Sterilisation pouches: the indicator says steam arrived, not that the instrument is sterile

The sterilisation pouch is the last link in the chain and the one attracting most errors, because it appears the simplest step.

The indicator printed on the pouch is the first element misunderstood. A process indicator changes colour when exposed to a combination of temperature and steam, and attests that the pouch passed through a cycle — not that the cycle was effective.

The distinction is not formal. A class 1 process indicator changes even in a cycle that is too short or with a poorly distributed load. Verifying effectiveness requires multiparameter indicators placed within the load, and periodically biological controls with spores.

A changed indicator on a pouch is a necessary but not sufficient condition: it states that the pouch did not remain outside the autoclave, which is useful information nonetheless and the reason the indicator exists.

The seal is where sterility is most often lost, and almost always without anyone noticing. An incomplete seal or one with channels leaves an entry route for microorganisms during storage.

Self-sealing pouches have an adhesive strip removing the need for a heat sealer, but require attention to the fold: the pre-marked line must be followed, because an irregular fold leaves a corner open.

Heat sealing offers more uniform tightness, provided the temperature is correct. A sealer running too hot burns the film and creates micro-holes; too cool and it does not fuse, so the pouch opens at first handling.

Seal width is specified by standard and is not a cosmetic detail: below six millimetres tightness is not assured over time, and a narrow seal fails during storage more than during the cycle.

Pouch filling affects the outcome of the cycle. A pouch filled beyond three quarters prevents steam circulating around the instrument, and the centre of the load may not reach the parameters.

The instrument should be placed with hinged parts open and the tip towards the paper side, which is the steam-permeable one. A closed instrument is not sterilised inside its hinge.

Storage validity depends not on time but on integrity. The thirty- or ninety-day expiry marking is an organisational convention; an intact pouch kept in a closed cupboard maintains sterility far longer, while a handled pouch loses it in a day.

The correct criterion is event-based, not date-based: a pouch must be reprocessed if it has been dropped, wetted, folded, or if the seal shows signs of opening, regardless of when it was closed.

In summary, the indicator says the pouch entered the autoclave, the seal determines whether it stays sterile until use, and validity depends on how it was stored more than on how much time has passed. These are three distinct concepts that in daily practice merge into one.