The long-term learning curve of holmium laser enucleation of the prostate (HoLEP) in the en-bloc technique: a single surgeon series of 500 consecutive cases

Purpose To evaluate perioperative parameters, clinical outcomes, and the learning curve of holmium laser enucleation of the prostate (HoLEP) of a single surgeon in 500 consecutive cases. Methods Demographic parameters, outcomes, and adverse events were evaluated. The learning curve for HoLEP in en-bloc technique of the first 500 consecutive patients was analyzed in clusters of 100 (clusters 1–5) using the Wilcoxen rank test, Chi² test and Kruskal Wallis test. Results Enucleation weight was similar in the clusters 1,2,3, and 5 (62 g, 63 g, 61 g, 61 g), in cluster 4 it was slightly higher at 73 g. There was a significant reduction in operating time from 67 min (cluster 1) to 57 min (cluster 2), 46 min (cluster 3), 53 min (cluster 4), and 43 min (cluster 5), p < 0.001. Enucleation efficiency (g/min) showed a steady increase (1.72, 2.24, 2.79, 2.92 vs. 2.99, p < 0.001). Laser energy efficiency also improved (2.17 vs. 2.12 vs. 1.71 vs. 1.65 vs. 1.55; p < 0.001). There was no measurable learning curve regarding the length of hospital stay (mean 2.5 days), catheterization time (1.9 days), hemoglobin drop (approx. 1 g/dl) or complications (p > 0.1). Conclusions HoLEP using the en-bloc technique is a safe and highly effective method. Over time, a slight but steady learning curve and improvement in operation time, enucleation efficiency and laser energy efficiency were shown even for an experienced surgeon - after 500 cases, still no plateau was reached. There was no measurable learning curve regarding blood loss, complications, length of hospital stay, and catheterization time.


Introduction
While TUR-P was regarded as the gold standard for the surgical treatment of BPH up to a size of 80 cm³ for several decades, endoscopic enucleation techniques are increasingly replacing TUR-P as a size independent alternative [1].Even though different energy sources for enucleation are associated with different benefits and challenges, several studies have shown that ultimately, technique and surgeon´s experience are more important for the outcome than the energy source itself [2].
For many years, two-and three-lobe techniques with late apical release were the standard methods for enucleation in HoLEP.Lately, en-bloc techniques are gaining increasing acceptance.The en-bloc technique with early apical release as described by Saitta et al. [3] was developed in an effort to reduce the incidence of transient incontinence, a cumbersome side effect that occurs in up to 10% of patients treated with late apical release techniques [4].In this technique, the sphincter is detached from the adenoma at the start of the procedure, and the mucosa covering the sphincter is carefully preserved in a circumferential manner, thereby reducing mechanical stress during the procedure [5].
The number of cases above which a surgeon can perform HoLEP safely, with satisfactory efficiency and good results can be estimated at 50 cases, requiring a careful case selection [6].Therefore, the question arises as to what happens after 50 carefully selected cases when the surgeon starts challenging himself with larger glands and less optimal conditions.
To our knowledge, it has not yet been evaluated whether the learning curve for HoLEP stagnates at one point or increases over time, even for very experienced surgeons.Therefore, the aim of this study is to evaluate the learning curve of HoLEP for a surgeon over his first 500 consecutive cases to determine whether further improvements can be expected and whether complication rates are affected.

Parameters
The following preoperative parameters were retrospectively collected from the patients' electronic medical records: Age, body mass index (BMI), International Prostate Symptom Score (IPSS), IPSS related quality of life (IPSS-QoL), International Index of Erectile Function (IIEF), total prostate specific antigen (PSA), peak urinary flow rate (Q-max), postvoid residual urine volume (PVR), transrectal ultrasound-determined prostate volume (TRUS volume), and oral anticoagulation.In addition, the following parameters enucleation weight, enucleation time, enucleation efficiency (enucleation weight / enucleation time; g/min), operation time, morcellation efficiency (morcellation weight / morcellation time; g/min), hemoglobin loss, laser time efficiency (laser time / weight; min/g), laser energy efficiency (laser energy / weight; kJ/g), length of hospital stay, and the time to catheter removal.Furthermore, transurethral reinterventions and complications according to the Clavien-Dindo classification as well as the Complication Comprehensive Index (CCI) [7] within the first 30 days postoperatively were evaluated.

