MONITORING SYSTEM FOR CARDIAC SURGICAL OPERATIONS WITH CARDIOPULMONARY BYPASS

Abstract

A monitoring system for cardiac operations with cardiopulmonary bypass comprising: a processor operatively connected to a heart-lung machine; a pump flow detecting device connected to a pump of the heart-lung machine to continuously measure the pump flow value and send it to the processor; a hematocrit reading device inserted inside the arterial or venous line of the heart-lung machine to continuously measure the blood hematocrit value and to send it to the processor; a data input device to allow the operator to manually input data regarding the arterial oxygen saturation and the arterial oxygen tension; computing means integrated in the processor to compute the oxygen delivery value on the basis of the measured pump flow, the measured hematocrit value, the preset value of arterial oxygen saturation, and the preset value of arterial oxygen tension; and a display connected to the processor to display in real-time the computed oxygen delivery value.

Claims

1. A method of continuously monitoring a patient's parameters in real-time during a surgical operation including cardiopulmonary bypass using a heart-lung machine having a controller, the method comprising: continuously detecting a pump flow rate value from a pump of the heart-lung machine during the surgical operation; continuously detecting a hematocrit value of the patient during the surgical operation; continuously obtaining an arterial oxygen saturation value of the patient during the surgical operation; calculating in real-time during the surgical operation, with the controller, an indexed oxygen delivery value based on the continuous arterial oxygen saturation value of the patient, the continuous hematocrit value of the patient, and the continuous measure of the pump flow rate value; and continually displaying in real-time on a display the calculated indexed oxygen delivery value calculated by the controller.

2. The method of claim 1, further comprising: setting an indexed oxygen delivery threshold value; continuously comparing the calculated indexed oxygen delivery value with the threshold value during the surgical operation; and triggering an alarm in real-time if the calculated indexed oxygen delivery value breaches the threshold value.

3. The method of claim 2, wherein the alarm is triggered when the calculated indexed oxygen delivery value falls below the threshold value.

4. The method of claim 2, further comprising: showing the alarm in real-time on the display; and displaying in real-time on the display during the surgical operation, the continuous measure of the pump flow rate value and the continuous measure of the hematocrit value.

5. The method of claim 2, further comprising calculating in real-time an accumulated amount of time that the threshold value has been breached.

6. The method of claim 5, wherein the alarm is not triggered when the accumulated amount of time is less than a time threshold.

7. The method of claim 6, wherein the time threshold is 5 minutes.

8. The method of claim 5, wherein the accumulated amount of time is a consecutive amount of time in a given time window.

9. The method of claim 5, wherein the accumulated amount of time is a nonconsecutive amount of time in a given time window.

10. The method of claim 1, further comprising continuously measuring and displaying the patient's body temperature.

11. The method of claim 10, wherein setting the indexed oxygen delivery threshold value includes calculating the indexed oxygen delivery threshold value from the measured patient's body temperature.

12. The method of claim 1, further comprising calculating in real-time during the surgical operation, with the controller, a hemoglobin value based on the continuous measure of the hematocrit value.

13. The method of claim 12, wherein the display is configured to display a plurality of windows, wherein continually displaying includes displaying graphically the indexed oxygen delivery value as a function of time in a first window of the plurality of windows, the continuous measure of the pump flow rate in a second window of the plurality of windows, and displaying the hemoglobin value in a third window of the plurality of windows.

14. The method of claim 13, wherein continually displaying further includes displaying at least one of the indexed oxygen delivery value, an elapsed time from start of cardiopulmonary bypass, a body surface area, and a body temperature, each in an additional individual window.

15. The method of claim 14, wherein the first window is larger than the second window, the third window, and the additional individual widow.

16. The method of claim 1, further comprising determining a body surface area of the patient, wherein calculating the indexed oxygen delivery value is further based on the body surface area of the patient.

17. The method of claim 1, further comprising continuously detecting exhaled carbon dioxide at the heart-lung machine, providing a preset gas flow value, and calculating indexed carbon dioxide production based on the preset gas flow value and measured exhaled carbon dioxide.

18. A method of continuously monitoring a patient's parameters in real-time during a surgical operation including cardiopulmonary bypass using a heart-lung machine having a controller, the method comprising: continuously detecting a pump flow rate from a pump of the heart-lung machine during the surgical operation; continuously measuring and displaying the patient's body temperature; continuously detecting a hematocrit value of the patient during the surgical operation; continuously obtaining an arterial oxygen saturation value of the patient during the surgical operation; calculating in real-time during the surgical operation, with the controller, an indexed oxygen delivery value based on the continuous arterial oxygen saturation value of the patient, the continuous hematocrit value of the patient, and the continuous measure of the pump flow rate value; continually displaying in real-time on a display the calculated indexed oxygen delivery value calculated by the controller; setting an indexed oxygen delivery threshold value by calculating the indexed oxygen delivery threshold value from the measured patient's body temperature; continuously comparing the calculated indexed oxygen delivery value with the threshold value during the surgical operation; and triggering an alarm in real-time if the calculated indexed oxygen delivery value breaches the threshold value.

