Intraosseous (IO) access is a specialized procedure used when medical personnel cannot quickly establish a standard intravenous (IV) line in a patient experiencing an emergency. Rapid access to the circulatory system is necessary during events like cardiac arrest, shock, or major trauma. The IO route provides a reliable alternative for delivering fluids, medications, and blood products directly into the bloodstream without the delays associated with difficult IV placement. This technique has become a widely accepted standard for obtaining rapid vascular access in emergency and pre-hospital settings across all age groups.
Defining Intraosseous Access
Intraosseous access involves inserting a needle through the hard outer shell of a bone (the cortex) into the inner bone marrow cavity (the medullary space). This method bypasses the peripheral veins, which may be collapsed or difficult to locate in patients who are dehydrated or in shock. The bone marrow cavity is highly vascular, containing a network of small vessels called sinusoids that drain directly into the systemic circulation.
This medullary space functions as a non-collapsible vein, allowing for the rapid delivery of nearly any substance that can be given intravenously. The rigid structure of the bone prevents the marrow vessels from shrinking, ensuring continuous access even when the patient has low blood pressure. IO access is a temporary bridge, typically used for up to 24 hours until a more stable form of intravenous access can be secured.
Where IO Needles Are Placed
The choice of IO insertion site depends primarily on the patient’s age, body size, and the specific circumstances of the emergency. Sites are selected based on having a large medullary cavity, easily identifiable bony landmarks, and minimal overlying tissue, which ensures quick and successful placement.
One common location for IO access in adults is the proximal humerus, located near the shoulder joint. Insertion is performed on the greater tubercle, a bony prominence on the upper part of the arm bone. This allows infused fluids to quickly enter the central circulation via the superior vena cava, and flow rates can be significantly higher compared to other access points.
The tibia (shin bone) is another location for IO access in both adults and children. In adults, the proximal tibia site is located a few centimeters below the kneecap on the inner flat surface. For children, the proximal tibia is the preferred site, but the distal tibia (just above the ankle) is also used. The distal femur is frequently used in infants and very young children due to its accessibility.
The Procedure: Insertion, Pain Management, and Removal
The IO procedure begins with identifying the correct anatomical landmark and preparing the site using aseptic technique to minimize the risk of infection. Modern IO insertion often uses a battery-powered driver device, similar to a small drill, which drives the needle through the bone cortex. This method provides a controlled, rapid insertion, often resulting in a “pop” as the needle enters the marrow space.
Once the needle is secured, correct placement is confirmed by attempting to aspirate bone marrow or by flushing the line with saline solution without observing swelling around the site. While the insertion itself is quick, the subsequent infusion of fluids or medications is often painful for a conscious patient, as the pressure builds within the bone cavity.
To manage this pain, a local anesthetic, such as preservative-free lidocaine, must be administered directly through the IO line before the main infusion begins. A typical adult dose involves slowly injecting 20 to 40 milligrams of two percent lidocaine into the IO catheter, allowing it to dwell for about one minute to numb the internal space. This step is important for patient comfort and is often followed by a saline flush and a second, smaller dose of lidocaine.
Once the patient is stabilized and a long-term intravenous line is established, the IO catheter must be removed, ideally within 24 hours of insertion to reduce the risk of complications. Removal is accomplished by attaching a syringe to the hub, rotating it clockwise, and pulling the needle straight out of the bone, followed by applying pressure to the site.