Intra operative awareness due to malfunctioning of anaesthesia machine - A rare incidence

A 15 year old female patient of ASA class I was posted for implant removal from left forearm under general anaesthesia. Intraoperative period was uneventful. In the immediate postoperative period, she became restless which subsided after administration of haloperidol and promethazine intramuscularly. On interview, she complained of intraoperative awareness. Thorough checking of the anaesthesia machine revealed that the floats in both oxygen and nitrous oxide rotameters were moving up even when both nitrous oxide cylinders were closed and one oxygen cylinder was kept open. The diaphragm of oxygen failure safety valve was found to be ruptured which allowed oxygen to flow through nitrous oxide flow meter. Preoperative checking of the anaesthesia machine could not identify these abnormalities. Thus, meticulous checking of anaesthesia machine including the oxygen failure safety valve, intraoperative monitoring of depth of anaesthesia, use of oxygen and end-tidal anesthetic gas analyzer may be helpful to prevent such an incident. DOI: http://dx.doi.org/10.4038/slja.v21i2.5235