Objective—To compare cardiac output measured in
the pulmonary artery and a carotid artery by use of
thermal and electrical impedance dilution.
Animals—7 fit, clinically normal Standardbreds
between 2 and 5 years of age.
Procedure—Transient changes in electrical impedance
and temperature of blood were induced by bolus
injections of ice-cold saline hypertonic (6% and 9%
NaCl) solutions. Cardiac output was calculated by
applying Stewart-Hamilton principles to the indicator
dilution transients. Measurements were made during
sequential exercise episodes on a level treadmill over
approximately an 8-fold range of cardiac output values.
Results—We detected agreement between cardiac
output determined by use of electrical impedance
dilution at the pulmonary artery and carotid artery.
Cardiac output from thermal dilution measured at the
carotid artery exceeded that measured at the pulmonary
artery. Cardiac output from the thermal dilution
technique exceeded cardiac output from the electrical
impedance dilution technique at both locations.
Conclusions and Clinical Relevance—The electrical
impedance indicator is conserved on first transit;
therefore cardiac output measured by electrical
impedance dilution at the carotid artery is reliable over
a large range of values. Thermal dilution provides a
larger estimate of cardiac output, compared with the
electrical impedance dilution technique, probably
because of a loss of indicator. The transpulmonary
electrical impedance dilution technique may have
potential for clinical application, particularly in animals
in which catheterization of the pulmonary artery is not
appropriate or blood loss must be minimized. (Am J
Vet Res 2005;66:878–884)
PROCEDURES Dogs were randomly assigned to receive either oxygen (Fio2 > 0.9 [100% oxygen]; n = 11; control group) or a mixture of nitrogen and oxygen (Fio2 = 0.4; 11; 40% oxygen group) as the carrier gas for isoflurane while anesthetized. All dogs were allowed to breathe spontaneously while anesthetized. For each dog, the Pao2, Paco2, other indices of oxygenation, and extent of sedation were monitored at predetermined times during and for 1 hour after anesthesia. Measured variables were compared between the 2 treatment groups and over time within each treatment group.
RESULTS None of the measured variables differed significantly between the control and 40% oxygen groups at any time during the postanesthesia period. Within each treatment group, the Paco2 and extent of sedation decreased over time during the postanesthesia period.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that indices of oxygenation did not differ significantly between healthy dogs in which the Fio2 was maintained at > 0.9 and those in which the Fio2 was maintained at 0.4 while anesthetized for ovariohysterectomy. Thus, the addition of nitrogen to the carrier gas for an inhalant anesthetic conferred neither an advantage nor disadvantage in regard to oxygenation during the first hour of anesthesia recovery.
PROCEDURES Cats were randomly assigned to receive maropitant (1 mg/kg [0.45 mg/lb], SC; maropitant group; n = 32) or saline (0.9% NaCl) solution (0.1 mL/kg [0.045 mL/lb], SC; control group; 34) 20 hours before IM administration of dexmedetomidine (20 μg/kg [9.1 μg/lb]) and morphine (0.1 mg/kg). Following administration of dexmedetomidine and morphine, the incidences of emesis, retching, and signs of nausea (sialorrhea and lip licking) were compared between the 2 groups. The aversive behavioral response of each cat to injection of maropitant or saline solution was scored on a visual analogue scale by each of 4 observers who were unaware of the treatment administered.
RESULTS Only 1 of 32 cats in the maropitant group vomited, whereas 20 of 34 control cats vomited. The incidences of emesis and retching for the maropitant group were significantly lower than those for the control group. The incidence of signs of nausea did not differ between the 2 groups. Visual analogue scale scores for the maropitant group were significantly higher than those for the control group.
CONCLUSIONS AND CLINICAL RELEVANCE Results of the present study indicated that administration of maropitant to healthy cats approximately 20 hours prior to administration of dexmedetomidine and morphine significantly decreased the incidence of emesis but did not decrease the incidence of signs of nausea. However, maropitant appeared to cause substantial discomfort when injected SC.
OBJECTIVE To evaluate potential associations between preanesthetic administration of acepromazine or dexmedetomidine and development of arterial hypotension or bradycardia in isoflurane-anesthetized dogs undergoing ovariohysterectomy.
ANIMALS 341 dogs.
PROCEDURES Medical records were searched to identify dogs that underwent ovariohysterectomy between January 2009 and December 2010 and received hydromorphone with acepromazine or dexmedetomidine as preanesthetic agents. Demographic data, sedative and anesthetic drugs, duration of anesthesia, average vaporizer setting, positive pressure ventilation, occurrence of hypotension (mean arterial pressure < 60 mm Hg) or bradycardia (> 50% reduction in heart rate, compared with the preanesthetic value), time to first occurrence and duration of hypotension, and treatment with dopamine or anticholinergic agents were recorded. Data were compared between dogs that received acepromazine and dexmedetomidine. Logistic regression was used to investigate associations between the treatments of interest (and other putative risk factors) and development of hypotension or bradycardia.
