Heat Damage Zones Created by Different Energy Sources Used in the Treatment of Benign Prostatic Hyperplasia in a Pig Liver Model

Abstract

Introduction:

There are different types of transurethral prostatic surgeries and the complication profiles are different. This study aims to compare the heat damage zones (HDZ) created by five different technologies in a pig liver model.

Materials and Methods:

Monopolar resection, bipolar resection, electrovaporization, and Greenlight™ lasers of 120 and 180 W were used to remove fresh pig liver tissue in a simulated model. Each procedure was repeated in five specimens. Two blocks were selected from each specimen to measure the three deepest HDZ.

Results:

The mean of HDZ was 295, 234, 192, 673, and 567 μm, respectively, for monopolar resection, bipolar resection, electrovaporization, Greenlight laser 120 W, and Greenlight laser 180 W, respectively. The Greenlight laser produced one to three times deeper HDZ than the other energy sources (p=0.000).

Conclusion:

Both 120 and 180 W Greenlight lasers produced deeper HDZ than the other energy sources. Urologists need to be aware of HDZ that cause tissue damage outside the operative field.

Introduction

Monopolar transurethral resection of prostate (TURP) has been the gold standard treatment of benign prostatic hyperplasia.¹ However, since the development of bipolar TURP, transurethral electrovaporization of prostate (TUEVP), and photoselective vaporization of prostate (PVP) by 120 and 180 W Greenlight™ lasers, more options have been opened to urologists that could be tailor-made for their patients.² Although the efficacies of monopolar TURP, bipolar TURP, TUEVP, and 120 W Greenlight laser were shown to be similar, the complication profiles of these technologies were different.³ Through the modes of cutting, coagulation, and vaporization, heat will be generated to the prostatic surface, which provides hemostatic capability and possible complications by creating a heat damage zone (HDZ).⁴ An understanding of the HDZ of these technologies is important to investigate the pathophysiology of the procedure-related complications and to prevent external urinary sphincter damage that may not be apparent to the surgeons during the procedure.

In this study, we aim to investigate the HDZ of monopolar TURP, bipolar TURP, TUEVP, and Greenlight lasers at 120 and 180 W by using a pig liver model.

Materials and Methods

Simulation model

A pig liver model was used in this study. Fresh pig livers were bought from the market in the morning on the day of the procedure. A pig liver block of 10×20 cm was cut and mounted on the designated simulator with a ruler (Fig. 1). Transurethral surgeries of the five treatment options were performed on pig liver blocks. For each procedure, the energy source was applied at the rate of 1 cm per second for 10 minutes. Each energy source was repeated in five different specimens by a single surgeon.

FIG. 1.

The simulation model used in the current study.

Energy source

Monopolar resection (26F Karl Storz monopolar resectoscope with cutting at 100 W), bipolar resection (Olympus SurgMaster TURis with ESG-400 electrosurgical generator with cutting at 200 W, effect 2), bipolar electrovaporization (Olympus SurgMaster TURis with button electrode, ESG-400 electrosurgical generator with cutting at 200 W, effect 2), Greenlight laser at 120 W (AMS HPS system), and Greenlight laser at 180 W (AMLS XPS system) were used in the current study; 1.5% Glycine solution was used during monopolar resection and physiologic saline was used for the bipolar resection, bipolar electrovaporization, and Greenlight laser.

Assessment of the HDZ

After the procedures, all the specimens were fixed by 10% buffered formalin and were examined by a dedicated pathologist. The pathologist was blinded for the energy source that was applied to the specimen. Two tissue blocks were sampled from each specimen and were processed into paraffin blocks. Sections were prepared from each paraffin block, and the slides were stained by hematoxylin and eosin (Fig. 2). A micrometer was mounted on the eyepiece of the microscope for measurement of the HDZ, and the three deepest areas of the HDZ on each slide were measured. The HDZ was defined as the depth of the resection surface with cellular distortion and loss of normal tissue architecture after application of energy (Fig. 3). For each energy source, there were totally 30 measurements to assess the HDZ.

FIG. 2.

Cut section of the gross pig liver specimen after fixation in formalin (resection surface indicated by arrows).

FIG. 3.

Microscopic image of the heat damage zone (HDZ) in a pig liver specimen with the deepest area indicated by a bar (hematoxylin and eosin).

Statistical analysis

The Statistical Package for the Social Sciences (SPSS) v20.0 for Mac was used for statistical analysis. All the measurements were analyzed by usual descriptive statistics. All the tests were two-sided with a statistical significance set at p<0.05. One-way ANOVA test and Tukey's HSD test were used to compare the difference in the HDZ among different energy sources. The HDZ of monopolar resection is compared with the HDZ of the other energy sources by the Mann–Whitney U test.

Results

The results of the HDZ of all five energy sources are listed in Table 1. One-way ANOVA test of the HDZ among different energy sources was statistically significant (p=0.000). Tukey's honest significant difference (HSD) test showed that both Greenlight lasers of 120 and 180 W produced deeper HDZs than monopolar resection, bipolar resection, and bipolar electrovaporization.

Table 1.

