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Canadian Journal of Anesthesia 47:176-178 (2000)
© Canadian Anesthesiologists' Society, 2000
Clinical Report

Biting the laryngeal mask : an unusual cause of negative pressure pulmonary edema

Jean-Michel Devys, MD, Christine Balleau, MD, Christian Jayr, MD and Jean-Louis Bourgain, MD

From the Département d'Anesthésie, Institut Gustave Roussy, 68, Rue Camille Desmoulins, 94805 Villejuif cedex, France.

Dr Jean-Michel Devys, Département d'Anesthésie, Hôpital Robert Debré, 48, Boulevard Serurier, 75 019 Paris, France. Phone: 33-1-42-11-44-37; Fax: 33-1-42-11-52-09.


   Abstract
TOP
 Abstract
Introduction
 Case report
 Discussion
 Conclusion
 References
 
Purpose: To describe negative pressure pulmonary edema due to biting of the laryngeal mask tube at emergence from general anesthesia.

Clinical features: A healthy patient underwent general anesthesia using a laryngeal mask airway and mechanical ventilation. During recovery, the patient strongly bit the laryngeal mask and made very forceful inspiratory efforts until the mask was removed. Five minutes later, the patient developed dyspnea and had an hemoptysis of 50 ml fresh blood. Chest radiograph showed bilateral alveolar infiltrates. Pharyngo-laryngeal examination was normal. Bronchoscopy revealed no injury but diffuse pink frothy edema fluid. Clinical examination and chest radiograph became normal after 12 hr of nasal oxygen therapy confirming airway obstruction as the most available cause of this pulmonary edema.

Conclusion: Airway obstruction due to biting of a laryngeal mask tube may result in negative pressure pulmonary edema.


   Introduction
TOP
 Abstract
 Introduction
Case report
 Discussion
 Conclusion
 References
 
BITING a laryngeal mask airway is a common and usually uncomplicated event at emergence from general anesthesia.1 We report the case of a healthy adult patient who developed pulmonary edema following upper airway obstruction related to the biting of a laryngeal mask tube. We discuss the importance of placing a bite block when a laryngeal mask is used during general anesthesia and the benefit of measuring the concentration of protein in edema fluid to identify the mechanism of negative pressure pulmonary edema.


   Case report
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 Abstract
 Introduction
 Case report
Discussion
 Conclusion
 References
 
A 19-yr-old male patient, physical status ASA 1 (weight 66 kg, height 1.76 m), scheduled for surgery to a cutaneous nevus was deeply anesthetized with 2 µgkg–1 fentanyl and 3 mgkg–1 propofol to allow insertion of a size-4 laryngeal mask. No bite block was used. General anesthesia was maintained with isoflurane and a N2O/O2 mixture with mechanical ventilation. The duration of surgery was 45 min and 500 ml Ringer's Lactate were infused. The patient was transferred to the recovery room at the conclusion of surgery breathing spontaneously with supplemental oxygen (6 lmin–1) via a T-piece connected to the laryngeal mask. In the recovery room, the patient began to swallow, cough, and vigorously bite the laryngeal mask tube. He then started to make very forceful inspiratory efforts. The arterial haemoglobin oxygen saturation (SpO2) decreased to 50% before successful removal of the laryngeal mask. Thereafter, the patient breathed normally and the SpO2 recovered to 98% with 10 lmin–1 of oxygen via a face mask. Cardiac and pulmonary auscultation were normal. Five minutes after removal of the mask, the patient developed moderate dyspnea and had an hemoptysis of 50 ml fresh blood. Upon auscultation of the chest, crackles were heard in both lung fields. Chest radiograph (FigureGo) showed diffuse bilateral pulmonary edema. The arterial blood sample showed: pH 7.36, PaO2 59 mmHg, PaCO2 46 mmHg, SaO2 89% with FiO2 0.21. The oropharyngolaryngeal examination revealed no oropharyngolaryngeal injury, but the presence of blood beyond the vocal cords. Fibreoptic bronchoscopy performed under local anesthesia showed no tracheo-bronchial injury but diffuse bilateral pink frothy edema fluid. Also, bronchoscopy showed no evidence of gastric contents in the airways. Cardiac auscultation, electrocardiogram and cardiac enzymes were normal. The patient was transferred to the intensive care unit with nasal oxygen. Neither diuretics neither non-invasive mechanical ventilation were used. After 24 hr, he was discharged from ICU to the surgical ward. Vital signs, temperature, clinical examination, chest radiograph and arterial blood gases were normal.



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  		FIGURE Chest radiograph obtained immediately following development of hypoxemia and bilateral rales. The radiograph shows diffuse bilateral alveolar infiltrates.

