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The Lucas CPR Device And Pregnancy

April 5, 2018 The Trauma Pro Leave a comment

Here’s an image of the Lucas automated CPR device. Here’s a question for you: can you use the Lucas chest compression device in a pregnant patient?

The official company answer is “no.” Obviously, this is one those areas that is tough to get research approval on, and the number of pregnant patients who might need it is very small. So basically, we have little experience to go on.

That being said, the reality is that prehospital agencies can and do use it for these patients on occasion. There is only one published case report that I could find (see reference below). The thing that makes using this device a little more challenging is that, to optimize blood pressure, late term pregnant patients need to have the uterus rolled off of the vena cava. This means tipping the patient to her left.

As you can see from the picture above, the design of the Lucas makes this a bit difficult. However, it can be done, either by tipping the board the patient is on or wedging something under the right side of the back plate.

And as always, make sure that you adhere to your local policies and procedures, or have permission from your medical director to use this device in this particular situation.

Reference: Cardiac arrest and resuscitation with an automatic mechanical chest compression device (LUCAS) due to anaphylaxis of a woman receiving caesarean section because of pre-eclampsia. Resuscitation 68(1):155-159, 2005.

General

Trauma Mythbusters: Removing Bullets With Metal Instruments

April 2, 2018 The Trauma Pro Leave a comment

I’ve heard this time and time again over the years. Don’t remove a bullet using metal forceps or a hemostat. Don’t drop it into a metal pan. Have you heard these, too? Is it true?

The idea is that rifling marks on the bullet that would help match it to a particular weapon may be damaged through mishandling, interfering with any criminal investigation.

So I decided to go to a reputable source. I asked a local police firearms and munitions expert the question. The result:

Myth busted! The amount of damage to the bullet due to handling with metal instruments is negligible and will not interfere with an investigation. Many of the bullets used in crimes are jacketed with copper or other metals, which are resistant to damage anyway. The surgeon would have to make an intentional effort to damage the bullet enough to interfere with a ballistics investigation. And I don’t recommend that anyway!

General

Where Did The Hypodermic Needle Gauge System Come From?

March 28, 2018 The Trauma Pro Leave a comment

Yesterday, I wrote about one of the weirder measurement systems in medicine, the French (or Charrière) system for catheter sizes. Today, I’ll deal with another arcane system, the gauge system for hypodermic needles.

I’ve always wondered how this worked. Lower numbers somehow indicate bigger needles. And to make it more confusing, there are two conflicting gauge systems, the Birmingham Wire Gauge (aka the Stubs Iron Wire Gauge) and the Stubs Steel Wire Gauge. Confusing, right? And these two are actually a little different.

Hypodermic needle sizes are based on the Birmingham gauge system (G). The Gauge indicates the outer diameter (OD) of the wire used to make the needle, but is inversely related to it. And to top it off, there is no real mathematical formula that relates gauge to the OD. If you are that interested, you have to consult a printed table.

Needle gauge ranges from 7G (4.57mm OD) to 34G (0.18mm OD). There is also little correlation of the inner diameter to gauge, as the wall thickness decreases as the OD of the needle decreases. As an interesting tidbit, there is an International Standards Organization (ISO) standard for single-use needles that determines the color coding of the hub. I always wondered who thought those up!

Okay, so needle gauge is based on the size of the wire used to make them. What about IV catheters? Just to make it more confusing, IV catheter size indicates the size of the needle used to insert them. So an 18G IV catheter has an inner diameter that is almost identical to the OD of its needle. The outside diameter of the catheter will be a tiny bit bigger. Got it?!

So there you have it. Amaze your friends with your arcane knowledge about tubes and needles and catheters!

General

Where Did The French Tube Size System Come From?

March 27, 2018 The Trauma Pro Leave a comment

Medicine sure has some weird measurement systems. Besides the more standardized units like microliters, milligrams, and International Units, we’ve got some odd stuff like French (tubes) and gauge (needles). When dealing with tubes and catheters, the size is usually specified in French units.

Where did the French system come from? It was introduced by a Swiss-born gentleman named Joseph-Frédéric-Benoît Charrière. He moved to Paris and was apprenticed to a knife maker. At the age of 17, he founded a company that manufactured surgical instruments. His company developed and improved a number of surgical instruments, including hypodermic needles and various catheters.

Charrière introduced the system for describing catheters based on their outer diameter (OD). It was actually named after him, and in France one will occasionally see catheters described in Ch units. Unfortunately, we Americans had a hard time pronouncing his name, and changed it to the French system (Fr).

So what’s the translation? The Ch or Fr number is the outer diameter of a catheter in millimeters multiplied by 3. It is not the outer circumference in millimeters, and the use of pi is not involved. So a big chest tube (36 Fr) has an OD of 12 mm, and a bigger chest tube (40 Fr) has an OD of 13.33 mm.

Tomorrow: Where did the needle gauge size come from?

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