Numerous instances of tracheal tube obstruction have been reported as a result of blood clot or dried secretions , endotracheal tube compression or kinking , or cuff displacement . Likewise, tracheal tube obstruction with foreign bodies has been reported including chewing gum [4,5], a piece of a carbon dioxide sampling tube  and plastic caps off prefilled syringes . In this case we report an endotracheal tube obstruction due to oral medication.
An 84-yr-old female with a long-standing history of obesity, hypertension and non-insulin-dependent diabetes mellitus was admitted to the hospital for a vitrectomy under general anaesthesia. She gave no history of difficulty in swallowing or of any neurologic disorder. Medications included oral furosemide and metformin twice a day. At 8.00a.m. on the day of surgery, furosemide and metformin tablets were administered orally with a small sip of water. The patient arrived in the operating room at 8.45a.m. and an intravenous cannula was inserted. After monitoring, the patient was preoxygenated and anaesthesia was induced with fentanyl 200 μg, propofol 150 mg and succinylcholine 80 mg, and laryngoscopy was attempted. Visualization of the larynx was described as Grade 3, according to the Cormack and Lehane classification, and intubation was performed at the second attempt with a 7 mm armoured endotracheal tube (Safety Flex; Mallinckrodt Medical, Athlone, Ireland). After intubation, attempts to ventilate the patient encountered a high airway resistance with virtually no air entry on auscultation of the chest. There was neither chest movement nor carbon dioxide on capnography. The difficulty in ventilation was assumed to be due to equipment malfunction, but after 30 s, desaturation occurred and we decided to withdraw the endotracheal tube and proceed with mask ventilation. After removal of the tube, a foreign body plug was noted, virtually occluding the distal end of the tube (Fig. 1). Intubation was subsequently performed with another 7 mm armoured endotracheal tube and anaesthesia continued without any further incident. After examination of the object and referring to the patient's chart, we were able to identify the foreign body as a metformin tablet.
After reviewing the medical literature we have found only one case of endotracheal tube obstruction secondary to oral preoperative medication . In our case report, the signs of endotracheal tube obstruction were demonstrated by the difficulty in ventilating, the absence of carbon dioxide and the rapid desaturation. The causes of obstruction must be distinguished from other causes of difficult ventilation such as endobronchial mucous plugs or blood clots, bronchospasm, tension pneumothorax, massive aspiration, chest wall rigidity and equipment malfunction. When ventilation is impossible, a quick differential diagnosis needs to be performed. Visual inspection of the tube, fibre-optic visualization of the airway, mask ventilation and reintubation must be considered when airway obstruction occurs after intubation. An attempt to pass a suction catheter down the tube may differentiate between an endotracheal tube obstruction and other causes of increased inspiratory pressure. Reintubation will be the appropriate next step to establish a patent airway. Prompt recognition of endotracheal tube obstruction and appropriate actions are essential to prevent morbidity and mortality.
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