Surgical Steps That Elongate Operative Time in Robot-Assisted Radical Prostatectomy Among the Obese Population

Abstract

Introduction:

The association between increased body mass index (BMI) and prolonged operative time (OT) in robot-assisted laparoscopic radical prostatectomy (RLRP) has been suggested before. It is unclear, however, which RLRP step contributes to this finding. We aimed to assess the association between BMI and duration of RLRP steps.

Patients and Methods:

Records of patients who underwent RLRP between 2003 and 2009 were reviewed retrospectively. Demographics (including BMI) and OT were recorded. We reviewed total OT (incision to closure) and separate duration of sequential steps of RLRP: In room to incision (preparation), incision to robot docking (port-placement), docking to endopelvic fascia dissection end (retroperitoneal space development), dorsal vein complex (DVC) control, DVC-control end to prostate detachment (prostate dissection), vesicourethral anastomosis (anastomosis), and undocking time (undocking). We divided this cohort into BMI groups (<25, 25.0 to 29.9, 30.0 to 34.9, and ≥35) and compared their characteristics and OT.

Results:

A total of 555 patients were analyzed. OT was significantly different across BMI groups with medians of 159, 181, 178, and 191 minutes for BMI <25, 25 to 29.9, 30 to 34.9, and ≥35 kg/m², respectively (P = 0.002). For BMI <25, preparation and prostate dissection were significantly shorter. There was a correlation between higher BMI and longer time of prostate dissection with nerve-sparing technique (P = 0.016), but not with a non–nerve-sparing approach (P = 0.658). Higher BMI was associated with longer times of DVC-control and vesicourethral anastomosis (P = 0.048 and P = 0.035, respectively).

Conclusions:

Higher BMI is significantly associated with prolonged total OT for RLRP with specific steps (preparation, nerve-sparing dissection, DVC-control, anastomosis) responsible for this result. These data need to be considered when planning RLRP in the obese population.

Introduction

O besity is becoming an increasing morbidity worldwide. According to the World Health Organization, obesity is defined as body mass index (BMI) of 30 kg/m² or more, while BMI more than 25 kg/m² is considered overweight.¹ Worldwide, there were approximately 1.6 billion overweight and at least 400 million obese adults (age 15 years or older) in 2005. It is projected that by the year 2015, approximately 2.3 billion adults will be overweight and more than 700 million will be obese.¹

The association between increased BMI and prolonged operative times (OT) has been shown in open radical prostatectomy (either in the perineal or retropubic approach)² as well as laparoscopic radical prostatectomy.^3
–5 Robot-assisted laparoscopic radical prostatectomy (RLRP) is no exception.^6

–13

Little is known, however, concerning the specific steps of the procedure that are responsible for the increase in OT. In this study, we investigated the association between BMI and OT of specific sequential steps of RLRP.

Patients and Methods

After approval from our Institutional Review Board, we searched our prospectively maintained electronic database for records of consecutive patients undergoing RLRP between 2003 and 2009 within our structured teaching program that involved three chief residents and one fellow each year, under the mentorship of a single surgeon. RLRPs were performed using the DaVinci S surgical system (Intuitive Surgical Inc, Sunnyvale, CA) and the same transperitoneal technique described by Orvieto and associates.¹⁴

We collected the following variables: Age, ethnicity, BMI, preoperative prostate-specific antigen value, OT, nerve-sparing technique (yes/no), lymph node dissection, estimated blood loss (EBL), prostate weight, and margin status. OT were detailed as follows: Total OT (incision to closure) and separate duration of sequential steps of RLRP—in room to incision (preparation); incision to robot docking (port placement); docking to endopelvic fascia dissection end (retroperitoneal space development); dorsal vein complex (DVC) control; DVC-control to prostate detachment (prostate dissection); vesicourethral anastomosis time (anastomosis), and undocking time (undocking). Lymph node sampling times were not included in the present analysis. Records with missing OT or BMI data were excluded.

The cohort was divided into BMI groups (<25, 25–29.9, 30–34.9, and ≥35 kg/m²). We compared their characteristics and OT using chi square and rank sum tests as appropriate. P values for trend were obtained by linear regression and linear by linear association tests. Data are reported as median (interquartile range) or number (%) unless otherwise specified. Statistical analyses were performed using the SPSS v17 software (SPSS Inc, Chicago, IL). P values <0.05 were considered significant.

Results

Of 705 recorded cases, a total of 555 records were identified that matched the criteria. Median BMI was 28.1 kg/m² (25.8–30.8 kg/m²) and median total OT was 176 minutes (146–219 min). Patient characteristics and comparison between BMI groups are detailed in Table 1. There were no significant differences in demographic and perioperative variables.

