A fifty five year-old male patient was scheduled for a total laryngectomy under general anesthesia. A tracheostomy was performed on the administration day due to respiratory difficulty. All data of the preoperative routine check were within acceptable limits including incomplete RBBB on EKG. Just prior to starting the inhalation anesthesia, an armored tube (RUsch) was inserted instead of a silver cannula. Near the end of operation, signs of hypercapnia appeared as tachycardia and hypertension. Therefore, tracheobronchial suction was attempted but the suction catheter did not go through the armored tube. At that time, we decided there was an obstruction inside the tube. So, the armored tube was changed to a Portex tube. Thereafter, tachycardia and hypertension returned to normal intraoperative levels and we disocvered that the armored tube was obstructed almost completely by a blood clot.