Heat Damage Zone of Five Different Energy Sources

Energy source	Mean±SD (μm)	95% CI (μm)	p-Value (compared with HDZ of monopolar resection)
Monopolar resection	291.1±16.5	257.6, 324.7	—
Bipolar resection	238.7±29.6	178.0, 299.3	0.003
Bipolar electrovaporization	191.7±21.5	147.7, 235.6	0.000
Greenlight™ laser 120 W	672.7±48.2	574.0, 771.3	0.000
Greenlight laser 180 W	567.0±30.9	503.8, 630.2	0.000

SD=standard deviation; CI=confidence interval; HDZ=heat damage zone.

Discussion

With the developments of different minimally invasive surgeries, the efficacy of functional outcomes among monopolar TURP, bipolar TURP, TUEVP, and Greenlight laser were found to be similar, but with different the complication profiles.³ TUEVP has more postoperative clot retention, and Greenlight laser has more bladder neck stenosis and dysuria, despite both of them using vaporization techniques.³ On the other hand, Greenlight laser was shown to have superior hemostatic ability and could be performed safely in patients on ongoing anticoagulation.⁵

This is the first study, using a single model, comparing the HDZ among five different energy sources. The fresh pig liver model is used in the current study because it is rich in blood to facilitate the effect of Greenlight laser. We show that the Greenlight lasers in both 120 and 180 W provide one to three times more HDZs than monopolar resection, bipolar resection, and bipolar electrovaporization. The HDZ is markedly different between Greenlight laser and bipolar electrovaporization, which may explain that more bladder neck stenosis and urethral pain after Greenlight laser can be related to deeper underlying tissue damage. Postoperative clot retention, which may signify the technology to have less coagulation ability, was shown to be 4.3%–5.3% for monopolar TURP, bipolar TURP, and TUEVP, but 0.0% in Greenlight laser.³ This finding corresponded to our results that Greenlight laser had a deeper HDZ than the other technologies.

The membranous urethra in men was 2–2.5 cm on average.⁶ Our results showed that the HDZ created by various technologies was unlikely to cause significant damage to the external urinary sphincter. Meta-analysis from Ahyai³ showed the stress urinary incontinence rate was 0%–0.6% among these technologies. However, careful operation with resection or vaporization proximal to the verumontanum was the key to preserve urinary continence after surgery.

Various models, including canine prostate,⁷ pig kidney,^8,9,10 bovine prostate,¹¹ and human prostate,^12

–15 were adopted to investigate the HDZ created by various technologies (Table 2). Although the definitions of coagulation zones were consistent among different models, using different tissue model, energy settings, and methods to report the HDZ made direct comparison of HDZs among different studies difficult. Our pathologist reviewed the HDZ of human prostate tissue from our center and found that the glandular acini of the prostate had a much deeper HDZ than the fibromuscular region (Fig. 4). If the maximal HDZ of the glandular acini in the human prostate specimen was reported, the HDZ might be overestimated. Therefore, our results were more consistent with the studies reporting an average value of the measured HDZ. The major strength of our study was using a single model to report the HDZ among these technologies in a tissue with consistent texture. Using the pig liver model was unique to previous studies, yet a fairly consistent result was obtained compared with those studies reporting average HDZs of their study tissues. However, the major weaknesses of our study included using nonhuman tissue and the fresh liver model might have more deoxyhemoglobin than human tissue.

FIG. 4.

Microscopic image of human prostate specimen showing that the HDZ of the fibromuscular region (arrows) was thin in the specimen in general, but the glandular acini had a much deeper HDZ (asterisk) (hematoxylin and eosin).

Table 2.

Heat Damage Zone Measured by Different Studies with Different Models

			Results
Study	Model	Definition of HDZ	Monopolar resection	Bipolar resection	Bipolar electrovaporization	Greenlight laser 120 W	Greenlight laser 180 W
Huang and colleagues⁷	Canine prostate	10 sites with an equal interval	200.8±19.3	237.8±20.1
Qu and colleagues⁸	Pig kidney	12 measurements per slide and average maximum to minimum	140	217
Qu and colleagues⁹	Pig kidney	12 measurements per slide and average maximum to minimum	147±18.9	225.1±35.8
Kauffman and colleagues¹¹	Bovine prostate	At 3, 5, 6, 7, and 9 o'clock of the prostate				1000–1400
Wendt-Nordahl and colleagues¹⁰	Pig kidney	Not specified	216.0±42.3	236.3±36.7
Maddox and colleagues¹²	Human prostate	Maximum measurement			2400±840
Akgul and colleagues¹³	Human prostate	Not specified	1520±1290	3200±1530	3150±1650
Huang and colleagues¹⁴	Human prostate	10 sites at equal intervals	122.5±22.2	141.4±24.3
Huang and colleagues¹⁵	Human prostate	10 sites at equal intervals	127.6±27.8	148.5±31.6
Kang and colleagues¹⁶	Bovine prostate	Maximum measurement				1310	1090

Conclusion

Both 120 and 180 W Greenlight lasers produced deeper HDZs than the other energy sources. This may explain the unique complication profile and hemostatic ability of PVP. Urologists need to be aware of the HDZ that causes tissue damage outside the operative field.

Footnotes

Acknowledgment

The study is supported by the Multidisciplinary Simulation and Skills Centre of Queen Elizabeth Hospital.

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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