Background In some hemodynamically stable patients with traumatic pneumothorax, conventional vital signs may have limited sensitivity in detecting early disease progression. Quantitative bedside indicators capable of dynamic monitoring are therefore needed.

Objective To evaluate the diagnostic performance of a six-zone point-of-care ultrasound (POCUS) counting method in identifying tension physiology in a standardized progressive pneumothorax animal model, and to compare pressure tolerance and hemodynamic compensation between left- and right-sided pneumothorax.

Methods Thirty-two healthy adult Bama miniature pigs (body weight 45 - 50 kg) were randomly assigned to left-sided (n=16) or right-sided pneumothorax groups (n=16). Under general anesthesia and mechanical ventilation, a double-lumen catheter was inserted via the sixth intercostal space at the mid-axillary line for stepwise intrapleural air insufflation (60 mL per step, 2-min interval). Cardiac output (CO), mean arterial pressure (MAP), and intrapleural pressure (IPP) were continuously monitored. Standardized six-zone POCUS examinations were performed by blinded operators at each stage. Tension physiology was operationally defined as a ≥50% reduction in CO from baseline with preservation of an arterial waveform. Pearson correlation analysis was used to assess the relationship between the number of ultrasound-involved zones and CO, and receiver operating characteristic (ROC) curve analysis was performed to determine the optimal zone threshold for identifying tension physiology.

Results CO declined progressively with increasing IPP, whereas MAP reduction occurred relatively later. The number of involved zones detected by POCUS was significantly negatively correlated with CO (P < 0.001). ROC analysis demonstrated that ≥4 involved zones provided the best diagnostic performance (AUC=0.961). The right-sided group required significantly lower IPP to reach the tension physiology endpoint compared with the left-sided group (P < 0.001).

Conclusion Six-zone POCUS counting may serve as a bedside semi-quantitative indicator of increasing risk of circulatory compromise during progressive pneumothorax. There is a significant side-related difference in intrapleural pressure upon reaching the tension physiology endpoint, suggesting that the affected side should be incorporated into clinical assessment to improve the accuracy of disease progression monitoring.