Estimation of Optimal Chest Compression Depth based on Chest Computed Tomography in Thai Patients. 
Objective : Many studies evaluated chest internal diameters using radiological assessment to estimate the better chest compression depth and position during cardiopulmonary resuscitation but the results varied among ethnic groups.This study aimed to identify the chest compression depth across BMI groups in Thai patients when simulated compression depth was delivered in 1/2, 1/3, 1/4 of external chest anteroposterior diameter (EAPD) and 5-6 cm depth according to the current guidelines.
METHODS : A total of 421 consecutive chest computed tomography scans (male 50.8%) were reviewed across BMI groups (BMI under 18.5, 18.5-24.99, 25-29.99, and over 30 kg/m2 ). The external anteroposterior diameter (EAPD) were measured from the skin anteriorly at mid-lower half of sternum to the skin on the posterior thorax and will be used as an external marker for simulated chest compression. The internal diameter (ID) were calculated from internal chest wall to surface of the cardiac wall. The Residual chest depth was calculated by ID minus simulated compression depth and targeted less than 20 mm. The patients in conditions which may alter thoracic or cardiac anatomy (COPD, Cor pulmonale, ventricular hypertrophy) were excluded.
RESULTS : 421 patients (male 50.8%, age 57±14 years) equally in each BMIs. Mean height in male (166.53±0.92cm) and female (155.22±0.57cm.) were recorded but there’s no different across BMIs in the same gender. The more patients’ weight, the larger EAPD were identified ( r 0.78 ). By simulated chest compression at lower half sternum, the compression depth at 1/3 of EAPD provided the best residual chest depth in all BMI groups (32.45±10.18 vs 35.17±10.95 vs 34.77±8.86 vs 33.42±9.60 mm. for BMI <18.5 vs 18.5-24.99 vs 25-29.99 vs over 30 kg/m2 respectively; p=0.16). The cardiac ventricle were best exposed at sternoxiphoid junction area but there’s possible intra-abdominal organ injury identified. (Liver 34% of cases). 
CONCLUSIONS :  The chest compression at 1/3 of EAPD depth could be the optimal compression depth in Thai population. The further clinical study may need to identify the association with survival outcomes.

Estimation of optimal chest compression depth based on chest computed tomography in Thai patients