Miscellaneous Medical Facts

criteria must be sufficient as well as necessary

Always leave 0.1 ml of air in the syringe for IM and SC injections to keep back leakage from ocurring

Add 10 mcg of epi to each cc of lido. 1:10000 = 100 mcg per cc so add 0.1 cc per cc of lido

Celcius & Fahrenheit

Add 40

Multiply or Divide by 1.8

Subtract 40

French instrument maker, Charrière was famous for his attention to detail and perfectionism. At that time, there was very poor standardization for measuring catheters and tubes. Charrière, in 1842 developed a system still in use to standardize these gauges. In his system, one Charrière is equal to 1/3 millimeter diameter. To this day, in most other parts of the world, catheters and such are sized based on their Charrière gauge (abbreviated ch).

However, in the land that made pommes frits french fries, a Charrière has been renamed a French.

Thus, a catheter that is 18 french (or 18 ch in the rest of the world), is 6 mm in diameter. French divided by 3 equals millimeters in diameter. (RaneyFacts)

What if you have a liter of NS and want D5NS? Well, easy enough, D5 (or 5% dextrose) means 5 grams dextrose per 100 cc, right? Since the bag is a liter, that means 50 grams dextrose. So, add two amps of D50 to that sucker and now you have D5! Right? Well, not quite

Since these volumes are so close (100 cc added to 1000), the volume added is significant (unlike adding 0.3 cc to 30). In actuality, the final solution would be roughly 4.5% concentration (50 grams/1100cc) and the NS would be slightly diluted.

That having been said, this works, in practice, for the addition of two amps or less to a liter.

——————————————————————————– From the FDA: What’s in a Label? A Guide for the Anesthesia Practitioner [Volume 103(1) July 2005 pp 179-185 of anesthesiology or canadian journal of anesthesia??)

Esmolol Dosing

Weight in Kg/2=loading dose over 1 minute

Multiply this by 0.1 to get drip rate per minute

Thus, a catheter that is 18 french (or 18 ch in other parts of the world), is 6 mm in diameter. French divided by 3 equals millimeters in diameter.3. Useful Facts and FiguresOk, What About Other Gauges? A loaded question

Gauge, as relates to thickness, has at least seven currently used and completely different definitions in this country alone. Aside from French gauge noted above, the following also have their own gauge measurement/definition (37)

Shotgun a measurement of the internal diameter of a shotgun barrel. Specifically, the number of lead balls of this same diameter that it takes to make up one pound. Thus 12-gauge means 12 lead balls, each of a size that fit a shotgun barrel, would weigh one pound. So higher gauge = smaller diameter barrel (20 gauge means it would take 20 balls to equal one pound).
Fabric (and knitting needles, not surgical needles see below) an expression of the fineness of knitted fabric: the number of loops of thread in 1.5 inches of fabric. Also the needles used for such knitting. Higher gauge = finer thread/smaller needles.
Sheet metal a measurement of the thickness: as with wire, relates to repetitive passes through a press, resulting in smaller gauge. A gauge of 10 represents 0.1345 inch (3.416 millimeters) and each increase of 1 in the gauge number corresponds to a reduction of about 10% in the thickness. Higher gauge = smaller thickness.
Plastic film – a measurement of thickness: one gauge equals 0.01 mils. Higher gauge = thicker film
Wire, or American Wire Gauge (AWG) the one we are interested in:

American wire gauge is the convention currently used to relate the size of our straight or injection needles those used for IVs and IM injections. It is not the same as that used for suture needles (see below). The reader will note that injection needles get smaller as the number gets larger, while the opposite is true of suture needles (see also the discussion of zeros below). AWG originally came from how many times the original material passed through a stretching machine. As it is passed through each time, it got thinner. For this reason, the higher the number, the smaller the wire. To this day, dies are used in a similar fashion, but with precise final sizes. With time, a formula was developed to ensure uniformity of wire sizes. Since the attempt was to come up with a derived formula that approximated already used wire gauges (i.e. it was retrofitted), the formula is quite non-intuitive (I am NOT making this up! – apologies to Dave Barry):

n gauge = 0.005·92^((36-n)/39)) , in inches [^ indicating raised to the power]
Note that sizes with a numerical value of less than zero became needed over time. The common practice was simply to begin adding more zeros. The next larger wire size (smaller numerical value!) after 0 is 00, followed by 000, 0000, etcetera. For ease of writing these successive zeros are also written as: 1/0, 2/0, 3/0, and so on. Note further that the same adding of zeros is used with suture gauge, by convention 0000 in suture size is usually called 4-0 (suture convention uses the dash rather than the slash). To put it differently, counting down numerically by this convention would be: 3, 2, 1, 0, 00 (or 2/0), 000 (or 3/0), 0000 (or 4/0), etc. We pronounce each of these as the number followed by oh, so 4-0 suture is four-oh.
For the formula above the sizes of 2/0, 3/0, 4/0, and up are represented by -1, -2, -3, etc.

So, a 5/0 wire (represented by -4 in the formula) would have a diameter of about ½ inch (ouch!), while a 27 gauge infiltration needle has a diameter of about 14 mils (a mil = one thousandth of an inch). An 18 gauge needle has a diameter of about 0.04 inches or about 1 mm.Well, What About Suture Sizing (57-60)As we all know, suture and suture needles get larger with larger sizing the opposite of that just discussed with needles for injection (remember that 00, or 2-0, is numerically larger than 000, or 3-0). And we know that a 5-0 suture is not ½ inch in diameter (as with AWG), so whats with suture? As you might guess, that is something again altogether different Suture sizing was developed with the purpose of the suture (tissue to be closed) as the primary consideration (whether intended for closing skin, muscle, etc). It takes into account the size and strength of the material, as well as the elasticity and tie-ability (how well it holds a knot). The intention was that all suture of similar designation should be able to be used for the same tissue and purpose. For example, you would know that any 3-0 suture would have the physical characteristics making it suitable for closing skin.

However, with the changing and widely available materials, eventually a sizing convention was reached, assigning limits to the upper and lower acceptable diameters for suture:

USP SIZE

DIAMETER LIMITS (mm)

METRIC SIZE

(10 x mm)

ABSORBABLE SUTURES (Catgut Chromic and Plain)

NON-ABSORBABLE AND SYNTHETIC ABSORBABLE SUTURES

–

6-0

0.070 – 0.099

0.7

6-0

5-0

0.100 – 0.149

5-0

4-0

0.150 – 0.199

1.5

4-0

3-0

0.200 – 0.249

3-0

2-0

0.300 – 0.339

2-0

0.350 – 0.399

3.5

0.400 – 0.499

0.500 – 0.599

3,4

0.600 – 0.699

–

0.700 – 0.799

The differences in actual diameters for absorbable versus nonabsorbable relates to the above noted utility sizing meaning that absorbable sutures, in order to have the same holding characteristics for adequate amount of time, need in general to be a larger size. For example: gut would have to be thicker to hold long enough to assure adequate healing than would nylon, since it will weaken more rapidly with time. As you can see, newer synthetic absorbables are able to delay the weakening effects of time such that they are about the same size as non-absorbable suture. By convention, the needle attached to the suture is of a similar size as the suture. Thus, a needle attached to 5-0 nylon would be about 0.15 mm in diameter, while a 5/0 needle (by AWG wire convention) would be about 13 mm in diameter (1/2 inch). Again remember that both 5-0 and 5/0 refer to 00000 and represent a number that is numerically 5 times smaller than 0. And that by convention suture uses the dash, while AWG uses the slash Confused yet? Dont shoot the messenger!Getting Back to Formula (and changing gears)Lets say you are working in a small community ED, and a patient comes in with a laceration to the head. You want to use lidocaine with epinephrine but you just used up the last bottle (this has happened to me before!). All you have is plain lidocaine and the usual ED drugs. Not wishing to sound like a Chem final, how can you easily mix up 1% lidocaine with epinephrine using these ingredients? You know that 1% lidocaine contains epinephrine at 1:100,000 (youve seen this on the bottle). You also have epinephrine for subcutaneous administration at 1:1000. Hmm. What does 1:100,000 mean? 1:1000? For that matter what does 1% mean? Why didnt someone teach me this in medical school? Dont panic, it is really easy. Start with the realization that percent (%) is equal to 1:100, just nobody writes it that way. Then realize that each of these ratios represents grams per cubic centimeters (or mls). So:

1% = 1:100 = 1 gram per 100 cc = 1000 mg/100cc = 10 mg/cc (standard lidocaine for infusion concentration)

1:1000 = 1 gram per 1000 cc = 1000 mg/1000 cc = 1 mg/cc (as in epi for sub-Q)

1:100,000 1 gram per 100,000 cc = 1000mg/100,000 cc = 0.01 mg/cc

You also note that the bottle of 1% plain lido is a 30cc bottle. So: 0.01 mg/cc times 30 cc equals 0.3 mg. Since you have epinephrine at 1 mg/cc, you can draw up 0.3 cc of this solution (use a tuberculin syringe) and add it to the lidocaine jar. Viola! You now have 1% lidocaine with epinephrine 1:100,000!! You are so slick.And About that D50

With this knowledge, we know that D50 contains 50 grams per 100 cc (50 is 50%). So, that 50 cc amp contains 25 grams of dextrose. Of course, you could have read that off the side of the syringe, but now we have understanding! What if you have a liter of NS and want D5NS? Well, easy enough, D5 (or 5% dextrose) means 5 grams dextrose per 100 cc, right? Since the bag is a liter, that means 50 grams dextrose. So, add two amps of D50 to that bag and now you have D5! Right? Well, not quite Since these volumes are so close (100 cc added to 1000), the volume added is significant (unlike adding 0.3 cc to 30). In actuality, the final solution would be roughly 4.5% concentration (50 grams/1100cc) and the NS would be slightly diluted. That having been said, this works, in practice, for the addition of two amps or less to a liter. Now go forth, and do mixers!Speaking of Dextrose

You are presented with a patient that is poorly responsive, diaphoretic and tachycardic. The patient is wearing a bracelet that tells you he is diabetic and the rapid finger-stick shows a glucose of 24. Why, if this patient is in extremis from a critically low glucose, are you now going to administer dextrose? Why, pray tell, dont you give GLUCOSE?!? Well, thats also quite easy – you are: Dextrorotary glucose = dextrose (1) while levorotary glucose = levulose = fructose. By convention, per Dorlands (and others), naturally occurring dextrorotary glucose is referred to as glucose, while synthetic dextrorotary glucose is called dextrose. To be complete, some purists claim that glucose is the hydrated form and dextrose the dehydrated form. Were that true, however, we should be giving that patient an amp of G50.Since Were Talking about Purists…

We are taught that – and many texts refer to – the sniffing position as being the correct position to use for intubating. Well, which sniffing position is correct? Several texts state sniff the morning air position. Try this (I also call it the what IS that smell? position). This position puts your head and neck both straight back, basically pointing your nose toward the ceiling. Clearly, this results in too much neck extension, and is the wrong position. While I have no doubt the authors know the right position, they are not articulating it well. Being a bit (ok, maybe more than a bit) silly, it is obvious that sniffing your underarm (the did I bathe? sniff), sniffing your breath (in your hand, the will she/he kiss me? sniff), and sniffing cocaine are all similarly wrong positions. Others have mentioned (more correctly, but not exactly right) that the correct position is best described as the position one would assume to smell a rose that is being offered to smell. Anatomically, this is described as flexing the neck on the chest, while extending the head on the neck (see top drawing, where OA, TA, and PA = oral, tongue, and pharyngeal axis respectively; note the shoulders flat on the table/stretcher, also position A in the illustration).

