Continuous caudal epidural and subarachnoid anesthesia in mares: a comparative study.

A new technique for producing continuous caudal epidural analgesia (CEA) and caudal subarachnoid analgesia (CSA) in adult horses (mares) without causing loss of pelvic limb function is described. A modified 17-gauge Huber-point directional needle was used to place a catheter with stylet into either the epidural or subarachnoid space at the lumbosacral intervertebral junction. The catheter was positioned at either the midsacral (S2-3) subarachnoid space or caudal portion of the sacral (S-3 to S-5) epidural space in 7 mares. The position of the catheter was confirmed radiographically. A 2% solution of mepivacaine HCl was used at an average dose of 0.061 +/- 0.013 mg/kg (1.3 +/- 0.3 ml) to produce CSA and 0.196 +/- 0.034 mg/kg (4.1 +/- 0.7 ml) to produce CEA. Onset of analgesia to superficial and deep muscular pinprick stimulation was faster with CSA than it was with CEA (8.2 +/- 2.4 minutes vs 21.4 +/- 3.8 minutes). Maximal caudal analgesia extended from spinal cord segments S-1 to coccyx during CSA and CEA. Periods of analgesia were shorter with CSA than with CEA (70.0 +/- 21.8 minutes vs 102.1 +/- 13.2 minutes). Perineal (S-4 to S-5) dermatome subcutaneous temperature was increased after epidural and subarachnoid injections of mepivacaine HCl solution. Heart rate, respiratory rate, systolic, diastolic, and mean arterial blood pressures, pulse pressure, rectal temperature, arterial blood gas tensions (PaCO2, PaO2), pHa, hematocrit, and total solid concentrations did not change significantly (P greater than 0.05) from base-line values after injection. The benefits and potential complications of CSA and CEA in horses are discussed.

Hemodynamic effects of unilateral segmented lumbar epidural analgesia in cattle.

Hemodynamic measurements, arterial and mixed venous blood gas tensions, and pH were determined in 12 adult cows (mean weight 538 kg) following the injection of 8 ml of 5% procaine between the first and the second lumber vertebra into the epidural space. Comparison of base-line data with obtained during unilateral segmented lumbar analgesia between T(13) and L(3) segments indicated significant decreases (P is less than 0.05) in total peripheral resistance and diastolic and mean arterial blood pressures, and significant increases (P is less than 0.05) in heart rate and cardiac output. Arterial and mixed venous blood gas tensions and pH, O(2)-uptake, stroke volume, left ventricular stroke work, left ventricular minute work and hematocrit did not change significantly (P is less than 0.05). Cardiovascular and respiratory values in two cows (mean weight 700 kg) given xylazine (50 mg, IM), were depressed from base-line data, but did not change significantly (P is less than 0.05) during unilateral segmental epidural analgesia of segments T(13 to L(3). The nonsedated healthy cow tolerates sympathetic vasomotor blockade between T(13) and L(3) segments well and is able to mobilize circulatory mechanisms effectively.

Effects of segmental subarachnoid analgesia on arterial blood pressure, gas tensions, and pH in adult conscious cows.

Arterial blood pressure, blood gas tensions (PaCO2, PaO2), and pH (pHa) were determined in 16 adult, nonpregnant Holstein cows (620 +/- 54 kg) given subarachnoid injection of a 5% procaine hydrochloride solution at the T13-L1 intervertebral space. Analgesia, as determined by response to superficial and deep muscular pinpricks at the L1 dermatome, was delayed (onset) 7 to 15 minutes, and it lasted (duration) 28 to 83 minutes. Thoracolumbar analgesia extending between spinal cord segments T9 and L4 on 1 or both sides of the spine produced significant (P less than 0.05) increases in heart rate and decreases in respiratory rate, but otherwise had no effect (P less than 0.05) on systolic, diastolic, and mean arterial blood pressures, PaCO2, PaO2, and pHa. Similarly, no significant changes (P less than 0.05) of physiologic variables were observed in a control group of 5 cows given a subarachnoidal injection of 0.9% sodium chloride solution at 1 hour before procaine hydrochloride was injected. It was concluded that the unsedated, healthy cow tolerates segmental subarachnoid analgesia between spinal segments T9 and L4 well and that this analgesia is not adversely affected by hypoxemia, respiratory acidosis, or hypotension.