Technique and laser settings
HoLEP was performed with the Pulse 120 Moses® Holmium Laser (Lumenis, Yokneam Illit, Israel) with a Slim-line® 550 or Moses® 550 Laserfiber.Morcellation was performed using the Piranha® morcellation system in combination with a 26-Fr continuous-flow laser resectoscope (both Richard Wolf, Knittlingen, Germany).The surgeon performed the enucleation in the en-bloc technique with early apical release as described by Saitta [3].Laser settings for enucleation were 2 J 50 Hz short pulse or Moses Pulse.Coagulation was performed at 1 J and 40 Hz with long pulse setting.Bipolar coagulation was routinely performed in most cases after the enucleation to ensure optimal hemostasis.

Statistical analysis
Descriptive statistics were carried out to present the baseline and perioperative characteristics.Quantitative data were expressed as mean and standard deviation (SD), and categorical date as absolute and relative frequencies.The cases were analyzed in clusters of 100 (clusters 1-5).The number of clusters was chosen for practical reasons, 5 were chosen corresponding to cluster sizes of 100 patients per cluster.The Kruskal-Wallis test was used to compare perioperative characteristics to different experience levels of the surgeon.Spearman's correlation analysis was performed to analyze the relationship between the variable of interest and the number of surgical cases.All statistical analyses were carried out with JMP v14 (SAS Institute, Cary, NC, USA).The level of significance was set at 0.05.

Baseline characteristics
A total of 500 consecutive patients, who underwent HoLEP at our department between January 2021 und September 2023 and were all operated by the same surgeon, were included in the analyses.Baseline characteristics of the patient cohort are summarized in Table 1.Just over a third of the patients (n = 195, 38.7%) were taking an oral anticoagulant preoperatively.All preoperative parameters except for the TRUS volume of the prostate were comparable in the cluster analysis of 100 cases each.For the total cohort of 500 cases, the mean TRUS volume was 93.20 ± 50.36 cm [3].

Perioperative parameters
The perioperative parameters are displayed in Table 2.The mean enucleation weight was 64.68 ± 46.54 g and the time for enucleation was 25.77 ± 16.63 min on average.The mean total operation time was 51.39 ± 28.43 min.Blood loss was low with a mean hemoglobin drop of 0.91 ± 1.04 g/dl.The patients kept their catheters for an average of 1.92 ± 0.89 days and left the hospital after an average of 2.6 ± 1.47 days.The overall complication rate was low at 15.4% (n = 77), with the vast majority of complications being minor (Clavien Dindo grade I and II) and no severe complications (Clavien Dindo grade IV and V) occurring.The mean Comprehensive Complication Index was 16.34 ± 9.26.CDC grade I complications (n = 39, 7.8%) were urinary retention and prolonged gross hematuria, CDC grade II complications (n = 29, 5.8%) were mainly urinary tract infections (n = 22, 4.8%) and single cases of anemia, COPD exacerbation, subileus or hypertonia.Two patients needed an endoscopically guided catheter placement due to urinary retention (CDC grade IIIa, 0.4%).CDC grade IIIb complications occurred in seven patients (1.4%), six of them needed reintervention due to bleeding, and one needed a secondary morcellation.Of the six reinterventions due to bleeding or tamponade, three occurred early within 48 h of the surgery and three occurred delayed after discharge from the hospital.

Operation time
The Kruskal-Wallis test showed a significant difference in operation time between the 5 clusters (p < 0.001).The operation time decreased from 64.05 ± 26.60 min in the first 100 consecutive cases to 42.02 ± 27.75 min in the last 100 consecutive cases (cases 401 to 500) (Fig. 1c).

Lasing energy efficacy
The development of lasing energy efficiency is shown in Fig. 1d.The amount of energy (KJ) used per gram of enucleated tissue decreased significantly, indicating an increase in efficiency (Kruskal-Wallis test: p < 0.001) from 2.18 ± 0.95 kJ/g in the first 100 consecutive cases to 1.55 ± 0.90 kJ/g in the last 100 consecutive cases (cases 401 to 500).

Enucleation efficiency
The enucleation efficiency increased significantly (Kruskal-Wallis test: p < 0.001) from 1.73 ± 0.71 g/min in the first 100 consecutive cases to 2.99 ± 1.38 g/min in the last 100 consecutive cases (cases 401 to 500).The cluster analysis is shown in Fig. 1a using a box plot diagram.
The Spearman rank correlation analysis revealed a statistically significant positive correlation between enucleation efficiency and the number of consecutive cases (p < 0.001, ρ = 0.3878) (Fig. 1b).cluster, as enucleation efficiency improved in comparison to Clusters 1,2 and 3.The gradual, linear improvement in enucleation time, despite the consistent use of the same surgical technique, laser, and energy settings, is intriguing.We hypothesize that the key distinction between a novice and an expert lies in the effective use of the instrument for mechanical traction, aiding laser dissection.This balance of mechanical traction and microdissection with the holmium laser, combining visual and tactile input, is inherently complex and seems to get better over time.Data on laser usage supports this: as surgeons use laser energy more effectively, likely helped by improved traction techniques, efficiency increases.Also, the closing gap between laser-activation and enucleation times indicates a more efficient use of both time and energy.Our hypothesis is supported by the findings of Kosiba et al. [16].
Comparing OR times and enucleation efficiency, they were significantly shorter than most surgeons using a two or three lobe technique [17][18][19], and similar or higher compared to other high volume surgeons using an en-bloc technique [3,5,20,21], highlighting the excellent efficiency of this method [5,20,22].
We did not differentiate if pulse modulation was used or not in the evaluation, since a recent study analyzing

