Prone, Lateral, and Flexed: Patient Positioning for Percutaneous Nephrolithotomy

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Prone, Lateral, and Flexed: Patient Positioning for Percutaneous Nephrolithotomy

Robert J. Sowerby,¹ A. Andrew Ray,² & R. John D’A. Honey³

¹ Division of Urology, Mackenzie Health Hospital, Vaughan, ON, Canada

² University of Toronto, Royal Victoria Regional Hospital, Barrie, ON, Canada

³ Department of Surgery, University of Toronto, Toronto, ON, Canada

Introduction

Positioning for percutaneous nephrolithotomy (PCNL) is an important, yet often neglected, aspect of the procedure. Operators invariably become wedded to one position, yet with knowledge and experience of other positions there is the freedom to choose the most appropriate technique for the case at hand. Since the introduction of percutaneous renal surgery for stone disease by Fernstrom and Johansson in 1976 [1] there has been a proliferation of case series addressing various modifications to patient positioning, including the lateral decubitus [2–4], modified lateral [5], reverse lithotomy [6], split‐leg [7–9], and supine [10] positions. However, most of these have not gained widespread acceptance other than prone and, to a lesser extent, the supine positions. Today, PCNL is usually performed with the patient in the prone position. A recent survey of Endourological Society members found that 86% of respondents used the prone position, 10% supine, and 4% lateral decubitus [11]. We have previously described a prone‐flexed modification that confers several advantages over the conventional prone technique [12].

In this chapter, we review in detail both the conventional prone technique as well as our prone‐flexed modification. Additionally, we describe the lateral technique and our lateral‐flexed modification technique, which we find particularly useful in morbidly obese patients and those with severe kyphoscoliosis. We have also attempted to provide an anatomic explanation for the known complications associated with PCNL, including the rare complications related to patient positioning, and how attention to patient positioning can mitigate these issues. Finally, we also provide an overview of the literature comparing prone to supine PCNL.

Prone and prone‐flexed positions

Due to the retroperitoneal location of the kidneys and their proximity to the flank, PCNL is most commonly performed in the prone position with straightforward access to the collecting system [11]. However, when the procedure was being developed in the early 1980s, direct calyceal puncture was not thought to be important, provided that puncture was along the avascular line of Brödel. It has since been recognized that puncture directly into a calyx provides the safest access for stone removal [13, 14]. At present, the majority of PCNLs are performed with the patient prone and access is obtained through a posterior or posterolateral calyx. This position confers numerous advantages, with the main disadvantages being the time required for patient repositioning and anesthetic concerns in the morbidly obese (Table 12.1). We have previously shown that the prone‐flexed position, a simple modification to conventional prone positioning, has several additional advantages [12] and can be implemented on most operating room (OR) tables that permit fluoroscopy. Some OR tables may have to be reversed in order to produce adequate space for the C‐arm image intensifier. This space is increased significantly by flexion of the table during prone‐flexed PCNL.

Table 12.1 Patient repositioning to and from prone adds to OR time.

	Technique	Advantages	Disadvantages
Prone	Patient is prone with a padded bolster under the upper thorax to facilitate ventilation	Large field with wide choice of calyces for access Easy end‐on access to the posterior calyces Easiest access to upper pole Wide space for instrument manipulation Renal pelvis is dependent with easier access to mobile stones Optimal position for fluoroscopically guided access (bullseye or triangulation) Minimal interference from the OR table	Patient repositioning from prone adds to OR time May have difficulty with ventilation in obese patients Risk of respiratory or cardiovascular compromise Theoretical risk of ocular complications
Prone‐flexed	Patient is prone, with a padded bolster under the upper thorax to facilitate ventilation Flexed at the waist 30–40° Knees are flexed 15–20°	Similar advantages to prone position Further increased working space Flattening the lumbar lordosis decreases instrument conflicts with buttock May convert supra‐11th to supra‐12th or supra‐12th to infracostal access by displacing the kidneys caudally Reduces skin to stone distance Reduces chance of spleen or liver injury	Similar disadvantages to prone position Extra padding needed due to head‐down position May increase airway pressures
Prone split‐leg	Patient prone, with the genitalia at the bottom of the OR table Legs on padded adaptors and abducted up to 45°	Similar advantages to prone position May perform ureteroscopy without patient repositioning or fear of contaminating instruments Allows endoscopic‐guided access	Similar disadvantages to prone position Patient is further down the OR table, away from the anesthesiologist May be difficult to demonstrate posterior calyces especially with dilated calyces May require endoscopic‐guided access

