Do you have answer for this. If I say None of the dialysis machine gives the actual TMP Do you believe this. Most of the dialysis machine has only one pressure sensor at the pre or post dialysate circuit. so it never gives the acutal tmp. If you have to check the acutal tmp You have to have the mean of Pre and post dialyser blood side pressure and pre and post dialyser dialysate compartment pressure.By doing this you can chech the back filteration too.Why dont any manufacturer think about this, for details contact abkas@yahoo.com

I belive only for cost reasons.
It is less expensive to determinate the other pressure via software.

Bacfiltration occur only at the venous end of the dialyzer. The only hemodialysis equipment that monitor backfiltration is the Baxter Tina hemodialysis machine. It's monitor the venous pressure blood side and venous dialysate pressure (dialysate in). The TMP= venous - dialysate in. A 0 TMP means 0 backfiltration and a - TMP means that you are doing backfiltration at the venous side of the dialyzer. This doesn't take in consideration the oncotic pressure. Even if you use the full TMP equation,You won't get the backfiltration value. It will give you the true Kuf of the dialyzer.

TMP is calculated by the dialysis machine. Various machines use different algorythims. The alarm limit windows must be set for TMP depending on the type of dialyser used. Localized TMP is also calculated by some machines because the dialyzer has a pressure gradient and TMP is not the same from one end of the dialyzer to the other.

quote:

Originally posted by Marc:
Bacfiltration occur only at the venous end of the dialyzer. The only hemodialysis equipment that monitor backfiltration is the Baxter Tina hemodialysis machine. It's monitor the venous pressure blood side and venous dialysate pressure (dialysate in). The TMP= venous - dialysate in. A 0 TMP means 0 backfiltration and a - TMP means that you are doing backfiltration at the venous side of the dialyzer. This doesn't take in consideration the oncotic pressure. Even if you use the full TMP equation,You won't get the backfiltration value. It will give you the true Kuf of the dialyzer.

Baxter tina has dialysate pressure sensor at post dialysate line. It doesnt calculate the TMP by taking the average of vp nd Ap(post arterial Chamber) minus average of Pre and post dialysate pressure. So I strongly feel that none of the HD Machine has this facility.

[QUOTE]Originally posted by nua:
[B]
Baxter tina has dialysate pressure sensor at pre dialysate line. It doesnt calculate the TMP by taking the average of vp nd Ap(post arterial Chamber) minus average of Pre and post dialysate pressure. So I strongly feel that none of the HD Machine has this facility.

what would be the point of an "actual tmp" anyway? What useful info would it serve, I view the tmp display as a reference (similar to db) the pressures in different points of the dialyzer and through out the treatment are going to be in constant flux. The important thing is that the programmed uf goal is obtained and the patient reaches their dry weight, the rest of it is all window dressing. I think we're obssessing on a minute point.

TMP was once important for calculating the UF rate using the KUF of the dialyzer. Now it's really only useful to show problems in the blood circuit such as a kink or clot. No you are right no manufacturer shows the true TMP in the center of the dialyzer but estimates in different places. This is why the Fresenius has a higher TMP for the same UF rate and dialyzer as the Gambro equipment, or the Tina. The Tina shows it at the worst position for back filtration, the venous end. Therefore if you have a negative TMP there is high chance of back filtration, a risk of high flux dialyzers. However we do sodium ramping to "add" sodium to a patient's bloodstream, also other electrolyes go across the membrane from the dialysate side to the blood side, therefore I feel that we always have backfiltration of some level even if the TMP is always positive. I hope this helps.