Quantitation of colonic injury from argon laser, neodymium: YAG laser and monopolar electrocautery applied to flat mucosa and small sessile polyps of the canine colon

This study determined the optimum laser energy for ablation of colonic mucosal lesions and small sessile polyps in the canine colon. Neodymium (Nd):YAG laser, argon laser, and monopolar electrocautery were applied to exposed canine colonic mucosa for various application times at various power settings. At the minimum energy level necessary to ablate mucosa, the Nd:YAG laser caused greater muscularis injury than the argon laser and monopolar electrocautery. At higher energy levels, monopolar electrocautery and Nd:YAG laser caused greater muscularis injury than argon laser. Small surgically created polyps in the canine colon were ablated endoscopically with the three energy sources. Single-session complete polyp ablation occurred most frequently with Nd:YAG laser and least frequently with argon laser. The depth of tissue injury beneath polyp ablation sites was least with argon laser and greatest with Nd:YAG laser. This study suggests that the argon laser is safer than the Nd:YAG laser or monopolar electrocautery for coagulation of flat colonic mucosal lesions. Although the argon laser is safer for the coagulation of small sessile colonic polyps, it may be less effective than monopolar electrocautery or the Nd:YAG laser for the single-session fulguration of polyps greater than 5 mm in diameter.     

Efficacy and safety of Nd. YAG laser for the treatment of bleeding from radiation proctocolitis

BACKGROUND: Bleeding due to radiation proctocolitis is a frequent and severe complication of radiotherapy in cancers of the pelvis. AIM: The aim of this study was to evaluate the efficacy and safety of endoscopic treatment with Nd:YAG laser in this condition. PATIENTS AND METHODS: A series of 9 patients with radiation-induced damage in the rectum and sigma were treated with endoscopic Nd:YAG laser until significant bleeding stopped and endoscopic features of proctocolitis improved. They received a median of 3 laser treatments (range 1-10) over a maximum time period of 11 months. RESULTS: In 4 cases, bleeding ceased and, in 4, it was reduced to occasional spotting. In the remaining patient, laser therapy led to only a transient improvement, but did not modify the requirement of blood transfusion. In the 5 patients also suffering from urgency, incontinence and/or rectal mucoid discharge, the laser therapy course also relieved these symptoms. No significant treatment-related complications were observed. CONCLUSIONS: Endoscopic Nd: YAG laser is a useful and safe treatment for patients with bleeding due to radiation proctocolitis.     

Laser ablation of human atherosclerotic plaque without adjacent tissue injury

Seventy samples of human cadaver atherosclerotic aorta were irradiated in vitro using a 308 nm xenon chloride excimer laser. Energy per pulse, pulse duration and frequency were varied. For comparison, 60 segments were also irradiated with an argon ion and an Nd:YAG (neodymium:yttrium aluminum garnet) laser operated in the continuous mode. Tissue was fixed in formalin, sectioned and examined microscopically. The Nd:YAG and argon ion-irradiated tissue exhibited a central crater with irregular edges and concentric zones of thermal and blast injury. In contrast, the excimer laser-irradiated tissue had narrow deep incisions with minimal or no thermal injury. These preliminary experiments indicate that the excimer laser vaporizes tissue in a manner different from that of the continuous wave Nd:YAG or argon ion laser. The sharp incision margins and minimal damage to adjacent normal tissue suggest that the excimer laser is more desirable for general surgical and intravascular uses than are the conventionally used medical lasers.     

Endoscopic laser treatment. II. Comparison of the efficacy of high and low power photocoagulation in control of severely bleeding experimental ulcers in dogs.

