**10. Importance of optimal in‐line positioning of ultrasound image monitor for accurate and quick nerve block**

Although ultrasound guidance for providing regional anesthesia has great potential, as described above, it is not easy to perform for novice practitioners. When using ultrasound, the operator is required to mentally restructure two‐dimensional images presented on a display into the three‐dimensional relationship of the target with the needle. This spatial conversion represents a major hurdle for precise performance of an ultrasound‐guided pro‐ cedure. It has been shown that an ergonomic layout of the equipment utilized with the patient that allows the operator's gaze to run in a straight line from the puncture site to the ultrasound image display along the direction of needle insertion is important for accurate and quick spatial recognition of the needle position [28]. However, since the operating room can become crowded with numerous medical devices, the ultrasound machine is sometimes positioned out of the line of sight of the puncture field, which disturbs spatial recognition of the needle position for the operator, increasing the difficulty of the procedure. Based on these considerations, we speculated that the position of the ultrasound image display in relation to the operator is a vital factor for achieving success with ultrasound‐guided procedures.

Imaging technology has progressed significantly in recent years and modern devices are widely used in the medical field. In particular, digital tablets, such as the iPad and iPad Mini (Apple Japan LLC, Tokyo, Japan), are gaining use as viewers for X‐ray and 3‐dimensional images during surgical procedures. These small lightweight displays can be easily placed in nearly any position by the operator and may be ideal for use during ultrasound‐guided procedures.

**Figure 16.** Ultrasound probe positioning and ultrasound images obtained during performance of caudal block.

42 Current Topics in Anesthesiology

To verify the importance of image position in ultrasound guided procedures, we developed a system for wireless real‐time transfer of images vfrom an ultrasound image display consist‐ ing of a wireless video transmitter (VT‐100; Scalar Co., Tokyo, Japan) and an iPad Mini. The VT‐100, a battery‐operated, ultra‐compact, and lightweight portable transmitter (approxi‐ mately 290 g, including batteries) can simultaneously send video images from a single iPad Mini to other multiple iPads by Wi‐Fi with a short delay of 0.067 s. However, the resolution of transferred images is somewhat low at 320 × 240 dots per inch (dpi), with a frame rate of more than 15 frames per second (fps). Thus, we have made fine adjustments to the image quality to allow the VT‐100 to be suitable for ultrasound image transmission. The modified VT‐100 is connected to an ultrasound machine (ProSound Alpha 7; Hitachi‐Aloka Medical Ltd., Tokyo, Japan) via a video cable and ultrasound images are transferred to a single iPad Mini via Wi‐Fi (**Figure 18**). Dedicated software (AirMicro; Scalar Co.) is installed on the iPad Mini for view‐ ing images. Furthermore, the iPad Mini is attached to a special flexible arm with a holder for easy positioning in the area around the operating table.

**Figure 18.** iPad Mini (Apple Japan LLC, Tokyo, Japan), VT‐100 wireless video transmitter encircled in red (Scalar Co., Tokyo, Japan), and ProSound Alpha 7 ultrasound equipment (Hitachi‐Aloka Medical Ltd., Tokyo, Japan). With our method, ultrasound image signals from the ProSound Alpha 7 are transmitted by a conventional coaxial video cable to the VT‐100, then sent wirelessly to the iPad Mini by Wi‐Fi without any image reproduction delay.

We investigated success rate and time required for ultrasound‐guided radial artery cath‐ eterization performed by novice residents when using this system in two image positions (**Figure 19**). The operators were asked to insert a catheter into the radial artery using a short‐ axis out‐of‐plane approach with a crossover method (**Figure 20**) with use of either the ultra‐ sound machine placed at the head side of the patient across the targeted forearm (conventional method, *n* = 20) or the iPad ultrasound imaging transmission system (iPad Mini + VT‐100 method, *n* = 20). When the latter was employed, the iPad was positioned so that the ultrasound images were viewed above the forearm in alignment with the operator's eyes and direction of needle puncture.

