"Blow-torch phenomenon" during laser assisted excision of a thyroglossal cyst at the base of the tongue.

We report a case of blow-torch phenomenon encountered during diode laser assisted excision of a thyroglossal cyst in a child. This is first such case report from India and highlights an unusual complication which anesthesiologists need to be aware of due to the increasing use of operative laser.

Introduction

Blow-torch phenomenon is a known complication during of laser surgery. It is caused by ignition of anesthetic gases induced by a laser beam. It is seen with the use of lasers that do not make use of optical fibers for laser beam delivery, such as carbon-dioxide (CO2) lasers which use articulated arm technology. Diode lasers have replaced CO2 lasers today. They have optical fibers for delivery of the laser at the site of surgery, facilitating more precision and control.

Case Report

A 7-year-old boy was admitted for excision of a cystic swelling at the posterior aspect of the base of the tongue a few centimeters anterior to the valleculae. The smallest laser endotracheal tube (ETT) available was of 7-mm outer diameter (OD) and an internal diameter of 5.5 mm. After induction of anesthesia with propofol, followed by administration of suxamethonium intravenously (IV), nasotracheal intubation was done with this tube. Anesthesia was maintained oxygen in air, atracurium, intermittent boluses of propofol, and fentanyl IV. Throat was packed with saline-soaked roller gauze.

The saline-soaked throat pack was obstructing the field of vision of the surgeon and also restricting the outward pull of the tongue as cyst was large (3 × 3 cm) and placed posteriorly. The throat pack was removed to facilitate surgery. The surgeon assured that adequate precautions would be taken to avoid bringing the diode laser delivery handle tip in contact with the ETT. Toward the end of the surgical laser excision, the tip of the handle accidently slipped and touched the ETT. We heard a very short “pop” like noise which lasted for about 1–2 s. The exhaled gas from the expiratory valve also smelt of smoke for about a minute or so. There was however no change in hemodynamics, drop in SpO2 or reduction in air entry/chest expansion. We discontinued oxygen and ventilated with air. As the surgery had been completed and we were able to ventilate the lungs, we reversed the neuromuscular blockade. A small dose of IV steroid dexamethasone (4 mg IV) was given. After tracheal extubation, a flexible laryngopharyngoscope was passed to visualize the trachea up to the carina and fortunately everything appeared to be normal.

The removed ETT [Figure 1] had a very small circular hole and the inner aspect of the tube was black distal to the hole [Figure 2]. The cuff was intact but the tubing from the pilot balloon to the cuff was damaged, which is typically seen in “interior blow-torch phenomenon.” Patient recovered well and was shifted to postoperative, ward, monitored and given humidified oxygen and discharged next day.

Figure 1

Endotracheal tube showing the charred aspect

Figure 2

Inset of charred region

Discussion

Diode lasers are used with low power setting and do not usually cause perforation or damage to polyvinyl chloride (PVC) ETT coming in direct contact. Though studies have shown silicon and red rubber tubes to be more resistant to ignition compared to PVC, some studies have reported that PVC is less flammable than silicon or red rubber, having a flammability index of 0.26 vs. 0.19 for silicon and red rubber, respectively.[1] Use of laser resistant material wrapped around PVC ETT or double-cuffed silicon-coated ETT is however more safe.[23] We did not use it due to nonavailability but rather used a PVC ETT. Laser-resistant ETT are bulkier and more rigid than conventional ETT and thus need careful insertion to prevent mucosal abrasions.

In the event of a blow-torch phenomenon, upper airways are usually involved. Inhalation of smoke can cause chemical injury, bronchospasm, and respiratory failure. PVC tubes burn more vigorously and hydrochloric acid may be produced, which is a pulmonary toxin. In case of such an airway fire, oxygen should be temporary discontinued, damaged ETT removed, trachea reintubated with a fresh ETT, and the pharynx flushed with cold saline. A rigid or fiberoptic bronchoscopy examination should be done to look for damage and pieces of burned ETT. Humidified oxygen, steroids, and antibiotics must be administered and at times controlled ventilation and tracheostomy may become necessary.[1] Postoperatively, patient should be intensively monitored and a chest X-ray should be taken.

Surgeons must ensure that laser energy is not reflected from smooth metal surfaces or directed at sensitive structures. Applying protective metal foil wraps to ETT, such as aluminum or copper has been advocated.[3-5] The ETT cuff can be filled with colored saline and placed far distally in trachea and the visible cuff covered with moistened cotton pledgets, which should be remoistened as needed. Laser resistant tubes are available for use during laser surgery. To reduce the obstruction in the surgical field, by airway instruments, even techniques of spontaneous ventilation or intermittent apnea with intravenous anesthetics have been used.[6] Clear communication must be ensured and protocols followed to manage and avert such crisis.