Various effects of the CO2-, the neodymium-YAG-, and the argon-laser irradiation on bladder tissue

Dose-related tissue effects of the CO2 and noncontact Nd:YAG lasers in the canine glottis

OBJECTIVES

The CO2 laser is the standard for control of recurrent respiratory papillomatosis because of its predictable action on laryngeal tissue. The noncontact neodymium:yttrium aluminum garnet (Nd:YAG) 1064-nm laser is generally not used in the larynx owing to the lack of data on its tissue effects, and its potential lack of safety in the larynx. Combined Nd:YAG and CO2 laser treatments have been used safely in the tracheobronchial tree to eradicate recurrent respiratory papillomas. The objectives of this study were to describe and evaluate a method for applying the noncontact Nd:YAG laser to the larynx, to compare the tissue effects of the Nd:YAG, CO2, and combined Nd:YAG and CO2 lasers in the canine larynx, and to extrapolate canine tissue data to the human.

METHODS

The CO2, Nd:YAG, and combined Nd:YAG/CO2 lasers were applied to the glottis in four mongrel dogs. Laryngectomy was performed and the tissue was examined histologically. The nature and degree of tissue injury were analyzed relative to laser type and energy data.

RESULTS

In the canine larynx, the CO2 laser vaporized the surface epithelium and caused varying degrees of edema and necrosis of the lamina propria. The Nd:YAG laser did not cause ulceration but did show a greater degree of thermal damage to the lamina propria. Combined Nd:YAG/CO2 applications resulted in separation of the perimysial fibers from the muscle fibers of the vocalis muscle.

CONCLUSION

These findings suggest that the noncontact Nd:YAG laser can be applied in a controlled fashion to the canine larynx at appropriate power densities. Anatomical differences between human and canine larynges are considered. Extrapolation to humans is proposed.

Laser treatment of bladder cancer

— Many authors have reported safety and efficacy of laser treatment, expecially Nd:YAG Laser, for superficial bladder cancer. The many advantages of this treatment include a presumed smaller recurrence rate, also favoured by better laser ability to achieve a limphatic blockage, and an undoubtedly very small treatment-related mortality. This induces laser photocoagulation to be considered a safe procedure, feasible with a mild anaesthesia and under Day Hospital management. On the other hand the main limits of this procedure are the great difficulties in the histological evaluation of tumoral specimens after laser treatment and poor effectiveness on deep bladder wall infiltrating tumours. A critical analysis of literature data follows and our experience in the laser treatment of superficial bladder tumours.

The Nd:YAG laser treatment of hemangioma

An Nd:YAG laser was used in the treatment of 160 patients with hemangioma from January 1989 to January 1993. Irradiance was between 800 and 1600 W/cm 2 with energy between 400 and 1600 J/cm 2. The best results with almost total restoration were obtained in 21 of the 160 patients (13%). The size of the hemangioma was reduced by more than 50% in 88 cases (55%), by less than 50% in 56 cases (35%), and by a negligible amount in 3 cases (2%). Side effects as found in 160 patients or 10% included slow healing, superficial skin necrosis, and occurrence of scars. Most hemangiomas can shrink by themselves. However, the treatment is needed for cases with risk of various side effects including scar formation, sepsis, bleeding, or abnormal growth of an organ. We concluded that the Nd:YAG laser is a very useful instrument in the treatment of abnormality of blood vessels, such as hemangioma.

ND: YAG nomogram dosimetry scale for the bladder

Bowel perforation and damage to surrounding organs is probably the most significant risk with the use of Nd-YAG laser in the bladder. To prevent this unwanted damage, a nomogram dosimetry scale was developed by delivering different settings of laser energy via a cystoscope to 25 female pigs. One week following treatment, exploratory laparotomy and cystectomy were performed. Microscopic analysis of the depth of laser irradiation was accomplished. From this study it was learned that, although the greater the energy delivered, the deeper the tissue damage, this is not uniform. Pulsed energy produced a deeper effect than continuous energy. The use of 30 watts of either pulsed or continuous energy for no longer than 15 seconds (450 joules) or 10 watts of either form of energy for less than 30 seconds (300 joules) did not produce bowel perforation. Other different combinations of high number of watts or pulses translated into transmural necrosis of the bladder with or without perforation and with or without bowel injury. Other factors such as density, thickness, color and temperature of tissue, type and wave length of laser and optimal focusing played a significant role in the final outcome. Useful information for human clinical use may be extrapolated from this experimental model.

