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Use of the laryngeal mask airway in preventing airway fires during adenoidectomies in children: a study of 25 patients.

Abstract

We report the results of our study of 25 children who underwent adenoidectomy under general anesthesia with a laryngeal mask airway to determine their risk of fire in the oropharynx. We explain the distinct advantage that such an anesthetic technique has with respect to minimizing the conditions that may contribute to an airway fire. We also discuss additional advantages of using a laryngeal mask airway during adenoidectomies.

Introduction

As the use of electrocautery in oropharyngeal airway surgery has increased during the past decade, so has the risk of airway fires because of the presence of combustible materials in the oxygen-rich operative environment. Several instances of airway fires have been reported during tracheostomies and tonsillectomies. (1,2)

As has been previously reported, minimizing airway leaks from uncuffed endotracheal tubes during tonsillectomies can dramatically reduce the oxygen concentration at the tonsillar fossa and thereby reduce the risk of airway fires associated with electrocautery use. (3) In this article, we report the results of our study with respect to minimizing the conditions that increase the risk of airway fire by the use of a laryngeal mask airway (LMA) (LMA Flexible; The Laryngeal Mask Company, Ltd., Mahe, Seychelles) in children undergoing adenoidectomies under general anesthesia.

Patients and methods

We prospectively studied 25 consecutive patients aged 2 to 16 years (12 boys and 13 girls) undergoing adenoidectomy under general anesthesia with an LMA (table). The general anesthetic (sevoflurane, nitrous oxide, and oxygen) was supplemented with intravenous morphine as needed for analgesia. Children younger than 10 years of age were induced by inhalation, and those who were older were induced with 2 to 3 mg/kg of IV propofol. The size of the LMA employed was based on the patient's weight and the results of the anesthesiologist's clinical evaluation. After placement, the LMA was inflated with air to allow positive-pressure ventilation without clinical evidence of an airway leak.

After induction and LMA placement, anesthesia was maintained with 2 to 3% sevoflurane, nitrous oxide, and oxygen at 2 liters each during the entire surgical procedure. Patients were ventilated with positive pressure, and peak airway pressures were maintained at approximately 16 to 18 cm of water. A Crow-Davis mouth gag was inserted to facilitate the surgical procedure.

Nitrous oxide and oxygen concentrations were measured with a Datex-Engstrom AS/3 anesthetic monitor equipped with an AS/3 airway module. Inspiratory concentrations (% Insp) of both nitrous oxide and oxygen were recorded by a gas-sampling line attached to a standard anesthetic circuit. A 14 French Airlife oxygen catheter was then placed in the superior oropharynx, and nitrous oxide and oxygen concentrations were again sampled (% OP).

Results

No airway fires occurred during the course of this study despite the use of electrocautery to achieve hemostasis. Airway gas analysis at the superior oropharynx revealed that the gas concentrations were essentially the same as those of room air (nitrous oxide: 0%; oxygen: 21%). There were no cases in which upper airway gas analysis revealed evidence of gas concentrations approaching or similar to the delivered anesthetic gas percentages. One patient (female, aged 6 years) had to have the LMA replaced with the next largest size (from size 2.5 to 3) to achieve an adequate airway seal.

Discussion

The LMA has had widespread use in the delivery of anesthesia during the past several years. Its advantages when used for general anesthesia include providing airway support, minimizing dead space, and allowing the use of positive-pressure ventilation. It is also less likely than an endotracheal tube to stimulate undesirable respiratory and cardiovascular reflexes.

As the use of electrocautery in tonsillectomies and adenoidectomies has increased over the years, so has the theoretical risk of airway fires secondary to its use in an oxygen-rich environment. With the increased use of the LMA for otolaryngeal procedures, surgeons and anesthesiologists need to be familiar with the advantages and disadvantages such a technique offers.

As has been described elsewhere, the origination of an airway fire requires a combustible material, an ignition source, and an oxidizing agent? Measures to prevent surgical fires must include addressing the risk factors that can be minimized during a procedure. The risk of airway fire with the use of general endotracheal anesthesia for adenoidectomy is low; our previous study showed that conditions that increased the risk of airway fires only occurred at airway leak pressures above 12 cm of water. (3) We have found that the use of the LMA for such procedures provides the distinct advantage of keeping the oxidizing sources (i.e., nitrogen and oxygen) to an absolute minimum.