RESULTS For dogs that received acepromazine, the odds of developing hypotension were 2.61 times those for dogs that received dexmedetomidine. Hypotension occurred earlier and lasted longer in dogs that received acepromazine, and this group was treated with dopamine more frequently than the group that received dexmedetomidine. Lower body weight was associated with increased odds of hypotension. Odds of developing bradycardia were greater for dogs sedated with dexmedetomidine (vs acepromazine) and for dogs that underwent anesthetic induction with propofol or a ketamine-benzodiazepine combination (vs thiopental).
CONCLUSIONS AND CLINICAL RELEVANCE Anesthetic complications differed between isoflurane-anesthetized dogs undergoing ovariohysterectomy after premedication with acepromazine or dexmedetomidine in this study; future prospective investigations are warranted to investigate these effects in other, less homogenous populations of dogs.
Objective—To determine whether dogs that received eyedrops containing phenylephrine and scopolamine would have a higher mean arterial blood pressure (MAP) when anesthetized than would dogs that did not receive the eyedrops.
Animals—37 nondiabetic and 29 diabetic dogs anesthetized for phacoemulsification and 15 nondiabetic dogs anesthetized for corneal ulcer repair (control dogs).
Procedures—Medical records were reviewed to identify study dogs. Dogs undergoing phacoemulsification received 2 types of eyedrops (10% phenylephrine hydrochloride and 0.3% scopolamine hydrobromide) 4 times during a 2-hour period prior to the procedure. Control dogs did not receive these eyedrops. Heart rate and MAP were measured before surgery in all dogs 10 and 5 minutes before, at the time of (t0), and 5 (t5) and 10 (t10) minutes after atracurium administration.
Results—MAP was greater in the 2 groups that received the eyedrops than in the control group at t0 and t5; at t10, it was greater only for the nondiabetic dogs that received eyedrops. Nine nondiabetic dogs and 1 diabetic dog anesthetized for phacoemulsification had at least 1 MAP value > 131 mm Hg; 73% of MAP values > 131 mm Hg were detected within 10 minutes after atracurium administration. At no time did a control dog have an MAP value > 131 mm Hg.
Conclusions and Clinical Relevance—Anesthetized dogs pretreated with eyedrops containing phenylephrine and scopolamine had higher MAP values than dogs that did not receive the eyedrops, suggesting the drops caused hypertension. Atracurium may interact with the eyedrops and contribute to the hypertension.
OBJECTIVE To evaluate whether the ultrashort-acting neuromuscular blocking agent gantacurium can be used to blunt evoked laryngospasm in anesthetized cats and to determine the duration of apnea without hemoglobin desaturation.
ANIMALS 8 healthy adult domestic shorthair cats.
PROCEDURES Each cat was anesthetized with dexmedetomidine and propofol, instrumented with a laryngeal mask, and allowed to breathe spontaneously (fraction of inspired oxygen, 1.0). The larynx was stimulated by spraying sterile water (0.3 mL) at the rima glottidis; a fiberscope placed in the laryngeal mask airway was used to detect evoked laryngospasm. Laryngeal stimulation was performed at baseline; after IV administration of gantacurium at doses of 0.1, 0.3, and 0.5 mg/kg; and after the effects of the last dose of gantacurium had terminated. Duration of apnea and hemoglobin oxygen saturation (measured by means of pulse oximetry) after each laryngeal stimulation were recorded. Neuromuscular block was monitored throughout the experiment by means of acceleromyography on a pelvic limb.
RESULTS Laryngospasm was elicited in all cats at baseline, after administration of 0.1mg of gantacurium/kg, and after the effects of the last dose of gantacurium had terminated. The 0.3 and 0.5 mg/kg doses of gantacurium abolished laryngospasm in 3 and 8 cats, respectively, and induced complete neuromuscular block measured at the pelvic limb; the mean ± SE duration of apnea was 2 ± 1 minutes and 3 ± 1.5 minutes, respectively. Hemoglobin oxygen saturation did not decrease significantly after administration of any dose of gantacurium.
CONCLUSIONS AND CLINICAL RELEVANCE Gantacurium may reduce tracheal intubation-associated morbidity in cats breathing oxygen.
Objective—To determine accuracy and precision of a
point-of-care hemoglobinometer for measuring hemoglobin
concentration and estimating PCV in horses.
Procedure—Blood samples were obtained from 43
horses examined at a veterinary teaching hospital.
Hemoglobin concentration was measured with the
hemoglobinometer and by means of the standard
cyanmethemoglobin method; PCV was measured by
centrifugation. Blood samples were also obtained
from 12 healthy horses, and PCV of aliquots of these
samples was altered to approximately 5 to 80% by
removing or adding plasma. Hemoglobin concentration
and PCV were then measured.
Results—For samples from the clinic patients, hemoglobin
concentrations obtained with the hemoglobinometer
were less than concentrations obtained with
the cyanmethemoglobin method; however, there was
a linear relationship between concentrations obtained
with the 2 methods. Breed, sex, body weight, and
duration of sample storage did not significantly affect
the difference between hemoglobin concentrations
obtained with the 2 methods. There was a significant
linear relationship between PCV and hemoglobinometer
hemoglobin concentration (PCV = [2.83 X
hemoglobin concentration] − 0.62). For samples from
the healthy horses, a substantial negative bias was
evident with the hemoglobinometer when hemoglobin
concentration exceeded 16 g/dL.
