Internal leakage of oxygen flush valve

Corresponding author: Sung Ha Mun, M.D., Department of Anesthesiology and Pain Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, 108, Pyoung-dong, Jongro-gu, Seoul 110-746, Korea. Tel: 82-2-2001-2001, Fax: 82-2-2001-2326, E-mail: [email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. CC The oxygen flush valve receives oxygen from the pipeline inlet or cylinder pressure regulator and delivers a high flow of unmetered oxygen directly to the common gas outlet [1]. Internal leakage in the flush valve may result in delivery of an oxygen-enriched mixture to an anesthetized patient, causing lighter anesthesia than intended [2,3]. Authors report an experience of internal leakage in the oxygen flush valve owing to the wear of the O-ring. A 6-year-old boy (height : 110 cm, weight : 18 kg) was admitted to the hospital for tonsillectomy. He had no particular medical history and no present illness categorized as American Society of Anesthesiologists class I. There were no abnormal findings on the pre-operative blood test, EKG, or the chest x-ray. Vital signs before induction of anesthesia were blood pressure 100/65 mmHg, heart rate (HR) 110 beats/min, and oxygen saturation (SpO2) 99%. Before anesthetic induction, a positivepressure leak test did not detect any leak. To induce anesthesia, thiopental sodium 100 mg and rocuronium bromide 15 mg were intravenously administered and endotracheal intubation was performed. Intraoperative anesthesia was maintained with sevoflurane 2-2.5 vol%, N2O 2 L/min, and O2 2 L/min using the semiclosed-circuit anesthesia machine (Modulus CD, DatexOhmeda, GE Healthcare, Madison, WI, USA). Intraoperative vital signs of the patient were systolic blood pressure 110-130 mmHg, diastolic blood pressure 65-80 mmHg, HR 120-140 beats/ min, and SpO2 100%, showing no significant changes. While monitoring the child, however, an anesthesiologist found that the concentration of sevoflurane indicated on the anesthesia gas analyzer was significantly lower than that set at the sevoflurane vaporizer (the concentration at the sevoflurane vaporizer setting was 2% but at the gas analyzer was 1.2%). In addition, the oxygen analyzer indicated that oxygen concentration was higher than the setting: oxygen was delivered at 50%, but the oxygen concentration measurer indicated the delivery of 60% oxygen). Suspecting a malfunction of the vaporizer, at first, we checked whether or not the sevoflurane vaporizer was properly set up, but could not detect any particular problems. Then, we attempted desflurane for the inhaled anesthetics, but the issue was not resolved. In case the anesthetic depth may be lower than intended, fentanyl 25 μg was intravenously provided. Because the operation was close to completion, we proceeded with the operation, while the sevoflurane vaporizer setting increased to 3 vol%. After completion of the operation, we requested a repair on the machine to the manufacturer, and they discovered a leak in the oxygen flush valve. At the followup visit, following anesthesia, no awareness during general anesthesia was observed and he was discharged without any complications. The oxygen flush valve is a device to allow direct communication between the oxygen high-pressure circuit and the lowpressure circuit. When the oxygen flush button is depressed, the oxygen flush valve will open and deliver 100% oxygen flow of 35 to 75 L/min to the breathing circuit and mainly provide jet ventilation. Malfunction of the oxygen flush valve, although rare, may result in serious adverse events such as barotraumas or intra-anesthetic awareness. Mann et al. [3] reported an event of malfunction regarding the oxygen flush valve, where routine external checks revealed no problems and the valve superficially appeared to be normal. According to the report, a spiral fracture on the plastic shaft of the oxygen flush valve