Objective—To evaluate the degree of postoperative pain in dogs undergoing elective castration or ovariohysterectomy (OHE); determine whether an association exists between surgeon experience, incision length, or surgery duration and degree of postoperative pain; and determine whether analgesic treatment decreases expression of postoperative pain behaviors.
Design—Randomized controlled clinical trial.
Animals—426 client-owned dogs undergoing OHE or castration.
Procedures—Dogs underwent OHE or castration performed by an experienced veterinarian or a fourth-year veterinary student. Dogs were randomly assigned to 1 of 4 treatment groups: no perioperative analgesic treatment (n = 44), preoperative administration of morphine (144), preoperative administration of nalbuphine (119), and postoperative administration of ketoprofen (119). Dogs were evaluated while in the hospital before anesthesia and for 4 hours after surgery and once a day at home for 3 days after surgery.
Results—Dogs in all 4 groups had significant increases in overall pain scores after surgery, compared with baseline scores. There were significant differences among groups, with control dogs having significantly higher increases in overall pain scores than dogs in the other groups. Factors that did not influence the frequency or severity of pain-related behaviors included breed, individual hospital, anesthetic induction protocol, surgeon experience, and duration of surgery.
Conclusions and Clinical Relevance—Results suggested that dogs expressed behaviors suggestive of pain following OHE and castration, that analgesic treatment mitigated the expression of pain-related behaviors, and that surgeon experience and surgery duration did not have any effect on expression of pain-related behaviors.
Procedure—Lidocaine hydrochloride (loading infusion, 1.3 mg/kg during a 15-minute period [87.5 μg/kg/min]; maintenance infusion, 50 μg/kg/min for 60 to 90 minutes) was administered IV to dorsally recumbent anesthetized horses. Blood samples were collected before and at fixed time points during and after lidocaine infusion for analysis of serum drug concentrations by use of liquid chromatography-mass spectrometry. Serum lidocaine concentrations were evaluated by use of standard noncompartmental analysis. Selected cardiopulmonary variables, including heart rate (HR), mean arterial pressure (MAP), arterial pH, PaCO2, and PaO2, were recorded. Recovery quality was assessed and recorded.
Results—Serum lidocaine concentrations paralleled administration, increasing rapidly with the initiation of the loading infusion and decreasing rapidly following discontinuation of the maintenance infusion. Mean ± SD volume of distribution at steady state, total body clearance, and terminal half-life were 0.70 ± 0.39 L/kg, 25 ± 3 mL/kg/min, and 65 ± 33 minutes, respectively. Cardiopulmonary variables were within reference ranges for horses anesthetized with inhalation anesthetics. Mean HR ranged from 36 ± 1 beats/min to 43 ± 9 beats/min, and mean MAP ranged from 74 ± 18 mm Hg to 89 ± 10 mm Hg. Recovery quality ranged from poor to excellent.
Conclusions and Clinical Relevance—Availability of pharmacokinetic data for horses with gastrointestinal tract disease will facilitate appropriate clinical dosing of lidocaine.
Objective—To compare cardiovascular effects of sevoflurane alone and sevoflurane plus an IV infusion of lidocaine in horses.
Animals—8 adult horses.
Procedures—Each horse was anesthetized twice via IV administration of xylazine, diazepam, and ketamine. During 1 anesthetic episode, anesthesia was maintained by administration of sevoflurane in oxygen at 1.0 and 1.5 times the minimum alveolar concentration (MAC). During the other episode, anesthesia was maintained at the same MAC multiples via a reduced concentration of sevoflurane plus an IV infusion of lidocaine. Heart rate, arterial blood pressures, blood gas analyses, and cardiac output were measured during mechanical (controlled) ventilation at both 1.0 and 1.5 MAC for each anesthetic protocol and during spontaneous ventilation at 1 of the 2 MAC multiples.
