Is Venous to Arterial Conversion (v-TAC) of Blood Gas Reliable in Critical Ill Patients in the ICU?

Study Overview
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Brief Summary
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Objective: Arterial blood gas (ABG) is essential in the clinical assessment of potential acutely ill patients venous to arterial conversion (v-TAC), a mathematical method, has recently been developed to convert peripheral venous blood gas (VBG) values to arterialized VBG (aVBG) values. The aim of this study is to test the reliability of aVBG compared to ABG in an intensive care unit (ICU) setting. Method: Consecutive patients admitted to the ICU with pH values <7,35 or >7,45 are included in this study. Paired ABG and aVBG samples are drawn from patients via arterial catheter, central venous catheter and/or peripheral venous catheter and compared.

Detailed Description
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Arterial blood gas (ABG) analysis is essential in assessment of respiratory and metabolic status in acutely ill patients. In comparison to peripheral venous blood (PVG) sampling, the ABG sampling procedure is more painful for the patient and technically more challenging for the clinician to perform. Other drawbacks of ABG sampling include adverse events such as subcutaneous hematoma, arterial thrombosis or embolization, and pseudoaneurysms. Peripheral venous blood gas (VBG) sampling has been suggested as an alternative to the ABG procedure. This procedure causes less patient discomfort and the sample can be analysed in combination with other venous blood tests. Studies have revealed that pH and bicarbonate have good correlation, whereas venous and arterial blood gasses (pO2 and pCO2) show low agreement. However, a new method has been developed to calculate ABG values mathematically from peripheral venous blood by use of venous to arterial conversion (v-TAC) software (Obimedical, Denmark), supplemented with oxygen saturation measured by pulse oximetry. The principle of the method is a mathematical transformation of VBG values to arterialized values (aVBG) by simulating the transport of blood back through the tissue. Initial testing of the method in an emergency department setting showed acceptable clinical congruence between arterial and mathematically arterialized pH and pCO2 with a small difference (+/- SD) on 0.001 +/- 0.024 and 0.00 0.46 kPa, respectively. However, inaccurate values of pO2 were seen when oxygen saturation measured by pulse oximetry was above 96%, due to the flat shape of the oxygen dissociation curve (ODC). Although most patients in the ICU have arterial catheters therefrom ABG can be drawn, applying arterial catheter is difficult or even impossible in some patients. In relation to step-down some patients get arterial catheters removed and in the event of deterioration in patients acid-base or respiratory disease aVBG could prove useful as a minimally invasive tool to assess patients status. The aim of this study is to investigate if v-TAC is reliable and safe to use in patients with critically respiratory or metabolic disease admitted to the ICU.

Official Title
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Utility of Mathematically Converted Venous to Arterial Blood Gas for Clinical Monitoring

Conditions
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Respiratory Insufficiency, Metabolic Disease, Acidosis, Alkalosis, Sepsis, Abdomen, Acute

