Product description concerning v-tac

Transcription

1 Product description concerning v-tac v-tac software calculates arterial blood gas values from venous peripheral blood gas measurement, combined with arterial oxygen saturation v-tac Product description 1

2 Product description concerning Table of contents The v-tac conversion method... 1 v-tac in clinical practice... 1 When can v-tac be used?... 1 Implementation, IT architecture and operation... 2 v-tac printed report... 2 Benefits from application of v-tac... 3 How does v-tac work?... 4 Assumptions... 4 The v-tac software step-by-step... 4 The acid-base mass-action and mass-balance simulator... 5 Validation of v-tac... 6 Methods and material... 6 v-tac accuracy and precision plots... 7 ph... 7 pco po Robustness of v-tac... 9 v-tac input checks... 9 Arterio-venous (A-V) difference... 9 v-tac used on capillary or arterial blood... 9 Consequences of faulty or in-accurate SpO2 measures... 9 Sensitivity to BE and RQ Conclusion v-tac Parameter Guide Input parameters Output parameters References Version number: 2.0 Revision date: 14 January 2019

3 The v-tac conversion method v-tac (Venous-to-Arterial-Conversion method) is an advanced software application that calculates arterialised acid-base and blood gas values from values in the peripheral venous blood, supplemented with the arterial oxygen saturation level, also called SpO 2, measured by a pulse oximeter. For a more throughout description of the v-tac method, please see the section How does v-tac work? v-tac in clinical practice It is simple to operate v-tac in daily clinical practice. After installation of the v-tac software, the workflow is as follows: 1) Draw a peripheral venous blood sample. 2) Measure SpO 2 simultaneously with a pulse oximeter. 3) Enter the venous blood sample into the blood gas analyser and start the analysis (see Figure 1A). 4) Enter the SpO 2 value (see Figure 1B). 5) Operate the blood gas analyser as usual. 6) The v-tac software calculates the arterial blood gas values, which instantly become available to the clinician. When can v-tac be used? v-tac can be used on patients age 18 and above with any clinical condition and who have been clinically assessed as showing sufficient peripheral perfusion. Indications include: stable and representative SpO 2 can be measured, peripheral limb is warm, red and dry, a pulse can be felt, capillary response is normal. v-tac should not be used if: there is difficulty measuring SpO 2 (on the arm used for the sample), the peripheral limb is cold/blue, there is a long stasis time for blood sampling, the patient develops catecholamines (or similar). v-tac cannot be used on patients with SpO 2 below 75% (default is 80%). Figure 1: Constructed example of blood gas analyser with v-tac configuration v-tac Product Description 1

4 Implementation, IT architecture and operation The v-tac software application works seamlessly with existing blood gas analysers on the market. Market leading blood gas analysers can be configured so that a button named v-tac and an input field for entering the SpO 2 value appear as illustrated in the constructed example in Figure 1. The v-tac software is not installed on the blood gas analyser itself. Instead, the v-tac software is a stand-alone software application designed to run on a small footprint Windows virtual server or a dedicated computer in the hospital s IT environment. A single instance of the v-tac software can service all blood gas analysers in the hospital. To enable the v-tac feature on existing blood gas analysers, a simple configuration of each blood gas analyser is needed. During normal operation, the v-tac software operates seamlessly as a black-box and does not require any attention or application management. The blood gas analyser transmits the v-tac marked venous blood gas results to a central hospital system. The v-tac software fetches the venous blood gas and SpO 2 values from the IT system, typically by interfacing data management applications from leading blood gas analyser manufacturers, then calculates the v-tac arterial results and forwards the results to the hospital information system, where they can be accessed instantly by the clinical staff. The v-tac software also automatically and instantly creates a report, which can be printed on a standard network printer, should this be requested. Figure 2 illustrates the principle of how the v-tac solution works with the blood gas analyser. v-tac printed report The v-tac printed report is completely customisable. A constructed example is shown in Figure 3. The printed report includes: Patient information The entered SpO 2 value v-tac calculated arterial blood gas results (shown in the red box in Figure 3) The original venous blood gas values measured by the blood gas analyser (shown in the blue box in Figure 3). Figure 2: The principle of hospital IT architecture Figure 3: Constructed example of a v-tac printed report v-tac Product Description 2

