A bone marrow infusion, more commonly called intraosseous (IO) infusion, is a technique for delivering fluids, medications, or blood products directly into the marrow cavity of a bone, where they pass almost immediately into the bloodstream. It works because the spongy interior of certain bones is laced with tiny blood vessels that never collapse, even during severe shock when regular veins in the arms and legs become impossible to find. The technique has been around since the 1920s, fell out of favor for decades, and has seen a strong comeback as emergency medicine has recognized that speed of access can determine whether a patient survives.
Why Bone Marrow Works as a Vascular Highway
The inside of a bone is not solid. Large bones contain a network of sinusoidal vessels, small blood-carrying channels that drain directly into the central venous circulation. When a needle is placed through the hard outer shell of a bone and into this marrow space, anything injected there gets swept into these sinusoids and into the bloodstream within seconds. The key advantage over a standard IV line is reliability: peripheral veins can be flat or invisible in a patient who is dehydrated, in shock, burned, or obese, but the marrow cavity stays accessible because the rigid bone around it prevents collapse.
A pharmacokinetic study comparing sternal IO delivery to central venous delivery during cardiac arrest found that drugs reached their peak concentration at roughly the same time by both routes, and the IO route delivered about 86% as much drug as the central venous route overall, with no statistically significant difference between the two.1Resuscitation. Pharmacokinetics of intraosseous and central venous drug delivery during cardiopulmonary resuscitation A separate study in healthy adults showed that morphine given through a tibial IO needle was bioequivalent to morphine given intravenously, with no meaningful differences in how quickly the drug reached peak blood levels or how much of it the body absorbed.2American Journal of Emergency Medicine. Does intraosseous equal intravenous? A pharmacokinetic study In practical terms, medications injected into bone marrow reach the heart and brain about as fast as those given through a traditional IV.
Where the Needle Goes
Three primary sites are used for IO access today: the proximal tibia (the flat area just below the kneecap), the proximal humerus (the upper arm near the shoulder), and the sternum (the breastbone).3PubMed Central. Sternal Intraosseous Devices: Review of the Literature Each has trade-offs.
The proximal tibia is the most widely taught and most commonly used site, partly because the bone is easy to locate by feel and lies just under the skin. It is often the default in both adults and children. The humerus is popular in military and prehospital settings because it can be accessed even when a patient’s legs are trapped or injured. The sternum, specifically the manubrium (the upper portion of the breastbone), sits closer to the central venous system than either the tibia or the humerus, which gives it a speed advantage.3PubMed Central. Sternal Intraosseous Devices: Review of the Literature
A cadaver study that measured flow rates under high pressure across all three sites found striking differences. The sternum allowed a mean flow rate of about 94 mL per minute, the humerus about 57 mL per minute, and the tibia about 31 mL per minute.4Journal of Trauma and Acute Care Surgery. Intraosseous infusion rates under high pressure: A cadaveric comparison of anatomic sites That threefold difference between the sternum and tibia matters when a trauma patient needs large volumes of fluid quickly. The tibial site also had the most insertion difficulties in that study. Still, the tibia remains the go-to for many providers because the anatomy is familiar and the technique is straightforward.
When Clinicians Reach for IO Access
IO infusion is not the first choice for vascular access. It is a rescue technique. A systematic review of IO use in adults concluded that it should be implemented in all critical situations when peripheral venous access cannot be easily obtained.5PubMed Central. Use of intra-osseous access in adults: a systematic review That typically means cardiac arrest, severe trauma with hemorrhagic shock, major burns, septic shock, or any scenario where time is running out and nobody can land an IV line.
Current resuscitation guidelines from organizations like the American Heart Association and the European Resuscitation Council endorse IO access as a rapid alternative when IV access fails or would take too long. In cardiac arrest specifically, getting drugs like epinephrine into the bloodstream within the first few minutes can influence outcome, and IO provides a route that most trained providers can establish in under a minute.
The technique has also found a firm niche in military medicine. A registry analysis of combat casualties found that IO access was used predominantly for volume resuscitation with blood products, including whole blood transfusion, in patients with severe penetrating injuries and signs of hypovolemic shock. The proximal tibia was the most common insertion site, and first-attempt success was high, with an overall insertion success rate of 85% and no major acute complications documented.6BMJ Military Health. Prehospital intraosseous access in combat trauma: a retrospective registry analysis
The Devices Used
Modern IO devices are designed to punch through the hard outer cortex of bone quickly and with minimal effort. The two broad categories are spring-loaded devices and battery-powered drills. A spring-loaded device like the Bone Injection Gun (BIG) uses a compressed spring to drive a needle through bone cortex in a single firing action. A battery-powered device like the EZ-IO uses a small drill to rotate a specially designed needle through the cortex, somewhat like a cordless screwdriver.7PubMed. Comparison of two intraosseous access devices in adult patients under resuscitation in the emergency department: A prospective, randomized study Sternal-specific devices like the FAST1 use a different mechanism tailored to the thinner cortex of the breastbone and incorporate a depth-limiting feature to avoid going too deep.
