Rule of Halves

[Armor10]

Hello all,
I'm currently working for a system that uses (The Rule of Halves) for RSI.
I have never heard of this.
Essentially, if the Pt's GCS is <8 we half the dose of our induction agent.
Problem is, I can't find any information, Study's, or basically anything on this. Is this good practice, bad practice?
Anyone know where this is coming from?
Thanks

 

[KellyBracket]

"GCS < 8" is a heterogeneous group.

If the patient is hemodynamically stable, but has altered mentation, then you probably don't need to give the same doses of sedative, but it might still be a good policy. Drunks can pick some weird times to wake up and get aggro.

Usually, people talk about reducing induction doses in the hemodynamically unstable patients. The idea is that a full dose of drugs that are usually fine for a patient with a good pressure can kill a patient with a tenuous or low pressure, and that the stressed metabolism of the shocky patient only needs a small dose of sedative to work.

These two sources have references to primary literature.

http://lifeinthefastlane.com/education/ccc/rapid-sequence-induction-of-the-shock-patient/
http://emcrit.org/podcasts/intubation-patient-shock/

 

[Carlos Danger]

I've never heard of it, and frankly it sounds like a horrible practice to me.

As the doc said, decreasing your dose in a hypotensive patient is prudent, but someone who is obtunded from a high ICP is not someone who needs to experience the dramatic SNS discharge that accompanies intubation.

 

[jwk]

I can tell you there is absolutely no such animal in anesthesia and critical care. Where did this anomaly originate?

 

[Handsome Robb]

Well...we've got two anesthesia providers in here saying they've never heard of it...

Now anesthesia does not equal EM but I'd expect midlevels, especially these two, to know their trade...ie anesthetizing someone and intubating them.

 

[jwk]

Well...we've got two anesthesia providers in here saying they've never heard of it...

Now anesthesia does not equal EM but I'd expect midlevels, especially these two, to know their trade...ie anesthetizing someone and intubating them.

Don't disagree at all about cutting the dose - but the "rule of halves" is something I've never heard of.

 

[KellyBracket]

Agree that, as EM, I've never heard of any specific "rule of halves." My guess is that this rule is backed up by the same level of evidence as "GCS ≤ 8, intubate."

EMCRIT did a segment with a trauma anesthesiologist (http://emcrit.org/podcasts/trauma-resuscitation-dutton/), and his recc's square with my experience - cut waaaay back in the the sympathomimetic, critical trauma/cardiovascular patient.

 

[Rialaigh]

Just curious but is this in reference to etomidate or?

Our system is going to Ketamine to provide a more stable drug for hypotensive patients.

 

[Handsome Robb]

Don't disagree at all about cutting the dose - but the "rule of halves" is something I've never heard of.

Absolutely. It makes total sense. I've been off today apparently when it comes to conveying what I mean haha.

 

[Armor10]

For us either one. We half the dose of Ketamine, and Etomidate. I understand because of the Hypotensive effects of Etomidate. The practice makes sense. I'm just wondering where this came from. We use evidence based medicine here. I'm looking for a study....something....Thanks for the help guys.

 

[SandpitMedic]

Our system is going to Ketamine to provide a more stable drug for hypotensive patients.

I wish. Ketamine is in our protocol, yet no agency carries it.

If I found a genie....

 

[Carlos Danger]

For us either one. We half the dose of Ketamine, and Etomidate. I understand because of the Hypotensive effects of Etomidate. The practice makes sense. I'm just wondering where this came from. We use evidence based medicine here. I'm looking for a study....something....Thanks for the help guys.

Yeah, again, I've never heard of reducing the dose unless the patent is hemodynamically unstable. Even then, it wouldn't usually be necessary with ketamine, except possibly for certain specific clinical scenarios.

I'd be interested in hearing where this originated from and what the rationale is. Please share when you uncover it.

 

[Handsome Robb]

Ketamine is pretty hemodynamically stable is it not?

 

[Carlos Danger]

Ketamine is pretty hemodynamically stable is it not?

According to the textbooks, ketamine is a direct myocardial depressant, but the depressant effects are normally more than offset by the SNS stimulation that it elicits, with the net effect being that an induction dose normally causes an increase in BP and HR.

In a patient who is already maximally SNS-stimulated (massive volume depletion, severe sepsis, etc.) however, further norepi release doesn't occur and the cardiac depressant effects could cause a catastrophic hypotension. My understanding is that this concern is mostly theoretical; I have never seen it or heard of it, but then again ketamine is not generally used for induction where I am, even in hemodynamically challenged patients.

And then there is problem of tachycardia. Ketamine can cause a significant increase in HR, which is a concern when certain types of heart defects exist.