A 70-YEAR-OLD unrestrained female driver was involved in a head-on motor vehicle collision. On arrival at the trauma room, she was only experiencing pain in her right knee. There was no shortness of breath. Her medical history was remarkable for asthma and hypertension. On examination, her respiratory rate was 18 breaths per minute. Breath sounds were decreased over the left hemithorax. Bowel sounds were not heard. Her room-air arterial blood gas pH was 7.38, with PO2and PCO2levels of 145 mm Hg and 44 mm Hg, respectively, and a bicarbonate level of 28 mEq/L. Radiograph images (Figure 1and Figure 2) showed marked elevation of the left hemidiaphragm.