Congenital tracheomalacia is characterized by a weakness of the tracheal wall due to softening of the supporting cartilage and hypotonia of the myoelastic element . Fibreoptic bronchoscopy is often used to diagnose tracheomalacia . Local anaesthesia to the airway is preferable to general anaesthesia for examination, because it is possible to observe the anatomical changes of the airway during physiological respiratory phases and during coughing [1-4]. However, in children, general anaesthesia may be required due to difficulty in obtaining co-operation [2,5,6]. Spontaneous breathing is usually maintained, because muscle relaxation will mask a flaccid airway .
There have been only a few reports of anaesthetic management of the patient with a tracheomalacia [5-7]. We report a case of airway obstruction, which occurred during diagnostic bronchoscopy in a child with suspected tracheomalacia.
A 1-yr-old girl, height 66 cm, weight 7 kg, with suspected congenital tracheomalacia, was scheduled for diagnostic fibreoptic bronchoscopy. Although she was born as a premature infant and had growth retardation, no other congenital abnormalities were detected. She had had several apnoeic attacks during the previous few months when she had coryza. There was no evidence of external compression of the trachea, such as a mediastinal mass or cardiovascular abnormality. In order for the trachea to be accurately assessed, it was planned to avoid tracheal intubation. We therefore decided to use the laryngeal mask with preparation for tracheal intubation in case of airway obstruction.
No premedication was given. In the operating room, a blood pressure cuff, electrocardiograph and pulse oximeter were attached and intravenous (i.v.) access was secured. Anaesthesia was induced by inhalation of increasing concentration of sevoflurane up to 3% in oxygen. As the anaesthesia was deepened, spontaneous breathing became irregular and airway obstruction occurred mainly during expiration. Manual ventilation of the lungs using a facemask was difficult. We gave vecuronium 1.0 mg i.v. to facilitate tracheal intubation. However, because it became possible to ventilate the lungs after the relaxant had taken effect, we judged that tracheal intubation was not mandatory at that moment.
A size 2 laryngeal mask was inserted, which further improved ventilation. After a swivel connector with a rubber seal had been attached to the laryngeal mask, an otolaryngologist passed a fibrescope through to inspect the airway. No obvious narrowing of the trachea was found during this period of manual lung ventilation. Arterial haemoglobin oxygen saturation (SpO2) remained at 100% during the bronchoscopy.
The otolaryngologists requested that spontaneous breathing to be allowed to resume. When this occurred (without the need for the administration of any antagonist), airway obstruction occurred due to marked tracheal collapse during each expiration. The SpO2 decreased to 70%. An endotracheal tube (internal diameter 3.0 mm) was inserted without further delay (and without the need for any further neuromuscular blocking drug). It was then possible to ventilate the lungs adequately and the SpO2 increased rapidly.
The neuromuscular blockade was antagonized using neostigmine 0.35 mg (with atropine 0.15 mg), and the trachea was extubated after the patient had regained consciousness and spontaneous breathing had fully returned. No further complications occurred. A diagnosis of congenital tracheomalacia, extending from the lower trachea to the left bronchus, was made.
During normal breathing, intrapleural pressure is always slightly more subatmospheric than the intratracheal pressure and thus the airway is held open [8,9]. However, during forced expiration (such as coughing or in the patient who needs to overcome the increased airway resistance at a lower trachea) both intrapleural pressure and alveolar pressure markedly increase. Because the pressure decreases along the airway toward the thoracic outlet, the trachea will be subjected to a compressing transmural pressure increasing toward the thoracic outlet [8,9].
The effects of general anaesthesia and muscle relaxation on the integrity of the trachea have not been elucidated. The intrathoracic pressure during expiration is lower during general anaesthesia than in the awake state  and it has been claimed that tracheal collapse is less severe during general anaesthesia . Continuous positive airway pressure with or without intermittent positive pressure ventilation has been reported to alleviate tracheal collapse [9-12]. When positive pressure is applied to the airway during forced expiration, the gradient between the intrathoracic and intratracheal pressures is reduced; therefore, tracheal collapse is, in theory, less likely to occur during controlled ventilation than during spontaneous breathing. In fact, in our patient, airway obstruction occurred during spontaneous breathing and obstruction disappeared by initiating controlled ventilation after injection of a muscle relaxant.
Although there is a theoretical risk of airway obstruction during general anaesthesia in patients with a collapsible airway , there have been several reports of airway management without tracheal intubation, such as the use the laryngeal mask, for diagnostic fibrescopy [4,5,14-16]. However, in our patient, airway obstruction with hypoxia did occur, confirming that the laryngeal mask may not secure the airway reliably in the face of airway obstruction. It seems reasonable to conclude that caution is required when the laryngeal mask is used in a patient with tracheomalacia, and equipment for tracheal intubation must always be readily available. In view of the possibility of airway obstruction occurring at any time, full monitoring should always be attached during anaesthesia, and venous access secured before induction of anaesthesia.
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