5 Benefits from application of v-tac The application of v-tac triggers a chain of benefits and improvements leading to significant clinical, operational and cost benefits particularly for management of patients suffering from respiratory compromise. Since blood gas testing is a critical tool throughout the patient journey from admission to discharge, the benefits from application of v-tac are not restricted to a single department or a special application. v-tac makes arterial blood gas values instantly and easily available The blood sample for venous blood gas can be drawn in combination with other regular blood tests, thus obviating arterial punctures and reducing time to care. Clinicians are given a baseline to monitor patient improvement/deterioration from time of admission. v-tac can reduce the use of arterial lines in the ICU and thereby reduce the risk of side effects such as injuries to the arteries. By reducing the use of arterial lines, v-tac improves patient mobility. v-tac can reduce the need for repeated arterial punctures, frequent in certain treatments such as Non-Invasive Ventilation (NIV) and may improve timely monitoring of this patient group. Patient benefits through v-tac from less pain and side effects associated with arterial punctures. Patients often fear arterial punctures and may delay admission on purpose. v-tac enables a task-transfer from medical doctors to other staff groups such as nurses, which can reduce the burden on logistics, free clinician time and improve workflow in the wards. v-tac can enhance nurseautonomy and up-scale nurse-led care, where nurses take over more responsibility, which may improve compliance and outcomes and reduce length-of-stay. v-tac Product Description 3

6 How does v-tac work? The v-tac software calculates arterial blood gas values from peripheral venous blood gas measurements, combined with pulse oximetry measurement of arterial oxygen saturation, using algorithms and mathematical models that simulates the transport of blood back through the tissues. The v-tac software step-by-step The principle steps of the software are illustrated in Figure 4 and the details of this mathematical transformation now follow: Assumptions To perform this simulation two assumptions are required: First it is assumed that the amount of strong acid added to the blood on its passage through the tissues is small or zero, such that a change in base excess (BE) from the venous sampling site to the arterial site (ΔBE av) is approximately zero. For peripheral venous blood, this is likely to be true if the peripheral limb has a clearly recognizable arterial pulse, a normal capillary response, and a normal colour and temperature. For central or mixed venous blood this assumption is less likely to be true, as the different organ systems can add different and substantial amounts of acid into the blood circulation in situations with e.g. anaerobic metabolism. In addition, it is assumed that the respiratory quotient (i.e. the rate of CO 2 production (VCO 2) to O 2 utilisation (VO 2)) over the tissue sampling site, cannot vary outside the range 0.7 and 1.0. RQ of the tissue cells can only vary between 0.7 and 1.0, being 0.7 in aerobic metabolism of fat and 1.0 in aerobic metabolism of carbohydrate. Whilst R, the respiratory exchange ratio, measured at the mouth, may vary outside this range, the RQ over the tissue sampling site can only do so if there is a rapid flow of acid, base or CO 2 in or out of the tissues where peripheral venous sampling occurs. This may occur in situations involving rapid disturbance of acid base status, such as in exercise. However, in a warm, well perfused extremity this rapid re-distribution is less likely. This means that anaerobically sampled venous blood can be arterialised mathematically by simulating the removal/addition, respectively, of a constant ratio (RQ) of CO 2 and O 2 over the tissues. This simulation is being performed until the arterialised oxygen saturation matches the arterial oxygen saturation measured by a pulse oximeter. (3) v-tac uses an approximation of RQ=0.82 for the conversion. For information about the impact of v-tac calculated results from variation of BE and RQ, see Table 4 in section Sensitivity to BE and RQ. Figure 4: Principles of the v-tac method. First an anaerobic venous blood sample is drawn to provide values of the acid-base and oxygen status of the peripheral venous blood. As input, the v-tac software uses the following values: ph v, p vco 2, p vo 2, Hbv, S vo 2, methaemoglobin (fmethb v) and carboxyhaemoglobin (fcohb v) and the arterial oxygen saturation measured by a pulse oximeter. fmethb v and fcohb v are optional and can be replaced by constants v-tac Product Description 4

