The study aimed to explore the relationship between bodyweight and decline in CPR compression depth in a healthy student population, whilst also considering physiological changes during CPR and VO2max of the rescuers.
Forty-six students at the University of Derby were independently certified in CPR. Mean age (21.22 years ±2.16); height (174.78cm ±10.55); weight (72.89kg ±12.74); Body fat % (19.15±7.42); Time since CPR certification (9.65 Months ±6.75); Female (N= 18, 39.1%); Male (N= 28, 60.9%). The protocol consisted of three trials; 1). Familiarization with testing procedures; 2). Participants performed continuous compression only CPR until they were unable to continue, with 10 minutes cut-off. CPR performance was measured on Laerdal QCPR Full Body mannequin. The mannequin was placed on the Bertec Force Plate to continually measure vertical force. A metronome was set at 110bpm to maintain rate; 3) An incremental VO2max test using an athlete led protocol (Hamlin, et al., 2012), with Vehrs, et al., (2007) sub-max test to warmup, enabling scalability for future research. During trial 1 and 2, HR (Polar HR monitor H10); VO2 (VO2 Master) were measured. RPE (Borg Scale, 6-20) was utilized to measure perceived exertion (Upper limb/Lower limb/Cardiovascular). Blood lactate was tested pre-post each trial (Biosen C-Line).
Rescuers had a mean relative VO2max of 52.51±13.10 ml.kg.min-1 indicating a high fitness level. A positive moderate correlation was observed between bodyweight and time to decline in compression depth performance (r=0.448, p=0.002, β=0.83). The force plate data identified that 50-60mm compression depth requires 514-570N of downward force respectively. This enabled identification of the exact second rescuers dropped below effective compression depth without subsequent recovery. The heavier group (>72.89kg) were able to perform CPR for significantly longer prior to decline in performance (mean260.13 (s) ±186.45) compared to the lighter (72.89kg) group (mean158.36 (s) ± 153.13) p=0.047. BLa levels post CPR were (2.85±1.35mmol/L) lower than anaerobic threshold (4mmol/L) with VO2 and HR also suggesting CPR was an aerobic activity for this population.
Both groups' mean time to decline in CPR compression depth exceeded the two-minute recommended changeover period. Due to large variability a 1-minute changeover could potentially be a more inclusive practice to maintain chest compression depth, if balanced against minimizing disruptions. CPR performance decline was not explained by the physiological variables measured indicating aerobic activity. This conflicted with rescuer's perception of effort. Future studies should be conducted in working age practitioners and explore local muscle fatigue and joint biomechanics.
CPR is a vital skill for healthcare professionals, including Physiotherapists. Better understanding the relationship between bodyweight and fatigue can contribute towards informing guidelines in relation to recommended change over time.
Fatigue
Bodyweight
