16 Mahesh R. Desai & Arvind P. Ganpule Muljibhai Patel Urological Hospital, Nadiad, Gujarat, India Percutaneous renal access can be achieved with either ultrasound or fluoroscopy guidance. The method of choice depends on training and personal preference. The side effects of extensive radiation during therapeutic procedures are wellknown, which is the main drawback of fluoroscopy [1]. Ultrasound has several strengths as an interventional tool. It is readily available, relatively inexpensive, and portable. It emitsno radiation and provides guidance for access in multiple, transverse, longitudinal, and oblique planes. Its greatest advantage is use for real‐time monitoring of the needle tip, which guides proper placement of the needle and avoidance of important viscera. An added advantage is that it can be used in conjunction with Doppler to avoid important vascular structures lying along the needle path. Percutaneous ultrasound‐guided access is the simplest and most direct technique to drain a hydronephrotic collecting system. It is most often utilized to place a temporary urinary diversion because of an obstructing stone or pyonephrosis. It has also been used successfully to relieve upper tract obstruction secondary to malignancy. Ultrasound‐guided nephrostomy puncture is preferred for patients in whom retrograde ureteral access is unsuccessful. It is also a method of choice in pregnancy when there is a need for deobstruction. Allergies to topical or injectable local anesthetic and coagulopathy are the only relative contraindications to ultrasound‐guided renal access [2]. The ultrasound‐guided approach has proven to be safe and efficacious in the pediatric population [3], for renal stones in transplanted kidneys [4], and in pelvic renal ectopia [5]. Contemporary issues regarding ultrasound as a method to guide access are: In this chapter, we discuss these issues in light of the existing literature. We also describe our technique of achieving percutaneous renal access with ultrasound. The “transducer,” or “scanning probe” as it is known, is the most important and expensive component of the ultrasound machine. The transducer emits ultrasound pulses and receive echoes during scanning. Ultrasound access requires a dedicated transducer with an ultrasound frequency ranging from 3.5 to 5.0 MHz. The monitor used for intervention should ideally be equipped with an electronic dotted line which shows the needle path. The needle guide that is attached to the ultrasound transducer helps preventdisplacement of the needle from its proper trajectory. The scans from these probes are fan shaped. These scanners can be used when the space for scanning is narrow as they show a very small acoustic window, and are primarily used in gynecologic and cardiac ultrasound. They can be useful when performing nephrostomies in the pediatric age group. These probes produce rectangular scans and are most commonly used for gaining percutaneous renal access. These probes are most commonly used for scanning the breast and thyroid.The ideal transducer for renal access is a convex transducer of 3.5 MHz, focused at 7–9 cm. If such a transducer is not available, then either a linear or sector transducer of 3.5 MHz is necessary. If children or thin patients are to be scanned, then a 5 MHz smaller transducer with a focus at 5–7 cm is required. Alternatively, a sector probe can be used in this situation (Figure 16.1). Figure 16.1 Smaller probes help in gaining access in children. The puncture guide attachment helps direct the needle. Using an 18G needle to access the renal collecting system helps with the introduction of a 0.035 or 0.038 inch guidewire into the collecting system. When ultrasound‐guided access is to be achieved, the rigidity of the 18G needle compared to the 21G needle is advantageous for accurately directing the needle tip as it is advanced through the fascial planes. The 18G needle tip is also readily identifiable with realtime ultrasonography guidance. Although routine needles can be used for this purpose, the echo tip needle (Cook Medical, Bloomington, IN, USA) is helpful in achieving ultrasound‐guided access; the needle tip is scored and this increases the reflectivity and visualization on ultrasound. The needles are available in three or two parts (Figure 16.2). The three‐part needle is useful for instilling contrast after ultrasound‐guided puncture as the needle does not need to be removed from the puncture guide. Another variant of the needle has a Teflon sheath which allows instillation of contrast and a guidewire. Figure 16.2 (a) Three‐ and (b) two‐part needle. Before starting, it is necessary to visually check which side of the transducer produces which side of the image. Although most of the times there is an indicator on the ultrasound probe for orientation, this is best done by placing a finger at one end of the transducer and seeing where it appears on the screen; if the orientation is incorrect, the transducer should be rotated through 180°. On a renal scan the liver or spleen helps in orienting the upper pole. The machine should be calibrated properly before use and in such a way that there is a black background with white echoes [6]. Clear visibility of the needle is key to the success of ultrasound‐guided needle access (Figure 16.3). The most common reason for nonvisualization of the needle tip is nonalignment of the needle tip and transducer. This can be achieved by proper alignment. Although alignment is challenging when done freehand, it will improve with experience and occasionally a mechanical attachment can be used [7]. Figure 16.3 If the needle is aligned properly, then the shaft of the needle is visualized throughout its course. If the needle is not visualized it may be either off‐center or angled away from the transducer. A “bobbing” or “in–out jiggling” movement of the tissue in the superficial plane helps decide the path of the needle. This movement also helps push the soft tissue away from the needle path and clear visualization of the needle[7].A few other ways in which the needle can be better visualized are by increasing the reflectivity by using large caliber needles, scoring the needle tip (see above), and keeping the bevel of the needle facing upwards. This is the method of choice for ultrasound‐guided access at our center. We use the 3.5/5 MHz probe (Profocus™, B & K Medical, Denmark) with a Doppler attachment. We typically keep one bolster under the patient’s lower chest and the other at the level of the iliac crest. We consider that with the patient in the prone position and bolsters in these positions, the bowels and viscera tend to drop down, thus minimizing the chance of bowel injury.
Percutaneous Nephrolithotomy Access Under Ultrasound
Introduction and indications for ultrasound‐guided renal access
Instrumentation
Types of transducer
Sector probes
Convex probes
Linear array probes
Access needles
Ultrasound technique
Orientation and calibration of the image
Needle visualization
Ultrasound‐guided access with a needle guide
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