This work was a retrospective analysis of data collected from patient files. The prostate size was based on the accurate resection weight (what seems to us to be more critical) and not the sonographically estimated preoperative volume.

The main results of this study can be interpreted as follows:

Increasing surgeon’s experience and resection weight accelerated the resection speed during M-TURP. Significant differences between the individual groups were found with heavier resection weights up to 100 g, leading to a higher resection speed. Despite the further increase in the mean value from 1.1 to 1.3 g/min, the differences in the resection speed between group 4 (over 100 g) and group 3 (80–99.9 g) showed no significance (no further increase > 80 g). We were able to show that the relationship between the duration of the surgery and the amount of tissue resected was not linear. The reason for this finding may be the increased and deeper resection of larger tissue chips at the beginning of M-TURP.

The cut-off values for the occurrence of severe complications (Clavien–Dindo ≥ IIIb) were 59.5 g for the resection weight and 82.5 min for the surgical time. Hb loss increased proportionally to the resection weight. Significantly more blood transfusion had to be administered in the group with the heaviest resection weight (≥ 100 g). Sodium loss revealed critically low postoperative levels only in the group with the heaviest resection weight.

The short-term outcome of M-TURP did not significantly differ between the groups.

There are only a few comparable studies in the literature.

Persu et al. achieved an average resection speed of 1.8 mL/min in their study, with 42 of their 100 resections with a preoperative size of > 80 mL being operated on in two stages [11]. The lack of information on the resected prostate tissue, rate of transfusion, and incidence of TUR syndrome prevented a more extensive comparison.

Kwon et al. conducted a study among 48 patients and reported that 19 patients had a mean preoperative prostate size of 124.6 mL [12]. However, only an average of 32.6 mL was resected, and the mean resection speed was 0.28 mL/min.

Marsh and Whitaker achieved an average resection speed of 1.01 g/min in their 102 patients [13]. All patients had a resection weight of > 40 g, and 13 had a resection size of > 80 g. However, with 77 patients who required a transfusion with an average of 1.9 erythrocyte concentrates and 2 patients who died, their values are well above our values.

Herein, the data collected and analyzed in Table 5 on the need to administer blood transfusion were noteworthy. Although there was significant heterogeneity between the groups, this could be explained only by the more than randomly frequent need for the substitution of erythrocyte concentrates in the group with a resection weight of > 100 g (29.2%). Our evaluation led to the conclusion that with an increase in the resection weight, the occurrence of perioperative Hb loss also increases (Table 4), but this is valuable only from a resection weight of > 100 g wherein the administration of erythrocyte concentrates becomes necessary (Table 5).

The probability of TUR syndrome increases with decreasing postoperative serum sodium levels. Table 6 shows that in three patients, the postoperative serum sodium levels dropped below 120 mmol/L, while one patient from the group II had a sodium level of 120 mmol/L. In our evaluation, only the number of severe sodium losses in the group with a resection weight of > 100 g achieved statistical significance.

As indicated in the analyses of Hb and sodium losses, the distribution of complications was also significantly heterogeneous. Table 7 shows how the frequency of serious complications ≥ IIIb increased with an increasing resection weight from 1.9% to 16.7%. This is reflected in the distribution of TUR syndrome: four of the five TUR syndrome cases that occurred in the groups with a resection weight of > 80 g. However, one patient in the group with a resection weight of 80 − 99.9 g developed symptoms of TUR syndrome even with a postoperative sodium level of 127 mmol/L.

In the group with a resection weight of 59.9 g, there was no occurrence of TUR syndrome. In the group with smaller prostate sizes of 10–59.9 g, five of the eight major complications (Table 7) occurred among the patients operated on by less-experienced surgeons. In only 385 patients, the information documented in their files was sufficient to determine the postoperative outcome. Deterioration was noted in 2.3% of the patients; improvement in 84.7%.

As expected, the speed of the resection increased with the expertise and experience of the surgeon (Table 2). Since a surgeon’s experience is not constant but increases with the frequency of performing the procedure, the wealth of experience at the end of the evaluation period was chosen as the parameter. This can mean a lack of clarity in the border areas (for example, from a less-experienced to an experienced surgeon). In contrast, the quality of a surgeon arguably depends on not only the sheer number of operations but also the individual surgical skill. However, the number of operations at the end of the evaluation period seemed to us the best defined from these considerations.

