|Year : 2015 | Volume
| Issue : 1 | Page : 38-41
Determining the angle and depth of puncture for fluoroscopy-guided percutaneous renal access in the prone position
Gyanendra Sharma, Anshu Sharma
Department of Urology, and Department of Radiology, Chitale Clinic Pvt. Ltd., 165 D Railway Lines, Solapur, Maharashtra, India
|Date of Web Publication||1-Jan-2015|
Dr. Gyanendra Sharma
Chitale Clinic Pvt. Ltd., 165 D Railway Lines, Solapur - 413 001, Maharashtra
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: Optimal renal access is necessary for ensuring a successful and complication-free percutaneous nephrolithotomy. We describe a technique to determine the angle and depth of puncture for fluoroscopy-guided percutaneous renal access in the prone position.
Materials and Methods: Forty-two consecutive patients undergoing percutaneous nephrolithotomy from January 2014 had a fluoroscopy-guided access in the prone position. Using the bull's eye technique, the site of skin puncture and the angle of puncture were determined. These parameters were utilized to calculate, mathematically, the depth of the targeted calyx. These measurements were then utilized for puncture. The actual depth of puncture was then calculated. The number of attempts, time of fluoroscopy and difference between estimated and actual depth were noted and analyzed.
Results and Limitations: There was a difference of 0-3 mm between the estimated and the actual depth at which puncture was made. Single-attempt puncture was possible in >95% cases. No complications related to access were observed.
Conclusion: By estimating the angle and depth of puncture, the percutaneous renal access becomes technically less challenging.
Keywords: Fluoroscopy, learning curve, percutaneous nephrolithotomy, percutaneous renal access
|How to cite this article:|
Sharma G, Sharma A. Determining the angle and depth of puncture for fluoroscopy-guided percutaneous renal access in the prone position. Indian J Urol 2015;31:38-41
|How to cite this URL:|
Sharma G, Sharma A. Determining the angle and depth of puncture for fluoroscopy-guided percutaneous renal access in the prone position. Indian J Urol [serial online] 2015 [cited 2019 Jul 16];31:38-41. Available from: http://www.indianjurol.com/text.asp?2015/31/1/38/145291
| Introduction|| |
Optimal renal access is necessary for ensuring a successful and complication-free percutaneous nephrolithotomy. Antegrade fluoroscopy-guided percutaneous renal access in the prone position is commonly performed using either the bull's eye technique or the triangulation technique.  The correct angle and depth for puncture of the desired calyx is obtained by seeing the position of the tip of the needle and adjusting it using the C arm fluoroscopy in the anteroposterior and vertical direction (in the bull's eye technique) and oblique direction (in the triangulation technique).  If the correct angle and the depth of puncture can be determined initially, the percutaneous renal access would become technically less challenging and would significantly decrease the learning curve. We present our experience of using a simple mathematical principle to determine the angle and depth of puncture in fluoroscopy-guided percutaneous renal access in the prone position.
| Materials and Methods|| |
From January 2014 to April 2014, 42 patients underwent percutaneous nephrolithotomy. Informed consent of the patients for the procedure was taken. All procedures were performed under general anesthesia. The technique of percutaneous renal access was as described below. All cases were performed by a single surgeon (GS). The number of attempts taken, the total time taken and the fluoroscopy screening time taken to achieve access were recorded.
Under general anesthesia, with the patient prone and the C arm in the anteroposterior position, diluted contrast was instilled via the pre-placed ureteric catheter to opacify the collecting system. With the respiration suspended at end expiration by the anesthesiologist, the desired calyx was selected and the skin site corresponding to the target calyx was marked on the back as point A [Figure 1]. The C arm was then rotated 30° towards the surgeon and the 18G diamond tip needle was held over the targeted calyx to get the bull's eye effect. The site on the skin over the targeted calyx is marked here as point B [Figure 1]. The angle that the needle is making with the patient's back is calculated using a protractor, which is positioned in a way that it is parallel to the operating table [Figure 2].
|Figure 1: Point C is the target calyx and point A is the point on the skin corresponding to point C, with the C arm in the anteroposterior position. Point B is the point on the skin surface corresponding to point C, with the C arm rotated 30° toward the surgeon|
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|Figure 2: The angle of puncture being determined using the protractor held parallel to the operating table and the C arm rotated 30° toward the surgeon|
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If we consider the target calyx as point C, we have an imaginary triangle, ∆ ABC [Figure 1], from the skin to the target calyx with the following measurements known to us:
- The distance between points A and B marked on the skin
- 90° angle at A, as the C arm is at 90° in the anteroposterior position.
