Evaluation of cardiovascular effects of total intravenous anesthesia with propofol or a combination of ketamine-medetomidine-propofol in horses

OBJECTIVE: To evaluate the cardiovascular effects of total IV anesthesia with propofol (P-TIVA) or ketamine-medetomidine-propofol (KMP-TIVA) in horses. ANIMALS: 5 Thoroughbreds. PROCEDURES: Horses were anesthetized twice for 4 hours, once with P-TIVA and once with KMP-TIVA. Horses were medicated with medetomidine (0.005 mg/kg, IV) and anesthetized with ketamine (2.5 mg/kg, IV) and midazolam (0.04 mg/kg, IV). After receiving a loading dose of propofol (0.5 mg/kg, IV), anesthesia was maintained with a constant rate infusion of propofol (0.22 mg/kg/min) for P-TIVA or with a constant rate infusion of propofol (0.14 mg/kg/min), ketamine (1 mg/kg/h), and medetomidine (0.00125 mg/kg/h) for KMP-TIVA. Ventilation was artificially controlled throughout anesthesia. Cardiovascular measurements were determined before medication and every 30 minutes during anesthesia, and recovery from anesthesia was scored. RESULTS: Cardiovascular function was maintained within acceptable limits during P-TIVA and KMP-TIVA. Heart rate ranged from 30 to 40 beats/min, and mean arterial blood pressure was > 90 mm Hg in all horses during anesthesia. Heart rate was lower in horses anesthetized with KMP-TIVA, compared with P-TIVA. Cardiac index decreased significantly, reaching minimum values (65% of baseline values) at 90 minutes during KMP-TIVA, whereas cardiac index was maintained between 80% and 90% of baseline values during P-TIVA. Stroke volume and systemic vascular resistance were similarly maintained during both methods of anesthesia. With P-TIVA, some spontaneous limb movements occurred, whereas with KMP-TIVA, no movements were observed. CONCLUSIONS AND CLINICAL RELEVANCE: 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.     

Influence of three anesthetic protocols on glomerular filtration rate in dogs

OBJECTIVE: To investigate renal function in clinically normal dogs when awake and during anesthesia with medetomidine; xylazine, ketamine, and halothane (XKH) combination; or propofol. ANIMALS: 10 adult female Beagles. PROCEDURES: At intervals of 15 days, dogs were administered medetomidine (0.05 mg/kg, IV); XKH combination (xylazine [1 mg/kg, IV], ketamine [5 mg/kg, IV], and halothane [1% end-tidal concentration]); or propofol (6 mg/kg, IV) to induce anesthesia or no treatment. Glomerular filtration rate was assessed on the basis of renal uptake (RU; determined via renal scintigraphy) and plasma clearance (CL) of technetium 99m-labeled diethylenetriamine pentaacetic acid ((99m)Tc-DTPA). RESULTS: In awake dogs, mean +/- SEM RU was 9.7 +/- 0.4% and CL was 3.86 +/- 0.23 mL/min/ kg. Renal uptake and CL of (99m)Tc-DTPA were not significantly modified by administration of XKH (RU, 11.4 +/- 0.9%; CL, 4.6 +/- 0.32 mL/min/kg) or propofol (RU, 9.7 +/- 0.3%; CL, 3.78 +/- 0.37 mL/min/kg). Half-life elimination time of plasma (99m)Tc-DTPA decreased significantly in XKH-anesthetized dogs, compared with the value in awake dogs (14.4 minutes and 28.9 minutes, respectively). However, glomerular filtration rate was significantly decreased by administration of medetomidine (RU, 3.9 +/- 0.1%), and the time to maximum kidney activity was significantly increased (867 +/- 56 seconds vs 181 +/- 11 seconds without anesthesia). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that anesthesia with propofol or an XKH combination did not alter renal function in healthy Beagles, but anesthesia with medetomidine decreased early RU of (99m)Tc-DTPA.     

