There are a number of items with designed incompatibility in anesthesia machines.
Pipeline gas-supply connections are available in a few different configurations. The diameter
indexing safety system (DISS) is a common configuration. The thread and inner
diameters vary to prevent accidental connections to a wrong supply. Virtually all
machines use E cylinders as backup supplies. Backup oxygen is vital for patient safety
and must always be available. Cylinders use the pin index safety system (PISS) to prevent
wrong connections. Holes in cylinders work in conjunction with pins in the yokes. For
anesthesia-supply gases (oxygen, nitrous oxide, and air), one pin location is fixed, and the
other varies depending on gas type. One inherent weakness in this system is that if the
wrong pin pulls out or breaks, it could lead to a misconnection