Chest wall mechanics during mechanical chest compression and its relationship to CPR-related injuries and survival

Abstract

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.

Keywords: Cardiopulmonary resuscitation; Out-of-hospital cardiac arrest; Sudden death; Thoracic injuries.

Fig. 1

Example cases of chest compression force variation. Case A (9): A 54-year old male received 9 minutes of manual CPR and 107 minutes of mechanical CPR. BMI: 31.2. The median compression force was 330 N with a high negative compression force variation (≤-95 N). The thoracic height at the beginning of CPR was 257 mm and 240 mm at the end. He presented 10 bilateral rib fractures and 1 sternal fracture. Case B (8): A 29-year-old woman received 9 minutes of manual CPR and 41 minutes of mechanical CPR. BMI: 49.5. The median compression force was 490 N with low compression force variation. The thoracic height at the beginning of CPR was 243 mm and 243 mm at the end. There was no thoracic injury secondary to CPR. Case C (5): A 51-year-old male received 27 minutes of manual CPR and 13 minutes of mechanical CPR. BMI: 26.2. The median compression force was 510 N with a high positive compression force variation (≥95 N). The thoracic height at the beginning of CPR was 204 mm and 204 mm at the end. He presented 6 bilateral rib fractures and 1 sternal fracture together with serious visceral injuries. Abbreviations: CPR = cardiopulmonary resuscitation, BMI = body mass index, N = newtons.

Fig. 2

Compression force variation overtime distributed in three groups (threshold = 95 N).