Intraosseous (IO) access is a specialized medical technique used to administer fluids, medications, and blood products directly into the bone marrow cavity. This procedure serves as a rapid and effective alternative to traditional intravenous (IV) access when peripheral veins are inaccessible or when establishing a venous line would be too slow in a life-threatening scenario. The bone marrow contains a rich network of non-collapsible veins, acting as a direct conduit to the central circulatory system. IO access is reserved exclusively for time-sensitive, emergency situations where immediate delivery of therapeutic agents is necessary to stabilize the patient.
Clinical Situations Requiring IO Access
IO access is necessary in medical emergencies when securing a standard IV line is difficult, delayed, or impossible. Advanced life support guidelines recommend the IO route if establishing peripheral venous access would delay critical treatment, particularly during cardiopulmonary resuscitation (CPR). IO access is often prioritized when multiple IV attempts have failed, or if obtaining access is estimated to take longer than 90 seconds.
The patient’s physiological state often dictates the need for this route, as conditions causing severe vascular collapse can make peripheral veins difficult to locate. Indications include cardiac arrest of any rhythm, profound states of shock (hypovolemic, septic, or cardiogenic), and severe trauma or burns resulting in poor peripheral perfusion. IO infusion is a temporary solution, typically used for up to 24 hours until a more reliable IV or central line can be established. Once the IO device is in place, nearly all medications, fluids, and blood products administered intravenously can be given through the bone marrow route using the same dosing protocols.
Anatomical Insertion Sites
The choice of insertion site depends on the patient’s age, anatomy, and the specific IO device used. The goal is to access a large marrow cavity beneath thin cortical bone.
Proximal Humerus
In adults, the proximal humerus is a preferred site because it offers the fastest systemic uptake due to its proximity to the central circulation. The insertion point is typically located at the greater tubercle, approximately 2 centimeters above the surgical neck of the humerus.
Proximal Tibia
The proximal tibia, or shin bone, is another common site for both adult and pediatric patients due to its large, flat surface and easily identifiable landmarks. The site is located 1 to 2 centimeters below and slightly medial to the tibial tuberosity, the bony prominence just below the knee. In pediatric patients, care must be taken to avoid the epiphyseal growth plate, the region of cartilage responsible for bone growth.
Distal Tibia and Sternum
The distal tibia serves as a reliable backup when proximal sites are unavailable or contraindicated. This site is situated on the flat, medial surface of the bone, about 3 centimeters above the medial malleolus (the bony projection on the inside of the ankle). The manubrium of the sternum, the upper part of the breastbone, is also used by some specialized devices.
Equipment Used for Intraosseous Infusion
The specialized hardware for IO access is designed to penetrate the dense outer layer of bone (cortical bone) and deposit a catheter into the medullary space. Older settings may utilize manual IO needles, which resemble bone marrow aspiration needles and require significant manual force and a twisting motion for insertion.
The current standard of care relies on powered or automatic devices, which ensure rapid, controlled, and consistent insertion. These systems include battery-operated drivers, such as the EZ-IO, and spring-loaded devices like the Bone Injection Gun (BIG) or NIO. Powered drivers use a reusable motor unit and disposable needle sets tailored to the patient’s size and insertion depth. The controlled mechanism allows the needle to pass through the bone cortex quickly and efficiently, minimizing the risk of bending or causing excessive trauma.
Overview of the Insertion Procedure
The IO procedure begins with identifying the correct anatomical landmarks and cleansing the skin at the chosen site with an antiseptic solution. For conscious patients, a local anesthetic is typically infiltrated into the skin and the periosteum (the membrane covering the bone) to manage pain before insertion. The specialized needle is then advanced through the soft tissue until it rests against the bone surface.
The IO needle is driven into the bone, manually or with a powered device, usually perpendicular to the flat surface until a distinct sensation of “pop” or “give” is felt. This sensation confirms that the needle tip has successfully broken through the dense cortical layer and entered the marrow cavity. After the stylet, the inner portion of the needle, is removed, placement is confirmed by aspirating bone marrow or by flushing the line with saline, which should flow easily without leakage into the surrounding soft tissue.
The catheter is then secured to the patient’s limb using a specialized dressing to prevent dislodgement during movement or transport. The IO line is ready for infusion, often requiring a pressure bag or syringe driver because the natural resistance of the marrow space can slow gravity-fed fluid flow. This procedure requires specialized training and must only be performed by certified medical professionals in emergency settings.