Impact of Body Mass Index on Outcomes Following Anatomic GreenLight Laser Photoselective Vaporization of the Prostate

Abstract

Introduction:

Obesity can lead to increased risk of perioperative complications in surgical patients, but evidence is lacking regarding the impact of obesity on bladder outlet surgery outcomes. We sought to assess the safety and efficacy of GreenLight photoselective vaporization of the prostate (PVP) in obese patients by comparing functional outcomes and complications in men, stratified according to the body mass index (BMI).

Materials and Methods:

A retrospective analysis was undertaken of 424 men who underwent 180W GreenLight PVP between 2012 and 2016 at two tertiary medical centers. Patients were stratified based on the World Health Organization (WHO) classification of obesity as determined by BMI. Normal weight men had BMI <25 kg/m², overweight men had BMI between 25 and 30 kg/m², and obese men had BMI greater than 30 kg/m². Primary endpoints examined were differences in intraoperative outcomes and incidence of intraoperative and postoperative complications between BMI groups. Secondary endpoints were improvements in the International Prostate Symptom Score, quality of life score, and the uroflowmetry variables, maximum urinary flow rate and postvoid residual.

Results:

The BMI groups did not differ regarding operative time or lasing time after matching for prostate volume, but overweight patients in the matched cohort still required higher mean energy use than normal weight men (258.6 kJ vs 233.9 kJ; p = 0.017). No significant differences between BMI groups were observed for intraoperative complications, postoperative complications, or readmission rates. All functional parameters were significantly improved at 24 months for each group, with no differences in improvement between groups. On multivariable analysis, BMI was not a significant predictor for outcomes following PVP.

Conclusions:

Increased BMI has a negligible effect on intraoperative parameters and does not affect postoperative complication rates or functional outcomes. GreenLight XPS 180W PVP is a safe and effective procedure in overweight and obese men.

Introduction

Obesity is a major public health concern worldwide and its prevalence is continually increasing.¹ Over one-third of adults are considered obese in the United States.^2,3 Obesity is often associated with other significant comorbidities and its presence also increases the risk for several chronic diseases.⁴ Furthermore, obesity has been implicated as a risk factor for increased perioperative complications in surgical patients.⁵

Several studies have demonstrated an association between benign prostatic hyperplasia (BPH) progression and obesity,^6,7 and such overweight patients have also been shown to have inferior functional outcomes following transurethral resection of the prostate (TURP) and open prostatectomy (OP) for treatment of BPH.^8,9 BPH is a highly prevalent disease, affecting 70% of men aged 60–69 years and over 80% of men over the age of 70.¹⁰ In the setting of increasing obesity prevalence and a continually aging male population, it is imperative to characterize the effect of obesity on surgical BPH management across treatment modalities.

GreenLight laser photoselective vaporization of the prostate (PVP) is a widely utilized treatment modality for BPH and has demonstrated similarity to TURP in regard to perioperative and postoperative outcomes.¹¹ Multiple authors have investigated the effects of large prostate volumes (PVs) on outcomes associated with PVP,^12,13 but there remains a paucity of evidence regarding the impact of obesity on bladder outlet obstruction surgery outcomes. We sought to assess the safety and efficacy of PVP in obese patients by comparing functional outcomes and complications in a group of men stratified according to different BMI groups.

Materials and Methods

Patient population

This study is a retrospective review of a prospectively maintained database of consecutive men undergoing PVP for BPH with the GreenLight XPS 180W system at our CHUM academic institution. Surgeries were performed by high-volume surgeons at two tertiary medical centers between 2012 and 2016. Inclusion criteria were all men treated for BPH with PVP. Exclusion criteria were men treated with the 120-W HPS system, those with prostate cancer, and those with neurogenic bladders. A total of 424 cases were identified and included in the study following exclusions. Cases were stratified according to the BMI category for data analysis according to World Health Organization (WHO) recommendations as follows: normal weight (<25 kg/m²), overweight (>25–30 kg/m²), and obese (>30 kg/m²). Treatment indications were in accordance with American, Canadian, and European guidelines.^14
–16

Surgical technique

All men underwent 532-nm laser PVP under anesthesia using GL 180W XPS, as previously described.¹⁷ Patients were administered preoperative antibiotic prophylaxis according to standard practice guidelines. A two-way 22F catheter with a 30-cc balloon was placed postoperatively. The catheter was removed at the surgeon's discretion, usually 24 hours following the procedure. Patients were seen postoperatively for follow-up at 3, 6, and 12 months, and annually thereafter.

