Morphine concentrations in distal thoracic limb synovial fluid following intravenous regional limb perfusion in horses.

Abstract

Twelve adult horses were randomly assigned to 2 groups in a prospective experimental trial. A pneumatic tourniquet (425 mmHg) was placed, under sedation, proximal to the carpus on one randomly chosen thoracic limb. A cephalic vein catheter was placed distal to the tourniquet to establish an intravenous regional limb perfusion technique (IVRLP) with morphine (0.1 mg/kg) diluted with saline 0.9% to 0.1 mL/kg, and the tourniquet left in place for 30 minutes. Horses were euthanized at 1 h (Group I) or 6 h (Group II) following the IVRLP and synovial fluid from the radiocarpal, intercarpal, metacarpophalangeal, distal interphalangeal, and digital flexor tendon sheath was obtained from the injected and contralateral (control) limb immediately after. Morphine concentrations were determined using liquid chromatography-mass spectrometry. An unpaired t-test was used to compare morphine concentrations from both groups (P < 0.05). Synovial morphine concentrations were detected in the injected limb in all horses in Group I, except in one horse in the radiocarpal joint, and detected in 5 of 6 horses in Group II. Mean synovial concentrations ranged between 301.8 ± 192.3 and 608 ± 446.6 ng/mL in Group I and between 27.0 ± 17.7 and 136.8 ± 103.6 ng/mL in Group II and were significantly higher in Group I between paired anatomical sites of both groups for the radiocarpal and distal interphalangeal joints, and the digital flexor tendon sheath. In conclusion, concentrations of morphine after IVRLP can be detected in synovial fluid distal to the tourniquet at 1 and 6 hours in horses.