The present findings agree with those of the survey by Cury et al., who demonstrated an increase in the resection speed with an increase in the experience of the surgeon in their analysis of 77 patients [14]. In their study, the average resection speed was 1.07 g/min, and the maximum resection speed was 2.25 g/min in the group operated on by the most experienced surgeons; these values are comparable to those in our group operated on by very experienced surgeons (0.9 and 2.8 g/min, respectively). However, Cury et al. did not analyze the resection speed as a factor related to the resection weight. Since the present study was a retrospective analysis, there was a systematic bias in the distribution of the resection weight across the groups divided according to surgeon’s experience. Thus, 31 of the 48 patients with a resection weight of ≥ 80 g were operated on by very experienced surgeons (65%), 14 by experienced surgeons (29%), and only 3 by less-experienced surgeons (6%). Therefore, we re-examined the influence of surgeon’s experience and resection weight using a two-factor ANOVA. There was a significant increase in the resection speed in association with both surgeon’s experience and resected tissue volume. There was also a significant association between surgeon’s experience and resected tissue volume.

We were able to determine the value limits for the resection weight and surgical time in terms of severe complications: 59.5 g and 82.5 min, respectively. For minor complications, the limit for the resection weight was 57.5 g only. In 2008, Reich et al. also set a value limit of 60 g for the critical resection weight, without going into detail about the determination of this value and without differentiating between slightly severe and severe complications [2]. With an almost identical patient group overall, we were able to confirm this value limit with our work.

This study has several significant limitations to its interpretability, primarily because it was a retrospective analysis. Owing to insufficient documentation, values, ​​such as the preoperative sonographically measured prostate volume, could not be included in our analysis. This is a main criticism, because it severely limits comparability with other studies. Further, the distribution of the patients into the individual groups according to surgeon’s experience was first not randomized; second, a surgeon’s wealth of experience is not fixed but continually develops. Both points imply a bias. We tried to take this was taken into account when examining the speed of resection using the ANOVA. Finally, the data were derived from only a limited number of surgeons from only one department. All of these points lead to the limitation of generality, and thus, generalization of the results should be undertaken with caution.

In the literature, the size of the prostate is usually given as a preoperative sonographically determined value, which, in contrast to the resection weight, can be subject to greater fluctuations and measurement inaccuracies [15, 16]. Since this preoperative sonographic value was not recorded in the present work, a direct comparison with previous studies is difficult.

The resection weight is usually well below the values ​​measured preoperatively, as can be seen in the work of Kwon et al. (32.6 of 124.6 mL = 26.2%) and Cury et al. (12.4 of 45 g = 27.6%, 13.8 of 46.3 g = 29.8%, and 33.3 of 51 g = 65.3%) in which even the most experienced surgeons resect an average of no more than 65% of the tissue measured preoperatively [12, 14]. At best, the latter would estimate the preoperative sonographically measured critical prostate volume in our series to be about 90 g. Other works report average values ​​between 34.7 and 54% [17, 18].

This finding suggests that some of the glands in our patient population had a resection weight well above the 80 g limit preoperatively. Hakenberg et al. and Antunes et al. showed that the percentage of resected tissue has no influence on the outcome [19, 20]. Park et al. reported the missing influence of the amount of resected tissue relative to the volume of the transitional zone [21]. Milonas et al. showed that 30–35% of the entire prostate should be resected to achieve a very good outcome [22]. Yucel et al. were able to show in their work on resection of the prostate with a size of more than 80 g determined via sonography that there were no serious complications [23]. However, the resection weight averaged 52.21 ± 7.59 g and was therefore close to the cut-off value determined herein.

Considering limitations in the interpretability of this purely retrospective study with consequently unmeasurable parameters, as well as the mentioned biases and limited generality, we can cautiously draw some conclusions: Larger prostates are resected with higher speed, but a resection weight of more than 60 g might increase the risk of severe complications. We showed that the resection speed increased with an increasing resection weight. We also confirmed the influence of the experience of the surgeon on the speed of resection.

The indication for M-TURP in patients with a sonographically estimated prostate volume of about 80–90 mL should at least be regarded critically. However, one must also consider individual patient factors and ongoing rapid advances in surgical techniques that could mitigate the risks associated with larger resections.