Benign prostatic hyperplasia (BPH) is one of the most prevalent urological conditions in middle-aged and elderly men. Pharmacological treatment has limitations, while traditional surgical treatment has drawbacks such as high surgical risks and postoperative complications. Therefore, in the past decade or so, a lot of research is being conducted on microinvasive surgical treatment of BPH. Among them, selective photovaporization of the prostate (PVP) using the green laser (Greenlight) is expected to gradually replace traditional transurethral resection of the prostate (TURP) as an effective method for the new generation of BPH treatment because of its low risk and few postoperative complications. Sun Jie, Department of Urology, Shanghai Renji Hospital
Benign prostatic hyperplasia (BPH) is one of the most common conditions of the urinary system in middle-aged and elderly men. There are limitations in drug treatment. In the past decades, transurethral resection of the prostate (TURP) was considered the gold standard for the treatment of BPH, but there are drawbacks such as high surgical risks, many postoperative complications, and long postoperative recovery time, so a large number of studies on new treatments for BPH are being conducted in the past decade or so.
The first successful transurethral laser resection of the prostate (VLAP) was performed by Costello et al. in 1992 with good clinical results, after which the advantages of laser technology in the treatment of BPH have slowly emerged. In 1997, Kuntzman et al. performed the first animal trial of the 60W KTP laser and soon used it in clinical treatment. 80W KTP was first used in clinical BPH treatment in 1998 and achieved significant results. Laserscope launched 80W power (peak power 280W) green laser PV system to further improve the green laser system. Through clinical application and research in recent years, the green laser is expected to gradually replace the traditional transurethral resection of prostate (TURP) as the best method for the new generation of BPH treatment with its advantages of low surgical risk, few postoperative complications and short recovery time. This article briefly reviews the principles, methods, advantages, and current research findings related to the PVP procedure.
Principle.
1. Green laser.
The light emitted from different laser media may be visible, infrared or ultraviolet light. The laser in the visible range is divided into different colors according to the wavelength, and the green laser is the visible light with the wavelength of 532nm.
The Nd:YAG laser with a wavelength of 1064nm is transformed into a KTP laser with a wavelength of 532nm through the frequency doubling of a potassium titanium phosphate (KTP) crystal, which is also known as the greenlight-laser, while the Nd:YAG is an infrared light.
2.Prostate selective photovaporization (PVP)
The PVP procedure applies the feature that the KTP laser can be selectively absorbed by the oxygenated hemoglobin in the prostate tissue, but not by water, so it is also named Prostate Selective Photoplethysmography (PVP). It has been confirmed that the patient’s preoperative hemoglobin level does not affect the effect of PVP.
The procedure can be performed under lumbar or local anesthesia. During the procedure, fiber optics are introduced into the prostate tissue through a continuously flushed cystoscope, and the KTP laser acts on the prostate tissue in a near-contact mode through the fiber and delivers all the energy to the tissue, forming an effective precipitation that effectively and rapidly vaporizes (tissue temperature above its boiling point and is instantaneously evaporated), cuts, and coagulates (tissue temperature below its boiling point but above the protein denaturation starting temperature point). Intraoperative bubble formation is a sign of effective vaporization, and the absence of bubble formation indicates coagulation necrosis.
The operator should extend the fiber 1 to 2 cm beyond the cystoscope during the procedure, slowly swing the fiber from side to side, and circumnavigate the prostate in a clockwise or counterclockwise direction starting at the bladder neck for one week, and repeat the procedure after moving the cystoscope outward. the criterion for the end point of the PVP procedure is to leave a lumen at the prostatic urethra similar to that of TURP.
The green laser optically penetrates to a depth of only 0.8 mm, and the high laser energy concentration at the superficial tissue level results in the highest power density per unit volume of tissue, thus allowing for very effective vaporization. At the same time, the laser beam forms a 1-2mm wide coagulation zone on the tissue surface, which provides good hemostasis. Since the KTP laser is not absorbed by water, the energy is not consumed in water during the near-contact mode vaporization, creating a clear field of view that is not obscured by bubbles. It should also be noted that the best vaporization effect is achieved when the fiber is 0.5mm away from the prostate tissue, and as the distance increases, the power density decreases accordingly.
Efficacy and advantages and disadvantages.
1. Efficacy.
The efficacy of BPH surgery can be evaluated by comparing and analyzing (objectively) the improvement of symptoms (AUA symptom score, quality of life score) and related parameters (including prostate volume, urinary flow rate, residual urine, etc.) in BPH patients before and after PVP surgery. Early clinical trials have initially demonstrated significant improvements in both subjective and objective outcomes of green laser in patients with BPH.
