Ultrasonography-Guided Percutaneous Nephrolithotomy in the Flank Position Versus Fluoroscopy-Guided Percutaneous Nephrolithotomy in the Prone Position: A Comparative Study

Abstract

Background and Purpose:

Gaining access to the pyelocaliceal system in percutaneous nephrolithotomy (PCNL) is routinely performed using fluoroscopic guidance with the patient in a prone position. We compared ultrasonography-guided access for PCNL with the patient in the flank position with conventional fluoroscopy-guided access.

Patients and Methods:

A total of 60 patients were randomly separated into two 30-patient groups—namely, ultrasonography-guided access with the patient in the flank position as group 1, and fluoroscopy-guided access with the patient in the prone position as group 2. In group 1, the entire procedure was performed under ultrasonography guidance.

Results:

Successful access was achieved 100% in both groups. The success rate was 86.7% in group 1 and 90% in group 2 (P = 0.45). The residual stone rate (stone ≥4 mm) was 13.3% in group 1 and 10% in group 2. The access duration was 14.5 ± 2.6 minutes and 9.4 ± 2.3 minutes in groups 1 and 2, respectively (P < 0.05). No significant differences for complications without any adjacent injuries were detected in both groups. Furthermore, the average hospital stay was 2.7 ± 0.3 and 2.9 ± 0.3 days accordingly for groups 1 and 2 (P = 0.89).

Conclusion:

Ultrasonography has a high ability to access calculi more easily through the pyelocaliceal system with the patient in the flank position. It is convenient for urologists, and the return to the supine position is possible easily when necessary. Besides, PCNL under ultrasonography guidance and with the patient in the flank position has high success rates and limited complications; hence, we recommend this technique as an alternative procedure for fluoroscopy-guided PCNL.

Introduction

S ince its first introduction in 1976 and with improvements in the the technique and equipment improvements in the next three decades, percutaneous nephrolithotomy (PCNL) has become an accepted management option for urolithiasis.^1
–3 Now, PCNL is the treatment of choice for patients with kidney stones that are larger than 2 cm in diameter.⁴ Other indications include lower pole calculi, cystine stone disease, abnormal renal anatomy, and stones that are not amenable to ureteroscopy or extracorporeal shockwave lithotripsy (SWL).^5,6

Traditionally, PCNL has been performed with the patient in the prone position.⁷ Nonetheless, in obese patients and those with compromised cardiopulmonary states and skeletal deformity, the prone position is not considered as suitable.⁸ PCNL mainly relies on fluoroscopy, exposing both the patient and the surgical team to radiation.⁹ Although surgeons use protective gowns during fluoroscopy-guided PCNL, this protection is nowhere near complete. Radiation exposure in the absence of complete protection can affect the surgical team long-term, and it is not dose dependent.

The study was designed to compare ultrasonography (US)-guided PCNL with the patient in the flank position with fluoroscopy-guided PCNL with the patient in the prone position. In fact, the objectives of this study are to present totally US-guided PCNL and evaluate our preliminary results, then compare them to the results of standard fluoroscopy-guided PCNL wih the patient in the prone position.

Patients and Methods

A total of 60 patients who were candidates for PCNL in our urology center were enrolled in the study between January 2007 and October 2008. The inclusion criteria were pelvic or caliceal stones that were larger than 2.5 cm in diameter. Patients with kidney anomalies, uncontrolled coagulopathies, and histories of PCNL or open renal stone surgeries were excluded. One surgical team, whose members were experienced in PCNL, accomplished all operations. Using pseudorandomization,¹⁰ patients were assigned to two 30-patient groups. Group 1 consisted of those who underwent US-guided PCNL in the flank position. Some information, such as demographic data, including age, sex, stone laterality, and the size (the mean diameter) in these patients, was recorded.

