Abstract
Midogas ® (CIG Australia) nitrous oxide/oxygen blenders are commonly used in delivery wards in Australia. In this case report we describe an incident where a small hole in the diaphragm of the oxygen failure alarm in a Midogas nitrous oxide/oxygen blender led to retrograde flow of oxygen contaminating the nitrous oxide pipeline supply to the operating theatres and the delivery ward. This caused a reduced level of nitrous oxide to the patient in theatre, but there was no adverse outcome. However, if the oxygen pipeline pressure had been lower than the nitrous oxide pipeline pressure, the contamination would have been reversed, potentially resulting in a hypoxic mixture being delivered to many patients. Suggestions are made as to a method of prevention of this problem.