19. The method of claim 18, further comprising: showing the alarm in real-time on the display; and displaying in real-time on the display during the surgical operation, the continuous measure of the pump flow rate value and the continuous measure.

20. The method of claim 19, further comprising calculating in real-time an accumulated amount of time that the threshold value has been breached, wherein the alarm is not triggered when the accumulated amount of time is less than a time threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0098] FIG. 1 is a graph illustrating the relationship between VO2 and DO2 in an athlete under physical exercise.

[0099] FIG. 2 is a graph illustrating the relationship between VO2 and DO2 in a patient under cardiac operation.

[0100] FIG. 3 is a graph illustrating the relationship between VCO2 and VO2.

[0101] FIG. 4 is a graph illustrating the relationship between LAC and VCO2i.

[0102] FIG. 5 is a schematic view of a heart-lung machine connected to the patient and a block diagram of a monitoring system according to the invention.

[0103] FIG. 6 is a block diagram illustrating in a more detailed way a monitoring system according to the invention.

[0104] FIG. 7 is a front view of a monitoring device according to the invention, showing a screen view of the display.

[0105] FIG. 8 is a view of a monitoring device according to the invention similar to FIG. 7, in a minimal configuration.

[0106] In the following description, and with reference to FIGS. 5, 6, 7, and 8, the monitoring system for cardiac operations with cardiopulmonary bypass is described, according to the invention.

[0107] FIG. 5 shows a patient 1 laying on a surgical table 2. A heart-lung machine, comprehensively identified by the number 3, is connected to the patient 1. As already known in the art, a heart-lung machine 3 comprises a venous extracorporeal circuit, collecting blood from the venous system of the patient. A roller or centrifugal mechanical pump 4 pumps the venous blood from a venous extracorporeal circuit towards an oxygenator 5, whose role is removing CO2 from the venous blood and supplying oxygen (02). The blood oxygenated by the oxygenator 5, is sent, again by the same roller or centrifugal pump 4, to an arterial extracorporeal circuit connected to the arterial system of the patient, therefore creating a total bypass of the heart and lungs of the patient.

DETAILED DESCRIPTION

[0108] The monitoring system, according to the invention, comprehensively identified by the reference number 10, is operatively connected to the heart-lung machine 3. The monitoring system 10 comprises a processor able to perform calculations, as subsequently explained, and a monitor screen or display 11 that works as an interface with the operator.

Manual Data Input from the Operator

[0109] Using the knob 50 (FIGS. 7 and 8), placed in the front part of the monitoring system 10, the operator may input data that will be stored by the processor memory of the monitoring system 10. Data manually inserted by the operator are: [0110] (1) Height and weight of the patient. [0111] (2) The arterial oxygen saturation (Sat(a)). This value, during CPB procedures, is usually 100%. However, in case of extraordinary events like an oxygenator malfunction, the value of (Sat(a)) may decrease. In this case, the operator may manually change this value using the knob 50. [0112] (3) The arterial oxygen tension (PaO2) value. This PaO2 value is measured by the perfusionist on the arterial blood of the patient with blood gas analysis, using an adequate and specific device.

[0113] (4) The gas flow value (Ve). This Ve value is established by the perfusionist operating the heart-lung machine 3. Generally, the Ve is regulated with a flow-meter, in a range between 1 and 5 L/min, according to the patient's parameters. This Ve value rarely changes during a CPB procedure, and therefore can be manually inserted by the operator. However, as an alternative, the monitoring system 10 may include an electronic flow-meter connected to the heart-lung machine 3, to continuously detect the Ve value.

Heart-Lung Machine Interfaced Data

[0114] The monitoring device 10 is equipped with some electrical connections to the heart-lung machine 3, as to continuously receive data collected by adequate sensors placed in specific positions of the heart-lung machine. These continuously collected data are: [0115] (1) Patient's body temperature (T). This temperature Tis continuously measured by a temperature probe inserted inside the esophagus or the rectum of the patient. The temperature probe 40 sends an electronic signal of the temperature to a monitor of the heart-lung machine visualizing, in real-time, the temperature value. In this case, it is sufficient to interface with an electrical connection the monitor of the heart-lung machine 3 with the monitoring device 10, for a continuous input of the temperature value T. [0116] (2) Exhaled carbon dioxide (eCO2). This eCO2 value is continuously measured through a CO2 detector 41 placed at the gas escape of the oxygenator 5 to detect the sidestream CO2 exhaled from the oxygenator 5. The CO2 detector 41 can be any kind of CO2 detector among the various commercially available and re-usable capnographs. [0117] (3) Hematocrit (HCT). The HCT value is continuously measured through a hematocrit reading cell 42 placed inside the arterial or venous circuit of the heart-lung machine 3. For instance, in FIG. 5, the hematocrit reading cell 42 is placed inside the arterial line between the pump 4 and the oxygenator 5. The hematocrit reading cell 42 is commercially available and disposable. [0118] (4) Pump flow (Qp). The Qp value is continuously measured through the Doppler reading cell 43, placed on the arterial line of the heart-lung machine 3. This kind of Doppler reading cell 43 measures the blood flow on the basis of the Doppler principle (red cells velocity).

