Effects of intravenous lidocaine overdose on cardiac electrical activity and blood pressure in the horse.
Authors: Meyer G A, Lin H C, Hanson R R, Hayes T L
Journal: Equine veterinary journal
Summary
# Editorial Summary: Intravenous Lidocaine Toxicity in the Horse Meyer and colleagues administered escalating doses of intravenous lidocaine to 19 clinically normal horses to establish the serum concentration threshold at which toxicity manifests, specifically monitoring cardiovascular and electrical cardiac effects. Using a loading dose of 1.5 mg/kg followed by continuous infusion of 0.3 mg/kg/min until skeletal muscle tremors appeared, they identified the toxic threshold as a mean serum concentration of 3.24 ± 0.74 micrograms/ml (range 1.85–4.53 micrograms/ml). Although statistically significant changes occurred in ECG parameters—including P wave duration, PR interval, RR interval and QT interval—these alterations remained within published normal ranges and produced no clinically meaningful effects on heart rate, blood pressure or respiratory rate. These findings are reassuring for equine practitioners: therapeutic lidocaine administration at appropriate doses carries a reasonable safety margin before reaching concentrations that impair cardiac function, suggesting that careful dosing protocols will not produce haemodynamically significant complications in clinical settings. For farriers and veterinarians using intravenous lidocaine for analgesia or regional anaesthesia, this work underscores the importance of adhering to established dose guidelines whilst indicating that minor ECG changes, should they occur at therapeutic levels, are unlikely to warrant clinical concern.
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Practical Takeaways
- •When using intravenous lidocaine in horses, maintain serum concentrations below 1.85 µg/ml to avoid intoxication; skeletal muscle tremors signal that toxic levels have been reached.
- •ECG changes observed with lidocaine use in horses are electrically detectable but clinically benign and do not indicate need for intervention if concentrations remain below intoxication threshold.
- •Systemic cardiovascular parameters (heart rate, blood pressure) are reliable indicators that lidocaine toxicity has not occurred; their stability does not exclude electrical ECG changes.
Key Findings
- •Serum lidocaine intoxication in horses occurred at concentrations of 1.85–4.53 µg/ml (mean 3.24 ± 0.74 µg/ml), defined by onset of skeletal muscle tremors.
- •Statistically significant but clinically insignificant changes occurred in P wave duration, P-R interval, R-R interval, and Q-T interval at toxic serum concentrations.
- •Heart rate, blood pressure, and respiratory rate remained unchanged from baseline values despite lidocaine-induced ECG changes.
- •No clinically significant cardiovascular effects were observed at serum lidocaine concentrations below those producing toxicity signs.