EP-4742253-A1 - A METHOD FOR COMPENSATING THE EFFECTS OF GAS CONTAMINATION FOR A VENOUS BLOOD SAMPLE

EP4742253A1EP 4742253 A1EP4742253 A1EP 4742253A1EP-4742253-A1

Abstract

The invention relates to a computer-implemented method for compensating the effects of gas contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample, or blood sampled elsewhere, taken in a vacuum tube from a subject, such as human patient. The vacuum tube has a volume of residual gas (V g ) together with the blood. The method has a mathematical model with physiological sub-models simulating development in blood together with this residual gas, including sub-models describing: 1) the diffusion of gasses between the residual gas and the blood sample, 2) the effects of the diffusing gas in the blood in the vacuum tube, and 3) the effects of the diffusing gas in the residual gas in the vacuum tube. The mathematical model then calculates a modified set of blood variables (BV) to compensate for the physical and/or chemical interactions between the residual gasses and the blood sample in the time following sampling and before blood gas measurement. By accounting for this contamination of the blood sample, calculation of the actual values of blood variables seen in the patient is possible.

Inventors

REES, STEPHEN EDWARD
THOMSEN, Lars Pilegaard
Shastri, Lisha
Nevirian, Bahareh

Assignees

Aalborg Universitet

Dates

Publication Date: 20260513
Application Date: 20241111

Claims (16)

A computer-implemented method for compensating the effects of gas contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample, or blood sampled elsewhere, taken in a vacuum tube from a subject, the method comprising: - providing a blood sample taken in a vacuum tube, said vacuum tube having a known or estimated volume of residual gas (V g ) together with the blood sample, - performing a blood gas measurement of said blood sample resulting in a set of blood variables (BV') indicative of acid-base, oxygenation and/or electrolyte status in said blood sample, - providing a mathematical model based on a plurality of physiological sub-models simulating development in blood together with said residual gas, the mathematical model comprising: o a first sub-model describing the diffusion of gasses between the residual gas and the blood sample, o a second sub-model describing the effects of the diffusing gas on the blood in the vacuum tube, and o a third sub-model describing the effects of the diffusing gas on the residual gas in the vacuum tube, and - applying said mathematical model to calculate a modified set of blood variables (BV) indicative of the corresponding acid-base, oxygenation and/or electrolyte status of said blood sample so as to at least partly compensate for the physical and/or chemical interactions between the residual gasses and the blood sample in the time following sampling and before blood gas measurement.
The computer-implemented method according to claim 1, wherein the mathematical model is based on an assumption that the vacuum tube is completely closed so that the total mass of oxygen and carbon dioxide is constant regardless of gas diffusion between blood and the gas phase in the vacuum tube.
The computer-implemented method according to any of the preceding claims, wherein the second sub-model describing the effects of the diffusing gas on the blood in the vacuum tube is calculating total concentrations of O 2 and CO 2 , along with the buffer base concentration in blood, from measurements in the blood and/or gas partial pressures due the diffusion according to, or substantially according to, the equation: tCO 2 , b , tO 2 , b , BB b = acid base model pHp PCO 2 , b PO 2 , b tHb T b , wherein the acid base model refers to a biochemical mathematical model of the acid-base chemistry of blood.
The computer-implemented method according to any of the preceding claims, wherein the mathematical model takes into account a dependency on temperature of the gas phase and/or the blood phase in the vacuum tube during the time delay (TD) from blood sampling to the blood gas measurement.
The computer-implemented method according to any of the preceding claims, wherein the mathematical model takes into account a dependency on temperature of the gas phase and/or the blood phase the during the blood gas measurement.
The computer-implemented method according to any of the preceding claims, wherein the third sub-model describing the effects of the diffusing gas on the residual gas in the vacuum tube, the third sub-model describing for, one or more, of the following: - the relationship between partial pressure and fraction of O 2 and CO 2 depending on atmospheric pressure (AP), - the volume of O 2 and CO 2 in the gas phase as the fraction of these gases multiplied by the volume of the gas phase ( V g ) , - the mass of O 2 and CO 2 from the volume of these gasses and the molar density ( ρ ) of an ideal gas, and - the total concentration of O 2 and CO 2 in the gas phase can then be calculated as mass divided by the volume of the gas phase ( V g ).
The computer-implemented method according to any of the preceding claims, wherein the first sub-model is based on an assumption that the partial pressure of oxygen in the gas phase, PO 2,g , is equal to or mathematically related to the partial pressure of oxygen in the blood phase, PO 2,b in the vacuum tube.
The computer-implemented method according to any of the preceding claims, wherein the first sub-model is based on an assumption that the partial pressure of carbon dioxide in the gas phase, PCO 2,g , is equal to or mathematically related to the partial pressure of carbon dioxide in the blood phase, PCO 2,b in the vacuum tube.
The computer-implemented method according to any of the preceding claims, wherein the mathematical model is based on an assumption that immediately after blood sampling, the gas phase in the vacuum tube will have fractions of oxygen and carbon dioxide being approximately equal to atmospheric conditions.
The computer-implemented method according to any of the preceding claims, wherein the mathematical model takes into account that the partial pressure of carbon dioxide or oxygen in the gas phase, (PCO 2,g , PCO 2,g ) is not in equilibrium with the partial pressure of carbon oxygen or oxygen in the blood phase, (PCO 2,b , PCO 2,b ) in the vacuum tube, at least during the initial part of the time delay (TD) from blood sampling to the blood gas measurement.
The computer-implemented method according to any of the preceding claims, wherein the mathematical model calculates backwards in time from blood variables (BV') in the measured blood to blood gas variables (BV) in the sampled blood before diffusion has occurred.
The computer-implemented method according to any of the preceding claims, wherein the mathematical model calculates forwards in time from blood variables (BV) in the sample blood to blood variables (BV') when measured after diffusion has occurred.
The computer-implemented method according to any of the preceding claims, wherein the set of blood variables (BV) are chosen from the group consisting of: pH, PCO 2 , POz, SO 2 , Hb, FMetHb, FCOHb, glucose, lactate, Na + , Cl - , Ca 2+ , and/or K + .
A computer-implemented system for compensating the effects of gas contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample, or blood sampled elsewhere, taken in a vacuum tube from an associated subject, the system being arranged for: - receiving a blood sample taken in a vacuum tube, said vacuum tube having a known or estimated volume of residual gas (V g ) together with the blood sample, - performing a blood gas measurement of said blood sample resulting in a set of blood variables (BV') indicative of acid-base, oxygenation and/or electrolyte status in said blood sample, - operating a mathematical model based on a plurality of physiological sub-models simulating development in blood together with said residual gas, the mathematical model comprising: o a first sub-model describing the diffusion of gasses between the residual gas and the blood sample, o a second sub-model describing the effects of the diffusing gas on the blood in the vacuum tube, and o a third sub-model describing the effects of the diffusing gas on the residual gas in the vacuum tube, and - applying said mathematical model to calculate a modified set of blood variables (BV) indicative of the corresponding acid-base, oxygenation and/or electrolyte status of said blood sample so as to at least partly compensate for the physical and/or chemical interactions between the residual gasses and the blood sample in the time following sampling and before blood gas measurement.
A computer program product being adapted to enable a computer system comprising at least one computer having data storage means in connection therewith to control a system according to claim 14, such as a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 1.
The use of the method and/or the system according to any of claims 1-15 for compensating the effects of gas contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample, or blood sampled elsewhere, taken in a vacuum tube from a subject.

