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Veins may become temporarily blocked if the internal lining of the vein swells in response to repeated injury or irritation. This may be caused by the needle, the substance injected, or donating plasma. Once the swelling subsides the circulation will often become re-established.
Permanent vein collapse occurs as a consequence of:
- Long-term injecting
- Repeated injections, especially with blunt needles
- Poor technique
- Injection of substances which irritate the veins; in particular, injection of liquid methadone intended for oral use.
Smaller veins may collapse as a consequence of too much suction being used when pulling back against the plunger of the syringe to check that the needle is in the vein. This will pull the sides of the vein together and, especially if they are inflamed, they may stick together causing the vein to block. Removing the needle too quickly after injecting can have a similar effect.
Collapsed veins may never recover. Much smaller veins are created by the body to circulate the blood, but they are not adequate for injections or IVs.
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