7 through configuration. See Table 5 at the end of this document for a description of all input parameters. Step 1: v-tac performs an input check on the venous blood gas values calculated by the blood gas analyser. For more information about the v-tac input check please see section v- TAC input checks. Step 2: The venous measurements ph v, p vco 2, p vo 2, S vo 2, Hbv, fmethb v, and fcohb v are used to calculate the total CO 2 concentration (t vco 2), total O 2 concentration (t vo 2), base excess (BE v), and the concentration of 2,3- diphosphoglycerate (2,3-DPG v) in the venous blood for which the oxygen dissociation curve passes through the measured venous po 2,v and SO 2,v. (2) These calculations are performed by using an acid-base mass action and mass balance simulator described in section The acid-base mass-action and massbalance simulator. Step 3: We assume that the concentration of haemoglobin (thb), the total concentration of plasma non-bicarbonate buffer (tnbb p), the concentration of 2,3-DPG and BE are the same in arterial and venous blood: thb a = thb v tnbb p,a = tnbb p,v 2,3-DPG a = 2,3-DPG v BE a = BE v Step 4: Calculation of the total concentration of O 2 and CO 2 in arterial blood is then performed by simulating addition of a concentration of O 2 (ΔO 2), to the venous blood and removing a concentration of CO 2 (ΔCO 2, where ΔCO 2 = RQ ΔO 2) from the venous blood: to 2,a = to 2,v + O 2, tco 2,a = tco 2,v - RQ * O 2 Calculated values of arterialised blood tco 2- (B) a,c; to 2- (P) a,c; Hb a; BE a,c; t anbbp and DPG a are then used to calculate the remaining variables describing arterialised blood, i.e. ph a,c, p aco 2,c, p ao 2,c and S ao 2,c also using the acid-base mass action and mass balance simulator described below, but in a reverse of the process. Step 5: The calculated arterialised oxygen saturation S ao 2 is then compared with that measured by the pulse oximeter (SpO 2). The difference between the two giving an error = S ao 2 SpO 2. By varying the value of ΔO 2 and repeating steps 4, a value of ΔO 2 can be found for which the error is zero. At this point, the ΔO 2 represents the concentration of O 2 added, and RQ multiplied by ΔO 2 the concentration of CO 2 removed, so as to transform venous to arterialised blood. For this value of ΔO 2, calculated values of all variables describing arterialised blood should be equal to measured arterial values. The calculated arterial output blood gas values include ph a,c, p aco 2,c, p ao 2,c (up to 10 kpa), HCO 3- (P) a,c, Base Excess (BE a,c), to 2- (P) a,c and tco 2- (B) a,c. See Table 6 at the end of the document for a detailed description of all output parameters. Optional feature: If FiO 2 is entered on the blood gas analyser, the v-tac software will calculate the PaO 2/FiO 2 ratio, which is required for calculation of the SOFA score. Step 6: Before the mathematical process is completed, v-tac performs several output checks on the calculated arterial blood gas values. More details of the v-tac algorithm can be found in the original scientific publication (1). The acid-base mass-action and mass-balance simulator What makes the v-tac algorithm possible is the use of mathematical models of acid-base and blood chemistry based on Siggaard-Andersen (4), and extended by Rees and Andreassen (2). The combined model is a comprehensive set of connected mass action and mass balance equations, to keep track of the masses of CO 2, O 2 and binding effects to haemoglobin (oxygen carrying and non-oxygen carrying) and the relationship between values of po 2 and SO 2 in the blood, known as the oxygen dissociation curve. It represents plasma bicarbonate and non-bicarbonate buffers and the buffering on the amino end and side chains of the haemoglobin molecule. The model accounts for the Bohr-Haldane effects. (1) (2) It should be noted that in this model, BE is defined as the concentration of strong acid necessary to titrate fully oxygenated blood to a ph p 1 = 7.4, at a pco 2 = 5.33 kpa. In the conventional definition (called Actual Base Excess (ABE)), BE is defined without fully oxygenating the blood. Because of Bohr-Haldane effects, ABE values therefore depend upon oxygen level and are not the same in arterial and venous blood, even in the absence or addition of acid or base in to the blood from the tissue. In the definition of BE used here, values of BE are independent of O 2 level and will only change if strong acids or bases are added and the model therefore accounts for the Bohr-Haldane effects. (3) 1 The subscript p is used to refer to the plasma fraction of blood. v-tac Product Description 5