Results—Cardiorespiratory variables did not differ significantly between anesthetic protocols. Blood pressures were highest at 1.0 MAC during spontaneous ventilation and lowest at 1.5 MAC during controlled ventilation for either anesthetic protocol. Cardiac output was significantly higher during 1.0 MAC than during 1.5 MAC for sevoflurane plus lidocaine but was not affected by anesthetic protocol or mode of ventilation. Clinically important hypotension was detected at 1.5 MAC for both anesthetic protocols.
Conclusions and Clinical Relevance—Lidocaine infusion did not alter cardiorespiratory variables during anesthesia in horses, provided anesthetic depth was maintained constant. The IV administration of lidocaine to anesthetized nonstimulated horses should be used for reasons other than to improve cardiovascular performance. Severe hypotension can be expected in nonstimulated horses at 1.5 MAC sevoflurane, regardless of whether lidocaine is administered.
Objective—To determine effects of a continuous rate infusion of lidocaine on the minimum alveolar concentration (MAC) of sevoflurane in horses.
Animals—8 healthy adult horses.
Procedures—Horses were anesthetized via IV administration of xylazine, ketamine, and diazepam; anesthesia was maintained with sevoflurane in oxygen. Approximately 1 hour after induction, sevoflurane MAC determination was initiated via standard techniques. Following sevoflurane MAC determination, lidocaine was administered as a bolus (1.3 mg/kg, IV, over 15 minutes), followed by constant rate infusion at 50 μg/kg/min. Determination of MAC for the lidocaine-sevoflurane combination was started 30 minutes after lidocaine infusion was initiated. Arterial blood samples were collected after the lidocaine bolus, at 30-minute intervals, and at the end of the infusion for measurement of plasma lidocaine concentrations.
Results—IV administration of lidocaine decreased mean ± SD sevoflurane MAC from 2.42 ± 0.24% to 1.78 ± 0.38% (mean MAC reduction, 26.7 ± 12%). Plasma lidocaine concentrations were 2,589 ± 811 ng/mL at the end of the bolus; 2,065 ± 441 ng/mL, 2,243 ± 699 ng/mL, 2,168 ± 339 ng/mL, and 2,254 ± 215 ng/mL at 30, 60, 90, and 120 minutes of infusion, respectively; and 2,206 ± 329 ng/mL at the end of the infusion. Plasma concentrations did not differ significantly among time points.
Conclusions and Clinical Relevance—Lidocaine could be useful for providing a more balanced anesthetic technique in horses. A detailed cardiovascular study on the effects of IV infusion of lidocaine during anesthesia with sevoflurane is required before this combination can be recommended.
Objective—To determine the effect of a constant-rate
infusion of fentanyl on minimum alveolar concentration
(MAC) of isoflurane and to determine the interaction
between fentanyl and a benzodiazepine agonist
(diazepam) and antagonist (flumazenil) in isoflurane-anesthetized
Animals—8 mixed-breed adult dogs.
Procedure—Dogs were anesthetized with isoflurane
3 times during a 6-week period. After a 30-minute
equilibration period, each MAC determination was
performed in triplicate, using standard techniques.
Fentanyl was administered as a bolus (10 µg/kg of
body weight, IV) that was followed by a constant infusion
(0.3 µg/kg per min, IV) throughout the remainder
of the experiment. After determining isoflurane-fentanyl
MAC in triplicate, each dog received saline
(0.9% NaCl) solution, diazepam, or flumazenil. After
30 minutes, MAC was determined again.
Results—Fentanyl significantly decreased isoflurane
MAC (corrected to a barometric pressure of 760 mm
Hg) from 1.80 ± 0.21 to 0.85 ± 0.14%, a reduction of
53%. Isoflurane-fentanyl-diazepam MAC (0.48 ±
0.29%) was significantly less than isoflurane-fentanylsaline
MAC (0.79 ± 0.21%). Percentage reduction in
isoflurane MAC was significantly greater for fentanyldiazepam
(74%), compared with fentanyl-saline (54%)
or fentanyl-flumazenil (61%). Mean fentanyl concentrations
for the entire experiment were increased over
time and were higher in the diazepam group than the
saline or flumazenil groups.
Conclusion and Clinical Relevance—Fentanyl
markedly decreased isoflurane MAC in dogs.
