Introduction

The incidence of kidney cancer continues to rise in the US, in large part attributed to early and enhanced detection of incidental masses with cross-sectional abdominal imaging [1–3]. Partial nephrectomy (PN) offers comparable oncologic control [4] and improved renal function [5] when compared to radical nephrectomy. It is recommended as standard therapy for stage T1a and many T1b renal tumors [6]. Accordingly, the utilization of robot-assisted partial nephrectomy (RAPN) is also increasing [7, 8]. RAPN affords an operation with less blood loss, shorter length of stay, more rapid convalescence, and improved cosmesis when compared to open PN [9]. Furthermore, urologists may favor RAPN over laparoscopic partial nephrectomy (LPN) as it offers more favorable renal function recovery, shorter length of stay (LOS), and shorter warm ischemia time (WIT) [10]. It also provides relative technical advantages [11] and a shorter learning curve [12] when compared to LPN.

Robotic surgery affords the surgeon the advantages of enhanced visualization and dexterity. The sacrifice for these advantages is being physically separated from the patient. The surgeon relinquishes some control of skilled, precise maneuvers to the bedside assistant. Trepidation exists amongst some robotic surgeons regarding the relative acumen and experience of their bedside assistant; many of these concerns are based on early robotic experience and are descriptive only [13–18]. We sought to formally examine the significance of the post-graduate year (PGY) of the bedside assistant on surgical outcomes in RAPN at an academic center.

Patients and methods

Study population

After Institutional Review Board approval, we performed a retrospective review of a prospectively maintained database of 414 consecutive RAPN performed by four experienced robotic surgeons at our institution from April 2011 to September 2014. Exclusion criteria included any incomplete or unclear documentation of the level of the assistant. Data collected included: age, gender, body mass index (BMI), American Society of Anesthesiologists score, Charlson comorbidity index (CCI), tumor size, nephrometry score, surgical approach, laterality, operative time, use of off-clamp technique, WIT, estimated blood loss (EBL), need for renal pelvis repair, LOS, complications, positive surgical margins, and pathology. A senior-level assistant was defined as a resident in his or her PGY-4 or -5, or a fellow. Junior-level assistants were considered to be PGY-2, PGY-3, or a nurse first assistant at the bedside. The nurse first assistant had participated in <20 robotic cases. Physician assistants (PAs) are not employed for assistance at the bedside at our institution. In cases where a senior- and junior-level resident were both noted assistants, the junior resident was considered the bedside assistant. In such circumstances, it is our practice that the more senior assistant is unscrubbed and performs portions of the case at the console.

Statistical analysis

Univariate analyses were performed using Wilcoxon rank-sum test for numerical variables and Chi-square test of independence for categorical metrics. Multivariate analyses were performed to assess for a relationship between the level of experience of the assistant and the following outcomes: operative time, EBL, WIT, LOS, presence of a postoperative complication, and surgical margin status. The multivariate models controlled for the following variables: BMI, age, surgeon, gender, pathologic tumor size, nephrometry score, off-clamp status, CCI, need for pelvicaliceal repair, and approach (retro- vs. transperitoneal). Models for LOS, margin status, and complications additionally controlled for EBL and operative time. Linear regression, Poisson, and logistic regression models were used for continuous, counting, and binomial data, respectively. All statistical analysis was performed in R version 3.2.0.

Results

The total number of patients meeting inclusion criteria was 414. Junior-level assistants were present in 115 cases, and senior-level assistants in 299. See Table 1 for patient and surgical characteristics. After univariate analysis, patient and tumor characteristics were similar except for BMI which was greater in the senior assistant group (31.5 vs. 29.9 kg/m2, p = 0.031). In regard to surgical parameters, the percentage of off-clamp procedures was greater in the senior assistant group (98/299 (32.8 %) vs. 23/115 (20.0 %), p = 0.011).

Table 1 Patient and surgical characteristics in robot-assisted partial nephrectomy cases for which there was a junior- or senior-level bedside assistant
Full size table

Based on univariate analysis, LOS was shorter for the senior assistant group (2.23 vs. 2.38 days, p = 0.048) however, this relationship did not persist after multivariate analysis. No differences in outcomes were witnessed between the junior and senior assistant groups, including for operative time, EBL, WIT, LOS, presence of a postoperative complication, and surgical margin status (Table 1).