Description

FIELD OF THE INVENTION The present invention relates to a computer-implemented method for compensating the effects of gas or air contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample, or blood sampled elsewhere, taken in a vacuum based blood collection tube (hereafter referred to as a vacuum tube). The invention also relates to a corresponding system for measurement of blood, and a corresponding computer programme product. BACKGROUND OF THE INVENTION Measurement of blood acid-base status is usually performed in arterial or venous blood samples using standardized blood gas sampling tubes. In contrast, collection of blood for other purposes, often venous blood, are usually sampled in vacuum tubes. Vacuum tubes function such that the under-pressure of the tube draws blood from the patient. This is simple, and therefore beneficial but means that, following the sampling, the tube is partially filled with air. The volume of the air depends on the design of the tube and hence the initial under-pressure, with volumes between one-quarter to three-quarters of the tube not uncommon. The contamination of the blood sample with the remaining volume of air means that values of blood gasses will be contaminated resulting in significant bias in measurement of acid-base status. This prevents the routine use of vacuum tubes for all venous samples which could jeopardize standardized sampling and improved workflow. Hence, an improved method for compensating the effects of gas or air contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample taken in a vacuum tube would be advantageous, and in particular a more efficient and/or reliable method would be advantageous. OBJECT OF THE INVENTION It is a further object of the present invention to provide an alternative to the prior art. In particular, it may be seen as an object of the present invention to provide a method that solves the above-mentioned problems of the prior art with gas or air contamination. SUMMARY OF THE INVENTION Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a computer-implemented method for compensating the effects of gas contamination of acid-base, oxygenation and/or electrolyte status for a venous blood sample, or blood sampled elsewhere, taken in a vacuum tube from a subject, the method comprising: providing a blood sample taken in a vacuum tube, said vacuum tube having a known or estimated volume of residual gas (Vg) together with the blood sample,performing a blood gas measurement of said blood sample resulting in a set of blood variables (BV') indicative of acid-base, oxygenation and/or electrolyte status in said blood sample,providing a mathematical model based on a plurality of physiological sub-models simulating development in blood together with said residual gas, the mathematical model comprising: o a first sub-model describing the diffusion of gasses between the residual gas and the blood sample,o a second sub-model describing the effects of the diffusing gas on the blood in the vacuum tube, ando a third sub-model describing the effects of the diffusing gas on the residual gas in the vacuum tube, andapplying said mathematical model to calculate a modified set of blood variables (BV) indicative of the corresponding acid-base, oxygenation and/or electrolyte status of said blood sample so as to at least partly compensate for the physical and/or chemical interactions between the residual gasses and the blood sample in the time following sampling and before blood gas measurement. The invention is particularly, but not exclusively, advantageous for obtaining a method to simulate the changes in blood variables seen in a vacuum tube because of gas or air contamination. This is advantageous as the use of vacuum tubes for routine acid-base and oxygen analysis is expected to significantly improve clinical workflows. It is common that blood sampling for acid-base and oxygenation status be taken at different time-points, and by different personnel, than vacuum tube sampling of blood. By accounting and correcting for the contamination of the blood sample due to residual gas, the present invention may allow an acid-base sample to be drawn with other samples in vacuum tubes, and allow for the calculation of the actual values of blood variables seen in the patient. The effects of gas distribution between blood and gas phases in the vacuum tube are thought to occur rapidly, for example within 5 min. or 10 min. However, it is contemplated that the present invention can be combined with other mathematical models for compensating a delay between sampling and blood gas measurements accounting for in particular the acid produced due to the red blood cell (RBC) metabolism. Definitions: In the context of the present invention, it's to be understood that the method may be used to - at least partly - compensate for the p