Effect of intravenous administration of tramadol hydrochloride on the minimum alveolar concentration of isoflurane in rabbits

Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.
American Journal of Veterinary Research (Impact Factor: 1.35). 08/2009; DOI: 10.2460/javma.235.4.404
Source: OAI

ABSTRACT OBJECTIVE: To evaluate the effect of IV administration of tramadol hydrochloride on the minimum alveolar concentration of isoflurane (ISOMAC) that prevented purposeful movement of rabbits in response to a noxious stimulus. ANIMALS: Six 6- to 12-month-old female New Zealand White rabbits. PROCEDURES: Anesthesia was induced and maintained with isoflurane in oxygen. A baseline ISOMAC was determined by clamping a pedal digit with sponge forceps until gross purposeful movement was detected or a period of 60 seconds elapsed. Subsequently, tramadol (4.4 mg/kg) was administered IV and the posttreatment ISOMAC (ISOMAC(T)) was measured. RESULTS: Mean +/- SD ISOMAC and ISOMAC(T) values were 2.33 +/- 0.13% and 2.12 +/- 0.17%, respectively. The ISOMAC value decreased by 9 +/- 4% after tramadol was administered. Plasma tramadol and its major metabolite (M1) concentrations at the time of ISOMAC(T) determination varied widely (ranges, 181 to 636 ng/mL and 32 to 61 ng/mL, respectively). Intervals to determination of ISOMAC(T) and plasma tramadol and M1 concentrations were not correlated with percentage change in the ISOMAC. Heart rate decreased significantly immediately after tramadol administration but by 10 minutes afterward was not different from the pretreatment value. Systolic arterial blood pressure decreased to approximately 60 mm Hg for approximately 5 minutes in 3 rabbits after tramadol administration. No adverse effects were detected. CONCLUSIONS AND CLINICAL RELEVANCE: As administered, tramadol had a significant but clinically unimportant effect on the ISOMAC in rabbits. Higher doses of tramadol may provide clinically important reductions but may result in a greater degree of cardiovascular depression.

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    ABSTRACT: Objective-To evaluate the effect of a continuous rate infusion (CRI) of lidocaine on the minimum alveolar concentration (MAC) of isoflurane in rabbits. Animals-Five 12-month-old female New Zealand White rabbits (Oryctolagus cuniculus). Procedures-Rabbits were anesthetized with isoflurane. Baseline isoflurane MAC was determined by use of the tail clamp technique. A loading dose of lidocaine (2.0 mg/kg, IV) was administered followed by a CRI of lidocaine at 50 μg/kg/min. After 30 minutes, isoflurane MAC was determined. Another loading dose was administered, and the lidocaine CRI then was increased to 100 μg/kg/min. After 30 minutes, isoflurane MAC was determined again. Plasma samples were obtained for lidocaine analysis after each MAC determination. Results-Baseline isoflurane MAC was 2.09%, which was similar to previously reported values in this species. Lidocaine CRI at 50 and 100 μg/kg/min induced significant reductions in MAC. The 50 μg/kg/min CRI resulted in a mean plasma lidocaine concentration of 0.654 μg/mL and reduction of MAC by 10.5%. The 100 μg/kg/min CRI of lidocaine resulted in a mean plasma concentration of 1.578 μg/mL and reduction of MAC by 21.7%. Lidocaine also induced significant decreases in arterial blood pressure and heart rate. All cardiopulmonary variables were within reference ranges for rabbits anesthetized with inhalation anesthetics. No adverse effects were detected; all rabbits had an uncomplicated recovery from anesthesia. Conclusions and Clinical Relevance-Lidocaine administered as a CRI at 50 and 100 μg/kg/min decreased isoflurane MAC in rabbits. The IV administration of lidocaine may be a useful adjunct in anesthesia of rabbits.
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    ABSTRACT: Cardiovascular effects of tramadol were evaluated in dogs anesthetized with sevoflurane. Six beagle dogs were anesthetized twice at 7 days interval. The minimum alveolar concentration (MAC) of sevoflurane was earlier determined in each dog. The dogs were then anesthetized with sevoflurane at 1.3 times of predetermined individual MAC and cardiovascular parameters were evaluated before (baseline) and after an intravenous injection of tramadol (4 mg/kg). The administration of tramadol produced a transient and mild increase in arterial blood pressure (ABP) (P=0.004) with prolonged increase in systemic vascular resistance (SVR) (P<0.0001). Compared with baseline value, mean ABP increased significantly at 5 min (119% of baseline value, P=0.003), 10 min (113%, P=0.027), and 15 min (111%, P=0.022). SVR also increased significantly at 5 min (128%, P<0.0001), 10 min (121%, P=0.026), 30 min (114%, P=0.025), 45 min (113%, P=0.025) and 60 min (112%, P=0.048). Plasma concentrations of tramadol were weakly correlated with the percentage changes in mean ABP (r=0.642, P<0.0001) and SVR (r=0.646, P<0.0001). There was no significant change in heart rate, cardiac output, cardiac index, stroke volume, pulmonary arterial pressure, right atrial pressure and pulmonary capillary wedge pressure. In conclusion, the administration of tramadol produces a prolonged peripheral vascular constriction in dogs anesthetized with sevoflurane, which is accompanied with a transient and mild increase in arterial blood pressure. It also indicated that the degree of vasoconstriction might depend on the plasma concentration of tramadol.
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Jun 1, 2014