Chevalier Jackson, 1934 (38)

Well, what IS the best position? As originally described by Chevalier Jackson in 1934 (38), and recently validated by Levitan (39) using his patented Airway Cam (Airway Cam Technologies, Inc., Wayne, PA), the shoulders are elevated, and the neck and head are positioned even higher (see illustration, from Jacksons paper). Levitan names this the head elevated laryngoscopy position, or HELP. I would describe this as a sniffing the pot of soup position. Again, try it most ranges (with a tall soup pot!) are of the height that you will instinctively bend your shoulders forward and do the right stuff with your head and neck. Sniffing the deli meat (imagine leaning over a tall counter) is another example, or the what is rotten in the cupboard? position Most of us automatically go to this position, without giving it much thought, when we get in difficult airway situations (assuming no c-spine injury). But we should embrace and teach this as the normal method not the one we fall back on.Speaking of Airways, What IS the True Apnea Interval?Most of you know, after years of having this hammered in by airway teachings that there is a long apnea interval if the patient has been adequately pre-oxygenated. This refers to the amount of time that your patient can go without breathing before the oxygen saturations will drop below 90%. Adequate pre-oxygenation consists of either breathing high concentration oxygen (non-rebreather mask) for at least five minutes, or eight vital-capacity breaths (or eight big bags via bag-valve-mask). Benumof showed that up to eight minutes is the expected interval for a healthy 70 kg patient (40). Hmm. Lets consider that as it relates to Emergency Medicine. I dont know about you, but I rarely intubate healthy patients. Come to think of it, most of mine are pretty sick. And obese, inevitably obese… What are their apnea intervals? And what about kids?
These questions are answered by the same article, by Benumof (40), and are illustrated by the graph from the article:

We can see that a moderately ill 70 Kg adult will desaturate in less than 5 minutes, and an obese (presumed healthy?) adult in about 2.5 minutes. Children (again, healthy in this chart) similarly will desaturate more quickly, as they have relatively less vital capacity and a higher relative oxygen metabolism. An obese and moderately ill child may desaturate very rapidly. Also, this assumes proper preoxygenation. As we all know, this is not always possible, either due to time constraints or pathophysiology. While I live and teach by these numbers (Benumofs), I also regularly see patients desaturate in less than 30 seconds. We must be sure to take these things into account when performing airway interventions, and be sure to include them in our teachings.4. Other Interesting and Useful OdditiesLomotil ® (44,45)This is an interesting and useful concoction of diphenoxylate 2.5mg and atropine 0.025 mg per tablet, for diarrhea (Lomotil named for low motility).OK, quickly now why is the atropine added? The recommended dose is two tablets, or 0.05 mg atropine per dose. Remember that the smallest recommended dose of atropine is 0.1 mg since doses less than this in children can cause paradoxical bradycardia (at smaller doses it can have cholinergic rather than anticholinergic effects). So why give half that amount to an adult? What are we, CRAZY?!?

