Blood Studies I: ABG and VBG

An ABG test measures blood pH, oxygen-carrying capacity, oxygen and carbon dioxide levels, and bicarbonate ions. It assesses the lungs' ability to supply oxygen and remove carbon dioxide, reflecting ventilation status. ABG also indicates kidney function through bicarbonate ion reabsorption or excretion, revealing metabolic status such as metabolic acidosis or alkalosis.

Before ABG collection, verify whether the patient uses oxygen and at what percentage and liters per minute. Avoid changing oxygen therapy settings or suctioning for 20 minutes before collection to ensure accurate results. Document the patient's current oxygen therapy status, as this information is essential for interpreting blood gas values.

Use a heparinized syringe to collect ABG samples from the radial, brachial, or femoral artery, or from an indwelling arterial catheter. Expel all air bubbles from the syringe and immediately place the sample on ice unless analysis occurs within one minute. After collection, press the site for 5 minutes to prevent hematoma formation.

ABG studies assess lung function in oxygen delivery and carbon dioxide removal, reflecting ventilation and metabolic status. VBG studies estimate the balance between oxygen used by tissues and oxygen returning to the heart. VBG is performed when ABG collection is not feasible and can be obtained from venous circulation using central venous catheters.

Mixed venous oxygen saturation (SO2) levels, the most accurate indicator of oxygen balance, can only be obtained from blood samples drawn from a pulmonary artery catheter. Central venous oxygen saturation samples drawn from a central venous catheter inserted in the superior vena cava provide the best alternative for patients without pulmonary artery catheters and closely approximate SO2 levels.

Blood gas samples must be placed on ice immediately after collection to prevent clotting and preserve sample integrity. If analysis will occur within one minute, ice storage is not required. Proper storage ensures accurate measurement of oxygen, carbon dioxide, and pH levels, which are essential for assessing respiratory and metabolic function.

ABG studies are often ordered for acutely ill patients or those with respiratory disorders to assess oxygen delivery and ventilation status. VBG studies are performed when drawing ABGs is not feasible. Both studies help healthcare professionals make informed decisions about treatment strategies by evaluating the body's oxygen supply and utilization.