Cardiovascular effects of total intravenous anesthesia using ketamine-medetomidine-propofol (KMP-TIVA) in horses undergoing surgery

Cardiovascular effects of total intravenous anesthesia using ketamine-medetomidine-propofol drug combination (KMP-TIVA) were determined in 5 Thoroughbred horses undergoing surgery. The horses were anesthetized with intravenous administration (IV) of ketamine (2.5 mg/kg) and midazolam (0.04 mg/kg) following premedication with medetomidne (5 µg/kg, IV) and artificially ventilated. Surgical anesthesia was maintained by controlling propofol infusion rate (initially 0.20 mg/kg/min following an IV loading dose of 0.5 mg/kg) and constant rate infusions of ketamine (1 mg/kg/hr) and medetomidine (1.25 µg/kg/hr). The horses were anesthetized for 175 ± 14 min (range from 160 to 197 min). Propofol infusion rates ranged from 0.13 to 0.17 mg/kg/min, and plasma concentration (Cpl) of propofol ranged from 11.4 to 13.3 µg/ml during surgery. Cardiovascular measurements during surgery remained within clinically acceptable ranges in the horses (heart rate: 33 to 37 beats/min, mean arterial blood pressure: 111 to 119 mmHg, cardiac index: 48 to 53 ml/kg/min, stroke volume: 650 to 800 ml/beat and systemic vascular resistance: 311 to 398 dynes/sec/cm⁵). The propofol Cpl declined rapidly after the cessation of propofol infusion and was significantly lower at 10 min (4.5 ± 1.5 µg/ml), extubation (4.0 ± 1.2 µg/ml) and standing (2.4 ± 0.9 µg/ml) compared with the Cpl at the end of propofol administration (11.4 ± 2.7 µg/ml). All the horses recovered uneventfully and stood at 74 ± 28 min after the cessation of anesthesia. KMP-TIVA provided satisfactory quality and control of anesthesia with minimum cardiovascular depression in horses undergoing surgery.     

Anesthetic and cardiopulmonary effects of total intravenous anesthesia using a midazolam, ketamine and medetomidine drug combination in horses

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 microg/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 MKM-drug 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.     

Medetomidine,ketamine, and sevoflurane for anesthesia of injured loggerhead sea turtles: 13 cases (1996-2000)

OBJECTIVE: To determine safety and efficacy of an anesthetic protocol incorporating medetomidine, ketamine, and sevoflurane for anesthesia of injured loggerhead sea turtles. DESIGN: Retrospective study. ANIMALS: 13 loggerhead sea turtles. PROCEDURE: Anesthesia was induced with medetomidine (50 microg/kg [22.7 microg/lb], IV) and ketamine (5 mg/kg (2.3 mg/lb], IV) and maintained with sevoflurane (0.5 to 2.5%) in oxygen. Sevoflurane was delivered with a pressure-limited intermittent-flow ventilator. Heart rate and rhythm, end-tidal partial pressure of CO2, and cloacal temperature were monitored continuously; venous blood gas analyses were performed intermittently. Administration of sevoflurane was discontinued 30 to 60 minutes prior to the end of the surgical procedure. Atipamezole (0.25 mg/kg [0.11 mg/lb], IV) was administered at the end of surgery. RESULTS: Median induction time was 11 minutes (range, 2 to 40 minutes; n = 11). Median delivered sevoflurane concentrations 15, 30, 60, and 120 minutes after intubation were 2.5 (n = 12), 1.5 (12), 1.25 (12), and 0.5% (8), respectively. Heart rate decreased during surgery to a median value of 15 beats/min (n = 11). End-tidal partial pressure of CO2 ranged from 2 to 16 mm Hg (n = 8); median blood gas values were within reference limits. Median time from atipamezole administration to extubation was 14 minutes (range, 2 to 84 minutes; n = 7). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that a combination of medetomidine and ketamine for induction and sevoflurane for maintenance provides safe, effective, controllable anesthesia in injured loggerhead sea turtles.     