The EZ-IO has become the dominant device in many emergency departments and EMS systems because of its ease of use and consistent success rates. Providers often describe the sensation of inserting it as similar to using a power drill on soft wood: the needle advances through cortex and then meets noticeably less resistance once it enters the marrow space. Once the needle is seated, an extension set is attached and fluids or drugs are pushed through just as they would be through a regular IV catheter.
What It Feels Like for the Patient
This is where the conversation gets uncomfortable, because IO infusion can hurt. A study of emergency department patients who were conscious during IO access found that about 65% experienced moderate to severe pain during the initial puncture. The flushing phase, when saline is pushed rapidly through the needle to confirm placement and clear the line, was even worse: roughly 73% of those patients reported moderate to severe pain during flushing, which was significantly higher than the pain reported during the continuous infusion that followed.8PubMed Central. Characterization and management of pain across phases of intraosseous infusion in emergency department patients with non-cardiac arrest
The pain sources differ by phase. The puncture activates pain fibers in the skin and the periosteum, the thin membrane that covers bone and is densely packed with nerves. The flush pain comes from a sudden spike in pressure inside the marrow cavity, which stretches the bone’s interior lining. This is sometimes described by patients as a deep, intense ache or pressure rather than a sharp surface pain.
Lidocaine injected slowly through the IO catheter before flushing and infusion is the standard approach for pain control in conscious patients. In volunteer studies, doses of 40 to 80 mg of preservative-free lidocaine were administered through the IO catheter over about two minutes before flushing began.9Annals of Emergency Medicine. Volunteer Studies of Pain Management During Intraosseous Infusion The lidocaine numbs the marrow cavity and periosteum from the inside out. In cardiac arrest, pain management is obviously not a concern. But in conscious patients receiving IO access because their veins are inaccessible, the pain issue is real and worth managing aggressively.
Complications and Safety Profile
IO infusion is considered safe overall, but it is not without risks. The most feared complication is compartment syndrome, a condition where fluid leaks out of the bone into the surrounding muscle compartment, builds up pressure, and threatens the blood supply to the limb. Case reports have documented this occurring after misplaced or dislodged IO needles allowed fluids to extravasate into surrounding tissue.10PubMed Central. Compartment Syndrome Resulting From Improper Intraosseous Cannulation: A Case Report 11PubMed. Compartment syndrome following intraosseous infusion
However, a nationwide study looking at long-term complications from prehospital IO access provides some reassurance. Among all living patients followed, none developed compartment syndrome or osteonecrosis (bone tissue death). The incidence of osteomyelitis, a bone infection, was below 0.1% in adults, and the infections that did occur became evident within about six months. Among 237 children who received IO access, no complications were identified during 180 days of follow-up.12Resuscitation. An assessment of long-term complications following prehospital intraosseous access: A nationwide study
The practical takeaway is that compartment syndrome from IO is rare but not theoretical. It tends to occur when the needle is not properly seated in marrow, when the needle passes through both sides of the bone, or when infusions run for extended periods without checking the limb. Providers are trained to watch for swelling around the insertion site and to limit IO dwell time, generally removing the needle as soon as conventional IV access is established, ideally within 24 hours.
Drawing Blood Through the IO Needle
One practical question that comes up in emergency settings is whether blood drawn from the bone marrow can be used for lab tests. The answer is a qualified yes for some values but not all. A study comparing IO blood samples to arterial blood found good agreement for pH, glucose, and lactate, which are among the most clinically useful values in a crashing patient. However, potassium was consistently higher in IO samples, and hemoglobin and hematocrit showed too much variability to be reliable.13PubMed Central. Intraosseous blood samples for point-of-care analysis: agreement between intraosseous and arterial analyses
A separate analysis using a portable analyzer confirmed that IO and venous samples showed clinically acceptable agreement for pH, base excess, sodium, ionized calcium, and glucose in stable patients.14Resuscitation. Reliability of blood gas, electrolytes and glucose analysis on bone marrow aspirate using the i-STAT point-of-care analyser The elevated potassium finding is important to know about because a falsely high potassium reading could lead a clinician to treat a problem that doesn’t exist. In general, IO samples are useful for getting a rough metabolic picture while working to establish better access, but they should not be interpreted exactly as you would a standard blood draw.
