mittyri
★★  

Russia,
2015-02-03 15:28
(3341 d 06:28 ago)

Posting: # 14366
Views: 5,746
 

 Backups; volume of blood during the sampling [Study Per­for­mance]

Dear All,

I would like to discuss some points during the study conducting which we are faced in one site.
1. Backups.
In this site backups are invited at the beginning of 1st and 2nd periods.
So in case when volunteer was excluded due to some reasons before the beginning of 2nd perod (during the 1st period or during the wash-out), the invited backup starts the 2nd period with other volunteers.
For example: 22 volunteers, one of them (R03, sequence RT) broke his leg during the washout. The backup is invited to the 2nd period, but this backup should be dosed with RIMP, because for him it's a "1st period"! After washout he'll be invited at the "2nd period" and dosed with TIMP.
By the way all biosamples will be analyzed.
For me it looks strange. What do you think about this procedure?

2. During the sampling a nurse inject little volume of heparine solution to catheter after each blood draw. To avoid the contact of heparin solution and vacutainer the nurse takes away little volume of blood before each next blood drawing.
What do you think? Is it really necessary to remove 'heparinized' blood from the catheter?

Kind regards,
Mittyri
Helmut
★★★
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Vienna, Austria,
2015-02-03 15:54
(3341 d 06:02 ago)

@ mittyri
Posting: # 14367
Views: 4,649
 

 Backups: rather not

Hi Mittyr,

❝ 1. Backups. […]


❝ For me it looks strange. What do you think about this procedure?


Outdated. We abandoned it 20 years ago. Nowadays you should start with the estimated sample size plus some additional subjects according to the expected dropout rate. Even, if you don’t add subjects the loss in power is less than most people think. See this thread; you could loose a lot of subjects until power substantially decreases.
Detlew implemented some useful functions in PowerTOST last October. Try:

library(PowerTOSt)
pa.ABE(CV=0.21, minpower=0.7)


In your example (n 22) with five (!) dropouts you still have 72% power.

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d_labes
★★★

Berlin, Germany,
2015-02-03 17:39
(3341 d 04:17 ago)

@ Helmut
Posting: # 14368
Views: 4,725
 

 Ehre wem Ehre gebührt

❝ Detlew implemented some useful functions in PowerTOST last October. Try:


library(PowerTOSt)

❝ pa.ABE(CV=0.21, minpower=0.7)


The original code of the pa.xyz() functions is from a well known user/admin of this forum!

Regards,

Detlew
Ohlbe
★★★

France,
2015-02-04 00:30
(3340 d 21:26 ago)

@ mittyri
Posting: # 14369
Views: 4,612
 

 Backups; volume of blood during the sampling

Dear Mittyri,

I'll only answer the second part of your post, as Helmut already answered the first.

❝ 2. During the sampling a nurse inject little volume of heparine solution to catheter after each blood draw. To avoid the contact of heparin solution and vacutainer the nurse takes away little volume of blood before each next blood drawing.

❝ What do you think? Is it really necessary to remove 'heparinized' blood from the catheter?


That's indeed the standard practice, in order to avoid diluting the plasma sample with the heparinised saline contained in the void volume of the catheter (though the dilution factor would be rather limited). Could also avoid issues in the bioanalytical phase.

I see one more advantage: when removing this small volume of blood you can ensure that the catheter is not blocked. It gives a few more seconds to try and unblock it, or to switch to plan B, without delaying the sample too much.

Regards
Ohlbe
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