To the Editor
Medical gas distribution systems are extremely safe, reliable, and conform to National Fire Protection Association requirements.1 The quality standards and the safety features in the modern anesthesia workstations further reduce any error in delivering anesthetic gases to the patient.2 There can still be a possibility of flaws in the medical gas distribution system or anesthesia machine leading to catastrophic results.3–6 We report influx of water into the flowmeter assembly of an anesthesia work station (GE Datex Ohmeda Aestiva/5; GE Healthcare, Madison, WI) during the administration of general anesthesia.
The incident occurred after induction of general anesthesia in a 30-year-old man, ASA physical status II patient with a diagnosis of subglottic tracheal stenosis, scheduled for rigid bronchoscopic assessment followed by laser excision of the stenotic lesion. After induction of anesthesia with propofol, muscle relaxation was achieved using rocuronium bromide and his trachea was intubated with a laser endotracheal tube (Mallinckrodt™, Mallinckrodt Dar S.R.L., Mirandola, MO, Italy) with internal diameter of 5.5 mm. We planned to maintain anesthesia with oxygen in air, intermittent boluses of rocuronium, fentanyl, and rate-controlled infusion of propofol IV. When we opened the air flowmeter control, we observed a sudden influx of water entering the air rotameter tube and subsequently spilling in the rotameter tubes of the nitrous oxide and oxygen (Fig. 1). We also noticed that on rotating the flowmeter control knob of all 3 gases, there was no movement of their respective bobbin (Fig. 2), and thus, the flow rate of the gases delivered to the patient could not be accurately measured. The anesthesia gas delivery circuit was immediately disconnected, and the patient’s lungs were ventilated with a manual resuscitator (AMBU® bag mask valve, Ambu International A/S, Ballerup, Denmark) attached with an ancillary oxygen source available in the operating room. Fortunately, a biomedical engineer was available who disconnected the Schrader gas hose quick-connects of air, oxygen, and nitrous oxide from the gas wall outlets. The gas wall outlets were inspected, and it was found that moisture was accumulated at the air gas wall outlet. He then performed a pipeline purge test by holding a white cloth over the air gas wall outlet followed by heavy intermittent purging of the gas. Initially, the white cloth held over the air gas wall outlet was found to be dampened by the moisture. The purging was continued until water was no longer observed to dampen the cloth. After assurance of dry air from the air gas outlet, a second anesthesia machine was connected to the same pipeline gas supply and surgery was completed uneventfully.
On investigating the cause, it was found that the water trap in the air hose just upstream of the anesthesia machine air inlet hose connection was filled with water (Fig. 3). Water traps are used to prevent contaminants like dust, particulates, and residual water from entering the anesthesia machine. These water traps are mainly used in our critical care unit ventilators where medical air is frequently used and are occasionally filled with water. In anticipation of a similar problem, we deliberately attached this water trap to one of our anesthesia machines stationed in an operating room where medical air is frequently used.
Subsequently, the medical air supply was inspected and showed that the automatic drain downstream to the receiver found to be clogged and thus replaced immediately. Fortunately, that day in which the event described in this letter occurred, medical air was not used in any other operating suite.
We infer that this incident most likely occurred due to a faulty drain in the medical air supply system leading to influx of water from the air hose to the rotameter tubes. Tanaka et al.7 observed a similar problem during the preoperative check of anesthesia machine wherein the moist air was detected while connecting the hose to the gas wall outlet for compressed air. Several reports describe the medical gas (air/nitrous oxide) pipeline distribution system contaminated by water condensation due to accidental exposure to the atmosphere during maintenance.8,9 If we had performed the manufacturer’s recommended preuse checkout of the machine, this problem would have been detected preoperatively.
Lakesh K. Anand, MD (Anaesthesia), FIMSA, FCCP, MAMS
Dheeraj Kapoor, MD (Anaesthesia), FCCP
Sunita Kazal, MD (Anaesthesia)
Department of Anaesthesia and Intensive Care
Govt. Medical College and Hospital
1. Bielen RP Health Care Facilities Handbook. NFPA 99. 20057thed Quincy, MA National Fire Protection Association
2. ASTM F1850—00(2005), Standard Specification for Particular Requirements for Anesthesia Workstations and Their Components. 2005 West Conshohocken, PA American Society for Testing and Materials DOI: 10.1520/F1850-00R05. Available at: www.astm.org/Standards/F1850.htm
3. Glen J, Marshall S. Gas leak related to Draeger Primus anaesthetic machine. Anaesthesia. 2010;65:750
4. Jones AR, Orton JK. Power loss with the Aestiva/5 anaesthetic machine. Anaesthesia. 2010;65:414–5
5. Elizaga AM, Frerichs RL. Nitrogen purging of oxygen pipelines: an unusual cause of intraoperative hypoxia. Anesth Analg. 2000;91:242–3
6. Herrera A, Bueno F. Failure of the central oxygen supply to a surgical area. Analysis of a critical incident. Rev Esp Anestesiol Reanim. 1995;42:96–9
7. Tanaka A, Hirotada K. Trouble in the compressed air delivery system during the preoperative check. J Jpn Soc Clin Anesth. 2001;21:502–6
8. Hay H. Contamination of piped medical gas supply with water. Eur J Anaesthesiol. 2000;17:512–4
9. Arya VK, Arora V. Water in a nitrous oxide flowmeter. Indian J Anaesth. 2010;54:175–6