Total intravenous anesthesia with ketamine–medetomidine–propofol in horses

Propofol is a potentially useful intravenous anesthetic agent for total intravenous anesthesia (TIVA) in horses. The purpose of this study was to compare the anesthetic and cardiorespiratory effects of TIVA following the administration of propofol alone(P–TIVA) and ketamine–medetomidine–propofol (KM–P–TIVA) in adult horses. The carotid artery was translocated to a subcutaneous position during TIVA with P–TIVA (n = 6) or KM–P–TIVA (n = 6). All horses were premedicated with medetomidine [0.005 mg kg^–1, intravenously (IV)]. Anesthesia was induced with midazolam (0.04 mg kg^–1 IV) and ketamine (2.5 mg kg IV). All horses were orotracheally intubated and breathed 100% oxygen. The KM drug combination (ketamine 40 mg mL^–1 and medetomidine 0.05 mg mL^–1) was infused at a rate of 0.025 mL kg^–1 hour^–1. Subsequently, a loading dose of propofol (0.5 mg kg^–1, bolus IV) was administered to all horses; surgical anesthesia (determined by horse response to incision and surgical manipulation, positive response being purposeful or spontaneous movement of limbs or head) was maintained by varying the propofol infusion rate as needed. Arterial blood pressure and HR were also monitored. Both methods of producing TIVA provided excellent general anesthesia for the surgical procedure. Anesthesia time was 115 ± 17 (mean ± SD) and 112 ± 11 minutes in horses anesthetized with KM–P–TIVA and P–TIVA, respectively. The infusion rate of propofol required to maintain surgical anesthesia with KM–P–TIVA was significantly less than for P–TIVA (mean infusion rate of propofol during anesthesia; KM–P–TIVA 0.15 0.02 P–TIVA 0.23 ± 0.03 mg kg^–1 minute^–1, p = 0.004). Apnea occurred in all horses lasting 1–2 minutes and intermittent positive pressure ventilation was started. Cardiovascular function was maintained during both methods of producing TIVA. There were no differences in the time to standing after the cessation of anesthesia (KM–P–TIVA 62 ± 10 minutes versus P–TIVA 87 ± 36 minutes, p = 0.150). The quality of recovery was good in KM–P–TIVA and satisfactory in P–TIVA. KM–P–TIVA and P–TIVA produced clinically useful general anesthesia with minimum cardiovascular depression. Positive pressure ventilation was required to treat respiratory depression. Respiratory depression and apnea must be considered prior to the use of propofol in the horse.     

Clinical comparison of xylazine and medetomidine for premedication of horses

OBJECTIVE: To compare the analgesic and cardiopulmonary effects of medetomidine and xylazine when used for premedication of horses undergoing general anesthesia. DESIGN: Randomized clinical trial. ANIMALS: 40 horses. PROCEDURE: Twenty horses were premedicated with medetomidine (10 microg/kg [4.5 microg/lb], i.m.) and the other 20 were premedicated with xylazine (2 mg/kg [0.9 mg/kg], i.m.). Horses were then anesthetized with a combination of guaifenesin and ketamine; anesthesia was maintained with halothane. Additional doses of medetomidine or xylazine were given if horses were not sufficiently sedated at the time of anesthetic induction. After induction of anesthesia, sodium pentothal was administered as necessary to prevent limb movements. Hypotension was treated with dobutamine; hypoventilation and hypoxemia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored. RESULTS: Scores for the quality of the transition to inhalation anesthesia were significantly higher for horses premedicated with medetomidine than for horses premedicated with xylazine. However, other scores, recovery times, and numbers of attempts needed to achieve sternal recumbency and to stand were not significantly different between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that medetomidine is suitable for premedication of horses undergoing general anesthesia. Analgesic and cardiopulmonary effects of medetomidine were similar to those of xylazine, except that the transition to inhalation anesthesia was smoother when horses were premedicated with medetomidine, rather than xylazine.     