The coagulative efficacy of a "high power" argon laser which delivers 6.5 +/- 1.0 w was compared to that of a "low power" argon laser which delivers 1.0 +/- 0.1 w. The wave-guide angle of divergence was 8 degrees. For the high power laser, the distance between the wave-guide tip and the mucosa varied from 1.0 to 1.5 cm with a delivered power density range of 160 to 487 w per cm2. For the low power laser, the distance between the tip and mucosa varied from 0.7 to 1.3 cm with a power density of 35 to 146 w per cm2. Group A consisted of acute experiments in 6 heparinized dogs in which 51 standard-sized acute gastric ulcers extending into the submucosa were made at laparotomy via a large gastrotomy. Ulcer bleeding rates were quantified into three categories of severity. Within each category, ulcers were randomized to high power, low power, or untreated control. All 19 low power-treated ulcers and 16 untreated controls continued bleeding; 13 of 16 high power-treated ulcers stopped bleeding completely. Representative ulcers were examined histologically. Group B consisted of chronic experiments on 31 ulcers in 7 unheparinized dogs. These ulcers were either treated with high power or left as untreated controls. Dogs were killed and the ulcers were examined histologically at 7, 14, and 28 days. Only rarely did the laser injury penetrate into the muscularis externa. There were no perforations. By 14 days, all lesions were covered with normal surface epithelium. These data encourage further development of congruent to 7.0 w argon laser photocoagulation for eventual clinical use in man.     

Argon laser photocoagulation in the dog stomach.

Laser photocoagulation is one of a number of methods currently under investigation for the endoscopic treatment of gastrointestinal haemorrhage. The Argon ion and Neodymium Yttrium Aluminium Garnet (Nd YAG) lasers are theoretically suitable as the beam from each may be transmitted via a flexible fibre. Argon laser photocoagulation has been shown to be effective and we have elucidated which factors determine its safety and efficacy. Studies on normal canine gastric mucosa showed that the depth of tissue damage depended chiefly on the total incident laser energy on any one spot, and that below 50 J the risk of perforation was extremely low. The energy density was much less important. The haemostatic effect depended more on the laser power. In artificial bleeding gastric ulcers in heparinised dogs the most effective level was 7--9 W, at which 22 out of 23 ulcers (96%) stopped bleeding completely, compared with one out of 12 controls. Photocoagulation was achieved in these cases with energies well within the safe limits. The procedure was effective endoscopically, and these results justify early clinical studies in man.     

Laser photocoagulation for gastrointestinal bleeding.

Endoscopic laser photocoagulation is one of the exciting developments in the field of gastrointestinal endoscopic therapy. However, much work needs to be done before these techniques should be allowed to proliferate into widespread use. There are few controlled randomized clinical studies evaluating any endoscopic treatment of bleeding, including argon laser and Nd:YAG laser photocoagulation. Despite this, uncontrolled clinical trials of both argon and Nd:YAG laser photocoagulation have begun. Laser photocoagulation of bleeding upper gastrointestinal lesions should be considered a procedure in an experimental stage of development, to be performed only under protocol studies at endoscopic research centres. Only after this or any other haemostatic technique has been proven effective and safe in thorough animal trials and then in controlled clinical trial should it be considered ready for general clinical use.     

The tissue effect of second generation argon plasma coagulation (VIO APC) in comparison to standard APC and Nd:YAG laser in vitro

BACKGROUND: The aim of this study was to evaluate the effect of 2nd generation argon plasma coagulation (VIO APC) with respect to the tissue destruction capacity, and to compare it with standard APC and Nd:YAG laser. METHODS: 2nd generation APC (VIO APC2, Erbe, Germany), standard APC (APC 300/Erbotom ICC 200, Erbe) and Nd:YAG laser (KTP/YAG XP 800; Laserscope, San Jose, California) were applied in 35 porcine livers. Using APC, power settings (30-120 W), application time (2 and 5 sec) and gas flow (1 and 2 l/min) were varied. Using Nd:YAG laser, 30-60 W were applied (flow 21/min). Diameter and depth of tissue coagulation were evaluated. RESULTS: Using VIO APC, maximum coagulation depth was 6 mm (maximum diameter 15 mm). In comparison to standard APC, the coagulation effect was significantly higher (p < 0.001). There was no significant difference in the mean depth achieved by VIO APC and Nd:YAG laser using 30- 60 W and an application time of 2 sec (p < 0.05). Using maximum energy available for the 2 systems, maximum depth achieved by VIO APC (6 mm) was higher than the one caused by Nd:YAG laser (4 mm). CONCLUSIONS : VIO APC was more effective than standard APC. Using medium power and a limited application time, it was as effective as Nd:YAG laser. The high effectiveness of VIO APC should be a topic of clinical education.     