The first clinical application of the 60WKTP laser was performed in 1996 in 10 patients at MayoClinic in the United States. Intraoperatively, the F22 cystoscope was applied with continuous flushing with sterile water, and the patients showed no significant blood loss or flushing fluid absorption, no need for continuous bladder flushing after surgery, and all patients had their catheters removed within 24 h. The maximum urinary flow rate improved from a mean of 8 mL/s preoperatively to 19.4 mL/s, a significant improvement of 142%; no difficulty in urination, hematuria, or need for re-catheterization occurred after surgery. However, due to the slow vaporization rate of the 60WKTP laser, it is mostly used for BPH patients with prostate volume <60ml. In this case, the average power of the laser needs to be increased so that tissue vaporization can be performed faster and more efficiently.
With the 80W KTP lateral delivery laser system (GreenLightPV system), the maximum peak laser power is 280 W and the average power is 30-80 W. Intraoperative laser-specific cystoscopy with F23 continuous irrigation is used, and the irrigation solution is normal saline. In a study of 139 patients treated with 80WKTP, the mean procedure time was 38.7mins, with no significant change in blood sodium concentration before and after the procedure. 32% of patients did not require indwelling catheterization after the procedure, and the mean indwelling catheterization time was 14.1hrs. One year later, patients had an 82% decrease in AUA symptom scores (from 24 to 4.3 points preoperatively); quality of life scores The maximum urinary flow rate increased from 7.8 ml/s before surgery to 22.6 ml/s, with a mean improvement of 190%; the residual urine volume decreased by 78% (from 114.3 ml to 24.8 ml before surgery); and the prostate volume decreased by 37% (from 54.6 ml to 34.3 ml before surgery). Thirteen patients (9.4%) had postoperative dyspareunia lasting more than 10 days (10 days to 6 months), of which only 4 patients required pharmacological intervention; 12 patients (9%) had transient hematuria for more than 10 days; 9 patients (6.5%) had transient urinary incontinence; 7 patients (5%) required re-catheterization due to postoperative urinary retention; none of the patients required reoperation .
In the 5-year follow-up of patients with PVP, there was a 79% decrease in AUA scores, an 80% improvement in quality of life scores, a 173% increase in maximum urinary flow rate, an 18% reduction in prostate volume, and a 77% reduction in residual urine.
A study of PVP complications in 406 BPH patients with a mean age of 72 years confirmed that PVP has a low rate of intraoperative and postoperative complications and is a very safe surgical procedure for the treatment of BPH.
2. Advantages
PVP can remove the enlarged large prostate tissue during the operation, with significant therapeutic effect, which can significantly improve the subjective and objective results of patients; the laser beam forms a coagulation band on the surface of the tissue at the same time of the operation, which plays a hemostatic role, with less bleeding during the operation and less likely to cause hematuria after the operation; continuous bladder irrigation with sterile water or saline can be performed during the operation, and the irrigation fluid is hardly absorbed, which does not affect the blood sodium concentration of patients before and after the operation; postoperative bladder The postoperative bladder flushing time and catheter retention time are short, and some patients do not even need continuous bladder flushing and do not need intubation; the recovery time of patients is short, and they can resume normal life and work soon; the postoperative period will not cause retrograde ejaculation and sexual dysfunction.
PVP is also effective in patients with acute urinary retention, patients on oral anticoagulant therapy, older patients with comorbid chronic medical disease (>80 years), patients with prostate volume >60 g, and patients with severe heart disease or dementia who cannot tolerate TURP surgery.
In terms of treatment costs, a comprehensive comparison of the costs of preoperative treatment and examination, surgical costs, treatment of complications, and reoperation costs demonstrated that PVP is the most cost-effective surgical procedure for BPH compared to other microinvasive procedures and TURP.
3. Disadvantages
Since PVP cuts the prostate tissue by vaporization, no specimen is sent for pathological examination after surgery, so it needs to be combined with PSA and prostate aspiration for clear diagnosis before surgery, and if tumor tendency is found, it should be treated separately.
Comparison.
1. Other types of laser surgery
(1) Transurethral laser resection of the prostate (VLAP)
Since 1992, when Costello et al. first successfully performed transurethral laser resection of the prostate (VLAP) with good clinical results, VLAP was used in the early 1990s as an effective treatment for BPH. VLAP uses a continuously emitted Nd:YAG laser with an output power of up to 60 W, which is delivered to the prostate through a light conduction device. prostate area and vaporizes the tissue through contact patterns and thermal effects. However, this method is not conducive to widespread application because of the disadvantages associated with deep tissue necrosis (optical penetration depth of 10 mm) and deep coagulation layer (7 mm), and the necessity of using stents and catheters after surgery.
