IO Medication Flush
Objective: An intraosseous line is a vascular route. Give the same dose you would give IV, then flush. In adult arrest, start an IV if you can do it quickly. Use an IO if the IV fails or is delayed. Do not leave the drug in the marrow.
Why this matters
An intraosseous needle reaches the bloodstream through bone marrow. Marrow is thick. A drug left in the needle never reaches the heart.
Do not wait for a perfect IV and then forget the flush. Epinephrine left in the tibia did not reach the heart.
AHA 2025 teaching for adult arrest: start with an IV. Use an IO if the IV is not there or is taking too long. Use the same dose as IV. Then flush. Large trials did not show a survival advantage for starting with bone first.
- In adult arrest, start an IV if you can get it without delay. If the IV fails or is delayed, place an IO. Do not delay the first arrest drug while you debate the route.
- After every IO drug, push a rapid saline flush. Follow your device and your protocol. Then keep fluid moving.
- Fluids and blood need pressure. Gravity is slow through bone. Use a pressure bag or a syringe.
- A conscious IO hurts. A slow protocol dose of cardiac lidocaine, a short dwell, then a flush, is only for when your protocol says so. A patient in arrest does not need that step.
Clinical sequence
- Arrest or near-arrest without a fast IV: place the IO while CPR continues. Do not pause compressions for the drill.
- Confirm the line. The needle stands up. The flush goes in. Soft tissue does not swell. Pulling back marrow is optional. It can clog the needle. Follow your device training.
- Give the same dose you would give IV. Then flush. Say the drug is in, and the flush is in. Do not cut the dose because it is bone.
- Watch the leg or the arm for leakage. A failed IO plus a vasopressor can cause compartment syndrome. Pick another site if that bone is fractured, the skin is infected, there is a prosthetic joint, or you already used that bone on this call.
Teaching points
- Dose: the IO dose equals the IV dose for standard resuscitation drugs in usual teaching. Do not give half because it is bone.
- Flush: if you do not move the drug out of the marrow, it sits there. A rapid saline flush after each push is the step. Adult teaching is often about 10 mL. That is a flush volume, not a drug order. Follow your device and your protocol.
- IV versus IO in adult arrest: AHA 2025 recommends trying an IV first rather than starting with an IO. If the IV fails or is delayed, go to IO. Recent trials did not show a survival advantage for starting with bone. Do not delay the drugs.
- Do not use that site if the bone is fractured, the skin is infected, there is a prosthetic joint, or you already drilled that bone on this call.
- Children: IO is still a valid route. Site and needle size follow your device and your protocol. Tenfold math is a separate lesson. The flush still happens.
- Give the same dose you would give IV.
- The drug is in, and the flush is in.
- Start an IV if you can get it quickly. Use an IO if the IV fails or is delayed.
- Use a pressure bag for volume.
Common errors
- Pushing epinephrine into the IO hub and never flushing.
- Several minutes of failed IV attempts in a pulseless patient.
- Using a fractured tibia.
- A gravity drip labeled wide open that is actually a trickle.
Practice
One-minute check
With a partner: second round of CPR, no IV. You place a humeral IO. Say the next three actions, including the flush. Then the patient wakes and has severe pain with the infusion. What does the protocol usually let you consider?
Related: Medication Rights & Safety, Weight-Based Dosing Safety, High-Quality CPR.
Sources & Further Study
Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.
- NASEMSO National Model EMS Clinical Guidelines (2022) — U.S. EMS model language. Your protocol still decides.
- AHA 2025 Part 9: Adult ALS — In adult arrest, try an IV first rather than an IO. Use an IO if the IV fails or is delayed. Do not delay drugs.
- PARAMEDIC-3 (NEJM 2024) — IO versus IV in out-of-hospital cardiac arrest: similar 30-day survival. IO had a higher first-attempt success.
- IVIO (NEJM 2024) — IO versus IV first in out-of-hospital cardiac arrest: similar sustained return of circulation. IO had a higher first-attempt success.
Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.
Check Your Understanding
Questions drawn only from this lesson. After you check, the key is highlighted. Education practice — not a certification exam.