The cartridge contains the anesthetic solution.
- In the U.S. it contains 1.8ml (cc) of anesthetic solution. This amount may vary in other countries.
- Its components consist of a cylindrical glass tube, rubber stopper, aluminum cap and diaphragm.
- The glass cylinder is surrounded by thin plastic label that describes the contents and protects the patient if the cartridge cracks.
- The stopper is located at the end of the cartridge that receives the syringe harpoon. It is no longer color coded to the type of anesthetic used so the practitioner should double-check the contents of the cartridge before administrating the anesthetic solution to the patient. The stopper is slightly indented from the lip of the glass cylinder and the cartridge should not be used if it is flush.
- The aluminum cap is located at the opposite end from the plunger. It holds the diaphragm in place and is silver colored on all cartridges.
- The diaphragm is a semi-permeable membrane made of latex rubber through which the needle perforates. (For patients with latex allergies, anesthetic cartridges with non-latex stoppers are available.)
- The contents of the cartridge are local anesthetic, vasopressor drug, preservatives for the vasopressor, sodium chloride and distilled water (Figure 2).
- The local anesthetic interrupts the nerve impulses preventing them from reaching the brain.
- The vasopressor drug is used to reduce dispersion of the local anesthetic into the circulation and increases its duration of action. It lowers the pH of the cartridge solution which may lead to discomfort during injection.
- The vasopressor drug contains sodium bisulfite as an antioxidant. Patients may be allergic to bisulfite. Local anesthetics without vasopressor do not contain bisulfites and may be used as an alternative for these patients.
- Sodium chloride is added to the anesthetic solution to make it isotonic with the body tissues.
- Distilled water is added to provide the proper volume of solution in the cartridge.
Clinicians should be aware of possible problems with the cartridges:
Bubble in the cartridge – A small bubble may just be nitrogen gas used in the manufacturing process and is of no concern. A large bubble that extrudes the plunger beyond the rim of the cartridge is indicative of freezing and should not be used.
Burning on injection – This may be just a normal response to the pH of the drug especially those containing vasopressor. However, it can also be indicative of disinfecting solution leaking into the cartridge or overheating of the anesthetic solution from a defective cartridge warmer.
Leakage of solution – Leakage of solution during injection can result from improper alignment of the diaphragm and needle.
Broken cartridge – A crack in the glass cartridge may be a result of damage during shipping. It can also result from excessive force during engagement of the harpoon, a bent harpoon, or a bent needle leading to excessive pressure on the cartridge during injection.