Deborah V. Wilson

Intravenous tramadol: effects, nociceptive properties, and pharmacokinetics in horses.

OBJECTIVE To determine the optimal dose, serum concentrations and analgesic effects of intravenous (IV) tramadol in the horse. STUDY DESIGN Two-phase blinded, randomized, prospective crossover trial. ANIMALS Seven horses (median age 22.5 years and mean weight 565 kg). METHODS Horses were treated every 20 minutes with incremental doses of tramadol HCl (0.1-1.6 mg kg-1) or with saline. Heart rate, respiratory rate, step frequency, head height, and sweating, trembling, borborygmus and head nodding scores were recorded before and up to 6 hours after treatment. In a second study, hoof withdrawal and skin twitch reflex latencies (HWRL and STRL) to a thermal stimulus were determined 5 and 30 minutes, and 1, 2, 4 and 6 hours after bolus IV tramadol (2.0 mg kg-1) or vehicle. Blood samples were taken to determine pharmacokinetics. RESULTS Compared to saline, tramadol caused no change in heart rate, step frequency or sweating score. Respiratory rate, head height, and head nodding and trembling scores were transiently but significantly increased and borborygmus score was decreased by high doses of tramadol. Following cumulative IV administration of 3.1 mg kg-1 and bolus IV administration of 2 mg kg-1, the elimination half-life of tramadol was 1.91 ± 0.33 and 2.1 ± 0.9 hours, respectively. Baseline HWRL and STRL were 4.16 ± 1.0 and 3.06 ± 0.99 seconds, respectively, and were not significantly prolonged by tramadol. CONCLUSION AND CLINICAL RELEVANCE IV tramadol at cumulative doses of up to 3.1 mg kg-1 produced minimal transient side effects but 2.0 mg kg-1 did not provide analgesia, as determined by response to a thermal nociceptive stimulus.OBJECTIVE To determine the optimal dose, serum concentrations and analgesic effects of intravenous (IV) tramadol in the horse. STUDY DESIGN Two-phase blinded, randomized, prospective crossover trial. ANIMALS Seven horses (median age 22.5 years and mean weight 565 kg). METHODS Horses were treated every 20 minutes with incremental doses of tramadol HCl (0.1-1.6 mg kg(-1)) or with saline. Heart rate, respiratory rate, step frequency, head height, and sweating, trembling, borborygmus and head nodding scores were recorded before and up to 6 hours after treatment. In a second study, hoof withdrawal and skin twitch reflex latencies (HWRL and STRL) to a thermal stimulus were determined 5 and 30 minutes, and 1, 2, 4 and 6 hours after bolus IV tramadol (2.0 mg kg(-1)) or vehicle. Blood samples were taken to determine pharmacokinetics. RESULTS Compared to saline, tramadol caused no change in heart rate, step frequency or sweating score. Respiratory rate, head height, and head nodding and trembling scores were transiently but significantly increased and borborygmus score was decreased by high doses of tramadol. Following cumulative IV administration of 3.1 mg kg(-1) and bolus IV administration of 2 mg kg(-1), the elimination half-life of tramadol was 1.91 +/- 0.33 and 2.1 +/- 0.9 hours, respectively. Baseline HWRL and STRL were 4.16 +/- 1.0 and 3.06 +/- 0.99 seconds, respectively, and were not significantly prolonged by tramadol. CONCLUSION AND CLINICAL RELEVANCE IV tramadol at cumulative doses of up to 3.1 mg kg(-1) produced minimal transient side effects but 2.0 mg kg(-1) did not provide analgesia, as determined by response to a thermal nociceptive stimulus.

Postanesthetic esophageal dysfunction in 13 dogs.

Thirteen dogs with postanesthetic esophageal dysfunction were identified; 10 of these animals had esophageal stricture. Regurgitation was noted in six dogs during the inciting anesthetic event. Clinical problems common to all dogs included vomiting/regurgitation and weight loss. Coughing was noted in six dogs, and aspiration pneumonia was present in four of these dogs. The associated mortality rate was 23%. The duration of symptoms ranged from 17 to 150 days, and the diagnosis was often delayed (up to 76 days from onset of clinical signs to diagnosis). Postanesthetic esophageal dysfunction was a debilitating and costly problem that developed in one dog despite current preventative treatment.

Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses

OBJECTIVE To assess the effectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. DESIGN Retrospective study. ANIMALS Fifty-one adult horses aged 9.5 ± 6.9 years (range 1-23 years) and weighing 575 ± 290.3 kg. METHODS Records of horses presented to our clinic over a 3-year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. RESULTS Detomidine was administered as an initial bolus loading dose (mean ± SD) of 7.5 ± 1.87 μg kg-1. The initial infusion rate was 0.6 μg kg-1 minute-1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses. CONCLUSIONS Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. CLINICAL RELEVANCE An effective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide sufficient analgesia for surgery and a significant proportion of animals required supplemental sedatives and analgesics.

Response to nasopharyngeal oxygen administration in horses with lung disease

REASONS FOR PERFORMING STUDY Guidelines for administration of oxygen to standing horses are unavailable because previous investigations of the efficacy of oxygen administration to increase arterial oxygenation in standing horses have produced equivocal results. OBJECTIVE To determine the effect of nasal oxygen supplementation on inspired and arterial blood gas tensions in control horses and those with moderate to severe recurrent airway obstruction (RAO). METHODS Normal horses (n = 6) and horses during an attack of RAO induced by stabling (n = 6) were studied. Oxygen was administered through either one or 2 cannulae, passed via the nares into the nasopharynx to the level of the medial canthus of each eye. Intratracheal inspired oxygen and carbon dioxide concentration and arterial blood gas tensions were measured at baseline and during delivery of 5, 10, 15, 20 and 30 l/min oxygen. RESULTS Nasal cannulae and all but the highest oxygen flow rates were well tolerated. Fractional inspired oxygen concentration (F(I)O2) increased with flow but was significantly lower at all flow rates in horses with RAO compared with controls. Arterial oxygen tension (PaO2) was significantly increased (P < 0.001) by all flow rates, but was always lower in RAO-affected animals. At 30 l/min, PaO2 increased to 319 +/- 31 mmHg in control horses and 264 +/- 69 mmHg in horses with RAO. Additionally, a large arterial to end-tidal gradient for CO2 in RAO-affected horses was observed, indicating increased alveolar deadspace ventilation in these animals. CONCLUSIONS The use of nasal cannulae to deliver oxygen effectively increases both F(I)O2 and PaO2 in horses with moderate to severe RAO. Oxygen flow rates up to 20 l/min are well tolerated, but flow rates of 30 l/min produce occasional coughing or gagging. POTENTIAL RELEVANCE Oxygen therapy delivered by means of an intranasal cannula is a highly effective means of increasing arterial oxygen tension in horses with respiratory disease. Generally, flows of 10-20 l/min should be effective. If higher flows (20-30 l/min) are necessary, they should be delivered by means of 2 cannulae.

The effects of a single acupuncture treatment in horses with severe recurrent airway obstruction

Summary Reasons for performing study: Acupuncture may be recommended for horses with ‘heaves’ because it is being increasingly applied to treat human asthma. Therefore, its efficacy was investigated in horses with this asthmalike disease. Objective: To evaluate the efficacy of a single acupuncture treatment for the relief of airway obstruction in heaves-affected horses. Methods: The efficacy of a single acupuncture treatment was tested in 10 heaves-affected horses, and the effect of removal from the dusty stall environment in 5 heaves-affected horses. Before treatment, horses were stabled to induce airway obstruction and, apart from trips to the laboratory for pulmonary function measurements, they remained stabled for the duration of each treatment. The severity of airway obstruction was quantified by measurement of lung function before treatment (baseline), and at 20, 60, 120 and 240 mins and 24 h after the following treatments administered in random order: halter restraint and patting, a single acupuncture treatment by an experienced acupuncturist, and a single acupuncture treatment using predetermined points (recipe) by a veterinarian with no acupuncture training. In a second study, horses were untreated and remained either in their stall or in a paddock for all measurements of lung function, after baseline readings were made. Results: In the first study, after all treatments, there was a temporal improvement in maximal change in pleural pressure, pulmonary resistance, dynamic compliance, respiratory rate, and tidal volume that lasted less than 24 h. There was no specific effect of acupuncture treatment. In the second study, removal from the dusty environment did not produce an improvement in lung function in the first 6 h. We conclude that most of the improvements in lung function observed in the study were due to handling. Conclusions: Assessed objectively, a single acupuncture treatment during an attack of heaves causes no more improvement in lung function than does handling the horse. Potential relevance: Acupuncture should not replace conventional medical treatments for heaves.