Discussion
Despite anatomical enucleation being recognized for over 50 years as superior to TUR-P in achieving better objective voiding outcomes [8], TUR-P still dominates almost 80% of BPH surgeries in Germany [9] and the US [10].HoLEP not only surpasses TUR-P in improving BPH symptoms and objective voiding measures such as PVR, flow, and urodynamic parameters, but also reduces risks of bleeding, transfusion, and decreases the catheterization time and hospital stay [11,12].A common misconception is the fact that EEP is an option primarily for big glands, since it was seen as a successor of OSP, while in fact it is an excellent choice also for moderate sized glands with substantial advantages over TUR-P [13].The underutilization of EEP likely stems from its steep learning curve.While its short-term initial learning curve has been well-researched [6,14,15], the impact of long-term learning on perioperative outcomes and complications remains unclear.To address this, we analyzed these aspects in a high-volume surgeon's first 500-cases of enbloc HoLEP with early apical release.
Throughout the 500 cases, there was a gradual improvement in enucleation time, OR-Time, and enucleation efficiency.The increase in enucleation and OR-Time in Cluster 4 correlates with larger median prostate volumes in this en-bloc HoLEP is a safe and highly effective way to treat BPH.Although there is a long learning curve regarding the OR-time, the quality of the surgery (reflected in outcomes and complication) was not affected by this learning curve.surgeries of the same surgeon did not show any differences in perioperative outcomes or complications [23].
An encouraging finding from this study is the fact that the OR times and complication rates were short and low in the initial 100 cases already, so surgeons starting HoLEP should not be discouraged: the experience of 500 cases is not necessary to perform a high quality HoLEP, although OR-times will improve over time.Improvements are largely limited to the enucleation phase of the procedure.Looking at the total OR-times and considering turnover times, the improvements are relevant but not substantial.Unsurprisingly, there was no relevant improvement in coagulation-or morcellation times.From the start, complications were infrequent and mostly minor, showing no significant reduction over time.A low rate of bleeding complications requiring reintervention and a relatively minor decrease in hemoglobin levels was observed.This could be attributed to our hybrid coagulation strategy, which combines laser coagulation during the procedure and bipolar coagulation, particularly for mucosal bleeders at the bladder neck, at the end of the enucleation phase.
Although both catheterization time and hospital stay are longer than in most series from the USA [24][25][26][27][28], this is largely a reflection of the reimbursement system rather than the quality of the surgery, therefore, both catheter and hospitalization time is in line with other high volume HoLEP surgeons in Germany [13,17,[20][21][22].This study's retrospective design is a limitation, as some complications may have been overlooked if patients sought treatment elsewhere, either in other hospitals or outpatient settings.Additionally, being a single-surgeon series, the results reflect one individual's experience and may not be generalizable to other surgeons.Comorbidities were not included in the analysis.Additionally, the surgeon had experience in ThuLEP before this series, so the initial learning curve should not be compared to surgeons without previous experience in EEP.Despite these constraints, given that the study encompasses 500 consecutive cases over an extended period, it provides valuable insights into the long-term learning curve of HoLEP.

Conclusion
Over 500 cases, we saw steady improvements in enucleation efficiency, resulting in shorter surgery times, and this improvement continued without a clear limit.The presence of a long-term learning curve may suggest that it might be beneficial to focus training on high-volume HoLEP surgeons.The low rate of complications throughout the study shows that HoLEP is safe, even in the hands of less experienced surgeons -it will just take more time.To sum up,

Fig. 1
Fig. 1 Advancement over 500 cases: (A) enucleation efficiency in clusters; (B) enucleation efficiency in individual cases; (C) operation time in clusters; (D) lasing energy efficiency in clusters

Table 1
BMI = body mass index; IPSS = International Prostate Symptom Score; IPSS-QoL = International Prostate Symptom Score related quality of life; IIEF = International Index of Erectile Function; PSA = prostate specific antigen; Q max = peak urinary flow rate; PVR = post-void residual volume; TRUS = transrectal ultrasound, SD = standard deviation