Airway Conditions Change During General Anaesthesia

Significant airway changes occur during the administration of general anaesthesia, including a decrease in patients’ intraoral space and an increase in their neck thickness, according to results of a prospective cohort study presented at the 2014 Annual Meeting of the American Society of Anesthesiologists (ASA).

After extubation following general anaesthesia, the risk of difficult laryngoscopy and intubation can increase when airway management is required — particularly in patients with pre-existing factors associated with difficult airway, noted Junko Ushiroda, DDS, Nara Medical University, Nara, Japan. It seems that oedema formation in the airway during general anaesthesia plays a pivotal role, she added.

Dr. Ushiroda led a team of anaesthisologists in compiling data from 281 patients. Objective airway assessments were performed on supine patients in the operating room. The assessments were conducted before anaesthesia, and were repeated 5 minutes after patients met the standardised criteria following extubation.

The diameter of the sternothyroid muscle and neck circumference significantly increased (36.9 % ± 27.3% and 3.5 % ± 2.9%, respectively) in the postanaesthetic period, while oral, pharyngaeal, and total airway volumes significantly decreased (-24.2 % ± 20.3%, -26.6 % ± 36.2%, and -26.1 % ± 18.4%) in the postanaesthetic period. Some of these changes may have been influenced by surgical duration or perioperative fluid management (r = 0.12 to 0.22, indicating weak correlation).

The researchers calculated the changing rate of each study parameter using the formula: Postanaesthetic value / (Postanaesthetic − Preanaesthetic value). The paired student’s t-test was used to compare pre- and postanaesthetic values for individual airway assessments. Pearson’s correlation coefficient (r) was used to determine whether changing airway assessment rates correlated with age, height, body mass index, surgical duration, or intraoperative fluid balance. A P value less than .05 was considered significant.

Volumes of each patient’s pharynx, oral cavity, and total airway were obtained by the Acoustic Pharyngometer Eccovision computerised acoustic reflectometry system, with patients breathing through a respiratory mouthpiece. Diameter of the sternothyroid muscle at the level of the vocal cords was obtained using a linear ultrasound transducer, and the amount of anterior neck tissue was quantified by averaging the diameter of the sternothyroid muscle obtained 15 mm to the left and right of the central axis. Neck circumference was measured at the thyroid cartilage.