Effect of Acetaminophen Alone and in Combination with Morphine and Tramadol on the Minimum Alveolar Concentration of Isoflurane in Rats.

BackgroundIt has been observed that acetaminophen potentiates the analgesic effect of morphine and tramadol in postoperative pain management. Its capacity as an analgesic drug or in combinations thereof to reduce the minimum alveolar concentration (MAC) of inhalational anesthetics represents an objective measure of this effect during general anesthesia. In this study, the effect of acetaminophen with and without morphine or tramadol was evaluated on the isoflurane MAC.MethodsForty-eight male Wistar rats were anesthetized with isoflurane in oxygen. MACISO was determined from alveolar gas samples at the time of tail clamping without the drug, after administering acetaminophen (300 mg/kg), morphine (3 mg/kg), tramadol (10 mg/kg), acetaminophen (300 mg/kg) + morphine (3 mg/kg), and acetaminophen (300 mg/kg) + tramadol (10 mg/kg).ResultsThe control and acetaminophen groups did not present statistically significant differences (p = 0.98). The values determined for MACISO after treatment with acetaminophen + morphine, acetaminophen + tramadol, morphine, and tramadol were 0.98% ± 0.04%, 0.99% ± 0.009%, 0.97% ± 0.02%, and 0.99% ± 0.01%, respectively.ConclusionsThe administration of acetaminophen did not reduce the MAC of isoflurane and did not potentiate the reduction in MACISO by morphine and tramadol in rats, and therefore does not present a sparing effect of morphine or tramadol in rats anesthetized with isoflurane

Cardiovascular effects of constant rate infusions of lidocaine, lidocaine and dexmedetomidine, and dexmedetomidine in dogs anesthetized at equipotent doses of sevoflurane

This study evaluated the cardiovascular effects of a constant rate infusion (CRI) of lidocaine, lidocaine and dexmedetomidine, and dexmedetomidine in dogs anesthetized with sevoflurane at equipotent doses. Treatments consisted of T1-Lidocaine [loading dose 2 mg/kg body weight (BW), IV, and CRI of 100 g/kg BW per min] at 1.4% end-tidal of sevoflurane (FESEV); T2-Dexmedetomidine (loading dose 2 g/kg BW, IV, and CRI of 2 g/kg BW per hour) and FESEV 1.1%; and T3-Lidocaine-Dexmedetomidine using the same doses of T1 and T2 and FESEV 0.8%. Constant rate infusion of lidocaine did not induce any cardiovascular changes; lidocaine and dexmedetomidine resulted in cardiovascular effects similar to dexmedetomidine alone. These effects were characterized by a significant (P 0.001) decrease in heart rate, cardiac output, cardiac index, oxygen delivery, and pulmonary vascular resistance index, and a significant (P 0.001) increase in mean and diastolic arterial pressure, systemic vascular resistance index, pulmonary arterial occlusion pressure and oxygen extraction ratio, compared with baseline values. In conclusion, a CRI of lidocaine combined with dexmedetomidine produces significant cardiovascular changes similar to those observed with dexmedetomidine alone

Effects of Lidocaine, Dexmedetomidine or Their Combination on the Minimum Alveolar Concentration of Sevoflurane in Dogs

The aim of this study was to determine the effects of lidocaine (LIDO) and dexmedetomidine (DEX) or their combination (LIDO-DEX), administered by constant-rate infusion (CRI), on the minimum alveolar concentration (MAC) of sevoflurane in dogs. Seven healthy mongrel dogs were used with a 2-week washout interval between treatments in this study. Anesthesia was induced with propofol and maintained with sevoflurane in oxygen, and MAC of sevoflurane was determined after 90 min equilibration period in the dogs (SEV-MAC_). Then, sevoflurane MAC was determined again in the dogs after 45 min equilibration period of one of the following treatments: an intravenous loading dose of lidocaine 2 mg/kg followed by 6 mg/kg/hr CRI (SEV-MAC_); an intravenous loading dose of dexmedetomidine 2 µg/kg followed by 2 µg/kg/hr CRI (SEV-MAC_); or their combination (SEV-MAC_). These SEV-MACs were determined in duplicate. Data were analyzed using ANOVA and post hoc Tuckey test when appropriate. The SEV-MAC_ was 1.82 ± 0.06%, SEV-MAC_ was 1.38 ± 0.08%, SEV-MAC_ was 1.22 ± 0.10%, and SEV-MAC_ was 0.78 ± 0.06%. The CRI administration of lidocaine, dexmedetomidine and their combination produced a significant reduction in the MAC of sevoflurane by 26.1 ± 9.0% (P<0.0001), 43.7 ± 11.8% (P<0.0002) and 54.4 ± 9.8% (P<0.0001), respectively. The MAC reduction was significantly greater after the CRI combination of lidocaine and dexmedetomidine when compared with lidocaine CRI (P<0.0001) or dexmedetomidine CRI treatments (P<0.025)

Blood gas, bicarbonate and lactate values obtained when determining the MAC in the different treatment groups.

