Objective—To compare the anesthetic and cardiorespiratory effects of total IV anesthesia with propofol (P-TIVA) or a ketamine-medetomidine-propofol combination (KMP-TIVA) in horses. Design—Randomized experimental trial. Animals—12 horses. Procedure—Horses received medetomidine (0.005 mg/kg [0.002 mg/lb], IV). Anesthesia was induced with midazolam (0.04 mg/kg [0.018 mg/lb], IV) and ketamine (2.5 mg/kg [1.14 mg/lb], IV). All horses received a loading dose of propofol (0.5 mg/kg [0.23 mg/lb], IV), and 6 horses underwent P-TIVA (propofol infusion). Six horses underwent KMP-TIVA (ketamine [1 mg/kg/h {0.45 mg/lb/h}] and medetomidine [0.00125 mg/kg/h {0.0006 mg/lb/h}] infusion; the rate of propofol infusion was adjusted to maintain anesthesia). Arterial blood pressure and heart rate were monitored. Qualities of anesthetic induction, transition to TIVA, and maintenance of and recovery from anesthesia were evaluated. Results—Administration of KMP IV provided satisfactory anesthesia in horses. Compared with the P-TIVA group, the propofol infusion rate was significantly less in horses undergoing KMP-TIVA (0.14 ± 0.02 mg/kg/min [0.064 ± 0.009 mg/lb/min] vs 0.22 ± 0.03 mg/kg/min [0.1 ± 0.014 mg/lb/min]). In the KMP-TIVA and P-TIVA groups, anesthesia time was 115 ± 17 minutes and 112 ± 11 minutes, respectively, and heart rate and arterial blood pressure were maintained within acceptable limits. There was no significant difference in time to standing after cessation of anesthesia between groups. Recovery from KMP-TIVA and P-TIVA was considered good and satisfactory, respectively. Conclusions and Clinical Relevance—In horses, KMP-TIVA and P-TIVA provided clinically useful anesthesia; the ketamine-medetomidine infusion provided a sparing effect on propofol requirement for maintaining anesthesia.

ABSTRACT. The anesthetic and cardiopulmonary effects of midazolam, ketamine and medetomidine for total intravenous anesthesia (MKM-TIVA) were evaluated in 14 horses. Horses were administered medetomidine 5 µg/kg intravenously as pre-anesthetic medication and anesthetized with an intravenous injection of ketamine 2.5 mg/kg and midazolam 0.04 mg/kg followed by the infusion of MKMdrug combination (midazolam 0.8 mg/ml-ketamine 40 mg/ml-medetomidine 0.1 mg/ml). Nine stallions (3 thoroughbred and 6 draft horses) were castrated during infusion of MKM-drug combination. The average duration of anesthesia was 38 ± 8 min and infusion rate of MKM-drug combination was 0.091 ± 0.021 ml/kg/hr. Time to standing after discontinuing MKM-TIVA was 33 ± 13 min. The quality of recovery from anesthesia was satisfactory in 3 horses and good in 6 horses. An additional 5 healthy thoroughbred horses were anesthetized with MKM-TIVA in order to assess cardiopulmonary effects. These 5 horses were anesthetized for 60 min and administered MKM-drug combination at 0.1 ml/kg/hr. Cardiac output and cardiac index decreased to 70-80%, stroke volume increased to 110% and systemic vascular resistance increased to 130% of baseline value. The partial pressure of arterial blood carbon dioxide was maintained at approximately 50 mmHg while the arterial partial pressure of oxygen pressure decreased to 50-60 mmHg. MKM-TIVA provides clinically acceptable general anesthesia with mild cardiopulmonary depression in horses. Inspired air should be supplemented with oxygen to prevent hypoxemia during MKM-TIVA. KEY WORDS: equine, ketamine, medetomidine, midazolam, total intravenous anesthesia.

Cardiovascular measurements remained within acceptable values in artificially ventilated horses during P-TIVA or KMP-TIVA. Decreased cardiac output associated with KMP-TIVA was primarily the result of decreases in heart rate.

ABSTRACT. The bispectral index (BIS) was evaluated as an indicator of central nervous system (CNS) depression in horses anesthetized with propofol. Five non-premedicated horses were anesthetized with 7 mg/kg, IV propofol and the minimum infusion rate (MIR) of propofol required to maintain anesthesia was determined during intermittent positive pressure ventilation in each horse. The BIS was determined 20 min later and after stabilization at 2.0 MIR, 1.5 MIR, and 1.0 MIR. The BIS was also recorded after the cessation of propofol infusion when the horses regained spontaneous breathing and swallowing reflex. The MIR and plasma concentration (Cp) of propofol were 0.20  0.03 mg/kg/min and 17.5  4.0 g/ml, respectively. The BIS value and Cp were 59  13 and 26.7  8.6 g/ml at 2.0 MIR, 63  9 and 22.9  9.7 g/ml at 1.5 MIR, 64  13 and 20.1  5.9 g/ml at 1.0 MIR, 64  24 and 13.0  2.8 g/ml at return of spontaneous breathing, and 91  4 and 11.0  3.4 g/ml when the swallowing reflex returned, respectively. The BIS value was significantly less in anesthetized horses compared to horses once swallowing returned (p=0.025). The BIS value was significantly correlated with the propofol Cp (r=-0.625, p=0.001). There was not a significant difference in the BIS values during the MIR multiples of propofol. The BIS was a useful indicator of awakening but did not indicate the degree of CNS depression during propofol-anesthesia in horses.KEY WORDS: bispectral index (BIS), equine, propofol.

