Method and apparatus for determining the body temperature of a patient

Abstract

The present invention relates to a method of determining the body temperature or a temperature correlated therewith of a patient connected to an extracorporeal blood circuit, wherein the extracorporeal blood circuit has a heat exchanger which is flowed through by blood at one side and by a heat carrier medium at the other side, wherein the temperature (T.sub.di) of the heat carrier medium at the inlet side is measured at the inlet of the heat exchanger and the temperature (T.sub.do) of the heat carrier medium at the outlet side is measured at the outlet of the heat exchanger and the volume flow of the heat carrier medium (Q.sub.d) is measured; and in that the temperature (T.sub.bi) of the blood at the inlet side is determined at the inlet of the heat exchanger in accordance with the relationship T.sub.bi=T.sub.di (Q.sub.d/D) (T.sub.doT.sub.di), where the value D is a value characteristic of the heat transfer by the heat exchanger.

Claims

1. A method of determining the body temperature or of a temperature correlated therewith of a patient connected to an extracorporeal blood circuit, wherein the extracorporeal blood circuit has a heat exchanger which is flowed through by blood at one side and by a heat carrier medium at the other side, characterized in that the temperature (LH) of the heat carrier medium at the inlet side is measured at the inlet of the heat exchanger and the temperature (Tao) of the heat carrier medium at the outlet side is measured at the outlet of the heat exchanger and the volume flow of the heat carrier medium (Q.sub.d) is measured; and in that the temperature (T.sub.bi) of the blood at the inlet side is determined at the inlet of the heat exchanger in accordance with the relationship
T.sub.bi=T.sub.di+(Q.sub.d/D)(T.sub.doT.sub.di)(1) where the value D is a value characteristic of the heat transfer by the heat exchanger.

2. A method in accordance with claim 1, characterized in that the heat exchanger is a dialyzer; and/or in that the temperature correlated with the body temperature is the temperature of the blood in the extracorporeal circuit; and/or in that the calculated temperature is supplied as an actual value to a regulation and the temperature regulation of the body temperature or of the temperature correlated therewith is carried out using the change of the temperature of the heat carrier medium as the adjustment value.

3. A method in accordance with claim 1, characterized in that the value D is determined, with a known characteristic k.sub.0 A of the heat exchanger, from the relationship
D=Q.sub.b(e.sup.1)/(e.sup.(Q.sub.b/Q.sub.d))(2) where =k.sub.0 A (Q.sub.dQ.sub.b)/(Q.sub.dQ.sub.b) or
D=Q.sub.b(1e.sup.)/(1+(Q.sub.b/Q.sub.d))(3) with the formula (2) applying to the flowing through of the heat exchanger in a counter flow and the formula (3) applying to the flowing through of the heat exchanger in coflow, and with the value Q.sub.b representing the volume flow of the blood through the heat exchanger.

4. A method in accordance with claim 1, characterized in that the value D is measured in that a temperature change is carried out at the side of the heat carrier medium and the time development of the temperature of the heat carrier medium at the inlet and at the outlet is integrated over time and the value D is determined from the relationship
D=Q.sub.d(1A.sub.do/A.sub.di)(4) where A.sub.do represents the area, optionally corrected by a baseline, below the temperature curve over time at the outlet side of the heat exchanger and A.sub.di represents the area, optionally corrected by a baseline, below the temperature curve over time at the inlet side of the heat exchanger.

5. A method in accordance with claim 1, characterized in that the value D is determined from the relationship
D=fQ.sub.b(5) where provision is preferably made that the value f is 1 or is in the range 10.1 or 10.2.

6. A method in accordance with claim 1, characterized in that the blood temperature in the extracorporeal circuit is measured and a relationship is established between the measured value (T.sub.art) and the value determined in accordance with formula (1) by regression, preferably by linear regression, preferably in accordance with the relationship
T.sub.art=a T.sub.bi+b(6) with provision preferably being made that T.sub.art is calculated from the regression equation and that the body temperature is determined in accordance with the relationship
T.sub.Krper=T.sub.Umgebung+(T.sub.artT.sub.Umgebung)exp(L/Q.sub.b)(7) where is the thermal conductivity per length unit of the hose piece of the extracorporeal circuit between the arterial vessel port and the heat exchanger and L is the length of this hose piece.

7. A method in accordance with claim 1, characterized in that the body temperature or a value correlated therewith, its difference with respect to a reference value and/or its change speed is monitored, with provision preferably being made that an alarm is output on an exceeding or falling below of a limit value or limit value range of one of the aforesaid values.