Based on multivariate analysis, postoperative complications were not associated with resident experience level (p = 0.916). They were, however, associated with CCI >3 and performing the procedure off clamp (p = 0.023 and p = 0.047, respectively). Operative time was 9.3 min longer and trended toward significance in the junior-level group (p = 0.051). Tumor size and BMI were both associated with increased operative time (p < 0.001). EBL was not associated with resident experience level (p = 0.488) but was associated with tumor size (p < 0.001) and nephrometry score (p = 0.040). The results of this multivariate analysis can be found in Table 2.

Table 2 Multivariate analysis of patient and surgical characteristics with perioperative outcomes in robot-assisted partial nephrectomy
Full size table

A sub-group multivariate analysis was performed which excluded off-clamp procedures. In the on-clamp cohort of RAPNs (N = 325), there was no difference between cases done with junior- or senior-level assistance in terms of operative time, EBL, WIT, LOS, complications, or positive margin status (p = 0.14, 0.50, 0.35, 0.86, 0.53, and 0.87, respectively).

Discussion

The surgeon–patient relationship is unique and deeply valued. With the advent of robotic surgery, tactile feedback is forfeited for the benefits of superior visualization and precision of surgical maneuvers. The bedside assistant is, therefore, relied upon heavily. The level of experience of the assista

nt can be a source of anxiety for the surgeon. In the present study, we found the outcomes were similar between cases performed with either a junior- or senior-level assistant. There were no differences between the assistant levels for operative time, EBL, WIT, LOS, presence of a postoperative complication, or surgical margin status. Operative time did trend toward being shorter in cases with senior-level assistants (p = 0.051).

After univariate analysis, there was a difference in LOS between senior- and junior-level assistants (2.23 ± 1.24 vs. 2.38 ± 1.24 days, p = 0.048). However, the results of multivariate analysis did not corroborate this relationship. It is likely that this small, but statistical, difference can be attributed to surgeon-specific practices; after controlling for surgeon, the difference was nullified. A similar explanation may apply to the univariate discrepancy in off-clamp procedures (98/299 (32.8 %) vs. 23/115 (20.0 %) for senior vs. junior assistants, p = 0.011). This is substantiated by the fact that surgeon 1 had a senior-level assistant 153/218 (70.2 %) of the time, compared to surgeon 2 with 120/152 (78.9 %). It is known within our institution that surgeon 2 performs off-clamp RAPN more often, per his preference. An unintended bias may be present regarding the assignment of senior-level assistants more often to surgeon 2, as there was no randomization of residents to each surgeon’s case.

Few previous authors have objectively examined the significance of the bedside assistant’s experience. Sgarbura et al. assessed the experience of bedside assistants in thoracic, digestive, and gynecologic robotic surgery [18]. The authors found that those assistants with formal training had improved efficiency for simple tasks such as placing instruments. More complicated tasks (e.g., application of stapler, and deployment of endobag), however, were pre-selected for assistants with ≥150 cases of laparoscopic experience [18]. In 2014, McMillan et al. queried the National Surgical Quality Improvement Program (NSQIP) database of 5087 robotic-assisted radical prostatectomies, performed with or without the assistance of a resident [19]. There were no differences in operative time or complications between the groups. Although when stratified by PGY status, those cases with a PGY >1 did have longer operative times. Importantly, in the absence of resident assistance, the level of training of the assistant was not defined.

Kern et al. compared resident and fellow involvement in minimally invasive versus open PN [20]. Although unable to qualify whether cases were done robotically or laparoscopically, the authors found higher complications rates in those performed with resident assistance compared to “attending alone.” Further, they found that the presence of a PGY ≥6 was associated with greater postoperative morbidity. Lastly, Ruhotina et al. reviewed the NSQIP database of urologic minimally invasive operations including 573/786 (72.9 %) PNs with resident involvement [21]. There was no difference in complications for any of the procedures. Due to the nature of the database, no distinction could be made between robotic and laparoscopic procedures. The authors also acknowledged the need for studies assessing WIT, EBL, and positive surgical margins. Such data are presented for the first time in the present manuscript. Furthermore, the present cohort is homogenous in regard to the small number of surgeons from a single institution.