To verify the importance of image position in ultrasound guided procedures, we developed a system for wireless real‐time transfer of images vfrom an ultrasound image display consist‐ ing of a wireless video transmitter (VT‐100; Scalar Co., Tokyo, Japan) and an iPad Mini. The VT‐100, a battery‐operated, ultra‐compact, and lightweight portable transmitter (approxi‐ mately 290 g, including batteries) can simultaneously send video images from a single iPad Mini to other multiple iPads by Wi‐Fi with a short delay of 0.067 s. However, the resolution of transferred images is somewhat low at 320 × 240 dots per inch (dpi), with a frame rate of more than 15 frames per second (fps). Thus, we have made fine adjustments to the image quality to allow the VT‐100 to be suitable for ultrasound image transmission. The modified VT‐100 is connected to an ultrasound machine (ProSound Alpha 7; Hitachi‐Aloka Medical Ltd., Tokyo, Japan) via a video cable and ultrasound images are transferred to a single iPad Mini via Wi‐Fi (**Figure 18**). Dedicated software (AirMicro; Scalar Co.) is installed on the iPad Mini for view‐ ing images. Furthermore, the iPad Mini is attached to a special flexible arm with a holder for

We investigated success rate and time required for ultrasound‐guided radial artery cath‐ eterization performed by novice residents when using this system in two image positions (**Figure 19**). The operators were asked to insert a catheter into the radial artery using a short‐ axis out‐of‐plane approach with a crossover method (**Figure 20**) with use of either the ultra‐ sound machine placed at the head side of the patient across the targeted forearm (conventional method, *n* = 20) or the iPad ultrasound imaging transmission system (iPad Mini + VT‐100 method, *n* = 20). When the latter was employed, the iPad was positioned so that the ultrasound images were viewed above the forearm in alignment with the operator's eyes and direction of

the VT‐100, then sent wirelessly to the iPad Mini by Wi‐Fi without any image reproduction delay.

**Figure 18.** iPad Mini (Apple Japan LLC, Tokyo, Japan), VT‐100 wireless video transmitter encircled in red (Scalar Co., Tokyo, Japan), and ProSound Alpha 7 ultrasound equipment (Hitachi‐Aloka Medical Ltd., Tokyo, Japan). With our method, ultrasound image signals from the ProSound Alpha 7 are transmitted by a conventional coaxial video cable to

easy positioning in the area around the operating table.

44 Current Topics in Anesthesiology

needle puncture.

**Figure 19.** Positional relationships with conventional method and iPad Mini with VT100 method. With the conventional method, the ultrasound machine (ProSound Alpha 7) is placed at the head side of the patient and the puncture operator stands on the caudal side, with the patient forearm between them. With the iPad Mini with VT100 method, the axis running from the eye of the operator to the puncture needle and ultrasound image displayed on the iPad Mini are aligned as closely as possible along a straight line.

**Figure 20.** Representative series of four ultrasound images obtained during insertion of a radial artery catheter. A:before catheter insersion, B and C :during catheter insertion, D:completion of catheter insertion

We found that the success rate was significantly higher (100 vs. 70%, *p* < 0.02) and catheteriza‐ tion time significantly shorter (28.5 ± 7.5 vs. 68.2 ± 14.3 s, *p* < 0.001) with the iPad system (iPad Mini + VT‐100 method) as compared to the ultrasound machine alone (conventional method). These results indicated that alignment of the visual axis of the operator, ultrasound images, and direction of needle puncture increased success rate and also reduced procedure time when performing ultrasound‐guided catheterization (**Figure 21**).

**Figure 21.** An ergonomic in‐line arrangement of the image display, direction of needle insertion, and visual axis of the operator is crucial for successful and quick completion of ultrasound‐guided procedures.

The position of the ultrasound image display is sometimes overlooked. However, we have found it to be a key point for successful and easy completion of ultrasound‐guided proce‐ dures, especially when performed by practitioners with a low level of experience. For this purpose, our iPad system may be effective. In addition, it allows the ultrasound machine to be placed behind the operator, with only the display in front of their face, thus enabling a nerve block to be performed with overhand movements (**Figure 22**).

**Figure 22.** As shown in this representative image, the ultrasound machine is positioned behind the operator, who performs a paravertebral nerve block procedure on a prone patient while observing ultrasound images on an iPad.
