Apparatus and method of controlling an extracorporeal blood treatment

• US 9,770,546 B2
• Filed: 08/08/2013
• Issued: 09/26/2017
• Est. Priority Date: 09/28/2012
• Status: Active Grant

• Current Assignee: Gambro Lundia AB (Baxter International Inc.)
• Original Assignee: Gambro Lundia AB (Baxter International Inc.)
• Inventors: Vasta, Alessandro
• Primary Examiner(s): Bass, Dirk
• Application Number:
  US14/428,276
• Publication Number:
  US 20150258269A1
• Time in Patent Office: 1,510 Days
• Field of Search: 210137
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1613 Profiling or modelling of patient or predicted treatment evolution or outcome
• CPC Class Codes: A61M 1/34 Filtering material out of the blood by passing it through a membrane, i.e. hemofiltration or diafiltration
• CPC Class Codes: A61M 1/36 Other treatment of blood in a by-pass of the natural circulatory system, e.g. temperature adaptation, irradiation ; Extra-corporeal blood circuits
• CPC Class Codes: A61M 1/3607 Regulation parameters
• CPC Class Codes: A61M 1/3624 Level detectors; Level control
• CPC Class Codes: A61M 1/3627 Degassing devices; Buffer reservoirs; Drip chambers; Blood filters
• CPC Class Codes: A61M 1/3663 Flow rate transducers; Flow integrators
• CPC Class Codes: A61M 2205/3306 Optical measuring means
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/3365 Rotational speed
• CPC Class Codes: A61M 2205/3375 Acoustical, e.g. ultrasonic, measuring means
• CPC Class Codes: A61M 2205/3379 Masses, volumes, levels of fluids in reservoirs, flow rates
• CPC Class Codes: A61M 2205/3389 Continuous level detection A61M2205/3393 takes precedence

Abstract

An apparatus is described for extracorporeal blood treatment (1), comprising a treatment unit (2), an extracorporeal blood circuit (8) and a fluid evacuation line (10). The apparatus comprises a control unit (21) connected with a pressure sensor (13, 14) and with a blood pump (9) and configured to move the blood pump (9), generating a variable flow (Q(t)) with a constant component (Q_b) and a variable component (Qvar(t)) having a nil average value; the variable flow generates, in the expansion chamber (11, 12), a progression of the pressure that is variable over time (P(t)) with a pressure component (Pvar(t)) oscillating about an average value (P_avg). The control unit receives, from the sensor, a plurality of values (P_j) and calculates the average value of the pressure (P_avg), acquires an estimated value of volume variation (AP) in the expansion chamber (11, 12) connected to the variable flow component (Qvar(t)), calculates, as a function of the pressure values (P_j), an estimated value of pressure variation (AP) in the expansion chamber (11; 12) that is representative of the oscillating pressure component (Pvar(t)) and determines a representative magnitude of a blood level (L) in the expansion chamber (11, 12) as a function of the average value (P_avg) of the pressure (P(t)), of the estimated value of volume variation (AV) and of the estimated pressure variation (AP) in the expansion chamber.

Claims

1. An apparatus for extracorporeal blood treatment comprising:

at least a treatment unit having at least a first chamber and at least a second chamber separated from one another by a semipermeable membrane;

at least a blood removal line connected to an inlet port of the first chamber and predisposed to remove blood from a patient;

at least a blood return line connected to an outlet port from the first chamber and predisposed to return treated blood to the patient;

at least an expansion chamber placed at least in one of the blood removal line and the blood return line, the expansion chamber being arranged in use to contain a predetermined quantity of gas in an upper portion and a predetermined quantity of blood at a predetermined level in a lower portion thereof, the blood removal line, the blood return line, the first chamber and the at least an expansion chamber being part of an extracorporeal blood circuit;

at least a blood pump operating at the extracorporeal blood circuit such as to move the blood in the circuit;

at least a pressure sensor associated to the expansion chamber and configured to enable determining pressure values internally of the expansion chamber;

at least a fluid evacuation line connected to an outlet port of the second chamber; and

