SYSTEM, COMPUTER SYSTEM AND COMPUTER PROGRAM FOR DETERMINING A CARDIOVASCULAR PARAMETER

Abstract

The invention relates to a system for determining a cardiovascular parameter in a patient, wherein the system is adapted to work in conjunction with an extracorporeal blood treatment device (ECBTD) connectable to a patient's vascular system, wherein the ECBTD comprises a first circuit, the system comprising: a liquid-filled, second circuit thermally connected to the first circuit of the ECBTD via a heat exchanger, temperature changing means for generating a temperature change in the second circuit, temperature sensors TS2up and TS2down arranged in the second circuit upstream and downstream of the heat exchanger, respectively. A computer system connected to the temperature sensors and the temperature changing means is adapted to induce a temperature bolus within the first circuit of the ECBTD via the temperature changing means. From the individual temperature recorded as a function of time, temperature curves T2up(t) and T2down(t) are derived and evaluated.

Claims

1. A system for determining a cardiovascular parameter in a patient, wherein the system is adapted to work in conjunction with an extracorporeal blood treatment device (ECBTD, 10) connectable to a patient's vascular system via an afferent line (11) and an efferent line (12), wherein the ECBTD (10) comprises a first circuit with at least one pump (13) arranged between the afferent (11) and the efferent line (12) for pumping the blood of the patient, the system comprising: a) a liquid-filled, second circuit thermally connected to the first circuit of the ECBTD via a heat exchanger, b) temperature changing means for generating a controlled temperature change in the second circuit, c) a temperature sensor TS2up arranged in the second circuit upstream of the heat exchanger, and a temperature sensor TS2down arranged in the second circuit downstream of the heat exchanger, d) a computer system (40) connected to the temperature sensors TS2up and TS2down and to the temperature changing means, which is adapted to induce a temperature change within the first circuit of the ECBTD via the temperature changing means, to record each temperature as a function of time and to evaluate the respective temperature curves T2up(t) and T2down(t), wherein the computer system is further adapted to compute a relation of T2up(t) and T2down(t)1 in order to determine and control the characteristics of the time-dependent changes in the temperature generated by the temperature changing means, wherein T2down(t)1 is derived from temperature data measured by TS2down at a first time, and to determine the cardiovascular parameter of the patient from the relation of T2up(t) and T2down(t)2), wherein T2down(t)2 is derived from temperature data measured by TS2down at a second time.

2. System according to claim 1, additionally comprising a temperature sensor TSpat for measuring the local temperature of the patient's blood at a place of the patient's vascular system downstream of the ECBTD, wherein the computer system (40) is further connected to TSpat and further adapted to record Tpat as a function of time and to evaluate the temperature curve Tpat(t), and to determine the cardiovascular parameter of the patient from the relation of T2up(t), T2down(t)1 and Tpat(t).

3. System according to any one of claim 1 or 2, wherein the temperature changing means induce periodically a controlled temperature change in the first circuit of the ECBTD.

4. System according to any of the preceding claims, wherein the temperature changing means generate a temperature bolus.

5. System according to any of the preceding claims, wherein the computer system is adapted to control at least one pump in the second circuit, wherein said at least one pump in the second circuit is connected to the temperature changing means, such that the speed of the at least one pump in the second circuit is adapted to generate a steep temperature differential.

6. System according to claim 5, wherein the at least one pump in the second circuit is arranged upstream of the heat exchanger.

7. System according to any of the preceding claims, wherein the temperature changing means are arranged downstream of the at least one pump in the first circuit.

8. System according to any one of the preceding claims, wherein the temperature changing means comprise switching means for switching between at least two different temperatures.

9. System according to claim 8, wherein the switching means are arranged to switch between at least two different fluid-filled reservoirs.

10. System according to any one of the preceding claims, wherein the ECBTD is an extracorporeal membrane oxygenator (ECMO) device.