The cardiopulmonary effects of severe blood loss in anesthetized horses

OBJECTIVE To characterize the acute cardiopulmonary effects of severe hemorrhage in anesthetized horses. STUDY DESIGN Prospective experimental study. ANIMALS Three geldings and six mares, aged 14.4 ± 2.7 years, weighing 486 ± 41 kg (range: 425-550 kg). METHODS Horses were anesthetized using xylazine, guaifenesin, ketamine and halothane or isoflurane. Cardiovascular variables, hematocrit, total solids, capillary refill time (CRT) and color of mucous membranes were measured as blood was collected from the carotid artery into sterile plastic bags. Arterial blood gas analysis was also performed. RESULTS The average amount of blood collected from these horses was (mean ± SD) 53 ± 4.8 mL kg-1 bodyweight (range: 23-32 kg) over 39 ± 4 minutes. Hematocrit decreased from 38 ± 3 to 32 ± 2% after induction of anesthesia and did not change significantly over the period of blood loss. Total solids decreased significantly after induction of anesthesia, and over the period of blood loss. Systolic, mean, diastolic and pulse pressures decreased as blood was lost. Heart rate did not change significantly. Capillary refill time increased from 1.6 ± 0.4 seconds to 4.8 ± 1.3 seconds as blood loss increased. Mucous membrane color deteriorated progressively. Arterial PO2 decreased significantly over the period of blood loss. CONCLUSIONS Hematocrit and heart rate do not change significantly during acute severe hemorrhage in the anesthetized horse. Arterial blood pressure, pulse pressure and PaO2 decrease as blood loss increases. Changes in mucous membrane color and CRT also occur as blood loss increases. CLINICAL RELEVANCE During severe hemorrhage in the inhalant-anesthetized horse, both heart rate and hematocrit remain unchanged. Blood pressure decreases and changes in arterial PO2 correlate most strongly with volume of blood lost.

Prevalence and risk factors for canine post-anesthetic aspiration pneumonia (1999-2009): a multicenter study

OBJECTIVE To determine the incidence of canine post-anesthetic aspiration pneumonia (AP) and to identify anesthetic agents, procedures and management factors associated with the development of AP. STUDY DESIGN Multicenter, randomized, case-controlled retrospective study. ANIMALS Two hundred and forty dogs affected with AP and 488 unaffected control dogs. METHODS Electronic medical record databases at six Veterinary colleges were searched for dogs, coded for anesthesia or sedation and pneumonia from January 1999 to December 2009. The resultant 2158 records were hand-searched to determine eligibility for inclusion. Diagnosis of AP was made radiographically. Two unaffected control dogs were randomly selected for each affected dog, from a list of dogs that underwent sedation or anesthesia in the same time period and did not develop aspiration pneumonia. Fifty-seven factors were then evaluated for association with aspiration pneumonia. Data analysis was performed using univariate Chi-square or student t-tests, then multivariate logistic regression. RESULTS Incidence of post-anesthetic AP was 0.17%, from 140,711 cases anesthetized or sedated over the 10 year period. Two anesthesia-related events were significantly associated with development of AP: regurgitation and administration of hydromorphone at induction. Administration of anticholinergics was not associated with AP. Procedures associated with increased odds of aspiration pneumonia included laparotomy, upper airway surgery, neurosurgery, thoracotomy and endoscopy. Orthopedic surgery, ophthalmologic surgery, dental procedures, MRI, CT, bronchoscopy, cystoscopy, tracheoscopy and neutering were not associated with development of AP. Three patient factors were associated with the development of AP: megaesophagus, and a history of pre-existing respiratory or neurologic disease. Sixty-nine% of dogs with two or more of the above independent predictive variables developed AP. CONCLUSION AND CLINICAL RELEVANCE Most anesthetic agents and procedures were not associated with the development of AP. We need to devise and evaluate strategies to protect at risk patients.

