A good pial opening is essential to minimize the risk of subdural placement of neuromonitors.

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Jun 13, 2020 | Posted by in NEUROSURGERY | Comments Off on 7 Invasive Neuromonitoring Techniques

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