Endoscopic Nd:YAG laser treatment of severe radiation injury of the lower gastrointestinal tract: long-term follow-up

We report a series of patients with severe radiation injury treated with endoscopic laser photocoagulation. Eight patients with recurrent lower gastrointestinal bleeding secondary to procosigmoiditis were treated with endoscopic Nd:YAG laser therapy. Patients were followed for an average of 21.7 months after the first laser treatment. Average transfusion requirements and hospital admissions per patient-month were 0.93 and 0.27, respectively, in the prelaser period and 0.18 and 0.06, respectively, in the entire period following the first laser treatment. A total of 26 laser treatments were performed. There were three major (prolonged ileus) and one minor (pain) complication. We conclude that endoscopic Nd:YAG laser photocoagulation is a safe, effective, and lasting treatment in severe, symptomatic radiation injury of the lower gastrointestinal tract.     

Palliative laser therapy for tumours of the gastrointestinal tract.

The argon ion and Nd: YAG lasers were used initially in the mid 1970s to produce haemostasis in acutely bleeding peptic ulcers. With the evolution of treatment techniques, the main area of use of the Nd: YAG laser has now become the palliation of upper and lower GI malignancies. Thermal ablation of tumours may be achieved endoscopically by non-contact laser application at high power, or in the contact mode using artificial sapphire probes at much lower energy levels. Still lower powers can be employed therapeutically using interstitial hyperthermia, and this is best applied endoscopically to exophytic tumour nodules in the gut lumen or to tumours localized ultrasonically in solid organs, such as the liver or pancreas. PDT involves destruction of previously photosensitized tumours by the cytotoxic action of singlet oxygen released on exposure of the neoplastic tissue to light of an appropriate wavelength. Although the theory is attractive, the available experimental and clinical information suggests that treatment should, for the present, be confined to small or early malignancies whose depth of invasion can be verified by endoscopic ultrasound or other imaging techniques. PDT carries the biological advantage of healing by regeneration with preservation of connective tissue stroma, while the Nd: YAG laser causes destruction by thermal coagulation or vaporization and subsequent healing by fibrosis. Laser therapy of GI tumours expands the range of therapeutic endoscopic procedures in a relatively safe and readily repeatable manner which achieves high patient tolerance. By reducing morbidity, mortality and time spent in hospital, it offers significant advantages in the palliative treatment of conditions previously managed by conventional surgery, and also offers opportunities for treatment of previously inoperable disorders. Developments in laser technology and diagnostic imaging techniques are likely to promote laser therapy in the future as a primary treatment modality.     

The influence of 15(R)-15 methyl PGE2, methyl ester, on Nd:YAG laser-induced gastric ulcers

The effect of 15(R)-15 methyl PGE2 on the evolution of gastric ulcers induced by endoscopic Nd:YAG laser photocoagulation was studied. By continuous application of 50 to 70 watt power for 4 sec at a distance of 15 mm from the gastric mucosa, reproducible ulcers can be induced. The effect of the drug in nonantisecretory doses (10 micrograms/kg) on the acute ulcer formation and on the healing rate was evaluated in mongrel dogs by light microscopy. Local administration or oral pretreatment did not influence the size or depth of acute ulcers (7.4 mm in diameter) as compared to a control series (7.2 mm). Pretreatment for several days, however, had a marked beneficial effect on the healing rate of the ulcers (1.71 mm after 7 days compared to 2.76 mm for the control series). From these data it may be concluded that 15(R)-15 methyl PGE2 has a beneficial effect on ulcer healing, even in nonantisecretory doses.     