Group 2 comprised patients who underwent fluoroscopy-guided PCNL in the prone position. Preoperative evaluation consisted of tests such as urinalysis, urine culture, and renal function test. In patients with active urinary tract infection, appropriate treatments were administered. Excretory urography (intravenous urography) was performed if the serum creatinine level was below 1.8 mg/dL preoperatively. Postoperative radiographic examination included plain abdominal radiography of the kidneys, ureters, and bladder. US was also performed 48 hours after surgery in all patients to detect residual stones and perirenal collections.

Informed consent forms were signed by all enrolled patients. The study was approved by the Ethics Committee at our hospital.

Operative technique

With the patient in the lithotomy position under general anesthesia, an open-ended 6F ureteral catheter was advanced into the renal pelvis under direct cystoscopic vision. After fixing the internal Foley catheter, the patient was repositioned to the standard flank position with a bolster below the ipsilateral flank in group 1 and to the prone position in group 2.

In group 1 patients, by performing US with a 3.5-MHz probe through the posterior abdominal wall and detecting the pyelocaliceal system and location of the calculi, an 18-gauge access needle that was attached to the side of the ultrasound probe passed into the appropriate calix through the fornix. After achieving puncture of the caliceal system and with urine flowing out, a 0.035 inch J-tipped guidewire was introduced into the targeted calix. We injected 50 mL normal saline serum to induce hydronephrosis when hydronephrosis did not exist.

The nephrostomy tract was dilated by a one-shot 28F or 30F Amplatz dilator under US guidance. After dilatation, a 30F Amplatz sheath passed to the target calix.

All these steps were under real-time US through the anterior abdominal wall, so the surgeon could detect entering the instrument's shadow through the caliceal system from the bottom side of the image. Minimizing renal movement during dilation of the tract is an important step to reduce the possibility of collecting system perforation. To get the least renal movement, both puncture of the system and tract dilation were performed at the same phase of respiration (inspiration or expiration) and combined with extra-abdominal compression (by hand or ultrasound probe).

By using a rigid nephroscope and Swiss pneumatic lithotripsy, stones were fragmented and extracted by grasping forceps. After stone removal and final nephroscopy under ultrasonographic control for any residual stone detection, Amplatz sheaths were removed, and the skin were sutured (tubeless procedure).

Patients in group 2 underwent classic fluoroscopy-guided PCNL. For this group of patients, after ureteral catheterization and repositioning to the prone position, contrast was injected through the ureteral catheter. After that, under the fluoroscopy guidance, an 18-gauge needle was passed. Next steps, including guidewire insertion, nephrostomy tract dilation, Amplatz insertion, and stone removal were the same as described for the patients in group 1, yet carried out under fluoroscopy guidance.

Arterial blood gas level was checked right before and 10 minutes after the repositioning.

Stone-free status and residual stone burden were determined by plain abdominal radiography and renal US studies routinely obtained 1 month after treatment. The success rate was defined as stone-free patients and patients with residual stones less than 4 mm evaluated by these studies.

A number of factors, such as demographic characteristics, the duration of the operation, the location of the stones, the changes in hemoglobin level, the arterial blood gas level, success rate (stone-free rate), residual stone rate, successful access rate, the complications, and the hospitalization period, were compared between the two groups. Statistical analysis was performed using the t test and chi-square test when appropriate. In our study, P < 0.05 was considered statistically significant.

Results

Demographic and clinical characteristics of patients are shown in Table 1. Successful access was achieved 100% in both groups. The success rate was 86.7% in group 1 and 90% in group 2 (P = 0.45). The residual stone rate (stone ≥4 mm) was 13.3% in group 1 and 10% in group 2; patients were referred for SWL. Intraoperative bleeding occurred in two (6.7%) patients in group 1 and one (3.3%) patient in group 2 (P = 0.47); therefore, all were controlled by balloon tamponade. Blood transfusion was needed for one patient in group 1. Postoperative bleeding did not occur in any patient. Injury to adjacent organs, such as liver, duodenum, spleen, and major vessels, did not occur.

Table 1.

