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Closed chest compressions (CCC) are a key component of resuscitation from medical causes of cardiac arrest, but when haemorrhage, the leading cause of preventable battlefield deaths, is the likely cause there is little evidence to support their use. Resuscitation protocols for traumatic cardiac arrest (TCA) highlight the importance of addressing reversible causes, such as the administration of fluids to treat hypovolaemia. This study evaluated whether CCC were beneficial following haemorrhage-induced TCA and additionally whether resuscitation with blood improved physiological outcomes.The study was conducted with the authority of UK Animals (Scientific Procedures) Act 1986 using 39 terminally anesthetised Large White pigs (35 kg, 29–40 kg) instrumented for invasive physiological monitoring. Following instrumentation and baseline measurements, animals underwent tissue injury (captive bolt to the right thigh) and controlled haemorrhage (30% blood volume). Mean arterial blood pressure (MAP) was maintained at 45 mmHg for 60 min, followed by a further controlled haemorrhage to a MAP of 20 mmHg. As arterial blood and pulse pressures spontaneously deteriorated further over a 5 min period, the randomised resuscitation protocol was initiated as follows: CCC (n=6); IV 0.9% saline (Sal n=8); IV autologous whole blood (WB n=8); IV saline +chest compressions (Sal +CCC n=9); and IV whole blood +chest compressions (WB +CCC n=8). 3×10 ml/kg fluid boluses were administered using the Belmont Rapid Infuser (200 ml/min). CCC were performed using the LUCAS II Chest Compression System.Outcome was attainment of return of spontaneous circulation (ROSC) 15 min post-resuscitation. ROSC was categorised by MAP (MAP ≥50 mmHg=ROSC; MAP >20 <50 mmHg=partial ROSC; MAP ≤20 mmHg=dead).Outcome was significantly worse in the group that received CCC compared to WB and Sal groups (6/6 dead versus 0/8 and 0/8 respectively) (p<0.0001).A significantly higher number of animals attained ROSC in WB compared to Sal group (6/8 versus 0/8 ROSC and 2/8 versus 8/8 partial ROSC respectively) (p=0.0069).There were some none significant differences between WB and WB+CCC groups (6/8 versus 5/8 ROSC, 2/8 versus 1/8 partial ROSC and 0/8 versus 2/8 dead respectively) (p=0.4411).No animals attained ROSC in the Sal and Sal+CCC groups however significantly more animals died in the Sal+CCC group (0/8 versus 0/9 ROSC, 8/8 versus 2/9 partial ROSC and 0/8 versus 7/9 dead respectively) (p=0.0023).CCC were associated with increased mortality compared to intravenous fluid resuscitation. Resuscitation with whole blood demonstrated the greatest physiological benefit as demonstrated by highest numbers of animals achieving ROSC.