Clinical evaluation of total intravenous anesthesia using a combination of propofol and medetomidine following anesthesia induction with medetomidine, guaifenesin and propofol for castration in Thoroughbred horses

Seven Thoroughbred horses were castrated under total intravenous anesthesia (TIVA) using propofol and medetomidine. After premedication with medetomidine (5.0 μg/kg, intravenously), anesthesia was induced with guaifenesin (100 mg/kg, intravenously) and propofol (3.0 mg/kg, intravenously) and maintained with constant rate infusions of medetomidine (0.05 μg/kg/min) and propofol (0.1 mg/kg/min). Quality of induction was judged excellent to good. Three horses showed insufficient anesthesia and received additional anesthetic. Arterial blood pressure changed within an acceptable range in all horses. Decreases in respiratory rate and hypercapnia were observed in all horses. Three horses showed apnea within a short period of time. Recovery from anesthesia was calm and smooth in all horses. The TIVA-regimen used in this study provides clinically effective anesthesia for castration in horses. However, assisted ventilation should be considered to minimize respiratory depression.     

Comparison of the cardiopulmonary effects of anesthesia maintained by continuous infusion of ketamine and propofol with anesthesia maintained by inhalation of sevoflurane in goats undergoing magnetic resonance imaging

OBJECTIVE: To compare the cardiopulmonary effects of anesthesia maintained by continuous infusion of ketamine and propofol with anesthesia maintained by inhalation of sevoflurane in goats undergoing magnetic resonance imaging. ANIMALS: 8 Saanen goats. PROCEDURES: Goats were anesthetized twice (1-month interval) following sedation with midazolam (0.4 mg/kg, IV). Anesthesia was induced via IV administration of ketamine (3 mg/kg) and propofol (1 mg/kg) and maintained with an IV infusion of ketamine (0.03 mg/kg/min) and propofol (0.3 mg/kg/min) and 100% inspired oxygen (K-P treatment) or induced via IV administration of propofol (4 mg/kg) and maintained via inhalation of sevoflurane in oxygen (end-expired concentration, 2.3%; 1X minimum alveolar concentration; SEVO treatment). Cardiopulmonary and blood gas variables were assessed at intervals after induction of anesthesia. RESULTS: Mean +/- SD end-expired sevoflurane was 2.24 +/- 0.2%; ketamine and propofol were infused at rates of 0.03 +/- 0.002 mg/kg/min and 0.29 +/- 0.02 mg/kg/min, respectively. Overall, administration of ketamine and propofol for total IV anesthesia was associated with a degree of immobility and effects on cardiopulmonary parameters that were comparable to those associated with anesthesia maintained by inhalation of sevoflurane. Compared with the K-P treatment group, mean and diastolic blood pressure values in the SEVO treatment group were significantly lower at most or all time points after induction of anesthesia. After both treatments, recovery from anesthesia was good or excellent. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that ketamine-propofol total IV anesthesia in goats breathing 100% oxygen is practical and safe for performance of magnetic resonance imaging procedures.     

Intramuscular anesthesia of bonito and Pacific mackerel with ketamine and medetomidine and reversal of anesthesia with atipamezole