Patient Demographic and Clinical Characteristics

	Group 1	Group 2	P value
Mean age (years)	40.8 ± 6.9	39.4 ± 10.6	0.55
Male (%)	18 (60)	19 (63.3)	0.79
Body mass index	27.8 ± 3.4	26.7 ± 4.7	0.12
Stone diameter	28.7 ± 3.3	27.4 ± 3.2	0.13
Number of stones	2 ± 1.1	2.1 ± 1.5	0.77
Stone location
Superior calix (%)	3 (10)	2 (6.7)
Middle calix (%)	7 (23.3)	7 (23.3)
Inferior calix (%)	14 (46.6)	17 (56.6)
Renal pelvis (%)	6 (20)	4 (13.3)
Hydronephrosis			–
Mild (%)	12 (40)	14 (46.6)
Moderate (%)	16 (53.3)	11 (36.6)
Severe (%)	2 (6.6)	5 (16.6)
Left side stone (%)	8 (26.7)	14 (46.7)	0.11

The mean access duration was 14.5 ± 2.6 minutes and 9.4 ± 2.3 minutes (P < 0.05) and the mean operative time was 44.7 ± 6.4 minutes and 34.9 ± 5.1 minutes (P < 0.05) in groups 1 and 2, respectively. One (3.3%) patient in each group experienced fever after surgery and was treated conservatively.

Catheters were removed 1.8 ± 0.4 days and 2.1 ± 0.4 days after operation in groups 1 and 2, respectively. The mean postoperative (±standard deviation) hospital stay time was 2.7 ± 0.3 and 2.9 ± 0.3 days, respectively. Table 2 summarizes the intraoperative and postoperative patient data in the two groups.

Table 2.

Intraoperative and Postoperative Data

	Group 1	Group 2	P value
Access
Superior calix (%)	1 (3.3)	1 (3.3)	–
Middle calix (%)	5 (16.5)	3 (10)
Inferior calix (%)	24 (80)	26 (85.8)
Hemoglobin level (mg/dL)
Before operation	12.8 ± 2.1	12.1 ± 1.9	NS*
After operation	13.6 ± 1.1	13.2 ± 1.0	NS
Change	−0.33 ± 0.3	−0.41 ± 0.26	NS
Intraoperative bleeding (%)	2 (6.7)	1 (3.3)	NS
Postoperative bleeding (%)	0	0	NS
Injury to adjacent organs	0	0	NS
Pyelocaliceal system disruption (%)	0	0	NS
Arterial blood gas changes
Pa O₂ (mmHg)	−21.2	−9	NS
Pa CO₂ (mmHg)	−0.58	1.9	NS
HCO₃ (mmHg)	−2.6	−0.51	NS
O₂ saturation (mm Hg)	−0.2	−0.8	0.057
Mean access time (minutes)	14.5 ± 2.6	9.4 ± 2.3	<0.05
Mean injection attempt	2.2 ± 0.5	1.8 ± 0.4	NS
Unsuccessful access (%)	0	0	NS
Mean operative time (minutes)	44.7 ± 6.4	34.9 ± 5.1	<0.05
Mean hospital stay (days)	2.7 ± 0.3	2.9 ± 0.3	NS
Success rate (%)	26 (86.7)	27 (90)	NS
Residual stone > 4 mm	4 (13.3)	3 (10)	NS
Hematoma or urinoma	0	0	NS

NS = not significant.

There were no significant differences with regard to factors including hemoglobin drop and hospital stay between the two groups. Arterial blood gas analysis revealed no significant differences between the two groups before and 10 minutes after the repositioning.