Percutaneous lithotomy in the prone and prone‐flexed positions (see Video 12.1)

Retrograde pyelogram and choice of calyx

To perform fluoroscopically guided access, a high‐quality retrograde pyelogram is essential. Consequently, we begin all procedures with the patient positioned supine. Once the patient has been intubated under general anesthesia, and the genitalia prepped with providone‐iodine, flexible cystoscopy is performed. In men, this is performed with the patient supine, while the frog‐leg position is useful in women. A 5 Fr Flextip (Cook Medical) ureteral catheter with a terminal side hole, which facilitates aspiration, is passed into the collecting system. Urine is completely aspirated and replaced with radiographic contrast to identify all calyces. Urine is less dense than contrast and, as a result, any urine left within the collecting system will tend to collect at the highest point within the kidney and float on top of the contrast. This property can be helpful to the surgeon when distinguishing anterior and posterior calyces. In the supine position, posterior calyces are identified by the presence of denser contrast within them, while anterior calyces appear paler due to the mixture of contrast with urine. Conversely, when the patient is repositioned prone, posterior calyces often appear paler. If too much pure urine without contrast is present, these calyces may be poorly visualized or even invisible.

A C‐arm image intensifier is used to examine the anatomy of the collecting system and the position of all stones. Four fluoroscopic images are captured: a scout image to identify all calculi, an anteroposterior (AP), and two obliques. These images help create a mental three‐dimensional (3D) picture of the calyceal anatomy, and can be referred to during the procedure. In the anterolateral view, the posterior calyces are viewed from the side and appear longer, whereas in the anteromedial view, they are seen through the central axis of the kidney and are viewed end‐on, appearing shorter (Figure 12.1).

Image described by caption. — **Figure 12.1** 3D model of the lower pole renal collecting system of the right kidney with the patient in supine position. The posterior calyx is dependent, filling with dense contrast. Anterior calyces are paler due to the mixture of contrast with less dense urine. (a) With the C‐arm rotated 30° toward the left side of the patient, the posterior calyx is viewed end‐on and appears shorter. (b) Anteroposterior (AP) view. (c) With the C‐arm rotated 30° toward the right side of the patient, the posterior calyx is viewed from the side and appears longer.

Reproduced with permission of Mary Ann Liebert, Inc. Publishers.

A ureteral occlusion balloon (Cook Medical) is then inserted over a guidewire, positioned at the ureteropelvic junction. A three‐way valve is attached and connected to a 10 ml syringe and intravenous tubing leading to a bottle of contrast. This allows aspiration and infusion of additional contrast as needed during the case. Using an occlusion balloon has several benefits. First, the balloon prevents stone fragments from falling into the ureter. Second, the constant pressure of contrast in the renal collecting system ensures a persistent pyelogram, facilitating calyx identification when the patient is repositioned prone. Third, flow of contrast under gravity distends the collecting system, providing a larger target for access. Fourth, free return of contrast out through the needle allows the surgeon to rapidly confirm successful puncture of the chosen calyx. Finally, the occlusion balloon is secured externally to a Foley catheter using a Tegaderm™ (3 M) to allow for easy separation, and wrapped in sterile towels where is exits from the urethra, allowing for sterile insertion of a double J stent on a tether in a retrograde fashion at the end of the procedure.

Renal puncture and dilation of the tract

With a Foley catheter in situ and the ureteral occlusion balloon secured externally, we reposition the patient prone with the assistance of additional staff members. Generous padding is placed under the knees, feet, and chest to prevent pressure injury and to facilitate ventilation (Figure 12.2). The eyes are taped to prevent corneal abrasions and the head is placed in a prone position foam headrest with cut‐out holes for the eyes, nose, and endotracheal tube. We have found that there is no one support that is universally appropriate for all patients, so several options are available at all times. In the prone position there tends to be hyperextension of the cervical spine but with flexion in the prone‐flexed position the head drops forward and reverses this hyperextension. To prevent brachial plexus injury, the arms should be kept below the level of the chest, and are both externally rotated at the shoulder, and flexed at the elbow. Again, generous padding is utilized. Finally, a safety strap is placed across the buttocks.

