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

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.

Wound healing after transoral angiolytic laser surgery for early glottic carcinoma

OBJECTIVES/HYPOTHESIS

Wound healing after transoral angiolytic laser surgery for early glottic carcinoma was analyzed to identify factors influencing healing and clinical significance of persistent granulation tissue.

STUDY DESIGN

Retrospective review.

METHODS

A retrospective review of 100 consecutive patients undergoing endoscopic angiolytic laser surgery for T1 and T2 glottic carcinoma was performed. Patients with prior radiation or incomplete data were excluded. Postoperative endoscopic images were analyzed for time to healing, size and location of wound, and presence of granulation tissue. Three blinded, independent raters graded wound appearance and presence of granulation tissue.

RESULTS

Seventy-nine patients healed without need for intervention at a median of 3.5 months. Two patients had office-based ablation of granulation without biopsy and healed. The remaining 19 patients had biopsy for granulation tissue. Wounds that underwent biopsy at >3 months were more likely to contain carcinoma (5/6 patients, 83%) than wounds that were biopsied <3 months (2/13 patients, 15%) (P = .004). Presence of granulation significantly correlated with resection involving anterior commissure (P = .01), > 75%vocal fold length (P = .006), and depth into muscle (P = .001). Delayed healing (>3 months) correlated with T2b tumors (P = .02), depth into ligament (P = .002) and anterior commissure involvement (P = .04). T1a carcinomas more commonly healed in <3 months (P = .005).

CONCLUSIONS

Many vocal fold wounds heal completely within 3.5 months after angiolytic laser surgery for early glottic carcinoma. Larger and deeper wounds are more likely to heal with granulation tissue. Granulation can resolve without surgical intervention; however, granulation present > 3 months warrants biopsy due to increased risk of malignancy.

LEVEL OF EVIDENCE

4 Laryngoscope, 129:435-440, 2019.

Novel Device for Tissue Cooling during Endoscopic Laryngeal Laser Surgery: Thermal Damage Study in an Ex Vivo Calf Model

Objectives:

Minimizing collateral thermal damage during endoscopic laryngeal laser surgery remains a priority, and tissue cooling is one way to achieve this goal. Cooling systems utilizing compressed air have been shown to reduce the extent of thermal trauma on the vocal folds, but these units are not ideal for endoscopic applications because cooling is inefficient at the low airflows needed. We examined whether a novel vortex cooling device that generates cooled air at low flow rates would provide a cooling benefit beyond that which could be obtained by using room-temperature air for cooling tissue or by using no cooling during simulated laryngeal laser surgery.

Methods:

A continuous-wave thulium laser was used to incise glottic tissue in 12 calf vocal folds. Cooling was achieved with a prototype vortex cooler (9°C air output; flow rate, 3 L/min), and tissue temperature measurements were compared to those with room-air cooling and no cooling. Thermal damage was analyzed histologically by measuring the depth of lactate dehydrogenase inactivation surrounding the mucosal incision. The cooling conditions were tested during time-constant cuts (8 seconds) and depth-constant cuts (into the thyroarytenoid muscle).

Results:

During time-constant cuts, comparison between vortex cooling and room-air cooling revealed that vortex cooling resulted in a thermal damage zone that was 14% smaller (519 versus 603 μm; p < 0.05). During depth-constant cuts, vortex cooling created a thermal damage zone that was 32% smaller than that created with no cooling (p < 0.01) and 9% smaller than that created with room-air cooling (p < 0.01).

Conclusions:

Vortex cooling reduces thermal damage more effectively than room-air cooling or no cooling during both time-constant and depth-constant thulium laser cuts.

Subepithelial Vocal Fold Infusion: A Useful Diagnostic and Therapeutic Technique

Objectives:

Preservation of the maximum amount of subepithelial superficial lamina propria (SLP) remains an important goal during microlaryngoscopic surgery of phonatory mucosa. Volume expansion of the SLP (Reinke's space) with subepithelial infusion of saline solution has been widely adopted since its introduction in 1991. This technique has evolved so that it is currently used to assist with determining the depth of vocal fold disease, defining residual pliable SLP, enhancing microsurgical precision, and identifying unrecognized disease. The purpose of this investigation was to examine the indications, methods, and benefits of subepithelial infusion of saline solution as an adjunct technique during phonomicrosurgery.

Methods:

In a prospective case series, we collected data on 280 consecutive microlaryngoscopy procedures performed over a 12-month period. Subepithelial infusion of saline solution was included in 178 procedures.

Results:

New disease was identified in 20 of the 178 patients (scar in 15, sulcus in 4, and a mucosal bridge in 1). The depth of needle placement varied depending on the specific disease: 118 of the 178 infusions were done just below the epithelial basement membrane, and 60 infusions were performed deeper within the SLP, just superficial to the vocal ligament. The infusion technique provided surgical assistance in multiple ways, including identifying residual SLP (130 patients), defining the SLP-lesion interface (65 patients), lifting scar (60 patients), providing tension for cordotomy (47 patients), expanding the SLP volume to protect against laser damage (45 patients), and providing hydrostatic compression of vascular ectasias or varices for photoangiolysis (7 patients). The microlaryngoscopy procedures during which infusion was not performed (102 of 280 procedures) were primarily for nonglottic cancer (46 patients), stenosis (30 patients), or arytenoid granuloma (13 patients).

Conclusions:

Subepithelial infusion of the SLP with saline solution is a useful microsurgical adjunct during diagnosis and treatment of phonatory mucosal lesions.