Aim To determine compression force variation (CFV) during mechanical cardiopulmonary resuscitation (CPR) and its relationship with CPR-related injuries and survival. Methods Adult non-traumatic OHCA patients who had been treated with mechanical CPR were evaluated for CPR-related injuries using chest X-rays, thoracic computed tomography or autopsy. The CFV exerted by the LUCAS 2 device was calculated as the difference between the maximum and the minimum force values and was categorised into three different groups (high positive CFV = 95 newton (N), high negative CFV = -95 N, and low variation for intermediate CFV). The CFV was correlated with the CPR injuries findings and survival data. Results Fifty-two patients were included. The median (IQR) age was 57 (49–66) years, and 13 (25%) cases survived until hospital admission. High positive CFV was found in 21 (40.4%) patients, high negative CFV in 9 (17.3%) and a low CFV in 22 (42.3%). The median (IQR) number of rib fractures was higher in the high positive and negative CFV groups compared with the low CFV group [7(1–9) and 9 (4–11) vs 0 (0–6) (p = 0.021)]. More bilateral fracture cases were found in the high positive and negative CFV groups [16 (76.2%) and 6 (66.7%) vs 6 (27.3%) (p = 0.004)]. In the younger half of the sample more patients survived until hospital admission in the low CFV group compared with the high CFV groups [5 (41.7%) vs 1 (7.1%) (p = 0.037)]. Conclusions High CFV was associated with ribcage injuries. In the younger patients low CFV was associated with survival until hospital admission.