Table 1.

Demographic, Clinical, and Perioperative Characteristics Stratified by Body Mass Index

	BMI (kg/m²)
Variable	<25	25–29.9	30–34.9	≥35	P value
Number	100	286	135	34
Age (years)	61 (56–67)	60 (55–64)	60 (55–64)	59 (54–63)	0.125
African American	16 (16.0%)	51 (17.8%)	32 (23.7%)	9 (26.5%)	0.276
PSA (ng/mL)	5.2 (3.9–6.8)	5.4 (4.0–7.1)	4.8 (3.8–6.9)	5.5 (3.7–7.7)	0.554
Prostate weight (g)	44 (36–58)	44 (36–56)	47 (38–59)	53 (41–64)	0.052
NS technique	55 (55.0%)	171 (59.8%)	85 (63.0%)	19 (55.9%)	0.636
EBL	150 (100–200)	150 (100–239)	150 (100–200)	150 (100–200)	0.624
PSM	17 (17.0%)	70 (24.5%)	26 (19.3%)	7 (20.6%)	0.376

BMI = body mass index; PSA = prostate-specific antigen; NS = nerve sparing; PSM = positive surgical margins; EBL = estimated blood loss.

Total OT were significantly different across BMI groups with medians of 159, 181, 178, and 191minutes in BMI <25, 25 to 29.9, 30 to 34.9, and ≥35 kg/m², respectively (P = 0.002). A detailed analysis of subsequent operation steps duration is reported in Table 2. Patient preparation, retroperitoneal space development, as well as prostate dissection durations were significantly different across BMI groups. In patients with BMI <25, all of these times were consistently shorter compared with larger patients.

Table 2.

Operative Times of Sequential Steps Stratified by Body Mass Index

	BMI kg/m ²
Variable	<25	25–29.9	30–34.9	≥35	P value	P for trend
Number	100	286	135	34
Preparation	39 (35–45)	42 (36–48)	44 (38–50)	42 (35–49)	0.003	0.008
Port placement	15 (12–19)	15 (12–19)	16 (13–20)	15 (14–18)	0.529	0.655
Retroperitoneal space development	17 (13–25)	20 (15–30)	22 (15–30)	19 (15–30)	0.027	0.066
DVC time	6 (5–8)	7 (5–10)	6 (5–10)	7 (5–10)	0.124	0.048
Prostate dissection	47 (38–63)	55 (42–75)	55 (42–74)	55 (42–80)	0.046	0.065
Non–NS	53 (41–80)	60 (45–81)	58 (45–77)	56 (46–90)	0.885	0.658
NS	45 (35–53)	55 (40–70)	54 (40–72)	50 (40–68)	0.010	0.016
Anastomosis	32 (25–44)	35 (26–47)	37 (25–50)	39 (30–51)	0.134	0.035
Undocking	7 (5–10)	7 (5–10)	7 (5–10)	8 (5–10)	0.671	0.879
Total OT	159 (137–202)	181 (151–220)	178 (148–230)	191 (162–225)	0.002	0.006

BMI = body mass index; DVC = dorsal vein complex; NS = nerve–sparing; OT = operative time.

When stratified by the nerve-sparing (NS) approach, the time of prostate dissection showed significant differences across BMI groups only in cases where NS technique was performed (P = 0.010); in cases of non-NS technique, no differences were apparent between the times of prostate dissection (P = 0.885). There was a correlation between higher BMI and longer times of prostate dissection with NS technique (P = 0.016). Interestingly, when analyzing trends, higher BMI was also associated with longer times of DVC control as well as vesicourethral anastomosis (P = 0.048 and P = 0.035, respectively).

Discussion

With the expected increase in the obese population around the world, we are witnessing an increase in the overweight and obese population diagnosed with prostate cancer. This, in turn, reflects on the RLRP population characteristics with larger patients undergoing surgery.