Comparison of antinociceptive, cardiovascular, and respiratory effects, head ptosis, and position of pelvic limbs in mares after caudal epidural administration of xylazine and detomidine hydrochloride solution.

OBJECTIVE: To examine and compare effects of 2 alpha 2-adrenergic receptor agonists, xylazine and detomidine, administered into the sacrococcygeal epidural space to induce safe and effective perineal analgesia on cardiovascular and respiratory functions, head ptosis, and position of pelvic limbs in healthy mares. ANIMALS: 8 healthy mares. PROCEDURE: Blood samples were drawn and systemic hemodynamics were determined, including cardiac output and pulmonary arterial, systemic arterial, and right atrial pressures. Two-way ANOVA with repeated measures was used to detect significant (P < 0.05) differences between mean scores of perineal analgesia, cardiorespiratory variables, head ptosis, and position of pelvic limbs in mares before and during a 3-hour testing period. Analgesia was determined by lack of sensory perception to electrical stimulation at the perineal dermatome and no response to needle prick stimulation in dermatomes extending from the coccyx to T15. Avoidance responses to electrical current and needle prick stimulation and behavioral changes (head ptosis, position of pelvic limbs) were quantitatively assessed by use of a scoring system. RESULTS: Epidurally administered xylazine induced perineal analgesia and variable bilateral caudal analgesia extending from the coccyx to S3 dermatome, with minimal cardiovascular and respiratory depression, head ptosis, changes in position of pelvic limbs, and no urination in standing mares. Epidurally administered detomidine induced perineal analgesia, variable bilateral analgesia with dermatomal spread ranging from coccyx to S3 and coccyx to T15, with cardiovascular depression, marked head ptosis, changes in position of pelvic limbs, and diuresis in standing mares. Onset of perineal analgesia after xylazine and detomidine administrations was 13.1 +/- 3.7 and 12.5 +/- 2.7 minutes (mean +/- SD), respectively. The period of perineal analgesia was significantly (P < 0.05) longer in mares after epidural xylazine administration than after epidural detomidine administration (165 to > 180 minutes vs 160 +/- 8 minutes). CONCLUSIONS: Caudal epidurally administered xylazine (0.25 mg/kg of body weight in 8 ml of 0.9% NaCl) offers the most desirable conditions in mares: long-term perineal analgesia (> 2.5 hours), with minimal cardiopulmonary depression, head ptosis, changes in pelvic limb position, and no urination in standing mares during a 3-hour test period.

Segmental thoracolumbar subarachnoid analgesia in cows.

A new technique for producing segmental subarachnoid analgesia in adult cows without causing complete loss of locomotor control is described. Segmental subarachnoid analgesia was produced in 18 adult nonpregnant Holstein-Friesian cows. A 17-gauge Huber point directional needle was used to place a catheter with a stylet into the subarachnoid space at the lumbosacral intervertebral space and advance it craniad to the thoracolumbar intervertebral space. The position of the catheter was confirmed radiographically in 8 cows. A 5% solution of procaine hydrochloride was injected through the catheter. The volume injected varied between 1.5 ml (8 cows) and 2 ml (10 cows). The rate of injection was approximately 0.5 ml/30 s. In 5 cows, 1.5 or 2 ml of normal saline solution was injected intrathecally 1 hour before the injection of procaine hydrochloride. These cows served as the control group. Segmental analgesia was achieved 7 to 10 minutes after completing the procaine hydrochloride injection and extended between spinal cord segments T9 and L4 on one or both sides of the spinal cord. The average duration of analgesia, as determined by response to superficial and deep muscular pinprick stimulation at the I1 dermatome, was 43.7 +/- 17.6 minutes, with a range of 22 to 80 minutes. Significant decreases (P less than 0.05) in respiratory rate and rectal temperature and increases in heart rate and subcutaneous temperature occurred in cows given procaine hydrochloride. The clinical application of the technique was demonstrated in one surgical procedure described. The advantages and disadvantages of segmental subarachnoid analgesia compared with segmental epidural analgesia are discussed.

Segmental thoracolumbar spinal (subarachnoid) analgesia in conscious horses.

A new technique for producing segmental subarachnoid analgesia in adult horses without causing complete loss of locomotor control is described. A 17-gauge Huber point (Tuohy) needle was used to place a catheter with a stylet into the subarachnoid space at the lumbosacral intervertebral space in 13 adult horses (weighing 500 +/- 60 kg, representing both sexes) and to advance the catheter craniad to the thoracolumbar area. The position of the catheter was confirmed radiographically. A 2% mepivacaine hydrochloride solution (1.5 ml, 30 mg) was injected through the catheter at a rate of 0.5 ml/60 s. Segmental analgesia, as determined by the horses' responses to superficial and deep muscular pinpricks, occurred within (onset) 5 to 10 minutes of injection and lasted (duration) 42.4 +/- 15 minutes (min-max, 25 to 68 minutes). Maximal thoracolumbar analgesia extended from spinal cord segments T12 to L3 on both sides of the spinal column. Subarachnoid injection of mepivacaine hydrochloride caused significant (P less than 0.05) increases in heart rate and subcutaneous temperature and decreases in respiratory rate and rectal temperature. Significant changes (P less than 0.05) were not observed in a control group of 7 horses after subarachnoidal injection of sterile water (1.5 ml). The surgical application of segmental subarachnoid analgesia was demonstrated in 1 horse. The benefits and potential complications of segmental subarachnoid analgesia in horses are discussed.

Hemodynamic and respiratory effects of segmental subarachnoid analgesia in adult Holstein cows.

Hemodynamic measurements, arterial and mixed venous blood gas tensions, and pH were determined in 13 adult, nonpregnant Holstein cows (511.3 +/- 77.3 kg) after subarachnoid injection of a 5% procaine hydrochloride solution (av dosage level of 0.162 +/- 0.026 mg/kg) at the thoracolumbar (T13-L1) intervertebral space. Segmental analgesia occurred within 8 to 12 minutes after completing the procaine HCl injection and extended between spinal cord segments T7 and L3 on both sides of the spinal column. The average duration of analgesia, as determined by the cows' responses to superficial and deep muscular pinpricks, was 35.8 +/- 8.5 minutes (25 to 60 minutes, min-max). Subarachnoid injection of procaine HCl caused a significant (P less than 0.05) increase in heart rate and significant (P less than 0.05) decreases in pulse pressure and rectal temperature. Cardiac output, stroke volume, left ventricular stroke work, left ventricular minute work, total peripheral resistance, arterial blood pressure, arterial and mixed venous blood gas tensions, pH, oxygen transport, oxygen uptake, PCV, and total solids did not change significantly (P greater than 0.05) from base-line values. Similarly, no significant changes (P greater than 0.05) were observed in a group of 5 control cows after subarachnoid injection of sodium chloride solution (1.5 ml, 0.9%) at the T13-L1 intervertebral space. Segmental subarachnoid analgesia caused minimal circulatory disturbance and was well tolerated by adult, conscious, unsedated cows.

Caudal analgesia induced by epidural or subarachnoid administration of detomidine hydrochloride solution in mares.

Seven adult mares were used to determine the analgesic, CNS, and cardiopulmonary effects of detomidine hydrochloride solution after epidural or subarachnoid administration, using both regimens in random sequence. At least 1 week elapsed between experiments. A 17-gauge Huber point (Tuohy) directional needle was used to place a catheter with stylet into either the epidural space at the first coccygeal interspace or the subarachnoid space at the lumbosacral intervertebral junction. Catheters were advanced so that the tips lay at the caudal sacral (S5 to S4) epidural space or at the midsacral (S3 to S2) subarachnoid space. Position of the catheter was confirmed radiographically. A 1% solution of detomidine HCl was injected into the epidural catheter at a dosage of 60 micrograms/kg of body weight, and was expanded to a 10-ml volume with sterile water to induce selective caudal epidural analgesia (CEA). A dose of 30 micrograms of detomidine HCl/kg expanded to a 3-ml volume with spinal fluid was injected into the subarachnoid catheter to induce caudal subarachnoid analgesia (CSA). Analgesia was determined by lack of sensory perception to electrical stimulation (avoidance threshold > 40 V, 0.5-ms duration) at the perineal dermatomes and no response to superficial and deep muscular pinprick stimulation at the pelvic limb and lumbar and thoracic dermatomes. Maximal CEA and CSA extended from the coccyx to spinal cord segments T15 and T14 at 10 to 25 minutes after epidural and subarachnoid drug administrations in 2 mares. Analgesia at the perineal area lasted longer after epidural than after subarachnoid administration (142.8 +/- 28.8 minutes vs 127.1 +/- 27.7 minutes). All mares remained standing. Both CEA and CSA induced marked sedation, moderate ataxia, minimal cardiopulmonary depression, increased frequency of second-degree atrioventricular heart block, and renal diuresis. All treatments resulted in significantly (P < 0.05) decreased heart rate, respiratory rate, systemic arterial blood pressure, PCV, and plasma total solids concentration. To the contrary, arterial carbon dioxide tension, plasma bicarbonate, and standard base excess concentrations were significantly (P < 0.05) increased. Arterial oxygen tension, pH, and rectal temperature did not change significantly from baseline values. Results indicate that use of detomidine for CEA and CSA in mares probably induces local spinal and CNS effects, marked sedation, moderate ataxia, mild cardiopulmonary depression, and renal diuresis.

Analgesic, hemodynamic, and respiratory effects induced by caudal epidural administration of meperidine hydrochloride in mares.

OBJECTIVE: To determine the analgesic, hemodynamic, and respiratory effects induced by caudal epidural administration of meperidine hydrochloride in mares. ANIMALS: 7 healthy mares. PROCEDURE: Each mare received meperidine (5%; 0.8 mg/kg of body weight) or saline (0.9% NaCl) solution via caudal epidural injection on 2 occasions. At least 2 weeks elapsed between treatments. Degree of analgesia in response to noxious electrical, thermal, and skin and muscle prick stimuli was determined before and for 5 hours after treatment. In addition, cardiovascular and respiratory variables were measured and degree of sedation (head position) and ataxia (pelvic limb position) evaluated. RESULTS: Caudal epidural administration of meperidine induced bilateral analgesia extending from the. coccygeal to S1 dermatomes in standing mares; degree of sedation and ataxia was minimal. Mean (+/- SD) onset of analgesia was 12 +/- 4 minutes after meperidine administration, and duration of analgesia ranged from 240 minutes to the entire 300-minute testing period. Heart and respiratory rates, rectal temperature, arterial blood pressures, Hct, PaO2, PaCO2, pHa, total solids and bicarbonate concentrations, and base excess were not significantly different from baseline values after caudal epidural administration of either meperidine or saline solution. CONCLUSIONS AND CLINICAL RELEVANCE: Caudal epidural administration of meperidine induced prolonged perineal analgesia in healthy mares. Degree of sedation and ataxia was minimal, and adverse cardiorespiratory effects were not detected. Meperidine may be a useful agent for induction of caudal epidural analgesia in mares undergoing prolonged diagnostic, obstetric, or surgical procedures in the anal and perineal regions.

Analgesic, hemodynamic, and respiratory effects of caudal epidurally administered xylazine hydrochloride solution in mares.

OBJECTIVE: To examine effects of 0.25 mg of xylazine/kg of body weight diluted to a total volume of 6 ml/450 kg with sterile 0.9% NaCl, administered into the epidural space of the sacrococcygeal joint on perineal analgesia, sedation, ataxia, and respiratory and cardiovascular function in standing mares. DESIGN: Randomized, blinded study, using xylazine (treatment) and 0.9% NaCl (controls). At least 2 weeks elapsed between the treatments. ANIMALS: Eight healthy mares. PROCEDURE: Blood samples were drawn. Systemic hemodynamics were determined, including cardiac output and pulmonary arterial, systemic arterial, and right atrial pressures. Two-way ANOVA with repeated measures was used to detect significant (P < 0.05) differences between mean scores of analgesia, sedation, ataxia, and cardiorespiratory variables before and during a 3-hour testing period. Analgesia was determined by lack of sensory perception to electrical stimulation at the perineal dermatome and no response to needle prick stimulation extending from coccyx to S3 dermatomes. Sedation was determined by head ptosis. RESULTS: Epidurally administered xylazine induced variable bilateral caudal analgesia extending from coccyx to S3, with minimal sedation, ataxia, and cardiovascular and respiratory depression in standing mares. Analgesia was attained at 15 +/- 6 minutes and lasted for 165 to over 180 minutes. Heart and respiratory rates, systolic, diastolic, and mean arterial blood pressure, PCV, hemoglobin concentration, arterial oxygen content, and oxygen transport were decreased after xylazine, but not 0.9% NaCl, treatment. Cardiac output, stroke volume, mean right atrial pressure, mean pulmonary artery pressure, systemic vascular resistance, pulmonary vascular resistance, arterial and mixed venous pH and gas tensions (PO2 and PCO2), oxygen consumption, blood temperature, and rectal temperature did not change significantly (P < 0.05) after epidural administration of xylazine or 0.9% NaCl. CONCLUSIONS: Caudal epidurally administered xylazine (0.25 mg/kg in 6 ml of 0.9% NaCl) can be given safely to induce prolonged (>2 hours) caudal analgesia with minimal sedation, ataxia, and circulatory and respiratory disturbances in conscious, standing mares.

Influence of atipamezole on effects of midsacral subarachnoidally administered detomidine in mares.

OBJECTIVE: To examine effects of atipamezole on detomidine midsacral subarachnoidally-induced analgesia, cardiovascular and respiratory activity, head ptosis, and position of pelvic limbs in healthy mares. ANIMALS: 10 healthy mares. PROCEDURE: Using a randomized, blinded, crossover study design, mares received detomidine (0.03 mg/kg of body weight, diluted in 3 ml of CSF) midsacral subarachnoidally, followed by atipamezole (0.1 mg/kg [test]) or sterile saline (0.9% NaCl) solution (control), i.v. 61 minutes later and saline solution (3 ml, midsacral subarachnoidally) on a separate occasion, at least 2 weeks later. Analgesia was determined by lack of sensory perception to electrical stimulation at the perineal dermatome and no response to needle-prick stimulation extending from the coccygeal to T15 dermatomes. Arterial acid-base (pH, standard bicarbonate, and base excess values), gas tensions (PO2, PCO2), PCV, total solids concentration, heart and respiratory rates, rectal temperature, and arterial blood pressure were determined, and mares were observed for sweating and urination. Mean scores of perineal analgesia, head ptosis, position of pelvic limbs, and cardiovascular and respiratory data were compared for the 3-hour test period. RESULTS: Subarachnoidally administered detomidine induced perineal analgesia (mean +/- SD onset, 9.0 +/- 4.6 minutes; duration, 130 +/- 26 minutes), marked head ptosis, moderate changes in pelvic limb position, cardiovascular and respiratory depression, sweating in analgesic zones, and diuresis. Intravenously administered atipamezole significantly reduced mean scores of detomidine-induced perineal analgesia, head ptosis, pelvic limb position, sweating and diuresis; partially antagonized detomidine-induced bradycardia; and did not effect detomidine-induced bradypnea. CONCLUSIONS AND CLINICAL RELEVANCE: Most effects of midsacral subarachnoidally administered detomidine, except bradycardia and bradypnea, were reversed by atipamezole (0.1 mg/kg, i.v.), indicating that most of the actions of detomidine were mediated via activation of alpha2-adrenergic receptors.

Effects of intravenously administered yohimbine on antinociceptive, cardiorespiratory, and postural changes induced by epidural administration of detomidine hydrochloride solution to healthy mares.

OBJECTIVE: To determine effects of i.v. administered yohimbine on perineal analgesia, cardiovascular and respiratory activity, and head and pelvic limb position in healthy mares following epidural administration of detomidine hydrochloride solution. ANIMALS: 8 healthy mares. PROCEDURE: Each mare received detomidine hydrochloride (0.06 mg/kg of body weight), administered in the caudal epidural space, followed 61 minutes later by yohimbine (0.05 mg/kg; test) or sterile saline (0.9% NaCl) solution (control), administered i.v., in a randomized, crossover study design with > or = 2 weeks between treatments. Analgesia was determined by lack of sensory perception to electrical stimulation of perineal dermatomes and needle-prick stimulation of coccygeal to 15th thoracic dermatomes. Arterial pH, PaCO2, PaO2, heart and respiratory rates, rectal temperature, arterial blood pressure, and cardiac output were determined, and mares were observed for sweating and urination. Mean scores obtained for test and control groups were compared. RESULTS: Intravenously administered yohimbine significantly reduced mean scores of detomidine-induced perineal analgesia, head ptosis, changes in pelvic limb position, and sweating and diuresis; antagonized detomidine-induced decreases in heart rate and cardiac output; but did not affect detomidine-induced decrease in respiratory rate. CONCLUSIONS AND CLINICAL RELEVANCE: Most effects of epidurally administered detomidine, except bradypnea, were antagonized by yohimbine, suggesting that detomidine may influence respiratory rate by mechanisms other than stimulation of alpha2-adrenoceptors, or that yohimbine induces respiratory depressant effects. Yohimbine may be an effective alpha2-adrenoceptor antagonist for all but respiratory depression following epidural administration of detomidine to mares.

Segmental epidural and subarachnoid analgesia in conscious horses: a comparative study.

Six adult horses were used to compare the effects of segmental epidural analgesia (SEA) and segmental subarachnoid analgesia (SSA). A 17-gauge Huber point directional needle was used to place a catheter with stylet into the epidural space or the subarachnoid space at the lumbosacral intervertebral junction and to catheterize the thoracolumbar epidural or subarachnoid space. The position of the catheter was confirmed radiographically. A 2% solution of mepivacaine hydrochloride was used at average doses of 80 mg (4 ml) to produce SEA and 30 mg (1.5 ml) to produce SSA. Onset of analgesia in response to superficial and deep muscular pinprick stimulations was significantly (P less than 0.05) faster in horses with SSA than with SEA (8.0 +/- 1.9 minutes vs 15.8 +/- 3.8 minutes). Maximal thoracolumbar analgesia extended from spinal cord segments T14 to L3 on both sides of the spinal column during SSA and from T12 to L2 on one or both sides during SEA. Duration of analgesia lasted significantly (P less than 0.05) longer in horses with SEA than in those with SSA (80.8 +/- 16.9 minutes vs 44.8 +/- 14.5 minutes). There was a significant (P less than 0.05) increase in subcutaneous temperature at the right and left 18th thoracic (T18) dermatomes and decreases of respiratory rate and rectal temperatures in horses with SEA. Respiratory rate and rectal temperature were not significantly (P greater than 0.05) decreased in horses with SSA.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma lidocaine concentrations in conscious horses after cervicothoracic (stellate) ganglion block with 1% lidocaine HCl solution.

Arterial and/or central venous plasma concentrations of lidocaine were determined in 12 nonmedicated adult horses (422 +/- 59 kg of body weight, mean +/- SD) after injecting a 1% lidocaine HCl solution into the cervicothoracic ganglion (CTG). A mean dosage of 2.9 +/- 0.5 mg of lidocaine/kg of body weight was used to induce unilateral CTG blockade in 8 horses and 4.8 +/- 0.8 mg was used to induce bilateral CTG blockade in 4 horses. Blood samples were collected before and at 5, 15, 30, 45, 60, 75, 90, 105, and 120 minutes after injection. The plasma lidocaine concentrations were determined by use of gas chromatography (sensitivity less than 0.01 microgram/ml). Cervicothoracic sympathetic blockade was characterized by Horner's syndrome and by profuse sweating over the face, neck, and thoracic limbs. Mean maximal venous concentrations of lidocaine were 0.86 +/- 0.33 microgram/ml at 26.3 +/- 6.9 minutes after unilateral CTG blockade, and 1.14 +/- 0.25 micrograms/ml at 31.2 +/- 18.9 minutes after bilateral CTG blockade. The mean venous and arterial concentrations of lidocaine were not significantly different at 45 and 120 minutes after injection. Venous concentrations of lidocaine were consistently higher than were concentrations in simultaneously collected arterial blood samples in 2 horses in which the right CTG and brachial plexus were temporarily anesthetized after repeated administration of 100 ml of lidocaine into the right CTG.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of xylazine, guaifenesin, and ketamine hydrochloride for restraint in horses.

A combination of intramuscular xylazine plus intravenous guaifenesin and ketamine hydrochloride was evaluated as a method for chemical restraint and casting of the adult horse. This drug combination provided safe and rapid induction of the horse and uneventful recovery from lateral recumbency. Cardiopulmonary function remained within base-line values for the adult horse, although cardiac output, arterial blood pressure, and arterial partial pressure of oxygen were decreased from base-line values. Xylazine, guaifenesin, and ketamine hydrochloride provided safe induction to general anesthesia with the inhalation anesthetics halothane or enflurane. Respiratory rate was significantly lower and arterial carbon dioxide higher during maintenance anesthesia with enflurane than with halothane. Recovery from general anesthesia was more rapid after enflurane than after halothane anesthesia.

Plasma mepivacaine concentrations after caudal epidural and subarachnoid injection in the horse: comparative study.

The venous plasma concentrations of mepivacaine were determined in 7 adult mares (420 +/- 17.1 kg) given an injection of a 2% solution of the hydrochloride at either the sacral (S2-3 to S5-C1) epidural space or the midsacral (S2-3) subarachnoid space. An average dose of 91.4 +/- 15.7 mg (4.6 +/- 0.8 ml) was needed to produce caudal epidural analgesia (CEA) and 26.7 +/- 5.4 mg (1.3 +/- 0.3 ml) to produce caudal subarachnoid analgesia (CSA). Maximal caudal analgesia extended from spinal cord segments S-1 to coccyx during CEA and CSA. The onset of analgesia as measured by response to superficial and deep muscular pinprick stimulations was significantly (P less than 0.05) faster in mares with CSA than with CEA (8.3 +/- 2.4 minutes vs 21.4 +/- 3.8 minutes). The period of analgesia was significantly (P less than 0.05) longer in mares with CEA than with CSA (80.0 +/- 11.5 minutes vs 67.4 +/- 26.3 minutes). The rate of vascular absorption of mepivacaine from the epidural space was significantly (P less than 0.05) faster than from the subarachnoid space. Maximum venous plasma concentrations of mepivacaine were similar (P greater than 0.05) after epidural and subarachnoid injections (0.05 +/- 0.03 micrograms/ml and 0.05 +/- 0.03 micrograms/ml) at the same times after mepivacaine administration (51.4 +/- 33.4 minutes and 53.6 +/- 24.3 minutes).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiopulmonary effects of narcotic agonists and a partial agonist in horses.

The cardiopulmonary effects of the narcotic agonists morphine, meperidine, oxymorphone, and methadone and of the partial agonist pentazocine were examined in the pain-free adult horse. The drugs produced dysphoric followed by euphoric effects. Increases in heart rate, arterial blood pressure, and cardiac output were observed in all horses with all drugs. Arterial blood pressure remained increased even after heart rate and cardiac output had returned to base-line values. Respiratory rate generally remained unchanged or increased shortly after drug administration and then decreased insignificantly (P less than 0.05) below base-line values at later times. Arterial pH and blood gas values (Paco2, Pao2) did not change.

Evaluation of xylazine and ketamine hydrochloride for anesthesia in horses.

The cardiopulmonary effects resulting from the combination of xylazine and ketamine hydrochloride were evaluated in the adult horse. Xylazine (1.1 mg mg/kg) administered intravenously prior to or simultaneously with ketamine hydrochloride (2.2 mg/kg; intravenous) provided excellent analgesia and light anesthesia in all horses. Cardiac output, arterial blood pressure, pulmonary arterial pressure, central venous pressure, and pulmonary arterial wedge pressure remained within normal limits for the adult horse. Evidence of respiratory acidosis developed with time during the anesthetic period. Induction and recovery from anesthesia appeared smooth and excitement-free. In the horse, larger dosages of ketamine hydrochloride (6.6 mg/kg) following sedation with xylazine (1.1 mg/kg; intravenous) were accompanied by muscular tremor and rigidity, mydriasis, oculogyric movements, sweating, hypertension, tachycardia, and increased rectal temperature during recovery from anesthesia. Providing there is good sedation from xylazine, the combination of xylazine and ketamine hydrochloride as a short-term intravenous anesthetic technique in the horse appears safe and acceptable providing reasonably stable cardiopulmonary function. If the sedative properties of xylazine are not apparent or if excessive dosages of ketamine hydrochloride are used, the drug combination results in serious side effects precluding its use for anesthesia in the horse.

Influence of tolazoline on caudal epidural administration of xylazine in cattle.

Eight adult female cattle (6 Holstein, 1 Jersey, 1 Brown Swiss) were used to determine the antagonistic effects of tolazoline, and alpha 2-adrenoceptor antagonist, on xylazine-induced (via caudal epidural administration) depression of CNS, respiratory, and cardiovascular activity and rumen motility. A 2% solution of xylazine HCl was injected into the epidural space at the first coccygeal interspace, using a dosage of 0.05 mg/kg of body weight, diluted to a 5-ml volume with sterile water, and administered at a rate of approximately 1 ml/30 s. Eight minutes after xylazine injection, either tolazoline (0.3 mg/kg) or saline solution (4 ml) was administered IV. All 8 cattle were treated, using both regimens in a random sequence; at least 1 week elapsed between treatments. Epidurally administered xylazine induced caudal analgesia (S3 to coccyx), as evaluated by no response to superficial and deep muscular pinprick, and induced sedation, cardiopulmonary depression, and inhibition of rumen motility, but all cattle remained standing. Tolazoline effectively reversed xylazine-induced rumen hypomotility, and partially antagonized xylazine-induced cardiopulmonary depression without affecting sedation and desirable local (S3 to coccyx) analgesic effects.

Spinal fluid concentrations of mepivacaine in horses and procaine in cows after thoracolumbar subarachnoid analgesia.

The CSF concentrations of mepivacaine in 10 Standardbred horses and of procaine in 10 Holstein cows given the drugs by thoracolumbar subarachnoid injection were determined. Mepivacaine hydrochloride was injected into the horses (502 +/- 60.5 kg) at an average dosage of 30 mg (1.5 ml of 20 mg/ml solution). Analgesia was produced 7.5 +/- 4.3 minutes after injection, extended between spinal cord segments T13 and L3 on both sides of the spinal column, and lasted 47 +/- 18.7 minutes at the T18 dermatome. Procaine hydrochloride was injected into cows (614 +/- 51.5 kg) at a dosage ranging between 75 mg and 100 mg (1.5 ml and 2 ml of 50 mg/ml solution). Analgesia was produced 8.2 +/- 2.0 minutes after injection, extended between spinal cord segments T11 and L4 on both sides of the spinal column, and lasted 47 +/- 17.5 minutes at the T13 dermatome. The critical CSF concentrations of local anesthetics required to eliminate response to pinprick stimulation were 204.4 +/- 90.3 micrograms of mepivacaine/ml in horses and 197.0 +/- 86.1 micrograms of procaine/ml in cows. Average CSF concentrations at 120 minutes after injections were made were 16.8 +/- 15.5 micrograms of mepivacaine/ml and 30.6 +/- 17.1 micrograms of procaine/ml. In in vitro experiments to determine the rates of hydrolysis of mepivacaine and procaine in CSF, significant changes (P greater than 0.05) were not seen in the CSF concentrations of mepivacaine in horses and procaine in cattle after a 120-minute incubation (37 C). The analgesic threshold concentrations of mepivacaine in CSF of horses and procaine in CSF of cows were similar.(ABSTRACT TRUNCATED AT 250 WORDS)