Neodymium-YAG laser therapy for vascular lesions

Three patients with port-wine stains with a nodular surface, one patient with macrocheilia resulting from a port-wine stain, and one patient with a capillary hemangioma were treated with a Nd-YAG laser (mediLas, MBB-AT, Munich). Irradiance was between 800 and 1,600 watts/cm2, with energy fluence between 400 and 1,600 joules/cm2. Treatments were performed with local anesthesia on an outpatient basis. In all patients, marked improvements could be obtained after only a few treatments. Histologically there was necrosis of epidermis and dermis immediately after laser application, and ectatic vessels contained coagulated erythrocytes. Depth of coagulation was up to 3.5 mm. Quick restoration of epidermis was observed. After some days, macrophages, fibroblasts, and capillary blood vessels grew into the agglutination thrombi and ectatic vessels were replaced by granulation tissue and, later, by fibrous tissue. In comparison with the argon laser, the Nd-YAG laser coagulates at a much deeper level, but processes of tissue repair take longer and fibrosis is more pronounced after Nd-YAG laser application. Clinically, therefore, scar formation is more likely. Chilling the skin surface during irradiation and shorter exposure times may be effective in reducing the risk of scar formation in the future.

Urologic dosimetry studies with the Nd:YAG and CO2 lasers: bladder and kidney

Dose recommendations for the use of the Nd:YAG and CO2 lasers have been accepted with little laboratory analysis. We have examined both endoscopic and open applications in the bladder and open applications on the kidney with the lasers over a variety of power and pulse duration settings. In addition, we have studied the effect of varying the temperature of the tissue and irrigation solution on the depth of penetration. We found that with the Nd:YAG laser, the maximum depth of penetration in our animal model was only 2.62 mm in the bladder. This occurred during an endoscopic treatment with settings of 50 W at 4 seconds with irrigation solution of 25 degrees C. The depth of penetration using current recommendations of 40 W for 2 seconds was less than 1 mm at all temperatures. Room temperature irrigation solution may be the ideal compromise, but higher-power long-pulse durations or repeated treatments to the same area may be necessary to achieve penetrations of 3-5 mm. In open applications on bladder and kidney, the maximum depth of penetration in our animal model was 2.75 mm, which was found during a treatment with settings of 60 W at 4 seconds with the kidney parenchyma at 25 degrees C. Using the CO2 laser on open applications of bladder strips, we obtained a maximum depth of penetration of 1.75 mm at 30 W of power for 1/2 second at 85 degrees C tissue temperature. Unfortunately, penetration by the CO2 laser is accompanied by vaporization of tissue, leaving a large crater. Minimal injury exists beyond this area. In the kidney, we obtained a maximum depth of penetration of 1.75 mm at 30 W of power at 25 degrees C and 20 W of power at 2 degrees C each for 1/2 second.

Effects of Nd:YAG laser photoradiation on intra-abdominal tissues: a histological study of tissue damage versus power density applied

Liver, spleen, and pancreas were subjected to laser photoradiation of 50- to 100-Watt power levels. Samples were evaluated by light microscopy at 0 hours and 7, 14, and 21 days. Four zones of cellular damage were visible in liver and pancreas: coagulum, cavitation, acidophilia, and transition. Only the first three zones were clearly visible in the spleen. Mean lateral tissue penetration was 3.1 mm in liver, 3.3 mm in spleen, and 1.0 mm in pancreas. No significant increase in lateral penetration occurred with increasing power. Normal healing was observed in liver and spleen. Pancreatitis was found in all samples at 7 days postoperatively. At power levels of 80 W or less, recovery was observed. Above 80 W, pancreatic pseudocysts and necrosis led to death of the animals.

CO2 laser surgery in urology

The characteristics, advantages, and disadvantages of the CO2 laser to various clinical situations in urologic surgery are described and evaluated. Conditions treated routinely with the laser are presented and future possible uses discussed.