OBJECTIVE: To determine anesthetic effects of ketamine and medetomidine in bonitos and mackerels and whether anesthesia could be reversed with atipamezole. DESIGN: Clinical trial. ANIMALS: 43 bonitos (Sarda chiliensis) and 47 Pacific mackerels (Scomber japonica). PROCEDURE: 28 bonitos were given doses of ketamine ranging from 1 to 8 mg/kg (0.5 to 3.6 mg/lb), i.m., and doses of medetomidine ranging from 0.2 to 1.6 mg/kg (0.1 to 0.7 mg/lb), i.m. (ratio of ketamine to medetomidine, 2.5:1 to 20:1). Doses of atipamezole equal to 1 or 5 times the dose of medetomidine were used. The remaining 15 bonitos were used to determine the anesthetic effects of ketamine at a dose of 4 mg/kg (1.8 mg/lb) and medetomidine at a dose of 0.4 mg/kg (0.2 mg/lb). The mackerels were given ketamine at doses ranging from 11 to 533 mg/kg (5 to 242 mg/lb) and medetomidine at doses ranging from 0.3 to 9.1 mg/kg (0.1 to 4.1 mg/lb; ratio of ketamine to medetomidine, 3:1 to 800:1). Doses of atipamezole equal to 5 times the dose of medetomidine were used. RESULTS: I.m. administration of ketamine at a dose of 4 mg/kg and medetomidine at a dose of 0.4 mg/kg in bonitos and ketamine at a dose of 53 to 228 mg/kg (24 to 104 mg/lb) and medetomidine at a dose of 0.6 to 4.2 mg/kg (0.3 to 1.9 mg/lb) in mackerels was safe and effective. For both species, administration of atipamezole at a dose 5 times the dose of medetomidine reversed the anesthetic effects. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that a combination of ketamine and medetomidine can safely be used for anesthesia of bonitos and mackerels and that anesthetic effects can be reversed with atipamezole.     

Infusion of a combination of propofol and medetomidine for long-term anesthesia in ponies

OBJECTIVE: To determine the minimal infusion rate of propofol in combination with medetomidine for long-term anesthesia in ponies and the effects of atipamezole on recovery. ANIMALS: 12 ponies. PROCEDURE: Ponies were sedated with medetomidine (7 microg/kg of body weight, IV). Ten minutes later, anesthesia was induced with propofol (2 mg/kg, IV). Anesthesia was maintained for 4 hours, using an infusion of medetomidine (3.5 microg/kg per hour, IV) and propofol at a rate sufficient to prevent ponies from moving after electrical stimulation. Arterial blood pressures and blood gas analysis, heart rates, and respiratory rates were monitored. For recovery, 6 ponies were given atipamezole (60 microg/kg, IV). Induction and recovery were scored. RESULTS: Minimal propofol infusion rates ranged from 0.06 to 0.1 mg/kg per min. Mean arterial blood pressure was stable (range, 74 to 86 mm Hg), and heart rate (34 to 51 beats/min) had minimal variations. Variable breathing patterns were observed. Mean PaO2 (range, 116 to 146 mm Hg) and mean PaCO2 (range, 48 to 51 mm Hg) did not change significantly with time, but hypoxemia was evident in some ponies (minimal PaO2, 47 mm Hg). Recovery was fast and uneventful with and without atipamezole (completed in 20.2 and 20.9 minutes, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Infusion of a combination of medetomidine and propofol was suitable for prolonged anesthesia in ponies. Recovery was rapid and uneventful. A combination of propofol and medetomidine may prove suitable for long-term anesthesia in horses. Monitoring of blood gases is essential because of potential hypoxemia.     

Cardiopulmonary effects of a medetomidine-ketamine combination administered intravenously in gopher tortoises

OBJECTIVE: To determine whether IV administration of a combination of medetomidine and ketamine depresses cardiopulmonary function in healthy adult gopher tortoises. DESIGN: Prospective study. ANIMALS: 3 adult male and 3 adult female nonreleasable gopher tortoises. PROCEDURE: Prior to the study, carotid and jugular catheters were surgically placed in each tortoise for blood collection, direct arterial blood pressure monitoring, and drug administration. Heart rate, direct carotid arterial blood pressure, and body temperature were measured before and every 5 minutes for 45 minutes after IV injection of medetomidine (100 microg/kg [45.5 microg/lb]) and ketamine (5 mg/kg [2.3 mg/lb]). Carotid arterial blood samples were collected before and 5, 15, 30, and 45 minutes after medetomidine-ketamine administration to determine pH, PO2, and PCO2. Atipamezole (500 mg/kg [227 microg/lb], IV) was administered 30 minutes after administration of medetomidine-ketamine. RESULTS: The medetomidine-ketamine combination caused a moderate increase in arterial blood pressure, and moderate hypercapnia and hypoxemia. There were no significant changes in heart rate or body temperature. Intravenous administration of atipamezole rapidly induced severe hypotension. CONCLUSIONS AND CLINICAL RELEVANCE: The combination of medetomidine and ketamine administered IV resulted in effective short-term immobilization adequate for minor diagnostic procedures in gopher tortoises. This combination also caused moderate hypoventilation, and it is recommended that a supplemental source of oxygen or assisted ventilation be provided. Atipamezole administration hastens recovery from chemical immobilization but induces severe hypotension. It is recommended that atipamezole not be administered IV for reversal of medetomidine in tortoises and turtles.     