Diazepam, but not flumazenil, further decreased
isoflurane-fentanyl MAC. Our results indicate that
diazepam enhances, whereas flumazenil does not
affect, opioid-induced CNS depression and, possibly,
analgesia in dogs. (Am J Vet Res 2001;62:555–560)
Objective—To evaluate the use of xylazine and ketamine
for total IV anesthesia in horses.
Procedure—Anesthetic induction was performed on
4 occasions in each horse with xylazine (0.75 mg/kg,
IV), guaifenesin (75 mg/kg, IV), and ketamine
(2 mg/kg, IV). Intravenous infusions of xylazine and
ketamine were then started by use of 1 of 6 treatments
as follows for which 35, 90, 120, and 150 represent
infusion dosages (µg/kg/min) and X and K represent
xylazine and ketamine, respectively: X35+K90
with 100% inspired oxygen (O2), X35+K120-O2,
X35+K150-O2, X70+K90-O2, K150-O2, and X35+K120
with a 21% fraction of inspired oxygen (ie, air).
Cardiopulmonary measurements were performed.
Response to a noxious electrical stimulus was
observed at 20, 40, and 60 minutes after induction.
Times to achieve sternal recumbency and standing
were recorded. Quality of sedation, induction, and
recovery to sternal recumbency and standing were
Results—Heart rate and cardiac index were higher
and total peripheral resistance lower in K150-O2 and
X35+K120-air groups. The mean arterial pressure was
highest in the X35+K120-air group and lowest in the
K150-O2 group (125 ± 6 vs 85 ± 8 at 20 minutes,
respectively). Mean PaO2 was lowest in the
X35+K120-air group. Times to sternal recumbency
and standing were shortest for horses receiving
K150-O2 (23 ± 6 minutes and 33 ± 8 minutes, respectively)
and longest for those receiving X70+K90-O2
(58 ± 28 minutes and 69 ± 27 minutes, respectively).
Conclusions and Clinical Relevance—Infusions of
xylazine and ketamine may be used with oxygen supplementation
to maintain 60 minutes of anesthesia in
healthy adult horses. (Am J Vet Res 2005;66:1002–1007)
Objective—To evaluate the effects on oxygen delivery
(DO2) of 2.5 and 5 cm H2O of positive end-expiratory
pressure (PEEP) applied to the dependent lung
during one-lung ventilation (OLV) in anesthetized dogs
with a closed thoracic cavity.
Animals—7 clinically normal adult Walker Hound
Procedure—Dogs were anesthetized, and catheters
were inserted in a dorsal pedal artery and the pulmonary
artery. Dogs were positioned in right lateral
recumbency, and data were collected during OLV
(baseline), after application of 2.5 cm H2O of PEEP for
15 minutes during OLV, and after application of 5 cm
H2O of PEEP for 15 minutes during OLV.
Hemodynamic and respiratory variables were analyzed
and calculations performed to obtain DO2, and
values were compared among the various time points
by use of an ANOVA for repeated measures.
Results—PEEP induced a significant decrease in
shunt fraction that resulted in a significant increase in
arterial oxygen saturation. However, it failed to significantly
affect arterial oxygen content (CaO2) or cardiac
output. Thus, DO2 was not affected in healthy normoxemic
dogs as a net result of the application of
Conclusions and Clinical Relevance—The use of
PEEP during OLV in anesthetized dogs with a closed
thoracic cavity did not affect DO2. Use of PEEP during
OLV in dogs with a closed thoracic cavity is recommended
because it does not affect cardiac output and
any gain in CaO2 will be beneficial for DO2 in critically
ill patients. (Am J Vet Res 2005;66:978–983)
Objective—To evaluate the effects of one-lung ventilation
(OLV) on oxygen delivery (DO2) in anesthetized
dogs with a closed thoracic cavity.
