A22-year-old man is hypotensive and tachycardic after a shotgun wound to the left shoulder. his blood pressure is initially 80/40 mm hg. after 2 liters of crystalloid solution his blood pressure increases to 122/84 mm hg. his heart rate is now 100 beats per minute and his respiratory rate is 28 breaths per minute. his breath sounds are decreased in the left hemithorax, and after initial iv fluid resuscitation, a closed tube thoracostomy is performed for decreased left breath sounds with the return of a small amount of blood and no air leak. after chest tube insertion, the most appropriate next step is