The minimum infusion rate (MIR) of propofol for total intravenous anesthesia after premedication with xylazine in horses

To investigate an adequate infusion rate of propofol for total intravenous anesthesia (TIVA) in horses, the minimum infusion rate (MIR) comparable to the minimum alveolar anesthetic concentration (MAC) of inhalation anesthetic was determined under constant ventilation condition by intermittent positive pressure ventilation (IPPV). In addition, arterial propofol concentration was measured to determine the concentration corresponding to the MIR (concentration preventing reaction to stimulus in 50% of population, Cp(50)). Further, 95% effective dose (ED(95)) was estimated as infusion rate for acquiring adequate anesthetic depth. Anesthetic depth was judged by the gross purposeful movement response to painful stimulus. MIR and Cp(50) were 0.10 +/- 0.02 mg/kg/min and 5.3 +/- 1.4 microg/ml, respectively. ED(95) was estimated as 0.14 mg/kg/min (1.4MIR).     

Effect of variable-dose propofol alone and in combination with two fixed doses of ketamine for total intravenous anesthesia in cats

OBJECTIVE: To determine the minimum infusion rate (MIR50) for propofol alone and in combination with ketamine required to attenuate reflexes commonly used in the assessment of anesthetic depth in cats. ANIMALS: 6 cats. PROCEDURE: Propofol infusion started at 0.05 to 0.1 mg/kg/min for propofol alone or 0.025 mg/kg/min for propofol and ketamine (low-dose ILD] constant rate infusion [CRI] of 23 microg/kg/min or high-dose [HD] CRI of 46 microg/kg/min), and after 15 minutes, responses of different reflexes were tested. Following a response, the propofol dose was increased by 0.05 mg/kg/min for propofol alone or 0.025 mg/kg/min for propofol and ketamine, and after 15 minutes, reflexes were retested. RESULTS: The MIR50 for propofol alone required to attenuate blinking in response to touching the medial canthus or eyelashes; swallowing in response to placement of a finger or laryngoscope in the pharynx; and to toe pinch, tetanus, and tail-clamp stimuli were determined. Addition of LD ketamine to propofol significantly decreased MIR50, compared with propofol alone, for medial canthus, eyelash, finger, toe pinch, and tetanus stimuli but did not change those for laryngoscope or tail-clamp stimuli. Addition of HD ketamine to propofol significantly decreased MIR50, compared with propofol alone, for medial canthus, eyelash, toe pinch, tetanus, and tail-clamp stimuli but did not change finger or laryngoscope responses. CONCLUSIONS AND CLINICAL RELEVANCE: Propofol alone or combined with ketamine may be used for total IV anesthesia in healthy cats at the infusion rates determined in this study for attenuation of specific reflex activity.     

Effects of ketamine and magnesium on the minimum alveolar concentration of isoflurane in goats

