Fluid replacement is an activity which is designed to to make up for losses of body fluid, ensuring that the balance of fluid in the body stays even. Fluid plays a number of important roles in the body, making a stable balance of fluids very important. There are several ways in which fluid replacement can be accomplished, and a number of settings in which it may be called for by medical professionals.
People classically lose body fluid through sweating, and they also lose fluid volume with vomiting, diarrhea, and blood loss. If fluid levels are allowed to decline too low, a patient can experience life threatening complications. Cholera, for example, famously weakens patients with severe watery diarrhea which can eventually lead to death. Likewise, an athlete who works out vigorously and does not drink adequate fluids can develop complications as his or her body struggles to make up for the fluid loss caused by sweating.
One method for fluid replacement is simply to drink fluids. For people of normal health and activity level, the water needed for fluid replacement can come directly from the diet, although some people also like to drink extra water. Individuals who have extremely low fluid levels cannot just drink plain water, because it can encourage fluid shifts between intracellular, intervascular, and interstitial space in the body, which can be dangerous. As a result, oral fluids used for patients who have experienced fluid loss are usually mildly saline and may have added electrolytes, so that the composition of body fluids remains stable.
Intravenous fluid replacement can be used when someone is dangerously dehydrated. Delivering fluids intravenously gets them into locations where they are needed as quickly as possible. Saline solutions and other fluid solutions can be delivered intravenously, along with blood, which is used for fluid replacement when people have experienced blood loss so that people do not develop complications as a result of a dangerous decline in blood products. Blood and saline can also be given together, and blood products such as plasma may also be delivered separately as needed.
In some cases, fluids will be injected directly into areas of muscle, or introduced to the body through the rectum. These techniques may be used when someone cannot keep fluids down, making an oral option unwise, but does not need immediate rehydration intravenously.
Hospitals aren't the only place for fluid replacement. Athletes, people sweating in hot weather, and physical laborers are often encouraged to intake fluids orally to stay healthy. By drinking fluids steadily throughout the day, these individuals can prevent drops in body fluid levels which could be dangerous.