I began a propofol-ketamine
(PK) clinical trial in 1992, using
propofol hypnosis to block keta-
mine hallucinations or dyspho-
rias. Over the next year, I
watched in amazement as my
first 50 PK patients quickly
emerged from anesthesia with
no need for opioids. Until then, I
hadn't heard about N-methyl, D-
aspartate (NMDA) receptors, much less their critical midbrain loca-
tion.
Over the next 5 years and 1,200-plus patients, I continued to observe
the same effectiveness with the same 50 mg ketamine dose, whether
in 100-pound female patients or 250-pound male patients. Ketamine,
which prevents transmission of painful sensation to the cortex by
blocking midbrain NMDA receptors, is the only IV anesthetic not
given on a per-body-weight basis. The effective dissociative dose of
ketamine isn't related to body weight.
The adult brain weighs about 3 to 4 pounds and doesn't vary with
body weight. The midbrain is a very small part of the adult brain, and
the NMDA receptors are a very small part of that very small part. A 50
mg dose of ketamine saturates 98 to 99% of those midbrain NMDA
receptors.
"Nifty fifty"
Now, for the last 25 years, I've never begun a case without what I call
the "nifty fifty"— 50 mg IV ketamine 2 to 3 minutes before stimula-
tion, injection or incision. The propofol, incrementally titrated —
either to loss of lid reflex/loss of verbal response or to a BIS reading
Anesthesia Alert
AA
2 6 • O U T PA T I E N T S U R G E R Y M A G A Z I N E • M A R C H 2 0 1 7
AN ODE TO PK
My Life's Work
In 9 Words
Measure the brain
Preempt the pain
Emetic drugs abstain
— Barry L. Friedberg, MD
