Percutaneous nephrolithotomy (PCNL) was introduced in the late 1970s and remains an effective operative modality for the extraction of a relatively large stone burden from the pelvicalyceal system of the kidney. According to the latest version of European Association of Urology (EAU) guidelines, PCNL comprises the standard procedure for voluminous renal stones exceeding a maximum diameter of 2 cm, while it remains a valid option for smaller stones [1].
During the historical route of PCNL, the technological developments contributed to the evolvement of the surgical procedure, with new types of energy generators, high energy output systems, energy transfer through flexible probes and smaller access sheaths and instruments [2]. A parallel change, which remains a matter of debate, is the ideal patient position for the PCNL procedure. Historically, PCNL was introduced as a procedure performed in the prone position, which is the most frequently selected variant still in present. However, in 1987 was presented for the first time the supine position- based variant, and nowadays there are several variants of the prone, supine, and lateral positions for PCNL surgery, each one with its combination of advantages and disadvantages [2].
The prone position was initially selected for performing PCNL procedures, which was based on the notion that it is accompanied by a reduced risk for intraabdominal organ injury. The wider surface area for puncture and gaining access to the pelvicalyceal system is recognized as the main advantage of the prone position [3]. Furthermore, the feasibility of performing PCNL in patients with kidney disorders, such as the horseshoe kidney, the shorter length of the access tract, and the limited kidney mobility represent additional advantages of the prone position, which remains the main positioning option for the 77% of the urologists performing PCNL and the optimal approach for the young urologists with limited expertise [3]. On the other hand, supine PCNL is considered beneficial in terms of cardiovascular and airway control, anesthesiological safety, and reduced risk of peripheral nerve injury and thromboembolism [4]. Moreover, supine positioning is characterized by improved ergonomics for operation room personnel and increased feasibility of performing combined intrarenal surgery by combining the percutaneous and retrograde access to the pelvicalyceal system. Additionally, the downward orientation of the access sheath during supine PCNL allows the faster evacuation of fluids and stone fragments, which theoretically can contribute to the reduction of the high intrarenal pressure - associated complications [4]. Supine positioning represents a major change in PCNL procedure, which is the main reason for the attachment of even experienced endourologists to the prone approach.
Regarding the results and the safety profile of PCNL, the majority of the studies showed the equivalence of the prone and supine positions. Two meta-analyses demonstrated a significantly shorter operative time for the supine approach and equal complication rates [5,6]. The supine position was associated with a lower stone-free rate in one of these meta-analyses [6].. The data of the largest patient database for PCNL results (CROES PCNL Global Study) showed a longer operation time and lower stone-free rate for the supine approach, which can be attributed to different definitions of operative time and variability in the examination of residual stones [7]. Stone-free rates and complications of the two approaches were equal according to the results of a randomized comparative study, while the mean blood loss, the mean operative time, the mean hospital stay, and the parameters of anesthesiological risk showed an advantage of supine PCNL [8]. In a recent retrospective comparison of the prone position with three variations of the supine position, no difference was found in terms of stone-free rate, blood loss, hospital stay, and complications, while the complete supine position was associated with shorter operative time [9]. According to the most recent meta-analysis, supine position seems to achieve a lower stone-free rate, but with lower complication rates compared to the prone position [10].
Relating to postoperative complications of PCNL surgery, symptomatic urinary infection comprises the most common postoperative event, with 10.5–39.8% of the patients developing postoperative fever and 0.3- 1% of the patients developing sepsis [2]. Most of the available reports agree on the factors that affect the risk of postoperative infectious complications. The data from the CROES PCNL Global Study revealed that the positivity of preoperative urine culture, the presence of staghorn calculus or preoperative nephrostomy, the lower patient age, and diabetes were independent predictors of developing postoperative fever [11]. A report on 227 patients undergone PCNL surgery after antibiotic pretreatment showed the presence of staghorn calculus as the sole factor with an independent effect on risk for fever or sepsis [12]. A recent meta-analysis on the important factors for the manifestation of postoperative infection incorporated the results of prospective and retrospective studies into the quantitative synthesis. This report concluded that the status of preoperative urine culture, the status of stone culture, the number of access points, and the blood transfusion were representative of the preoperative presence of bacteria and the extent of kidney trauma during the PCNL procedure, which are the major predictors of postoperative infection [13]. According to the results of a recent report on the effect of preoperative factors on postoperative infectious complications, the occurrence of severe infection depends not only on the presence of bacteria in preoperative specimens but also on a subset of patient biochemical parameters, which reflect the interaction of uropathogens with patient homeostasis [14].
Focusing on the comparison of prone to supine position in terms of results, complications, and especially postoperative infectious events, we collected the preoperative and postoperative data of patients undergone PCNL surgery. Through the analysis of the above data, we sought the significant factors, which influence the possibility of infectious complications, and additionally, we examined the independent effect of these factors on postoperative infectious events.