11. System according to claim 10, wherein the temperature changing means are comprised in an oxygenator of the ECMO.

12. System according to any of the preceding claims, wherein one pump of the ECBTD provides for a flow rate of >200 ml/min.

13. System according to any one of the preceding claims, additionally comprising a temperature sensor TS1up arranged in the afferent line of the first circuit of the ECDB upstream of the heat of exchanger, wherein the computer system is connected to the temperature sensor TS1up and adapted to record the temperature from temperature sensor TS1up as a function of time and to evaluate a temperature curve T1up(t) in order to determine a temperature deviation T.sub.ECBTD associated with the ECBTD.

14. System according to claim 13, wherein the computer system is adapted to compute a relation of T2up(t), T2down(t), T.sub.ECBTD and Tpat(t) in order to determine the cardiac output.

15. System according to any of the preceding claims, wherein the cardiovascular parameter is cardiac output (CO), extravascular lung water (EVLW), global enddiastolic volume (GEDV) or systemic organ perfusion and indices derived therefrom.

16. A method of determining a cardiovascular parameter utilizing the system according to any one of claims 1 to 15, comprising the steps a) inducing in the first circuit of the ECBTD a temperature change, the temperature deviation for inducing the temperature change being generated by the temperature changing means in the second circuit, the first circuit of the ECBTD being thermally coupled to the second circuit via a heat exchanger, b) detecting a temperature T2up in the second circuit by means of temperature sensor TS2up arranged in the second circuit upstream of the heat exchanger, and detecting a temperature T2down in the second circuit by means of temperature sensor TS2down arranged in the second circuit downstream of the heat exchanger, c) determining the time-dependent change of the temperature by computing a relation of T2up(t) and T2down(t)1, wherein T2down(t)1 is derived from temperature data measured by TS2down at a first time, and determining the cardiovascular parameter of the patient from said relation of T2up(t) and T2down(t)2, wherein T2down(t)2 is derived from temperature data measured by TS2down at a second time.

17. Method according to claim 16, additionally including steps b′) detecting a local temperature Tpat of the patient's blood by means of a temperature sensor TSpat arranged at a place of the patient's vascular system downstream of the ECBTD, and c′) determining the cardiovascular parameter of the patient from the relation of T2up(t) and T2down(t)1 and Tpat(t).

18. Computer system adapted to working in conjunction with a system for determining a cardiovascular parameter according to any one of claims 1 to 15, wherein the computer system comprises connecting means for connecting the computer system to temperature sensors TS2up and TS2down and to the temperature changing means, and access means for accessing executable instructions for causing the computer system a) to control temperature changing means in the second circuit in order to generate a controlled temperature change in the second circuit, b) to monitor temperatures T2up and T2down, measured by temperature sensors TS2up and TS2down as a function of time and determine the respective temperature curves T2up(t) and T2down(t) and c) to compute a relation of T2up(t) and T2down(t)1 in order to determine the characteristics of the time-dependent change of the temperature generated by the temperature changing means, wherein T2down(t)1 is derived from temperature data measured by TS2down at a first time, and to determine the cardiovascular parameter of the patient from a relation of T2up(t) and T2down(t)2, wherein T2down(t)2 is derived from temperature data measured by TS2down at a second time.

19. Non-volatile, computer readable storage medium having stored data representing instructions for determining a cardiovascular parameter in a system according to any one of claims 1 to 15, wherein the instructions are readable by a computer system for causing the computer system a) to control the temperature changing means in the second circuit in order to generate a controlled temperature change in the second circuit, b) to monitor temperatures T2up, and T2down measured with temperature sensors TS2up and TS2down, as a function of time (t) and determine the respective temperature curves T2up(t), T2down(t), and c) to compute a relation of T2up(t) and T2down(t)1 in order to determine the characteristics of the time-dependent change of the temperature generated by the temperature changing means, wherein T2down(t)1 is derived from temperature data measured by TS2down at a first time, and to determine the cardiovascular parameter of the patient from a relation of T2up(t) and T2down(t)2, wherein T2down(t)2 is derived from temperature data measured by TS2down at a second time.