The angle of the needle at point B determined by the protractor (angle ABC). With this available data, the distance from point B (on the skin surface) to the point C (the target calyx) is calculated using the Law of Sines. This is easily done by the Universal Triangle Solver application on Google play ® (easily downloaded on any smart phone). Herein, if we have two angles and one side of a triangle, then we can calculate the other angle and sides. For example, if the angle ABC i.e the angle at the point B is 65° and the distance AB is 4 cm, and as the angle CAB is always 90° , then, by the Universal Triangle Solver, we have the distance B to C calculated as 9.5 cm, which is the depth of puncture. Thus the depth and angle of puncture are estimated using the bull's eye technique.
The same principle can be applied in the triangulation technique. The C arm is brought to its anteroposterior position. The line of puncture is determined in alignment with the infundibulum from point A. On this line, the point B1 is marked. The distance between A to B1 is equal to the distance between A to B [Figure 3]. From the point B1, access can be obtained using the triangulation technique. The angle of puncture is as determined by the protractor earlier using the bull's eye principle. The depth of puncture is the same as calculated earlier. As the angle of entry is known and the depth is pre-calculated, the needle is advanced with the C arm in the anteroposterior position only (without the need to take it in the oblique position) and the target calyx is punctured. Aspiration of clear fluid confirms a successful puncture. Then, the length of the needle outside the skin is measured and is subtracted from the actual length of the needle to calculate the actual depth at which the puncture was made.
|Figure 3: The distance between point A to point B1 is equal to the distance between point A and point B|
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| Results|| |
A total of 42 patients underwent percutaneous nephrolithotomy, 30 males and 12 females, with age ranging from 10 to 77 years. There were 24 lower pole, 11 mid pole and seven upper pole punctures. The approach was infracostal in 21 patients, above the 12 th rib in 14 patients and above the 11 th rib in seven patients. All the patients underwent a successful renal puncture. No complications were noted even in cases with supracostal access. In 39 patients, access could be obtained with a single attempt, while two attempts were needed in three patients. The fluoroscopy screening time for achieving access was measured from the time point A was marked till successful urine aspiration was performed. This ranged from 20 to 78 s, with an average of 30 s. The time taken for puncture was calculated from the time point A was marked till successful urine aspiration was performed. This ranged from 72 s to 240 s, with a mean of 90 s. The difference between the depth calculated and the actual depth at which the calyx was punctured ranged from 0 to 3 mm. There were no oblique movements of the C arm even in the triangulation technique as the angle of entry was pre-determined.
| Discussion|| |
A properly obtained percutaneous renal access is critical for the success of a percutaneous nephrolithotomy.  A correct access should fulfill the following criteria to guarantee safe access and avoid complications: Access is to be performed from a posterolateral position, through the renal parenchyma, toward the center of the calyx posterolaterally, toward the center of the renal pelvis and without damaging any major blood vessels.  Complex visual and spatial skills are required in performing this task, especially when using a C arm fluoroscopy unit.  Achieving an optimal percutaneous renal access requires that the puncture should be from an appropriate position on the skin, through a correct angle so as to hit the calyx properly. The site of skin puncture is easily determined by the bull's eye technique. With the C arm angled toward the surgeon by 30° from the vertical in the axial plane, the point where the needle tip, its hub and the targeted calyx are in line, seen as a bull's eye effect on the C arm, is the site where the skin should be punctured (point B in [Figure 1]).
Determining the correct point of skin puncture is important in the triangulation technique because a skin puncture that is too medial or lateral to the desired optimum point of entry would result in a tract of variable length and angle of entry in the calyx.  This would interfere with proper access and would hamper the efficient use of the rigid nephroscope. If the angle of entry is not optimum, then it would cause excessive torque on the parenchyma during maneuvering of the nephroscope in the pelvicalyceal system. , Sharma et al. have described the technique of determining the site of skin puncture, which is a hybrid of the bull's eye and triangulation techniques.  The site of skin puncture by the triangulation technique would correspond to point B1 (as in [Figure 3]). The distance from point A to point B1 is equal to the distance between point A and point B. The rationale behind this technique is that, in a circle, the radius remains the same irrespective of the direction in which it is measured from the center of the circle. Here, the targeted calyx is the center of an imaginary circle. Thus, the distance from point A to point B constitutes the length of the radius. Hence, when the site of skin puncture is determined in the triangulation technique, its distance from the targeted calyx should be equal to the radius as calculated by the bull's eye technique. , If the site of skin puncture would be medial or lateral to this point B1, then the angle of entry into the calyx and the length of the tract would not be optimum. 