[0119] If the pump 4 of the extracorporeal circuit is a centrifugal pump, it is already equipped with the Doppler reading cell 43. Conversely, if the pump 4 is a roller pump, the Doppler reading cell 43 may be added. In the alternative, the Doppler reading cell 43 may be omitted, since the roller pump head is provided with a flow measuring system. In this case, the data regarding the pump flow Qp is directly sent to the monitoring device 10.

[0120] With specific reference to FIG. 6, the operation of the monitoring system 10 is described below. The processor of the monitoring system 10 includes a first computing program 12 that, based on the weight and height of the patient as input by the operator calculates, according to pre-defined tables, the body surface area (BSA) of the patient.

[0121] The BSA value is sent to a second computing program 13 that receives the input value of the pump flow Qp as detected by the pump 4 of the heart-lung machine 3. The second computing program 13 calculates the indexed pump flow Qpi, according to the relationship Qpl=Op/BSA

[0122] A third computing program 14 receives the input value HCT as detected by the hematocrit reading cell 43 placed inside the venous or arterial line of the heart-lung machine. The third computing program 14, based on the equation (6), calculates the hemoglobin value Hb. The Hb value is sent to the display 11 and displayed in a window 51 of the display 11 (FIG. 7).

[0123] The pump flow indexed Qpi computed by the second computing program 13 and the hemoglobin value Hb computed by the third computing program 14 are sent to a fourth computing program 15 that receives as input values the values of arterial oxygen saturation (Sat(a)) and arterial oxygen tension (PaO2) manually entered by the operator. The fourth computing program 15, according to the equation (4), calculates the indexed oxygen delivery value (DO2i).

[0124] As shown in FIG. 7, the DO2i value is visualized in real time in a window 53 of the display 11 and as a graphical pattern 52 (as a function of time). The display 11 is provided with a chronometer window 56 showing the time passed from the beginning of the CPB.

[0125] As shown in FIG. 6, the DO2i value is sent to a comparator 18 which compares it to a threshold value of DO2icrit that is displayed in a window 54 (FIG. 7) of the display 11. This threshold value is set at 270 ml/min/m.sup.2 at a temperature between 34° C. and 37° C., and decreases as a function of temperature, in a linear fashion.

[0126] Therefore the threshold value of DO2icrit be preset by the operator or may be calculated by a computing program 17 depending on the temperature value T determined by the temperature probe 40. The temperature T value determined by the probe 40 is sent to the display 11 to be displayed in a window 55.

[0127] When the DO2i value falls below the DO2icrit, the comparing device 16 sends a control signal to an alarm 16 that is triggered, alerting the operator of a potentially dangerous condition.

[0128] The alarm 16 is not triggered by brief decreases of the pump flow Qp (often needed during CPB). Therefore, the alarm 16 could be set to be activated after 5 minutes of consecutive detection of a DO2i below the DO2icrit. However, a recording of all the periods of low flow can be made, to analyze and avoid the possibility that many short periods of low flow may create an additional effect. It is reasonable to consider no more than 20 minutes (as a total) of DO2i below the DO2icrit during a normal CPB lasting about 90 minutes. The monitoring device 10 is equipped with a computing program 19, which receives as input values the exhaled carbon dioxide eCO2 as detected by the CO2 sensor 41 and the gas flow Ve set by the operator. According to these input data, the computing program 19 calculates the indexed carbon dioxide production VCO2i applying the equation (9).

[0129] The VCO2i value as calculated by the computing program 19 is sent to the display 11 and displayed in real time in a window 57 (FIG. 7) in its graphical relationship 58 as a function of time.

[0130] The VCO2i value is sent to a second comparator 20 which compares it with an anaerobic threshold value VCO2icrit set by the operator; by default the VCO2icrit is preset at 60 ml/min/m.sup.2. As shown in FIG. 7, the display 11 is provided with a window 59 showing the value of anaerobic threshold VCO2icrit set by the operator.

[0131] Back to FIG. 6, when the VCO2i exceeds the VCO2icrit an alarm signal is sent to a second alarm 21, which, when triggered, alerts the operator of a warning condition.

[0132] Moreover, as shown in FIG. 7, the display 11 is provided with: a window 60 where the gas flow value Ve set by the operator is displayed; a window 61 where the indexed pump flow value Qpi arriving from the computing program 13 is displayed; and a window 62 where the body surface area of the patient is displayed as calculated by the computing program 12.

[0133] The monitoring system 10 can be equipped with a data recording system and a printer interface, and/or a digital data recording system. The display 11 could include two configurations: a complete configuration, as the one shown in FIG. 7, and a reduced configuration, only considering the DO2 parameter, as shown in FIG. 8.

[0134] The above description and accompanying drawings are provided for the purpose of describing embodiments of the invention and are not intended to limit the scope of the invention in any way. It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods for cardiac operations without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

REFERENCES

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