8 Validation of v-tac Methods and material The accuracy of v-tac has been validated in several clinical studies in which venous blood gas and SpO 2 measurements converted to arterial values by v-tac were compared to simultaneous arterial blood gas measurements. The accuracy of the v-tac calculated values vs. arterial blood gas is comparable to the accuracy of repeated arterial blood gases for blood gas parameters, including ph, pco 2, po 2 (up to 10 kpa / 75 mmhg), HCO 3- and base excess. The study population includes a broad range of patients from emergency departments, pulmonary departments and intensive care units with various diagnoses, including COPD, sepsis, asthma, pneumonia and lung cancer (5) (6) (7) (3) (8) (9) (10) 2 (11). Thus, v-tac has been validated on both spontaneously breathing patients and on mechanically ventilated patients, including patients on non-invasive ventilation (NIV). The patient cohort included both haemodynamically stable and unstable patients. Ideally the pair of samples should be collected simultaneously. In the studies, the arterial blood gas samples were drawn shortly before the venous blood gas samples were drawn. The time between drawing of the arterial blood gas and the v-tac samples was typically between 2 and 5 minutes (6). The accuracy of both arterial blood gas and venous blood gas is affected by pre-analytical errors in the time span from the blood sample is drawn and until it is analysed and by analytical errors. In addition, both arterial blood gas and venous blood gas are affected by biological fluctuations. When comparing two subsequent measurements on human specimen, the biological change will have an impact on the result. This becomes evident when comparing v-tac to the repeatability of arterial blood gas vs. arterial blood gas and capillary blood gas vs. arterial blood gas. Table 1 shows the statistical variation of the v-tac calculated arterial blood gas vs. the reference arterial blood gas measurement and statistical variation of measured arterial blood gas vs. measured arterial blood gas repeatability. Table 1: Statistical variation (95% confidence interval). v-tac vs. arterial blood gas (ABG): pooled data from references (5) (6) (7) (3) (8) (9) (10). Arterial blood gas vs. arterial blood gas: (* (7), ** (11)) v-tac vs. ABG ABG vs. ABG Unit ph ± ± 0.027* pco 2 ± 0.54 (4.05) ±0.45* (3.38) po 2 (0-8 kpa) ± 0.9 (6.75) ±1.21** (9.09) kpa (mmhg) kpa (mmhg) The accuracy includes the contribution from all error sources, including variation from SpO 2. Figure 5: Collection of blood samples. ABG: arterial blood sample (7) (11) 2 Group B excluded due to 15 minutes between sample pairs v-tac Product Description 6

9 v-tac accuracy and precision plots The following plots compare ph, pco 2 and po 2 for v-tac vs. arterial blood gas (ABG1), shown as black dots, with arterial blood gas (ABG2) vs. arterial blood gas (ABG1) repeatability, shown as red dots. ph pco2 v-tac Product Description 7

