Figure 5: Example of measurements performed in transverse spinous process view. Note: (A) At the C4 level, Skin-Muscle Distance (SMD) and Skin-Lamina Distance (SLD) are respectively 2.85 mm and 25.83 mm. (B) At the L4 level, SMD and SLD are 6.60 mm and 27.56 mm. The images were obtained by means of a Sonoscape P50 Ultrasound (Sonoscape Europe s.r.l., Rome, Italy). The O2-O3 mixture was produced by means of a Multiossigen Medical 99IR generator (Multiossigen S.p.A., Gorle, Bergamo, Italy).