Paramedic Out-of-Hospital Cardiac Arrest Case Volume Is a Predictor of Return of Spontaneous Circulation

Jenna E. Tuttle, MHS, NRP; Michael W. Hubble, PhD, NRP


Western J Emerg Med. 2018;19(4):654-659. 

In This Article


This study is the first to examine the relationship between paramedic OHCA case volume and ROSC in a U.S. EMS system. We found that patients treated by paramedics with 15 or more OHCA exposures in the previous five years were 21% more likely to attain ROSC. Few previous studies have investigated this relationship among paramedics, and none have done so in a U.S. EMS system.

Dyson et al. measured the association between paramedic OHCA exposure and patient survival in Victoria, Australia.[4] In their study they found that OHCA exposure during the preceding three years had a positive impact on patient survival. The odds of survival increased for every additional increase in the median OCHA exposure. Compared with patients treated by paramedics with a median of ≤ 6 arrests during the preceding three years, the odds of survival were higher for patients treated by paramedics with 7–11 (OR [1.26]), 12–17 (OR [1.29]), and >17 (OR [1.50]) OHCA exposures. Interestingly, they did not find any relationship between paramedic career experience and survival, suggesting that career longevity alone does not convey any benefit in terms of patient outcomes following OHCA.

Another salient finding by Dyson et al. was that patient survival decreased when six months or more had lapsed since the previous OHCA exposure.[4] They noted that this time frame is similar to the post-training decay rate of advanced life support skills after training, reported by Yang et al.[2,4]

The only previous investigation involving a U.S. EMS system was conducted in King County, Washington, by Gold and Eisenberg.[9] Although they did not specifically evaluate the impact of OHCA exposures on survival, they did examine the influence of the number of years of paramedic career experience of the primary (code leader) and secondary (skills) paramedic on patient survival.[9] They found no association between years of paramedic experience and survival for the primary paramedic (OR [1.01], 95% confidence interval [CI] [0.99–1.03]), but they did find a positive relationship between experience and survival for the secondary paramedic (OR [1.02], 95% CI [1.00–1.04]). They speculated that treatment of cardiac arrests tends to be protocol-driven events and on-scene decision-making, and ultimately survival, is not sensitive to paramedic career experience. In contrast, they surmised that the "skills paramedic" did become more proficient at rendering treatments as career experience increased and this resulted in improved outcomes. However, they did not report skills success rates or time to treatments, so it is unclear if these measures were actually influenced by career experience. In our dataset, we did not find any improvement in on-scene performance between lead paramedics with and without 15 or more OHCA experiences other than a shorter time to administer the first dose of vasopressors for the more experienced paramedics (Table 4). Unfortunately, we did not have data to compare on-scene performance of the secondary (skills) paramedics with respect to cumulative OHCA experience.

Suspecting a link between endotracheal intubation (ETI) experience and OHCA survival, Wang et al. compared outcomes among paramedics with low (1-10 tracheal intubations in the preceding six years), medium (11-25 tracheal intubations), high (26-50 tracheal intubations), and very high (greater than 50 tracheal intubations).[10] After adjusting for factors known to influence patient outcome and using low cumulative experience as the reference category, they found a significant survival benefit among paramedics with very high ETI exposure (OR [1.48], 95% CI [1.15–1.89]).[10] This finding lends credence to the hypothesis of Gold and Eisenberg that OHCA survival is influenced by increased levels of proficiency of the "skills paramedic" rather than the team leader whose decision-making role is somewhat dictated by protocol.[9] In our study we focused only on OHCA exposure and did not evaluate cumulative skills experience.

If our findings and those of Dyson et al. are accurate, then a case volume-survival relationship exists between paramedics' OHCA experience and patient survival.[4] In general terms, this relationship is not unique to EMS and OHCA as clinical case volume has been linked to patient outcomes in other settings and patient conditions.[11–13] The greater issue, then, is devising strategies to ensure that paramedics have adequate case volumes to obtain and maintain proficiency in OHCA management. In the study by Dyson et al. on average, paramedics were exposed to two OHCA per year and 10% of their workforce had no OHCA exposure during their seven-year study.[4] In our study, patients were treated by paramedics who averaged 24 OHCA during the preceding five years, yet 41% of the patients were treated by paramedics who had fewer than the 15-case threshold that was associated with increased odds of ROSC. Combined, these studies suggest that other forms of skills maintenance are needed.

To address the problem of infrequent exposure to specific patient populations and skills opportunities, some EMS systems have instituted strategies whereby paramedics specialize in certain patients or procedures, such as cardiac arrest.[14] These paramedics are then dispatched to all relevant calls in an effort to coalesce experience among a smaller group of clinicians. Such strategies mimic the rapid response team approach used in hospitals, which has been demonstrated to reduce mortality.[15–17] The disadvantage to this strategy is that turnover may eventually exhaust this cadre of highly experienced clinicians that must then be replaced with clinicians who have had relatively few cumulative exposures. Thus, this may only be a short-term strategy that ultimately results in minimal experience among the bulk of clinicians. Moreover, we were unable to identify any published reports on the effectiveness of this strategy.

Another approach to maintaining skills proficiency is through high-fidelity simulation. This strategy has been used successfully to increase survival rates in the hospital setting.[18,19] However, its use in EMS training programs varies,[20] and there are no published reports correlating simulation training among paramedics with improved OHCA outcomes. Nonetheless, in low call-volume settings this may be the best option to maintain resuscitation skills.