# Where Did The Hypodermic Needle Gauge System Come From?

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!

# Where Did The French Tube Size System Come From?

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 Mythbusters: NSAIDs And Fracture Healing

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:

• There were 4x as many total subjects in the “NSAIDS are okay” papers than in the “avoid NSAIDS” papers
• The quality of the “NSAIDS are okay” papers were significantly higher than “avoid NSAIDS” group (59 vs 40)
• Interestingly, the “avoid NSAIDS” papers are cited twice as often
• All of the reviews ended with my pet peeve catch phrase “further (good) research is needed”

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:

1. Effects of nonsteroidal anti-inflammatory drugs on bone formation and soft-tissue healing. J AM Acad Orthop Surg 12:139-43, 2004.
2. Effect of COX-2 on fracture-healing in the rat femur. J Bone Joint Surg Am 86:116-123, 2004.
3. Effects of perioperative anti-inflammatory and immunomodulating therapy on surgical wound healing. Pharmacotherapy 25:1566-1591, 2005.
4. Pharmacological agents and impairment of fracture healing: what is the evidence? Injury 39:384-394, 2008.
5. High dose nonsteroidal anti-inflammatory drugs compromise spinal fusion. Can J Anaesth 52:506-512, 2005.
6. Nonsteroidal Anti-Inflammatory Drugs and Bone-Healing: A Systematic Review of Research Quality. JBJS Rev 4(3), 2016.

# Ever Wonder Where The Golden Hour Came From?

Everywhere you turn in the trauma and EMS world, you run into the concept of the “golden hour.” Basically, it refers to the idea that it’s important to get an injured patient to definitive care promptly, or mortality begins to rise. It has been used to justify a lot of what we do in trauma care and trauma systems. But where did this come from? And is it true?

The BTLS course attributes the term to R Adams Cowley from the ShockTrauma Center in Baltimore. Unfortunately, no references are given. A biography of Cowley entitled Shock-Trauma names him the author of the term, basing it on dog research. No references were given.

A review of Cowley’s research reveals a few tidbits. A case series of patients implies that speed is good, but does not analyze time to definitive care. It does reference older work by other authors, but once again, no relationship between timing and outcome is evaluated.

A textbook edited by Cowley contains a reference to an article about “Cowley’s golden hour.” This article contains a statement that “patients are assumed to be dying and much of the golden hour has passed.” It goes on to state that the first 60 minutes after injury determines the patient’s mortality. It, in turn, refers to another of his earlier articles. This one states that “the first hour after injury will largely determine a critically injured person’s chance for survival.” No data or reference is given.

Bottom line: The concept of the “golden hour” has taken on a life of its own. Yes, it’s a good idea. And yes, there is some actual data to support it, although the quality is somewhat lacking. But this does point out the need to question everything, even some of our most deeply held beliefs. They are not always what they seem to be.

Reference: The Golden Hour: scientific fact or medical urban legend? Acad Emerg Med 8(7):758-760, 2001.

# The Rectal Exam In Trauma Continues to “Pass”?

This topic continues to come up from time to time. I still see trauma programs that perform the good, old-fashioned digital rectal exam on nearly every trauma patient. But is it really necessary?

In the not so distant past, it was standard operating procedure to perform a digital rectal exam in all major trauma patients. The belief had always been that valuable information about blood in the GI tract, the status of the urethra, and the neuro exam (rectal tone) could be gleaned from this exam.

Unfortunately, a finger in the bum also serves to antagonize or even further traumatize some patients, especially those who may be intoxicated to some degree. On a number of occasions I have seen calm patients become so agitated by the rectal exam that they required intubation for control.

So is it really necessary? A study in 2001 conducted over a 6 month period (1) showed that the rectal exam influenced management in only 1.2% of cases. The authors felt that there was some utility in 3 special cases:

• Spinal cord injury – looking for sacral sparing
• Pelvic fracture – looking for bone shards protruding into the rectum
• Penetrating abdominal trauma – looking for gross blood

A more recent 2005 study (2) was also critical of the rectal exam and found that using “other clinical indicators” (physical exam and other diagnostic study information) was at least equivalent, changing management only 4% of the time. They concurred with the first two indications above as well.

Bottom line: For most major trauma patients, the rectal exam is not worth the patient aggravation it causes. I still recommend it for the 3 special cases listed above, however, as there are no equivalent exams for these potentially serious patient problems. And remember, DON’T do it while the patient is in the logroll position. No patient likes a rectal exam, so they’ll do their best to defeat your puny attempt at spine precautions if you have them on their side. Supine, frog-leg only.

References:
1. Porter, Urcic. Am Surg. 2001 May;67(5):438-41.
2. Esposito et al. J Trauma. 2005 Dec;59(6):1314-9.