OBJECTIVE: To evaluate the effects of ketamine, magnesium sulfate, and their combination on the minimum alveolar concentration (MAC) of isoflurane (ISO-MAC) in goats. ANIMALS: 8 adult goats. PROCEDURES: Anesthesia was induced with isoflurane delivered via face mask. Goats were intubated and ventilated to maintain normocapnia. After an appropriate equilibration period, baseline MAC (MAC(B)) was determined and the following 4 treatments were administered IV: saline (0.9% NaCl) solution (loading dose [LD], 30 mL/20 min; constant rate infusion [CRI], 60 mL/h), magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h), ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min), and magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h) combined with ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min); then MAC was redetermined. RESULTS: Ketamine significantly decreased ISOMAC by 28.7 +/- 3.7%, and ketamine combined with magnesium sulfate significantly decreased ISOMAC by 21.1 +/- 4.1%. Saline solution or magnesium sulfate alone did not significantly change ISOMAC. CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine and ketamine combined with magnesium sulfate, at doses used in the study, decreased the end-tidal isoflurane concentration needed to maintain anesthesia, verifying the clinical impression that ketamine decreases the end-tidal isoflurane concentration needed to maintain surgical anesthesia. Magnesium, at doses used in the study, did not decrease ISOMAC or augment ketamine's effects on ISOMAC.     

Use of a combination of propofol and fentanyl, alfentanil, or sufentanil for total intravenous anesthesia in cats

OBJECTIVE: To determine the cardiorespiratory effects of an i.v. infusion of propofol alone or in association with fentanyl, alfentanil, or sufentanil in cats and, for each combination, the minimal infusion rate of propofol that would inhibit a response to noxious stimuli. DESIGN: Randomized crossover study. ANIMALS: 6 cats. PROCEDURE: Cats were anesthetized 4 times in random order. After i.v. administration of fentanyl, alfentanil, sufentanil, or saline (0.9% NaCl) solution, anesthesia was induced with propofol (7 mg/kg 13.2 mg/lb], i.v.) and maintained for 90 minutes with a continuous infusion of propofol in conjunction with fentanyl (0.1 microg/kg/min [0.045 microg/lb/min]), alfentanil (0.5 microg/kg/min [0.23 microg/lb/min]), sufentanil (0.01 microg/kg/min [0.004 microg/lb/min]), or saline solution (0.08 mL/kg/min [0.036 mL/lb/min]). RESULTS: Minimal infusion rate of propofol required to prevent a response to a noxious stimulus was higher when cats received saline solution. After 70 minutes, minimal infusion rate of propofol was significantly higher with fentanyl than with sufentanil. Decreases in heart rate, systolic blood pressure, rectal temperature, and respiratory rate were detected with all treatments. Oxygen saturation did not change significantly, but end-tidal partial pressure of carbon dioxide increased with all treatments. There were no significant differences in recovery times or sedation and recovery scores among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that infusion of propofol in combination with fentanyl, alfentanil, or sufentanil results in satisfactory anesthesia in cats.     

Comparison of the effects of morphine administered by constant-rate intravenous infusion or intermittent intramuscular injection in dogs

OBJECTIVE: To compare physiologic and analgesic effects of morphine when given by IV constant-rate infusion or by IM injection to dogs undergoing laparotomy and to determine pharmacokinetics of morphine in dogs following IV constant-rate infusion. DESIGN: Prospective randomized controlled trial. ANIMALS: 20 dogs. PROCEDURE: Dogs undergoing laparotomy were treated with morphine beginning at the time of anesthetic induction. Morphine was administered by IV infusion (0.12 mg/kg/h [0.05 mg/lb/h] of body weight) or by IM injection (1 mg/kg [0.45 mg/lb]) at induction and extubation and every 4 hours thereafter. Treatments continued for 24 hours after extubation. RESULTS: Blood gas values did not indicate clinically significant respiratory depression in either group, and degree of analgesia (determined as the University of Melbourne Pain Scale score) and incidence of adverse effects (panting, vomiting, defecation, and dysphoria) were not significantly different between groups. Dogs in both groups had significant decreases in mean heart rate, rectal temperature, and serum sodium and potassium concentrations, compared with preoperative values. Mean +/- SEM total body clearance of morphine was 68 +/- 6 ml/min/kg (31 +/- 3 ml/min/lb). Mean steady-state serum morphine concentration in dogs receiving morphine by constant-rate infusion was 30 +/- 2 ng/ml. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that administration of morphine as a constant-rate IV infusion at a dose of 0.12 mg/kg/h induced effects similar to those obtained with administration at a dose of 1 mg/kg, IM, every 4 hours in dogs undergoing laparotomy. Panting was attributed to an opioid-induced resetting of the hypothalamic temperature set point, rather than respiratory depression.     