a control unit connected to the at least a pressure sensor, with the pump, and configured to;

move the blood pump to generate a variable blood flow comprising a constant flow component equal to a desired value of blood flow and a variable flow component oscillating about the constant component and having a substantially nil average value, the variable blood flow component generating, at least in the expansion chamber, a pressure progression that is variable over time comprising a pressure component oscillating about an average value;

receive from the at least a pressure sensor a plurality of measured pressure values for a time period comprising a plurality of oscillations of the pressure about the average value, the pressure values being measured in successive time instants;

calculate, as a function of the pressure values, an average value of the pressure;

acquire an estimated volume variation value in the expansion chamber linked to the variable flow component;

calculate, as a function of the pressure values, an estimated pressure variation in the expansion chamber representing the oscillating pressure component; and

determine a representative magnitude of a blood level in the expansion chamber as a function of the average value of the pressure, the estimated volume variation value and the value of the estimated pressure variation in the expansion chamber.

2. The apparatus of claim 1, wherein the control unit is programmed to determine the representative magnitude of the blood level in the expansion chamber by exploiting the ideal gas law, the ideal gas law being applied to a modelled representation of the apparatus substantially constituted by a superposing of:

an open system in which the expansion chamber is considered to be in a stationary state and interested only by the constant flow component and the internal pressure in the expansion chamber is correspondingly a constant pressure equal to the mean value; and

a partially closed system in which only an access to the expansion chamber, selected from between an inlet for the blood and an outlet for the blood, is open and subject to a volume variation representative of the variable flow component oscillating about the constant component and a pressure value representing the oscillating pressure component.

3. The apparatus of claim 1, wherein the control unit is programmed to determine the magnitude representing the blood level in the expansion chamber using the following mathematical relation:

4. The apparatus of claim 1, wherein the average pressure value is calculated as a function of a plurality of measured pressure values relating to a time period comprising a plurality of blood flow oscillations about the constant component and consequently a plurality of oscillations of the pressure about the average value.

5. The apparatus of claim 4, wherein the time period comprises at least three oscillations.

6. The apparatus of claim 1, wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of reading from a memory of an estimated pre-set value of volume variation, the selection being operated according to at least one of parameters included in the group consisting of:

a type of extracorporeal circuit installed on the apparatus;

a type of extracorporeal blood treatment;

a type of blood pump;

the desired blood flow value;

a pressure upstream or downstream of the blood pump;

a type of pump tract;

the average pressure in the expansion chamber;

an index of ageing of the pump tract; and

the number of revolutions accumulated by the blood pump.

7. The apparatus of claim 1, wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of calculating the estimated value as a function of at least a parameter selected in the group consisting of:

the pressure values measured, the constant blood flow component, an indicator of an ageing of a blood tract and a preceding estimated air volume in the expansion chamber.

8. The apparatus of claim 1, wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of calculating the estimated value using the following mathematical relation:

Δ

V_n=k₀+k₁·

P_n+k₂·

n_impn+k₃·

Q_bn+k₄·

V_n-1

in which;

n is the generic index indicating the n-th measurement output of the air volume;

Δ

V_n is the estimated variation of volume Δ

V at the nth step of measurement of the air volume;

k₀, k₁, k₂, k₃, k₄ are experimentally-determined constants;

P_n is the average of the pressure values measured at the end of the n-th measuring step of the air volume;

n_imp_n is the accumulated number—

or a value proportional to the accumulated number—

of revolutions of the blood pump;

Q_bn is the average value of the blood flow at the end of the n-th measuring step of the air volume; and

V_n-1 is the estimated measurement of the air volume obtained from the preceding calculation, and wherein the mathematical relation is adopted in the event that the average value of the blood flow is less than 400 ml/min.

