Equine postanesthetic forelimb lameness: intracompartmental muscle pressure changes and biochemical patterns.

The research paper investigates the occurrence of postoperative forelimb lameness in horses as a result of prolonged halothane anesthesia and its relationship with certain biochemical parameters and intracompartmental muscle pressure changes.

Research Purpose and Method

• The primary aim of this study was to understand the biochemical and pressure changes happening in a horse’s forelimb muscles during prolonged anesthesia, and how these changes could correlate with postoperative lameness, a common condition observed in horses after undergoing surgical anesthesia.
• The researchers performed detailed monitoring of a range of parameters including muscle pressures, cardiac output, blood pressure, blood gases, and acid-base status in the right and left forelimbs of horses during anesthesia. They also tracked the levels of electrolytes and enzyme activities for seven days post-anesthesia.
• The study was conducted on healthy horses that were maintained in left lateral recumbency while under deep halothane anesthesia for 180 to 240 minutes.

Evaluation and Findings

• Among the six horses that were under observation, five developed post-anesthetic forelimb lameness. The symptoms of lameness included muscle plaque formation and other clinical signs that closely resembled those seen after surgical anesthesia.
• The researchers noticed significant changes in certain parameters such as hematocrit, plasma potassium, and serum inorganic phosphate values by the end of anesthesia, alongside a decrease in plasma chloride values.
• Other measurements such as blood lactate, serum AST, and serum CPK also showed significantly high levels in the post-anesthetic period.
• The muscle pressures in the left forelimb (contact limb), specifically in the triceps, were found to be potentially high enough to affect blood flow adversely, though not sustained when the horses were moved after anesthesia.
• However, no clear correlation was established between the severity of postanesthetic lameness and any of the measured values.

Research Conclusion

• The research provides evidence of experimentally induced postanesthetic lameness, which seemed to be primarily associated with the development of myositis, an inflammation of muscle tissue.
• The study also suggests the possibility of local hypoxia (lack of sufficient oxygen) as one of the likely causative factors for myositis, as increased blood lactate and inorganic phosphate levels preceding the increased CPK activity were observed.