Local Anesthetics, Amides
Local anesthetics block the initiation and conduction of nerve impulses.
Lidocaine (Xylocaine)
Lidocaine is an amide local anesthetic used in 1-2% concentration. The 1% preparation contains 10 mg of lidocaine for each 1 mL of solution; the 2% preparation contains 20 mg of lidocaine for each 1 mL of solution. Lidocaine inhibits depolarization of type C sensory neurons by blocking sodium channels.
To improve local anesthetic injection, cool the skin with ethyl chloride before injection. Use a 25- or 27-gauge needle to inject 2-5 mL of local anesthetic (eg, lidocaine 1%) into the subcutaneous tissue. Make sure the solution is at body temperature. Infiltrate very slowly to minimize the pain. The time from administration to onset of action is 2-5 minutes, and the effect lasts for 1.5-2 hours.
Buffering the solution helps reduce the pain of local lidocaine injection. Sodium bicarbonate can be added to injectable lidocaine vials (1 part bicarbonate to 9 parts lidocaine) to produce buffered lidocaine. The shelf-life of buffered lidocaine is approximately 1 week at room temperature. All vials should be marked "buffered," labeled with the time and date, and signed by the person who created the buffered mixture.
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Anterior view of right knee.
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Anatomic landmarks for knee arthrocentesis.
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Infiltration of local anesthetic via medial parapatellar approach (left knee).
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Left-knee aspiration via medial parapatellar approach.
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Application of bandage after left-knee aspiration.
