Pharynx volume derived from three-dimensional computed tomography is associated with difficult intubation in spinal deformity surgery: A retrospective cohort study

Spinal abnormality surgery, including surgery for ankylosing spondylitis and idiopathic scoliosis, can present significant challenges to anesthesiologists because of the potential difficult airway. The bedside screening tests routinely used to detect difficult airways are highly variable. Pharynx volume calculated using three-dimensional (3D) computed tomography (CT) may play a role in predicting difficult airways. We conducted a retrospective cohort study on patients (aged ≥14 years) who received orthopedic surgery for ankylosing spondylitis/idiopathic scoliosis under general anesthesia. Volume of the pharynx air space was calculated through volume rendering technique by 3D reconstruction of patients’ cervical spine CT. Patients were divided into 2 groups according to their pharynx volume, pharyngeal volume lower than 16 mL (n = 11) and equal or higher than 16 mL (n = 13). Pharynx volume in low volume group was 10.4 ± 3.6 mL (n = 11), and the counterpart in high volume group was 20.8 ± 5.5 mL (n = 13). The incidence of difficult intubation was significantly higher in low pharynx volume group than in high pharynx volume group (54.5% (6/11) vs 7.6% (1/13), P = .023). Bedside screening tests including modified Mallampati test, inter-incisor gap and thyromental distance, or radiological variables such as anterior neck soft tissue thickness to vocal cords were not different between the 2 groups. Smaller pharynx volume played an important role in difficult airways for patients undergoing orthopedic surgery for ankylosing spondylitis/idiopathic scoliosis.