ABSTRACT. Sparing effects of carprofen and meloxicam with or without butorphanol on the minimum alveolar concentration (MAC) of sevoflurane were determined in 6 dogs. Anesthesia was induced and maintained with sevoflurane in oxygen, and MAC was determined by use of a tail clamp method. The dogs were administered a subcutaneous injection of carprofen (4 mg/kg) or meloxicam (0.2 mg/kg), or no medication (control) one hour prior to induction of anesthesia. Following the initial determination of MAC, butorphanol (0.3 mg/ kg) was administered intramuscularly, and MAC was determined again. The sevoflurane MACs for carprofen alone (2.10 ± 0.26%) and meloxicam alone (2.06 ± 0.20%) were significantly less than the control (2.39 ± 0.26%). The sevoflurane MACs for the combination of carprofen with butorphanol (1.78 ± 0.20%) and meloxicam with butorphanol (1.66 ± 0.29%) were also significantly less than the control value after the administration of butorphanol (2.12 ± 0.28%). The sevoflurane sparing effects of the combinations of carprofen with butorphanol and meloxicam with butorphanol were additive.

ABSTRACT. The anesthetic sparring and cardiovascular effects produced by midazolam 0.8 mg/ml-ketamine 40 mg/ml-medetomidine 0.05 mg/ml (0.025 ml/kg/hr) drug infusion during sevoflurane in oxygen (MKM-OS) anesthesia was determined in healthy horses. The anesthetic sparring effects of MKM-OS were assessed in 6 healthy thoroughbred horses in which the right carotid artery was surgically relocated to a subcutaneous position. All horses were intubated and ventilated with oxygen using intermittent positive pressure ventilation (IPPV). The end-tidal concentration of sevoflurane (ET SEV ) required to maintain surgical anesthesia was approximately 1.7%. Heart rate and mean arterial blood pressure averaged 23-41 beats/min and 70-112 mmHg, respectively. All horses stood between 23-44 min after the cessation of all anesthetic drugs. The cardiovascular effects of MKM-OS anesthesia were evaluated in 5 healthy thoroughbred horses ventilated using IPPV. Anesthesia was maintained for 4 hr at an ET SEV of 1.7%. Each horse was studied during left lateral (LR) and dorsal recumbency (DR) with a minimum interval between evaluations of 1 month. Cardiac output and cardiac index were maintained between 70-80% of baseline values during LR and 65-70% of baseline values during DR. Stroke volume was maintained between 75-85% of baseline values during LR and 60-70% of baseline values during DR. Systemic vascular resistance was not different from baseline values regardless of position. MKM-OS anesthesia may be useful for prolonged equine surgery because of its minimal cardiovascular depression in both of lateral and dorsal recumbency.

ABSTRACT. Tramadol is an atypical opioid analgesic widely used in small animal practice. This study was designed to determine the effect of a single intravenous (IV) dose of tramadol on the minimum alveolar concentration (MAC) of sevoflurane in dogs. Six beagle dogs were anesthetized twice to determine the sevoflurane MAC with or without an administration of tramadol (4 mg/kg, IV) at 7 days interval. The sevoflurane MAC was determined using a tail clamp method in each dog ventilated with positive pressure ventilation. The tramadol administration produced a significant reduction in the sevoflurane MAC by 22.3 ± 12.2% (1.44 ± 0.28% with tramadol versus 1.86 ± 0.30% without tramadol, P=0.010). This MAC reduction had been determined from 122 ± 19 to 180 ± 41 min following the tramadol administration. During this period, the plasma concentrations of tramadol and its metabolite, O-desmethyltramadol (M1), decreased from 429 ± 64 to 332 ± 55 ng/ml and from 136 ± 24 to 114 ± 68 ng/ml, respectively, but these changes were not statistically significant. There was no significant difference in heart rate, mean arterial blood pressure and SpO 2 between the control and tramadol treatment. The dogs that received tramadol treatment sometimes breathed spontaneously. Therefore, their respiratory rates significantly increased, and PETCO 2 decreased during the MAC determination. In conclusion, the single IV dose of tramadol produced a significant reduction in the sevoflurane MAC in dogs.

ABSTRACT. Minimally invasive cardiac output was determined using transthoracic bioimpedance (BICO), partial carbon dioxide rebreathing (NICO) and transesophageal Doppler echocardiography (TEECO) and compared to thermodilution (TDCO) in 6 beagle dogs. The dogs were 2 years old, weigh between 9.1-13.0 kg and were anesthetized with nitrous oxide-oxygen-sevoflurane. All dogs were administered a neuromuscular blocking drug and artificially ventilated during anesthesia. Thirty paired measurements of TDCO and each noninvasive method were collected during low, intermediate, and high values of cardiac output achieved by varying the depth of anesthesia and the administration of dobutamine. Cardiac output values ranged from 1.10-2.50 L/min for BICO compared to 0.81-4.88 L/min for TDCO; 0.70-2.60 L/min for NICO compared to 0.89-4.45 L/min for TDCO; and 0.59-4.37 L/min for TEECO compared to 0.57-4.15 L/min for TDCO. The limits of agreement and percentage error were -0.58 ± 1.56 L/min and ± 75.4% for BICO, -1.04 ± 1.08 L/min and ± 56.0% for NICO, and 0.03 ± 0.26 L/min and ± 12.3% for TEECO compared to TDCO. In conclusion, TEECO provided the best agreement to TDCO in sevoflurane anesthetized beagle dogs. KEY WORDS: beagle dog, cardiac output, minimally invasive measurement.