Two pictures of the EZ IO device.
Intraosseous infusion (IO) is the process of injecting directly into the marrow of a bone. This provides a non-collapsible entry point into the systemic venous system. This technique is used to provide fluids and medication when intravenous access is not available or not feasible. Intraosseous infusions allow for the administered medications and fluids to go directly into the vascular system. A comparison of intravenous (IV), intramuscular (IM), and intraosseous (IO) routes of administration concluded that the intraosseous route is demonstrably superior to intramuscular and comparable to intravenous administration (in delivering paediatric anaesthetic drugs). This route of fluid and medication administration is an alternative one to the preferred intravascular route when the latter cannot be established in a timely manner. Intraosseous infusions are utilized when trauma patients have compromised intravenous access and need immediate delivery of life saving fluids and medications. 
This American Heart Association guideline cited two randomized controlled trials, one of 60 children and one of electively cannulated hematology/oncology patients. In addition, uncontrolled studies have been performed, one of which reported 72% to 87% rates of successful insertion.
The needle is injected through the bone's hard cortex and into the soft marrow interior which allows immediate access to the vascular system. The IO needle is positioned at a 90 degree angle to the injection site, and the needle is advanced through manual traction, impact driven force, or power driven. Each IO device has different designated insertion locations. The most common site of insertion is the antero-medial aspect of the upper, proximal tibia as it lies just under the skin and is easily located. This is on the upper and inner portion of the tibia. Other insertion sites include the anterior aspect of the femur, the superior iliac crest and the head of the humerus.
An IO infusion can be used on adult or pediatric patients when traditional methods of vascular access are difficult or otherwise cause unwanted delayed management of the administration of medications. The IO site can be used for 24 hours and should be removed as soon as intravenous access has been gained. Prolonged use of an IO site, lasting longer than 24 hours, is associated with osteomyelitis (an infection in the bone).
Intraosseous infusions have several contraindications. Avoid sites that have known, or suspected fracture, appears to be infected, or where the skin is burned. Medical conditions that might also preclude the use of intraosseous infusion include osteopenia, osteopetrosis, and osteogenesis imperfecta as fractures are more likely to occur. The procedure also only allows for one attempt per bone meaning another route of infusion must be secured, or a different bone chosen.
Although intravascular access is still the preferred method for medication delivery in the prehospital area, IO access for adults has become more common. As of 2010, American Heart Association no longer recommends using the endotracheal tube for resuscitation drugs, except as a last resort when IV or IO access cannot be gained. The IO is becoming more common in civilian and military based pre-hospital emergency medical services (EMS) systems globally.
Intraosseous access has roughly the same absorption rate as IV access, and allows for fluid resuscitation. For example, sodium bicarbonate can be administered IO during a cardiac arrest when IV access is unavailable. High flow rates are attainable with an IO infusion, up to 125 milliliters per minute. This high rate of flow is achieved using a pressure bag to administer the infusion directly into the bone. Large volume IO infusions are known to be painful. 1% lidocaine is used to ease the pain associated with large volume IO infusions in conscious patients. 
The automatic intra-osseous devices allow quick and safe access to the patient's vascular system for fluid and drug administration. There are several FDA approved IO devices: The BIG Bone Injection Gun and The NIO New Intra Osseous device are automatic intra-osseous infusion device used by military and civilian healthcare systems; the battery-powered EZ-IO and hand-powered Fast1, Fast Combat and Fast Responder. Other devices include the Cook IO needle and the Jamshidi 15G.
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