Biomedical Engineering Reference
In-Depth Information
TABLE 11.2
Comparison of Pros and Cons of Disposable Versus
Stainless Steel Systems
Disposable
Stainless Steel
Pros
Presterile, ready to use
Proven technology
Easy setup
Scalability virtually unlimited
Eliminates CIP/SIP
Low capital outlay
Low validation requirements
Increased flexibility
Cons
New technology
Hard to clean and maintain
Volume limitations
Large capital investment
Extensive CIP/SIP cycle
Extensive validation
Expensive installation
Accessories also of stainless steel
level is elevated (>1,000 colony-forming units, or cfu, per unit), as may occur
with very large single-use systems, higher doses may be required to achieve
sterility.
Sterility assurance level (SAL) is a term used in microbiology to describe
the probability of a single unit being nonsterile after it has been subjected to
the sterilization process. For example, medical device manufacturers design
their sterilization processes for an extremely low SAL— “one in a million”
devices should be nonsterile. SAL is also used to describe the killing efficacy
of a sterilization process, where a very effective sterilization process has a
very low SAL.
In microbiology, it is impossible to prove that all organisms have been
destroyed because (1) they could be present but undetectable simply because
they are not being incubated in their preferred environment, and (2) they
could be present but undetectable because their existence has never been
discovered. Therefore, SALs are used to describe the probability that a given
sterilization process has not destroyed all of the microorganisms.
Mathematically, SALs referring to probability are usually very small num-
bers and so are properly expressed as negative exponents (“the SAL of this
process is 10 to −6”). SALs referring to the sterilization efficacy are usually
much larger numbers and so are properly expressed as positive exponents
(“the SAL of this process is 10 to 6”). In this usage, the negative effect of
the process is sometimes inferred by using the word
reduction
(“this process
gives a six-log reduction”). Because of this ambiguity, group discussions of
SAL must define the terminology before setting standards.