The diffusion and practice of new surgical technology are a concern as they pertain to appropriate, standardized training and credentialing [22]. Although most of this focus relates to the surgeon, the rest of the operative team, and particularly the bedside assistant, need to be comfortable performing delicate tasks. At present, there is no specific certification required for an assistant with a critical and highly technical role in RAPN. Thiel et al. constructed a structured bedside assistant training program for robotic prostatectomy [23]. In the study, the participants viewed the course as being very beneficial, although no objective evidence of improvement in the assistant’s skill or the patient’s outcomes is available. At our institution, no dedicated training is required for bedside assistance during robotic operations. However, junior-level residents are required to attend a session each year with the da Vinci representative and experienced, robotically trained faculty. Along with training for console-specific techniques, topics such as docking the robot and manual clutching of the robotic arms are discussed. Residents are able to practice operating the robot using virtual trainers to simulate surgical techniques. All residents are encouraged to use the robotic trainer that is available in the simulation center as their time allows. In addition, the responsibilities during a robotic case are typically assigned in graduated fashion. As such, residents experience a predictable number of robotic cases in each of their post-graduate years. Future study may address the objective changes in accuracy and speed of bedside assistants performing surgical maneuvers in an ex vivo model.

The findings detailed herein do not intend to diminish the vitality of the role of the bedside assistant nor undermine the importance of the assistant’s competence. As previous authors have noted, the assistant’s performance is critical to the safe and successful performance of a robotic operation [23]. Sur et al. found that if the assistant amasses mistakes, surgical efficacy and outcomes depreciate, leading to undo morbidity and open conversion [24]. Other authors have noted that relative inexperience of a bedside assistant can relate to untoward intraoperative complications such as aortic punctures and difficulties with lost needles [25, 26]. As a result of such reports and the implicit apprehension a surgeon might have in delegating surgical acts, some robotic surgeons have looked toward minimizing the role of the assistant. Techniques such as employing the robotic fourth arm, ultrasonic TilePro software (Intuitive Surgical, Sunnyvale, CA) [15], and barbed suture for renorrhaphy [27] have been suggested. The TilePro system allows the console surgeon to remain at the console and independently manipulate the intracorporeal ultrasonic probe while viewing the live image. Likewise, barbed suture has been utilized by some due to its increased efficiency, which may in part be due to the reduced number of maneuvers designated to the bedside assistant [e.g., cutting suture, applying Hem-o-lok clips (Teleflex Incorporated, Morrisville, NC)].

Our study presents limitations inherent to a retrospective study. Although not quantifiable, the difference in BMI may represent an unconscious selection bias, whereby a surgeon arranged for a more senior assistant. This is not, however, common practice at our institution as assignments are made by the chief resident, not by staff urologists. Further, the experience is from a single institution with a high-volume robotic practice. Dedicated robotic operating room staff (nurses and surgical technicians) are present for robotic cases. Therefore, the results may not be translatable to every practice type. Finally, the experience of surgical technicians and PAs, who are employed for bedside assistance in other practice types, was not evaluated in the present study. Residents and/or fellows assist during the vast majority of robotic procedures at our institution (<20 cases were performed with the assistance of a nurse first assistant). Certainly some well-experienced PAs, nurse practitioners, and surgical technicians may be far more facile with bedside maneuvers and the progression of a case, so as to provide an advantage in terms of operative time and other surgical outcomes. Future studies may compare the surgical outcomes of those surgeries assisted by residents and fellows versus PAs and technicians, based on the number of cases experienced. Finally, we endorse the education of novice bedside assistants, both physicians and non-physicians, before performing any robotic surgery.

Conclusions

Robotic technology may confer relative technical advantages to the surgeon during RAPN. In exchange, the surgeon must rely heavily upon the bedside assistant to perform skilled operative maneuvers. There is common concern about the impact of the assistant’s level of experience. However, at a large academic center, PGY level is not associated with any quantifiable difference in surgical outcomes.