Opened 10 years ago

Closed 8 years ago

#127 closed enhancement (fixed)

Revise or add sibling to [drp]

Reported by: Lloyd McKenzie Owned by:
Priority: minor Milestone:
Component: Keywords: SDTM Drop
Cc: Gunther Schadow

Description (last modified by Gunther Schadow)

In SDTM, code C69442 "drop" (abbreviation "gtt") is defined as .05 mL (i.e 20 drops per millilitre). A quick google search suggests that this ratio is the most common (though not only) interpretation of the unit "drop". Suggest either correcting the conversion on the existing unit or defining an additional unit with the new conversion.

Discussion from Gunther: We have [drp] in UCUM defined as 12 drops per mL. Now we have an alternative proposal of 20 drops per mL. I don't know where I originally got the 12 drops per mL from and I would be inclined to make a correction on the definition of drop if we can prove that 12 was not correct to begin with and instead 20 is correct.

My own original research using a 20 mL syringe filled to 5 mL shows that 1 mL has 25 drops of water, when tensides are added, the number goes up to 45. A saturated saline solution required 30 and plant oil 35. The speed of dropping, pressure and position of the syringe or the lumen of the outlet, open or partially clogged with wax, did not have a significant influence on the number of drops.

As a conclusion 12 drops per mL is far outside of what was achievable with this experiment. However, labeled drop size of infusion kits is between 10 and up to 60 drops pe mL. I am sure that those micro-drops can be achieved by working the dripper in a certain way, however, I am not sure how to achieve drops as large at 10 per mL, either way these drop sizes seem to require special equipment which should label its drop sizes specifically.

Change History (1)

comment:1 Changed 8 years ago by Gunther Schadow

Description: modified (diff)
Resolution: fixed
Status: newclosed

as a conclusion, changing it to 20 drops per mL seems to be the minimum one can do to fix the original 12.

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