 

   Discussion
TOP
 Abstract
 Introduction
 Case report
 Discussion
Conclusion
 References
 
With the use of a laryngeal mask airway, emergence from general anesthesia can be associated with complications.1 Airway obstruction is common whatever the time of removal of the laryngeal mask, whether the patient be awake or still anesthetised.1 Airway obstruction may be due to laryngospasm, poor positioning of the device, or biting the tube of the laryngeal mask. In this report, laryngospasm may have been the cause of airway obstruction, but the complete resolution of inspiratory effort after mask removal argues against this explanation. Moreover, physical examination did not show any residual stridor. These findings suggest that biting down on the tube of laryngeal mask was the most likely cause of airway obstruction. Biting down on the tube of laryngeal mask is common and is not usually a serious adverse event.1 However, Brain2 has recommended the use of a bite block whenever a laryngeal mask airway is used. This report shows the importance of placing a bite block during general anesthesia using a laryngeal mask and of leaving it in place until removal of the laryngeal mask to prevent obstruction of the tube.

This is the first case report of negative pressure pulmonary edema associated with biting of a laryngeal mask tube. Some cases of pulmonary edema associated with the laryngeal mask have been reported, but were related to insertion difficulties3 or to laryngospasm during anesthesia.4 Pulmonary edema related to upper airway obstruction is well described in children and adults5 and is related to the large transpulmonary pressure gradients generated when trying to breathe against an obstructed airway. The very high negative intrapleural pressure provides high negative hydrostatic pressure in the pulmonary interstitium and increases venous return to the right heart and hydrostatic pressure in the pulmonary microvasculature favouring formation of pulmonary edema. In this case, pulmonary edema was clearly related to airway obstruction. Moreover, in this young healthy patient, cardiac function was normal and there was no sign of oro-pharyngo-laryngo-bronchial injury or of aspiration of gastric contents. A recent publication indicates that this type of pulmonary edema has a hydrostatic etiology without increased alveolo-capillary membrane permeability.6 The authors measured the ratio of total protein concentration between pulmonary edema fluid and plasma witch is an established, accurate method for distinguishing hydrostatic from increased permeability pulmonary edema.6 A ratio of less than 0.65 is characteristic of hydrostatic pulmonary edema, whereas patients with increased-permeability pulmonary edema, as seen in acute lung injury, have a ratio between 0.75 and 1.0.6 In this case, the mechanism of negative pressure pulmonary edema remains uncertain: the appearance of fresh blood suggests local disruption of alveolo-capillary membrane but the blood became ultimately frothy, possibly indicating another cause of the pulmonary edema as secondary hydrostatic or increased permeability. Unfortunately, the protein concentration of the edema fluid was not measured in this patient. Appearance of fresh blood may also be due to tracheo-bronchial vessels injury as described by Bhavani-Shankar et al.4 but such lesions were not found during bronchoscopy.


   Conclusion
TOP
 Abstract
 Introduction
 Case report
 Discussion
 Conclusion
References
 
Partial or complete airway obstruction due to biting of laryngeal mask is a common and usually uncomplicated event. However, airway obstruction due to biting of a laryngeal mask tube may result in negative pressure pulmonary edema.

Accepted for publication November 7, 1999.


   References
TOP
 Abstract
 Introduction
 Case report
 Discussion
 Conclusion
 References
 
1 Gataure PS, Latto IP, Rust S. Complications associated with removal of the laryngeal mask airway: a comparison of removal in deeply anaesthetised versus awake patients. Can J Anaesth 1995; 42: 1113–6.[Abstract/Free Full Text]

2 Brain AIJ. The laryngeal mask-a new concept in airway management. Br J Anaesth 1983; 55: 801–5.[Abstract/Free Full Text]

3 Ezri T, Priscu V, Szmuck P, Soroker D. Laryngeal mask and pulmonary edema (Letter). Anesthesiology 1993; 78: 219.

4 Bhavani-Shankar K, Hart NS, Mushlin PS. Negative pressure induced airway and pulmonary injury. Can J Anaesth 1997; 44: 78–81.[Abstract/Free Full Text]

5 Lang SA, Duncan PG, Shephard DAE, Ha HC. Pulmonary oedema associated with airway obstruction. Can J Anaesth 1990; 37: 210–8.[Abstract/Free Full Text]

6 Kallet RH, Daniel BM, Gropper M, Matthay MA. Acute pulmonary edema following upper airway obstruction: case reports and brief review. Respiratory Care 1998; 43: 476–80.




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This Article
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Right arrow Cardiothoracic Anesthesia, Respiration and Airway

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