Parasympathetic Tone Changes in Anesthetized Horses after Surgical Stimulation, and Morphine, Ketamine, and Dobutamine Administration.
Authors: Ruíz-López Patricia, Morgaz Juan, Quirós-Carmona Setefilla, Navarrete-Calvo Rocío, Domínguez Juan Manuel, Gómez-Villamandos Rafael Jesús, Granados M M
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Monitoring autonomic nervous system activity during equine surgery remains clinically challenging, particularly when assessing pain perception and drug effects in anesthetised patients. Researchers tracked parasympathetic tone activity (PTAm), heart rate, and mean arterial pressure in 20 anesthetised horses before and after surgical incision, then following administration of morphine, ketamine, and dobutamine as clinically indicated. Notably, surgical incision itself failed to produce measurable changes in PTAm despite the nociceptive stimulus, and morphine similarly had no effect on parasympathetic tone; however, ketamine significantly decreased PTAm at 3 minutes post-administration, whilst dobutamine administration (used to maintain MAP above 62 mmHg) did not alter parasympathetic activity. The lack of correlation between PTAm changes and concurrent alterations in heart rate or mean arterial pressure suggests that parasympathetic tone measurement is an unreliable standalone indicator of sympathetic activation or pain response under general anaesthesia in horses. This finding has important implications for practitioners relying on heart rate and blood pressure as pain indicators during surgery, as these parameters may not reflect true nociceptive responses, and suggests that ketamine's clinical effects during equine anaesthesia may involve direct autonomic modulation rather than purely opioid-sparing analgesia.
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Practical Takeaways
- •Ketamine administration during equine anesthesia measurably affects autonomic nervous system activity by decreasing parasympathetic tone—monitor for this when using ketamine as a co-induction or maintenance agent
- •Parasympathetic tone alone is not a reliable indicator of pain response or sympathetic activation during equine surgery; use multiple parameters (HR, MAP, other pain indicators) for anesthetic assessment
- •Morphine and dobutamine do not adversely affect parasympathetic tone in anesthetized horses, supporting their use in equine anesthetic protocols without concern for autonomic imbalance via this mechanism
Key Findings
- •Parasympathetic tone activity (PTAm) decreased 3 minutes after ketamine administration (0.5 mg/kg IV) in anesthetized horses
- •Surgical incision did not produce significant changes in PTAm despite being a nociceptive stimulus
- •Morphine (0.2 mg/kg IV) and dobutamine infusion did not modify PTAm in anesthetized horses
- •PTAm showed poor correlation with heart rate and mean arterial pressure, suggesting it is a limited indicator of sympathetic activation under general anesthesia