Application of pulsed and continuous wave 1.32 and 1.06 microns wavelengths of the Nd:YAG laser in the canine tracheobronchial tree: a comparative study

Minimizing Thermal Damage During Thulium Laser-Assisted Partial Arytenoidectomy: Pulsed Versus Continuous Cutting in an Ex-Vivo Calf Model

OBJECTIVES

The 2 µm-wavelength thulium laser is an effective cutter during partial arytenoidectomy, but thermal trauma can damage adjacent laryngeal tissue. Pulsing laser energy may reduce trauma when compared to continuous-wave cutting. This study measured temperature changes, thermal trauma, and time to complete partial arytenoidectomy, with and without pulsing, in an ex-vivo calf model.

METHODS

Tissue temperature and time to complete a trans-cartilaginous cut were measured during partial arytenoidectomy on ex-vivo calf vocal folds (N = 24) using a thulium laser in continuous-wave (CW, N = 12) and pulsed-wave (PW, N = 12) modes. Energy was 5 W for CW and PW cuts; pulse-widths were 250, 500, and 750 ms. Thermal damage was analyzed histologically by measuring the depth of lactate dehydrogenase (LDH) inactivation perpendicular to the laser-cut edge at the vocal process. Paired t-tests compared CW and PW modes.

RESULTS

Change in temperature was lower using CW (6.5°C) compared to PW modes (250 ms = 18°; 500 ms = 16°; 750 = 19°; P < .05). Trans-cartilaginous cuts were completed faster using CW (37 seconds) compared to PW (250 ms = 136 seconds; 500 ms = 61 seconds; 750 = 44 seconds; P < .05), and both modes delivered the same total Joules. The average depth of LDH depletion (thermal damage) was similar for all cuts.

CONCLUSIONS

1. Thulium laser cuts in continuous-mode unexpectedly produced less tissue heating yet created similar thermal damage than pulsed-mode cuts during simulated partial arytenoidectomy. 2. Trans-cartilaginous cuts were completed significantly faster in continuous-mode as compared to pulsed-mode cutting. 3. Pulsing the thulium laser does not minimize thermal damage compared to continuous wave cutting during thulium laser-assisted partial arytenoidectomy.

19th EURETINA Congress Keynote Lecture: Diabetic Retinopathy Today

In the last decades, significant changes have been taking place regarding the pathogenesis of diabetic retinopathy (DR) and the complex mechanisms that eventually lead to the various manifestations of the disease, including diabetic macular edema (DME). DR was first considered a pure microvascular disease, due to the evident capillary structural changes (microaneurysms), fluid extravasation, and lipid exudation. With the advent of fundus fluorescein angiography, the concept of ischemia and the correlation between peripheral nonperfusion and neovascularization has been introduced, which was eventually followed by the advent of new therapeutic strategies, such as peripheral photocoagulation. Nowadays, thanks to more advanced imaging techniques, namely optical coherence tomography (OCT), OCT angiography, and wide-field imaging (imaging up to 200° of the retina in a single shot), it became clear that other elements participate in the occurrence of DR and DME, including inflammation and neurodegeneration. In the future, integration of standard investigations with new diagnostic devices would allow the prompt recognition of DR even before clinical signs of the disease are ophthalmoscopically evident, and the development of personalized treatment for both retinopathy and DME will be available.

Cooling the "oven": a temperature study of air and glottal tissue during laser surgery in an ex vivo calf larynx model

OBJECTIVES

Endoscopic microlaryngeal laser surgery performed with general anesthesia through a laryngoscope speculum generates heat that accumulates at the distal lumen, creating an "oven" effect and potentially causing bystander thermal damage to nontarget tissue such as the contralateral vocal fold. We report the effects of cooling on air and tissue temperatures that occurred during simulated laryngeal laser surgery with KTP and thulium lasers in an ex vivo calf model.

METHODS

Ten fresh excised calf larynges were studied at room temperature. Laser energy was applied to one vocal fold for 2 minutes, with or without cooling, while temperatures were monitored with sensors placed within the glottal lumen or inserted superficially into the contralateral vocal fold. A pulsed KTP laser (525 mJ) was used for 5 larynges, and a thulium laser (7 W, continuous) was used for the other 5 larynges.

