IO Meds Need a Flush
Objective: Use IO as a real vascular route: same dose as IV, flush after every drug, know when IV is still first, and not leave meds sitting in the hub.
Why This Is Hard
People treat an IO like a last-ditch straw, then under-flush it. Marrow is thick. A drug left in the needle never meets the heart. The street error is waiting too long for a pretty IV, or slamming drugs into bone and never flushing, so epinephrine lives in the tibia.
AHA 2025 teaching: start with an IV in adult arrest. IO is the backup if the IV is not there or is taking too long. Same dose as IV. Then flush. Three large trials did not show a survival win for starting with bone first.
- Start with an IV if you can get it without delay. If the IV is not there or is taking too long, drill. Do not delay the first arrest dose for philosophy.
- After every IO drug, push a rapid saline flush. Follow your device and protocol. Then keep the line moving.
- Fluids and blood need pressure. Gravity is slow through bone. Use a pressure bag or a syringe push.
- Conscious IO hurts. Protocol-dose cardiac lidocaine, slow, dwell, then flush — only if your protocol says so. Arrest patients do not need that step.
Street 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. Flush goes. Soft tissue does not balloon. Aspiration of marrow is optional and can clog. Follow your device training.
- Give the same dose you would give IV. Then flush. Say “epi in, flush in.” Do not half it because it is bone.
- Watch the calf or humerus for extravasation. A blown IO plus pressors can become a compartment syndrome. Pick another site if that bone is fractured, infected, prosthetic, or already used this call.
Field Rules
- Dose: IO dose equals IV dose for standard resuscitation drugs in usual teaching. You do not “half it because it is bone.”
- Flush: displace marrow or the drug sits. Rapid saline after each push is the move. Adult teaching is often about 10 mL — follow your device and protocol.
- IV vs IO in arrest: AHA 2025 recommends initial IV attempts over initial IO attempts in adult cardiac arrest. If the IV fails or is delayed, go IO. Recent trials did not show a survival win for starting with bone first. Do not delay drugs.
- Do not use that site if the bone is fractured, the skin is infected, there is a prosthetic joint there, or you already drilled that bone this call.
- Kids: still a valid route. Site and needle size follow your device and protocol. Tenfold math is a separate lesson. The flush still happens.
- Same dose as IV.
- Drug in — flush in.
- IV if it is immediate. IO if it is not.
- Pressure bag for volume.
Field Pitfalls
- Pushing epinephrine into the IO hub and never flushing.
- Three minutes of failed IV attempts in a pulseless patient.
- Using a fractured tibia.
- Gravity-drip “wide open” that is actually a trickle.
Practice
60-second drill
Partner: second round of CPR, no IV. You drill the humerus. Say the next three actions including the flush. Then: they wake up and scream when you infuse. What does protocol usually allow you to 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; protocol still wins
- AHA 2025 Part 9: Adult ALS — initial IV attempts are recommended over initial IO attempts in adult arrest; IO if IV fails or is delayed; do not delay drugs
- PARAMEDIC-3 (NEJM 2024) — IO vs IV in OHCA: similar 30-day survival; IO higher first-attempt success
- IVIO (NEJM 2024) — IO vs IV first in OHCA: similar sustained ROSC; IO higher first-attempt success
Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.
Check Your Understanding
Street decisions from this lesson only. After you check, the key is highlighted. Education practice — not a certification exam.