Anaesthetic safety with the carbon dioxide laser

[Specific aspects of anesthesiological management of laser surgery in otorhinolaryngology]

Transoral laser surgery has become a standard procedure in the treatment of benign and malignant neoplasms of the upper aerodigestive tract. As the laser cuts and coagulates simultaneously, intraoperative bleeding is reduced, thus improving visualization of the operative field. However, the specific risks for patients and personnel that are associated with this technique necessitate strict compliance with safety regulations and precautions. The safe anesthesiological and surgical management of such procedures requires explicit knowledge of the risks inherent to laser use, as well as close communication between surgeon and anesthesiologist throughout all operative and perioperative procedures. Although potentially fatal complications are rare, surgeon and anesthesiologist need to be aware of the dangers at all times and have exact knowledge of emergency measures. The use of suitable laser-resistant endotracheal tubes, total intravenous anesthesia and an optimized breathing gas mixture can contribute to minimize the occurrence of complications in otorhinolaryngology laser surgery.

[Specific aspects of anesthesiological management of laser surgery in otorhinolaryngology]

Transoral laser surgery has become a standard procedure in the treatment of benign and malignant neoplasms of the upper aerodigestive tract. As the laser cuts and coagulates simultaneously, intraoperative bleeding is reduced, thus improving visualization of the operative field. However, the specific risks for patients and personnel that are associated with this technique necessitate strict compliance with safety regulations and precautions. The safe anesthesiological and surgical management of such procedures requires explicit knowledge of the risks inherent to laser use, as well as close communication between surgeon and anesthesiologist throughout all operative and perioperative procedures. Although potentially fatal complications are rare, surgeon and anesthesiologist need to be aware of the dangers at all times and have exact knowledge of emergency measures. The use of suitable laser-resistant endotracheal tubes, total intravenous anesthesia and an optimized breathing gas mixture can contribute to minimize the occurrence of complications in otorhinolaryngology laser surgery.

Entflammungs- und Brandverhalten von biologischem Gewebe bei In-vitro-Bestrahlung mit dem CO2-Laser

BACKGROUND

Laser surgery in endoscopy has greatly enhanced the surgical armamentarium for treating various laryngeal and hypopharyngeal disorders, but harbours a risk of tissue ignition and inflammation of surgical and anaesthetic instrumentation. However, even if non-inflammable material is used, there is still a residual fire hazard from endogenous tissue that may develop an ignitable aerosol (so-called laser smog) as an effect of laser irradiation. The aim of this study was to investigate how tissue carbonisation and vaporisation contributes to the risk of airway fire.

METHODS

For the simulation of gas accumulation in the hypopharynx and larynx following the European standard ISO-11990, a cylindrical steel chamber with an open and a closed end has been used to simulate the operative setting. Pork meat chunks with a tissue composition similar to the larynx and hypopharynx such as fat, muscle, cartilage and bone were introduced into this chamber. Ventilation was achieved through jet ventilation with disposable, non-inflammable laser jet catheters. The tissue was then repeatedly exposed to a laser beam in super-pulse mode (pulse rate 250 Hz) with various intensities and exposure lengths at an impact angle of 75 degrees. The laser intensity was varied from 2 to 15 W. The type, duration, intensity and incidence of tissue ignition were recorded and analysed.

RESULTS

The degree of tissue ignition correlated with laser intensity. Low laser intensity caused spark formation whereas high intensity resulted in sustained tissue fire. The type of tissue had an impact on ignition intensity thereby showing lower ignition thresholds and higher ignition susceptibility in fat-containing tissue compared to muscle. The most important factor for occurrence of tissue ignition was the chamber oxygen concentration which displayed an inverse correlation with the time until tissue ignition. Oxygen concentrations of 35% led to tissue ignition in 42 s, 40% oxygen in 20 s. Oxygen concentrations higher than 60% resulted in immediate tissue ignition.

CONCLUSIONS

Despite the use of non-inflammable materials in endoscopic laser surgery of the upper airway and hypopharynx, the risk of tissue ignition remains due to the inflammable laser smog which is easily ignited in an oxygen-rich environment. Hence to minimise this risk, we recommend using oxygen concentrations lower than 40%, low laser intensities (<6 W) and limiting continuous laser activation to periods shorter than 10 s.

