Abstract Body:
Introduction: Traditional sternal piston-type CPR (SP-CPR) is associated with rib and sternal fractures in a large fraction of porcine cardiac arrest studies. Most investigators using SP-CPR “mold” the pig’s precordium to prevent piston movement and enhance the “cardiac pump.” This molding is essentially disruption of the sternocostal joints. Although circumferential constriction CPR (CC-CPR) applies more motive force to the chest, it spreads this force over a much larger area. This results in a less concentrated force which may cause less skeletal injury.

Hypothesis: CC-CPR may be associated with a lower incidence of thoracic skeletal injury.

Methods: Retrospective observational report of multiple porcine studies. Ventricular fibrillation was induced in female Yorkshire swine (n = 30, 28±5 kg). CPR was provided by means of pneumatic CC-CPR prototypes in all animals. Most received thoracoabdominal CPR with pneumatic bands around both the chest and the abdomen. Thoracic vest pressures ranged from 180–300mmHg with constriction rates from 80–120 per minute and duty cycles from 30-50%. Duration of resuscitation was typically 20 min. Examination for injuries was via visual inspection and palpation both externally and internally during postmortem by the team veterinarian. We used the fracture rates reported in previous porcine CPR studies as a historical control.

Results: In this large series of porcine studies with CC-CPR, which included per-constriction forces as great as 400kg and relatively long intervals of resuscitation, only 2 rib fractures were found, a rate of 0.07 fractures per pig. No sternal or chondral injuries were detected. We found four prior studies, all using SP-CPR, that appeared to reliably report a CPR-related fracture rate. The average rate was 4.45±1.6 per animal. Sternocostal joint disruption from “molding” did not appear to be reported as injury in published studies.

Conclusion: CC-CPR appears to be associated with a remarkably low rate of thoracic skeletal injury in porcine models, compared with historical controls. It is not known if this enhanced safety in animals will translate to patients in the clinical setting, most of whom will have received manual and/or sternal piston type CPR before CC-CPR can be initiated.