BehindTheMedspeak: Do redheads need more anesthesia?

joehead Brent Clemens asked me this question yesterday, noting that he'd just heard on NPR that redheads require 20% more anesthesia than "normal" [Brent's quotation marks] people.

I first learned of the association of red hair with an increased anesthesia requirement in 2002 when an abstract reporting the finding was presented at the annual meeting of the American Society of Anesthesiologists.

Then last year I heard from a redheaded joehead [joeheaded redhead?] who asked me whether or not it was true and if she should be concerned if she needed anesthesia.

I told her not to worry and that it wasn't an issue assuming her anesthesiologist was competent.

If he wasn't her red hair would be among the least of her problems. But I digress.

Having now been asked a second time about the association it becomes apparent that there are probably hundreds, perhaps thousands, maybe even millions of people asking the same question but not having the energy or wherewithal to pursue it.

So let's take a closer look.

I was going to have my crack research team handle it but as is all too often the case lately they're all flaked out so I'll take this one myself.

The original 2002 study that showed an increased requirement for anesthesia in redheads was presented in abstract form in October 2002 at the annual meeting of the American Society of Anesthesiologists by Dr. Edwin B. Liem of the University of Louisville School of Medicine's Outcomes Research Institute.

Liem noted that neither he nor anyone else had a clue as to why the association might exist.

In August of last year Liem and his colleagues published a formal scientific paper in the journal Anesthesiology reporting on their results as briefly presented in the abstract two years earlier.

Long story short: redheaded women required almost 20% more inhaled desflurane anesthesia than dark–haired women (below).

The scientists then studied another commonly used intravenous anesthetic drug called propofol to see if redheads required more: the answer was no.

Those findings were presented in October of last year in abstract form at the American Society of Anesthesiologists' annual meeting.

So what should you conclude?

Here's what I conclude — you can take this for what it's worth:

1) In one study of 20 women the inhaled anesthetic requirement for one particular agent — desflurane — was 20% greater if you were among the 10 redheads as opposed to those having dark hair.

2) In a second study of 20 women the injected anesthesia requirement for propofol was no different for redheads.

Now let's take these findings into the mind and operating room of a practicing anesthesiologist.

For example, me.

When I give anesthesia I don't give the dose in the textbooks or product brochures: I give the dose you need based on doing it tens of thousands of times and your individual, idiosyncratic, particular response to the drug.

Each patient is her or his own control.

I don't and never would compare you to a typical patient because there is no such thing.

Every individual reacts differently to every drug and even the same person will react differently on two consecutive days.

So it's not a cookbook approach: if it was, hey, a koala bear could give anesthesia.

Each particular person — redhaired, dark–haired, blonde, bald, whatever — is a scientific study of one.

If you need more desflurane, as judged by your blood pressure, heart rate, respiration and a million other things, then I'll give it to you.

If you need more propofol, same deal.

It's not your hair color that determines what you need — it's you.

If you have red hair you might need more of something and if that's the case you'll get it — it's not a problem, I've got plenty of anesthetic, believe me.

But guess what: the variation within any group, redheads included, is tremendous, way larger than the variation within a subgroup such as those with a particular hair color.

So there are redheads who require much less anesthesia than dark–haired people.

You give that redhead the average requirement and you'll be doing CPR before you can say "Bob's your uncle."

You find out she needs less by noting how she responds to a small dose before increasing the anesthetic level.

That's how it's done in the real world.

So the answer to Brent's question is yes, redheads can require 20% more anesthesia than dark–haired people.

But they can also require 20%, 40%, even 75% less.

The trick is knowing which.

Koala bears don't know that trick — but I do.