Airway ignition during CO₂ laser laryngeal surgery and high frequency jet ventilation

Abstract

We present a case of a patient submitted for extirpation of a neoplasm of the larynx, by means of carbon dioxide laser surgery. High frequency jet ventilation was applied by means of orotracheal intubation with two Teflon catheters, 2 mm in external diameter and 30 cm in length, attached with three equally placed strips of adhesive paper tape. One catheter was used to inject the jet volume and the other used to measure the airway pressure. The adhesive strips were moistened and FiO₂ was lower than 50%. After 30 min using the laser, an airway fire was noticed. Ventilation was interrupted and the catheters were removed. The patient was reintubated with an endotracheal tube of 6 mm ID and the surgical procedure was continued until the tumour was removed. Two factors contributed to the airway fire: the ignition of the lowest adhesive strip that had dried and the use of the laser in the mode of continuous pulsation.

Introduction

High frequency jet ventilation (HFJV) has been reported as an effective method during microsurgery of the larynx, including laser surgery. It allows adequate ventilation with minimal obstruction of the upper airway surgical field ^[1,2]. Whereas ventilation can be adequately and continuously monitored with conventional tubes, monitoring jet ventilation is considered difficult but necessary. Capnography and airway pressure measurement allows the effectiveness of the ventilation to be known and complications resulting from excessive airway pressure because of inadequate outflow from the lungs, in the case of laryngeal stenosis, being avoided ^[3]. The risk of barotrauma may be greater in patients with upper airway obstruction, a condition which is frequently seen in patients requiring microsurgery of the larynx. The use of the carbon dioxide laser for laryngeal surgery is now well established. It allows good haemostasis and is associated with minimal inflammatory reactions and oedema of the surrounding tissues. However, the use of the CO₂ laser does create many anaesthetic problems. The seriousness of laser-induced airway fire has led to the development of special techniques and equipment to minimize this risk ^[4]. We present a report of an airway fire associated with HFJV and a carbon dioxide laser.

Report

A 49-year-old man weighing 59 kg, diagnosed with a neoplasm of the right vocal cord was scheduled for extirpation of the lesion by means of CO₂ laser microsurgery. History and physical examination were unremarkable other than a heavy smoking history and a moderate alcoholic habit. He had been operated on for a perforated duodenal ulcer 20 years previously.

The anaesthetic technique used was as follows. Premedication with oral diazepam 10 mg was given the night before. When the patient arrived in the operating theatre, intravenous (i.v.) premedication with atropine 0.6 mg (0.01 mg kg⁻¹), dehydrobenzperidol 2 mg and alfentanil 600 μg (10 μg kg⁻¹) was administered. Pure oxygen was breathed via a facemask. The ECG, heart rate, peripheral oxygen haemoglobin saturation (SpO₂), end-tidal CO₂ and arterial tension were monitored. Anaesthetic induction was with alfentanil 600 μg (10 μg kg⁻¹), propofol 90 mg (1.5 mg kg⁻¹) and vecuronium bromide 3.6 mg (0.06 mg kg⁻¹). Anaesthesia was maintained with a continuous perfusion of propofol 8 mg kg⁻¹ h⁻¹, and two repeated doses of alfentanil 400 μg were administered during the surgical procedure, which had a duration of 40 min. Direct laryngoscopy was performed with the aid of a Macintosh laryngoscope blade, and orotracheal intubation was performed with two Teflon injection catheters, 2 mm internal diameter and 30 cm long, attached with three equally placed strips of adhesive paper tape (Steri-Strep, 3M Health Care, St Paul, Minnesota, USA) (Fig. 1). The first catheter was used to deliver the jet volume and the distal tip was located 2-3 cm below the vocal cords in the subglottic position. The second catheter was used to measure continuous tracheal air pressure and to enable end-tidal CO₂ to be monitored. The proximal tip of the second catheter was connected to a respiratory pressure transducer and the distal tip was located at the level of the carina. Before initiating the laser, the patient's eyes and face were protected with moist towels. The adhesive strips, placed on the endotracheal catheters, were also moistened.

Fig. 1: The two attached catheters used for applying and monitoring the high frequency jet ventilation.

The patient's lungs were ventilated with HFJV using an Ergojet CVT®, module of the Ergotronic 3 ventilator (Temel SA Inc, Valencia, Spain). The driving pressure was 3 bars, the respiratory frequency was 100 cycles min⁻¹, the percentage inspiratory time was 30, the inspiratory oxygen fraction (FiO₂), was initially at 70% (O₂/air mixture). From the initiation of the laser (power laser at 10-15 watts), FiO₂ was lower than 50%. The Ergojet CVT® allows continuous monitoring of airway pressure (P_AW) and peak inspiratory pressure values which ranged between 6 and 10 cm H₂O were obtained. End-expiratory pressure values ranged between 0 and 4 cm H₂O during the entire surgical procedure.

