Objective—To evaluate the use of midazolam, ketamine, and xylazine for total IV anesthesia (TIVA) in horses.
Animals—6 healthy Thoroughbred mares.
Procedures—Horses were sedated with xylazine (1.0 mg/kg, IV). Anesthesia was induced with midazolam (0.1 mg/kg, IV) followed by ketamine (2.2 mg/kg, IV) and was maintained with an IV infusion of midazolam (0.002 mg/kg/min), ketamine (0.03 mg/kg/min), and xylazine (0.016 mg/kg/min). Horses underwent surgical manipulation and injection of the palmar digital nerves; duration of the infusion was 60 minutes. Additional ketamine (0.2 to 0.4 mg/kg, IV) was administered if a horse moved its head or limbs during procedures. Cardiopulmonary and arterial blood variables were measured prior to anesthesia; at 10, 20, 30, 45, and 60 minutes during infusion; and 10 minutes after horses stood during recovery. Recovery quality was assessed by use of a numeric (1 to 10) scale with 1 as an optimal score.
Results—Anesthesia was produced for 70 minutes after induction; supplemental ketamine administration was required in 4 horses. Heart rate, respiratory rate, arterial blood pressures, and cardiac output remained similar to preanesthetic values throughout TIVA. Arterial partial pressure of oxygen and oxygen saturation of arterial hemoglobin were significantly decreased from preanesthetic values throughout anesthesia; oxygen delivery was significantly decreased at 10- to 30-minute time points. Each horse stood on its first attempt, and median recovery score was 2.
Conclusions and Clinical Relevance—Midazolam, ketamine, and xylazine in combination produced TIVA in horses. Further studies to investigate various dosages for midazolam and ketamine or the substitution of other α2-adrenoceptor for xylazine are warranted.
Objective—To determine the effect of dexmedetomidine, morphine-lidocaine-ketamine (MLK), and dexmedetomidine-morphine-lidocaine-ketamine (DMLK) constant rate infusions on the minimum alveolar concentration (MAC) of isoflurane and bispectral index (BIS) in dogs.
Animals—6 healthy adult dogs.
Procedures—Each dog was anesthetized 4 times with a 7-day washout period between anesthetic episodes. During the first anesthetic episode, the MAC of isoflurane (baseline) was established. During the 3 subsequent anesthetic episodes, the MAC of isoflurane was determined following constant rate infusion of dexmedetomidine (0.5 μg/kg/h), MLK (morphine, 0.2 mg/kg/h; lidocaine, 3 mg/kg/h; and ketamine, 0.6 mg/kg/h), or DMLK (dexmedetomidine, 0.5 μg/kg/h; morphine, 0.2 mg/kg/h; lidocaine, 3 mg/kg/h; and ketamine 0.6 mg/kg/h). Among treatments, MAC of isoflurane was compared by means of a Friedman test with Conover posttest comparisons, and heart rate, direct arterial pressures, cardiac output, body temperature, inspired and expired gas concentrations, arterial blood gas values, and BIS were compared with repeated-measures ANOVA and a Dunn test for multiple comparisons.
Results—Infusion of dexmedetomidine, MLK, and DMLK decreased the MAC of isoflurane from baseline by 30%, 55%, and 90%, respectively. Mean heart rates during dexmedetomidine and DMLK treatments was lower than that during MLK treatment. Compared with baseline values, mean heart rate decreased for all treatments, arterial pressure increased for the DMLK treatment, cardiac output decreased for the dexmedetomidine treatment, and BIS increased for the MLK and DMLK treatments. Time to extubation and sternal recumbency did not differ among treatments.
Conclusions and Clinical Relevance—Infusion of dexmedetomidine, MLK, or DMLK reduced the MAC of isoflurane in dogs. (Am J Vet Res 2013;74:963–970)
Objective—To determine the effects of IV administration
of enalaprilat on cardiorespiratory and hematologic
variables as well as inhibition of angiotensin converting
enzyme (ACE) activity in exercising horses.
Animals—6 adult horses.