Diphenoxylate is a meperidine (Demerol®) congener, but is very insoluble. In therapeutic doses, it has almost no systemic effects, exerting only local constipating ones. However, if someone were to take large doses, 40 to 60 mg, he would experience definite systemic opioid effects. Note this is 16 to 24 times the recommended dose, and 2 3 times the maximum recommended daily dose. The atropine is deliberately added as a dysphoric agent, to discourage deliberate abuse it is very well absorbed! Who would have thought? Speaking of Atropine… (46-48) Did you know that atropine is inevitable? For millennia a hardy and well known perennial shrub known as the deadly nightshade was used for murder by poisoning. For this reason, as will be explained, the famed Swedish botanist Carl von Linné (Carolus Linneaus) in the 1700s named the plant ‘atropa belladonna’. The main alkaloid from this plant (racemic hyoscyamine) is named after this plant’s first name: atropine (again, note the adoption of the -ine suffix see page 1). The unpurified extract, containing other alkaloids (including scopolamine), is called belladonna. It was this extract that was used for poisonings. Linné chose Atropa for the eldest of the three Greek Fates: Atropos. The fates were Klothos (the spinner), who spun the web of life; Lachesis (the apportioner) who measured its length; and Atropos (the inexorable or inevitable), who would cut the thread – sometimes impulsively and without warning (meaning life was suddenly and inexplicably, or inevitably, cut short as in murder). Thus, ‘atropine’ is ‘inevitable’! I love saying this at work always gets a few odd glancesBut why did Linne choose Belladona? (47,49)Most sources state this means beautiful lady, the literal translation from Italian. They note that women of the time used a tincture from this plant in their eyes, to cause them to dilate (and perhaps also causing their cheeks to flush) theoretically becoming more beautiful. Other references claim this came from folklore that told of the ability of the plant to lure men to their death by appearing as a beautiful lady. One reference (49) even stated the possibility of its referring to Bellona, the god of war as supposedly some priests would drink a potion containing belladonna to place them in a trance when praying to this god. Finally, Holzman notes that there is very little evidence that belladonna was ever used as a cosmetic, and proposes that in fact the name comes from buona donna the good lady. This, he postulates, was in sarcastic reference to the witches of the times, who practiced their art using such poisons (47). The truth may never be known, but it is interesting to note the possibilities.What About the Toxidrome?

Since we are discussing belladonna and the fact that it is poisonous, what about the oft- quoted anticholinergic toxidrome? Here is the correct (meaning original) saying:

Hot as a Hare (not Hades as some quote)

Blind as a Bat

Dry as a Bone

Red as a Beet

Mad as a Hen (not Hatter!!)

I was taught this saying (from an older Canadian text, see ref 44) and as the years have gone by, I have seen it published many different ways. As part of a toxicology lecture, I decided to find out what was right. With much searching and following other references, I found the earliest publication (that I could find) of this toxidrome mnemonic from HG Morton in the Journal of Pediatrics, circa 1939 (50). Why is this important? Not to mention the fact that in its original form it is much better poetically (having four beats per line), there is a more important reason: hatters became mad from exposure to mercury (see sidebar). This presents a source for confusion for the student, and should be avoided. Stick to Dr. Mortons mnemonic.

On Making Hats (51,52)

The making of wool felt has been around for centuries, arguably the first textile used. The process involved soaking the firs (typically rabbit or beaver) in a heated reddish-orange solution of mercury nitrate a process called carroting. Carroting causes the scales of a hair follicle to open up, allowing the hairs to lock more firmly together forming a strong mat that can then be shaped into a hat. This process, over time exposed the hatter to a large amount of mercury vapor, leading to mercury poisoning. The resulting CNS changes lead to the phrase mad as a hatter. The use of mercury in hat making was phased out in 1943.

And Finally: ShinglesWhy do we call varicella-zoster shingles? I have had some students offer that the rash might be compared to shingles on a roof. Interesting, but incorrect. It comes from the Latin cingulus which means girdle. Gird means to encircle as with a belt or band. A girdle is a device which encircles in such a fashion. With varicellas tendency to follow a dermatome around the body, it is clear to what cingulus refers. Shingle, on the other hand, comes from the Latin scindere meaning to splint reflecting the fact that the original wooden shingles were split from a log (also known as shakes presumably related to the jerky motion used to split them off). Over the years, slippage in pronunciation lead to cingulus becoming shingles a common occurrence, one that leads to new words and languages. Perhaps yet we will see Fireballs of the Eucharist (fibroids of the uterus), Smilin Mighty Jesus (spinal meningitis), Roaches of the Liver (cirrhosis) and Sixty-five Roses (cystic fibrosis) enter into legitimate medical usage! The reader can supply others, no doubt.The EndI hope you have enjoyed this as much as I enjoyed putting it together. Medical trivia and similar pertinent relevancies have always held a great deal of interest for me, and these facts and anecdotes can make teaching and learning a more enjoyable experience. Frequently, finding out the why of things, makes them easier to remember and understand. Remember: Le bon Dieu est dans les details! [God is in the details probably the origin of the devil is in the details, but enough already]

Gauge Conversion

Conversion units Charriere

Charriere = Ch, CH

– Synonym French gauge.