2 Photos of the configuration of OR table with padding and C‐arm displaying prone position (top) and prone‐flexed position of patient with the OR table flexed to 30–40° (bottom). — **Figure 12.2** Configuration of OR table with padding and C‐arm [96].

Reproduced with permission of John Wiley and Sons.

In the prone position, the natural, anterior lordosis of the spine is exaggerated. This complicates access by compressing the working space and leads to instrument conflicts with the buttocks. To avoid this, the table can be flexed 30–40° at the level of the lower abdomen (Figure 12.2) to open the space between the 12th rib and the posterior iliac crest (Figure 12.3). Flexion of the hips not only increases the working space on the patient’s flank [15], but also may rotate the ribs cephalad, further increasing the working space and, along with caudal displacement of the kidneys in this position, often converting a supracostal to an infracostal access or a supra‐11th rib to a supra‐12th rib access [12]. Wide skin preparation is performed from above the 10th rib to the buttocks and medially from the spinous process to the mid‐axillary line, laterally. We use chlorhexidine‐alcohol as it was shown to be superior to povidone‐iodine at preventing surgical site infections in the perioperative period in a multicenter randomized controlled trial (RCT) [16]. Due to the copious amount of irrigation necessary for PCNL, we use an adhesive neurosurgical drape with a drainage pouch connected to suction to direct fluid away from the patient. Only normal saline irrigation is used unless electrocautery is required, when it is changed to a non‐electrolyte solution. To prevent hypothermia, all irrigation fluid is heated to 42 °C in a warming cabinet.

Bullseye technique

The C‐arm is draped and used to identify the previously chosen posterior or posterior‐lateral calyx. Due to the change to the prone position, the posterior calyces are now less dense as the heavier contrast flows anteriorly (Figure 12.4). We favor a conventional bullseye technique for performing renal puncture in the prone position; however, a triangulation technique can also be used. Both methods are described in this chapter. Prone and prone‐flexed positioning allows maximal excursion of the C‐arm around the OR table, giving the widest possible unobstructed imaging windows. Flexing the table in the prone‐flexed position significantly increases the space below the table to allow movement of the C‐arm. In the prone position, the posterior calyces move in the opposite direction to the image intensifier of the C‐arm (Figure 12.4). With the C‐arm rotated 30° from the vertical, towards the operator, the posterior calyces move away, and shorten as one looks down the axis of the infundibulum. Using the bullseye technique, in this position, the calyx of choice is viewed end‐on. We use an 18G Trocar needle to puncture the calyx in the center of the papilla. This needle lacks a beveled edge and, as such, resists deflection away from the axis of puncture. The needle is inserted and advanced along the line of the X‐ray beam. To assess the depth of the needle, the C‐arm is periodically rotated away from the operator (Figure 12.4). To minimize radiation exposure to the surgeon’s hands, the needle can be held in a long Kelly forceps, aligned with the calyx under fluoroscopy, and advanced during expiration without fluoroscopy. Once the calyx is entered, and a free flow of contrast obtained, an Amplatz extra‐stiff or super‐stiff guidewire is passed down the needle into the collecting system.

Due to the presence of the occlusion balloon, we do not attempt to pass the guidewire down the ureter, although this may occur. A small depth‐gauge ring on the needle is adjusted to skin level to mark the depth between the skin and the collecting system. Knowledge of this measurement reduces radiation exposure during insertion of the fascial dilators and nephrostomy tract dilating balloon. Fascial dilators (6, 8, and 10 F) are used to dilate the tract and then a safety guidewire can be inserted using a 10 Fr dual‐lumen catheter (Cook Medical). The tract is then further dilated to 30 Fr with a nephrostomy tract dilating balloon (Cook Medical) over which a 34 Fr Amplatz sheath with a 30 Fr inner diameter is passed. Although different methods of tract dilation exist, including balloons, Amplatz serial dilators, and the Alken telescopic dilator among others, we favor balloon dilation. We have found this to be both quick and atraumatic, although this comes at increased cost.

