# Gauge size

I have a question for the PICC nurse community regarding gauge size. How do you use gauge size in your clinical practice....meaning, is it an indicator of flow to you or does it indicate something else? For example, if you were to have two different single lumen, 4fr PICCs; one with a guage size of 18 and one with a gauge size of 20....what would this mean to you?

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## Gauge sizes originated from

Gauge sizes originated from the wire industry and applies to round lumens. If the lumen is not round the surface area is measured and the assigned gauge size is equivalent to the gauge size of similar surface area. Lumen size determines 3 things - flow rates capable through the lumen, priming volume, and pressure ratings. The issue of pressure rating has recently changed though with the ability of smaller lumens to accomodate power injections. If I had a choice of a larger lumen vs a smaller lumen, I would always draw blood samples, transfuse blood/components, infuse IVFE through the larger lumen. Lumen size also dictates the priming volume or the amount required to lock the catheter. This is important for procedures such as TPA instillation. Lynn

Lynn Hadaway, M.Ed., RN, BC, CRNI

Lynn Hadaway Associates, Inc.

126 Main Street, PO Box 10

Milner, GA 30257

Website http://www.hadawayassociates.com

Office Phone 770-358-7861

## Gauge equates to flow rates

Gauge equates to flow rates to me. But you also have to factor in length. If you are looking for high gravity flow rates then a picc is not your answer. I recently researched this and was surprised to find out that an 18g 4fr. picc flows at about the same rate as a 22 gauge peripheral IV catheter. This is why most anethesiologists don't like piccs, which is good because most piccs don't like anethesiologists.

Darilyn Cole, RN, CRNI, VA-BC

PICC Team Mercy General Hospital Sacramento, CA

## Gauge size

In a nutshell: French size is the outside diameter, gauge is the diameter of the inner lumen. With the wide variety of products on the market (Power, non-power, single lumen, double lumen, triple lumen etc.) the outside diameter does not have a direct proportion to the inside diameter of the lumen.

As far as the flow rate? The information below was taken from a popular manufacturer's website (I am not affiliated with any company). Bottom line: you are going to have to know the flow rates for the catheters you are using. There are no “set in stone” correlations.

Catheter SizeLumensGaugeGravity Flow (ml/hr)Priming Volume (ml)Lumen Size I.D. (in)4 Fr

Single

18

540 ml/hr

0.45 ml

4 Fr

Single

18

540 ml/hr

0.45 ml

4 Fr

Single

18

798 ml/hr

0.62 ml

0.034 in.

5 Fr

Single

18

398 ml/hr

0.42 ml

0.035 in.

4 Fr

Single

18

1024 ml/hr

0.73 ml

5 Fr

Dual

18/18

498 ml/hr /498 ml/hr

0.65 ml /0.65 ml

4 Fr

Single

18

1,272 ml/hr

0.67 ml

5 Fr

Dual

18/18

515 ml/hr /515 ml/hr

0.55 ml /0.55 ml

0.034/0.034 in.

6 Fr

Dual

18/18

762 ml/hr /762 ml/hr

0.69 ml /0.69 ml

0.037/0.037 in.

5 Fr

Single

18

1,185 ml/hr

0.66 ml

5 Fr

Dual

18/18

578 ml/hr / 578 ml/hr

0.57 ml / 0.57 ml

6 Fr

Dual

18/18

753 ml/hr / 753 ml/hr

0.62 ml / 0.62 ml

5 Fr

Triple

18/ 20/ 20

982 ml/hr / 131 ml/hr / 131 ml/hr

0.76 ml / 0.43 ml / 0.43 ml

## Gauge size

In a nutshell: French size is the outside diameter, gauge is the diameter of the inner lumen. With the wide variety of products on the market (Power, non-power, single lumen, double lumen, triple lumen etc.) the outside diameter does not have a direct proportion to the inside diameter of the lumen.

As far as the flow rate? The information below was taken from a popular manufacturer's website (I am not affiliated with any company). Bottom line: you are going to have to know the flow rates for the catheters you are using. There are no “set in stone” correlations.

Catheter SizeLumensGaugeGravity Flow (ml/hr)Priming Volume (ml)Lumen Size I.D. (in)4 Fr

Single

18

540 ml/hr

0.45 ml

4 Fr

Single

18

540 ml/hr

0.45 ml

4 Fr

Single

18

798 ml/hr

0.62 ml

0.034 in.

5 Fr

Single

18

398 ml/hr

0.42 ml

0.035 in.

4 Fr

Single

18

1024 ml/hr

0.73 ml

5 Fr

Dual

18/18

498 ml/hr /498 ml/hr

0.65 ml /0.65 ml

4 Fr

Single

18

1,272 ml/hr

0.67 ml

5 Fr

Dual

18/18

515 ml/hr /515 ml/hr

0.55 ml /0.55 ml

0.034/0.034 in.

6 Fr

Dual

18/18

762 ml/hr /762 ml/hr

0.69 ml /0.69 ml

0.037/0.037 in.

5 Fr

Single

18

1,185 ml/hr

0.66 ml

5 Fr

Dual

18/18

578 ml/hr / 578 ml/hr

0.57 ml / 0.57 ml

6 Fr

Dual

18/18

753 ml/hr / 753 ml/hr

0.62 ml / 0.62 ml

5 Fr

Triple

18/ 20/ 20

982 ml/hr / 131 ml/hr / 131 ml/hr

0.76 ml / 0.43 ml / 0.43 ml