Method and apparatus for estimating a paco2 value for a patient subject to extra corporeal circulation

• US 20080097233A1
• Filed: 04/20/2005
• Published: 04/24/2008
• Est. Priority Date: 04/20/2004
• Status: Abandoned Application

• Current Assignee: Rikshospitalet-Radiumhospitalet HF
• Original Assignee: Rikshospitalet-Radiumhospitalet HF
• Inventors: Pedersen, Tore H., Kristiansen, Frode, Hogetveit, Jan Olav
• Application Number:
  US11/568,070
• Publication Number:
  US 20080097233A1
• Time in Patent Office: Days
• US Class Current: 600/531
• CPC Class Codes: A61B 5/14557 specially adapted to extracorporeal circuits
• CPC Class Codes: A61M 1/1698 Blood oxygenators with or without heat-exchangers intracorporal A61M1/1678; manufacturing of membranes therefor B01D67/00; semi-permeable membranes for separation processes characterised by their properties B01D69/00; semi-permeable membranes characterised by their material B01D71/00
• CPC Class Codes: A61M 1/367 Circuit parts not covered by the preceding subgroups of group A61M1/3621
• CPC Class Codes: A61M 2230/202 partial carbon oxide pressure, e.g. partial dioxide pressure (P-CO2)

Abstract

The invention relates to a method and an apparatus for estimating a P_aCO₂ value for a patient subject to extracorporeal circulation by means of an oxygenator. The method comprises the steps of measuring a P_exCO₂ value in the exhaust gas of the oxygenator and the patient'"'"'s arterial blood temperature value T_a, using a temperature sensor arranged in the oxygenator. The estimated P_aCO₂ value is then calculated, based on the measured P_exCO₂ value and the arterial temperature measurement. Advantageously, an average value determined from a predetermined number of recent P_exCO₂ values is used in the calculation. The calculation is performed by adding a correction term to the P_exCO₂ value, which is composed of a temperature dependent component and an offset component. The correction term may be adjusted by a user. The estimated P_aCO₂ value is presented on a display. A switch provides easy alteration between pH-stat mode and alpha-stat mode.

Claims

1. Method for estimating a value (P_aCO₂) representing the arterial partial pressure of CO₂ for a patient subject to extracorporeal circulation by means of an oxygenator, comprising the steps of:

measuring a value (P_exCO₂) representing the partial pressure of CO₂ in the exhaust gas of the oxygenator,

measuring a temperature value (Ta) representing the patient'"'"'s arterial blood temperature, and

calculating the estimated value (P_aCO₂) representing the arterial partial pressure of CO₂, dependent on said value (P_exCO₂) representing said partial pressure of CO₂ in said exhaust gas and said temperature value (T_a).

2. Method according to claim 1,

wherein said value (P_exCO₂) representing the partial pressure of CO₂ in said exhaust gas is low pass filtered, reducing the effects of rapid fluctuations in the measured value.

3. Method according to claim 1 or 2, wherein said value (P_exCO₂) is calculated as an average value of a number of recently measured values (P_exCO₂) of partial pressure in said exhaust gas.

4. Method according to one of the claims 1-3, wherein said step of calculating said estimated value (P_aCO₂) comprises

adding a correction value to the value (P_exCO₂) of partial pressure in said exhaust gas, said correction value being substantially linearly dependent on said temperature value (T_a).

5. Method according to claim 4,

wherein said correction value is calculated as a proportionality constant (a) multiplied by the temperature value (T_a) added to an offset constant (b).

6. Method according to claim 5,

wherein said proportionality constant (a) and said offset constant (b) are pre-generated by a calibration procedure and stored in a memory.

7. Method according to claim 5 or 6,

wherein said proportionality constant (a) and said offset constant (b) may be set or adjusted by an input device.

8. Method according to one of the claims 1-7,

wherein said step of measuring the temperature value (T_a) is performed by means of a temperature sensor arranged in an extracorporeal circuit which comprises said oxygenator.

9. Method according to one of the claims 1-8,

wherein said step of measuring the value (P_exCO₂) representing the partial pressure of CO₂ in the exhaust gas of the oxygenator comprises exposing a substantially continuous and laminar flow provided by the oxygenator exhaust output to the input of a CO₂ sensor.

10. Method according to one of the claims 1-9, further comprising the step of

displaying the estimated value (P_aCO₂) presenting the arterial partial pressure of CO₂ on a display.

11. Method according to one of the claims 1-10, reiterated as a pseudo-continuous process until the receipt of a stop signal.

12. Apparatus for estimating a value (P_aCO₂) representing the arterial partial pressure of CO₂ for a patient subject to extracorporeal circulation by means of an oxygenator, comprising

a measuring device for measuring a value (P_exCO₂) representing the partial pressure of CO₂ in the exhaust gas of the oxygenator,

a temperature measuring device for providing a temperature value (T_a) representing the patient'"'"'s arterial blood temperature, and

a processing device, arranged to perform the step of

calculating the estimated value (P_aCO₂) representing the arterial partial pressure of CO₂, dependent on said value (P_exCO₂) representing said partial pressure of CO₂ in said exhaust gas and said temperature value (T_a) representing the patient'"'"'s arterial blood temperature.

13. Apparatus according to claim 12, further comprising a low pass filter, low pass filtering said value (P_exCO₂) representing the partial pressure of CO₂ in said exhaust gas, reducing the effects of rapid fluctuations in the measured value.

14. Apparatus according to claim 12 or 13, wherein said processing device is arranged to calculate the value (P_exCO₂) as an average value of a number of recently measured values (P_exCO₂) of partial pressure in said exhaust gas.

15. Apparatus according to one of the claims 12-14, wherein said processing device is arranged to perform said step of calculating said estimated value (P_aCO₂) by adding a correction value to the value (P_exCO₂) of partial pressure in said exhaust gas, said correction value being substantially linearly dependent on said temperature value (T_a).

16. Apparatus according to claim 15,

wherein said processing device is arranged to calculate said correction value as a proportionality constant (a) multiplied by the temperature value (T_a) added to an offset constant (b).

17. Apparatus according to claim 16,

wherein said proportionality constant (a) and said offset constant (b) are pre-generated by a calibration procedure and stored in a memory.

18. Apparatus according to claim 16 or 17, further comprising an input device,

wherein said processing device is arranged for setting or adjusting said proportionality constant (a) and said offset constant (b) by means of the input device.

19. Apparatus according to one of the claims 12-18,

wherein said temperature value (Ta) is measured by means of a temperature sensor arranged in an extracorporeal circuit which comprises said oxygenator.

20. Apparatus according to one of the claims 12-19,

wherein said measuring device for measuring the value (P_exCO₂) representing the partial pressure of CO₂in the exhaust gas of the oxygenator comprises a CO₂ sensor arranged in conduit supplied by a substantially continuous and laminar flow provided by the oxygenator exhaust output.

21. Apparatus according to one of the claims 12-20, further comprising a display, wherein said processing unit is further arranged to display the estimated value (P_aCO₂) presenting the arterial partial pressure of CO₂ on said display.

22. Apparatus according to one of the claims 12-21, further comprising a stop signal operating device, wherein said processing device is arranged to reiterate said calculating step, using updated measurement values, until the receipt of a stop signal from the stop signal operating device.