Cardiopulmonary effects of reverse Trendelenburg position at 5° and 10° in sevoflurane-anesthetized steers.

OBJECTIVE: To assess the cardiopulmonary effects caused by reverse Trendelenburg position (RTP) at 5° and 10° in sevoflurane-anesthetized yearling steers. STUDY DESIGN: Prospective, experimental study. ANIMALS: Eight Holstein steers aged (mean ± standard deviation) 12 ± 2 months and weighing 145 ± 26 kg. METHODS: In the first phase of the study, the individual minimum alveolar concentration (MAC) of sevoflurane was determined using electrical stimulation. In the second phase, the effects of RTP were assessed. The animals were anesthetized on three separate events separated by ≥7 days in an incomplete crossover design: control treatment using a table without tilt (RTP0); treatment with the table at 5° RTP (RTP5) and table tilted 10° RTP (RTP10). Subjects were physically restrained in dorsal recumbency on the table, which was already tilted according to each treatment. Anesthesia was induced with sevoflurane at 8% in 5 L minute-1 oxygen via face mask followed by maintenance with sevoflurane at 1.3 MAC and spontaneous breathing. Cardiopulmonary variables were obtained immediately after instrumentation (T0) and then after 30, 60, 120 and 180 minutes (T30, T60, T120 and T180, respectively). RESULTS: The mean sevoflurane MAC for the eight steers was 2.12 ± 0.31%. Cardiac output was lower at all time points and the systemic vascular resistance index was higher at T120 and T180 in RTP10 compared with RTP0. Oxygen consumption was lower at T0 and at T180 in RTP10 compared with RTP0 and at all time points except T30 compared with RTP5. Oxygen extraction was lower at T0 in RTP10 compared with RTP0 and RTP5, and at T60 and T180 compared with RTP5. CONCLUSIONS AND CLINICAL RELEVANCE: RTP 5° and 10° did not improve ventilatory and oxygenation variables in sevoflurane-anesthetized steers when compared with no tilt, however the cardiovascular variables were adversely affected in RTP10.

Effects of dexmedetomidine combined with ropivacaine on sciatic and femoral nerve blockade in dogs.

OBJECTIVE: To evaluate motor and sensory blockade of combining dexmedetomidine with ropivacaine, administered perineurally or systemically, for femoral and sciatic nerve blocks in conscious dogs. STUDY DESIGN: Randomized, controlled, experimental study. ANIMALS: Seven healthy Beagle dogs, aged 3.3 ± 0.1 years and weighing 11.0 ± 2.4 kg. METHODS: Dogs were anesthetized with isoflurane on three separate occasions for unilateral femoral and sciatic nerve blocks and were administered the following treatments in random order: perineural ropivacaine 0.75% (0.1 mL kg-1) on each nerve and intramuscular (IM) saline (0.2 mL kg-1) (Gcon); perineural dexmedetomidine (1 µg mL-1) and ropivacaine 0.75% (0.1 mL kg-1) on each nerve and IM saline (0.2 mL kg-1) (GDPN); and perineural ropivacaine 0.75% (0.1 mL kg-1) on each nerve and IM dexmedetomidine (1 µg mL-1, 0.2 mL kg-1) (Gdim). Nerve blocks were guided by ultrasound and electrical stimulation and dogs were allowed to recover from general anesthesia. Sensory blockade was evaluated by response to clamp pressure on the skin innervated by the saphenous/ femoral, common fibular and tibial nerves. Motor blockade was evaluated by observing the ability to walk and proprioception. Sensory and motor blockade were evaluated until their full recovery. RESULTS: No significant differences in onset time to motor and sensory blockade were observed among treatments. Duration of motor blockade was not significantly different among treatments; however, duration of tibial sensory blockade was longer in the Gdpn than in the GDIM treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Although a longer duration of sensory blockade was observed with perineural dexmedetomidine, a significant increase compared with the control group was not established. Other concentrations should be investigated to verify if dexmedetomidine is a useful adjuvant to local anesthetics in peripheral nerve blocks in dogs.

