CORRELATION OF VENOUS BLOOD GAS ANALYSIS AND PULSE OXIMETRY (SPO₂) WITH ARTERIAL BLOOD GAS ANALYSIS IN CRITICALLY ILL PATIENTS
Keywords:
Arterial Blood Gas, Venous Blood Gas, Pulse Oximetry, Spo₂, Critical Illness, Acid–Base Balance, Ventilation, Oxygenation.Abstract
Background: The gold standard for evaluating ventilation, oxygenation, and acid-base balance in critically ill patients is ABG (Arterial Blood Gas) analysis. However, repeated arterial sampling is invasive, painful, and associated with complications. VBG (Venous Blood Gas) analysis and pulse oximetry (SpO₂) are less invasive alternatives that may provide comparable clinical information. The purpose of this study was to assess the relationship between ABG values and SpO₂ and VBG parameters in critically ill patients. Methods: A prospective cohort study was conducted in the Intensive Care Unit of MKCG Medical College and Hospital from October 2022 to March 2024. A total of 100 critically ill adult patients requiring ABG analysis were enrolled. Simultaneous ABG and VBG samples were collected from arterial and venous access sites, respectively, and analyzed at the bedside. Additional clinical parameters including heart rate, respiratory rate, temperature, mean arterial pressure, vasopressor use, and mechanical ventilation status were recorded. Correlations between arterial and venous pH, pCO₂, pO₂, and SpO₂ were analyzed statistically. Results: Among the 100 patients, 66% were male and 34% were female. Mechanical ventilation was required in 62% of patients, while 45% received vasopressor support. Central venous samples were obtained in 46% and peripheral venous samples in 54% of cases. Mean arterial pH, pCO₂, and pO₂ were 7.48 ± 0.10, 37.85 ± 16.58 mmHg, and 132.44 ± 58.12 mmHg, respectively, while corresponding venous values were 7.45 ± 0.09, 42.06 ± 16.70 mmHg, and 41.10 ± 11.29 mmHg. Significant positive correlations were observed between arterial and venous pH (p<0.0001), arterial and venous pCO₂ (p<0.0001), arterial and venous pO₂ (p=0.005), and SpO₂ with arterial pO₂ (p<0.0001). Conclusion: VBG analysis demonstrated strong correlation with ABG for pH and pCO₂, while SpO₂ correlated well with arterial oxygenation. The combination of VBG analysis and pulse oximetry can provide reliable bedside assessment of acid–base status, ventilation, and oxygenation in critically ill patients, reducing the need for repeated arterial sampling.