Once the site of puncture is determined, the next critical step is to access the center of a posterior calyx with the needle directed at an appropriate angle. This step of hitting the calyx at the depth often requires maneuvering the C arm in different directions, either toward the surgeon (in the bull's eye technique) or in an oblique cephalo-caudal direction (for the triangulation technique), and requires understanding a three-dimensional anatomy on a two-dimensional fluoroscopy monitor. It is at this juncture that multiple attempts are needed by the urologists and excessive use of fluoroscopy occurs, especially by a beginner. , Maintenance of needle orientation in one plane while making the adjustment in the other plane is critical for a proper puncture.  This is also the aspect that has the steepest learning curve for a urologist getting trained in percutaneous nephrolithotomy. 
In the technique described by us, we have assumed the target calyx as the center of a sphere. If we have to hit the center of a sphere from the surface, the distance traversed from any point on the surface to the center would be the same. Hence, once we have marked the point B on the skin surface using the bull's eye technique, and then marked the point B1 for the skin entry using the triangulation technique, then the distance from C to B or from C to B1 will be the same, i.e. the radius of the sphere. Also, the angle of entry from B or from B1 toward point C would be nearly the same, with only a minor difference because of the not so perfect flat contours of the body.
Once the angle is determined using the protractor (a very simple non-time consuming step), the depth of puncture can be calculated using the Universal Triangle Solver application from Google play (which can be downloaded free on any smart phone), wherein, by the Law of Sines, if we know the two angles and one side of a triangle then the other two sides can be calculated. Of course, there would be minimal difference in the estimated and the actual depth because of the not so flat contours of the body affecting the measurements. But, this minimal difference would not cause any major hindrance in achieving access by the technique described because the angle of puncture, and thus the trajectory of the needle, would not have much variation. This was seen by us in the present study. The difference between the calculated and the actual depth ranged from 0 to 3 mm. Also, as the angle of entry is known, the fluoroscopy screening time and the time needed to achieve puncture decreases as multiple movements of the C arm are not required. Various access techniques have been described in the literature, but, to the best of our knowledge, very few have described the method to calculate the depth and angle of puncture. Bheri first described the use of principles of trigonometry in calculating the depth of puncture.  He assumed that as the C arm is rotated 30° toward the surgeon, the angle of entry will be 60°. This is not the case as the angle of entry can vary due to the variable orientation of the calyces. Also, he described the technique with only the bull's eye method. Mues et al. used fluoroscopic projections directed at an angle of 30° to the head of the patient for lower pole entries and at 20° toward the opposite side of the surgeon for the middle and upper pole entries.  This technique again used a fixed angle of entry. Li et al.  have described a modified puncture technique using the stereotactic localization system, which used a specially designed goniometer to calculate the depth and achieve puncture. They selected a puncture point with the same distance vertically and horizontally, i.e. at 45° to the skin, as their technique was not effective when the puncture angle was less than 30°. They found that pre-calculating the depth helped in achieving better accuracy of puncture, shorter time and less bleeding. Hatipoglu et al.  have described a monoplanar access technique and shown that decreasing the movements of the C arm decreased the fluoroscopy screening time. The time taken for puncture and the fluoroscopy screening time for the same depend on a number variables of which the surgeon experience is a very important factor. 
The technique described by us is applicable for both the bull's eye and the triangulation methods. It describes the three most important things needed to achieve a successful percutaneous renal puncture: The site of skin entry, the angle of entry and the depth at which the puncture is achieved. It relies on simple tools. There could be some errors that could creep in especially if the protractor is not held parallel to the operating table, but this could be overcome easily with minimal experience (and the assistant telling that the protractor is parallel to the table or not). But, this study also has some limitations. It has been performed by a single surgeon. It has not been compared with other techniques. The applicability and validation of this technique in the hands of others is yet to be ascertained. This would need a controlled prospective study involving many surgeons of equal experience and comparison with the traditional technique. It would then ascertain whether this technique is associated with a lesser fluoroscopy time, more accuracy and lesser learning curve. The grade of hydronephrosis can affect the puncture, with the access being relatively easier for higher grades of hydronephrosis. This was not studied. However, if the angle, i.e. the trajectory of puncture, is correct, as described by this technique, the puncture would be easier and precise even in lesser grades of hydronephrosis.
| Conclusion|| |
Estimating the angle and depth of puncture by the technique described above helps in achieving a proper access with minimal difficulty, with reduced fluoroscopy exposure and minimal movements of the C arm, even in the triangulation technique. We believe that, if confirmed by a multicenter prospective study comparing it with the traditional technique, it would also help a trainee to gain proficiency in fluoroscopy-guided percutaneous renal access faster and with a shorter learning curve.
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[Figure 1], [Figure 2], [Figure 3]