Gastric ulcer healing after laser treatment in dogs

Endoscopic laser photocoagulation of ulcers is increasingly used to produce hemostasis in patients who are actively bleeding or in patients with stigmata of recent hemorrhage. Little information is available describing ulcer healing rates after laser treatments. The aim of this study was to compare the healing rates of gastric ulcers treated with laser energy (Nd:YAG) with untreated ulcers in dogs. Two standard gastric ulcers (12-14 mm diameter) were created in each dog stomach using an ulcer maker (Quinton) under endoscopic guidance and one was randomly selected for laser treatment (L), while the other served as control (C). Ten laser spots were applied circumferentially around the ulcer crater with a mean energy of 595 J per ulcer. Ten dogs were studied; four of which were sacrificed after one week and six after two weeks. Healing of treated ulcers was compared with that of control ulcers and expressed as a percentage of the initial ulcer surface. Histologic injury and reepithelialization were scored by two pathologists unaware of the treatment. Laser-treated ulcers healed significantly slower than untreated ulcers at one week (53% L vs 94% C, P less than 0.05) and histologic injury was greater in ulcers treated with laser photocoagulation. At two weeks, only 82% of the laser-treated ulcer surface was healed in comparison with 94% (P less than 0.05) healing in untreated ulcers, although the mean histologic injury score was not different at two weeks. Reepithelialization was decreased both at one week (11% L vs 71% C, P less than 0.01) and at two weeks (75% L vs 100% C, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Nd:YAG laser in treatment of seriously ill patients with gastrointestinal bleeding

Nd:YAG (neodymium:yttrium aluminum garnet) laser coagulation was used to treat 30 seriously ill patients with massive or prolonged gastrointestinal bleeding. An average of 7.5 units of blood was given prior to Nd:YAG laser treatment. Twenty patients showed no evidence of continued or recurrent bleeding after laser therapy, four patients rebled after 48 hours, three patients rebled within 48 hours, one patient continued to bleed despite the laser treatment but died of an unrelated cause, one patient required immediate surgery because of inability to control bleeding, and one patient died several hours after control of the bleeding. Although six patients died within 10 weeks, no patient exsanguinated. Nd:YAG laser treatment is a useful modality for controlling severe gastrointestinal bleeding in the seriously ill patient.     

Failure of cyanoacrylate tissue glue (Flucrylate,MBR4197) to stop bleeding from experimental canine gastric ulcers

A plastic tissue adhesive, trifluoroisopropyl 2-cyanoacrylate (Flucrylate^TM, MBR4197), was tested for hemostatic efficacy in acute laparotomy experiments using a canine model of acute bleeding gastric ulcer. An improved delivery system suitable for endoscopic use was developed. Hemostatic efficacy of the adhesive was tested in both briskly bleeding ulcers and in oozing ulcers after partial treatment with a heater probe. In pilot studies at laparotomy, primary and adjunctive cyanoacrylate therapy of 81 bleeding ulcers were evaluated in seven unheparinized foxhounds. Hemostasis was produced in 11% of ulcers treated with cyanoacrylate alone and in 31% of ulcers treated with cyanoacrylate as an adjunctive after partial heater-probe treatment; no sham-treated control ulcers stopped bleeding under the conditions of the experiment. To evaluate Flucrylate^TM using our standard heparinized ulcer model, a randomized study was performed in six heparinized foxhounds at laparotomy. Ulcers were randomized to treatment with cyanoacrylate alone, adjunctive cyanoacrylate, heater probe alone or untreated control. Sham-treated control ulcers or ulcers treated with cyanoacrylate alone did not stop bleeding; 42% of ulcers treated with cyanoacrylate as an adjunctive stopped bleeding; all ulcers treated with a heater probe stopped bleeding. In this experimental model of acute bleeding gastric ulcer, trifluoroisopropyl 2-cyanoacrylate (Flucrylate^TM, MBR4197) did not stop severe bleeding and was unpredictable as an adjunctive treatment.     

Current Status of Lasers for Arrhythmia Ablation

Current Status of Lasers for Arrhythmia Ablation. Wavelength specific effects and mode of laser operation allow either photocoagulation or tissue removal as a means of approaching arrhythmia ablation. Successful intraoperative ablation of ventricular tachycardias has been performed with the Nd: YAG laser (photocoagulation) and argon laser (tissue vaporization). The argon laser has been used intraoperatively for transection of accessory pathways. Experimental studies indicate a strong theoretical potential for Nd:YAG laser catheter ablation of ventricular tachycardia. Laser energy has been used experimentally to evaluate the possibility of AV junctional ablation/modification and accessory pathway ablation. Adaption of laser energy to effective catheter systems for arrhythmia ablation requires solutions to problems inherent in all catheter systems and some unique to laser energy. (J Cardiovasc Electrophysiol, Vol. 3, pp. 345–353, August 1992)     

Treatment of peptic ulcer severe bleeding.

