Sildenafil does not have a significant effect on the portal vein velocity, cross-sectional area, and congestion index in the dog

In veterinary medicine, sildenafil is most frequently used to treat pulmonary hypertension, but has also been investigated and used as a treatment for congenital megaesophagus and ischemic infarcts. With the increasing use, the effects of sildenafil on the portal vasculature in the dog have not been previously evaluated. The purpose of this study was to evaluate the effects sildenafil has on the portal vasculature, which anecdotally may have caused decreased portal vein pressure in an adult dog. The ultrasound cross-sectional area of the aorta, cross-sectional area of the portal vein, and portal vein blood flow velocity were acquired in dogs prior to administration, and 45, 90, and 120 min after oral administration of sildenafil for the treatment of pulmonary hypertension. Thirteen dogs were enrolled in the study. No statistically significant difference was detected between all measured values and the congestion index at all time points. A trend was identified that demonstrated progressively lower portal vein velocity with each evaluation, but this was not significant. Although this study had a small sample size, sildenafil was not shown to have a significant effect on the size or blood flow velocity of the portal vasculature. The hepatic buffer system, designed to maintain a constant blood flow to the liver, may be a contributing factor, but further studies with a larger sample size will be required for further evaluation.

Analgesic and Cardiopulmonary Effects of Epidural Romifidine and Morphine Combination in Horses

The study aim is to compare the effects of epidural administration of two different doses of romifidine combined with morphine in horses. A prospective crossover blinded experimental design was used. Five adult healthy horses two males and three females with a mean body weight of 380 ± 45 Kg (335-425 kg), were studied. Treatments consisted of romifidine 30 μg/kg (R30) or 60 μg/kg (R60) combined with morphine 0.1 mg/kg with a washout interval of 72 hours, administered through an epidural catheter placed at the first intercoccygeal space. Heart rate (HR) and respiratory rate (f_R), pH, blood gases, arterial blood pressures (mmHg), and threshold for electrical noxious stimulation was evaluated for 120 minutes and after 240 minutes of epidural injection. Data were collected before injections and every 15 minutes for 120 minutes, and at 240 minutes of epidural administration. Significant sedation occurred in both treatments with no statistically significant difference between them. There were significant changes in f_R and HR from baseline but no difference between treatments. Arterial blood pressures were significantly lower in R60 treatment from 75 up to 120 minutes post epidural injection. Analgesia was considered moderate for both treatments lasting longer with romifidine at 60 μg/kg. Epidurally administered romifidine and morphine combination in horses produces dose-dependent sedation, arterial hypotension, and antinociceptive effects.

Pharmacokinetics and pharmacodynamics of intravenous continuous rate infusion and repeated intramuscular administration of dexmedetomidine in standing horses

An ideal dexmedetomidine protocol has yet to be determined for standing sedation in horses. It was hypothesized that an IV bolus followed by CRI dexmedetomidine would have a quicker increase in plasma concentrations compared with repeated IM injections. In a crossover design, eight adult, female horses were randomly placed into two groups: the CRI group (IV bolus dexmedetomidine at 0.005 mg/kg followed by a CRI at 0.01 mg/kg/h for 15 min then 0.005 mg/kg/h for 60 min) and the IM group (dexmedetomidine at 0.01 mg/kg, followed by 0.005 mg/kg in 30-min intervals for 60 min). Clearance and elimination half-life were 134 ± 67.4 ml/kg/min and 44.3 ± 26.3 min, respectively, in the CRI group, and apparent clearance and half-life were 412 ± 306 ml/kg/min (Cl/F) and 38.9 ± 18.6 min, respectively, in the IM group. Analgesia was evaluated using mechanical pressure threshold. Intravenous dexmedetomidine produced faster onset of sedation and increased pressure threshold compared with IM administration. Individual horses had a large variability in dexmedetomidine plasma concentrations between CRI and IM administration. The odds of a decreased GI motility following IV administration was 12.34 times greater compared with IM administration.

General anesthesia with an injectable 8% v/v sevoflurane lipid emulsion administered intravenously to dogs

OBJECTIVE

To evaluate the potential of an intravenous (IV) sevoflurane formulation for maintenance of general anesthesia in dogs.

STUDY DESIGN

Prospective crossover design.

ANIMALS

Six healthy, mature, mixed-breed dogs, four males and two females, weighing 11.7 ± 3.4 kg.