Cardiovascular effects of a continuous rate infusion of lidocaine in calves anesthetized with xylazine, midazolam, ketamine and isoflurane.

OBJECTIVE: To assess the cardiovascular changes of a continuous rate infusion of lidocaine in calves anesthetized with xylazine, midazolam, ketamine and isoflurane during mechanical ventilation. STUDY DESIGN: Prospective, randomized, cross-over, experimental trial. ANIMALS: A total of eight, healthy, male Holstein calves, aged 10 ± 1 months and weighing 114 ± 11 kg were included in the study. METHODS: Calves were administered xylazine followed by ketamine and midazolam, orotracheal intubation and maintenance on isoflurane (1.3%) using mechanical ventilation. Forty minutes after induction, lidocaine (2 mg kg⁻¹ bolus) or an equivalent volume of saline (0.9%) was administered IV followed by a continuous rate infusion (100 µg kg⁻¹ minute⁻¹) of lidocaine (treatment L) or saline (treatment C). Heart rate (HR), systolic, diastolic and mean arterial pressures (SAP, DAP and MAP), central venous pressure (CVP), mean pulmonary arterial pressure (mPAP), pulmonary arterial occlusion pressure (PAOP), cardiac output, end-tidal carbon dioxide (Pe'CO2 ) and core temperature (CT) were recorded before lidocaine or saline administration (Baseline) and at 20-minute intervals (T20-T80). Plasma concentrations of lidocaine were measured in treatment L. RESULTS: The HR was significantly lower in treatment L compared with treatment C. There was no difference between the treatments with regards to SAP, DAP, MAP and SVRI. CI was significantly lower at T60 in treatment L when compared with treatment C. PAOP and CVP increased significantly at all times compared with Baseline in treatment L. There was no significant difference between times within each treatment and between treatments with regards to other measured variables. Plasma concentrations of lidocaine ranged from 1.85 to 2.06 µg mL⁻¹ during the CRI. CONCLUSION AND CLINICAL RELEVANCE: At the studied rate, lidocaine causes a decrease in heart rate which is unlikely to be of clinical significance in healthy animals, but could be a concern in compromised animals.

Continuous infusion of propofol in dogs premedicated with methotrimeprazine.

OBJECTIVE: To evaluate the cardiopulmonary and clinical effects of three different infusion rates of propofol in dogs premedicated with methotrimeprazine. STUDY DESIGN: Randomized experimental trial. ANIMALS: Ten healthy adult mixed-breed male and female dogs, weighing from 14 to 20 kg. METHODS: Dogs were premedicated with methotrimeprazine [1 mg kg-1 intravenously (IV)] followed by induction of anesthesia with 4.5 mg kg-1 of propofol IV and maintenance with propofol for 60 minutes as follows: T1, 0.2 mg kg-1 minute-1; T2, 0.3 mg kg-1minute-1; and T3, 0.4 mg kg-1minute-1. Heart rate (HR), respiratory rate (RR), mean arterial pressure (MAP), end-tidal CO2 (PETCO2), arterial hemoglobin O2 saturation, arterial blood gases, and pedal and cutaneous reflexes were measured before and 5, 10, 20, 30, 45 and 60 minutes after the beginning of the propofol infusion. Statistical analysis was performed using an anova. RESULTS: Heart rate increased during anesthesia in all cases and arterial blood pressure decreased only in dogs in the T3 category. Respiratory depression was proportional to the infusion rate of propofol. Muscle relaxation was satisfactory, but analgesia was inadequate in the three treatments. CONCLUSIONS: The infusion of 0.2-0.4 mg kg-1 minute-1 of propofol produced a dose-dependent respiratory depression. The presence of a pedal withdrawal reflex and marked cardiovascular responses to this noxious stimulus suggests that anesthesia may not be of sufficient depth for surgery to be carried out. CLINICAL RELEVANCE: Although several studies have been performed using propofol in animals, few studies have investigated the cardiopulmonary and analgesic effects with different doses. The determination of an adequate propofol infusion rate is necessary for the routine use of this intravenous anesthetic for the maintenance of anesthesia during major surgical procedures in dogs.