Effect of general anesthesia and minor surgical trauma on urine and serum measurements in horses

OBJECTIVE: To characterize the effect of general anesthesia and minor surgery on renal function in horses. ANIMALS: 9 mares with a mean (+/- SE) age and body weight of 9+/-2 years and 492+/-17 kg, respectively. PROCEDURE: The day before anesthesia, urine was collected (catheterization) for 3 hours to quantitate baseline values, and serum biochemical analysis was performed. The following day, xylazine (1.1 mg/kg, IV) was administered, and general anesthesia was induced 5 minutes later with diazepam (0.04 mg/kg, IV) and ketamine (2.2 mg/kg, IV). During 2 hours of anesthesia with isoflurane, Paco2 was maintained between 48 and 52 mm Hg, and mean arterial blood pressure was between 70 and 80 mm Hg. Blood and urine were collected at 30, 60, and 120 minutes during and at 1 hour after anesthesia. RESULTS: Baseline urine flow was 0.92+/-0.17 ml/kg/h and significantly increased at 30 and 60 minutes after xylazine administration (2.14+/-0.59 and 2.86+/-0.97 ml/kg/h respectively) but returned to baseline values by the end of anesthesia. Serum glucose concentration increased from 12+/-4 to 167+/-8 mg/dl at 30 minutes. Glucosuria was not observed. CONCLUSIONS AND CLINICAL RELEVANCE: Transient hyperglycemia and an increase in rine production accompanies a commonly used anesthetic technique for horses. The increase in urine flow is not trivial and should be considered in anesthetic management decisions. With the exception of serum glucose concentration and urine production, the effect of general anesthesia on indices of renal function in clinically normal horses is likely of little consequence in most horses admitted for elective surgical procedures.     

Anesthesia in Sheep With Propofol or With Xylazine-Ketamine Followed by Halothane

Objective- This study evaluates the clinical usefulness and anesthetic effect of propofol, and compares these effects with those of xylazine-ketamine-halothane anesthesia in sheep.
Study Design- Prospective, randomized, clinical trial. Animals or Sample Population- Fourteen healthy adult male sheep.
Methods- Sheep were randomly assigned to two different drug regimens: (1) Bolus injection of propofol (3 mg/kg, intravenously [IV]) followed by continuous intravenous infusion and (2) xylazine (0.11 mg/kg, IV) and ketamine (2.2 mg/kg, IV) for induction followed by halothane anesthesia. Heart rate, respiratory rate, and arterial blood pressures were monitored during anesthesia. Venous blood samples were collected for blood gas analysis. Quality of induction and recovery were also recorded.
Results- The average dose of propofol used to induce and maintain anesthesia was 6.63 ±2.06 mg/kg and 29.3 ±11.7 mg/kg/hr (0.49 ±0.20 mg/kg/min), respectively. The duration of propofol anesthesia was 45.3 ±13.2 minutes and recovery to standing occurred in 14.7 ±5.7 minutes. Sheep receiving xylazine-ketamine-halothane were anesthetized for 35.9 ±4.0 minutes and recovery to standing occurred within 28.5 ±7.5 minutes. Sheep anesthetized with propofol had a significantly higher heart rate, diastolic blood pressure and Pvo₂, and a lower Pvco₂ at 30 minutes and lower BE at 15 and 30 minutes than sheep anesthetized with xylazine-ketamine-halothane.
Conclusions- Propofol anesthesia was characterized by a smooth induction, effective surgical anesthesia and rapid recovery which was comparable to anesthesia with xylazine-ketamine-halothane.
Clinical Relevance- Propofol may be indicated in situations when it is desirable to maintain anesthesia with an intravenous infusion followed by a rapid recovery in healthy sheep.