Our results indicate that a properly placed LMA keeps the nitrous oxide source (when used as part of an inhalational anesthetic technique) at 0 (zero). In addition, the only other oxidizing source that is theoretically available is room-air oxygen at the operative site. Specifically, when the LMA was used, the measured superior oropharyngeal oxygen concentration (% OP [O.sub.2]) remained at 21% (room-air concentration) regardless of the inspired oxygen concentration (% Insp [O.sub.2]), which ranged from 36 to 62%. Keeping these two oxidizing sources to absolute minimum concentrations in the area of the operative site during electrocautery use is essential to minimizing the risk of an operative fire.

Other advantages exist for the use of an LMA for ad enoidectomies. The LMA was developed by Dr. Archie Brain, a British anesthesiologist, in the early 1980s. It was his premise that the traditional anesthesia face mask left the airway vulnerable to oropharyngeal secretions, while endotracheal intubation stimulated undesirable respiratory and cardiovascular reflexes and had the potential for injury to the teeth, larynx, and trachea. (4) The LMA reduces these drawbacks. For example, a properly placed LMA can minimize the passage of blood into the stomach because the LMA, by design, covers both the larynx and esophagus. This in turn may decrease the incidence of postoperative nausea and vomiting.

In addition, emergence from general anesthesia may be "smoother" with the use of an LMA because of the LMA's reduced stimulating effect compared to that of an endotracheal tube. Daum and O'Reilly, for example, in describing the use of the LMA in otolaryngeal surgery, noted a decrease in (1) the incidence of a hypertensive response on insertion, (2) the occurrence of postoperative sore throat, (3) the occurrence of coughing at the termination of the surgical procedure, and (4) the likelihood of bronchospasm when compared to the use of endotracheal intubation. (5) Less coughing on emergence as a result of the lack of direct tracheal stimulation may minimize surgical bleeding at the end of the procedure. Daum and O'Reilly also noted that with an LMA, it was impossible to inadvertently intubate the esophagus or the main stem bronchus during surgery.

With its reduced stimulation of the larynx and trachea, the LMA is probably the method of choice for children undergoing general anesthesia who have a history of irritable airway disease, laryngospasm after anesthesia, or subglottic stenosis. (6) Furthermore, a study comparing the use of uncuffed endotracheal tubes with the LMA for tonsillectomies and adenoidectomies showed a decreased incidence of blood aspiration with LMA use. (7)

One distinct disadvantage of LMA use in oropharyngeal surgery is in operative procedures that include tonsillectomies. Hem et al reported that access to the palatine tonsillar anatomy is reduced with the LMA compared with endotracheal intubation, resulting in the removal of less tonsillar tissue.(8) Webster et al found an increased rate of peripheral oxyhemoglobin desaturation (Sp[O.sub.2] <94%) upon placement of the LMA compared to tracheal intubation. (9) This study also described an increased rate of airway obstruction upon opening the Boyle-Davis mouth gag with an LMA, requiring the replacement of the LMA with an endotracheal tube in 5 of 55 (9.1%) of the cases. While no such conversion was needed during the present study, the use of the LMA for tonsillectomies may be limited because of its negative effect on surgical exposure.

We conclude that using the LMA for adenoidectomies is a safe and effective anesthetic technique that minimizes the factors that can increase the risk of an airway fire during electrocautery dissection. In addition, using an LMA for adenoidectomies offers other advantages that should be considered when choosing an anesthetic technique for these procedures in children.

References

(1.) Awan MS, Ahmed I. Endotracheal tube fire during tracheostomy: A case report. Ear Nose Throat J 2002;81 (2):90-2.

(2.) Lira HJ, Miller GM, Rainbird A. Airway fire during elective tracheostomy. Anaesth Intensive Care 1997;25(2): 150-2.