Adjuncts to assist with patient positioning

The prone‐flexed modification can add several advantages to the operating surgeon without any impediment to C‐arm movement. Adopting this position on an OR table without a flex option is still possible through the use of bolsters. The “Montreal mattress” is a preshaped surgical bolster that can be used as an adjunct for the support of prone patients [17]. The advantage of this device is the central cavity which allows for free movement of the abdomen. Theoretically, this should lessen respiratory compromise and minimize cardiovascular effects such as inferior vena cava obstruction. Another option is the radiolucent Wilson frame, an adjunct used by spinal surgeons to mimic the prone‐flexed position on a standard OR table. Its advantages include the ability to control the degree of flexion required as well as to use adjustable contour pads that allow for free excursion of the abdomen, preventing respiratory compromise. The main limitation to its use is the reduction in depth, preventing C‐arm movement, instrument manipulation, the working space within the C‐arm, and a reduction in magnification.

Advantages and disadvantages of the prone and prone‐flexed positions

As mentioned, the majority of PCNLs are still carried out with the patient in the prone position, with prior retrograde placement of a ureteral catheter or occlusion balloon under fluoroscopic control. This initial procedure can be performed with the patient either supine or prone. If performed while the patient is supine, it is necessary to position and drape the patient twice, prolonging OR time [18, 19]. By commencing the procedure with the patient in the prone position immediately following induction of general anesthesia, the patient will still require repositioning, but is draped only once [17]. A split‐leg modification can facilitate access to the external genitalia, for simultaneous antegrade and retrograde approaches [7, 8, 20]. In the prone position it may be difficult to access the anteriorly displaced ureteric orifices for the retrograde study, but with practice this can become routine. Additionally, if the procedure is started in the prone position, identification of the posterior calyces, especially in obstructed systems, may be difficult, or impossible. The presence of pure urine within the collecting system, especially if dilated, may result in urine floating on top of the denser contrast and render them invisible. For this reason, it is our preference to begin the procedure with the patient supine where the dense contrast sinks down into the posterior calyces.

Prone positioning for PCNL allows access to the entire flank, with a wide choice of access sites, especially when multiple accesses are required. Although still possible in the supine position, upper pole access is significantly easier when the patient is prone. An upper pole puncture has many advantages, including the ability to work down the renal axis, with minimal torque, as the more mobile lower pole rotates to align with the nephroscope. This reduces the chance of renal parenchymal shear and bleeding. Selection of an upper pole calyx is indicated in obese patients, as the upper pole is closer to the posterior abdominal wall than the lower pole. It is also indicated in patients with staghorn calculi, or stones in a horseshoe kidney, and facilitates access to multiple lower pole calyces with a single tract. In contrast, from the lower pole, visualization of the upper calyces with a rigid nephroscope is rarely possible. Finally, dilation into the upper pole is easier due to more adherent attachments to Gerota’s fascia limiting renal mobility, whereas the more mobile lower pole may move away from the operator during dilation and kink the guidewire. Despite these advantages, many authors still prefer a lower pole puncture with the reassurance that this approach will avoid thoracic complications. In our series, with a supracostal puncture, pleural complications occurred in 2.6% of patients [15].

The prone‐flexed modification that we describe provides several additional advantages over the traditional technique. First, and most obviously, the working space is further increased as the flank is significantly flattened, eliminating interference from the buttock during rigid nephroscopy through a lower pole tract (Figure 12.2) [12]. In addition, we have also shown that when in this position, the spleen is displaced medially and the kidneys are displaced inferiorly in the retroperitoneum [12]. This effect is most pronounced with the left kidney, which is lower than the right kidney in greater than 90% of cases. Also, due to this modification, with this displacement, a supra‐11th rib access may be converted to a supra‐12th rib, or a supra‐12th to an infracostal access. Finally, the flank is significantly flattened, eliminating interference from the buttock during rigid nephroscopy through a lower pole tract [10].

Lateral and lateral‐flexed positions

Although the prone‐flexed position for PCNL can be used for the obese patient, the lateral position has multiple advantages in these patients, and is sometimes the only feasible position for the morbidly obese patient with a body mass index (BMI) in excess of 50 kg/m² who cannot be ventilated prone or those with skeletal deformities, especially severe kyphoscoliosis. This position allows the protuberant abdomen and pannus to fall medially, taking the weight off the anterior abdominal wall as occurs when the patient is supine (Figure 12.5). This maximizes diaphragmatic excursion and facilitates general anesthesia. The pannus can also be supported separately if required.