After 30 min using the laser, ignition of the lowest adhesive strip (subglottic area) was noticed by the surgeon. The HFJV was immediately interrupted, the catheters removed, ventilation with a facemask was initiated and FiO₂ was raised to 100%. There was no desaturation and respiratory auscultation gave normal results. By means of a facemask with a endoscopy port (Endoscopy Mask VBM®, VBM, Medizintechnik Gmbh, Sulz, Germany), a fibreoptic bronchoscope (Olympus®, Olympus Optical Co. Ltd, Tokyo, Japan) was introduced and the upper airway was assessed. A small wound was seen at the level of the second tracheal ring, although the location of the wound did not anatomically correspond with the area of ignition. Following examination, the patient was reintubated with an endotracheal laser tube (Laser-Trach, Sheridan®, Kendall Co., Mansfield, Massachusetts, USA) 6 mm of ID with the cuff filled with saline solution, and the surgical procedure was continued for an additional 10 min. After finalizing the surgical procedure, the patient was able to be extubated without further clinical incident. There was no evidence of respiratory failure in the immediate postoperative period nor did the postoperative follow up reveal any changes. The ventilation catheter, after removal was found to be blackened by combustion where the adhesive tape had been placed (Fig. 2). No alteration in the catheter's wall was observed. The tracheal wound observed during the exploration with the fiberoptic bronchoscope must have been caused by a firing of the laser on an to unintentional zone due to the easy access to the surgical field due to the small catheters utilized for HFJV.

Fig. 2: The catheters were blackened by combustion where the adhesive tape had been placed.

Discussion

Risk factors which increase ignition

The most frequent complications during the use of the CO₂ laser for laryngeal surgery are ignition of the airway and of the endotracheal tube ^[5]. There are various contributing factors. Among these are the use of inflammable material in the airway including the endotracheal tubes, FiO₂ higher than 50%, high laser power, and extended exposure time with laser firing and failure to moisten the cotton gauze pads placed in the surgical field ^[6].

Risk factors present in our case which caused this occurrence

Authors who usually work in the ENT surgical area, always follow the guidelines of the Laser Safety Officer ^[6] when a CO₂ laser is used for laryngeal endoscopic surgery. We believe that various factors contributed to the occurrence reported here. The adhesive paper tape to which was attached the two catheters had a coefficient of ignition differing from that of Teflon, and is inflammable if not pre-moistened before being placed. In our case, the catheters were moistened with saline solution before intubation. However, during the course of the surgical procedure, a drying process occurred due to the heat of the laser beam, and by the continuous flow of expired air through the larynx. Also, continuous laser pulsation and laser firing time reached 20 s on occasions during the 30 min procedure time until the accident occurred. Within these 30 min, neither the ventilation catheters nor the aiding structures were re-moistened. Furthermore, the adhesive strips placed on the catheters and located in the subglottic region showed difficult access and poor visibility. For this reason, warning signs were difficult to detect. The presence of blood on the Teflon tubes has not been shown to be a major risk factor for ignition, but the possibility cannot be dismissed ^[7]. Moreover, the mode in which the laser was used was of continuous pulsation instead of intermittent pulsation. This increased the risk of the tubes and the strips overheating.

Proposed improvements

We consider that suppliers do not currently offer a suitable type of endotracheal catheter used to administer the HFJV. A suitable catheter should be made of material resistant to ignition and endowed with a reliable system of airway pressure measurement during ventilation, and should also be easily inserted in patients with laryngeal tumours. It should meet the standards set by a laser authority, manufactured with quality control and provide reproducible results in use.

The Hunsaker-Mon-Jet tube is now available for HFJV ^[8]. It is made of highly flame resistant fluoroplastic, offering the convenience of distal flanges for centering the tube in the trachea permitting better focus of the jet volume and limits the movement of the catheter once placed in the airway. The catheter has a side port for monitoring tracheal pressure and endtidal CO₂. However, we believe it presents two major disadvantages. First, the pressure meter is located above the gas injection port thereby producing inaccurate measurements of the tracheal pressure due to the turbulence generated by the continuous flow of expired air. During HFJV, continuous monitoring of airway pressure is necessary because it is recognized that the most severe risk of HFJV is the barotrauma. This risk may increase in the presence of airway obstruction, which is frequent in patients with laryngeal diseases ^[3]. It is recommended that the best position for the measurement of tracheal pressure is 10 cm below the jet ^[9]. Second, the Hunsaker tube wing system has a considerable large calibre at the flange level of the tube, which may cause damage during intubation and extubation in some laryngeal obstructive diseases.

The system of the two catheters that we use for HFJV is the device of choice in our Department ^[10] and it has several advantages. The catheters are made of Teflon which is one of the tested materials for laser use and which has shown a greater resistance to fire in a comparative study ^[8]. The asymmetric alignment and attachment of the tubes permits the pressure catheter to be placed in the airway at the desired depth. Furthermore, the intubation process is without difficulty given the small calibre of the tubes. However, this product is not available commercially, and the placement of the adhesive strips for the alignment of the catheters is not convenient and can slide out of place as they are not locked in the airway.

In view of the case described, we propose the omission of adhesive tape and of any other inflammable material which can be placed in the air passage and, in all cases, the frequent and regular moistening of the tubes. As endotracheal insertion of the unattached tubes is difficult given that the two tubes could diverge at their distal ends, we propose that intubation should be carried out by first introducing the pressure catheter and placing it deeper into the trachea and immediately afterwards the introduction of the injecting catheter to a position 2-3 cm below the vocal cords. In case of difficulty in positioning the catheter, we have on occasions utilized a number 6.5 i.d. PVC endotracheal tube which served as an introducing sleeve and which was removed after the insertion of jet catheters. In conclusion, we emphasize the necessity of being rigorous with the security measures when using the CO₂ laser in larynx surgery in respect of both surgical and anaesthetic equipment.