Unexpected Tracheomalacia in Marfan Syndrome During General Anesthesia for Correction of Scoliosis

Abstract

Tracheomalacia results in narrowing of the tracheal lumen during increased intrathoracic pressure caused by a thin tracheal wall. Symptomatic tracheomalacia is known to cause airway obstruction during general anesthesia (1). However, there are few reports showing these respiratory difficulties. We report an unexpected tracheomalacia exhibiting CO2 retention and an increased peak inspiratory pressure after the beginning of the operation; it was confirmed with fiberoptic bronchoscopy. Case Report A 12-yr-old boy was scheduled for a spine fusion operation because of scoliosis. He had undergone a Nuss operation (2) for correction of funnel chest. He had neither dyspnea nor chest pain and had clear breath sounds. Care was taken in positioning the patient prone in order not to derail the inserted bar or apply pressure to the chest. General anesthesia was induced without any problems. The peak inspiratory pressure (PIP) increased from 22 to 28 cm H2O, and ETco2 increased from 35 to 45 mm Hg after 1 h. Bilateral wheezing was detected without problems in the circuit or the tube. The chest radiograph showed no displacement of the Nuss bar compared with the previous films (Fig. 1). A fiberoptic bronchoscopy revealed narrowing of the tracheal lumen anteroposteriorly distal of the tube (Fig. 2). The narrowing was aggravated when surgeons pressed on the patient. Tracheomalacia was suspected, and the tube was advanced just above the carina. Two hours later, PIP increased and Spo2 decreased. Fiberoptic bronchoscopy revealed that the trachea was pressed on by the instruments. When the surgeons lifted the patient’s shoulder, the Spo2 returned to 100%. When the situation described previously resumed, surgeons paused and reduced pressure on the chest. At the end of the operation, the patient was transferred to the pediatric intensive care unit with the tube in situ. He was discharged 7 days after the operation without any problems.Figure 1: Chest radiograph showing that the inserted Nuss bar (arrow) was in the correct position.Figure 2: The film shows a narrowing of the tracheal lumen anteroposteriorly distal to the tip of the endotracheal tube.Discussion Dynamic compression of the intrathoracic airway in the expiratory phase is normal. It is elicited more readily during forced expiration when the intrathoracic pressure is intentionally increased, especially in patients with lung diseases such as chronic obstructive pulmonary disease. Tracheomalacia has been defined as an extreme degree of dynamic airway compression, in which the cross-sectional area of the trachea is reduced to less than half by expiratory compression (3,4). It produces a clinical picture that is barely distinguishable from that of bronchial asthma. It consists of prolonged, labored, and wheezy expiration and progressive asphyxia, which is resistant to an increased inspiratory oxygen concentration (5). Jokinen et al. (3) reported a tracheobronchomalacia in 97 (4.5%) of 2150 patients with a variety of pulmonary diseases. This patient had no history of respiratory difficulties or abnormalities. We believe that even if there were respiratory abnormalities, they would have been mistaken for symptoms of a funnel chest. Our patient, having undergone general anesthesia safely in the supine position, was thought to have no respiratory problems. However, when he was prone, the airway was compressed by both the spine and by the surgeons, and this aggravated the symptoms of tracheomalacia. Airway obstruction became worse on expiration with chest compression and the ETco2 increases, resembling a breathing circuit obstruction. There was concern that the escaped Nuss bar had resulted in respiratory compromise. Therefore, we thought that the increase in the PIP and ETco2 was due to the escaped bar, but it was found to be in place. Because there was no visible evidence of secretion or circuit, the inside of the endotracheal tube was examined with a fiberoptic bronchoscope, and a decrease in the diameter of the trachea was found. Although the patient had an airway problem, the operation could not be ended, and a tube was advanced just above the carina. Because the patency of the airway could not be maintained, the surgeons were asked to pause the operation whenever the PIP and the ETco2 had increased. The funnel chest correction was not complete, and symptoms of tracheomalacia were aggravated in the prone position. The mechanism by which the airway is obstructed during spontaneous breathing under general anesthesia and by which it is relieved by intermittent positive pressure ventilation remains unknown. It is probable that during normal breathing, the intrapleural pressure is always more negative than the intratracheal pressure, and the airway remains open (6,7). However, during forced expiration, the intrapleural and alveolar pressure markedly increase. Because the pressure decreases along the airway in the direction of the thoracic outlet, the trachea will be subjected to a compressing transmural pressure that increases toward the thoracic outlet (6,7). When positive pressure was applied to the airway during forced expiration, the gradient between the intrathoracic and intratracheal pressures was reduced. In fact, several authors have reported that a continuous positive airway pressure, with or without intermittent positive pressure ventilation, alleviates a tracheal collapse (6–9). In our patient, anesthesia was completed safely by using the tube for maintaining the patency of the diseased trachea.