(O-A4) Correlation and Agreement Between Arterial and Venous Blood Gas Analysis in Patients with Hypotension—an Emergency Department-based Cross-sectional Study

Objectives: The study aimed to determine the relationship and agreement between ABG and VBG for the parameters pH, pCO2, HCO3, lactate, and base excess in hypotensive patients in the ED and also to develop prediction models in measuring pH, pCO2, HCO3, lactate, and base excess in arterial and venous samples.

Background: Hypotension is one condition where findings of ABG and VBG comparability are inconsistent. Obtaining ABG in hypotensive patients in emergency settings is very difficult, so obtaining a VBG while performing cannulation is a better alternative. A few studies tried to study the correlation between arterial and venous samples in hypotensive patients, but their study findings were not uniform and varied widely. As their conclusions were inconsistent, we conducted our study to sort out the inconsistency to find the correlation and agreement between ABG and VBG in hypotensive patients.

Methods: A single-center, prospective study was performed from January 2021 to June 2022 in the Emergency Department of All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India, to evaluate the correlation and agreement between ABG and peripheral VBG measurements. The study included every adult hypotensive patient whom the ED physician found to be in need of both ABG and peripheral VBG analysis. Those who did not give consent and who had contraindications for ABG, an interval of more than 10 minutes between ABG and VBG, inappropriate sample transfer to the laboratory, and postcardiac arrest patients were excluded. An arterial sample (0.5–1 mL) was collected using a heparinized syringe from the radial artery at the wrist level. The venous blood sample was obtained from the cubital or dorsal hand veins. Both samples were collected with minimum delay (less than 10 minutes). Both samples were analyzed as soon as possible using a blood gas analyzer. All data will be entered into an Excel sheet and analyzed using SPSS 23.0 version.

Results: The study included 250 patients with a mean age of 53.25±15.71 years. 56.8% of patients were male. There were 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 those mentioned earlier. 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 for parameters that showed correlation and agreement.

Conclusions: ABG sampling causes most unpleasant patient experiences and is associated with complications like arterial injury, thrombosis, air embolism, hematoma, aneurysm formation, and reflex sympathetic dystrophy. The study concludes that we can use a VBG obtained while peripheral cannulation for blood gas evaluation as an alternative to ABG in hypotensive settings in ED. This can decrease the chance of needle stick injury while taking an ABG and consume less time for blood gas obtainment. The limitation was that it was a single center study and the study design and setting did not allow follow-up on the mortality of the patients studied.

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Funding (Optional): The authors received no financial support for the research.