What test assesses the return of blood circulation by observing color change in a capillary bed?

The correct choice is the assessment known as capillary refill. This test evaluates the efficiency of blood circulation by checking how quickly color returns to an area after it has been blanched, typically by applying pressure. It works on the principle that if a person has adequate blood circulation, then the capillary beds will refill quickly after being emptied of blood.

When assessing capillary refill, you typically press on a nail bed or a section of skin to temporarily cut off blood flow. Upon releasing the pressure, the color should return within a few seconds in a healthy individual. A delay in this color change may indicate potential issues with circulation or perfusion, which is critical information in emergency medical situations.

Other tests listed serve different purposes: pulse oximetry measures the oxygen saturation in the blood, blood pressure measurement determines the force of blood against the artery walls, and capnography is used to measure the concentration of carbon dioxide in exhaled breath. Each is important in its context, but only capillary refill specifically focuses on the return of blood circulation as indicated by color change in capillaries.