What are Implications for Drug Potency and Contamination during Handling of Local Anesthetic Glass Ampules?
Question: Does autoclaving an ampule of lidocaine diminish the drug’s potency? If one draws drug from an unsterilized ampule opened and held by an assistant, will unsterile glass particles contaminate the solution injected for spinal anesthesia. Independent of sterility, are minute glass particles in a spinal solution dangerous?
Answer: Stability of Local Anesthetics During Autoclaving
The amide local anesthetics such as lidocaine and bupivicaine are chemically very stable and will withstand autoclaving without significant degradation. The ester local anesthetics such as tetracaine are less stable and should not be subjected to repeated or prolonged autoclaving.
If the local anesthetic is in solution with other compounds (such as epinephrine, dextrose, or bicarbonate) them may be problem with autoclaving. For example, epinephrine solutions are subject to degradation and special autoclaving cycles may need to be used. The degree of breakdown depends upon several factors such as pH, oxygen content of the air in the ampule and the presence of any additives. Dextrose solutions are subject to carmelization with autoclaving and special autoclaving cycles may be necessary. Most sources suggest a cycle of 250 degrees F (121 degrees C) for 15 minutes at 15 PSI. Some quality assurance assay should be used to determine if your autoclaving cycle is effecting your ampules. Carbonated local anesthetic solutions should not undergo any form of heat sterilization.
Glass ampules are prepared from special medical grade glass. The ampules are filled with sterile solution and flame sealed. This sealing process results in a negative atmospheric pressure in the ampule once it cools down. The neck of the ampules are usually scored using a metal etch or chemical score. Upon breaking the ampule, it is very likely that small glass fragments will be drawn inside the ampule. The quantity and size of these fragments has been studied.
Particulate Contamination in Opening Glass Ampules
Perhaps one of the best reports was from R. L. Sabon from Medical College of Wisconsin, reported at the American Society of Critical Care Anesthesiologists meeting and winner of the 1988 Young Investigator Award.
It is possible to reduce the number and average size of particulate contaminants by using a filter needle when aspirating ampules. There are several reports of the effects of these particles when injected intravascularly but I could not find any reports of the effect of intrathecal injection of these contaminants. Based on intravascular complications one might theorize they could impair reabsorption of C.S.L (intravascular particles may cause microembolization to the lungs, cause local phlebitis and inflammation, and granulomas). Again, I have not found any reports of complications of spinal anesthetics attributed to particulate contamination. It was interesting to note that reusable ground-glass syringes can also be a source of glass particles and final filtration during injection may be the best means of reducing particles.
Microbiological Contamination Via Glass Fragments
Since the exterior of glass ampules are often not sterile, any glass fragment from the exterior could introduce microbiological contamination into the sterile solution. The type of organism and quantity would determine the degree of risk from this contamination. Wiping the exterior of the ampule would reduce the risk but would not assure external sterility. Filtration of the solution with a 0.2 2 micron fiber has been advocated to avoid bacterial and fungal contamination but does not protect from viral contamination. Despite this theoretical risk, I have found no reports of infection attributed to contamination through glass fragments upon opening the ampule.
Consequences of Intrathecal Injection of Particulate Contaminants
The consequences of intravenous injection of particulate contaminants have been studied by a number of investigators. Even small (5 micron) particles have been implicated in an increased incidence of phlebitis and pulmonary microemboli. Small fiber contaminants have been known to cause granuloma formation but this is unlikely with inert glass particles. As mentioned earlier, there is no data on the effects of intrathecal injection. Opinions vary on the significance of intravenous particular contamination with some recommending routine in-line wiring of all intravenous lines and others arguing the risk doesn’t justify this additional expense. Most practitioners I questioned routinely use a disk filter for epidural catheter injections but not for single-shot epidurals or spinal anesthetics. Few departments have specific policy of when to filter spinal and epidural injections.
Answer by: Mark P. Fritz, M.D., B.S. (Pharrn) Member, ASA Committee on Patient Safety and Risk Management, Medical College of Virginia
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