Obesity has been associated with diabetes, cardiovascular and musculoskeletal (ie, osteoarthritis) diseases, as well as malignancies (breast, colon, endometrial).¹ Although the role of obesity in the development of prostate cancer remains debatable,¹⁵ recent data suggest that this population has worse perioperative and postoperative outcomes compared with the normal weight population during and after RLRP. Correspondingly, obese patients have a higher chance of bleeding during RLRP,^6
–8,10,12 longer hospital stay,^6,8 larger disease volume,^10,11 higher rates of positive surgical margins,^8,10 and advanced pathologic stages.^8,11 Obesity has also been associated with longer times to recovery of sexual function, urinary control, and worse urinary bother symptom scores.^6,11

Of note, larger patients may be at increased risk of conversion to an open procedure^8,11 and a lower chance to undergo bilateral nerve sparing.^10,11

All series that have been published to date regarding RLRP in obese patients have consecutively shown increased OT, indicating more complex surgery compared with lean patients. Possible explanations for this finding include:

Deeper and narrowed true pelvis seen in the obese that may be associated with occasional exostosis of the symphysis pubis.^7,10

Increased intraoperative EBL.⁸

Suboptimal port placement, resulting in a longer distance from skin to operative field.^7,10

Robotic arms positioning in the obese patient that results in a more vertical angle of the instruments, whereby their path may be obstructed by the symphysis pubis and the pelvic brim.^7,8

Dissection through more intraperitoneal and pelvic fat planes, which in turn reduces visibility and mecessitates more effort to clear.^7,8,10,13

Obesity has also been associated with larger prostates in previous studies,^6,7,12 and this may constitute an additional explanation because a large gland needs longer and more complex dissection, resulting in an overall longer OT.

Sequential steps of RLRP in the obese population were previously studied by Khaira and colleagues¹³ who sought to investigate whether increased BMI elongates OT in RLRP. Sequential steps (ie, port placement, robot set-up, bladder release, endopelvic fascia dissection, DVC stitch, bladder neck dissection, seminal vesicle dissection, neurovascular bundle dissection, vesicourethral anastomosis, port closure) were prospectively recorded in a series of 285 patients undergoing RLRP, among whom 236 had a BMI of <30 kg/m² and 49 had a BMI of ≥30 kg/m². The authors found an overall increased OT in the obese population with significantly longer times needed for vesicourethral anastomosis and port closure. No significant differences were found in the remaining steps, however. Interestingly, their study suggested that larger prostate size may be associated with longer times for neurovascular bundle dissection, bladder release, and vesicourethral anastomosis, regardless of BMI and total OT.

Another study found no correlation between elongated anastomosis time and increased BMI.¹⁰

Our study consisted of 555 patients, among whom 169 were obese and 286 were overweight. Hence, we believe this reflects a mature series with much reliable observations. We found a significant trend, meaning that higher BMI is associated with longer anastomosis time. A possible explanation for this phenomenon lies in the large prostate volume that was recorded for the obese patients in our series. This may make the anterior urethral dissection more difficult, resulting in a shorter urethral stump and a technically challenging vesicourethral anastomosis.

Moreover, we found that patient preparation, retroperitoneal space development, as well as prostate dissection were consistently shorter in normal weight patients compared with larger ones.

In the case of NS technique, the time of prostate dissection was significantly longer in the obese population but showed no difference when NS was not performed. As proposed by others, these findings may reflect anatomic challenges (larger prostate size, increased amount of intraperitoneal and pelvic fat) as well as longer times probably needed for anesthesia induction and patient positioning.

Our study still has some limitations: The first limitation is the exclusion of lymph-node dissection from the statistical analysis. This is because of insufficient records, which resulted in low numbers of lymph node dissection per each BMI group. Given the overall increased intra-abdominal and intrapelvic fat seen among the obese, this might have elongated OT even more in the obese population compared with the normal weight patients.

The second limitation is the fact that our tertiary medical center is a teaching hospital whereby the various stages of RLRP are carried out by both mentor and trainees (ie, sixth year resident and second year endourology fellow) in an alternate manner. As shown previously,⁹ OT during RLRP is influenced by the surgeons' relative experience, being longer for early trainee and getting shorter throughout the learning curve achievement.

Because this series reflects multiple surgeons in various stages across their learning curves, total OT and OT elongation for sequential steps in RLRP may be longer than expected and may reflect learning curve delays.

Despite these limitations, we managed to prove the complexity of RLRP among the obese patients, and this should be kept in mind when counseling these patients in the clinic and when planning RLRP in an obese person. We believe that weight loss should always be considered before surgery.

Conclusions

Higher BMI is significantly associated with prolonged total OT for RLRP with specific steps (patient preparation, prostate dissection with NS technique, DVC control, and vesicourethral anastomosis) significantly responsible for this finding. This may reflect both anatomic and clinical challenges seen in the obese population and needs to be taken into account when counseling the obese patient in the clinic and when planning his surgery.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

References

WHO. Fact sheet No. 311- Obesity, September 2006. http://www.who.int/mediacentre/factsheets/fs311/en/index.html.

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