Abstract 16794: Variation in Achievable Chest Compression Depth Assessed by Cardiac MRI

Abstract

Introduction: Recommended chest compression depth during cardiopulmonary resuscitation (CPR) for adults was increased to 5-6 cm in 2010. According to the cardiac pump theory each compression squeezes blood from the heart and the amount of blood per compression would be expected to be limited by the blood filled structures directly underneath the compression point. Methods: Cardiovascular MR (CMR) survey axial scans acquired from consenting patients referred for CMR were analyzed. We measured the external anterior-posterior (AP) diameter (AP) and the cumulative height of blood-filled structures in the perpendicular line in an axial plane from the compression point in the center of the inter-nipple line (INL) (Compression line). Results are means with standard deviation (SD) and mean differences with 95 % confidence intervals (CI), P-values from unpaired, two-sided t-test. Results: We included 144 patients, age 52 (17), 110 (76 %) males, 74 (60 %) having one or more pathological finding from the exam. The most prominent structure identified in the studied midline was (decreasing order): Left Atrium (41 %), Right Ventricle (31 %), Right Atrium (12 %), Left Ventricular Outflow Tract (LVOT)/Root of Aorta (8 %), Pulmonary Outflow Tract (2 %), other (6 %). Altogether, LVOT was present in 35 % and Left Ventricle in only 2 % of compression lines. Mean (SD) AP diameter for males and females was 25 (2) cm and 22 (2) cm (mean difference 2 cm (95 % CI 1, 3; P<0.001)), and the blood filled length of the compression line (APblood) were 6.5 cm (2) and 4.7 cm (2) (mean difference 1.8 cm (95 % CI 1.1, 2.5, P<0.001)), respectively. This comprised 22 % (10) and 26 % (7) of the AP diameter, for men and women, respectively. In a linear regression gender, body mass index (BMI), but not pathological findings were significant predictors of external AP diameter. Only gender was found to predict APblood. Conclusions: In the average male 5-6 cm chest compression depth at the level of the INL seems feasible, but for over half of the women compressions deeper than 5 cm would probably compress connective and muscle tissue rather than just squeeze blood from the heart, even though the blood-filled proportion of the AP diameter was larger in women than in men.