Equine postanesthetic forelimb lameness: intracompartmental muscle pressure changes and biochemical patterns.
Authors: Lindsay, McDonell, Bignell
Journal: American journal of veterinary research
Summary
# Postanesthetic Forelimb Lameness: Pressure, Hypoxia and Myositis Prolonged halothane anesthesia in lateral recumbency creates predictable forelimb lameness through a combination of compartmental pressure elevation and muscle hypoxia. Lindsay and colleagues monitored intracompartmental pressures in the extensor carpi radialis and triceps brachii during 180–240 minutes of anaesthesia, whilst simultaneously tracking systemic parameters (cardiac output, blood gases, electrolytes) and muscle injury markers (AST, CPK, blood lactate) over a seven-day postoperative period. The dependent forelimb—particularly the triceps—developed dangerously elevated compartmental pressures exceeding 30 mm Hg, sufficient to compromise capillary perfusion, and five of six horses subsequently developed clinical lameness associated with myositis and muscle plaque formation. Biochemical evidence strongly suggested local tissue hypoxia as the primary driver: blood lactate and inorganic phosphate rose before CPK elevation, indicating anaerobic metabolism and cellular damage preceded frank myonecrosis. Whilst pressure elevation resolved when positional changes were introduced at anaesthesia termination, the lameness persisted, suggesting that the ischaemic insult during recumbency had already triggered inflammatory cascades that progressed independently. For practitioners, this research underscores the critical importance of positional changes during long procedures, aggressive haemodynamic support to maintain perfusion pressure, and recognition that postoperative lameness may reflect hours of compartmental ischaemia rather than intraoperative trauma alone.
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Practical Takeaways
- •Prolonged anesthesia in lateral recumbency carries significant risk of postoperative forelimb lameness—consider frequent positional changes during long procedures and close monitoring of recumbent time
- •Postanesthetic lameness appears related to muscle hypoxia and inflammation rather than a single measurable parameter, making prevention through proper positioning and anesthetic management more important than attempting to predict risk from pressure measurements
- •Elevated postoperative blood lactate and muscle enzymes (AST, CPK) indicate muscle damage; monitor recovery carefully and consider anti-inflammatory protocols if these markers are significantly elevated following prolonged anesthesia
Key Findings
- •Postanesthetic forelimb lameness was produced in 5 of 6 horses (83%) after 180-240 minutes of halothane anesthesia in lateral recumbency
- •Intracompartmental muscle pressures exceeded 30 mm Hg in contact limb triceps, potentially compromising capillary blood flow
- •Elevated blood lactate and inorganic phosphate preceded increased CPK activity, suggesting local hypoxia as a contributing factor to myositis development
- •High intracompartmental pressures did not persist after positional changes, but lameness still developed, indicating pressure alone is insufficient to explain the condition