– Definition Unit which expresses the external diameter in ⅓ mm where:

CH N° = ext. diameter in mm

Example: CH6 = 2mm

or CH4 = 1.33mm

– Field of use Tubes and drains.

French = F or FG

– Synonym French size, french gauge, charriere.

– Definition Unit which expresses the external diameter in ⅓ mm where:

1 FG = 1 CH = ⅓ mm

Attention: Some manufacturers offer catheters mesaured in INCHES.

Example: 5 FG = CH5 = 1.66mm = 0.066 INCH

– Field of use Exploratory catheters, tubes and drains.

Gauge = G, Ga, Gg, g

– Synonym British standard gauge.

– Definition Unit which expresses the external diameter of the object, in a range from 8 to 30, corresponding respectively to 4 and 0.3mm.

Attention: The gauge/mm correspondance may vary, due to figures being rounded off inconversion from inches to mm.

The higher the gauge, the smaller the external diameter.

The gauge gives the external diameter, but does not take account of the thickness of the wall, so does not give an idea of the external diameter.

Example: 22G = 0.7 to 0.9mm

18G = 1.1 to 1.3mm

– Field of use Short catheters, needles, microperfusers.

INCH = In or 

– Synonym In french: pouce

– Definition Unit used to express the external diameter of guides.

Example: 1 in = 1 inch = 25.4mm

1mm = 0.04 in = 0.04

– Field of use Guides for catheters.

PLASTEAU-BENIQUE = P.B

– Synonym Benique.

– Definition The Plasteau-Benique measurement corresponds to half the charriere measurement.

Unit which expresses the external diameter in 1/6 mm.

P.B N° = ext. diameter in mm

Example: 40 P.B = 20CH = 6.66mm

– Field of use Tubes for urology.

Approximate Metric Conversion Factors For Common Conversions

Length
Area
Mass (Weight)
Volume
Temperature
Mechanics
Energy
Light
Electricity
Tubing Related Formulae
French Catheter Scale
Needle Gauge Scale

When You Know Multiply by To Find Length inches 25.4 millimeters inches 2.54 centimeters feet 30 centimeters millimeters 0.04 inches centimeters 0.4 inches meter 3.3 feet Return to top Area square inches 6.5 square centimeters square feet 0.09 square meters square centimeters 0.16 square inches square meters 1.2 square yards Return to top Mass (weight) ounces 28 grams pounds 0.45 kilograms grams 0.035 ounces kilograms 2.2 pounds Return to top Volume pints 0.47 liters quarts 0.95 liters gallons 3.8 liters cubic feet 0.03 cubic meters cubic yards 0.76 cubic meters milliliters 0.03 fluid ounces liters 2.1 pints liters 1.06 quarts liters 0.26 gallons cubic meters 35 cubic feet cubic meters 1.3 cubic yards Return to top Temperature Fahrenheit 5/9 (after subtracting 32) Celsius Celsius 9/5 (then add 32) Fahrenheit

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Formulae

Mechanics

Coefficient of Frictionm = coefficient of friction F = force of friction N = force normal to surfaceVelocity Vav = average velocityd = distance travelledt = elapsed timeAcceleration a = acceleration Vf = final velocity Vi = initial velocityt = elapsed timeNewton’s 2nd Law of Motion F = forcem = massa = accelerationLaw of Universal Gravitation F = force of attraction G = gravitational constantm1m2 = product of massesd = distance between their centersCentripetal Force F = centripetal forcem = massv = velocityr = radius of pathPendulum T = periodl = lengthg = acceleration of gravityWork W = work F = forced = distanceMechanical Advantage IMA = ideal mechanical advantage FE = effort force FR = resistance force AMA = actual mechanical advantaged = distanceMechanical Equivalent of HeatW = work J = mechanical equivalent of heat Q = heat

