Comparison of two doses of lidocaine constant rate infusion on cardiopulmonary function and recovery in isoflurane-anesthetized horses.

Overview

• This study compares the effects of two different doses of intravenous lidocaine infusion on heart-lung function and recovery quality in horses anesthetized with isoflurane during arthroscopic surgery.
• They specifically examine outcomes under two ventilation methods: intermittent positive pressure ventilation (IPPV) and spontaneous ventilation (SV).

Study Design and Methods

• Type: Prospective, randomized, clinical trial.
• Subjects: 30 client-owned horses aged from 8 to 156 months, weighing 280 to 550 kg.
• Anesthetic protocol:
  • Premedication with xylazine, ketamine, and diazepam.
  • Maintenance with isoflurane and a constant rate infusion (CRI) of dexmedetomidine.
• Lidocaine administration:
  • Initial IV bolus of 2 mg/kg lidocaine given 15 minutes after anesthesia induction.
  • Then randomized to either a low dose (50 μg/kg/min) or high dose (100 μg/kg/min) lidocaine CRI.
  • Ventilation types: horses were assigned to either IPPV or SV groups, resulting in four groups: IPPV50, IPPV100, SV50, and SV100.
  • Lidocaine infusion was stopped prior to recovery.
• Measurements taken:
  • Cardiopulmonary variables including arterial and end-tidal CO2 tensions, arterial pH, and mean arterial blood pressure.
  • Plasma lidocaine concentrations during anesthesia and recovery phases.
  • Recovery quality, scored both numerically and descriptively.
• Statistical analysis used ANOVA and Kruskal-Wallis tests as appropriate.

Results

• Ventilation effects:
  • Spontaneous ventilation (SV) groups showed significantly higher arterial and end-tidal CO2 tensions than IPPV groups, indicating hypercapnia during SV (p < 0.0001).
  • SV groups exhibited lower arterial pH, consistent with respiratory acidosis.
• Blood pressure:
  • Mean arterial blood pressure differed by no more than 7 mmHg among groups.
  • However, SV100 and IPPV100 groups (higher lidocaine dose) had significantly higher mean arterial pressures compared to SV50 (p < 0.0001 and p = 0.0001 respectively).
  • SV100 also had higher blood pressure than IPPV50 (p = 0.044).
• Lidocaine plasma concentrations:
  • Concentrations during anesthesia were significantly higher in groups receiving the higher CRI dose (100 μg/kg/min), with p-values ranging from 0.0005 to 0.049.
  • Plasma lidocaine levels decreased significantly in all groups 20 minutes into recovery (p between < 0.0001 and 0.002), showing drug clearance.
• Recovery quality:
  • Numerical recovery scores were similar across all groups (p = 0.529).
  • Descriptive recovery scores also showed no significant difference (p = 0.413), with median scores indicating good quality recoveries regardless of dose or ventilation method.
  • Recovery scores median (range) per group were:
    • IPPV50: 2 (1,2)
    • IPPV100: 1 (1,3)
    • SV50: 2 (1,2)
    • SV100: 2 (2,3)

Conclusions

• Reducing or doubling the lidocaine infusion dose had minimal impact on cardiopulmonary function and quality of recovery in healthy horses undergoing arthroscopy under isoflurane anesthesia.
• Spontaneous ventilation led to elevated CO2 (hypercapnia) and lower blood pH, which can indicate hypoventilation.
• Both ventilation methods and lidocaine doses were well tolerated, with good recovery quality.
• These findings suggest flexibility in lidocaine dosing during equine anesthesia, but clinicians should be aware of the effects of ventilation mode on CO2 levels.