Medication Summary
The goals of pharmacotherapy are to reduce morbidity and prevent complications.
Local Anesthetics, Amides
Class Summary
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.
Tables
|
Appearance |
WBCs, cells/µL |
PMN cells |
Glucose concentration, mg/dL |
Protein concentration, g/dL |
Normal |
Clear |
< 150 |
< 0.25 |
Serum glucose |
1.3-1.8 |
Noninflammatory |
Clear |
< 3000 |
< 0.25 |
Serum glucose |
2-3.5 |
Inflammatory |
Cloudy |
>3000 |
< 0.75 |
< 25 |
>4 |
Purulent |
Cloudy |
>50,000 |
>0.9 |
< 25 |
>4 |
Hemorrhagic |
Bloody |
>2000 |
~0.3 |
Serum glucose |
… |
PMN = polymorphonuclear; WBC = white blood cell. |
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