As part of a larger study (North American LUCAS Evaluation—NALE), Yost et al set out to analyse the interruptions to CPR during application and use of the LUCAS™. They identify this as an important factor for consideration when using these devices, as if the delay is too long then this might outweigh potential benefits to the patient of MCC.
Two approaches to data collection were used: a brief survey after each out-of-hospital cardiac arrest (OOHCA) to establish pre-hospital providers' perceptions of the length of time associated with interruptions to CPR while applying the LUCAS™; and electrocardiograph (ECG) and impedance data downloaded from the LIFEPAK 12 monitor/defibrillators to measure actual time of interruptions.
Five performance features were measured: length of CPR interruption due to application of the LUCAS™; length of pre-shock interruptions; length of post-shock interruptions; compression fraction for MCC (% of time that compressions were occurring); compression rate for MCC.
In total, defibrillator data files with impedance data were collected for 113 cases. Of these, only 32 could be included in the full analysis of application times for a variety of reasons e.g. not having impedance data showing the transition from manual to mechanical compressions. The paper identifies that application of the LUCAS™ is recommended in two phases: A) place the back plate under the patient and then continue with a cycle of manual compressions; B) attach the top section to the back plate, position suction cup and pressure pad, and commence mechanical CPR.
Phase B CPR interruption was measured from the last sign of activity of manual compression through to the first sign of MCC—the latter was easy to identify as mechanical chest compressions are clearly identifiable on the ECG by their highly regular, almost rectangular shape.
Interruptions due to Phase A (application of back plate) is more problematic to analyse as it is not possible to be absolutely sure of the reason for any pause showing on the data files prior to starting MCC (one of the limitations of using retrospective data) as the delay may have been due to the application of the back plate or the interruption may have occurred due to other reasons. The median time for interruptions related to application and activation of the device was 32.5 seconds (IQR 25–61) with five cases being under 20 seconds and eight being in excess of 60 seconds. Correlation between pre-hospital providers’ perceptions and actual time of the interruptions was poor. Only five participants’ perceptions of interruption time matched the actual time, and in 50% of cases (n=16) the actual time was over twice as long as participants’ perceived estimates. In the complete data set of 113 cases, 49 shocks were delivered while the device was in situ with the median pre-shock interruption being 19 seconds (IQR 15–24) and post-shock being four seconds (1.5–8). Seven cases documented no pause. Based on analysis of 63 eligible data files, compression rate was determined to be 104/min (SD 4/min) and the compression fraction average was 0.88 (SD 0.09). Clearly there are limitations, including the retrospective nature of the study, and the small number of cases eligible for full data analysis, which restricts the generalisability of the results. Nonetheless the paper raises interesting areas for consideration.
The authors recommend that if the device is being introduced to services then the importance of only having short interruptions must be stressed; investment in education and training to ensure rapid application of the device by practitioners is essential; and the use of objective measures such as defibrillator recorded impedance data to enable practitioner feedback on actual (as opposed to perceived) interruption length could serve as a means for quality improvement.