Three-dimensional Reconstruction of the Spatial Distribution of Anaesthetic during Locoregional Anaesthesia

Background and aim of the study Ultrasound guided anaesthesia is nowadays a de facto standard for performing locoregional anaesthesia. However, in the clinical pratice, 2D ultrasound is commonly used [1,2], while only a few experiences describe the use of multiplanar imaging obtained with 3D devices [3]. Despite its limited clinical application, multiplanar imaging has been reported as a major improvement with respect to conventional ultrasound, as it eases the visualization of the correct positioning of the needle with respect to major vessel and nerves, thus reducing the incidence of errors, in particular of intrafascicular, intravascular and pleural injections. In this case report, the visualization of a volumetric reconstruction of the position of the needle and the distribution of the anaesthetic with respect to the target nerve, using a three-dimensional rendering of the acquired volume is described. Case Description The present experience concerns a 21 years, male ASA I patient who underwent axillary block that was performed for a scheduled upper arm surgery, after giving his informed consent. The block was performed with a combined of electrical stimulation and ultrasound guidance technique. After elicitation of the motor nerve response, we administered 5 ml of local anesthetic at a rate of 600 ml per hour. After the execution of the block, a 30 MyLab Gold (Esaote) with the LA523 linear transducer (7.5 MHz frequency) was used to record a movie, while the probe was slid along the axillary artery in the cranio-caudal direction for 5 cm. The film was elaborated to visualize the volumetric reconstruction of the distribution of the anesthetic with respect to the target nerve, using a tridimensional rendering of the acquired volume. In the present stage, the reconstruction of the volume occurs as an offline procedure. A semi-automated segmentation allows defining the regions corresponding to the nerve and the anaesthetic. The two regions are, at the moment, fed to a visualization program (MicroView, by GE Healthcare) which performs the actual rendering of the image. The outcome of the segmentation and reconstruction procedure is shown in Fig. 1. Discussion The image allows an easy visualization of the spatial distribution of the drug around the nerve, as the length of nerve exposed to anaesthetic has large impact on the treatment outcome [4]. Thus, we expect a possible optimization of the dose of the anaesthetic to be administered, with benefits for the patient (reduction of collateral effects, shortening of the procedure). Moreover, the 3D representation clearly shows the anatomic peculiarities (presence of septa, relative placement of vessels and nerves) which sometimes make the drug distribution unpredictable, with reduced efficacy of the block.