METHODS

Anesthesia was induced and maintained with propofol IV for instrumentation. Baseline measurements were recorded before administration of either sevoflurane in oxygen (Sevo-Inh) or lipid-emulsified sevoflurane 8% v/v in 30% Intralipid IV (Sevo-E), 0.5 mL kg(-1) over 5 minutes followed by an infusion at 0.1-0.3 mL kg(-1)  minute(-1) . Dogs were breathing spontaneously. The 'up-and-down' technique was used to determine the minimum alveolar concentration (MAC) of sevoflurane. Over 120 minutes, a tail clamp was applied every 15 minutes and sevoflurane administration was adjusted depending on the response. End-tidal sevoflurane concentration and variables were recorded at 30, 60, 90, and 120 minutes: heart rate (HR), systemic arterial pressure (sAP), respiratory rate (fR ), end-tidal carbon dioxide tension, hemoglobin oxygen saturation (SaO2 ), arterial pH and blood gases, blood urea nitrogen, alanine aminotransferase, creatine kinase, gamma-glutamyl transferase, and aspartate aminotransferase.

RESULTS

There were no significant differences between treatments for HR, sAP, fR , SaO2 , and biochemical variables (p > 0.05). pH and HCO3-were significantly decreased, and PaCO2 increased from baseline in Sevo-E (p < 0.05). MAC was significantly lower for Sevo-E than for Sevo-Inh, although the required dose of sevoflurane (g hour(-1) ) to maintain general anesthesia was not significantly different between treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of 8% v/v sevoflurane lipid emulsion IV was effective in maintaining general anesthesia in dogs, but resulted in moderate cardiopulmonary depression, metabolic and respiratory acidosis. The amount of sevoflurane (g hour(-1) ) required to maintain general anesthesia was significantly lower for inhaled than for IV sevoflurane.

Epidural administration of tiletamine/zolazepam in horses

OBJECTIVES

To evaluate the analgesic, physiologic, and behavioral effects of the epidural administration of tiletamine/zolazepam in horses.

STUDY DESIGN

Prospective, double-blind, randomized experimental study.

ANIMALS

Five adult, healthy horses aged 10-16 years and weighing (mean +/- SD) 400 +/- 98 kg.

METHODS

The horses were sedated with 1.0 mg kg(-1) intravenous (IV) xylazine, and an epidural catheter was placed into the first intercoccygeal intervertebral space. After a 48-hour resting period, epidural tiletamine/zolazepam, 0.5 mg kg(-1) (treatment I) or 1.0 mg kg(-1) (treatment II), diluted up to 5 mL in sterile water, was administered with a 1-week interval between the treatments. Heart rate, respiratory rate, arterial blood pressure, and sedation were evaluated. In order to evaluate the respiratory effects, blood from the carotid artery was withdrawn at time 0 (baseline), and then after 60 and 240 minutes. Analgesia was evaluated by applying a noxious stimulus with blunt-tipped forceps on the perineal region, and graded as complete, moderate, or absent. Data were collected before tiletamine/zolazepam administration and at 15-minute intervals for 120 minutes, and 4 hours after tiletamine/zolazepam administration. Data were analyzed with anova and Bonferroni's test with p < 0.05.

RESULTS

The results showed no significant difference between treatments in cardiovascular and respiratory measurements. Sedation was observed with both doses, and it was significantly different from baseline at 60, 75, and 90 minutes in treatment II. Moderate analgesia and locomotor ataxia were observed with both the treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

The results suggest that caudal epidural 0.5 and 1.0 mg kg(-1) tiletamine/zolazepam increases the threshold to pressure stimulation in the perineal region in horses. The use of epidural tiletamine/zolazepam could be indicated for short-term moderate epidural analgesia. There are no studies examining spinal toxicity of Telazol, and further studies are necessary before recommending clinical use of this technique.

