Hello, all. I am visiting Cuba this week and so will not be “broadcasting live.”
I will, however, dust off some oldies but goodies that haven’t been seen in quite some time. I’ll be back live next week.
Enjoy!
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!
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!
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?
Trauma hurts like hell. Over the years, we’ve developed quite a few ways of combating this pain. A number of drug classes have been developed to reduce it. One of the more common non-narcotic drug classes are the NSAIDs. As I’ve mentioned before, every drug has dozens of effects. Drug companies market a particular medication based on one of the predominant effects. All the others are considered side effects.
NSAIDs are not unique; they have lots of side effects as well. In 2003, several papers brought to light possible interactions between these drugs and fracture healing. Specifically, there were questions about these drugs interfering with the healing process and of increasing the number of delayed unions or nonunions. But once again, how convincing were these papers, really?
It would seem to make sense that NSAIDs could interfere with bone healing. This process relies heavily on the regulation of osteoblast and osteoclast function, which itself is regulated by prostaglandins. Since prostaglandins are synthesized by the COX enzymes, COX inhibitors like the NSAIDs should have the potential to impair this process. Indeed, animal studies in rats and rabbits seem to bear this out.
But as we have seen before, good animal studies don’t always translate well to human experience. Although a study from 2005 suggested that NSAID administration in older patients within 90 days of injury had a higher incidence of fracture nonunion, the study design was not a very good one. It is equally likely that patients who required these drugs in this age group may have been at higher risk for nonunion in the first place.
In fact, there are no large, prospective randomized studies that have explored the effect of short-term or long-term NSAID administration on fracture repair. But there have been several smaller studies that showed absolutely no effect on nonunion with short-term administration of this drug class. Yet the dogma that leads us to avoid giving these drugs persists.
A recent analysis looked at the quality of the published research, both for and against NSAID usage in fracture patients. They used the Coleman Methodology Score, which evaluates study size and type, mean followup, detailed description of treatment, subject selection, outcomes, and outcome assessment. The maximum score was 100.
Here are the factoids:
Bottom line: Once again, the animal data is clear but the human data is not. Although there are theoretical concerns about their use, there is not enough solid risk:benefit information to abandon short-term NSAID use in patients who really need them. NSAIDs can and should be prescribed in patients with short-term needs and simple fractures.
References: