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.

Warming with a forced air warming blanket minimizes anesthetic-induced hypothermia in cats.

OBJECTIVE: To evaluate the effectiveness of a forced-air warming blanket (FAWB) in minimizing anesthetic-induced hypothermia in cats, and to examine the relationship between esophageal and other estimates of body temperature during skin surface warming. STUDY DESIGN: Prospective, randomized cross-over trial. ANIMALS: Eight adult domestic shorthair cats (four males and four females) weighing 2.3 to 4.5 kg. METHODS: Each cat was anesthetized with halothane in oxygen on four occasions and covered with a modified FAWB. Air delivered to the cats by the FAWB was warmed to approximately 43 degrees C. Each trial lasted 90 minutes and was divided into two consecutive 45-minute periods, during which the FAWB was activated or inactivated thus creating four treatment trials: off/off, on/off, on/on, off/on. Measurements of body temperature from the caudal esophagus, deep rectum, toe-web, and tympanic membrane were recorded at regular intervals throughout each trial and compared. RESULTS: A steady decline in body temperature was observed throughout each trial. Mean body temperature in the cats receiving continual skin surface warming (on/on) was significantly higher than in those receiving no active warming (off/off) and those receiving delayed warming (off/on), from 45 minutes onwards. By 90 minutes, the mean body temperature of cats warmed continuously was 0.9 degrees C higher than in those with no active warming. Notable differences in body temperature were detected between all measurement sites, with the exception of esophagus versus rectum. Rectal and esophageal temperatures did not differ at any time point. Tympanic membrane temperatures measured with either device were lower than esophageal temperatures. CONCLUSIONS: The modified FAWB was effective in minimizing the degree of hypothermia experienced in cats anesthetized with halothane for 90 minutes. Deep rectal temperature was an accurate reflection of esophageal temperature in these cats. CLINICAL RELEVANCE: Forced air warming blankets may prove successful in minimizing anesthetic-induced hypothermia in cats.

Cardiorespiratory and anesthetic effects of propofol and thiopental in dogs.

OBJECTIVE: To compare cardiorespiratory and anesthesia effects of IV administered propofol and thiopental in dogs. ANIMALS: 6 healthy mixed-breed dogs. PROCEDURE: Each dog was anesthetized with isoflurane, then a thermistor catheter was inserted in the pulmonary artery. After a minimum of 2.5 hours of recovery, a catheter was placed in a cephalic vein for administration of lactated Ringer's solution and drugs. Propofol (8 mg/kg of body weight) or thiopental (19.4 mg/kg) was administered to each dog in a randomized crossover design study. All dogs were intubated and allowed to breathe 100% oxygen spontaneously. Heart rate and rhythm; systolic, diastolic, and mean arterial blood pressures; respiratory rate; end-tidal carbon dioxide concentration; tidal volume; and reflexes (toe web pinch, palpebral response, and jaw tone) were measured before and every 2 minutes for the first 10 minutes, then at 15, 30, and 60 minutes after drug administration. Cardiac output was determined at 0, 2, 6, 10, 15, 30, and 60 minutes, and blood samples were collected at 0, 2, 10, and 30 minutes. Time to endotracheal extubation, head lift, and ability to sit sternally and walk unaided were recorded. RESULTS: 3 of 6 dogs in each group were apneic after drug administration. Reflexes were decreased similarly for both anesthetic agents, but were not completely lost. Time to sternal position and walking unaided were significantly shorter in response to propofol. CONCLUSION: Anesthesia was rapid; however, respiratory depression and apnea were major adverse effects associated with propofol and thiopental. Propofol has the advantage of inducing rapid, coordinated anesthesia recovery.

Effects of a selective and a nonselective muscarinic cholinergic antagonist on heart rate and intestinal motility in dogs.

The effects of methoctramine, a cardioselective muscarinic cholinergic antagonist, on heart rate and small intestinal motor activity were compared to those of the nonselective competitive muscarinic antagonist, atropine. Methoctramine or atropine, 6, 10, 30, 60 micrograms/kg, or sterile isotonic saline, was administered intravenously to six conscious dogs in cross-over studies. Methoctramine administration caused dose-dependent tachycardia without affecting intestinal motility, while atropine administration caused dose-dependent tachycardia accompanied by significant reductions in small intestinal motility. Additionally, methoctramine did not inhibit intestinal smooth muscle contractile activity initiated by the muscarinic agonist bethanechol, while atropine inhibited bethanechol-induced contractile activity in a dose-dependent manner. Calculated, dosages of methoctramine and atropine required to produce a 50% increase in heart rate over baseline were 35.1 +/- 5.3 and 39.5 +/- 6.2 micrograms/kg, respectively. This dosage of atropine caused a 93 +/- 13.9% reduction in intestinal motility. These findings suggest that selective muscarinic antagonists may be useful drugs for those veterinary patients in which nonselective muscarinic antagonists have the potential to produce untoward effects on intestinal motility.

Nasotracheal intubation in calves.

Nasotracheal intubation can be accomplished in calves by use of a silicone nasotracheal tube of a Murphy design. For intubation, the calf's head and neck should be extended to facilitate tube passage through the naris into the ventral meatus and then through the larynx into the trachea. Preanesthetic medication may assist in tube passage by decreasing the alertness of the calf and decreasing the ability of the calf to swallow the tube into the esophagus. Nasotracheal intubation allows the inhalant anesthetic agent to be delivered with minimal room pollution and less stress to the calf. It would be useful for oral surgery when an orotracheal tube would obstruct the surgical site.

Epidural administration of bupivacaine, morphine, or their combination for postoperative analgesia in dogs.

OBJECTIVE: To compare the analgesic effects of epidural administration of morphine (MOR), bupivacaine hydrochloride (BUP), their combination (COM), and 0.9% sterile NaCl solution (SAL) in dogs undergoing hind limb orthopedic surgeries. DESIGN: Blinded, randomized clinical trial. ANIMALS: 41 healthy dogs admitted for elective orthopedic surgeries involving the pelvis or hind limbs. PROCEDURE: Analgesic and control agents were administered postoperatively prior to recovery from isoflurane anesthesia. Ten dogs received MOR, 0.1 mg/kg of body weight; 10 received BUP, 0.5%, 1 ml/10-cm distance from the occipital protuberance to the lumbosacral space; 11 received COM; and 10 received SAL epidurally. Dogs were monitored for 24 hours after epidural injection for pain score, heart and respiratory rates, blood pressure, time to required administration of supplemental analgesic agent, total number of supplemental doses of analgesic agent required, and plasma concentrations of cortisol, MOR, and BUP. RESULTS: Pain scores were significantly lower in dogs in the COM and BUP groups than in dogs in the SAL group. Pain scores also were significantly lower in dogs in the COM group than in dogs in the MOR group. Time to required administration of supplemental analgesic agent was longer for dogs in the COM group than for dogs in the MOR and SAL groups. Total number of supplemental doses of analgesic agent required was lower for dogs in the BUP and COM groups than for dogs in the SAL group. CLINICAL IMPLICATIONS: Postoperative epidural administration of COM or BUP alone provides longer-lasting analgesia, compared with MOR or SAL.

Methoctramine, a cardioselective muscarinic cholinergic antagonist, prevents fentanyl-induced bradycardia in the dog.

A controlled study examining the effects of the cardioselective muscarinic cholinergic antagonist methoctramine on fentanyl-induced bradycardia was performed in six dogs. Five doses of methoctramine (6, 10, 20, 30 and 60 micrograms/kg) followed by fentanyl (20 micrograms/kg) were administered randomly on separate days. Fentanyl caused a significant reduction in heart rate from baseline values. Moreover, fentanyl produced a variety of arrhythmogenic actions indicative of vagal hyperactivity, including sinus bradycardia, second-degree atrioventricular block and ventricular and supraventricular escape beats. Administration of methoctramine 5 min before fentanyl injection prevented the bradycardic effects of fentanyl in a dose-dependent manner, with high doses of methoctramine causing sinus tachycardia. Using regression analysis, the dose of methoctramine necessary to prevent fentanyl-induced bradyarrhythmias without causing tachycardia was calculated as 14.4 micrograms/kg. The study confirmed that fentanyl administration in the conscious dog causes profound bradycardia with bradyarrhythmias. The cardioselective muscarinic antagonist agent methoctramine prevented the bradycardic effects of fentanyl.

Butorphanol does not reduce the minimum alveolar concentration of halothane in dogs.

This study evaluated the effect of butorphanol tartrate, a synthetic opioid agonist-antagonist, on halothane minimum alveolar concentration (MAC) in dogs. Baseline halothane MAC was determined in each of six dogs. Butorphanol was administered and halothane MAC was redetermined. Each dog received butorphanol at 0.2, 0.4, and 0.8 mg/kg intravenously at 1 week intervals. Heart rate and arterial blood pressure decreased after butorphanol administration, but returned to baseline by 50 minutes. There was little effect on respiratory parameters. A halothane-sparing effect was not noted with any butorphanol dose.

Endotracheal tube displacement during cervical manipulation in the dog.

A retrospective study was performed to identify positional changes of endotracheal tubes (ETT) during cervical spine radiography in 153 dogs. Three neck positions were identified: traction, hyperextension, and flexion. A properly placed ETT was defined as having the caudal tip of the tube located between the caudal half of the fourth cervical (C) vertebra (C4) and the caudal half of C7. In the traction position, before neck flexion and extension, the caudal tip of 13% of ETT were located caudal to C7, and one tube was in the endobronchial position at the seventh thoracic (T) vertebra (T7). In the hyperextended position, 60% of ETT moved cranially. The average distance moved was 0.6 vertebral spaces. In the flexed position, all ETT moved caudally. The average distance moved was 3.5 vertebral spaces, with 81.8% of ETT located caudal to C7 and seven tubes in endobronchial positions. Endotracheal tube occlusion caused by kinking at the atlanto-occipital joint was seen in four dogs during flexion of the neck. Based on this study, ETT position should be monitored during cervical manipulation.

Evaluation of toenail blood samples for blood gas analysis in the dog.

Blood gas values were compared in blood collected from cut toenails and femoral arteries in 50 healthy crossbred dogs that were sedated and allowed to breathe room air spontaneously. Blood samples from cut toenails were collected by microcapillary technique with Natelson tubes. Femoral artery samples were collected by arterial puncture. Blood values for PO2, PCO2, pH, and HCO3 were compared. There was good correlation for pH, PCO2, and bicarbonate, but not for PO2. Microcapillary samples should be collected in 10 seconds or less for the most accurate results. A metal mixing "flea" was unnecessary. When properly handled, the Natelson tube technique provides an alternative method for collection of blood gas samples.

Evaluation of 25%, 50%, and 67% nitrous oxide with halothane-oxygen for general anesthesia in horses.

Twenty-five percent, 50%, and 67% nitrous oxide was administered to 12 horses anesthetized with halothane and oxygen. Compared to halothane-oxygen alone, there was no significant difference in heart rate, systolic, diastolic, or mean blood pressure values, arterial pH, PaCO2, or plasma bicarbonate values when nitrous oxide was included. A significant linear reduction in PaO2 values could be correlated with N2O:O2 concentrations. The halothane level required to maintain surgical anesthesia was reduced when nitrous oxide was administered, but it was not affected by changing the nitrous oxide concentrations. Nitrous oxide concentrations greater than 25% provide no additional reduction in halothane requirement and may be accompanied by PaO2 values that pose risk to the horse.

Comparison of histamine release induced by morphine and oxymorphone administration in dogs.

Cardiovascular effects (vasodilatation, hypotension) of morphine administration have been attributed to central actions and peripheral histamine release. In the study reported here, we compared plasma histamine (Hm) concentrations after morphine sulfate and oxymorphone HCl administration in conscious dogs. Five healthy adult dogs (mean body weight, 10.1 kg) were randomly administered morphine (2 mg/kg of body weight, IV) or oxymorphone (0.2 mg/kg, IV) by a 5-second bolus injection at weekly intervals. Venous blood samples (5 ml) were collected from jugular veins before and at 1, 2, 5, 15, 30, and 60 minutes after drug administration. Behavioral changes were recorded. Plasma was analyzed by a radioenzymatic technique, using purified histamine N-methyltransferase as an enzyme catalyst (sensitivity of assay, 40 pg Hm/ml). Mean base-line Hm value for all dogs was 0.55 ng/ml. The mean Hm value was significantly higher (P less than 0.05) than the base-line value at 1, 2, 5, 15, and 60 minutes after morphine administration (531.4, 251.0, 113.0, 31.5, and 1.0 ng of Hm/ml, respectively), but there were no significant increases in histamine values from base-line values at any time after oxymorphone administration. All dogs given morphine and 1 dog given oxymorphone showed excitatory behavior; 2 dogs given morphine and 3 dogs given oxymorphone salivated profusely.

Clinical signs, diagnosis, and treatment of alkalemia in dogs: 20 cases (1982-1984).

Alkalemia (pH greater than 7.50) was measured in 20 dogs admitted over a 3-year period for various clinical disorders. Alkalemia was detected in only 2.08% of all dogs in which blood pH and blood-gas estimations were made. Thirteen dogs had metabolic alkalosis (HCO3- greater than 24 mEq/L, PCO2 greater than 30 mm of Hg), of which 8 had uncompensated metabolic alkalosis, and of which 5 had partially compensated metabolic alkalosis. Seven dogs had respiratory alkalosis (PCO2 less than 30 mm of Hg, HCO3- less than 24 mEq/L); 4 of these had uncompensated respiratory alkalosis and 3 had partially compensated respiratory alkalosis. Ten dogs had double or triple acid-base abnormalities. Dogs with metabolic alkalosis had a preponderance of clinical signs associated with gastrointestinal disorders (10 dogs). Overzealous administration of sodium bicarbonate or diuretics, in addition to anorexia, polyuria, or hyperbilirubinemia may have contributed to metabolic alkalosis in 8 of the dogs. Most of the dogs in this group had low serum K+ and Cl- values. Two dogs with metabolic alkalosis had PCO2 values greater than 60 mm of Hg, and 1 of these had arterial hypoxemia (PaO2 less than 80 mm of Hg). Treatments included replacement of fluid and electrolytes (Na+, K+, and Cl-), and surgery as indicated (8 dogs). Six dogs with respiratory alkalosis had a variety of airway, pulmonary, or cardiac disorders, and 3 of these had arterial hypoxemia. Two other dogs were excessively ventilated during surgery, and 1 dog had apparent postoperative pain that may have contributed to the respiratory alkalosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of gastric lavage and thoracic cavity lavage in the treatment of severe hypothermia in dogs.