8. An apparatus for determining the body temperature or a temperature correlated therewith of a patient having an extracorporeal blood circuit, wherein the extracorporeal blood circuit has a heat exchanger which is flowed through by blood at one side and by a heat carrier medium at the other side; characterized in that the apparatus has measurement sensors which are arranged to measure the temperature (T.sub.di) of the heat carrier medium at the inlet side at the inlet of the heat exchanger and to measure the temperature (T.sub.do) of the heat carrier medium at the outlet side at the outlet of the heat exchanger and to measure the volume flow of the heat carrier medium (Q.sub.d); and in that the apparatus has a calculation unit which is configured to determine the temperature (T.sub.bi) of the blood at the inlet side at the inlet of the heat exchanger in accordance with the relationship
T.sub.bi=T.sub.di+(Q.sub.d/D)(T.sub.doT.sub.di)(1) where the value D is a value characteristic of the heat transfer by the heat exchanger.

9. An apparatus in accordance with claim 8, characterized in that the heat exchanger is a dialyzer and/or that the temperature correlated with the body temperature is the temperature of the blood in the extracorporeal circuit.

10. An apparatus in accordance with claim 8, characterized in that the apparatus comprises calculation means which are configured to determine the value D, with a known characteristic k.sub.0 A of the heat exchanger, from the relationship
D=Q.sub.b(e.sup.1)/(e.sup.(Q.sub.b/Q.sub.d))(2) where =k.sub.0 A (Q.sub.dQ.sub.b)/(Q.sub.dQ.sub.b) or
D=Q.sub.b(1e.sup.)/(1+(Q.sub.b/Q.sub.d))(3) with the formula (2) applying to the flowing through of the heat exchanger in a counter flow and the formula (3) applying to the flowing through of the heat exchanger in coflow, and with the value Q.sub.b representing the volume flow of the blood through the heat exchanger.

11. An apparatus in accordance with claim 8, characterized in that the apparatus comprises calculation means for determining the value D which are configured to carry out a temperature change at the side of the heat carrier medium and to integrate the time development of the temperature of the heat carrier medium at the inlet and at the outlet over time and to determine the value D from the relationship
D=Q.sub.d(1A.sub.do/A.sub.di)(4) where A.sub.do represents the area, optionally corrected by a baseline, below the temperature curve over time at the outlet side of the heat exchanger and Ad; represents the area, optionally corrected by a baseline, below the temperature curve over time at the inlet side of the heat exchanger; and/or in that the apparatus comprises calculation means which are configured to determine the value D from the relationship
D=fQ.sub.b(5) where provision is preferably made that the value f is 1 or is in the range 10.1 or 10.2.

12. An apparatus in accordance with claim 8, characterized in that the apparatus has monitoring means and/or alarm means which are designed to monitor the body temperature or a value correlated therewith or its difference with respect to a reference value and/or its change speed, with provision preferably being made that an alarm is output on an exceeding or falling below of a limit value or limit value range of one of the aforesaid values.

13. An apparatus in accordance with claim 8, characterized in that the apparatus is configured to determine the body temperature from a calculated or known value for T.sub.art in accordance with the relationship
T.sub.Krper=T.sub.Umgebung+(T.sub.artT.sub.Umgebung)exp(L/Q.sub.b)(7) where is the thermal conductivity per length unit of the hose piece of the extracorporeal circuit between the arterial vessel port and the heat exchanger and L is the length of this hose piece.

14. An apparatus in accordance with claim 8, characterized in that the apparatus has a regulation unit which is configured to regulate the body temperature of the patient or a temperature correlated therewith to a desired value or into a desired value range, wherein the regulation unit has an input for the calculated temperature as an actual value and is configured to compare it to a desired value or desired value range, and wherein the regulation unit is connected to an adjustment unit, in particular to a temperature control unit, which is configured to change the temperature of the dialyzate serving as an adjustment value if the actual value does not correspond to the desired value or if it does not lie in the desired value range.

15. A blood treatment device, in particular a dialysis machine, characterized in that the blood treatment device is formed with an apparatus in accordance with claim 8.

16. A blood treatment device, in particular a dialysis machine, characterized in that the blood treatment device has means for carrying out a method in accordance with claim 1.

Description

(1) There are shown:

(2) FIG. 1: a comparison of the values of the blood temperature (Tbi) calculated in accordance with formulas (1) and (5) and the measured values of the temperature (T_art (BTM)) of the blood in the arterial part of the extracorporeal circuit at the start of dialysis in C.;

(3) FIG. 2: a comparison of the calculated (dTbi) temperature change and of the measured change of the arterial blood temperature (dTart (BTM) during the dialysis; and

(4) FIG. 3: a schematic representation of a dialysis machine in accordance with the invention.

(5) FIG. 1 shows a comparison of calculated values and measured values for the arterial blood temperature of a patient at a start of dialysis on the data basis of 5000 values or treatments. The blood flow Q.sub.b amounted to 350-450 ml/min and the dialyzate flow Q.sub.d amounted to 500-700 ml/min. The value for D was calculated in accordance with formula (5) with f=1.1.

(6) FIG. 1 illustrates a good correlation between the calculation in accordance with the invention at the dialyzate side and the measurement of the temperature at the blood side, with the standard deviation of the difference of the two methods lying at 0.19 C. The systematic deviation can be determined by a correction with the aid of the coefficients determined from the regression in accordance with the formula T.sub.art=a T.sub.bi+b.

