Objective—To determine the effect of administration
of commercially available sodium bicarbonate
(NaHCO3) on carbon 13 (13C) isotopic enrichment of
carbon dioxide (CO2) in serum of horses.
Animals—7 healthy Thoroughbreds.
Procedure—Sodium bicarbonate (450 g) was administered
via nasogastric intubation to horses. Horses
had been fed a diet obtained from the same source
and had access to water from the same source for 3
months before the study. Blood samples were collected
immediately before and at 2, 4, 6, and 24 hours
after administration of NaHCO3. The concentration of
total CO2 in serum was measured by use of a commercial
analyzer. The 13C enrichment of bicarbonate in
serum was estimated by measurement of 13C enrichment
of CO2 released by acidification of the serum.
The 13C enrichment of commercially available NaHCO3
was also determined and compared with that of CO2
in serum of horses before administration of NaHCO3.
Results—Commercially available NaHCO3 had a 13C
enrichment significantly different from that of carbon
dioxide in serum of horses before treatment.
Administration of NaHCO3 increased the concentration
of total CO2 from pretreatment values. The 13C
enrichment of CO2 in serum was only transiently and
minimally affected after administration of NaHCO3.
Conclusions and Clinical Relevance—Administration
of NaHCO3 was not detected by measuring 13C enrichment
of CO2 in serum of horses. ( Am J Vet Res 2004;65:307–310)
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 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
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 determine the pharmacokinetic disposition of IV administered caffeine in healthy Lama spp camelids.
Animals—4 adult male alpacas and 4 adult female llamas.
Procedures—Caffeine (3 mg/kg) was administered as an IV bolus. Plasma caffeine concentrations were determined by use of high-performance liquid chromatography in 6 animals and by use of liquid chromatography-mass spectrometry in 2 llamas.
Results—Median elimination half-life was 11 hours (range, 9.3 to 29.8 hours) in alpacas and 16 hours (range, 5.4 to 17 hours) in llamas. The volume of distribution at steady state was 0.60 L/kg (range, 0.45 to 0.93 L/kg) in alpacas and 0.75 L/kg (range, 0.68 to 1.15 L/kg) in llamas. Total plasma clearance was 44 mL/h/kg (range, 24 to 56 mL/h/kg) in alpacas and 42 mL/h/kg (range, 30 to 109 mL/h/kg) in llamas.
Conclusions and Clinical Relevance—High-performance liquid chromatography and liquid chromatography-mass spectrometry were suitable methods for determination of plasma caffeine concentrations in alpacas and llamas. Plasma caffeine concentration-time curves were best described by a 2-compartment model. Elimination half-lives, plasma clearance, volume of distribution at steady state, and mean residence time were not significantly different between alpacas and llamas. Intravenous administration of caffeine at a dose of 3 mg/kg did not induce clinical signs of excitement.
Objective—To evaluate calcium balance and parathyroid
gland function in healthy horses and horses with
enterocolitis and compare results of an immunochemiluminometric
assay (ICMA) with those of an
immunoradiometric assay (IRMA) for determination of
serum intact parathyroid hormone (PTH) concentrations
Animals—64 horses with enterocolitis and 62 healthy
Procedures—Blood and urine samples were collected
for determination of serum total calcium, ionized calcium
(Ca2+) and magnesium (Mg2+), phosphorus, BUN,
total protein, creatinine, albumin, and PTH concentrations,
venous blood gases, and fractional urinary clearance
of calcium (FCa) and phosphorus (FP). Serum
concentrations of PTH were measured in 40 horses by
use of both the IRMA and ICMA.
Results—Most (48/64; 75%) horses with enterocolitis
had decreased serum total calcium, Ca2+, and Mg2+
concentrations and increased phosphorus concentrations,
compared with healthy horses. Serum PTH concentration
was increased in most (36/51; 70.6%) horses
with hypocalcemia. In addition, FCa was significantly
decreased and FP significantly increased in
horses with enterocolitis, compared with healthy horses.
Results of ICMA were in agreement with results of
Conclusions and Clinical Relevance—Enterocolitis
in horses is often associated with hypocalcemia;
79.7% of affected horses had ionized hypocalcemia.
Because FCa was low, it is unlikely that renal calcium
loss was the cause of hypocalcemia. Serum PTH concentrations
varied in horses with enterocolitis and concomitant
hypocalcemia. However, we believe low PTH
concentration in some hypocalcemic horses may be
the result of impaired parathyroid gland function. ( Am
J Vet Res 2001;62:938–947)