We demonstrated a decrease in CC depth over time for a single rescuer starting at 90 sec of CPR, without any change in CC rate, during actual in-hospital resuscitations during which real-time audiovisual feedback was provided. To our knowledge, this study represents the first to evaluate decay in CC quality (commonly associated with rescuer fatigue) during actual in-hospital cardiac arrest resuscitation efforts.
Our results stand in contrast to some of the previous studies on rescuer fatigue during simulated CPR. Hightower et al. reported a drastic drop in compression adequacy (a combined metric including depth and rate analysis) from 93% of compressions to 67% after only one min of CPR.13
After five min they found that only 18% of the delivered CCs were adequate. Conversely, in another manikin study Bjørshol et al. found no significant degradation in CC performance over 10 min of continuous efforts.12
Although we measured average CC depth rather than percentage of adequate compressions, our results suggest that the decrease in depth over time—and therefore the decrease in compression adequacy—is more gradual during actual cardiac arrest than demonstrated by Hightower et al., but does indeed occur as a real phenomenon of continuous CPR delivery. These differences could be attributed to differences in chest wall compliance between humans and mannequins or to the varied settings and participants in the simulation studies, where many of the psychological and physiological factors such as a sense of urgency, preparedness, and anxiety, as well as room crowding, noise levels, and team dynamics, are likely quite different from the actual cardiac arrest environment.
It should also be noted that although our findings were statistically significant, the magnitude of the decay in CC depth was moderate and the clinical significance of remains uncertain. However, based on prior work evaluating the accuracy of the CPR sensing technology utilized, it is likely that the measured compressions overestimate actual compression depth by as much as 28–40%, which would decrease subsequent compression depths below resuscitation guideline recommendations of 38–51 mm.17,18
The importance of this topic is additionally relevant to CPR in the out-of-hospital cardiac arrest setting, where bystanders and Emergency Medical Services personnel often perform CPR for more prolonged periods of time before arriving at the hospital. The investigation of such out-of-hospital CPR would allow for evaluation of CPR decay over longer durations of continuous CC delivery.
Our study is not without limitations. First, we were unable to gather the rescuers’ demographic data to assess whether any CC provider factors were linked to CPR quality. One might expect such characteristics as physical size and age, as well as experience, to play a role in an individual rescuer’s ability to deliver compressions; recent simulation work has highlighted such factors in CPR delivery.19
In previous studies of CPR decay and fatigue, Ochoa et al. reported that an observed decrease in compression quality did not depend on gender, age, height, weight or the rescuer’s profession. However, Ashton et al. found in their study that females achieved significantly fewer adequate compressions over a three minute period of CPR, and that this discrepancy was correlated with height and weight differences. Further work in which rescuers are identified during actual resuscitation efforts and linked to CPR performance will be required to further elucidate this issue. Other factors may play a role as well, such as presence or absence of a backboard, or the mattress compliance. These factors were unmeasured in our current study.
A second limitation was that these results were obtained using real-time audiovisual feedback during resuscitation and may not be generalizable to systems where feedback is not used. However, several prior clinical investigations have demonstrated that use of real-time feedback improves CPR quality.20–22
Therefore, our results likely underestimate the actual CPR decay from rescuer fatigue, as some fraction of rescuers may have maintained CPR quality despite initial fatiguing in response to feedback messages. In a similar limitation to the broad applicability of our work, the majority of resuscitations evaluated in this cohort took place in critical care settings, not on the general wards or Emergency Department. It is unclear whether parameters of CC decay and fatiguing would be different, however, based on location of event or local staffing. One might expect less CC decay in critical care settings, where staff are more experienced with CPR delivery, although future work will be required to test this hypothesis.