Procedure—Horses were trained by running on a
treadmill for 5 weeks. Training was continued
throughout the study period, and each horse also ran
2 simulated races at 120% of maximum oxygen consumption.
Three horses were randomly selected to
receive treatment 1 (saline [0.9% NaCl] solution), and
the remaining 3 horses received treatment 2
(enalaprilat; 0.5 mg/kg of body weight, IV) before
each simulated race. Treatment groups were
reversed for the second simulated race.
Cardiorespiratory and hematologic data were
obtained before, during, and throughout the 1-hour
period after each simulated race. Inhibition of ACE
activity was determined during and after each race in
Results—Exercise resulted in significant increases in
all hemodynamic variables and respiratory rate. The
pH and PO2 of arterial blood decreased during simulated
races, whereas PCO2 remained unchanged.
Systemic and pulmonary blood pressure measurements
and arterial pH, PO2, and PCO2 returned to
baseline values by 60 minutes after simulated races.
Enalaprilat inhibited ACE activity to < 25% of baseline
activity without changing cardiorespiratory or blood
gas values, compared with horses administered
Conclusions and Clinical Relevance—Enalaprilat
administration almost completely inhibited ACE activity
in horses without changing the hemodynamic
responses to intense exercise and is unlikely to be of
value in preventing exercise-induced pulmonary hemorrhage.
(Am J Vet Res 2001;62:1008–1013)
Objective—To compare systemic bioavailability and
duration for therapeutic plasma concentrations and
cardiovascular, respiratory, and analgesic effects of
morphine administered per rectum, compared with IV
and IM administration in dogs.
Animals—6 healthy Beagles.
Procedure—In a randomized study, each dog
received the following: morphine IV (0.5 mg/kg of
body weight), morphine per rectum (1, 2, and 5 mg/kg
as a suppository and 2 mg/kg as a solution), and a control
treatment. Intramuscular administration of morphine
(1 mg/kg) was evaluated separately. Heart and
respiratory rates, systolic, diastolic, and mean blood
pressures, adverse effects, and plasma morphine concentrations
were measured. Analgesia was defined as
an increase in response threshold, compared with
baseline values, to applications of noxious mechanical
(pressure) and thermal (heat) stimuli. Data were evaluated,
using Friedman repeated-measures ANOVA on
ranks and Student-Newman-Keuls post-hoc t-tests.
Results—Significant differences were not found in
cardiovascular, respiratory, or analgesia values
between control and morphine groups. Overall systemic
bioavailability of morphine administered per rectum
was 19.6%. Plasma morphine concentration after
administration of the highest dose (5 mg/kg) as a suppository
was significantly higher than concentrations
60 and 360 minutes after IV and IM administration,
respectively. A single route of administration did not
consistently fulfill our criteria for providing analgesia.
Conclusions and Clinical Relevance—Rectal administration
of morphine did not increase bioavailability
above that reported for oral administration of morphine
in dogs. Low bioavailability and plasma concentrations
limit the clinical usefulness of morphine
administered per rectum in dogs. (Am J Vet Res
Objective—To determine the anesthetic, cardiorespiratory,
and metabolic effects of 4 IV anesthetic regimens
in Thoroughbred horses recuperating from a
brief period of maximal exercise.
Animals—6 adult Thoroughbreds.
Procedure—Horses were preconditioned by exercising
them on a treadmill. Each horse ran 4 simulated
races, with a minimum of 14 days between races.
Races were run at a treadmill speed that caused horses
to exercise at 120% of their maximal oxygen consumption.
Horses ran until fatigued or for a maximum
of 2 minutes. Two minutes after exercise, horses
received a combination of xylazine hydrochloride (2.2
mg/kg of body weight) and acepromazine maleate
(0.04 mg/kg) IV. Five minutes after exercise, horses
received 1 of the following 4 IV anesthetic regimens:
ketamine hydrochloride (2.2 mg/kg); ketamine (2.2
mg/kg) and diazepam (0.1 mg/kg); tiletamine
hydrochloride-zolazepam hydrochloride (1 mg/kg); and
guaifenesin (50 mg/kg) and thiopental sodium (5
mg/kg). Treatments were randomized. Cardiopulmonary
indices were measured, and samples of
blood were collected before and at specific times for
90 minutes after each race.
