Scalenus anterior thickening: A novel predictor for mechanical ventilation weaning. A prospective observational study.

Objectives: To evaluate the feasibility and reproducibility of the scalenus anterior thickening fraction and its diagnostic accuracy to predict weaning outcomes.

Design: Prospective observational study conducted as 2 sub-studies: sub-study A, which included healthy volunteers, and sub-study B, which included critically ill patients undergoing mechanical ventilation weaning.

Setting: Single-center study conducted at a tertiary center over 6 months.

Participants: Twenty-one healthy volunteers were included in sub-study A, whereas sub-study B included 66 critically ill patients undergoing weaning from mechanical ventilation.

Interventions: A high-frequency linear transducer was placed horizontally at the level of the cricoid cartilage with the neck rotated to the opposite side; at this point, the scalenus anterior muscle can be visualized clearly. The M mode was then switched on in the middle of the muscle with the sweep speed adjusted to a minimum to allow multiple breaths to be obtained on the same screen. Inspiratory and expiratory thickness was measured as an average of 3 breaths; subsequently, the thickening fraction was calculated as (inspiratory thickness - expiratory thickness)/expiratory thickness and expressed as a percentage.

Main variables of interest: Accuracy of the scalenus anterior thickening fraction to predict failed weaning.

Results: Scalenus anterior thickening has good intra- and inter-observer reliability with interclass correlation coefficients of 0.79 and 0.8 for inspiratory and expiratory muscles, respectively. It also showed good accuracy in predicting failed spontaneous breathing trials with an area under the curve (95% confidence interval) of 0.92 (0.82-1) and 0.94 (0.84-0.98) for the right and left sides, respectively. Additionally, scalenus anterior thickening fraction could predict reintubation with an area under the curve of 1.00 (0.93-1.00) and 0.99 (0.91-1.00).

Conclusion: Scalenus anterior examination is a feasible tool with good interobserver reliability. The scalenus anterior thickening fraction could accurately predict weaning outcomes.