Conclusions and Clinical Relevance—Results suggest
that this hemoglobinometer is reasonably accurate
and precise when used to measure hemoglobin
concentration in blood samples from horses with a
hemoglobin concentration < 16 g/dL. (J Am Vet Med
OBJECTIVE To evaluate the efficacy of each of 3 incremental doses of MK-467 for alleviation of dexmedetomidine-induced hemodynamic depression in isoflurane-anesthetized cats.
ANIMALS 6 healthy adult domestic shorthair cats.
PROCEDURES Each cat was anesthetized with isoflurane and received a target-controlled infusion of dexmedetomidine estimated to maintain the plasma dexmedetomidine concentration at 10 ng/mL throughout the experiment. Heart rate (HR) and direct arterial pressures were measured at baseline (isoflurane administration only), during dexmedetomidine infusion, and before and after IV administration of each of 3 serially increasing doses (15, 30, and 60 μg/kg) of MK-467. Cardiac index (CI) and systemic vascular resistance (SVR) were recorded at baseline, during dexmedetomidine infusion, and at the mean arterial pressure nadir after administration of the 30- and 60-μg/kg doses of MK-467.
RESULTS Compared with baseline values, the dexmedetomidine infusion significantly decreased HR and increased arterial pressures. Each dose of MK-467 caused a significant decrease in arterial pressures and a significant, albeit clinically irrelevant, increase in HR (≤ 10%). Following administration of the 30- and 60-μg/kg doses of MK-467, all cats developed clinical hypotension (mean arterial pressure, < 60 mm Hg) even though CI and SVR returned to baseline values.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated administration of small doses of MK-467 to isoflurane-anesthetized cats receiving dexmedetomidine restored CI and SVR, but caused a substantial decrease in arterial pressures and only a marginal increase in HR. Therefore, caution should be used when MK-467 is administered to alleviate dexmedetomidine-induced hemodynamic depression in isoflurane-anesthetized cats.
To compare the duration of bupivacaine liposome suspension in the dog with that of bupivacaine and dexmedetomidine following a perineural injection.
8 healthy Beagles.
The left sciatic nerve of each dog was randomly assigned to an ultrasound-guided perineural injection with either bupivacaine liposome suspension (BLS) or with 0.5% bupivacaine with dexmedetomidine (1 µg/mL) (BUP-DEX). The contralateral nerve was assigned to the alternate agent. The sensory, motor, and proprioceptive functions were evaluated before the injection (baseline) and at 4, 10, 24, 48, 72, and 96 hours.
The block in 1 limb in the BLS treatment appeared to have failed (data set excluded). The motor scores of 2 individuals could not be evaluated leaving 5 limbs to evaluate in the BLS treatment and 6 in the BUP-DEX.
A total of 6 out of 7 limbs in the BLS achieved a complete sensory block. In 3 out of 5 treatments with BLS, motor block was only partial and in 2 not apparent at all. Proprioceptive block was partial in 5 out of 7 dogs in the BLS treatment. All functions were still completely obliterated at 10 hours in 6 cases in treatment BUP-DEX. All functions were restored in all cases by 96 and 24 hours after administration of BLS and BUP-DEX, respectively.
The blockade characteristics of bupivacaine liposome suspension were effective and long lasting. Motor and proprioceptive deficits may be inconsistent over time.
Objective—To evaluate the effects of hydromorphone,
hydromorphone and glycopyrrolate, medetomidine,
and butorphanol premedication on the difficulty
and time required to pass an endoscope into the
stomach and duodenum of cats anesthetized with
ketamine and isoflurane.
Design—Randomized complete block crossover
Animals—8 purpose-bred adult female cats.
Procedures—Each cat was premedicated and anesthetized
4 times with an interval of at least 7 days
between procedures. Cats were premedicated with
hydromorphone, hydromorphone and glycopyrrolate,
medetomidine, or butorphanol administered IM. Twenty
minutes after premedication, sedation was assessed by
use of a subjective ordinal scale. Cats received ketamine
administered IM, and 10 minutes later a cuffed
orotracheal tube was placed and anesthesia maintained
with isoflurane. Cats breathed spontaneously throughout
the procedure. When end-tidal isoflurane concentration
was stable at 1.4% for 15 minutes, endoscopy
was begun. The times required to pass the endoscope
through the cardiac and pyloric sphincters were recorded,
and the difficulty of endoscope passage was scored
by use of a subjective ordinal scale.
Results—No significant differences in difficulty or
time required to pass the endoscope through the cardiac
and pyloric sphincters were found among premedicant
groups. Premedication with medetomidine
resulted in the greatest degree of sedation and
longest time to return to sternal recumbency.
Conclusions and Clinical Relevance—Results suggest
that hydromorphone, hydromorphone and glycopyrrolate,
medetomidine, and butorphanol at the
doses tested can be used satisfactorily to premedicate
cats prior to general anesthesia for gastroduodenoscopy.
(J Am Vet Med Assoc 2004;225:540–544)