TL;DR: ⚪ Clean null — IO-first vs IV-first vascular access in OHCA: 30-day survival unchanged (4.5% vs 5.1%, P=0.74), though ROSC was numerically lower with IO-first.
1. Publication
- Title: A Randomized Trial of Drug Route in Out-of-Hospital Cardiac Arrest
- Acronym: PARAMEDIC-3
- Year & Journal: New England Journal of Medicine, published October 31, 2024 (2025;392(4):336-348)
- Citation: Couper K, Ji C, Deakin CD, et al. N Engl J Med. 2025;392(4):336-348. doi:10.1056/NEJMoa2407780
2. Context & Rationale
Background: Drug effectiveness (e.g., epinephrine) during OHCA is highly time-dependent. Intraosseous (IO) access may enable faster drug administration than intravenous (IV) access, but the effect on clinical outcomes was uncertain, with guidelines based on very low-certainty evidence.
Research Question/Hypothesis: In adults with OHCA requiring vascular access for drug administration, does an IO-first strategy improve 30-day survival compared with an IV-first strategy?
3. Design & Methods
- Study Type: Multicenter, open-label, pragmatic RCT
- Setting & Centers: 11 emergency medical systems, UK
- Population: Adults in OHCA requiring vascular access
- Intervention: IO-first vascular access strategy (n=3040)
- Comparator: IV-first vascular access strategy (n=3042)
- Statistical Power & Follow-Up: Primary: survival at 30 days. Secondary: any ROSC, favorable neurologic outcome at discharge (mRS≤3), no multiplicity adjustment.
4. Key Results
6082 patients randomized.
Outcome | IO-First | IV-First | Effect Size | 95% CI | p-value | Notes |
Survival at 30 days (primary) | 4.5% (137/3030) | 5.1% (155/3034) | Adjusted OR 0.94 | 0.68–1.32 | 0.74 | No significant difference |
Favorable neurologic outcome at discharge | 2.7% (80/2994) | 2.8% (85/2986) | Adjusted OR 0.91 | 0.57–1.47 | — | No significant difference |
Any ROSC | 36.0% (1092/3031) | 39.1% (1186/3035) | Adjusted OR 0.86 | 0.76–0.97 | — | Numerically lower ROSC with IO-first |
5. Internal Validity Assessment
Very large (6082-patient), multicenter, pragmatic RCT. Overall: Strong — large sample provides a precise, high-confidence null result for the primary survival outcome; the numerically lower ROSC with IO-first is a real, if secondary, signal worth noting despite the primary endpoint being clearly neutral.
6. External Validity Assessment
UK, 11-EMS-system OHCA population — broadly representative of real-world prehospital cardiac arrest care in similar emergency medical systems.
7. Strengths & Limitations
Strengths: Very large sample providing precise estimates; pragmatic, real-world prehospital design; concordant with the independently conducted Danish IVIO trial (this handbook).
Limitations: Open-label (unavoidable for a vascular-access-route comparison); some crossover (88/107 IO-group patients who received IV access as first successful access were categorized as crossover).
8. Interpretation & Practice Impact
Does not support routine IO-first vascular access over IV-first in OHCA — both approaches produce statistically similar 30-day survival, though the numerically lower ROSC rate with IO-first is a real secondary signal meriting consideration alongside guideline discussions.
9. Controversies & Subsequent Evidence
An accompanying commentary ("Intravenous Access Should Be Prioritized Over Intraosseous Access in Cardiac Arrest," Gottlieb, Ann Emerg Med) argues for a continued IV-first preference based on the concordant pattern across PARAMEDIC-3 and the IVIO trial (both numerically favoring IV, though neither reaching significance on the primary survival outcome). A combined systematic review/meta-analysis (3 RCTs, 9332 participants, including PARAMEDIC-3 and IVIO) is actively synthesizing this now-substantial evidence base.
10. Summary & Executive Takeaway
Summary: PARAMEDIC-3 randomized 6082 UK OHCA patients to IO-first or IV-first vascular access. 30-day survival was not significantly different (4.5% vs 5.1%, adjusted OR 0.94, P=0.74), though ROSC was numerically lower with IO-first (36.0% vs 39.1%, OR 0.86, 95% CI 0.76-0.97).
Overall Takeaway: IO-first and IV-first vascular access strategies produce statistically similar 30-day survival in OHCA, though a numerically lower ROSC rate with IO-first — concordant with the independently conducted Danish IVIO trial — has prompted some experts to argue IV access should remain the preferred first-line strategy where feasible.
11. Bibliography
- Vallentin MF, Granfeldt A, Klitgaard TL, et al. Intraosseous or Intravenous Vascular Access for OHCA (IVIO). N Engl J Med. 2025;392(4):349-360.
- Gottlieb M. Intravenous Access Should Be Prioritized Over Intraosseous Access in Cardiac Arrest [commentary]. Ann Emerg Med. 2026;87(4):451-452.
- Couper K, Andersen LW, Drennan IR, et al. Intraosseous and intravenous vascular access during adult cardiac arrest: systematic review and meta-analysis. Resuscitation. 2025;207:110481.