Description

BRIEF DESCRIPTION OF THE FIGURE

[0025] The drawing is purely schematic and, for the sake of clarity, not to scale. In particular, ratios between dimensions, especially diameter, length of lines etc. may differ. In practice, dimensions may be selected according to the requirements of the individual case or according to the dimensions of common standard parts.

[0026] FIG. 1 shows a schematic overview of the system according to the invention in cooperation with an extracorporeal blood treatment device, the interaction with the vascular system of a patient being shown for illustrative purposes.

DETAILED DESCRIPTION

[0027] FIG. 1 shows a schematic overview of the system according to the invention in cooperation with an extracorporeal blood treatment device (ECBTD). As an example for an ECBTD, FIG. 1 depicts an extracorporeal membrane oxygenator (ECMO), which is connected to the patient's circulatory system in a veno-venous configuration (vvECMO). An efferent line (11) conducts deoxygenated blood from the inferior caval vein to the ECMO device and an afferent line (12) returns oxygenated blood to the patient circulatory system via the superior caval vein. Regularly, both major veins are accessed via cannulation of the femoral veins in a patient. The ECMO may also be set up in other configurations, such as veno-arterial (vaECMO) or arteriovenous (avECMO). The ECMO comprises a pump (13) and a flow sensor (18) arranged in the first circuit between the afferent line (11) and the efferent line (12). The system comprises a liquid-filled, second circuit, which is thermally connected to the first circuit of the ECMO via a heat exchanger (14). As shown, the heat exchanger (14) operates by indirect transfer of thermal energy: both fluid-filled circuits are separated by an interface that prevents mixing of the patient's blood circulating in the first circuit of the ECMO with the thermal energy transfer medium, which usually is water or a comparable fluid, circulating in the second circuit. The heat exchanger may operate in any of the flow arrangements known from the art (parallel flow, counter-flow, cross-flow, diffuse flow). The exemplary heat exchanger operates in a preferred counter-flow mode with fluids entering the exchanger from opposite ends: the direction of flows in the first and second circuit is indicated by the arrows adjacent to the circuit lines. The temperature changing means (15) are arranged within the fluid-filled, second circuit. The temperature changing means may be of any variety known in the state-of-the-art; the two fluid-filled reservoirs depicted in FIG. 1 serve as an example for temperature changing means adapted to be switched between two fluids in circuit 2 with different temperatures. While the temperature of one reservoir may be close to the temperature of the patient's blood circulating in the first circuit of the ECMO (here: 38° C.), the second reservoir (151) is filled with cold fluid (25° C.) to be used for generating a controlled lower temperature in the second circuit. The movement of the fluid in the second circuit is generated by pump (17), which in the depicted example is located upstream with respect to the heat exchanger (14). By monitoring and controlling parameters of the pump (17) in the second circuit, such as e.g. speed and/or flow rate, relative to the flow detected by flow sensor (18) in the first circuit, the computer system (40) according to the invention can control the temperature changes in the second circuit generated by the temperature changing means and indirectly of the temperature changes induced in the first circuit of the ECMO, as explained below. The system further comprises a temperature sensor TS2up arranged in the second circuit upstream of the heat exchanger, and a temperature sensor TS2down arranged in the second circuit downstream of the heat exchanger, as well as a temperature sensor TSpat for measuring the local temperature of the patient's blood at a suitable place in the patient's vascular system downstream of the ECMO. As depicted, TSpat is arranged in a vessel of the patient's arterial system, e.g. the femoral artery, in a configuration suitable for TPTD measurements. The terms “downstream” and “upstream” regarding the arrangement of the temperature sensors in the second circuit refer to the respective direction of flow in the second circuit (and also within the associated part of the heat exchanger). The term “downstream of the ECMO” here refers to a place within the patient's arterial system. The system further comprises a computer system (40), comprising a monitor, wherein the computer system (40) is connected to temperature sensors (TS2up, TS2down, TSpat) and the temperature changing means. As shown here, the computer system is connected to switching means (16) which may switch between the two fluid-filled reservoirs of the temperature changing means, such that a temperature change, e.g. a temperature bolus, is generated in the second circuit. Said temperature change in the second circuit induces a traveling temperature deviation in the first circuit via the separating, heat conducting wall of the heat exchanger, i.e. the thermal energy carried by e.g. a cold bolus in the second circuit is transferred to the first circuit via the heat exchanger.