Variables

Data on the following preoperative variables were collected: patient age, body mass index (BMI), comorbidity score stratified according to the American society of Anesthesiologists (ASA), history of BPH surgery, including TURP, use of BPH medications (5-α reductase inhibitors and α-blockers), anticoagulation and antiplatelet use, and prostate-specific antigen (PSA) level (ng/mL). Pre- and postoperative maximum urinary flow rate (Q_max), symptom index score (IPSS), and postvoid residual (PVR) data were collected and analyzed as continuous variables. Prostate size was measured in all men using transrectal ultrasonography (TRUS). Finally, operative characteristics were collected, consisting of total operating time (minutes), laser time (minutes), energy used (kJ), and number of fibers.

Outcomes

Primary endpoints compared between BMI groups were intraoperative characteristics, intraoperative complications, and postoperative complications. Intraoperative outcomes included in the analysis were TURP conversions, transfusions, length of hospital stay, and number of patients discharged home with a Foley catheter. Postoperative adverse events were analyzed at 30 and 90 days following surgery and stratified using the Clavien–Dindo scale classification.¹⁸

Secondary endpoints were change in IPSS, quality of life (QoL) score, and uroflowmetry variables, Q_max and PVR.

Statistical analyses

Descriptive statistics for categorical variables were reported using frequencies and proportions. Continuous variables were described using means, medians, and interquartile range. Statistical analysis was performed using one-way ANOVA with post hoc analysis using Tukey's test for normally distributed variables, as confirmed by the Shapiro–Wilk test. The Kruskal–Wallis test with post hoc analysis using Dunn's test was performed for non-normally distributed variables. Pre- and postoperative measurements were analyzed using the paired Student's t-test. Categorical data were analyzed using the chi-squared test. Multivariable logistic regression analyses were used to identify predictors of perioperative outcomes and complications. Propensity score matching was performed to produce matched triplets as previously described.¹⁹ Adjustments were made for potential demographic confounders. Statistical analysis was performed using the R software environment. Statistical significance was set at p < 0.05. All tests were two-sided.

Results

Baseline characteristics

Descriptive characteristics of the study population stratified according to BMI group can be seen in Table 1. Overall, 424 men underwent GreenLight XPS 180W PVP for treatment of BPH. There were 148 normal weight men (group 1), 201 overweight men (group 2), and 75 obese men (group 3). Median follow-up was 2 years (range 0–72 months). Compared with normal weight men, obese men were younger (mean age 65.8 years vs 69.5 years; p = 0.014) and had higher prevalence of hypertension (69% vs 46%; p = 0.001), but neither of these parameters were different between overweight and obese men or overweight and normal weight men. Overweight men (mean PV: 81.3 cc) had larger TRUS PVs than normal weight men (mean PV: 67.9 cc; p = 0.011), but obese men did not have significantly different PVs than either normal or overweight men. No statistically significant differences between groups were identified for ASA score, PSA, previous TURP, BPH medication usage, diabetes status, or anticoagulant use.

Table 1.

Baseline Patient Demographics Stratified According to Body Mass Index Status

Variable	BMI tertiles
Variable	Normal weight	Overweight	Obese	p
Patients (N)	148	201	75
Age, years	69.5 ± 9.7	68 ± 8.6	65.8 ± 9.1	0.014
BMI	23.1 ± 1.3	27.1 ± 1.4	33.1 ± 2.9	<0.001
PV (cc)	67.9 ± 33.2	81.3 ± 43.2	73.7 ± 33.3	0.004
ASA score	1.93 ± 0.72	1.97 ± 0.68	2.08 ± 0.63	0.15
PSA (preoperative)	4.32 ± 3.9	4.97 ± 4.6	3.81 ± 3.8	0.21
Previous TURP, N (%)	17 (11)	23 (11)	6 (6)	0.68
5-ARI usage, N (%)	84 (57)	118 (59)	39 (52)	0.61
Alpha blocker usage, N (%)	125 (84)	172 (85)	66 (88)	0.83
Diabetes, N (%)	16 (10)	25 (12)	16 (21)	0.079
Hypertension, N (%)	69 (46)	112 (55)	52 (69)	0.001
Anticoagulant usage, N (%)	36 (24)	50 (25)	20 (27)	0.93
Antiplatelet drugs	9 (6.1)	6 (3.0)	1 (1.3)	0.15
Acetylsalicylic acid	27 (18)	40 (19.9)	17 (23)	0.74
Antithrombotic drugs	11 (7.4)	11 (5.5)	4 (5.3)	0.72

Bold indicates statistical significance (p < 0.05).

