Accuracy of anatomical landmarks for intercostal chest drain placement in non-obese and obese patients based on chest X-rays: A cohort study

Chest drain insertion is a lifesaving procedure. However, incorrect site selection can cause serious complications. Advanced Trauma Life Support guidelines recommend chest drain insertion at the fourth to sixth intercostal space (ICS) in the anterior to mid-axillary line. Nevertheless, anatomical variation, especially in obese patients, may limit the reliability of traditional surface landmarks. Therefore, this study aimed to evaluate the accuracy of the nipple line in males and inframammary fold in females for identifying the fourth to sixth ICS across different body mass index (BMI) categories. This single-center cohort study was performed at Vajira Hospital, Bangkok, Thailand, from May to June 2024 and included adult patients undergoing chest radiography with marked surface landmarks. Radiographs were reviewed to identify the ICS level corresponding to each landmark. The participants were stratified into obese (BMI ≥30 kg/m 2 ) and nonobese groups. Sensitivity, specificity, and accuracy were calculated, and diagnostic performance was assessed using receiver operating characteristic (ROC) curves. A total of 385 patients (770 hemithoraces) were analyzed. In nonobese males, the nipple line identified the fourth to sixth ICS with 40.19% sensitivity and 80.39% specificity. However, in obese males, the sensitivity and specificity dropped to 3.70% and 7.41%, respectively. In nonobese females, the inframammary fold achieved 34.09% sensitivity and 68.18% specificity. However, in obese females, the sensitivity and specificity dropped to 10.00%, with 20.00% accuracy. ROC analysis confirmed reduced landmark reliability in obese patients. The nipple line and inframammary fold show moderate accuracy in nonobese patients but are unreliable in obese individuals. Ultrasound guidance or alternative anatomical approaches should be considered to improve procedural safety.