Effects of epidural opioid analgesics on heart rate, arterial blood pressure, respiratory rate, body temperature, and behavior in horses

Heart rate, arterial blood pressures, respiratory rate, body temperature, and central nervous system excitement were compared before and after epidural administration of morphine (0.1 mg/kg), butorphanol (0.08 mg/kg), alfentanil (0.02 mg/kg), tramadol (1.0 mg/kg), the k-opioid agonist U50488H (0.08 mg/kg), or sterile water using an incomplete Latin square crossover design in five conscious adult horses. Treatments were administered into the first intercoccygeal epidural space. Significant (P <.05) reductions in respiratory rate were detected after epidural administration of morphine, alfentanil, U50488H, and sterile water. Additionally, significant (P <.05) head ptosis was observed within the first hour after administration of morphine, U50488H, and tramadol, but neither of these changes appeared to be of clinical significance. No treatment-related changes in motor activity or behavior were observed.

Epidural anesthesia and analgesia in horses

Intercoccygeal, or caudal, epidural injection of local anesthetics is a convenient method of producing analgesia and local anesthesia of the tail and perineal structures in conscious standing horses. This technique has been further developed to provide long duration analgesia and anesthesia by placement of catheters into the epidural space of horses. More recently, opioid, alpha-2 adrenergic agonists, ketamine and other analgesic agents have been administered by caudal epidural injection, providing pain relief in both conscious, standing and anesthetized, recumbent horses. This chapter describes the development of different anesthetic and analgesic epidural techniques in horses, methods for epidural injection and catheterization, and reviews the current literature related to epidural analgesia and pain control in horses.

Evaluation of the analgesic effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H in horses

OBJECTIVE

To evaluate and compare effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H on avoidance threshold to noxious electrical stimulation over the dermatomes of the perineal, sacral, lumbar, and thoracic regions in horses.

ANIMALS

5 healthy adult horses.

PROCEDURE

Using a Latin square complete repeated-measures design, horses were randomly assigned to receive 1 of 6 treatments (morphine, alfentanil, butorphanol, tramadol, U50488H, or sterile water) at intervals of at least 7 days. Agents were injected epidurally at the first intercoccygeal epidural space, and electrical stimulation was applied at repeated intervals for 24 hours to the dermatomes of the perineal, sacral, lumbar, and thoracic regions. Avoidance threshold to electrical stimulation was recorded.

RESULTS

Administration of butorphanol, U50488H, and sterile water did not induce change in avoidance threshold. Alfentanil increased avoidance threshold during the first 4 hours, but not significantly. Tramadol and morphine significantly increased threshold and analgesic effects. Complete analgesia (avoidance threshold, >40 V) in the perineal and sacral areas was achieved 30 minutes after tramadol injection, compared with 6 hours after morphine injection. Duration of complete analgesia was 4 hours and 5 hours after tramadol and morphine injections, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Epidural administration of tramadol and morphine induces long-lasting analgesia in healthy adult horses. Epidural administration of opioids may provide long-lasting analgesia in horses without excitation of the CNS.

Effects of lumbosacral subarachnoid catheterization in horses

OBJECTIVES

To evaluate the effects of long duration subarachnoid catheterization in horses on cerebrospinal fluid (CSF) cellularity and bacteriology, arterial blood pressure, heart rate, respiratory rate, rectal body temperature, and spontaneous locomotor activity.

STUDY DESIGN

Prospective experimental study.

ANIMAL

Five clinically normal healthy adults horses weighing 511 +/- 47 kg.

METHODS

Subarachnoid catheters were placed using sedation and local anesthesia and maintained for 48 hours in standing horses. Cerebrospinal fluid samples were tested for cellularity and bacteria growth. Heart rate, respiratory rate, arterial blood pressure, and body temperature were recorded. Locomotor activity was graded. One-way repeated measures ANOVA and Bonferroni's test were used to statistically compare data from baseline to 12, 24, and 48 hours.

RESULTS

Subarachnoid catheterization in horses produced an acute inflammatory reaction after 12 hours of catheterization, as evidenced by a statistically significant increase in CSF white blood cell count. No bacterial contamination was encountered. No significant differences were found in heart rate, respiratory rate, body temperature, and arterial blood pressure. The horses did not develop motor ataxia or proprioceptive deficits during 48 hours of catheterization.

CONCLUSIONS

Results of this study suggest that 48 hours of subarachnoid catheterization in horses does not produce clinical signs of neurologic dysfunction or cardiovascular and respiratory changes, even though an inflammatory reaction occurred.

CLINICAL RELEVANCE

Subarachnoid catheterization in horses is preferred for monitoring CSF pressure or for repeated collection. Understanding the effects of catheterization alone, allows the clinician to better interpret abnormalities in CSF collected.