Intrathoracic pressure impulse predicts pulmonary contusion volume in ballistic blunt thoracic trauma.

BACKGROUND: Blunt thoracic trauma including behind armour blunt trauma or impact from a less lethal kinetic weapon (LLKW) projectile may cause injuries, including pulmonary contusions that can result in potentially lethal secondary complications. These lung injuries may be caused by intrathoracic pressure waves. The aim of this study was to observe dynamic changes in intrathoracic hydrostatic pressure during ballistic blunt thoracic trauma and to find correlations between these hydrostatic pressure parameters (especially the impulse parameter) and physical damages.

METHODS: Thirty anesthetized pigs sustained a blunt thoracic trauma. In group 1 (n = 20), pigs were protected by a National Institute of Justice class III or IV bulletproof vest and shot with 7.62 NATO bullets. In group 2 (n = 10), pigs were shot by an LLKW. Intrathoracic pressure was recorded with an intraesophageal pressure sensor and three parameters were determined: intrathoracic maximum pressure, intrathoracic maximum pressure impulse (PI(max)), and the Pd.P/dt(max), derived from Viano's viscous criterion. Relative right lower lung lobe contusion volume was also measured.

RESULTS: Different thoracic loading conditions were obtained. PI(max) best correlated with relative pulmonary contusion volume (R² = 0.64 and p < 0.0001). This result was homogenous for all experiments and was not related to the type of chest impact (LLKW-induced trauma or behind armour blunt trauma).

CONCLUSIONS: The PI(max) is a good predictor of pulmonary contusion volume after ballistic blunt thoracic trauma. It is a useful criterion when the kinetic energy record or thoracic wall displacement data are unavailable, and the recording and calculation of this physical value are quite simple on animals.