Correlation and Agreement Between Arterial and Venous Blood Gas Analysis in Patients with Hypotension - An Emergency Department Based Cross Sectional Study

Abstract

Abstract Background Blood gas analysis is integral to assessing emergency department (ED) patients with acute respiratory or metabolic disease. Arterial blood gas (ABG) is the gold standard for oxygenation, ventilation, and acid-base status but is painful to obtain. Peripheral venous blood gas (VBG) is a valuable alternative as it is less painful and easy to collect. The comparability of ABG and VBG was studied in various conditions. But in hypotension, comparability is still a concern. So, we studied the correlation and agreement between ABG and VBG in hypotensive patients. Methodology: The study was conducted at the emergency department of a tertiary healthcare center in Northern India. Patients with hypotension above 18 years of age who satisfied the inclusion criteria were clinically evaluated. Patients who require ABG as a part of routine care were sampled. ABG was collected from the radial artery at the wrist level. VBG was obtained from the cubital or dorsal hand veins. Both samples were collected within 10 minutes and were analyzed. All ABG and VBG variables were entered in premade proforma. The patient was then treated and disposed of according to institutional protocol. Results Two hundred fifty patients were enrolled. The mean age was 53.25 ± 15.71 years. 56.8% were male. The study included 45.6% septic, 34.4% hypovolemic, 18% cardiogenic, and 2% obstructive shock patients. The study found a strong correlation and agreement for ABG and VBG pH, pCO2, HCO3, lactate, sodium, potassium, chloride, ionized calcium, blood urea nitrogen, base excess, and arterial/alveolar oxygen ratio. Hence, regression equations were made for the aforementioned. There was no correlation observed between ABG and VBG pO2 and SpO2. Our study concluded that VBG could be a reasonable alternative for ABG in hypotensive patients. We can also mathematically predict values of ABG from VBG using regression equations derived. Conclusions The study has shown strong correlations and agreements for most ABG and VBG parameters except pO2 and SO2. The study can predict an ABG mathematically using regression formulas formulated from a VBG. This will decrease needle stick injury, consume less time, and make blood gas evaluation easy in hypotensive settings.