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Ultrasound Measurement of the Subglottic Diameter in Pregnant Women
Abstract Number: S 34
Abstract Type: Original Research
Background: It is well established that physiological changes of pregnancy can lead to upper airway edema in parturients (1). It has been demonstrated that the Mallampati score changes throughout pregnancy and labor (2). However, in adults, the narrowest portion of the upper airway is at the level of the cricoid cartilage which guides the selection of endotracheal tube size. It has been shown that ultrasound is a feasible technology to reliably measure the subglottic diameter when compared to the gold standard of MRI (3). This study examines the dynamic changes of the subglottic diameter throughout pregnancy using ultrasonography.
Methods: We enrolled 53 gravid volunteers to have a tracheal ultrasound done at the following stages of pregnancy: second trimester, during labor, and after delivery of the placenta. The transverse width of the air column was measured at the level of the cricoid cartilage by a single operator.
Results: The average tracheal diameter measured during the second trimester was 1.17 cm (±0.11). With 40 subjects, the power is 80% to detect a clinically significant difference of 0.05 cm using a two-sided Wilcoxon test.
Conclusion: As of February 1, 2013 one-third of the subjects have delivered. This study is still in progress and it is premature to make any statistically significant conclusions.
1. Braveman FR et al. Anesthetics in Obstetrics in Clinical Anesthesia, 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009. p 1138-39.
2. Pilkington S et al. Increase in Mallampati score during pregnancy. Br J Anaesth 1995; 74(6): 638-42.
3. Lakhal K et al. The feasibility of Ultrasound to Assess Subglottic Diameter. Anesthesia and Analgesia 2007; 104(3): 611-14.