A 56-year-old male is in respiratory arrest following a head-on car crash while not wearing a seat belt. He has significant facial and torso trauma. You palpate an irregularity to his cervical spine at C-4. You should suspect his arrest is due to:

• A. Brain Stem Injury From Head Trauma
• B. Spinal Cord Compression Above the C-4 Level
• C. Tension Pneumothorax Inhibiting Chest Expansion
• D. Rupture of the Diaphragm Blocking Inhalation

Answer: (B)

The key idea is that the diaphragm, the primary muscle of breathing, is innervated by the phrenic nerve from the C3–C5 spinal levels. If there is a high cervical spine injury at or above C4, the neural pathways that control the diaphragm can be disrupted, leading to diaphragmatic paralysis and apnea. Seeing an irregularity in the cervical spine at C4 after a head-on crash strongly suggests a high cervical spinal cord injury with potential compression, which can cause respiratory arrest by shutting down diaphragmatic function.

Brain stem injury could also cause apnea, but the finding of a cervical spine abnormality makes a high-level spinal injury the most likely mechanism here. Tension pneumothorax would typically present with chest signs such as unequal breath sounds and severe distress, and diaphragmatic rupture would not immediately explain respiratory arrest in the absence of other focal signs.