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LETTER TO THE EDITOR

Synovial Fluid Concentration of Prostaglandin E2 Correlates with Pain Intensity After Knee Arthroscopic Procedures

Department of Anaesthesiology; Rikshospitalet-Radiumhospitalet Medical Center; Oslo, Norway; l.a.rosseland{at}medisin.uio.no (Rosseland, Krohn) Department Group of Clinical Medicine; University of Oslo; Oslo, Norway; Department of Anaesthesiology; Rikshospitalet-Radiumhospitalet Medical Center; Oslo, Norway (Stubhaug)

To the Editor:

The relationship between inflammation and acute postoperative pain is not well understood. Substance P, which is released from primary sensory neurons early in the local inflammatory process, induces mast cell degranulation and the release of cytokines and nerve growth factor. Prostaglandin E2 (PGE2) is stimulated by proinflammatory cytokines.

Two randomized controlled trials (RCT) were performed of intraarticular analgesics in general anesthesia with remifentanil as the sole analgesic (1,2). After the surgery no analgesics were given until patients had at least moderate pain and were included in the trials. In a subgroup of 20 patients, synovial fluid (SF) samples were drawn during the first hour after surgery. In these 20 patients we have analyzed whether perceived pain correlated with SF concentrations of mediators of inflammation. After surgery, pain was assessed on a 5-point verbal rating scale every 10 min. When patients reported moderate pain, SF was aspirated from an intraarticular catheter (n = 10), and the patients were included in RCT (1,2). If no pain or only mild pain was experienced, SF was collected 1 h after surgery (n = 10). [For methods and results in the two RCTs see Refs. (1,2).]

Interleukin (IL)-1, IL-8, and substance P were increased in all SF samples but did not correlate positively with pain intensity. The PGE₂ concentration was higher among patients with moderate pain compared with the patients with no or mild pain; 3428 pg/mL (SD = 2320) and 754 pg/mL (SD = 452), respectively (P = 0.020; Table 1).

This suggests a relation between SF PGE₂ concentration, inflammation, and pain intensity after knee arthroscopy. Further studies in this clinical acute pain model may confirm a central role of cyclooxygenase products in postoperative pain after knee arthroscopy.

REFERENCES

1. Rosseland LA, Stubhaug A, Grevbo F, et al. Effective pain relief from IA saline with or without morphine 2 mg in patients with moderate-to-severe pain after knee arthroscopy. A randomized, double-blind controlled clinical study. Acta Anaesthesiol Scand 2003;47:732–8.[Web of Science][Medline]
2. Rosseland LA, Helgesen KG, Breivik H, Stubhaug A. Moderate-to-severe pain after knee arthroscopy is relieved by intraarticular saline: a randomized controlled trial. Anesth Analg 2004;98:1546–51.[Abstract/Free Full Text]

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