The lateral‐flexed position is familiar to any urologist who performs open and laparoscopic renal surgery. This position significantly widens the space between the 12th rib and the iliac crest, flattening the folds of adipose tissue and facilitating percutaneous access (Figure 12.6). The increased distance between the 12th rib and iliac crest, produced by this flexion, is even more pronounced than the increase produced by flexion with the patient prone. This also elevates the thoracic cage in relation to the kidney on that side and reduces the need for supracostal access. Also, in this position, the relative lack of adipose tissue over the costovertebral angle is frequently surprising in these morbidly obese patients and, provided the upper pole calyx is chosen for access, it is frequently possible to use a standard‐length Amplatz sheath and nephroscope.

One disadvantage to flank positioning is that percutaneous access usually requires either ultrasound guidance or use of triangulation when using the C‐arm image intensifier, as opposed to the standard bullseye technique. This is partly because of the restricted arc of rotation of most C‐arms, but also because the metal side rails of most radiolucent tables prevent adequate visualization of the collecting system when the C‐arm is rotated to an exaggerated position. A randomized study comparing access using ultrasound in the lateral‐flexed position to fluoroscopy in the prone position achieved successful access in all cases (n = 60) with no difference in intraoperative bleeding but took longer (14.5 vs. 9.4 minutes for prone with fluoroscopy) [4]. Advantages of the lateral and lateral‐flexed positions are outlined in Table 12.2.

Table 12.2 Options for lateral patient positioning.

	Technique	Advantages	Disadvantages
Lateral	Patient in lateral decubitus with no break in the OR table	Familiar to urologists who perform open renal surgery Compared with prone, easier patient repositioning from supine Easiest identification of the posterior calyces Useful in morbid obesity or severe kyphoscoliosis Least effect on cardiac and respiratory function May be performed under epidural or local anesthesia alone Renal pelvis is dependent with easier access to mobile stones More ergonomic for the surgeon than prone position May perform nephroscopy and ureteroscopy simultaneously	Patient repositioning is required Fluoroscopy is technically limited necessitating triangulation or ultrasound‐guided access
Lateral‐flexed	Patient in lateral decubitus with 30–40° break in the OR table	Similar advantages to lateral position Significantly increased working space Reduces flank fat in morbidly obese patients May elevate the lower ribs, reducing the need for supracostal access	Similar disadvantages to lateral position
Modified lateral “Barts technique”	Patient in lithotomy with ipsilateral pelvis elevated 45° Shoulders rotated to be perpendicular to the OR table Ipsilateral leg is flexed and adducted, contralateral leg is fully abducted	May perform nephroscopy and ureteroscopy without patient repositioning Fewer cardiovascular and respiratory effects than prone Improved access to flank compared to supine	Requires significant patient mobility Not suitable for patients with musculoskeletal deformities Fluoroscopy is technically limited, as with lateral

PCNL in the lateral and lateral‐flexed positions (see Video 12.2)

As with prone or prone‐flexed PCNL, the procedure begins with a retrograde pyelogram and insertion of a ureteral occlusion balloon. This is performed with the patient supine in order to choose the most appropriate calyx, as described earlier (Figure 12.7). In the lateral‐flexed position the arms and legs are positioned as for open or laparoscopic renal surgery, and the patient is secured to the table with padded straps or tape over the upper chest and pelvis (Figure 12.5). An axillary roll or padded wedge with a groove to accommodate the dependent arm must be positioned to adequately support the chest and prevent positioning‐related injury. Extra padding must also be placed under the dependent knee and ankle to prevent pressure‐related complications.

The concept of triangulation is illustrated in Figures 12.8 and 12.9. With the C‐arm in the AP configuration, it is possible to determine the cephalad–caudal axis direction for puncture. Oblique views are then similarly used to determine the AP direction of puncture. In this view, dropping the hand holding the needle to direct the needle laterally toward the anteroaxillary line will target the more anterior part of the kidney. Elevating the hand holding the needle will direct the needle toward the spine and will aim it toward the more posterior part of the kidney.

With the patient in the lateral position and the C‐arm image intensifier placed on the abdominal side of the patient, the pelvicalyceal system is initially viewed in the AP position from above. The previously chosen calyx can be identified facing posteriorly towards the operator (Figure 12.10

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