Perfusion refers to the flow of blood through the vessels of the body, on its way to the capillary beds in various tissues which receive bloodflow. When someone experiences decreased blood flow, this can be quite dangerous, as the tissues in the body can be quickly damaged by restricted bloodflow. Most people who have looped a rubber band around a finger for a short time are familiar with what happens when the flow is reduced.
When patients are brought in during an emergency, one of the things tested during triage is perfusion. Limited blood flow can be a sign of a serious problem which needs to be addressed. One common way to test blood flow is simply to apply pressure to the skin, and then to wait to see how long it takes for blood to flow back into the site. A slow return of blood indicates decreased perfusion, a cause for concern.
In the process of perfusion, blood moves its way out from the heart, through a network of arteries, and into the smallest blood vessels in the body, the capillaries. As the blood flows through the capillaries, it brings vital nutrients to the tissues of the body, and helps to sweep away waste. Then, the blood flows back to the heart, where it is infused with oxygen again and set out all over again. Any interruption in this circulatory system can have a ripple effect on vessels and capillaries downstream.
This process can be turned to the advantage of medical personnel. For example, many medications are delivered directly into the bloodstream, with perfusion carrying the medication throughout the body. Sometimes, blood flow to a specific limb or area may be briefly restricted while medication is injected at the site, ensuring that the medication becomes concentrated in the area where it is needed most.
When blood flow is radically decreased, a patient runs the risk of dying or losing a limb. For example, if someone is in a car accident which causes him or her to be trapped in the car with a leg pinned, the circulation to that leg could be cut off, causing the tissues in the leg to die. Unless the patient is treated promptly, the limb might need to be amputated because of widespread tissue death. Poor perfusion can also cause organ failure, which can be a very serious problem, as the failure of one organ often puts stress on the others, leading to systemic organ failure and eventual death.