Animals—7 clinically normal adult Walker Hound
Procedure—Dogs were anesthetized. Catheters
were inserted in a dorsal pedal artery and the pulmonary
artery. Dogs were positioned in right lateral
recumbency. Data were collected at baseline (PaCO2
of 35 to 45 mm Hg), during two-lung ventilation, and
15 minutes after creating OLV. Hemodynamic and respiratory
variables were analyzed and calculations performed
to obtain DO2, and values were compared
among the various time points by use of an ANOVA
for repeated measures.
Results—OLV induced a significant augmentation of
shunt fraction that resulted in a significant reduction
in PaO2, arterial oxygen saturation, and arterial oxygen
content. Cardiac index was not significantly changed.
The net result was that DO2 was not significantly
affected by OLV.
Conclusions and Clinical Relevance—Use of OLV in
healthy dogs does not induce significant changes in
DO2, which is the ultimate variable to use when evaluating
tissue oxygenation. One-lung ventilation can
be initiated safely in dogs before entering the thoracic
cavity during surgery. Additional studies are necessary
to evaluate OLV in clinically affected patients and
variations in age, body position, and type of anesthetic
protocol. (Am J Vet Res 2005;66:973–977)
Objective—To assess the pharmacokinetics and pharmacodynamics of morphine in llamas.
Animals—6 healthy adult llamas.
Procedures—Llamas received morphine sulfate in a randomized crossover design. In phase 1, they received IV or IM administration of morphine at 0.05 or 0.5 mg/kg, respectively; in phase 2, they received IV administration of morphine at 0.05, 0.25, or 0.5 mg/kg. Plasma morphine and morphine-6-glucuronide concentrations were determined by validated methods. Body temperature, heart rate, respiratory rate, sedation, and analgesia were assessed and compared with plasma concentrations by regression analysis.
Results—Total body clearance was similar between IV administration of morphine sulfate at 0.25 and 0.5 mg/kg (mean ± SD, 25.3 ± 6.9 mL/min/kg and 27.3 ± 5.9 mL/min/kg, respectively), and linearity was demonstrated between these doses. Bioavailability of morphine following IM administration at 0.5 mg/kg was 120 ± 30%. Body temperature and sedation increased as the dose of morphine administered increased. Heart rate was unaffected by varying doses. Respiratory rate decreased as dose increased. Analgesia was difficult to assess as a result of high individual variability. Intravenous administration of morphine at 0.25 mg/kg provided the most consistent increase in tolerance to electric stimulation. Pharmacodynamic modeling revealed a sigmoidal relationship between plasma concentration and sedation score.
Conclusions and Clinical Relevance—Morphine was characterized by a large apparent volume of distribution and high systemic clearance in llamas. A prolonged half-life was observed with IM injection. Intravenous administration of morphine sulfate at 0.25 mg/kg every 4 hours is suggested for further study.
Objective—To evaluate herd-level risk factors for
seropositive status of cattle to 1 or more bluetongue
Animals—110 herds of cattle in Nebraska, North
Dakota, and South Dakota.
Procedure—Blood samples were collected before
and after the vector season. Samples were tested
for antibodies against bluetongue virus by use of a
commercially available competitive ELISA. Factors
evaluated included descriptors of geographic location
and management practices. Trapping of insect
vectors was conducted to evaluate vector status on
a subset of 57 operations. A multivariable logistic
regression model was constructed to evaluate associations.
Results—For the full data set, altitude and latitude
were associated with risk of having seropositive cattle
(an increase in altitude was associated with an
increase in risk, and a more northerly location was
associated with a decrease in risk of a premise having
seropositive cattle). Import of cattle from selected
states was associated with an increase in risk of having
seropositive cattle. From the subset of herds with
data on vector trapping, altitude and latitude were
associated with risk of having seropositive cattle, similar
to that for the full model. However, commingling
with cattle from other herds was associated with a
decrease in risk of seropositivity.
Conclusions and Clinical Relevance—Findings
reported here may be useful in generating additional
hypotheses regarding the ecologic characteristics of
bluetongue viruses and other vector-borne diseases
of livestock. Sentinel surveillance programs are useful
for documenting regionalization zones for diseases,
which can be beneficial when securing international
markets for animals and animal products. (Am J Vet