Effect of rapid and slow intravenous injection of sodium penicillin on arterial blood pressure in isoflurane-anesthetized horses during surgery.

OBJECTIVE

To determine the effects of rapid (1 minute) and slow (10 minutes) intravenous (IV) injection of sodium penicillin on arterial blood pressure in anesthetized horses.

STUDY

DESIGN

Prospective randomized clinical trial.

ANIMALS: A group of 29 client-owned horses of various breeds, 1-20 years old, with body masses of 360-710 kg.

METHODS

General anesthesia was induced with a variety of anesthetic protocols and maintained with isoflurane under mechanical ventilation, with hourly doses of IV lidocaine and an infusion of dexmedetomidine. Horses were administered IV intraoperative penicillin every 2 hours after the preoperative dose, reconstituted with 50 mL of saline (group small dilution, SD) and administered over 1 minute, or with 250 mL of saline (group large dilution, LD) administered over 10 minutes. Systolic, diastolic and mean arterial blood pressures (SAP, DAP, MAP), heart rate, end-tidal isoflurane and carbon dioxide, dobutamine rate and arterial electrolytes were recorded before and for 20 minutes after penicillin. Comparisons between and within groups were with two-way anova.

RESULTS

Dose and time to penicillin delivery during anesthesia were similar between groups. SAP decreased significantly by 4.8-9.6% (p < 0.0001-0.038), DAP by 12.7-25.4% (p = 0.0009-0.016) and MAP by 6.6-18.4% (p = 0.0009-0.028) from injection and for 15-20 minutes in group SD. In group LD, significant decreases in DAP (13.8-18.5%; p < 0.0001-0.005) and MAP (10.1-13.9%; p < 0.0001-0.003) occurred at 3-15 minutes, and DAP (p = 0.013 and 0.008) and MAP (p = 0.016 and 0.007) were higher than for group SD at 1 and 3 minutes. Dobutamine rate and other variables were similar between groups.

CONCLUSIONS AND CLINICAL RELEVANCE: Arterial blood pressure decreased with both SD and LD in anesthetized horses, but to a lesser extent in the slower, more diluted LD group.