Ultrasound Measurements of Anterior Soft Tissue Thickness to Predict Difficult Laryngoscopy in Pregnant Patients
Objective:
Obstetric patient airway management is becoming important, because of anatomical and physiological changes in the airway related to the pregnancy. The aim of our study was to compare the ultrasound (USG) measurements of 5 different levels of anterior neck soft tissue and other clinical screening tests for determination of difficult laryngoscopy in patients who underwent cesarean section operation with general anesthesia.
Materials and Methods:
Prospective, observational study included 140 pregnant women (18-45 years old, ASA I-II). Mallampati test, mouth opening, sternomental and thyromental distance, upper lip bite test, and neck circumference were recorded. The distance from the skin to the anterior aspect of the trachea was measured at 5 different levels: hyoid bone (zone 1), tirohyoidmembrane (zone 2), vocal cords (zone 3), thyroid isthmus (zone 4) and suprasternal notch (zone 5). An anaesthesiologist who was unaware of the clinical screening variables and USG results performed the laryngoscopy. According to Cormack and Lehane’s scale, patients were divided into two groups: a grade 1 or 2 was accepted easy laryngoscopy, whereas a grade 3 or 4 was considered difficult laryngoscopy.  

Results: Twenty of 140 patients were excluded from the study (meeting inclusion criteria (n=5), declined to participate (n=9), other reasons (n=5), and loss of USG recordings(n=3) ). 30 patients were classified as having difficult laryngoscopy (25 %). All of the patients were entubated succesfully. Amoung the other clinical screening tests for difficult laryngoscopy: limited mouth opening (<3cm), high Wilson's Risk Score (> 2), large neck circumference (> 40 cm), unable to bite the upper lip, and high mallampati score (III-IV) were found higher in the difficult laryngoscopy group (p<0.05). Also, BURP maneuver, use of gum elastic bougie, high intubation difficulty score (IDS ≥5), 3 more intubation attempts, airway difficulty rate were significantly higher in the difficult laryngoscopy group (p<0.05).
Conclusion(s): We found that high a mallampati score (III-IV), inability to bite the upper lip, limited mouth opening, large neck circumference and high Wilson's Risk Score were useful in preoperative bedside tests to determine difficult laryngoscopy. We believe that the use of BURP maneuver and gum elastic bougie will increase the success rate of endotracheal intubation. In our study, we did not find a statistically significant relationship between difficult laryngoscopy and the distance from the skin to the anterior surface of the trachea when measured with USG. We found that USG measurement of the anterior neck soft tissue has no effective benefit for predicting difficult laryngoscopy in pregnant patients.

Ultrasound measurements of anterior soft tissue thickness to predict difficult laryngoscopy in pregnant patients