An unusual cause of oxygen failure in the anesthesia machine.

Abstract

Dear Editor, A critical incident is being reported wherein a foreign body was detected in the oxygen pipeline inlet at the back of anesthesia workstation. The potentially catastrophic incident occurred during routine pre-use checkup of anesthesia workstation when there was no flow of oxygen on opening the flow control valve while pressure gauge on the pressure regulator of D-type oxygen cylinder was showing full pressure. The pressure gauge on the anesthesia machine was also showing no pressure. The oxygen cylinder and pressure regulator were changed but still there was no oxygen flow. It was then thought to change the connecting hose between cylinder and pipeline inlet at the machine end. As the NIST (non-interchangeable screw thread) connector was loosened from the machine end, an interesting finding was noticed, there was sudden movement of bobbin and oxygen flow started but soon the flow again ceased and the bobbin came back to the same position. Then again on opening the cylinder but keeping the connector at pipeline inlet slightly loosened led to the flow of oxygen and pressure gauge on the workstation also started showing pressure reading. Noticing this finding that loosening the NIST connector of the hose slightly from the pipeline inlet led to oxygen flow in the workstation led us to suspect a foreign body in the oxygen pipeline inlet of workstation. Subsequent careful search in the oxygen inlet led us to find a small black ring which was taken out with an 18 g needle as it was at the distal end of the inlet[Figure 1]. It was a small round rubber ring with a hole in the centre. Initially it was suspected it to be washer of the Bodock seal but closer inspection revealed it to be of different size.Figure 1: Foreign body in the oxygen inlet at the back of anesthesia machineNow the reason for absence of flow on tightening the connector was understood, probably because on tightening the rubber ring became flat and occluded the oxygen entry port of the inlet causing complete cessation of the oxygen flow. When the connector was slightly loosened, the central opening in the ring came back to its normal position thus allowing oxygen flow. The mechanism of entry of the foreign body at that unusual location could not be figured out since the same anesthesia machine has been in use for 4 years. The engineer of the manufacturer, Datex Ohmeda, was contacted and his viewpoint was that it could be a deliberate attempt by theatre personnel; however this could not be confirmed. The other possible explanation could be wear and tear of the ring that caused cessation of oxygen flow on being pressed tightly by metallic NIST connector[Figure 2].Figure 2: Worn out foreign body and NIST connectorThough there are many human errors and equipment malfunctions reported leading to oxygen supply failure[1], but such a presentation of a foreign body at the pipeline inlet has not been reported earlier. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.