The abbreviation IO stands for which route?

• A. Intramuscular
• B. Intraosseous
• C. Intravenous
• D. Subcutaneous

Answer: (B)

IO stands for intraosseous, a route that delivers fluids and medications into the bone marrow so they quickly reach the central circulation. This method is used when obtaining IV access is difficult or time-pressured, such as in emergencies or with uncooperative patients, because the bone’s marrow has rapid blood flow that allows fast absorption of drugs and fluids.

Think of how this differs from other routes: intramuscular injections go into muscle tissue and are absorbed more slowly; intravenous administration goes directly into a vein; subcutaneous injections go into the fatty tissue under the skin and are even slower and suitable for smaller volumes. Intraosseous access is achieved by inserting a needle into a bone—most commonly the tibia or femur in adults and children—and is typically used as a temporary measure until reliable IV access is established.