Discussion

PCNL has been the standard treatment method in a majority of renal-stone patients who are not candidates for SWL. There are a number of options for the needle guidance during PCNL, including fluoroscopy and US. The harmful effects of radiation are well confirmed, and for protection against these harmful effects, highly advanced fluoroscopies and protection shields are available, although none is fully effective. The severity of stochastic effects of radiation is not dose dependent and may cause genetic mutation and cancer in surgeons and patients. Based on the rule to use the lowest reasonably achievable radiation, the least dose has to be used.¹¹

The prone position has some disadvantages. For example, PCNL with the patient in the prone position cannot be performed in obese patients and patients with spinal anomalies and cardiovascular diseases. PCNLs with patients in the supine and flank positions were developed to overcome these problems. Although it is necessary that every endourologist increase his or her skills in supine and flank PCNL, it does not exclude the need for prone PCNL.¹²

Furthermore, the lateral position is the suitable one for urologists and it does not necessitate 180-degree rotation; thus, traumatic damages to the head and neck during rotation could be avoided. Because the e kidney is more accessible with the patient in the lateral position, US can be performed easily with better vision. In short, the advantages of US as a guidance modality include the lack of ionizing radiation, shorter procedure time, the decreased number of punctures, and the elimination of contrast agent administration.^13
–15

Osman and associates² reported 315 US-guided PCNLs; however, they accomplished tract dilation under fluoroscopy guidance. Desai and Jasani¹⁶ demonstrated the effectiveness and safety of US-guided PCNL in children; those patients who could not tolerate the prone position.¹⁷

Basiri and coworkers¹³ performed all steps of PCNL under US guidance and eliminated radiography. They also found that US at the end of PCNL helps to find residual calculi, particularly nonopaque and semiopaque calculi. The routine patient position is prone in PCNL. Patient position during PCNL can be either supine^17
–19 or flank^20,21 or reverse lithotomy,²² which are shown to be safe and effective if compared with the prone position.

The prone position provides a larger surface area for the choice of puncture site and a wider space for instrument manipulation.¹³ It is thought that the prone position can decrease the risk of colonic or splanchnic organ injuries^13,23,24; however, the prone position may be contraindicated for anesthesiologic reasons because of circulatory and ventilator difficulties, especially in obese patients.^25,26 It can also be difficult in patients with structural deformities, such as hip or lower limb contractures.¹⁸

Difficult assessment of the anterior or posterior deviation of percutaneous access under fluoroscopic guidance makes the lateral position inappropriate for the percutaneous approach to the kidney.²⁷ US has a high ability to detect the pyelocaliceal system in the flank position. This position does not need a 180-degree rotation that can be dangerous for the patient. Moreover, conversion to the supine position is easily possible if needed.

Gofrit and associates²¹ recommended using the lateral position for PCNL in morbidly obese patients and in patients with kyphosis to avoid severe hypoxemia and hypercarbia. Kerbl and coworkers²⁰ used PCNL with the patient in the flank position to reduce pulmonary compression of the patient. Nonethless, Manikandan and colleagues²⁸ showed that the prone position is associated with an improvement in both oxygenation and carbon dioxide elimination, the but lateral position is beneficial to oxygenation without affecting carbon dioxide elimination.

Karami and associates¹¹ reported PCNL under US guidance in 40 patients in the lateral position with an access rate of 100% and complete stone removal rate of 85%. In this study, PCNL in patients in the lateral position under US guidance was introduced as a safe and convenient procedure.

According to our study, we found no differences between arterial blood gas indicators in patients in the prone and flank positions. This is probably because we did not assess arterial blood gas levels through serial measurements; hence, their trivial changes might have been missed. We obtained arterial blood gas levels 10 minutes after repositioning (compared with 30 minutes in the study by Manikandan and colleagues²⁸); ours is obviously a far shorter time. Serial arterial blood gas assessments for a longer duration could help to find perfusion changes during operation.

Conclusion

In patients in the flank position, US is highly capable of detecting calculi, and access to the pyelocaliceal system is easier as well. This position does not need a 180-degree rotation that could be hazardous for the patient. It is also well known to urologists, and conversion to supine position could easily be made when necessary. Furthermore, in our experience, PCNL under US guidance and in the flank position is accompanied by high success rates and a few complications. Although it is clear that fluoroscopy should be available in the operating room, we recommend US-guided PCNL as a reasonable alternative procedure to a fluoroscopy-guided one.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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