(3.) Mattucci KF, Militana CJ. The prevention of fire during oropharyngeal electrosurgery. Ear Nose Throat J 2003;82(2): 107-9.

(4.) Brain AI. The laryngeal mask--a new concept in airway management. Br J Anaesth 1983;55(8):801-5.

(5.) Daum RE, O'Reilly BJ. The laryngeal mask airway in ENT surgery. J Laryngol Otol 1992; 106(1):28-30.

(6.) Ruby RR, Webster AC, Morley-Forster PK, Dain S. Laryngeal mask airway in paediatric otolaryngologic surgery. J Otolaryngol 1995;24(5):288-291.

(7.) Williams PJ, Bailey PM. Comparison of the reinforced laryngeal mask airway and tracheal intubation for adenotonsillectomy. Br J Anaesth 1993;70(1):30-3.

(8.) Hem JD, Jayaraj SM, Sidhu VS, et al. The laryngeal mask airway in tonsillectomy: The surgeon's perspective. Clin Otolaryngol Allied Sci 1999;24(2):122-5.

(9.) Webster AC, Morley-Forster PK, Dain S, et al. Anaesthesia for adenotonsillectomy: A comparison between tracheal intubation and the armoured laryngeal mask airway. Can J Anaesth 1993;40(12): 1171-7.

Charles J. Militana, MD; Michael K. Ditkoff, MD, FACS; Kenneth F. Mattucci, MD, FACS

From the Department of Anesthesiology (Dr. Militana) and the Department of Otolaryngology (Dr. Ditkoff and Dr. Mattucci), North Shore University Hospital, Manhasset, New York.

Reprint requests : Charles J. Militana, MD, Department of Anesthesiology, North Shore University Hospital, 300 Community Dr., Manhasset, NY 11030. Phone: (516) 562-8628; fax: (516) 562-1669; e-mail: cmilitana@NAPAnesthesia.com
Table. Patient characteristics and findings

Age (yr)/sex Weight LMA % Insp % Insp % OP
 (kg) size [O.sub.2] [N.sub.2]O [O.sub.2]

 2/F 14 2 50 49 21
 6/F 28 2.5 38 62 21
 7/M 37 3 36 44 21
 2/F 13 2.5 54 46 21
 6/M 14 3 54 46 21
 16/M 65 4 56 44 21
 7/M 22 2.5 54 46 21
 6/F 34 2.5 50 50 21
 5/M 20 2.5 54 46 21
 4/M 22 2.5 39 56 21
 2/M 15 2 47 53 21
 6/F 18 2.5 55 45 21
 4/F 15 2 54 46 21
 14/M 65 4 50 50 21
 4/F 20 2.5 37 63 21
 6/F 25 3 37 63 21
 10/M 35 3 40 60 21
 6/M 28 3 48 52 21
 3/M 15 2.5 50 50 21
 5/F 18 2.5 47 53 21
 7/M 24 2.5 50 50 21
 3/F 16 2.5 55 45 21
 7/F 18 3 62 38 21
 10/F 40 4 54 46 21
 3/F 32 2.5 55 45 21

Age (yr)/sex 9k OP
 [N.sub.2]O

 2/F 0
 6/F 0
 7/M 0
 2/F 0
 6/M 0
 16/M 0
 7/M 0
 6/F 0
 5/M 0
 4/M 0
 2/M 0
 6/F 0
 4/F 0
 14/M 0
 4/F 0
 6/F 0
 10/M 0
 6/M 0
 3/M 0
 5/F 0
 7/M 0
 3/F 0
 7/F 0
 10/F 0
 3/F 0

LMA = laryngeal mask airway; % Insp [O.sub.2] = inspiratory
concentration of oxygen; % Insp [N.sub.2]0 = inspiratory
concentration of nitrous oxide; % OP [O.sub.2] = oropharyngeal
concentration of oxygen; % OP [N.sub.2]0 = oropharyngeal
concentration of nitrous oxide.
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Author:Militana, Charles J.; Ditkoff, Michael K.; Mattucci, Kenneth F.
Publication:Ear, Nose and Throat Journal
Article Type:Report
Date:Oct 1, 2007
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