ASA = American Society of Anesthesiologists; BMI = body mass index; PSA = prostate-specific antigen; PV = prostate volume; TURP = transurethral resection of the prostate.

Perioperative outcomes

Perioperative outcomes can be seen in Table 2. In prematching analysis, overweight patients required increased mean operative time (67.1 minutes vs 57.9 minutes; p = 0.019), increased mean lasing time (32.9 minutes vs 28.7 minutes; p = 0.032), and higher mean energy use (278.7 kJ vs 239.3 kJ; p = 0.031) compared with men with normal BMI. No differences were observed between obese men and either of the other groups. After propensity score matching was performed with respect to PV, BMI groups no longer differed in regard to operative time and lasing time. However, overweight patients in the matched cohort still required higher mean energy use than normal weight men (258.6 kJ vs 233.9 kJ; p = 0.017). No significant differences between groups were observed in pre- or postmatch analysis regarding the number of TURP conversions, intraoperative transfusions, Foley catheter requirements, or mean length of hospital stay.

Table 2.

Prematching Comparison of Intraoperative Characteristics and Complications Between Body Mass Index Groups

	BMI tertiles
Variable	Normal weight	Overweight	Obese	p
Patients (N)	148	201	75
Operative time (minutes)	57.9 ± 24.9	67.1 ± 35.3	64.2 ± 30.1	0.019
Lasing time (minutes)	28.7 ± 13.8	32.9 ± 16.9	33.0 ± 15.4	0.032
Energy used (kJ)	239.3 ± 135.6	278.7 ± 149.3	270.9 ± 145.4	0.031
No. of fibers	1.06 ± 0.24	1.14 ± 0.44	1.17 ± 0.38	0.042
Conversion to TURP, N (%)	3 (2)	10 (5)	2 (3)	0.31
Transfusion, N (%)	0	2 (1)	0	0.35
Length of hospital stay, days	0.73 ± 1.4	0.73 ± 1.8	0.44 ± 0.72	0.54
Home with Foley, N (%)	25 (18)	29 (15)	9 (13)	0.67

Postoperative complications

Postoperative complications stratified according to BMI status can be seen in Table 3. There were no statistically significant differences between groups for postoperative complication rates. Overall complication rates at 30 days were 38%, 38%, and 31% for normal weight, overweight, and obese men, respectively (p = 0.5). Readmission rates at 30 days were not significantly different between groups (p = 0.8). The most common complications were Clavien I hematuria at 30 days and Clavien I lower urinary tract symptoms at 90 days postoperatively. Only one Clavien III complication (hematuria in an obese patient) was observed across the entire cohort for the study period. Hypertensive patients were not more likely to experience a bleeding complication than normotensive patients. The association between anticoagulant use and hematuria complications between groups was investigated using multivariate logistic regression, with antiplatelet, aspirin, and antithrombotic use included as potential confounders. None were significantly associated with hematuria complications of any Clavien level at 30 or 90 days.

Table 3.

Postoperative Complications and Readmission Rates Stratified According to Body Mass Index Status

Variable	Normal weight (n = 148)	Overweight (n = 201)	Obese (n = 75)	p
30-Day complications, n (%)
Overall	56 (38)	76 (38)	23 (31)	0.51
Hematuria
Clavien I	15 (10.1)	26 (12.9)	6 (8)	0.46
Clavien II	1 (0.6)	0 (0)	0 (0)	0.39
Clavien III	0 (0)	0 (0)	1 (1.3)	0.097
LUTS
Clavien I	12 (8.1)	16 (8.0)	5 (6.7)	0.93
Clavien II	1 (0.6)	5 (2.5)	0 (0)	0.19
AUR
Clavien I	14 (9.5)	11 (5.5)	4 (5.3)	0.29
Clavien II	0 (0)	0 (0)	1 (1.3)	0.097
Incontinence
Clavien I	1 (0.6)	2 (1.0)	1 (1.3)	0.89
Clavien II	1 (0.6)	2 (1.0)	0 (0)	0.68
UTI
Clavien I	0 (0)	1 (0.5)	1 (1.3)	0.39
Clavien II	5 (3.4)	6 (3.0)	1 (1.3)	0.67
30-Day readmission	9 (6.1)	12 (6.0)	6 (8)	0.83
90-Day complications, n (%)
Overall	49 (33)	65 (32)	24 (32)
Hematuria
Clavien I	3 (2.0)	4 (2.0)	1 (1.3)	0.93
Clavien II	1 (0.6)	0 (0)	0 (0)	0.39
LUTS
Clavien I	12 (8.1)	12 (6.0)	5 (4.0)	0.47
Clavien II	16 (10.8)	27 (13.4)	14 (18.7)	0.27
AUR
Clavien I	2 (1.4)	2 (1.0)	0 (0)	0.62
Incontinence
Clavien I	7 (4.7)	6 (3.0)	1 (1.3)	0.38
Clavien II	3 (2.0)	7 (3.5)	3 (4.0)	0.65
UTI
Clavien II	3 (2.0)	5 (2.5)	1 (1.3)	0.84

