The RAMER Reviews: The RAMER Reviews: Why Sensitivity Analysis Complicates Naloxone Use in Out of Hospital Cardiac Arrest
Written by: Quinn Bushman , DO; Edited by: Brian Smith, DO, MA, MMSc-Med
Introduction:
When a new observational study reports that a widely available drug improves survival in cardiac arrest, it is tempting to think we have an answer. The 2026 JAMA Network Open study by Wang and colleagues on naloxone in suspected opioid-associated out-of-hospital cardiac arrest (OA-OHCA) initially looks pretty convincing. Naloxone was associated with better survival, better neurologic outcomes, and more return of spontaneous circulation (ROSC). But once you look at the secondary analysis, the story becomes much more complicated.
The Study
Using registry data from 173 California EMS agencies, the investigators identified probable OA-OHCA using a simple field definition: age younger than 50 years and an unwitnessed arrest. In this primary cohort, patients who received naloxone had better outcomes across the board. Survival to hospital discharge was roughly 8% compared with 4% among patients who did not receive naloxone, with similar improvements in favorable neurologic outcome and sustained ROSC.
That is a meaningful signal. It is also exactly the type of association that can be difficult to interpret in observational resuscitation research. The authors recognized this and performed a sensitivity analysis that puts the primary findings to the test.
What Could Be Confounding the Results?
Out-of-hospital cardiac arrest has numerous potential confounders that are difficult to fully account for in a retrospective study.
Confounding variable 1: Was this actually a cardiac arrest?
Some patients who appear to be in cardiac arrest in the field may actually have severe opioid-induced respiratory depression with a pulse that is difficult to palpate. If these patients receive naloxone and regain adequate ventilation before progressing to true pulseless arrest, including them in the cardiac arrest cohort could make naloxone appear more effective than it actually is in true cardiac arrest.
Stress test: To address this possibility, the authors restricted the analysis to patients who received epinephrine during resuscitation. Because epinephrine is administered during ACLS for pulseless cardiac arrest, receiving epinephrine serves as a proxy that the patient was truly in cardiac arrest rather than respiratory arrest with a weak or difficult-to-detect pulse.
Result: The benefit largely disappeared. The adjusted absolute difference in survival fell to approximately +0.3 percentage points, with a confidence interval crossing zero. The associations with ROSC and favorable neurologic outcome were also no longer statistically significant.
At first glance, this seems to support the idea that misclassification explains the original association. But there is a problem: restricting the cohort to patients who received epinephrine introduces its own potential biases.
Why Didn't the Original Results Hold Up?
There are three reasonable ways to interpret what happened:
1. Some of the original benefit came from misclassified respiratory arrests. If naloxone primarily benefited patients with severe respiratory depression who still had a perfusing rhythm, removing those patients should weaken or eliminate the association—which is what happened. However, the authors point out that this probably does not explain everything. Among patients who did not receive epinephrine, approximately 82% were documented in asystole, suggesting that many were experiencing true cardiac arrest rather than respiratory arrest with a perfusing rhythm.
2. The restriction may have excluded the patients most likely to respond to naloxone. If naloxone provides benefit primarily when given early, some patients may achieve ROSC before epinephrine is ever administered. Requiring epinephrine would then preferentially remove these early responders from the analysis and bias the results toward no effect. This would also fit with prior work suggesting that any potential benefit from naloxone may be concentrated among patients who receive it early during nonshockable arrest.
3. The analysis may introduce resuscitation-time bias. A patient has to remain in cardiac arrest long enough to receive epinephrine. Requiring epinephrine therefore selects for patients with longer and potentially more refractory arrests, which already carry worse outcomes. A true benefit from naloxone could therefore disappear simply because the restricted cohort contains patients with more prolonged arrests. Without reliable timestamps for naloxone, epinephrine, and ROSC, there is no good way to fully account for this.
The observational data cannot tell us which of these explanations is correct. All three could produce essentially the same result, but each has a very different implication for whether naloxone actually improves outcomes in cardiac arrest.
Takeaway
The authors report a potential benefit, but they also provide an analysis that makes it difficult to interpret that benefit as causal. That does not weaken the study but it appropriately defines what we can and cannot conclude from observational data. These findings are hypothesis-generating and strengthen the case for a randomized trial, but they do not establish that naloxone improves survival in true cardiac arrest.
For clinicians and EMS systems, the practical takeaway remains largely unchanged. Naloxone remains reasonable in suspected OA-OHCA alongside high-quality CPR, consistent with AHA guidance, and this study does not suggest harm. What remains uncertain is whether naloxone itself improves survival. Ultimately, this study gives us a strong reason to conduct a larger, controlled trial.