Pediatric and Neonatal Considerations
IO access has a long history in pediatric emergency medicine, partly because small children’s veins are notoriously difficult to access even under calm conditions, let alone during an emergency. The proximal tibia is the preferred site in children for the same reasons it is in adults: the anatomy is predictable and the bone is accessible. However, the margins are tighter in the smallest patients.
Measurements of the marrow cavity at the standard IO insertion site found that the medullary diameter of the proximal tibia averaged only about 7 mm in neonates, 10 mm in infants up to a year old, and 12 mm in children aged three to four.15PubMed. Intraosseous access in neonates and infants: risk of severe complications – a case report A 7 mm target leaves very little room for error. If the needle is angled slightly wrong or advanced too far, it can breach the opposite cortex and send fluids into soft tissue rather than the marrow cavity. This narrow margin of safety means that IO placement in neonates requires careful attention to needle depth and angle, and providers typically use shorter needles designed for the smallest patients.
Despite these risks, the nationwide complication study mentioned earlier found no complications in the 237 children followed for six months after IO access, which suggests that when the technique is performed properly, the safety profile in children is comparable to that in adults.
Harvesting Bone Marrow for Therapeutic Use
The term “bone marrow infusion” occasionally refers to something quite different from IO emergency access: the collection and subsequent infusion of bone marrow for transplantation or regenerative medicine. In this context, marrow is aspirated (drawn out) from a donor site and then infused into a patient. The process of aspiration uses a thick needle, typically a Jamshidi cannula, which is advanced through the cortex of the iliac crest (the hip bone) into the marrow space. Small volumes of about 4 mL are drawn at a time, the cannula is repositioned within the bone, and the process repeats until enough marrow is collected.16PubMed Central. Lateral and posterolateral iliac crest approach for bone marrow aspirate harvest in regenerative orthopedic applications
Once collected, this marrow concentrate contains stem cells and progenitor cells that, when infused into a patient’s bloodstream, travel to the recipient’s marrow spaces through a process called homing. These transplanted cells migrate through the blood, cross into the bone marrow, and begin producing new blood cells. This is the basis of bone marrow transplantation for blood cancers, immune disorders, and other conditions. The “infusion” step itself looks unremarkable: the marrow product is given through a standard IV line, much like a blood transfusion. The complexity lies in the preparation, the matching, and the immunological consequences, not in the mechanical act of infusing the cells.
IO Access in Veterinary Medicine
Veterinary emergency medicine faces the same fundamental challenge as human medicine: animals in shock or cardiac arrest often have veins that are too constricted or too small to catheterize quickly. IO infusion has been adapted for dogs, cats, and other species using similar principles. A cadaver study in dogs evaluated IO placement at four sites and found that the femur and humerus were the easiest and fastest to access, while the tibia had significantly lower flow rates than the other sites under both gravity and pressurized infusion.17Frontiers in Veterinary Science. Intraosseous Catheter Flow Rates and Ease of Placement at Various Sites in Canine Cadavers The ileum (part of the pelvis) had the highest difficulty scores. These findings mirror the human experience in at least one respect: flow rates and ease of access vary widely by site, and the most anatomically convenient bone is not always the one that delivers fluid fastest.
In small exotic animals and neonatal puppies or kittens, IO access is sometimes the only viable option because peripheral veins are too tiny to catheterize at all. Veterinary practitioners often use standard hypodermic needles or spinal needles rather than the powered drill devices common in human emergency medicine, particularly in very small patients where the marrow cavity is only a few millimeters wide.
Common Misconceptions
One persistent myth is that IO infusion only works for saline or simple fluids. In reality, nearly any medication or fluid that can be given intravenously can be given through the IO route, including blood products, vasopressors, anesthetics, antibiotics, and contrast agents for imaging. The combat trauma data, where 84% of IO use involved blood products including whole blood, illustrates how far beyond basic saline this technique extends.
Another misconception is that IO access is exclusively a pediatric technique. While it was historically used more in children because of their difficult veins, the resurgence of IO in the past two decades has been driven largely by adult applications. Modern powered devices are designed and sized for adult bones, and the evidence base for pharmacokinetics, flow rates, and complication rates comes predominantly from adult studies. The pediatric roots of the technique sometimes lead people to underestimate how commonly it is now used in grown patients.
A third misunderstanding involves speed. People sometimes assume that because a needle is going into bone, the process must be slow and cumbersome. With a powered drill device, insertion takes roughly five to fifteen seconds once the needle touches the skin. Establishing IO access is often faster than placing a central venous catheter, which requires sterile preparation, ultrasound guidance, and threading a wire through a large vein, a process that can take ten minutes or more even in experienced hands. The entire point of IO is that it buys time while more definitive access is being arranged.