The success of a defined management policy op peptic ulcer haemorrhage which incorporates endoscopic therapeutic intervention depends on the early identification of a high risk group of patients and a high risk group of ulcers. The high risk group of patients consists of those likely to experience further bleeding on the basis of clinical prognostic indicators: shock and severe anaemia on admission and the pattern of bleeding; or tolerate rebleeding and emergency surgery poorly: patients over 60 years and those with associated disease. UGI endoscopy should be performed early (within 6-12 hours) in this group in order to identify the bleeding point and provide prognostic information regarding the risk of further haemorrhage. Peptic ulcers with major stigmata of recent bleeding (spurting or non-bleeding visible vessel) have high risk of rebleeding, the risk is even greater when major stigmata of recent haemorrhage (SRH) are associated with shock on admission. Patients with such ulcers should be monitored intensively and receive endoscopic haemostatic treatment in order to terminate active haemorrhage or prevent rebleeding thereby avoiding the need for emergency surgery with its attendant morbidity and mortality. Patients with ulcers with minor or no SRH have a very low risk of rebleeding and don't require intensive monitoring or endoscopic treatment and can be discharged from hospital early. Ulcers which cannot be completely characterized have an intermediate risk of rebleeding and should be managed as high risk lesions. Secondary to the anatomy of the visible vessel any haemostatic endoscopic treatment should be applied around, but avoiding, the sentinel clot. Well-designed randomized controlled trials of endoscopic haemostatic treatment of peptic ulcer haemorrhage in which stratification of risk was based on the SRH, have demonstrated for non-bleeding vessel a significant reduction in rebleeding and in emergency surgery, for spurting bleeding benefit was found only for the rebleeding risk. No advantage was demonstrated in each group of patients in term of mortality. Such studies also demonstrate the superiority of the Nd:YAG laser over the Argon laser. Perforation is a rare complication of Nd:YAG laser photocoagulation (less than 1%). Precipitation or aggravation of arterial haemorrhage during treatment of a visible vessel, as a result of a direct hit, is a more frequent complication (0-29%). Further laser treatment is successful in terminating 75% of these induced bleeds, the remainder requiring surgery. Preinjection of the ulcer with adrenaline does not appear to prevent this complication.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of Nd:YAG laser irradiation on ventricular myocardium in dogs using an artificial sapphire tip contact laser catheter]

To apply Nd:YAG laser irradiation through a new sapphire tip contact laser method to catheter ablation in treatment of tachy-arrhythmias, effects of laser irradiation on ventricular myocardium were investigated in 10 mongrel dogs. Nd:YAG lase (1064nm) discharges were delivered to different sites on the endomyocardium at power of 5, 10, 15, 20 or 25w with duration of 3, 5, or 10 seconds (sec.) respectively in closed beating hearts. Histopathologically, the lesion irradiated was clearly demarcated from the normal myocardium by the construction band necrosis zone. The depth of injured myocardium was less than 2mm with 3 sec. irradiations, with 5 sec. from 1 mm to 4 mm in proportion to power increase, with 10 sec. from 3mm to 8 mm in proportion to the power from 5w to 15w and could not be measured in cases of more than 20w irradiations. Although with every irradiation duration, the depth of injury increased in proportion to the power increase. With the same total energy, a longer time of irradiation produced deeper injury than a shorter time. This method makes it easier to keep the laser positioned to target than bare laser, and is suitable for use in catheter ablation.     

A randomized comparative study of laser photocoagulation, heater probe, and bipolar electrocoagulation in the treatment of actively bleeding ulcers

A randomized study was performed to compare the efficacy of Nd:YAG laser, heater probe, and bipolar electrocoagulation in the treatment of active bleeding from peptic ulcers. Nine hundred and forty-eight consecutive patients with upper gastrointestinal bleeding underwent endoscopy and 91 patients with active bleeding from peptic ulcer were randomized to receive laser (N = 30), heater probe (N = 31), and bipolar electrocoagulation (N = 30). The angulation of the probe to the ulcer base was assessed at endoscopy. The three treatment groups were comparable in their clinical and endoscopic characteristics. There was no significant difference among patients treated with laser, heater probe, and bipolar electrocoagulation in the rate of re-bleeding (10%, 19.4%, and 10%), duration of hospital stay (4, 4, and 5 days), and proportion requiring emergency surgery (7%, 13%, and 7%), but the cost per patient was higher with laser than heater probe and bipolar electrocoagulation. The angulation of the probe to the ulcer base did not affect the re-bleeding rate. No complication was reported. We conclude that the three modalities were equally effective and safe in endoscopic hemostasis but because bipolar electrocoagulation and heater probe were cheaper, they were recommended for use.     