A study was undertaken to compare warm gastric (Group 1) and closed thoracic cavity (Group 2) lavage for rewarming severely hypothermic dogs. Adult mongrel dogs were monitored by intra-arterial catheter, central venous catheter, and ECG, and by central venous, esophageal, and rectal temperature probes. Animals were externally cooled to an average of 21.2 C using ice bags. Eight Group 1 and eight Group 2 animals underwent continuous warm saline gastric or closed thoracic cavity lavage, respectively, using afferent and efferent nasogastric and thoracostomy tubes. No animal suffered ventricular fibrillation during tube placement. The closed lavage system consisted of a high-efficiency heat exchanger, a roller pump infusion device, and a heat exchange fluid bath. The lavage fluid circulated at a flow rate of 550 mL/min and a temperature of 39 C. Thoracic lavage animals were followed clinically for 24 hours for evidence of complications, then euthanized and autopsied. The mean time required to rewarm the animals 10 C by central venous temperature probe was 210.9 +/- 18.6 minutes for the gastric group and 99.3 +/- 23.0 minutes for the thoracic group (P less than .001). Rectal temperature consistently lagged behind central venous temperature during both the cooling and rewarming phases in both treatment groups. All of the thoracic lavage animals made an uneventful recovery. Continuous warm saline thoracic cavity lavage for core rewarming of severely hypothermic dogs is more effective than gastric lavage, and appears to be safe.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral resuscitation after cardiac arrest using hetastarch hemodilution, hyperbaric oxygenation and magnesium ion.

This study was done to investigate the effects of hemodilution, hyperbaric oxygenation, and magnesium sulfate on cerebral resuscitation. Sixteen mongrel dogs were anesthetized, and monitored via pulmonary artery catheter, arterial catheter and electrocardiogram. A left lateral thoracotomy was done. Ventricular fibrillation was obtained by application of a 6-volt AC current. Mechanical ventilation was stopped. Total arrest time was 12 min. All dogs were cardiac resuscitated within 6 min using internal massage, ventilation, bicarbonate, epinephrine and internal defibrillation. The animals were then randomized into three groups. Group I represented controls, and were not treated. Group II dogs received normvolemic hemodilution using hetastarch (Hespan) containing magnesium sulfate (2000 mg/l), resulting in a hematocrit of 20%-30%. Group III dogs received the above hemodilution plus compression in a hyperbaric oxygen chamber to 2 atmospheres absolute. Critical care management and hourly neurologic scoring was performed for 7 days by blinded observers. All dogs at the time of death underwent autopsies for gross study. Data analysis revealed no statistical difference among the three groups with respect to survival time, cardiac function or neurologic scoring.

Barbiturate anesthesia in greyhound and mixed-breed dogs: comparative cardiopulmonary effects, anesthetic effects, and recovery rates.

The cardiovascular effects, anesthetic effects, and recovery rates were evaluated in racing Greyhounds under barbiturate anesthesia. Greyhounds and mixed-breed dogs of similar body weights were given (by IV route) thiopental (15 mg/kg), thiamylal (15 mg/kg), methohexital (10 mg/kg), and pentobarbital (20 mg/kg). The anesthesia lasted longer in Greyhound than in non-Greyhound mixed-breed dogs given thiopental, thiamylal, and methohexital. The mean times from recumbency to standing were 3 to 4 times longer for Greyhounds anesthetized with thiobarbiturates than for non-Greyhound mixed-breed dogs anesthetized with the same drugs, with recovery times for some Greyhounds lasting more than 8 hours. With thiobarbiturate anesthesia, Greyhounds had long periods of respiratory depression, struggled, and relapsed into sleep, whereas in the other dogs, the recovery was quiet. Respiratory depression related to the stage of anesthesia was produced by all barbiturates, but did not result in significant changes in blood gas values. Rectal temperature decreased in all dogs, but did not result in significant hypothermia. Cardiovascular variables and acid-base estimations in Greyhounds were not significantly different from those in mixed-breed dogs before and during barbiturate anesthesia. Packed cell volumes in Greyhounds were significantly higher than those in non-Greyhound mixed-breed dogs after the thiobarbiturates and methohexital were administered. Total plasma protein concentrations were significantly lower in Greyhounds, compared with those in the other dogs before and during barbiturate anesthesia. Methohexital is a useful alternative to thiobarbiturates for short-duration barbiturate anesthesia in Greyhounds.