A casualty may be suffering from severe blood loss, severe burns, extreme vomiting, extreme diarrhea, heat injuries (heat stroke or heat exhaustion), or numerous other emergency situations. When such situations occur, it may be necessary to replace or maintain the supply of body fluids, electrolytes (body salts), and some nutrients or to administer necessary medication. Normally, adjustments in diet and the fluids that a person takes in can correct a mild loss of fluids and electrolytes; however, the casualty may be on the verge of shock or already in shock. In such instances, you must be prepared to initiate an intravenous (IV) infusion to restore lost fluids and electrolytes such as sodium, potassium, calcium, or chloride, or to administer medications. The gauge of the needle used ranges from a small size of 20 to a large size of 12. A thick solution or the need for a rapid infusion of fluids requires a larger bore and a larger vein.