Intervention / Treatment
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* Diagnostic Test: venous to arterial conversion (v-TAC)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: All patients admitted to the intensive care with the following: Arterial catheter for other purpose. Peripheral venous catheter or central venous catheter for other purpose. Exclusion Criteria: Normal pH in arterial blood gas.
Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Respiratory disease<br>Patients with acute respiratory insufficiency admitted to the ICU and with pH <7,35 or >7,45 | Diagnostic Test: venous to arterial conversion (v-TAC)<br>* Venous to arterial conversion (v-TAC) is a software (Obimedical, Denmark), which can convert venous blood gas values to arterial blood gas values. The principle of the method is a mathematical transformation of VBG values to arterialized values (aVBG) by simulating the transport of blood back through the tissue. To facilitate this simulation the following physiologically relevant assumptions were made: 1) The peripheral extremity was well perfused; 2) change in base excess across the tissue sampling site was approximately zero; 3) the respiratory quotient (rate of CO2 production and O2 utilisation over capillaries) could not vary outside the range 0.7 and 1.0, and 4) the haemoglobin concentration was constant from artery to vein.<br>|
| Metabolic disease<br>Patients with acute metabolic disease admitted to the ICU and with pH <7,35 or >7,45 | Diagnostic Test: venous to arterial conversion (v-TAC)<br>* Venous to arterial conversion (v-TAC) is a software (Obimedical, Denmark), which can convert venous blood gas values to arterial blood gas values. The principle of the method is a mathematical transformation of VBG values to arterialized values (aVBG) by simulating the transport of blood back through the tissue. To facilitate this simulation the following physiologically relevant assumptions were made: 1) The peripheral extremity was well perfused; 2) change in base excess across the tissue sampling site was approximately zero; 3) the respiratory quotient (rate of CO2 production and O2 utilisation over capillaries) could not vary outside the range 0.7 and 1.0, and 4) the haemoglobin concentration was constant from artery to vein.<br>|
| Sepsis<br>Patients with acute sepsis admitted to the ICU and with pH <7,35 or >7,45 | Diagnostic Test: venous to arterial conversion (v-TAC)<br>* Venous to arterial conversion (v-TAC) is a software (Obimedical, Denmark), which can convert venous blood gas values to arterial blood gas values. The principle of the method is a mathematical transformation of VBG values to arterialized values (aVBG) by simulating the transport of blood back through the tissue. To facilitate this simulation the following physiologically relevant assumptions were made: 1) The peripheral extremity was well perfused; 2) change in base excess across the tissue sampling site was approximately zero; 3) the respiratory quotient (rate of CO2 production and O2 utilisation over capillaries) could not vary outside the range 0.7 and 1.0, and 4) the haemoglobin concentration was constant from artery to vein.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Lin's Concordance correlation coefficient (CCC) | Comparison of pH between ABG and aVBG (from peripheral venous catheter). The closer CCC is to 1 the better correlation. | 1. january 2018 | 
| Lin's Concordance correlation coefficient (CCC) | Comparison of pCO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from peripheral venous catheter). The closer CCC is to 1 the better correlation. | 1. january 2018 | 
| Lin's Concordance correlation coefficient (CCC) | Comparison of pO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from peripheral venous catheter). The closer CCC is to 1 the better correlation. | 1. january 2018 | 
| Lin's Concordance correlation coefficient (CCC) | Comparison of pH between ABG and aVBG (from central venous catheter). The closer CCC is to 1 the better correlation. | 1. january 2018 | 
| Lin's Concordance correlation coefficient (CCC) | Comparison of pCO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from central venous catheter). The closer CCC is to 1 the better correlation. | 1. january 2018 | 
| Lin's Concordance correlation coefficient (CCC) | Comparison of pO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from central venous catheter). The closer CCC is to 1 the better correlation. | 1. january 2018 | 
| Bland and Altman's plot | Mean difference and 95% limits-of-agreement of pH between ABG and aVBG (from peripheral venous catheter) | 1. january 2018 | 
| Bland and Altman's plot | Mean difference and 95% limits-of-agreement of pCO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from peripheral venous catheter). | 1. january 2018 | 
| Bland and Altman's plot | Mean difference and 95% limits-of-agreement of pO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from peripheral venous catheter). | 1. january 2018 | 
| Bland and Altman's plot | Mean difference and 95% limits-of-agreement of pH between ABG and aVBG (from central venous catheter). | 1. january 2018 | 
| Bland and Altman's plot | Mean difference and 95% limits-of-agreement of pCO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from central venous catheter). | 1. january 2018 | 
| Bland and Altman's plot | Mean difference and 95% limits-of-agreement of pO2 (Unit of Measurement: kilopascal) between ABG and aVBG (from central venous catheter). | 1. january 2018 | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of patients with sepsis group. | Number and percentage of patients in 'sepsis' group. | 1. january 2018 | 
| Number of patient with metabolic disease | Number and percentage of patients in 'metabolic disease' group. | 1. january 2018 | 
| Number of patient with acute respiratory insufficiency | Number and percentage of patients in 'respiratory disease group' group. | 1. january 2018 | 
| Mean number of days until pH neutrality in sepsis group | Mean number of days until patients ABG pH was within the range 7.35-7.45 in 'sepsis' group. | 1. january 2018 | 
| Mean number of days until pH neutrality in patients with metabolic disease. | Mean number of days until patients ABG pH was within the range 7.35-7.45 in 'metabolic disease' group. | 1. january 2018 | 
| Mean number of days until pH neutrality in patients with respiratory disease. | Mean number of days until patients ABG pH was within the range 7.35-7.45 in 'respiratory disease' group. | 1. january 2018 | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Blood gas analysis, Critical care, venus to arterial conversion