AUR = acute urinary retention; LUTS = lower urinary tract symptoms; UTI = urinary tract infection.

Functional outcomes

Median follow-up in this study was 24 months. Following PVP, IPSS was significantly decreased compared with the baseline in all three groups at all follow-up endpoints (Fig. 1). Quality of life measures and noninvasive uroflowmetry parameters, PVR and Q_max, were all significantly improved at all endpoints after PVP for each group (Fig. 1).

FIG. 1.

Postoperative functional outcomes stratified according to BMI status. BMI = body mass index.

Multivariable analysis

Multivariable linear and logistic regression analysis was performed to identify predictors of perioperative outcomes and complications. After adjusting for all covariates, an increase in PV of 1 cc was associated with a 0.47-minute increase in operative time (p < 0.001, CI: 0.38 – 0.56), 0.19-minute increase in lasing time (p < 0.001, CI: 0.15–0.24), and 1.69 kJ increase in energy use (p < 0.001, CI: 1.26–2.11). All other variables included in the analysis did not reach statistical significance, including BMI as both a categorical and continuous variable.

Subgroup analysis

We considered that including men with a history of TURP or 5-ARI use in our overall analysis introduced the potential for confounding when analyzing differences between BMI groups, especially regarding intraoperative outcomes. An obese patient with a long history of finasteride use or extensive TURP, for example, might undergo PVP with a smaller prostate than a normal weight man with no 5-ARI history despite the expected direct relationship between PV and BMI. Thus, we performed a subgroup analysis after elimination of men with a history of either TURP or 5-ARI use (Table 4). The group numbers were reduced given that over 50% of men in each group in the overall cohort had a history of 5-ARI use, but we found that the only remaining significant difference between groups was in regard to hypertension: more men in both the overweight (p = 0.033) and obese (p = 0.037) groups had hypertension compared with the normal weight group. There were no longer any differences regarding intraoperative outcomes, including energy use.

Table 4.

Patient Characterization and Intraoperative Outcomes After Removal of Patients with History of Transurethral Resection of the Prostate or 5-Alpha Reductase Inhibitor Use from the Analysis

Variable	BMI tertiles			p
Variable	Normal weight	Overweight	Obese	p
Preoperative outcomes
Patients (N)	49	73	32
Age, years	69.7 ± 10.9	67.5 ± 8.3	65.9 ± 9.1	0.239
BMI	23.0 ± 1.3	27.1 ± 1.3	33.0 ± 3.0	<0.001
PV (cc)	74.6 ± 39.9	80.9 ± 41.7	74.7 ± 39.1	0.39
ASA score	1.85 ± 0.71	2.12 ± 0.71	2.06 ± 0.62	0.34
PSA (preoperative)	7.44 ± 13.2	7.10 ± 7.5	6.46 ± 12.2	0.20
Alpha blocker usage, N (%)	36 (73)	61 (84)	29 (91)	0.13
Diabetes, N (%)	4 (8)	9 (12)	8 (25)	0.09
Hypertension, N (%)	22 (45)	47 (64)	24 (75)	0.017
Intraoperative outcomes
Operative time (minutes)	62.9 ± 27.6	67.7 ± 34.1	65.6 ± 32.9	0.85
Lasing time (minutes)	31.8 ± 15.1	32.3 ± 15.0	33.6 ± 16.5	0.88
Energy used (kJ)	260.4 ± 146.9	279.0 ± 137.0	273.3 ± 150.3	0.63
No. of fibers	1.06 ± 0.24	1.10 ± 0.30	1.13 ± 0.34	0.60
Conversion to TURP, N (%)	3 (7)	4 (5)	0 (0)	0.34
Length of hospital stay, days	0.63 ± 1.3	0.75 ± 1.2	0.34 ± 0.48	0.29

Bold indicates statistical significance (p < 0.05).

