The 2020 AHA guideline states that high quality CC requires the following: (1) optimal hand position, (2) compressing the lower part of the sternum by at least one-third of the anterior-posterior diameter of the chest (equivalent to 4 cm in infants and 5 cm in adolescents), (3) achieving compression rate of 100 to 120 min− 1, and (4) allowing for complete chest recoil between each CC (24). In this study, we focused on the CC rates and depth as these parameters have shown a more significant role in affecting clinical outcome (25). Overall, our study found that the participants’ CC performance with AVF was similar to that with TLF. Although the average CC rate with AVF in our study was statistically significantly higher than that with TLF (121.8 min− 1 vs. 117.4 min− 1, p = 0.005) and slightly above the recommended target range, this may not be considered significant in real clinical settings.
The proportion of participants performing CPR at CC rates within the recommended target range of 100 to 120 min-1 was similar between AVF and TLF (48.6% and 51.4%, p = 0.824). However, the mean CC depth with both TLF and AVF in this study were below the recommended range, while the mean CC rate inclined toward 120 min− 1. This corroborated a previous study reporting significant decrease in CC depth as the CC rate increases (26).
With AVF, suboptimal compression depth can be due to difficulty in following the audio-visual prompts that demand competent eyes-ears-hands coordination. The heavy cognitive load resulted in reduced attention capacity towards multiple stimuli during CPR (27). Therefore, despite the AVF indicating inadequate compression depth, participants were inclined to ignore them and continued performing CC without corrective actions. The cognitive loads in CC are intrinsic, germane, and extraneous. Chest compressions are the intrinsic load, whereas the germane load is imposed while using an unfamiliar AVF device. Extraneous load occurs due to the requirement for participants to simultaneously look at the monitor, while listening to voice prompts and fine-tuning their CCs (28, 29). A similar conclusion was made by Brown et al in their study on measuring the task of performing CPR with AVF devices based on the National Aeronautics and Space Administration (NASA) Task Load Index. They reported significantly higher physical burden to CPR providers in multitasking feedback interpretation and formulating corrective measures to improve their compressions (30).
On the other hand, TLF would reduce the extraneous load as participants need to only listen to voice prompts. The germane load would depend on whether participants are familiar to receiving real-time feedback during CC. Team leaders were able to gauge and provide appropriate feedback on the correct compression rate through subjective visual assessment. This suggests that team leaders had conceptual and habitual tacit knowledge of the appropriate CC rate. Tacit knowledge is the implicit knowledge that one possesses based on personal experience (31). It is personal, intuitive, and difficult to be coded, transferred, or taught (32, 33). Schemata on how tacit knowledge and habitual practices influence the management of resuscitation in the ED and other departments have been provided in previous studies (34, 35). Interestingly, assessment and feedback on the CC depth by team leaders in this study were not as accurate as that on CC rate. This may be due to the misidentification of CC depth as adequate at higher compression rates (36).
A recent study (20) demonstrated better CPR quality with feedback device compared to human instructor feedback. Their study method had measured CPR quality as a composite score including correct hand position, adequate depth, compression rate and complete chest recoil. However, similar to our findings, the average CC rate in their study was comparable between feedback device and human instructor feedback, and their human instructor feedback group showed more compliance to CPR guidelines for CC depth.
CPR feedback devices were invented and innovated to automate conventionally human-led resuscitations. In a publication regarding automation of tasks with machines, multiple bottlenecks were identified impeding advancement towards task automation. These bottlenecks involved tasks that require complex manipulation and perception, creative-intelligence tasks, and social-intelligence tasks (37). Leading a resuscitation during CPR in a cardiac arrest is recognized as a complex and highly demanding task requiring case-by-case analysis and insight. Extrapolating these bottlenecks into our study may demonstrate AVF limitations in its ability to only provide objective perception in compression depth and rate. Thus, in more complex cardiac arrest cases, team leaders may be more proficient in employing both vertical and lateral thinking to mitigate suboptimal CC. Lateral thinking is defined as reasoning using an indirect and creative approach that may not be immediately obvious whereas vertical thinking is a thinking that proceeds in a stepwise manner while applying specific rules to reach a goal (38, 39). For instance, in one participant, the team leader had observed and gave feedback of her suboptimal CC attributed by not straightening and locking the elbows.
Furthermore, in our setting, the English language is not a native language and is the second spoken language for most residents. This discrepancy of language proficiency may have resulted in misinterpretation of some AVF prompts. We have noted during the study that most participants were inclined to push faster when the defibrillator audio feedback prompted “push harder”. In contrast, the language conversed by the team leader were a fusion of the native Malay language and conversational English language. Our participants felt that the team leader’s tonal voice was more reassuring as it instilled a sense of confidence and was easier to be understood compared to the machine’s monotonous audio prompts. Effective communication is expressed via spoken words, tone, resonance, pitch modulation and other forms of non-verbal communication (40), some of which, are absent in the AVF method. Perhaps, the socio-cultural variations of vocal intonation in these machines (such as using the local Malay language and dialect) should be considered by the manufacturers to strengthen participants engagement and comprehension.
Previous studies comparing device-led with human-led feedback reported conflicting findings (20, 21). As with Pavo et al, our findings found both methods to be comparable (21). We investigated whether participant’s preference of feedback methods influenced their CC quality, as this has not been previously explored. In our study, participants who perceived that they performed better with TLF and those who preferred TLF performed CC within the recommended range with TLF compared to AVF. However, this was not observed in participants who preferred AVF. Participants who perceived that they performed well with both AVF and TLF, and did not mind one method over the other performed the best.
Limitations
Our study had some limitations. Firstly, this was a single-center study with participants comprising of ED healthcare personnel and medical students. This may have resulted in selection bias and may not necessarily reflect the overall healthcare providers’ competency in CPR. Although all participants had prior training in BLS, their experience in CPR was likely diverse based on their profession. Secondly, team leaders were not randomized and were allocated to participants based on convenience due to their work schedule. Team leaders also varied in terms of experience and leadership positions. These factors may have resulted in the inter-team leader variability. Thirdly, this study was conducted in a manikin-based simulation setting. This allowed us to standardize the assessment, but it could only represent a real patient scenario to a limited extent. We also chose a shorter duration of CC (i.e. 1 min instead of the 2-min cycle periods in CPR guidelines) to minimize rescuers’ fatigue as our study aimed to assess whether human feedback or feedback device resulted in better CC performance. Results from previous studies showed that CPR quality started to decline after 1 minute due to fatigue (41, 42) regardless of rescuer strength (43), gender, weight, height, or rescuer’s profession (44). Fourthly, we did not have a control group (i.e. CC without feedback). Therefore, we do not know to what extent the CC performance was the effect of TLF or AVF alone or of the participants’ own knowledge and skills. Lastly, a potential Hawthorne effect may have influenced our results as participants were aware that they were being monitored throughout the simulated CC performance.