A 28-year-old woman is admitted 4 hours after a tibia fracture sustained in a motor vehicle collision. She develops severe pain in the anterior compartment of the leg unresponsive to parenteral analgesia. Examination reveals tense swelling, pain on passive ankle dorsiflexion, and intact dorsalis pedis pulse. A stat compartment pressure measurement shows 45 mmHg (diastolic BP 85 mmHg). What is the most appropriate next step?