Intracranial Pressure Monitors (EVD/bolt)
Background
Watch this NEJM video https://www.nejm.org/doi/full/10.1056/NEJMvcm1805314
Indications for EVD placement
1. ICP monitoring
2. CSF Diversion to treat hydrocephalus
3. Clearance of blood products (IVH) or Infectious Debris (severe meningitis/shunt infection)
4. Post-intra-op dural defect (skull base/posterior fossa procedure), need to promote healing
Steps when EVD is Decided
This is the exact order of operations to take when you know a patient is getting an EVD.
- Check labs and order CBC/Coags/T&S if any of it is missing
- Order Ancef 2g ASAP (takes a long time from the pharmacy)
- If patient is on AC/AP, make sure they are being reversed
- Order K centra as needed
- Order platelets if patient is on aspirin or possibly on aspirin
- if you're in the ED, they actually have their own blood bank and will get it directly from there, but confirm with nurse that it's on the way and verbalize that you need it. Ask for 2 units by default, can always return the second one.
- if you're in ICU, you need to call the PUH blood bank 412-647-5850 too. Ask charge in the ICU exactly what needs to be done. Don't assume it's on the way STAT.
- Order post-placement CTH while you have the chart open already
- Place the EVD order (set it at 10AMB and then just verbal change it once you confirm level later); can put in comments "ok to clamp while transporting to scan"
- Print an EVD & Blood consent and get family phone number from chart.
- also print all anticipated procedure consents e.g. Crani/Blood/Angio for a ruptured aneurysm
- Call the appropriate (ICU fellow/ED attending) to discuss and plan for sedation.
- Gather all supplies as listed below.
Supplies Needed and where to get them
| Items | Where to get in PUH | Notes |
Cranial Access kit OR Phasor Drill | All ICUs should have If all else fails, go to OR center aisle (kindly ask front desk) |
|
EVD catheter
| All ICUs should have If all else fails, go to OR center aisle (kindly ask front desk) |
|
| Clipper | ICUs will all have these | Ask for this early, as they are sometimes hard to find. |
| ICU Supply Rooms /ICU carts | |
Green chuck Blue pad | patient's room | Ask nurse to get this Green chuck is to elevate head/neck as needed Blue pad is to place under patient's head as shit will get bloody |
NOTE: on 4G/4F/5F, you can possibly trust nurses to get you everything, but on 6FG you can only trust them to get you a cranial access kit, just save yourself the time and get everything else yourself up front.
Steps for EVD Placement
Position the patient
- Take the time to do this right. Be efficient but don't rush this step, you will pay for it later.
- Make HOB flat (do this quickly as ICP will be rising)
- Rotate patient so that whole body is midline on the bed (yes it matters for your own orientation even if you're just at the head)
- Move patient north in the bed until head is creeping about 2-3 inches above the top edge (don't worry they'll slide back down)
- Re-elevate HOB to 30˚
- Adjust height of whole bed to make it ergonomic and comfortable for yourself
Pre-procedural
Administer 2g Ancef - can also be given up to 1 hour AFTER skin is cut (don't let this delay you)
Administer platelets if needed
Start sedation, if you are using ≥ 2 forms, ICU attending/fellow must be present and you cannot start without them. Possibly will need respiratory at bedside as well.
Measure
- Find Kocher's point
- Verify you are mid-pupillary
- Mark a 2cm incision centered at Kocher's point
Prepare your table (sterilly)
Prep
- Shave only up to Kocher's point and posteriomedially for an exit site.
- Chloroprep x 2 (WIDELY), watch the dripping into eyes/ears
- Drape w/ plastic cover, staple white sheets under plastic (be careful if patient is on an airbed, staple the plastic drape to white sheet, not to bed!)
