A 52-year-old male with a history of ankylosing spondylitis presents for emergency laparotomy following blunt abdominal trauma. On pre-operative assessment, he has severe cervical spine rigidity, limited mouth opening (inter-incisor distance 2 cm), and a prominent occiput. Induction is uneventful, but after administration of succinylcholine and loss of consciousness, you are unable to ventilate the patient's lungs with a bag-mask. What is the most appropriate next step?