10 po2 v-tac Product Description 8

11 Robustness of v-tac v-tac input checks Before the mathematical process is initiated, several checks take place, as illustrated in Figure 6. First the SpO 2 value must be within the range of 80% 3 to 100% and, secondly, the SpO 2 value must be greater than the s vo 2 value minus 4%. As the third step, the venous blood gas values must be physiologically plausible. If any of the checks fail, an error message explaining the cause of the error will appear, and no conversion will take place. Table 2: Arterial-Venous difference Direction of Arterial-Venous difference ph v is lower than pha p vco 2 is higher than pco 2a p vo 2 is lower than po 2a Approximate range ph unit 0-3 kpa ( mmhg) 0 - several kpa s vo 2 is lower than so 2a 0-70% It is evident that small A-V differences in saturation level are accompanied by small A-V differences in ph, pco 2 and po 2 and, vice versa, large differences in the A-V saturation level are accompanied by large A-V differences in ph, pco 2 and po 2. Although the exact A-V differences are very complex and vary significantly from patient to patient, the correlation between the difference in the A-V oxygen saturation and the differences in the A-V ph, pco 2 and po 2 are relatively linear in the individual patient. The physiological model in the v-tac software accounts for this. Due to the SpO 2 input checks (see Figure 6) and the design of the v-tac software, the v-tac software can only calculate arterial blood gas values of ph a,c to be higher than or equal to the ph v and p aco 2,c to be lower than or equal to the p vco 2 and, finally, p ao 2,c to be higher than or equal to p vo 2. Figure 6: v-tac input check The 4% tolerance on SpO 2 is to accommodate the following situation: In patients where the arterial blood flushes through the tissues with very small metabolism, the venous values will be close to arterial values. However, due to tolerance on pulse oximetry and blood gas testing, the SpO 2 value measured may be slightly below the s vo 2. In such cases, the s vo 2 value is used for the v-tac conversion. Arterio-venous (A-V) difference When arterial blood flows through the tissues of a peripheral limb, oxygen can be consumed, and acid can be produced in different forms through aerobic and anaerobic metabolism, whereas the reverse process is not physiologically plausible. Therefore, the direction of arterial-venous differences in values is predictable. Table 2 explains the direction and the approximate ranges of A-V differences that can be expected in a patient cohort suffering from a respiratory compromise. v-tac used on capillary or arterial blood If capillary or arterial blood is used as input on purpose or coincidently, the so 2 level measured in the capillary or arterial blood will be very close to or equal the SpO 2 level measured by pulse oximetry. As a result, the v-tac software will present output blood gas values that, in practice, will have only very minor or no corrections made compared to the original values. Consequences of faulty or inaccurate SpO2 measures The use of pulse oximetry to estimate the arterial saturation level is known to have a certain patient-to-patient variability. The accuracy of a standard pulse oximeter is typically ±4%, but in clinical praxis it may be as much as 10%. Underestimation of SpO 2 is not uncommon, e.g. if the pulse oximeter picks up a poor signal due to poor peripheral perfusion, incorrect positioning of the probe or similar. Another source of error is incorrect entering of the measured SpO 2 value on the blood gas analyser. 3 The default is 80% but can be as low as 75% by configuration v-tac Product Description 9