9. The apparatus of claim 1, wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of calculating the estimated value using the following mathematical relation:

Δ

V_n=k₀+k₁·

P_n+k₂·

n_impn+k₃·

Q_bn+k₄·

V_n-1+k₅·

P_n²

in which;

n is the generic index indicating the n-th measurement output of the air volume;

Δ

V_n is the estimated variation of volume Δ

V at the n-th step of measurement of the air volume;

k₀, k₁, k₂, k₃, k₄, k₅ are experimentally-determined constants;

P_n is the average of the pressure values measured at the end of the n-th measuring step of the air volume;

n_imp_n is the accumulated number—

or a value proportional to the accumulated number—

of revolutions of the blood pump;

Q_bn is the average value of the blood flow at the end of the n-th measuring step of the air volume; and

V_n-1 is the estimated measurement of the air volume obtained from the preceding calculation, and wherein the mathematical relation is adopted in a case that the average value of the blood flow is greater than 300 ml/min and less than 650 ml/min.

10. The apparatus of claim 1, wherein the step of calculating an estimated value of pressure variation is carried out using a mathematical relation, which is a function of a statistical indicator representative of the oscillating pressure component:

Δ

P=f{VarStat}

wherein;

Δ

P is the oscillating pressure component; and

VarStat is a statistical indicator representative of the oscillating pressure component.

11. The apparatus of claim 1, wherein the step of calculating an estimated value of pressure variation is carried out by means of a mathematical relation that is a function of a statistical indicator representing the oscillating pressure component and a constant obtained experimentally:

Δ

P=K_form·

VarStat

wherein;

K_form is a constant obtained experimentally; and

Δ

P is the oscillating pressure component.

12. The apparatus of claim 10, wherein the statistical indicator is a dispersion index summarily describing a quantitative statistical distribution of the measured pressure values.

13. The apparatus of claim 10, wherein the statistical indicator is a measurement indicating a distance of the pressure values from a central value, identified with the average value of the pressure or with the median of the pressure.

14. The apparatus of claim 13, wherein the statistical indicator is the standard deviation or the integral average.

15. The apparatus of claim 11, wherein the statistical indicator representing the oscillating pressure component is defined as:

16. The apparatus of claim 14, wherein the statistical indicator representing the oscillating pressure component is defined as:

17. The apparatus of claim 1, wherein the control unit is programmed to carry out the steps of moving the blood pump to generate a variable blood flow;

receiving from the at least a pressure sensor a plurality of measured pressure values for a time period comprising a plurality of oscillations of the pressure about the average value;

calculating, as a function of the pressure values, an average value of the pressure;

acquiring an estimated volume variation value in the expansion chamber linked to the variable flow component;

calculating, as a function of the pressure values, an estimated pressure variation in the expansion chamber representing the oscillating pressure component;

determining a representative magnitude of the blood level in the expansion chamber as a function of the average value of the pressure;

in relation at least to an arterial expansion chamber placed on the blood removal line.

18. The apparatus of claim 1, wherein the expansion chamber exhibits a ventilation opening configured to enable, in use, a passage of gas from or towards the expansion chamber, the apparatus further comprising at least an actuator operating on the ventilation opening to selectively inhibit or enable passage of gas.

19. The apparatus of claim 18, wherein the ventilation opening is positioned at an upper portion of the expansion chamber arranged, in use, to be facing upwards, and to be occupied by the gas and wherein the control unit is programmed such that, in the event of a verification of the blood level in the expansion chamber below a predetermined threshold, the control unit commands the actuator to enable the passage of gas in outlet from the ventilation opening.

20. The apparatus of claim 1, wherein the control unit is programmed such that, in the event of verification of the blood level in the expansion chamber of lower than a predetermined threshold, the control unit commands at least the blood pump to reduce or zero the blood flow rate in the extracorporeal blood circuit and substantially annul the passage of fluid through the semipermeable membrane of the treatment unit, the apparatus further comprising two intercept organs of the blood flow active on the extracorporeal circuit, one downstream of a venous expansion chamber along the blood flow direction in the extracorporeal blood circuit, the other upstream of an arterial expansion chamber, the control unit being active on the intercept organs to command the intercepting or not of the flow, the control unit further being programmed such that, in an event of verification of a blood level in the expansion chamber of lower than a predetermined threshold, the control unit commands the closure of the intercept organs of the blood flow.