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Energy

Kinetic Energy K.E. = kinetic energym = massv = velocityPotential Energy P.E. = potential energym = massg = acceleration of gravityh = vertical distance (height)Relationship between Mass and Energy E = energym = masse= velocity of light

Light

Wave Formulav = wave speedf = frequencyl = wave lengthUniformly Illuminated Surface E = illuminationY = luminous flux A = uniformly illuminated areaImages in Mirrors and Lenses So = object size Si = image size Do = object distance Di = image distanceFocal Length of Mirrors and Lensesf = focal length Dq = object distance Di = image distanceIndex of Refractionn= index of refractionqi = angle of incidenceqr = angle of refraction

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Electricity

Electric Current l = currentq = quantity of charget = timeCoulomb’s Law of Electrostatics F = force between two chargesk = proportionality constantq1q2 = product of chargesd = distance separating chargesCapacitance of a Capacitor C = capacitance of a capacitor V = potential difference between platesq = charge on either plateOhm’s Law of Resistance E = emf of source R = resistance of the circuit l = current in the circuitJoule’s Law H = heat energy l = current R = resistancet = timeFaraday’s Law of Electrolysism = mass l = currentz = electrochemical equivalentt = timeInduced emf: Coil in a Magnetic Field E = induced emf N = number of turnsDF/Dt = the change in flux linkage in a given interval of timeInduced emf: Conductor in a Magnetic Field E = induced emfl = length of conductorv = velocity of conductor across magnetic field B = flux density of the magnetic fieldInstantaneous Voltagee = instantaneous voltage Emax = maximum voltageq = displacement angleInstantaneous Currenti= instantaneous current Imax = maximum currentq = displacement angle

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Tubing Related Formulae

Burst Pressure (P) in lbs/sq. in. T = wall thickness in inches S = material tensile strength in P.S.I. O = outside diameter in inchesOperating Pressure (O.P.)OvalityConcentricity Concentricity % = min. wall / max. wall 100 Concentricity value = (max. wall – min. wall) concentricity %Specific Gravity (S.G.) S.G. = specific gravitym = massv= volume

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French Catheter Scale

French Size Inch Equivalent mm Equivalent 3F 0.039 1.0 4F 0.053 1.35 5F 0.066 1.67 6F 0.079 2.0 7F 0.092 2.3 8F 0.105 2.7 9F 0.118 3.0 10F 0.131 3.3 11F 0.144 3.7 12F 0.158 4.0 13F 0.170 4.3 14F 0.184 4.7 15F 0.197 5.0 16F 0.210 5.3 17F 0.223 5.7 18F 0.236 6.0 19F 0.249 6.3 20F 0.263 6.7 22F 0.288 7.3 24F 0.315 8.0 26F 0.341 8.7 28F 0.367 9.3 30F 0.393 10.0 32F 0.419 10.7 34F 0.445 11.3

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Needle Gauge Scale

Gauge Size Inch Equivalent mm Equivalent 13 0.095 2.413 14 0.083 2.108 15 0.072 1.829 16 0.065 1.651 17 0.058 1.473 18 0.049 1.245 19 0.042 1.067 20 0.035 0.889 21 0.032 0.813 22 0.028 0.711 23 0.025 0.635 24 0.022 0.559 25 0.020 0.508 26 0.018 0.457 27 0.016 0.406

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Go to source: TFX Medical OEM – Technical Reference – Common Conversions

The Majority of Bold Statements expressed during grand rounds lack scientific merit

(Med Ed 2007;Linthorst GE)