(7) In addition to an automatic registration and documentation of the body temperature at the start of the treatment, an automated monitoring for an exceeding of a threshold value can alternatively or additionally also take place with corresponding information to the nurse or physician. This can be necessary in order e.g. to draw attention to an inflammation.

(8) It is additionally or alternatively also conceivable that an alarm is output when the body temperature or its difference from a reference value such as from the starting value of the body temperature at the start of treatment or when its change speed exceeds or falls below a limit value or a limit value range.

(9) In the example shown in FIG. 1, the exceeding of an arterially measured temperature of 37.2 can be recognized with a sensitivity of 82% and a specificity of 98% by the measurement at the dialyzate side.

(10) FIG. 2 shows a comparison of values calculated in accordance with the invention, i.e. by sensors at the dialyzate side, and measured values for the change of the arterial blood temperature of a patient during the treatment on the data basis of 5000 values or treatments. The blood flow Q.sub.b amounted to 350-450 ml/min and the dialyzate flow Q.sub.d amounted to 500-700 ml/min. The value for D was calculated in accordance with formula (5) with f=1.1. A good correlation between the calculation in accordance with the invention at the dialyzate side and the measurement at the blood side is also shown here, with the standard deviation of the difference of the methods amounting to 0.17 C.

(11) In accordance with the invention, a monitoring of the intradialytic change of the patient temperature is thus also possible.

(12) As initially stated, a temperature increase can be an indication of an intolerance reaction, or a drop in blood pressure can result due to a temperature increase brought about by any causes.

(13) Due to the detection of the temperature change which preferably runs automatically, the dialysis machine can automatically output a warning against possible intolerance reactions, i.e. have corresponding output means, warn against possible impending drops in blood pressure, trigger a blood pressure measurement in an automated manner or increase its frequency, or lower the dialyzate temperature to counteract the increase in the body temperature or also to carry out a plurality of the aforesaid measures. The dialysis machine or other treatment device can have means to carry out one or more of these measures.

(14) In the example shown in FIG. 2, the presence of a temperature increase of more than 0.5 can be recognized with a sensitivity of 73% and a specificity of 90% by the measurement at the dialyzate side.

(15) As already stated above, the temperature determined in accordance with formula (1) or the temperature determined in accordance with T.sub.art=a T.sub.bi+b or the temperature determined in accordance with formula (7) can be used as an input value for the regulation of this temperature to a desired value or in a desired value range, for which purpose the temperature control unit 8 shown in FIG. 3 can be used and for which purpose the device has a regulation unit 9.

(16) The keeping constant of the temperature at the start of the dialysis is in particular possible using the method in accordance with the invention or using the apparatus in accordance with the invention without substantial losses in precision with respect to the method based on the measurement with sensors at the blood side since systematic deviations between the procedure in accordance with the invention and the reference are of no significance here.

(17) In accordance with the invention, only elements which are anyway present at a dialysis machine are preferably used for the temperature measurement, which brings along cost advantages. Temperature sensors arranged at the blood side can thus be dispensed with, for example.

(18) FIG. 3 shows a dialysis machine by means of which the method in accordance with the invention can be carried out or a dialysis machine in accordance with the invention. The blood pump 3 conveys blood out of the vessel port 1 via a first arterial needle 11a in the direction 2a and via a first blood line 4a to the blood side 5a of a dialyzer or other heat exchanger or heat exchanging device (both terms are used synonymously within the framework of the invention).

(19) The blood side 5a is in thermal contact with the dialyzate side 5b or with a second compartment 5b of the dialyzer 5 via one or more membranes.

(20) If it is a hemodialysis or hemodiafiltration, 5b is the dialyzate side of a dialyzer; with an apparatus for blood temperature control, it is the side of the heat exchanging device flowed through by a heat medium or a coolant.

(21) For the temperature control of the dialyzate or of the heat medium/coolant, the temperature control unit 8 serves as an adjustment member which can have elements such as heating and/or cooling elements, temperature sensors and regulation apparatus controlled in an analog or digital manner.

(22) The temperature of the liquid flowing into the second compartment 5b is measured upstream and downstream of the second compartment 5b by means of the temperature sensors 7a, 7b. The temperature control unit 8 can be controlled by the evaluation and/or regulation unit 9 with the aim of changing the blood temperature in the second blood line 4b by means of which the blood is conveyed through the venous port 11b in the direction 2b back to the patient.

(23) Apart from the sensors 7a, 7b, means for determining the liquid flow at the blood side and at the secondary side, i.e. at the dialyzate side, are also connected to the regulation unit 9.

(24) To determine the blood temperature in the line sections 4a and 4b and the body temperature and/or its time variations in the course of treatment, different calculations, described in more detail above, are carried out in the evaluation unit 9 and the results can be communicated to a display unit 10 or also via a different kind of communication such as over a network or a wireless communication such as to a smartphone.