An Intraosseous (IO) line is a rapid and reliable method for gaining vascular access, used exclusively in critical, life-threatening emergencies. This technique involves inserting a specialized needle directly into the bone marrow cavity, which functions as a non-collapsible entry point into the systemic venous system. IO access is reserved for situations where obtaining conventional peripheral intravenous (IV) access is impossible or would cause a dangerous delay in administering life-saving medications and fluids. This invasive route is a temporary measure, providing a bridge until a more definitive form of vascular access can be established.
Indications and Contraindications
IO access is indicated when a patient requires immediate circulatory access, but peripheral IV attempts have failed or are not feasible within a short timeframe, often cited as 60 to 90 seconds. Common scenarios include cardiopulmonary arrest, severe shock (hypovolemic or hemorrhagic), and major trauma or burns where vessels may be constricted or inaccessible. Any medication or fluid that can be delivered intravenously can be safely administered through an IO line during emergency resuscitation.
A few conditions serve as absolute contraindications that prevent the procedure at a specific site. These include a fracture in the bone chosen for insertion, or a fracture proximal to the intended site, which carries a high risk of extravasation and compartment syndrome. The presence of infection, such as cellulitis or a burn, over the planned insertion site also prohibits use due to the risk of introducing bacteria into the bone. Additionally, IO access should not be attempted on a bone that has had a previous IO attempt within the last 48 hours, or in patients with bone diseases like osteogenesis imperfecta or severe osteoporosis.
Preparation and Anatomical Targets
Preparation involves gathering the necessary equipment: a powered driver or manual device, a specialized IO needle, an antiseptic solution (like chlorhexidine), a stabilizing dressing, and a pressure infusion setup. Choosing the correct needle length is important; after the needle tip touches the bone, at least one indicator line on the shaft must be visible outside the skin to ensure the needle reaches the medullary space.
The primary anatomical targets for IO placement vary between adults and children. In adults, the most common sites are the proximal humerus and the proximal tibia. The proximal humerus is often preferred in resuscitation because it offers the highest flow rates, with the insertion site located over the greater tubercle, approximately 1 cm above the surgical neck.
For the proximal tibia, the site is generally 1-2 cm medial to the tibial tuberosity on the flat, anteromedial surface of the bone. Care must be taken to avoid the growth plate in younger patients. A secondary site for both adults and children is the distal tibia, found about 2-3 cm proximal to the most prominent aspect of the medial malleolus. Precise landmark identification is necessary for safe insertion and to avoid surrounding neurovascular structures.
Step-by-Step Insertion Technique
After selecting and preparing the site with an antiseptic agent, the clinician must ensure the limb is stabilized, often by placing a towel roll beneath the joint or having an assistant hold the extremity firmly. If the patient is conscious, local anesthesia (typically 1% preservative-free lidocaine) should be injected into the skin, subcutaneous tissue, and the periosteum to minimize pain. The specialized IO needle, attached to its driver, is placed on the insertion site at a 90-degree angle for the tibia, or a 45-degree angle aiming toward the opposite hip for the humerus.
The needle tip is advanced through the soft tissue until it contacts the bone cortex. The powered driver is then activated while applying gentle, consistent downward pressure. The process requires minimal force, as the driver penetrates the dense bone. The practitioner will recognize a sudden decrease or “pop” in resistance, signaling that the needle tip has broken through the cortex and entered the medullary space.
The driver is immediately released and removed, leaving the needle catheter securely embedded in the bone. The inner stylet is then unscrewed and removed, which must be immediately disposed of in a sharps container. The visible portion of the needle hub should feel stable and firmly seated in the bone, indicating successful placement.
Confirmation and Post-Procedure Care
Successful IO placement is confirmed by several clinical signs. Aspiration of dark, viscous bone marrow or blood into a syringe is the most definitive sign, though failure to aspirate does not mean the placement is unsuccessful. The needle itself should be stable and firmly fixed to the bone, not moving independently of the limb.
The primary confirmation step is the ability to flush the line freely with a small bolus of sterile saline without swelling or resistance around the insertion site. Extravasation (leakage of fluid into the surrounding soft tissue) is a sign of improper placement and necessitates immediate removal of the device. Following a successful flush, the IO device is secured using a specialized stabilization dressing to prevent dislodgement.
Because the bone marrow cavity offers resistance to flow, a pressure infusion device or a pressure bag set to approximately 300 mmHg is often necessary to achieve adequate flow rates for fluid or rapid medication delivery. The IO line should be removed as soon as alternative peripheral or central venous access is reliably established, ideally within 24 hours of placement to mitigate the risk of complications like osteomyelitis. The insertion site must be continuously monitored for signs of complications, including swelling, pain, or changes in the limb’s neurovascular status, which could signal compartment syndrome.