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Sterility Assurance Level (SAL) - A quick intro
Invasive Medical Devices are never fully “sterilized”, however you can control the level of sterility based on your product’s bioburden and sterilization.
When a product is sterilized, either by Ethylene Oxide or gamma radiation cycles (or other methods), the level of sterilization never guarantees that the product will be completely sterile. One reason for this is that the sterilization method works by reducing the number of viable microorganisms logarithmically.
Several factors result in the ultimate level of living organisms on medical devices following sterilization. The two factors that are usually at work are the number of microorganisms that sit on your product (known as bioburden) and the amount of sterilization that is applied.
BIOBURDEN (WHERE IT ALL BEGINS)
When a product is manufactured a number of microorganisms are introduced. Depending on the circumstances, such as whether or not a clean room is used, the level or degree of contamination will vary.
It is highly recommended that a medical device manufacturer of invasive or mucous or blood contacting devices, adopt a bioburden program early in development. Controlling the types and quantity of organisms coming into contact with your device results in controlling and demonstrating the level of sterility of that device. It is for this reason many manufacturers have put in place clean rooms with varying classifications for the manufacturing of their devices.
A good bioburden program can be demonstrated using metrics. Some manufacturers have adopted Statistical Process Control (SPC) techniques for quantifying the number of microorganisms introduced to their products during the manufacturing process. Over time those using SPC can show if their process is in control and whether any anomalies have been introduced into that process. Anomalies or spikes in the process can be an indication that something has gone wrong. An unusual spike in the amount of bioburden should result in a nonconformance and subsequent investigation.
In addition to the numbers of microorganisms it is equality important to determine the types of microorganisms that are present.