To the Editor:—
In the current days of high-tech equipment and well-defined safety regulations, technical failures are less likely to occur, and so are we to consider them when clinical complications happen. Endotracheal tube defects are probably seen by today's anesthesiologists as a thing of the past. A review of the literature showed that all of the cases reported in relation to defective tubes occurred when tubes were submitted to repeated sterilizations.
A 39-yr-old woman, with insignificant past medical history, was scheduled to undergo lumbar discectomy. General anesthesia was induced with thiopental (450 mg), fentanyl (150 μg), and vecuronium (8 mg). Tracheal intubation was performed with a 7-mm reinforced endotracheal tube (Safety Flex; Mallinckrodt Medical, Athlone, Ireland; expiration date 2006-09). The patient was positioned in prone position. Normal breath sounds were heard equally in both lungs. Anesthesia was maintained with sevoflurane (1.0–1.5%) and nitrous oxide (67%) in oxygen, and muscle relaxation was achieved with vecuronium bolus. Approximately 2 h after induction, we started to experience difficulties in ventilating the patient's lungs. Peak inspiratory pressure started to increase while compliance and tidal volume decreased. Pulmonary auscultation remained normal. The capnograph showed a positive deflection on the inspiratory phase; it was assumed that relaxation was insufficient, and a 4-mg bolus of vecuronium was administered. A suction catheter was used to remove possible airway secretions. It was noted that the catheter did not pass through the tube. Tube obstruction was then suspected. Ventilation became very difficult, even using bag ventilation. The patient was quickly returned to the supine position. The face, neck, and upper trunk showed congested veins. Bradycardia with bigeminism occurred and ventilation became impossible, but oxygen saturation did not decrease below 98%. The endotracheal tube was replaced with a new one. All abnormal variables returned to baseline. The patient was repositioned for surgery, and the procedure was completed without further complications. Recovery and the postoperative period were uneventful.
Later inspection of the tube showed a transparent halo on the outside surface. The inner view showed an intramural bubble that completely occluded the lumen. The 3-cm-long bubble was located 11.5 cm from the distal end. A fiberscope was used to obtain a photo of the bubble from the inside of the tube.
Ventilatory distress in the prone position may be a serious complication. The differential diagnosis included consideration of pneumothorax and bronchospasm, but auscultation of both lungs remained possible and was normal. In the case reported, ventilatory distress was due to a bubble protruding into the lumen of the tube. This bubble most probably was not due to any sort of extrinsic damage to the tube during its use. The inclusion of tiny air bubbles in the wall of a reinforced tube can be a result of the production procedure of this kind of tube.1Most certainly, nitrous oxide exposure and diffusion was the cause of expansion of the tube defect.2–4This would explain the fact that during the initial 2 h of the procedure, no problems were noted. The electrocardiographic changes observed were probably due to increased intrathoracic pressure caused during manual ventilation. This is reinforced by the striking congestion of the neck veins. It is possible that manual ventilation forced gases into the lungs but that some valve mechanism due to the presence of the bubble prevented expiration. This, combined with the 100% oxygen used, would also explain why the oxygen saturation did not decrease. It is interesting to note that oxygen saturation may not be an indicator of severe airway problems. To our knowledge, this is the first report of this kind of endotracheal tube obstruction with a disposable armored tube. It shows that even in modern days of increased attention to quality control, simple technical defects may occur. The manufacturer was notified about the incident.
* Hospital Geral de Santo António, Porto, Portugal. ialex@mail.telepac.pt
