Resuscitation of cardiac arrest patients in the prehospital setting is both labor- and skill-intensive. Survival rates from OHCA vary greatly by region,1,30–32
from 3.0% to 16.3% in one study,32
and the number and level of providers available in various systems have been postulated to contribute to this difference in survival. In a meta-analysis by Nichol et al., two- tier EMS systems were associated with a significant increase in survival to hospital discharge compared with one-tier systems (10.5% vs. 5.2%), suggesting that staffing patterns do affect patient outcomes from OHCA.23
However, the optimal crew configuration for response to these situations remains unknown. We evaluated objective measures of cardiac resuscitation to compare the effectiveness of crews composed of two, three, and four ALS providers.
The results of this study revealed no significant difference between all-paramedic crew size configurations in the NFF during CPR, a measure of effectiveness of CPR linked to maintaining adequate CPPs and improving survival.2–12,33
Prior studies had demonstrated that compressions are not performed as much as half of the time during CPR.14–29–34
It is, however, possible to obtain significantly lower NFFs, and Losert et al. documented a mean hands-off ratio of 0.13 among highly trained staff in an emergency department setting.35
Our study did find a decrease in baseline NFF across all groups when compared with our previous work, which may be attributed to the change from 15:2 to 30:2 in the compressions-to-ventilations ratio resulting from the 2005 AHA CPR guidelines and subsequent changes in paramedic education.6
This improvement in the baseline NFF is encouraging.
Though times to performance of individual procedures were not found to differ among groups, point estimates suggest that groups with three or four providers may successfully complete more specific ALS procedures compared with two-person groups. Additionally, there was a trend toward decreased time to endotracheal intubation with increasing number of ALS providers. This finding is consistent with the study by Bayley et al. comparing paramedic-paramedic versus paramedic-EMT groups.18
Whether this factor independently impacts survival is uncertain. In a retrospective study of 693 OHCA patients who had endotracheal intubation performed, Shy et al. found a correlation between intubation times and survival to discharge from the hospital.36
Additionally, Kramer-Johansen et al. demonstrated an improved NFF from 0.61 to 0.41 before and after endotracheal intubation.37
If early intubation does have a survival benefit, it may be through improvement of the performance of CPR as part of the resuscitation. However, while early intubation may decrease NFF by allowing for continuous compressions, this benefit must be weighed against the cessation of compressions associated with endotracheal intubation. Perhaps the use of alternative airway devices, which can be placed in less time and without interruption of compressions, represents a better strategy for resuscitation.
The findings of our study may help to explain the seemingly paradoxical results of Eschmann et al.19
In our study, we demonstrated a lack of improvement in the provision of BLS interventions such as effective CPR and timely defibrillation, which appear to be most important in the resuscitation of cardiac arrest patients. In fact, review of the resuscitation scenarios revealed numerous cases within our study groups where the provider performing chest compressions became distracted by the performance of ALS procedures, resulting in pauses between chest compressions.
This included assisting in preparing intubation equipment or medications, which temporarily interrupted CPR. These findings are consistent with prior work that identified a decrease in quality of CPR by BLS providers with increasing resuscitation complexity.14
Therefore, having more ALS providers on the scene may distract the group from performing CPR in favor of ALS procedures that do not have a proven survival benefit or that are dependent on the effectiveness of BLS interventions,6,12,20–28
and may explain the improved survival seen in two-tier versus one-tier EMS systems.23
Further studies using a mixed ALS-BLS crew with dedicated BLS providers may demonstrate improved times to ALS intervention without increasing NFF. For an increased number of providers to have an impact on survival in cardiac arrest, the findings of our study suggest that there must be a clear division of tasks and a renewed emphasis on the performance of effective CPR by dedicated providers.