RESULTS

Heating was slightly greater for the KTP laser than for the thulium laser with use of these parameters. The lumen temperatures for both lasers increased an average of 13.2 degrees C without cooling, but only 6.7 degrees C with cooling (p < 0.05). The contralateral vocal fold (subepithelial space) temperature increased an average of 6.8 degrees C without cooling, but only 4.2 degrees C with cooling (p > 0.05).

CONCLUSIONS

Cooling with room-temperature air during laryngeal laser surgery reduces luminal air and contralateral vocal fold temperatures. This effect is believed to be due to elimination of the plume of steam and smoke that significantly heats surrounding structures.

Multimodal imaging guidance for laser ablation in tracheal stenosis

OBJECTIVE/HYPOTHESIS

Laser-induced damage of tracheal wall microstructures might contribute to recurrence after bronchoscopic treatment of tracheal strictures. The purpose of this study was to demonstrate how multimodal imaging using white light bronchoscopy (WLB), endobronchial ultrasound (EBUS), and optical coherence tomography (OCT) might identify in vivo airway wall changes before and resulting from Nd:YAG laser ablation and dilation of tracheal stenosis.

STUDY DESIGN

Case study.

METHODS

Commercially available WLB, high frequency EBUS using a 20-MHz radial probe and time-domain, frontal imaging OCT systems were used to characterize the extent, morphology, and airway wall microstructures at the area of hypertrophic fibrotic tissue formation before, during and after treatment of postintubation tracheal stenosis.

RESULTS

WLB revealed the location of a complex, extensive, severe stricture. EBUS showed a homogeneous layer overlying a hyperechogenic layer corresponding to disrupted cartilage. OCT showed a homogeneous light backscattering layer and absence of layered microstructures, confirming absence in close proximity of normal airway wall. After laser ablation, OCT of charred tissue showed high backscattering and shadowing artifacts. OCT of noncharred tissue showed a thinner, homogeneous, light backscattering layer. EBUS showed thinner but persistent hypertrophic tissue suggesting incomplete treatment. WLB revealed improved airway patency postprocedure and recurrence 3 weeks later.

CONCLUSIONS

EBUS identified cartilage disruption and residual hypertrophic tissue, the evidence of which might contribute to recurrence. OCT revealed homogeneous light backscaterring representing persistent noncharred hypertrophic tissues but it did not visualize cartilage disruption. Future studies are warranted to confirm whether these technologies can help guide bronchoscopic treatments.

Effects of steel scalpel, ultrasonic scalpel, CO2 laser, and monopolar and bipolar electrosurgery on wound healing in guinea pig oral mucosa

OBJECTIVE

The study's objective was to compare instrument performance and tissue healing when steel scalpel, ultrasonic scalpel, monopolar or bipolar electrosurgical instruments, or CO2 laser was used in an animal oral surgery model.

STUDY DESIGN

Prospective, blinded, randomized.

METHODS

Adult guinea pigs (N = 70) were randomly assigned to 5 groups (14 animals per group) for excision of 2-cm, full-thickness oral mucosa using steel scalpel, ultrasonic scalpel, monopolar or bipolar electrosurgical instruments, or CO2 laser. Postoperative pain was measured indirectly using weekly body weight changes. Animals from each group were killed on days 0, 7, 14, 21, and 28. Specimens were harvested for blinded histopathological study and tensile strength measurement. Instrument performance (hemostasis, tissue coagulation, tissue sticking) and wound healing (tissue re-epithelialization, degree of inflammation) were primary outcomes. Statistical analysis was performed using analysis of variance.

RESULTS

The ultrasonic scalpel was the best tool in controlling hemostasis, tissue coagulation, and tissue sticking. Significantly higher body weight gain ( P<.05) was noted at day 7 for monopolar and CO2 laser groups. Greatest tensile strength was seen in the steel scalpel and ultrasonic scalpel groups at the end of 28 days. Tissue re-epithelialization was fastest for the steel scalpel and ultrasonic scalpel groups (complete by day 7). Complete re-epithelialization of wounds of all treatment groups occurred by day 28. All groups had acute inflammation. Complete resolution of inflammation by day 14 took place in the steel scalpel and ultrasonic scalpel groups only.