12 Arterialisation of ph a,c and p aco 2,c is dependent on the difference between SpO 2 and the venous so 2: Small difference => small correction Large difference => large correction The arterialisation of p ao 2,c is dependent on the absolute value of SpO 2 and the intersection with the Oxygen Dissociation Curve. The accuracy of the calculated p ao 2,c is least sensitive to inaccurate SpO 2 values at values below approximately 95%, whilst more sensitive to SpO 2 values from approximately 96% and above. Example 3: Asthma patient with very large A-V difference ( pha-v = 0.063, pco 2A-V = 2.48 kpa). SpO 2 measured to 99% (sao 2=97.3%). White cells show results of SpO 2 +/- 5% and 10% simulation. In this example, +5% and +10% are not possible because they exceed 100%. To illustrate the effect of inaccurate/faulty SpO 2 measurements, three examples have been selected based on real patient data. Example 1: COPD patient with average A-V difference. SpO 2 measured to 88% (slightly overestimated, SaO 2=85.3%). White cells show results of SpO 2 +/- 5% and 10% simulation. In this example, - 10% not possible, due to 80% lower limit. Table 3 below illustrates the typical impact of v-tac calculated results from variation of SpO 2. Table 3: Impact of v-tac results from variation of SpO2 (3) Error sources Typical impact of v-tac calculated results ph pco 2 (kpa) po 2 (kpa) Across entire range sao 2 = 88% sao 2 = 93% SpO 2 +2% N/A (> 10) SpO 2-2% Sensitivity to BE and RQ Table 4 below illustrates the typical impact of v-tac calculated results from variation of BE and RQ. Example 2: COPD patient with very small A-V difference. SpO 2 measured to 92% (SaO 2=92.4%). White cells show results of SpO 2 +/- 5% and 10% simulation. In this example, -5% and -10% are not possible, due to venous so 2=90%, and +10% is not possible because it exceeds 100%. Table 4: Impact of v-tac results from variation of BE and RQ (3) Error sources Typical impact of v-tac calculated results ph pco 2 (kpa) po 2 (kpa) ΔBEav ±0.2 mmol/l ±0.006 ±0.08 ±0.07 RQ ±0.08 ±0.005 ±0.10 ±0.06 Conclusion ph a,c and p aco 2,c calculated values are robust to inaccurate/faulty SpO 2 input values. The accuracy of p ao 2,c is dependent on the accuracy of the SpO 2 measurement. v-tac Product Description 10

13 v-tac Parameter Guide Input parameters Table 5: Input parameters required to run a v-tac arterialisation Description Unit Comment phv ph measured by a blood gas analyser from a venous blood sample ph-unit Mandatory pvco2 pvo2 SvO2 Hbv fmethbv fcohbv pco2 measured by a blood gas analyser from a venous blood sample Oxygen Partial Pressure (po2) measured by a blood gas analyser from a venous blood sample Venous oxygen saturation (SO2) measured by a blood gas analyser from a venous blood sample Venous haemoglobin measured by a blood gas analyser from a venous blood sample fmethb measured by a blood gas analyser from a venous blood sample fcohb measured by a blood gas analyser from a venous blood sample kpa mmhg kpa mmhg % fraction mmol/l g/dl g/l % fraction % fraction FiO2 Fraction of inspired oxygen. Entered on the blood gas analyser % fraction SpO2 Peripheral arterial oxygen saturation measured by a pulseoximeter. Entered on the blood gas analyser % fraction Mandatory Mandatory Mandatory Mandatory Optional - If not measured by blood gas analyser, a constant of 0.7% is used (configurable). Optional - If not measured by blood gas analyser, a constant of 1.3% is used (configurable). Optional - v-tac calculates the pao2/fio2 ratio if FiO2 is entered Mandatory - v-tac does not accept SpO2 below 75% (default limits are %) Output parameters Table 6: Output parameters Description Unit Comment pha, c Calculated arterial ph ph-unit paco2, c Calculated arterial pco2 kpa mmhg pao2, c Calculated arterial po2 kpa mmhg SaO2, c Calculated arterial SO2. % fraction If v-tac calculated po2 exceeds 10 kpa / 75 mmhg, v-tac reports po2 > 10 kpa or po2 > 75 mmhg On successful conversions, value is identical to the entered SpO2 value. Otherwise, an error message will appear. 2.3-DPG Calculated 2,3-diphosphoglycerate mmol/l By using venous blood, is it possible to determine 2.3-DPG with good accuracy. BEa, c Calculated arterial base excess mmol/l The concentration of strong acid necessary to titrate fully oxygenated blood to a ph = 7.4, at a pco2 = 5.33 kpa. Equivalent to ABE. The v-tac software accounts for the Bohr-Haldane effects. 4 HCO3 - (P)a, c Calculated actual arterial bicarbonate concentration mmol/l to2 - (P)a, c Calculated total arterial oxygen concentration mmol/l tco2 - (B)a, c Calculated total arterial carbon-dioxide concentration mmol/l PaO2/FiO2 ratio Calculated pao2/fio2 ratio kpa mmhg 4 In comparison, the conventional definition (called Actual Base Excess BE or ABE) is defined without fully oxygenating the blood. Actual Base Excess values, therefore depend upon oxygen level and are not the same in arterial and venous blood, even in the absence or addition of acid or base into the blood from the perfused tissues. In the definition of BE (not ABE), values of BE are independent of O2 level and will only change if strong acids or bases are added. (3) v-tac Product Description 11

