Title: Using venous versus arterial sampling to guide treatment decision making in exacerbations of COPD; a prospective cohort study
Funder: Department of Health (England)

Abstract: Currently patients admitted with an acute exacerbation of chronic obstructive pulmonary disease (COPD, lay term emphysema) have arterial blood gases performed by using a needle to access the radial or femoral artery. This arterial analysis is required to assess pH, carbon dioxide (CO2), and bicarbonate levels present in the blood in order to ascertain whether a patient is at risk of respiratory failure and to guide management such as prescription of oxygen therapy and the need for non-invasive ventilatory (NIV) support. Previously arterial analysis for oxygen level was also important, however this is now readily and reliably available using a non-invasive pulse oximetry monitor1. Arterial blood gas (ABG) analysis is technically difficult, painful for the patient, carries a small risk of serious adverse events for patients and of needlestick injury to clinical staff. Venous blood gas (VBG) analysis is easier, less painful, can be performed all staff and avoids patient and staff risks. Recently data has emerged suggesting that the relationship between pH and CO2 levels obtained with VBG and ABG sampling could allow venous blood to be used instead of arterial analysis. In particular, studies have shown that venous and arterial pH agree closely (average difference 0.04pH units) making them clinically interchangeable and that venous CO2 levels can be used to screen for hypercarbia2. We intend to discover whether arterial sampling can be replaced by venous sampling in a pragmatic study of 200 patients attending Nottingham University NHS Hospitals Trust with exacerbations of their COPD. With patient consent each time an ABG is performed a paired VBG will also be taken. Treatment decisions based on ABG samples will be documented. Currently treatment decisions are made according to a protocol using clinical features and blood gas analysis results; a fall in pH with a concurrent rise in CO2 normally leads to treatment with NIV. At the end of the study we will perform a posthoc analysis based on VBG findings to decide if VBG analysis can safely replace ABG analysis in guiding treatment decisions. We will also measure pain scores and attempts taken to obtain each sample3. We will publish our results. If our hypothesis that VBG can replace ABG sampling is correct we will disseminate them via the next COPD/ respiratory failure national guidelines. If VBGs can replace the use of ABGs in the assessment and monitoring of COPD exacerbations this will impact in 2 main areas: It will improve the patient experience with a reduction in pain. It will facilitate development of nurse led COPD assessment and NIV services. This will lead to more timely intervention and COPD assessment as, especially out of hours, the stretched on call service provided by junior doctors will not be required to provide ABG sampling. This will streamline service provision, and allow the development of nationally standardized practice.


Research activity codes: 4.2 EVALUATION OF MARKERS AND TECHNOLOGIES
Health categories: RESPIRATORY