Comparison of three ultrasound guided approaches to the lumbar plexus in dogs: a cadaveric study

OBJECTIVE To assess the accuracy of contrast material injection and the dispersion of injectate following ultrasound guided injections at the level of L6 and L7, in canine cadavers. STUDY DESIGN Prospective, randomized, experimental study. ANIMALS Twenty nine mixed breed canine cadavers (28.9 ± 6.0 kg). METHODS Three ultrasound-guided approaches to the lumbar plexus (LP) were compared: 1) a dorsal pre-iliac approach at the level of L6; 2) a lateral paravertebral approach at mid-L6; and 3) a lateral paravertebral approach at mid-L7. An isovolumic mixture of iodine-based contrast with new methylene blue (0.1 mL kg(-1)) was injected bilaterally in the juxta-foraminal region along the L6 or L7 nerve root. Computed tomography was performed followed by segmentation and 3D reconstruction of the lumbar spine and contrast material volumes using dedicated software. Distances between contrast material and the fifth through seventh lumbar foraminae, and length of femoral (FN) and obturator (ON) nerve staining were measured and compared between approaches (p < 0.05). RESULTS Injectate moved cranial and caudal to the site of injection, and dispersed into an ovoid shape between the quadratus lumborum, iliopsoas and psoas minor muscles. Injections at L7 resulted in significantly closer contrast proximity to the L6 and L7 foraminae (p < 0.001). Femoral nerve staining was similar for all approaches, ON staining was more consistent after L7 injections (p < 0.001). CONCLUSION AND CLINICAL RELEVANCE An ultrasound-guided lateral paravertebral approach to the LP proved very practical and accurate, with easy visualization of the plexus and associated nerves. To ensure that the ON is covered by injectate, an approach at the level of L7 is recommended. Further studies are necessary to determine if this correlates with clinically effective local anesthesia.

Anesthesia and sedation for late-term mares.

Heavily pregnant mares requiring anesthesia present special problems and challenges. The use of short-acting anesthetic agents, combined with inhalational anesthesia, mechanical ventilation, and blood pressure support, will ensure an optimal outcome by maintaining both maternal and fetal homeostasis. The provision of oxygen during recovery to the still gravid mare also is important for fetal survival.

The effect of four anesthetic protocols on the spleen in dogs

Splenic enlargement following administration of barbiturates has been well described in dogs; other agents have not been investigated. This study aimed to compare the effects of four anesthetic protocols on splenic size. Twenty-four fasted Beagle dogs scheduled for laparotomy were allocated to one of the four groups. Group 1: acepromazine and butorphanol followed by induction with thiopental; Group 2: acepromazine and butorphanol followed by induction with propofol; Group 3: medetomidine and butorphanol followed by induction with propofol; Group 4: medetomidine and butorphanol followed by induction with ketamine and diazepam. Anesthesia was maintained with halothane in oxygen, intravenous fluids were administered. Splenic length, width and height were measured once when the abdomen was opened and again just prior to closure. Spleens were also traced, the image was digitized, and the area was calculated. PCV and total solids were measured before and after pre-medication, after induction, and each time the spleen was measured. Data were analyzed using a Repeated Measures anova with splenic variables indexed by body surface area and dose of induction agent as a covariate. Area and width of the spleens were less in the dogs of Groups 2 and 3 than in those of the other groups. Splenic area and length did not change significantly during surgery. Dosage of propofol was not significantly different between Groups 2 and 3. Baseline PCV was not significantly different among groups and decreased significantly in all dogs, but at different times. In Groups 1 and 2, the decrease occurred after pre-medication, in Group 3 at induction, and in Group 4 during surgery. A significant decrease in TS occurred in all groups during surgery. We concluded that the use of propofol resulted in smaller spleen size during surgery than that following the use of thiopental. Multiple factors influenced the PCV.