CONCLUSION

Use of the ultrasonic scalpel produced faster re-epithelialization and greater tensile strength than laser or electrosurgical instruments, with results comparable to those seen with the steel scalpel.

Microdissection or microspot CO2 laser for limited vocal fold benign lesions: a prospective randomized trial

CO2 lasers have become an important technological advance and an integral tool for the laryngeal surgeon since the 1960s. Surgeons have used lasers for a variety of benign and malignant lesions in the larynx with good success. With better understanding of the microarchitecture of the vocal folds and the recognition of heat distribution into surrounding tissues that occurs with the use of standard CO2 lasers, questions and concerns have been raised regarding the use of the CO2 laser for benign lesions of the vocal folds. With the advent of the microspot CO2 laser with a spot size of less than 250 microm, the potential heat distribution to the deeper layers of the lamina propria has been reduced. The microspot CO2 laser has been suggested to be an appropriate tool for the excision of superficial benign lesions of the vocal fold and may be considered as an appropriate treatment alternative to microdissection. Only a limited number of studies have compared the efficacy of microdissection versus microspot CO2 laser surgery in the larynx, and no prospective, randomized trials have been performed.

OBJECTIVE

This study was designed to compare microspot CO2 laser excision and microdissection for superficial benign lesions confined to the free margin of the vocal fold.

STUDY DESIGN

A randomized, prospective trial comparing microspot CO2 laser excision and microdissection in the removal of nodules, polyps, and mucous retention cysts of the vocal fold.

METHODS

Acoustic and aerodynamic measures and videostroboscopic and perceptual audio recordings evaluated by a panel of blinded viewers and listeners were studied preoperatively and 2 to 3 weeks and 5 to 12 weeks postoperatively. Surgical and recovery times were compared between the two groups.

RESULTS

Thirty-seven patients met selection criteria and were enrolled, 21 in the microdissection group and 16 in the laser excision group. Significant improvements in videostroboscopic parameters were found over time in both groups. Significant improvements were noted for perceptual analysis over time for the laser excision group with nonsignificant improvements over time for the microdissection group. There was no difference in any measure between laser excision and microdissection at the two postoperative visits. There was no difference in surgical or recovery time between laser excision and microdissection. Acoustic and aerodynamic parameters were noncontributory in evaluating outcomes of treatment, since most values were normal before surgery.

CONCLUSION

No differences in clinical outcomes are identified when comparing microdissection with laser excision of nodules, polyps, and mucous retention cysts of the vocal folds.

Wound healing and soft tissue effects of CO2, contact Nd: YAG and combined CO2-Nd: YAG laser beams on rabbit trachea

Rabbit trachea was used as an experimental model to study tissue effects and healing of full-thickness tracheal lesions produced by CO2, contact Nd: YAG and combined, coaxial CO2-Nd: YAG (Combo) laser beams. Two power settings (10 W and 16 W) were used with CO2 and contact Nd: YAG lasers. Three different CO2/Nd:YAG power ratios (1:1, 1:2 and 1:4) and power settings (12 W 15 W and 16 W) were used with the Combolaser. Histological specimens for light and transmission electron microscopy were prepared immediately and 1, 3, 5, 7, 14 and 21 days postoperatively. The wound with the most precise and fastest healing was produced by contact Nd: YAG laser. CO2 laser produced a moderate amount of charring and the largest amount of coagulated tissue with a slightly prolonged healing period. In the acute phase, tissue defects produced by the Combolaser with power ratios 1:1 and 1:2 resembled the CO2 laser lesions but with slightly less charring. The power ratio 1:4 diminished the cutting properties of the beam considerably. During the healing period the Combolaser produced the most intensive inflammation and granulation tissue formation resulting in delayed regeneration of the lesion. In transmission electron micrographs the most severe damage to chondrocytes was seen after using the Combolaser. These findings indicate that the Combolaser produces deeper tissue damage than CO2 or contact Nd:YAG laser. However, the Combolaser appears to be suitable for tracheobronchial operations, owing to its good simultaneous cutting and haemostatic properties.