- Inject lidocaine at Kocher's point and at exit site posteriomedially
- Re-measure after injecting lido, the bubble will displace your prior marking
Craniostomy
- Knife down to bone
- Dissect under pericranium around 1-2 cm in every direction around your incision
- Stick caterpillar in there
- REMEASURE - don't be afraid to extend incision and reposition if you find that you need to at this step, that is the whole point of remeasuring
- Have a headholder be ready, tell them to reach under the plastic drapes (don't assume they know it's sterile)
- Drill perpendicular to bone
- Laterally: Aim for contralateral canthus
- Anterior-posterior: Tilt back to an angle until your catheter is parallel to ear
- If all else fails, just go perpendicular to skull
- Tactile changes you will fell from superficial to deep as you approach brain:
- outer table = cortical bone (tough)
- cancellous bone (becomes easy)
- inner table = cortical bone (again tough)
- Use a curved kelly to dig out bone chips
- Flush
Catheter Insertion
- Pierce dura with weapon in a cruciate fashion (two punctures)
- Before pass catheter through dura, ask for BP < 140
- Go slowly with the literal pass, this is the only thing you can do to prevent tract hemorrhages
- Go down until you see the string (at 6.5) at the OUTER table
Tie-down
Retention loop and closing
Connect to monitor
Post-placement scans
- window CTH to bone to see holes and make sure they are in vents
Exchanging an EVD
Prep differences
- Use betadine
Procedural differences
-
EVD Leveling
Remember EVD levels are set according to height of water in centimeters (cmH2O), different then height of mercury in millimeters (mmHg). Generally speaking the settings are used as follows
| EVD level | mmHg | Setting | Typical uses |
| 5 cm H2O | 3.7 | low | Encourage drainage (hydro, clearance of debris/blood) |
| 10 cm H2O | 7.4 | moderate | ICP monitor w/ little bit of drainage |
| 15-20cm H2O | 11-14 | high | Weaning the EVD (i.e. before you clamp it next) Before aneurysm is secured Posterior fossa mass (to prevent upward herniation) |
Troubleshooting
During Placement
- Not draining after initially seeing CSF
- Always check if you are air-locked. Just very gently suction in and out.
After Placement
- "The EVD is not working" / "The EVD is not tidaling"
- Re-level the EVD (laser to tragus), i.e. re-calibrate your 0 to be MB as you define it
- Clamp proximally (i.e. open to transducer, insert picture)
- zero it on the monitor and then rescale
- 'ICP is really high"
- Make sure you are clamped, transducer does not give accurate ICP measurement while EVD is opened!
How to prime a buretrol
- ICU nurses at PUH should generally know how to do this, but inevitably it will one day be on you, whether in the OR or at another gomey site.
Materials
Procedure
1.
2.
3.
Injecting intrathecal medications proximally into an EVD
Most commonly this is used to inject antibiotics and tPA to bust clots.
| MATERIALS | PROCEDURE |
| 1. Wear your sterile gloves Contaminate your non-dominant hand for next steps 2. With your contaminated non-dominant hand, lift up or move the proximal clamp from where it is next to the patient's head and place a blue towel sterilely in that location 3. Keep a grip on the proximal clamp with your non-dominant hand, use the sterile dominant hand to chloro-prep the proximal clamp at the site of injection (where your syringe will attach) and 6-12 inches distally and proximally along the tubing in every direction (Towards head and towards bag) 4. You may now rest the supposedly sterilized proximal clamp/tubing onto the blue towel. Most important part to keep sterile is really just the site of syringe attachment, so try to keep that upright and not even touching the blue towel even though that is theoretically sterile too. 5. Inject the syringe proximally. Go slowly, about 3 seconds per every cc you are injecting proximally. If you are following your medication injection with normal saline flushing, make sure the airlock is broken on your sterile flush and their is no air in it! |
Ordering tPA for intrathecal administration
Adults
generally, the dosing is 1 mg alteplate inside of 1 mL mixed w/ 2mL of NS. Here is an example of someone who had this order. The number of doses is dependent upon attg and scans.
Pediatrics
This is more weight-based. It will be attg dependent but it is reasonable to start with 0.5 mg alteplase and escalate to 1 mg alteplase as tolerated based on scans and also just attg preference.
Papers:
Pharmacokinetics and Pharmacodynamics of Tissue Plasminogen Activator Administered Through an External Ventricular Drain. See attachments for PDF of 3 papers on the topic.
Swapping a Shunt for an EVD
Note: Externalize shunt = take it out clavicle distal to valve, doesn't matter where you level the EVD as the valve is still controlling flow. The word remove implies you actual rip the whole thing out from proximal to distal.
What level do you set an EVD at after removing a Medtronic Strata shunt?
1) Option 1 = use table below
2) Option 2 = just multiply by 10
0.5–> 5
1.0–> 10
1.5 -> 15
2.0 -> 20
2.5 -> 20
Useful links
Notice where the glabella vs nasion is. You start measuring from NASION.