(2) Holmium laser prostatectomy (HoLAP)/ Holmium laser enucleation of the prostate (HoLEP)
In 1995, holmium laser (Ho:YAG) started to be used in clinical practice. Holmium laser is a pulsed near-infrared laser invisible to the naked eye with a wavelength of 2100 nm, which can be highly absorbed by water. The laser therefore vaporizes water in the tissue for cutting purposes through direct contact mode, which will inevitably diminish the cutting effect of the laser if direct contact cannot be maintained. Holmium laser has a very shallow tissue penetration of 0.4 mm, and very little tissue is effectively heated, which severely affects the rate of vaporization and limits the thickness of the coagulation layer and the hemostatic effect. HoLEP has good efficacy in patients with giant prostate.
Compared with PVP, all patients had significant improvement in symptoms, IPSS score and urinary flow rate after the procedure, all of which were not significantly different, but the operative time of HoLAP was significantly higher than that of PVP.
The following disadvantages limit the development of holmium laser in clinical practice: the laser cutting effect is easily attenuated during surgery, and the vaporization rate and hemostasis are not ideal; the large piece of prostate tissue removed during surgery must be pushed into the bladder and crushed before it can be aspirated out of the body through the urethra, which takes a considerable amount of time and prolongs the operative time; HoLEP requires the hyperplastic prostate to be removed closely to the peritoneum, and the operator must have a good grasp of the morphology between the gland and the surgical The learning curve is long.
2. Transurethral resection of the prostate (TURP)
Transurethral resection of the prostate is the most common clinical procedure for the treatment of BPH. During the surgery, a special electrodescope is placed through the urethra to reach the prostate, cutting the prostate tissue piece by piece, while stopping the bleeding by electric current thermal cautery, and placing a foly catheter to drain the urine after the surgery. Dilutional hyponatremia due to absorption of irrigation fluid through the veins on the resected wound, the prostatic peritoneum or bladder perforation, or the peritoneal layer of the resected prostate tissue during electrodesiccation predisposes to transurethral resection postoperative syndrome (TURS).
In comparison with PVP, both were found to significantly improve urinary flow rate, IPSS score, and prostate volume, but the TURP group was significantly higher than the PVP group in terms of hospital days, catheter insertion time, and complications.
TURP has the following disadvantages: complicated surgical procedure and high surgical risk; difficult intraoperative hemostasis, high intraoperative bleeding, and usually hematuria after surgery; long postoperative catheterization time and slow patient recovery (long hospitalization days); and common postoperative complications.
3. New generation green laser high performance system (HPS).
The 80WKTP laser has been proven to have significant therapeutic effect on BPH, but when dealing with large prostates, the energy limitation per unit time causes the procedure to take too long, which requires further updating of the current system to improve the laser vaporization effect. To overcome these shortcomings, the next generation Green Laser High Performance System (HPS) was created.
The system emits the same 532 nm wavelength laser and the same absorption characteristics, with the difference that a laser diode is used instead of an arc lamp as the laser source to excite the Nd:YAG laser bar, outputting a quasi-continuous laser with a multiplier of 532 nm wavelength and a power of 120 W. The vaporization efficiency is higher, and more tissue can be effectively vaporized in the same amount of time. The system is updated with additional dual power pedals: one for high power vaporization and one for low power coagulation. The system also uses a modified fiber, plus a highly reflective cap to limit backscatter side effects to prevent accidental laser injury to non-surgical areas.
The advantages of the HPS include higher vaporization and significantly shorter procedure times compared to 80WKTP when treating large glands; improved light quality and characteristics that allow the beam quality of the HPS to keep the focus essentially undiversified up to 3mm and limited divergence up to 5mm, meaning that the effect will remain consistent when vaporizing at distances up to 3-5mm from the fiber; system updates with additional vaporization The system is updated with an additional vaporization/coagulation dual power pedal, which can achieve rapid selection of vaporization or coagulation, helping the operator to locate the bleeding site and then quickly reduce the power to stop bleeding and reduce intraoperative bleeding; it also has significant therapeutic effect on patients with urinary retention, oral anticoagulant therapy, and prostate volume >80ml.
All preliminary studies so far have affirmed the efficacy of HPS for BPH, but as a new technique, further extensive clinical studies are needed to evaluate the advantages and disadvantages of this system.
Conclusions:
Studies in recent decades have shown that PVP has great potential to gradually replace TURP as a safe and effective treatment with the advantages of low surgical risk, few complications, rapid postoperative recovery, and good efficacy. However, since it cannot be sent for pathological examination after surgery, surgery needs to be performed on the basis of a clear preoperative diagnosis, and should be treated separately if tumor tendency is present.
The emergence of a new generation of HPS has further improved the green laser system, making it possible to increase the laser vaporization power and effectively shorten the operation time. In the near future, PVP is expected to become the gold standard in the treatment of prostate enlargement.