Unexpected tracheal narrowing during general anesthesia in the prone position of Duchenne muscular dystrophy patient -A report of two cases-
A 12-year-old boy (height 125 cm, weight 18.8 kg) with Duchenne muscular dystrophy (DMD) was scheduled for the correction of thoracolumbar scoliosis. Cobb's angle was 100°. Preoperative evaluation revealed that he was acceptable for general anesthesia, but he had decreased lung function. The FEV1 0.66 liter, /FVC 0.73 liter, FEV1/FVC 90%). He did not report any symptoms of insufficient respiration in his daily life. He was supported on the operating table with multiple padding due to scoliosis and posterolaterally bent neck. Anesthesia was induced intravenously with propofol and rocuronium, and he was then intubated successfully with a wire-reinforced tracheal tube (internal dimension 5.5 mm, SPIRAL-FLEX® reinforced tubes, Hudson RCI, Temecula, USA). The tracheal tube was fixed at 17 cm. Both lung sounds were clear with manual ventilation. Peak inspiratory pressure (PIP) was 16 cmH2O with volume-controlled mechanical ventilation, tidal volume (TV) 160 ml, respiration rate (RR) 16 per minute and FiO2 0.5. Anesthesia was maintained with intravenous propofol and remifentanil starting at the targeted effect concentration of 3 µg/ml and 3.5 ng/ml respectively via target controlled infusion (TCI). After internal jugular vein and radial artery catheterization, the patient was moved into the prone position. In the prone position, PIP reached up to 30 cmH2O, and a low-pitched wheezing sound was detected in both lungs, although no secretion was observed from suctioning via tracheal tube. We switched the ventilator mode from the volume-controlled type to the pressure-controlled type. The expirated TV ranged between 160-200 ml with set pressure at 25 cmH2O and RR 15 per minute. In this setting, arterial blood gas analysis (ABGA) was pH 7.43, PaO2 226 mmHg, and PaCO2 34 mmHg. A few minutes later, the expired TV gradually dropped to 120-140 ml at the same pressure-controlled ventilator setting. End tidal carbon dioxide concentration (EtCO2) increased gradually up to 50 mmHg. ABGA were at pH 7.25, PO2 224 mmHg and PCO2 60 mmHg. At this point, we decided to perform a fiberoptic bronchoscopy (LF-P, Intubation fiberscope, Olympus, Tokyo, Japan; FB). We found a narrowed, non pulsatile and nearly kissing tracheal wall between the carina and the tip of the tracheal tube using FB. Under the fiberscope guide, a wirereinforced tracheal tube was advanced over the narrowed portion of the trachea, and we fixed the tube at 20.5 cm. The tip of the tracheal tube was placed just above the carina. Afterwards, with TV 160 ml, RR 16 per minute in the volume-controlled ventilation mode, PIP maintained below 20 cmH2O, and EtCO2 was about 25 mmHg. The lung sounds of both lung fields were clear, so the remaining surgical procedure was done. At the end of the surgery, we changed the patient to the supine position. We set back the wire-reinforced tube to the previous position (17 cm) and observed the narrowed portion of trachea using FB. The narrowest part was acceptable for ventilation during positive ventilation and spontaneous respiration after the position change into supine. The emergence from general anesthesia was smooth without any complications.