<p>Blood gas, bicarbonate and lactate values obtained when determining the MAC in the different treatment groups.</p

Lidocaine, dexmedetomidine and their combination reduce isoflurane minimum alveolar concentration in dogs.

The effects of intravenous (i.v.) lidocaine, dexmedetomidine and their combination delivered as a bolus followed by a constant rate infusion (CRI) on the minimum alveolar concentration of isoflurane (MACISO) in dogs were evaluated. Seven healthy adult dogs were included. Anaesthesia was induced with propofol and maintained with isoflurane. For each dog, baseline MAC (MACISO/BASAL) was determined after a 90-minute equilibration period. Thereafter, each dog received one of the following treatments (loading dose, CRI): lidocaine 2 mg kg(-1), 100 µg kg(-1) minute(-1); dexmedetomidine 2 µg kg(-1), 2 µg kg(-1) hour(-1); or their combination. MAC was then determined again after 45- minutes of treatment by CRI. At the doses administered, lidocaine, dexmedetomidine and their combination significantly reduced MACISO by 27.3% (range: 12.5-39.2%), 43.4% (33.3-53.3%) and 60.9% (46.1-78.1%), respectively, when compared to MACISO/BASAL. The combination resulted in a greater MACISO reduction than the two drugs alone. Their use, at the doses studied, provides a clinically important reduction in the concentration of ISO during anaesthesia in dogs

Lidocaine, dexmedetomidine and their combination reduce isoflurane minimum alveolar concentration in dogs.

The effects of intravenous (i.v.) lidocaine, dexmedetomidine and their combination delivered as a bolus followed by a constant rate infusion (CRI) on the minimum alveolar concentration of isoflurane (MACISO) in dogs were evaluated. Seven healthy adult dogs were included. Anaesthesia was induced with propofol and maintained with isoflurane. For each dog, baseline MAC (MACISO/BASAL) was determined after a 90-minute equilibration period. Thereafter, each dog received one of the following treatments (loading dose, CRI): lidocaine 2 mg kg(-1), 100 µg kg(-1) minute(-1); dexmedetomidine 2 µg kg(-1), 2 µg kg(-1) hour(-1); or their combination. MAC was then determined again after 45- minutes of treatment by CRI. At the doses administered, lidocaine, dexmedetomidine and their combination significantly reduced MACISO by 27.3% (range: 12.5-39.2%), 43.4% (33.3-53.3%) and 60.9% (46.1-78.1%), respectively, when compared to MACISO/BASAL. The combination resulted in a greater MACISO reduction than the two drugs alone. Their use, at the doses studied, provides a clinically important reduction in the concentration of ISO during anaesthesia in dogs

Mean ± SD of minimum alveolar concentration of isoflurane (MAC_ISO) before (MAC_ISO/BASAL) and after one of the following treatments (MAC_ISO/T): lidocaine (LIDO), dexmedetomidine (DEX), or the combination LIDO-DEX in dogs (<i>n</i> = 7).

<p>The percentage (%) change in MAC_ISO after treatment was calculated from [(MAC_ISO after treatment – MAC_ISO/BASAL)/MAC_ISO/BASAL] X 100.</p><p>*Statistically different from MAC_ISO/BASAL (<i>p</i><0.05).</p>#<p>Statistically different from the rest of the treatments (<i>p</i><0.05).</p><p>Mean ± SD of minimum alveolar concentration of isoflurane (MAC_ISO) before (MAC_ISO/BASAL) and after one of the following treatments (MAC_ISO/T): lidocaine (LIDO), dexmedetomidine (DEX), or the combination LIDO-DEX in dogs (<i>n</i> = 7).</p

Mean ± SD of cardiovascular parameters and other variables measured immediately before the MAC determination of isoflurane (MAC_ISO/BASAL) and immediately before the final MAC of isoflurane (MAC_ISO/T) determination during constant rate infusion of lidocaine (LIDO), dexmedetomidine (DEX), or the combination LIDO-DEX.

#<p>Statistically different to baseline and to the rest of the treatments (<i>p</i><0.05).</p><p>Mean ± SD of cardiovascular parameters and other variables measured immediately before the MAC determination of isoflurane (MAC_ISO/BASAL) and immediately before the final MAC of isoflurane (MAC_ISO/T) determination during constant rate infusion of lidocaine (LIDO), dexmedetomidine (DEX), or the combination LIDO-DEX.</p