Ketamine use in TBI – the ICP goes down not up.

click for source

H/T Rob Bryant for tweeting the paper.

[blackbirdpie url=”https://twitter.com/RobJBryant13/status/271116807195217920″]

We all love ketamine, or at least Minh does. But there has always been the bogey man stories, that if you use ketamine in someone with a head injury, there brain will explode and you’ll get covered in lots of brain goo which is never  a good luck. As a result, I rarely see people reach for ketamine as an induction agent for these people.

There is increasing evidence that the ICP rise attributed to ketamine is likely a bit of a myth based on faulty early data and even faultier interpretation (a bit like lignocaine/adrenaline is bad for fingers…)

This study provides a little bit more ammo that ketamine is safe for ICP. It’s not gold standard, bullet proof evidence but the case is building.

Bar-Joseph, Gad, Yoav Guilburd, Ada Tamir, and Joseph N Guilburd. “Effectiveness of Ketamine in Decreasing Intracranial Pressure in Children with Intracranial Hypertension..” Journal of Neurosurgery. Pediatrics 4, no. 1: 40–46. doi:10.3171/2009.1.PEDS08319. PMID 19569909

METHODS

  • single centre in Israel in the PICU with kids with TBI
  • two groups, 
    • one who got ketamine for a procedure
    • the other who got ketamine for the ICP specifically
  • ketamine was 1-1.5mg/kg
  • all were on midaz and morphine as sedation
  • some had propofol as well
  • a bunch got mannitol or hypertonic saline or thiopental and some even had decompressive craniectomy

RESULTS

  • 30 patients, 82 episods of ketamine administration, most for treatment of raised ICP
  • it worked, it lowered the ICP by about 5mmHg in both groups of patients

Their only concern is that some of the prior studies showed ICP rises in those who were probably inadequately anaesthetised. This bunch of kids were doped up to the max and they say maybe that’s why the ketamine is safer.

They were surprised that the ketmaine actually lowered the ICP not just didn’t increase it.

This is, of course, a tiny little study and with all the different interventions going on you could make the argument that we can’t tell if it was the ketamine that lowered the ICP. None the less it’s still encouraging that the bogey man of raised ICP is a little bit mythical.

Raised ICP and Intracranial shunts – some notes

From the wonderful Roberts & Hedges

Raised ICP

  • normally ICP can rise to 80-100mmHg just when coughing/straining
  • being intracranial hypertension has a huge list of associated conditions so just cause you’ve got headache, normal CT and a raised pressure on LP doesn’t mean you’re done with the diagnosis
  • CSF is produced at 500 ml/day with a total of 150 ml in the system. This means there’s continuous circulation reabsorption. See the video for more details

[wpvideo Pzv6LzQp]

  • the two types of hydrocephalus are:
    • obstructive – expect big lateral ventricles and normal 4th as there’s a blockage somewhere
    • communicating – general big ventricles but all the piping is OK, it’s the filter/drain that’s blocked – think blood pluggin the arachnoid villi
  • one of the earliest clinical signs of raised ICP is reduced venous pulsation on fundoscopy – good luck with that…
  • the old hyperventilation to reduce pCO2 and reduce ICP is a bit dodgy as it also does exactly what you don’t want it to do – it reduces cerebral blood flow.
  • mannitol has two actions
    1. volume expander
    2. osmotic diuretic
  • if osmolality is already >320 then mannitol won’t work.
  • steroids work for vasogenic oedema from tumours but not anything else.
  • paracetamol is effective for fever – this was news to me as I thought the fever was very much “cerebral” and not due to normal pathways

Intracranial shunts

  • frequently put in for any long standing high ICP
  • headache, nausea, vomiting, visual disturbance – think shunt malfunction
  • failure of upward gaze an apparently sensitive sign
  • there are a whole bunch of shunts available, both in terms of design and function. Here’s a video of how to place one:

  • even more interesting, here’s a wonderful paper (free) of lots of different types of devices you might find in the head and neck, shunts included.

click for source

  • shunts are normally placed in the anterior horn of the right lateral ventricle as this is non-dominant for most people so any damage caused will hopefully be less significant
  • there are lots of reasons for malfunction
    • blood or debris in the proximal site (choroid plexus within the ventricle can get stuck in it
    • fracture of the tubing along its course
    • infection of the tubing along its course
    • something like a piece of omentum getting stuck in the distal port in the abdomen
  • there are characteristics of “valve pumping” that might tell you where the obstruction is but apparently they’re only present 5% of the time so i’ll not bother you with the details.
  • the valve looks like this:

  • when you press on it normal refill time should be about 15-30 secs. I have no where near enough experience to be able to press on these and have any ideas what it means. Anyone else have any thoughts on whether this is useful?
  • with sterile technique you can access it for CSF. Be sure and use a small needle and approach it at a shallow angle (about 30 degrees or so) rather than coming at it perpendicular to the skull. Apparently this reduces damage to the valve.
  • CT scan has sensitivity of 80% and shunt series (plain films of neck and abdo) has sens of 20% but you still need both. Obstruction isn’t a simple yes/no diagnosis a lot of the time and you need old CTs to compare with