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- Author or Editor: Wagner L. Ferreira x
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Objective—To determine effects of a continuous rate infusion of lidocaine on the minimum alveolar concentration (MAC) of sevoflurane in horses.
Animals—8 healthy adult horses.
Procedures—Horses were anesthetized via IV administration of xylazine, ketamine, and diazepam; anesthesia was maintained with sevoflurane in oxygen. Approximately 1 hour after induction, sevoflurane MAC determination was initiated via standard techniques. Following sevoflurane MAC determination, lidocaine was administered as a bolus (1.3 mg/kg, IV, over 15 minutes), followed by constant rate infusion at 50 μg/kg/min. Determination of MAC for the lidocaine-sevoflurane combination was started 30 minutes after lidocaine infusion was initiated. Arterial blood samples were collected after the lidocaine bolus, at 30-minute intervals, and at the end of the infusion for measurement of plasma lidocaine concentrations.
Results—IV administration of lidocaine decreased mean ± SD sevoflurane MAC from 2.42 ± 0.24% to 1.78 ± 0.38% (mean MAC reduction, 26.7 ± 12%). Plasma lidocaine concentrations were 2,589 ± 811 ng/mL at the end of the bolus; 2,065 ± 441 ng/mL, 2,243 ± 699 ng/mL, 2,168 ± 339 ng/mL, and 2,254 ± 215 ng/mL at 30, 60, 90, and 120 minutes of infusion, respectively; and 2,206 ± 329 ng/mL at the end of the infusion. Plasma concentrations did not differ significantly among time points.
Conclusions and Clinical Relevance—Lidocaine could be useful for providing a more balanced anesthetic technique in horses. A detailed cardiovascular study on the effects of IV infusion of lidocaine during anesthesia with sevoflurane is required before this combination can be recommended.
Objective—To compare cardiovascular effects of sevoflurane alone and sevoflurane plus an IV infusion of lidocaine in horses.
Animals—8 adult horses.
Procedures—Each horse was anesthetized twice via IV administration of xylazine, diazepam, and ketamine. During 1 anesthetic episode, anesthesia was maintained by administration of sevoflurane in oxygen at 1.0 and 1.5 times the minimum alveolar concentration (MAC). During the other episode, anesthesia was maintained at the same MAC multiples via a reduced concentration of sevoflurane plus an IV infusion of lidocaine. Heart rate, arterial blood pressures, blood gas analyses, and cardiac output were measured during mechanical (controlled) ventilation at both 1.0 and 1.5 MAC for each anesthetic protocol and during spontaneous ventilation at 1 of the 2 MAC multiples.
Results—Cardiorespiratory variables did not differ significantly between anesthetic protocols. Blood pressures were highest at 1.0 MAC during spontaneous ventilation and lowest at 1.5 MAC during controlled ventilation for either anesthetic protocol. Cardiac output was significantly higher during 1.0 MAC than during 1.5 MAC for sevoflurane plus lidocaine but was not affected by anesthetic protocol or mode of ventilation. Clinically important hypotension was detected at 1.5 MAC for both anesthetic protocols.
Conclusions and Clinical Relevance—Lidocaine infusion did not alter cardiorespiratory variables during anesthesia in horses, provided anesthetic depth was maintained constant. The IV administration of lidocaine to anesthetized nonstimulated horses should be used for reasons other than to improve cardiovascular performance. Severe hypotension can be expected in nonstimulated horses at 1.5 MAC sevoflurane, regardless of whether lidocaine is administered.
OBJECTIVE To assess the effects of a constant rate infusion (CRI) of remifentanil hydrochloride on left ventricular systolic and diastolic function in healthy propofol-anesthetized dogs.
ANIMALS 6 healthy Beagles.
PROCEDURES Each dog underwent 2 experimental treatments separated by a 7-day interval. In 1 treatment, anesthesia was induced with propofol and maintained with a CRI of propofol (0.6 mg/kg/min); dogs also received a CRI of saline (0.9% NaCl) solution. In the other treatment, anesthesia was similarly induced and maintained with propofol; dogs also received a CRI of remifentanil (0.3 μg/kg/min). Doppler echocardiographic and hemodynamic variables of interest were determined at baseline (before anesthesia) and at 20, 40, and 60 minutes following the simultaneous start of the 2 CRIs of each treatment; all CRIs were administrated for 60 minutes.
RESULTS For the 2 treatments, end-diastolic and end-systolic volume indices did not differ from baseline or at any time point. Peak tissue Doppler-derived mitral annulus systolic velocity decreased from baseline with both treatments; however, no differences were found between treatments at any time point. Mean arterial blood pressure decreased similarly with both treatments. Heart rate and Doppler-determined cardiac index decreased significantly with the propofol-remifentanil treatment, compared with findings for the propofol-saline solution treatment. For the propofol-remifentanil treatment, the ratio of peak velocity flow in early diastole to that in late diastole remained > 1.80, whereas the ratio of early to late Doppler-derived mitral annulus velocity had a normal relaxation pattern.
CONCLUSIONS AND CLINICAL RELEVANCE Results of this study indicated that a CRI of remifentanil administered along with a CRI of propofol does not impair left ventricular systolic and diastolic function in healthy dogs.