[0028] In an ideal heat exchanger there is no temperature gradient across the heat transfer surface; in actual configurations of the system of the present invention, where heat exchange is not impeded by e.g. an interposed gas exchange membrane or the like, heat transfer between the fluid-filled second and the first circuit is considered near complete. The cardiovascular parameter of the patient is subsequently determined by the computer system (40), preferably by TPTD, from analyzing the relation of T2up(t), T2down(t) and Tpat(t). As described above, the cardiovascular parameter may be determined in a system comprising only temperature sensors TS2 up and TS2 down. Here, the computer system is adapted to compute a relation of T2up(t) and T2down(t)1 in order to determine and control the characteristics of the time-dependent changes in the temperature generated by the temperature changing means, wherein T2down(t)1 is derived from temperature data measured by TS2down at a first time. Subsequently, the cardiovascular parameter may be determined from the relation of T2up(t) and T2down(t)2), wherein T2down(t)2 is derived from temperature data measured by TS2down at a second time. The exemplary system additionally comprises temperature sensor TS1up, which is arranged in the afferent line of the first circuit of the ECMO upstream of the heat exchanger (14). The computer system is connected to said temperature sensor TS1up and adapted to record the temperature from temperature sensor TS1up as a function of time to improve calibration, calculation of cardiovascular parameters and recirculation of blood in case of a vvECMO. The computer system (40) is adapted to compute a relation of T2up(t), T2down(t) and Tpat(t) in order to determine the cardiovascular parameter, e.g. cardiac output. Particularly in the cases where the ECBTD is a vvECMO device (shown here), requiring high flow rates, recirculation of the blood will affect the Tpat(t) a problem that may decrease the accuracy of cardiovascular parameter determination by TPTD. Thus, the temperature deviation related to the proportion of recirculation may be determined by relating T1up(t) to T2up(t) and T2down(t) in order to derive T.sub.ECBTD, the temperature deviation associated with the ECBTD. Accounting for recirculation enables a more accurate determination of the cardiovascular parameter by computing a relation of T2up(t), T2down(t), T.sub.ECBTD and Tpat(t). Thus, the system according to the invention advantageously enables the efficient detection and correction of an indicator loss due to the extracorporeal circuit, such that errors in the determination of cardiovascular parameters, e.g. of CO, during extracorporeal blood treatment, e.g. during ECMO treatment, may be minimized.

REFERENCES

[0029] Wietasch, G. J., Mielck, F., Scholz, M., Von Spiegel, T., Stephan, H., & Hoeft, A. (2000). Bedside assessment of cerebral blood flow by double-indicator dilution technique. Anesthesiology: The Journal of the American Society of Anesthesiologists, 92(2), 367-367.

REFERENCE NUMERALS

[0030] 10 extracorporeal blood treatment device, ECBTD [0031] 11 afferent line, towards ECBTD [0032] 12 efferent line, from ECBTD [0033] 13 pump within the first circuit [0034] 14 heat exchanger [0035] 15 temperature changing means [0036] 151 fluid-filled reservoir [0037] 16 switching means [0038] 17 pump within the second circuit [0039] 18 flow sensor, first circuit [0040] 40 computer system