Evaluation of electrofulguration in control of bleeding of experimental gastric ulcers

The safety and efficacy of electrofulguration for control of bleeding from standard canine experimental gastric ulcers was studied. At settings of 2, 5, and 8 on a Valleylab SSE-3 generator, 0.5-sec applications provided effective hemostasis. However, a setting of 2 required an excessive number of applications. Settings of 5 and 8 showed deep injury to the muscularis externa when examined histologically. In an attempt to reduce the depth of injury, a more easily ionizable gas mixture of 50% argon gas and 50% CO2 was compared to CO2 alone. At a generator setting of 5 with 0.5-sec applications the argon-CO2 mixture produced slightly less deep injury than CO2 alone, but the difference was not significant. Although electrofulguration was effective in stopping bleeding in these experiments, the tissue injury was unpredictable and deep.     

Yag laser photocoagulation and monopolar electrohydrocoagulation: randomized study of the hemostatic effect on experimental hemorrhagic ulcer in dogs

The purpose of this randomized study was to compare the effects of two methods of hemostasis--photocoagulation using YAG Neodyme laser and liquid monopolar electrocoagulation--on acute experimental bleeding ulcers created in the dog stomach with an ulcer-maker. One hundred and fifty-three lesions were made and randomized into 3 groups; 51 lesions were treated with photocoagulation and complete hemostasis was achieved in all cases. Hemostasis was obtained in 80 p. 100 of 51 ulcers treated with liquid electrocoagulation. Control untreated ulcers remained hemorrhagic after 45 min of observation. The mean external muscle injury on day 7 was 55 p. 100 after photocoagulation and 65 p. 100 after liquid electrocoagulation. On day 14, mean external injury was 60 p. 100 after photocoagulation and 75 p. 100 after liquid electrocoagulation (non-significant difference). On day 7, the mean re-epithelization index, expressed as the percentage of the original ulcer diameter, ranged from 8 to 10 p. 100 in each trial group. On day 14, reepithelization covered 78 p. 100 of control ulcers and 72 p. 100 of photocoagulated ulcers (NS). This percentage falls to 47 p. 100 in ulcers treated with liquid electrocoagulation (p less than 0.01 when compared with ulcers treated with photocoagulation). Photocoagulation seemed to be more efficient in ensuring hemostasis and external muscle injury was correlated with the energy delivered. External muscle injury could not be controlled by liquid electrocoagulation. However the difference in the percentages of mean external muscle injury between the two methods was not significant. Therefore, in man, the risk of perforation is certainly slight and not very different whatever the method of hemostasis considered.     

Endoscopic gastric vagotomy: a feasibility study using laser in dogs

The aim of this study was to explore the feasibility of an endoscopic approach to gastric vagotomy using the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser in dogs. Based on gross and histologic measurements, target zones for endoscopic vagotomy were defined with reference to mucosal side landmarks. Target zones containing the unbranched segments of the major intramural vagal branches were linear and symmetrically located anterior and posterior to the midline of the lesser curvature extending from the level of the esophagogastric junction to the proximal antral border. Because of minimal variability between dogs, this zone could be accessed endoscopically and reliably injured. Unfortunately, it was necessary to produce a nearly full thickness burn to interrupt the deep intramural vagal branches. Despite efforts to control dosimetry, delayed perforations occurred in three of four dogs. We conclude that endoscopic gastric vagotomy using the Nd:YAG laser is not feasible in the dog model because of difficulty controlling the depth of thermal injury. An endoscopic approach to vagotomy remains conceptually appealing because of the predictable location of and accessibility to a target zone.