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September 1, 2008

BehindTheMedspeak: 'Man Attacks Own Arm at Denny's'


That's the headline over a one-paragraph item on page A4 of today's dead tree iteration of the Washington Post.

Turns out the man was not out of his mind or psychotic but reacting rationally to a perceived threat.

First, the news as it appears in the online version of the paper.

    Modesto man tries to amputate own arm

    Police say a man tried to cut off his own arm at a restaurant in Modesto, Calif., because he thought he had injected air into a vein while shooting cocaine and feared he would die unless he took drastic action.

    Authorities say 33-year-old Michael Lassiter rushed into the Denny's restaurant late Friday and started stabbing himself in one arm with a butter knife he grabbed from a table.

    They say that when that knife didn't work Lasiter took a butcher knife from the kitchen and dug it into his arm.

    Police Sgt. Brian Findlen says Lassiter told officers he thought he needed to amputate his arm to keep himself from dying from the cocaine injection.

    Lassiter was taken to a hospital for treatment of severe cuts.

    The Denny's closed for the night.


Here's the KNX 1070 (Los Angeles) news radio website's report.

    Modesto man tries to cut off his own arm inside Denny's

    Police in Modesto say a man tried to cut off his own arm because he thought he had injected air into a vein while shooting cocaine and feared he would die from an embolism.

    33-year-old Michael Lassiter rushed into a Denny's restaurant late Friday night and started stabbing himself in one arm with a butter knife he grabbed from a table.

    When that didn't work, he barged into the kitchen, grabbed a butcher knife, and dug it into his arm.

    He ended up in a hospital with severe cuts telling officers he thought he needed to amputate his arm to save his life.


Now we'll go BehindTheMedspeak.

How much air injected IV does it take to kill a person?

Long answer short: 1 cc/kg, or about 75cc for a person weighing 165 pounds.

How much is 75cc?

The cube root of 75 is 4.2 — a volume of air 4.2cm (1.7 inches) on a side.

So a cubic volume of air 1.7 inches on a side is the LD50 (lethal dose in 50% of those who receive it).

That's a sizable amount of air when you're talking about inside the circulation.

I know these things because long ago and far away, in another century on the Left Coast during my anesthesiology residency, I used to notice small air bubbles in IV lines and wonder if they needed to be evacuated or not.

Most residents seemed pretty compulsive about clearing the lines but you know me — if it involves effort and I can do less, I'm all for it.

Anyway, I started reading the literature and that's where I found the figure on lethal air injection volume.

The mechanism of death is the formation of an "air lock" (top — yellow arrow) — the air gets trapped in the right side of the heart and blocks the flow of blood out to the lungs, resulting in insufficient flow back via the pulmonary veins to the left side of the heart and cardiac muscle hypoxia, which leads to cardiac arrhythmias, ventricular fibrillation and ultimately cardiac arrest and death.

But in the OR, I wondered, how much air is worth worrying about?


I took a new IV set with extension tubing attached, primed it with fluid, then took a 30cc syringe, filled it with air, and injected from the bag end until all the fluid was out and the tubing was filled with air.

Note to anxious readers: don't get your baggies in a twist, I did the experiment in the anesthesia workroom — not with a person attached to the business end of the IV tubing.



Guess how much air it took to fill the IV tubing?


Far less than the 75cc likely to cause a cardiac arrest in adults.

A little air bubble in the line or even an inch-long air segment is trivial and not worth bothering about.

And I never have since.

When other people get all worked up and turn stopcocks and get needles and syringes out to remove air from their lines, I never say anything.


Because it's not worth going through with them what I've just gone through with you, especially since they're doing the work.

Let it ride.

Now, back to our Denny's story.

Mr. Lassiter, not knowing that the minuscule amount of air he'd injected into himself was harmless, attempted to amputate his arm.

Logical response, especially if you've got IV cocaine helping you work through your decision tree.

Now, answer honestly: Aren't you glad you read bookofjoe?

I mean, where else are you gonna find this stuff — news you can really use?

September 1, 2008 at 03:01 PM | Permalink


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Growing up I was told by different health teachers in middle & high school that oxygen in the blood was lethal, even in very tiny amounts. I never knew that someone's body could take in that much air and still not cause have embolism. Great entry :-)

Posted by: Nikolas Schiller | Sep 23, 2008 2:36:06 AM

Hope you never use nitrous... hehe ;)

Posted by: herman Lim | Sep 2, 2008 6:31:17 AM

Joe, seriously, assuming I did inject or IV a lethal amount of air into my vein, how long would it take for it to be fatal? Would I have time to ask the gardner across the street to turn from the tree and use his chainsaw on my arm in time?
Of course, I now would have to worry about bleeding to death, but if the gardner has extra gas for the saw, he might be able to cauterize the wound and/or apply a tourniquet.

Posted by: itsrichard | Sep 1, 2008 6:22:35 PM

That is, bar none, the greatest blog post I have ever read.

Posted by: MC | Sep 1, 2008 4:24:06 PM

I too stopped bothering with those small bubbles long ago. However, what about a right to left shunt. What volume of air is dangerous in that scenario?

Posted by: QuietusLeo | Sep 1, 2008 3:55:45 PM

Nowhere else.

Posted by: Milena | Sep 1, 2008 3:22:03 PM

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