Congenital laryngomalacia

There is at present, very little information on congenital laryngomalacia in the anaesthetic literature. The purpose of this article is to review this topic, which in 90% of patients represents a benign self-limiting condition, disappearing by the age of two to five years. However, if untreated, the remaining 10% of cases can prove fatal. This severe form presents as persistent sternal recession, feeding difficulties, and failure to thrive, progressing to apnoeic attacks, cor pulmonale and eventually death. The developmental and functional anatomy of the larynx will be included, with a discussion of the pathophysiology and history of the disorder. Its diagnosis and a résumé of the various treatment strategies, will be presented. The anaesthetic management is controversial as is the surgical technology. Our technique, for diagnosis or definitive repair, is based upon suspension laryngoscopy using topical local analgesia and spontaneous ventilation. Halothane is then administered by insufflation into the pharynx, using a #8 nasopharyngeal catheter, and suction is applied to the mouth. During the surgical repair, an endotracheal tube (ETT), may be inserted, at the discretion of the anaesthetist and surgeon. Finally, the role of the dioxide CO2 laser and its hazards will be introduced.

Anaesthesia for airway obstruction in laryngo-onycho-cutaneous syndrome

A 4-year-old boy with laryngo-onycho-cutaneous syndrome underwent excision of an obstructive vocal cord lesion. There is only one previous case report of laryngeal involvement in this syndrome but the anaesthetic management has not been reported. The anaesthetic management for microlaryngobronchoscopy and laser surgery in this child with upper airway obstruction is described.

Subglottic haemangioma in the infant: contribution by CO2 laser

The availability of the low intensity CO2 laser beam, and the possibility of defocalization that is associated with control of subglottic high frequency jet ventilation, requires a more interventionist attitude regarding dyspnoea caused by a subglottic haemangioma in the infant. It is indeed possible reliably to reduce the size of the subglottic haemangioma, and thus to avoid a lengthy period of intensive care, as well as the problems of prolonged intubation or tracheostomy for drainage, while also avoiding long term steroid therapy. This approach in no way affects the spontaneous evolution of subglottic haemangioma in the infant; there is a tendency for the haemangioma to regress after the age of one year. The treatment does, however, permit a considerable improvement in the comfort of the infant's life during this difficult period between 3 and 12 months. We illustrate this new attitude by presenting a report on four cases.

High frequency ventilation in laser surgery of the larynx

For endolaryngeal laser surgery an anaesthetic technique is required which provides the surgeon good access to the larynx. High frequency ventilation of the lungs using a FG 14 insufflation catheter covered by aluminium foil has proved to give a nearly optimal condition for the surgeon, while the fully paralyzed patient is very well ventilated. This has been used in more than 1000 patients, 200 of them have been treated by the laser beam in the airway. A method of total intravenous anaesthesia is described using short acting drugs. This way early awakening after surgery in the airways prevents aspiration of blood or debris into the lungs.

A safe, nonflammable, all-metal, cuffless endotracheal Venturi ventilation system for use in laser surgery

In this preliminary study with seven dogs, ventilation with a Sanders bronchoscope attachment coupled to the Norton metal endotracheal tube and use of a jet O2 injector system proved adequate for sustained oxygenation and acid-base balance. This system is shown to be superior to the conventional anesthesia volume ventilator when used with the cuffless metal endotracheal tube. The ventilatory capability can be easily adjusted upward and downward by changing the driving pressures of the reducing valve. Peak intratracheal and transtracheal pressure measurements show the pressures encountered to be similar to those of conventional volume ventilation techniques. The use of the all-metal endotracheal tube in endolaryngeal laser surgery is discussed. The advantages of such a system lie in the elimination of a flammable endotracheal tube during laser endolaryngeal surgery while preserving adequate and stable ventilation.

Heat sink protection against lasering endotracheal cuffs

The ignition of an endotracheal cuff by CO2 laser impaction has proved troublesome in several ignition sequences. Metal foil tape wrapped around the shaft of the tube will provide adequate protection for it, but the tape does not extend to the thin-walled cuff. When normal saline solution is used instead of air to fill the cuff, heat is rapidly conducted away from the wall and the cuff is prevented from reaching its kindling temperature. If penetration should occur, a fine jet of saline solution instantaneously sprays the field, extinguishing any early combustion. The reaction time of the surgeon or an assistant is not a factor in prevention of thermal injury, no new equipment is required and preparation time is minimal.