PATIENT BUN ESTIMATOR FOR SORBENT HEMODIALYSIS
The invention relates to systems and methods for estimating a patient urea level at any arbitrary time during dialysis treatment. The systems and methods use either one or more urea sensors or any two of a pH sensor, ammonia sensor, and ammonium sensor to determine an amount of urea removed by a dialysate regeneration system. The systems and methods use the amount of urea removed by the dialysate regeneration system to estimate the patient urea level.
1 . A dialysis system, comprising:
a dialysate flow path fluidly connectable to a dialyzer; the dialysate flow path having a dialysate regeneration system comprising urease;
either a urea sensor or at least two sensors selected from: ammonia sensors, ammonium sensors, and pH sensors; and
a processor; the processor in communication with the urea sensor, ammonia sensor, ammonium sensor, and/or pH sensor; the processor programmed to determine an amount of urea removed by the dialysate regeneration system;
the processor further programmed to estimate a patient urea level from either one or more lookup tables or a mathematical model based on the amount of urea removed by the dialysate regeneration system;
the mathematical model using solutions to a formula:
dM
P
,
i
dt
=
G
P
,
i
-
(
Ind
)
J
i
(
V
P
,
M
P
,
i
,
C
Di
,
i
)
+
R
P
,
i
,
wherein M p,i is a mass of a species “i” in a patient, G p,i is a generation rate of the of the species “i” in the patient, J i is a total mass transfer rate of species “i” from the patient into a dialysate, C Di,i is a concentration of species “i” in a regenerated dialysate when the regenerated dialysate enters the dialyzer, R P,i is a production rate of species “i” due to chemical reactions, and Ind is a binary indicator variable for dialysis therapy with Ind=0 if dialysis is not occurring, and Ind=1 if dialysis is occurring.
2 . The dialysis system of claim 1 , wherein the mathematical model uses a formula:
CBi
Urea
tCrit
=
(
QDi
D
Urea
)
(
CDo
Urea
-
CDi
Urea
)
+
CDi
Urea
;
wherein CBi Urea tCrit is the patient urea level at time t; QDi is a dialysate flow rate exiting the dialyzer; D Urea is a dialysance of urea; CDo Urea is a urea concentration in a dialysate exiting the dialyzer; and CDi Urea is a urea concentration in the dialysate entering the dialyzer.
3 . The dialysis system of claim 1 , wherein the dialysate regeneration system comprises one or more sorbent cartridges.
4 . The dialysis system of claim 1 , wherein the sensors comprise a first urea sensor located upstream of the dialysate regeneration system and an optional second urea sensor located downstream of the dialysate regeneration system.
5 . The dialysis system of claim 1 , wherein the sensors comprise at least two of an ammonia sensor, an ammonium sensor, and a pH sensor located downstream of the urease and upstream of an ammonium and/or ammonia exchange material.
6 . The dialysis system of claim 5 , wherein the sensors are part of a combined pH, ammonium, and/or ammonia sensor.
7 . The dialysis system of claim 1 , the processor further programmed to estimate a urea reduction ratio based on a urea level of the patient at a beginning of a dialysis session and a urea level of a patient at an end of the dialysis session.
8 . The dialysis system of claim 1 , the processor further programmed to estimate a urea reduction ratio at an arbitrary time during treatment.
9 . The dialysis system of claim 1 , wherein the dialysis system has a single urea sensor upstream of the dialysate regeneration system.
10 . The dialysis system of claim 9 , the processor programmed to estimate the patient urea level at a beginning of a dialysis session.
11 . A method, comprising:
a) initiating a dialysis session for a patient using a dialysis system having a dialysate regeneration system comprising urease in a dialysate flow path;
b) determining an amount of urea removed by the dialysate regeneration system based on data received from either one or more urea sensors or at least two sensors selected from: ammonia sensors, ammonium sensors, and pH sensors;
c) estimating a patient urea level from a mathematical model or a lookup table based on the amount of urea removed by the dialysate regeneration system;
the mathematical model using solutions to a formula:
dM
P
,
i
dt
=
G
P
,
i
-
(
Ind
)
J
i
(
V
P
,
M
P
,
i
,
C
Di
,
i
)
+
R
P
,
i
,
wherein M p,i is a mass of a species “i” in the patient, G p,i is a generation rate of the of the species “i” in the patient, J i is a total mass transfer rate of species “i” from the patient into a dialysate, C Di,i is a concentration of species “i” in a regenerated dialysate when the regenerated dialysate enters a dialyzer, R P,i is a production rate of species “i” due to chemical reactions, and Ind is a binary indicator variable for dialysis therapy with Ind=0 if dialysis is not occurring, and Ind=1 if dialysis is occurring.
12 . The method of claim 11 , wherein the mathematical model uses a formula:
CBi
Urea
tCrit
=
(
QDi
D
Urea
)
(
CDo
Urea
-
CDi
Urea
)
+
CDi
Urea
;
wherein CBi Urea tCrit is the patient urea level at time t; QDi is a dialysate flow rate exiting the dialyzer; D Urea is a dialysance of urea; CDo Urea is a urea concentration in a dialysate exiting the dialyzer; and CDi Urea is a urea concentration in the dialysate entering the dialyzer.
13 . The method of claim 11 , wherein the sensors comprise a first urea sensor located upstream of the dialysate regeneration system and a second urea sensor located downstream of the dialysate regeneration system.
14 . The method of claim 11 , wherein the sensors comprise at least two of an ammonia sensor, an ammonium sensor, and a pH sensor located downstream of the urease and upstream of an ammonium and/or ammonia exchange material.
15 . The method of claim 11 , wherein the method is performed by a dialysis system.
16 . The method of claim 11 , wherein the patient urea level is estimated at a beginning of the dialysis session.
17 . The method of claim 11 , wherein the patient urea level is estimated at an end of the dialysis session.
18 . The method of claim 11 , wherein the patient urea level is estimated at an arbitrary time during treatment.
19 . The method of claim 11 , wherein the patient urea level is estimated at a beginning of the dialysis session and at an end of the dialysis session.
20 . The method of claim 19 , further comprising the step of estimating a urea reduction ratio and/or a dialysis adequacy based on calculations using the patient urea level at a beginning of a dialysis session and the patient urea level at the end of the dialysis session.