Discussion

In this study, we sought to examine the individual effect of obesity on GreenLight Laser PVP outcomes with the 180W XPS system. Previous studies have examined the effect of PV on outcomes following prostatic surgery, but there is paucity of evidence regarding the effect of BMI, particularly in regard to surgical treatment modalities for BPH.

Carmignani and colleagues studied the effect of obesity on patients undergoing thulium laser treatment for BPH.²⁰ They reported that operative time was not significantly increased in overweight and obese patients, in keeping with our results from the postmatching analysis. However, we found that overweight patients required slightly higher energy usage than normal weight men even when controlling for PV. Generally, increased energy use could be considered related to increased prostate size, but in the setting of matched PVs in this study, it may indicate that more control of intraoperative bleeding was required in overweight patients. We did not include data on perioperative blood loss in this study and thus cannot comment on differences between BMI groups, but it should be noted that groups did not differ on preoperative anticoagulant use and only two transfusions were required across the entire cohort. Regardless of the etiology for increased energy use in overweight patients, it is unlikely to be of appreciable clinical significance. Valdivieso and coworkers studied the effect of energy density usage on outcomes following PVP with the XPS 180W system.²¹ They found that increased energy usage was not associated with increased complication rates or differences in functional outcomes at 2 years. In the present study, there was also no difference in complications and functional outcomes between groups at 48 months. Overall, it is likely that the most important consideration with overweight patients who could require more energy usage would be health care resources. Although we did not assess cost-effectiveness, increased energy usage is likely closely associated with increasing hospital costs.

On multivariable analysis, we found that PV was independently associated with perioperative outcomes and was predictive of increased operative time, lasing time, and energy use. BMI was not an independent predictor of these outcomes. Furthermore, differences in operative and lasing times between BMI groups fell away after matching for PV was performed, and all differences fell away after removing patients with a history of TURP or 5-ARI use. Despite the positive correlation between BMI and PV reported previously,^6,7,22,23 changes in perioperative parameters appear to be mostly related to PV. In a recent study looking at similar outcomes with GreenLight XPS 180W PVP, Valdivieso and colleagues found that men with large prostates had longer operative times and greater number of fibers used.¹²

Perioperative complications did not differ between groups, including the number of TURP conversions, transfusion requirements, Foley catheter requirements, and length of hospital stay. These results are similar to those reported by Carmignani who examined the effect of BMI on thulium laser outcomes.²⁰ Complication rates, reported according to the Clavien–Dindo classification, were not different at 30 and 90 days. The most common types of complications were also similar between groups. Overall, our results confirm GreenLight 180W XPS PVP to be a safe procedure in both normal weight and overweight patients.

All BMI groups in our study showed improvement in postoperative functional outcomes throughout the study period. There were no differences between groups regarding the magnitude of improvement despite overweight patients requiring increased energy use. A recent prospective study found that men with metabolic syndrome (MS) had worse postoperative storage symptoms following TURP and OP compared with men without MS.⁸ The authors also found that increased waist circumference was associated with worsened functional recovery following both TURP and OP, as measured by IPSS. Sener and coworkers also studied the impact of MS on TURP outcomes and found that MS had a negative impact on postoperative IPSS, QoL, and maximum urine flow rate (Q_max).⁹ In contrast, Yang and colleagues found that men with higher BMI (>24) undergoing GreenLight had better IPPS and QoL improvements than those undergoing TURP.²⁴ Although we did not compare our outcomes with patients undergoing TURP or OP, our results support GreenLight as an efficacious procedure in patients with increased BMI. Providers may recommend PVP in patients with higher BMI or enlarged prostates if they are able to afford the cost of the procedure.

Despite our findings, our study is subject to several limitations, including its retrospective nature and unbalanced patient numbers in each group. In particular, the obesity group was relatively smaller than the normal and overweight groups, limiting detection of statistically significant differences in regard to outcomes. For multiple outcomes, statistically significant differences were found between the overweight and normal weight groups, but not between the obese group and either of the other groups. Loss to follow-up may limit detection of differences in long-term functional outcomes between BMI groups, although significant improvements were observed throughout the study period. Finally, all procedures in this study were performed by an expert surgeon who was well beyond the learning curve, which could limit the generalizability of our findings to less-experienced surgeons. Nevertheless, this is, to our knowledge, the first study to date examining the effect of obesity on outcomes following PVP using the XPS 180W system. Our findings are important in the setting of endemic obesity and high prevalence of BPH in the population.

Conclusions

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

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