Results—Each regimen induced lateral recumbency.
The quality of induction and anesthesia after ketamine
administration was significantly worse than after
other regimens, and the duration of anesthesia was
significantly shorter. Time to lateral recumbency was
significantly longer after ketamine or guaifenesinthiopental
administration than after ketaminediazepam
or tiletamine-zolazepam administration.
Arterial blood pressures after guaifenesin-thiopental
administration were significantly lower than after the
Conclusions and Clinical Relevance—Anesthesia
can be safely induced in sedated horses immediately
after maximal exercise. Ketamine-diazepam and tiletamine-
zolazepam induced good quality anesthesia
with acceptable perturbations in cardiopulmonary and
metabolic indices. Ketamine alone and guaifenesinthiopental
regimens are not recommended. (Am J Vet
Animals—48 client-owned dogs that underwent stifle joint surgery.
Procedures—Dogs undergoing tibial plateau leveling osteotomy were randomly assigned to receive a constant rate infusion of a combination of morphine, lidocaine, and ketamine; a lumbosacral epidural with morphine and ropivacaine; both treatments (ie, constant rate infusion and lumbosacral epidural); or only IM premedication with morphine. Indices of cardiorespiratory function and isoflurane requirement were recorded at 5-minute intervals during anesthesia. A validated sedation scoring system and the modified Glasgow composite measure pain score were used to assess comfort and sedation after surgery and anesthesia once the swallowing reflex returned and a body temperature of ≥ 36.7°C (98.1°F) was attained. Pain and sedation scores were acquired at 60-minute intervals for 4 hours, then at 4-hour intervals for 24 hours. Dogs with a postoperative pain score > 5 of 24 were given morphine as rescue analgesia.
Results—No differences in heart rate, respiratory rate, systolic arterial blood pressure, end-tidal Pco2, end-tidal isoflurane concentration, and vaporizer setting were detected among groups. No differences in pain score, sedation score, rescue analgesia requirement, or time to first rescue analgesia after surgery were detected.
Conclusions and Clinical Relevance—Pain scores were similar among groups, and all 4 groups had similar rescue analgesia requirements and similar times to first administration of rescue analgesia. All 4 analgesic protocols provided acceptable analgesia for 24 hours after stifle joint surgery.
Objective—To determine the effect of IV administration of crystalloid (lactated Ringer's solution [LRS]) or colloid (hetastarch) fluid on isoflurane-induced hypotension in dogs.
Animals—6 healthy Beagles.
Procedures—On 3 occasions, each dog was anesthetized with propofol and isoflurane and instrumented with a thermodilution catheter (pulmonary artery). Following baseline assessments of hemodynamic variables, end-tidal isoflurane concentration was increased to achieve systolic arterial blood pressure (SABP) of 80 mm Hg. At that time (0 minutes), 1 of 3 IV treatments (no fluid, LRS [80 mL/kg/h], or hetastarch [80 mL/kg/h]) was initiated. Fluid administration continued until SABP was within 10% of baseline or to a maximum volume of 80 mL/kg (LRS) or 40 mL/kg (hetastarch). Hemodynamic variables were measured at intervals (0 through 120 minutes and additionally at 150 and 180 minutes in LRS- or hetastarch-treated dogs). Several clinicopathologic variables including total protein concentration, PCV, colloid osmotic pressure, and viscosity of blood were assessed at baseline and intervals thereafter (0 through 120 minutes).
Results—Administration of 80 mL of LRS/kg did not increase SABP in any dog, whereas administration of ≤ 40 mL of hetastarch/kg increased SABP in 4 of 6 dogs. Fluid administration increased cardiac index and decreased systemic vascular resistance. Compared with hetastarch treatment, administration of LRS decreased blood viscosity. Treatment with LRS decreased PCV and total protein concentration, whereas treatment with hetastarch increased colloid osmotic pressure.
Conclusions and Clinical Relevance—Results indicated that IV administration of hetastarch rather than LRS is recommended for the treatment of isoflurane-induced hypotension in dogs.