Intensive care medicine

Critically ill

Blood gas analysis

Arterial blood

Oxygenation

Cardiology

Anesthesia

Venous blood

pCO2

Internal medicine

Arterial blood gas analysis

Medicine

Narrative review

Anesthesia & Analgesia

Arterial blood gas (ABG) analysis is used in critical care units to determine the degree of oxygenation, adequacy of ventilation, and the presence and severity of acid-base disturbances in the body. However, arterial puncture may result in complications, and the difficulty in acquiring arterial blood may delay care. Central venous blood gas (VBG) is a potentially more accessible alternative to ABG sampling. Current evidence suggests that pH and P co 2 obtained via peripheral VBG correlate well with ABG measurement. Nevertheless, the value of using central VBG to guide clinical decisions or as a surrogate for ABG is unclear. The purpose of this review is to explore the relationship between ABGs and central VBGs in critically ill patients. We performed a MEDLINE search using the following search terms: venous blood gas, arterial blood gas, and central venous blood gas. We excluded studies that did not involve human subjects, and only pH and P co 2 values were reviewed and examined from the studies included. All cited references from included studies were also reviewed to identify relevant literature. We identified 7 studies that met our criteria. In studies of hemodynamically stable patients, the mean difference between arterial and central venous pH and P co 2 was 0.03 units and 4–6.5 mm Hg, respectively. However, in patients with circulatory failure, the difference between central venous and arterial pH/P co 2 was 4-fold greater. We concluded that central VBG parameters of pH and P co 2 are potentially good surrogates for determining arterial pH and P co 2 in a stable patient without severe acid-base disturbances. Furthermore, central VBG can be used as a useful screening tool for arterial hypercapnia. In addition, we derived an adjustment formula for ABG conversion from central VBG: (1) arterial pH = venous pH + 0.05 units and (2) arterial P co 2 = venous P co 2 − 5 mm Hg.

Comparing Central Venous Blood Gas to Arterial Blood Gas and Determining Its Utility in Critically Ill Patients: Narrative Review