14 References 1. Rees, S E, et al. Mathematical modelling of the acid-base chemistry and oxygenation of blood: a mass balance, mass action approach including plasma and red blood cells. European Journal of Applied Physiology. 2010, 108, pp Rees, S E og Andreassen, S. Mathematical models of oxygen and carbon dioxide storage and transport: The acid-base chemistry of blood. Critical Reviews in Biomedical Engineering. 2005, 33, 3, pp Rees, S E, Toftegaard, M og Andreassen, S. A method for calculation of arterial acid-base and blood gas status from measurements in the peripheral venous blood. Computer Methods and Programs in Biomedicine. 2005, 81, pp Siggard-Andersen, O. Acid Base Balance. Encyclopedia og Respiratory Medicine Toftegaard, M, Rees, S E og Andreassen, S. Evaluation of a method for converting venous values of acid-base and oxygenation status to arterial values. European Journal of Emergency Medicine. 2009, 26, pp Rees, S E, et al. Converting venous acid-base and oxygen status to arterial in patients with lung disease. European Respiratory Journal. 2009, 26, pp Toftegaard, M, Rees, S E og Andreassen, S. Correlation between acid-base parameters measured in arterial blood and venous blood samples peripherally, from vena cavae superior, and from the pulmonary artery. European Journal of Emergency Medicine. 2008, 15, pp Klein, A C og Rittger, H. Validity and clinical use of mathematical arterialized venous blood gas with the v-tac approach for evaluation of arterial blood gas in patients with respiratory compromise. Deutche Gesellschaft für Pneumologie Manuel, A, et al. A method for calculation of arterial blood gas values from measurements in the peripheral blood (v -TAC). ERS Congress Thygesen, G, et al. Mathematical arterialization of venous blood in emergency medicine patients. European Journal of Emergency Medicine Mallat, J, et al. Thevenin. Repeatability of Blood Gas Parameters, pco2 Gap, and pco2 Gap to Arterial-to-Venous Oxygen Content Difference in Critically Ill Adult Patients. Medicine. 2015, 94, Andreassen, S og Rees, S E. Mathematical models of oxygen and carbon dioxide storage and transport: Interstitial fluid and tissue stores and whole-body transport. Critical Reviews in Biomedical Engineering. 2005, 33, 3, pp Oddershede, L, et al. The cost-effectiveness of venous-converted acid-base and blood gas status in pulmonary medical departments. ClinicoEconomics and outcomes Research. 2011, 3, pp Rees, S E, et al. Calculating acid-base and oxygenation status during COPD exacerbation using mathematically arterialised venous blood. Clin Chem Lab Med. 2012, 50, Kelly, AM, Klim, S og Rees, S E. Agreement between mathematically arterialised venous versus arterial blood gas values in patients undergoing non-invasive ventilation: a cohort study. Emerg Med J. 2014, 31, pp Crescioli, E, et al. Application of venous to arterial conversion (v-tac) software in the emergency medicine context. DEMC Lumholdt, M, et al. Mathematical arterialisation of peripheral venous blood gas for obtainment of arterial blood gas values: a methodological validation study in the clinical setting. Journal of Clinical Monitoring and Computing For more information about v-tac TM contact OBI Medical: Phone: sales@obimedical.com In vitro diagnostic medical device. The v-tac software meets the provisions of the Council Directive 98/79/EEC for In-vitro Diagnostic Medical Devices. Copyright 2018 OBI Medical ApS, Denmark. Contents may be freely reproduced if the source is acknowledged. v-tac Product Description 12