Epidural analgesia and anesthesia.

This review describes the beneficial effects of the use of epidural drugs for pre-emptive analgesia, intraoperative analgesia with an inhalant-sparing effect, and prolonged postoperative analgesia. Epidural morphine oxymorphone, or hydromorphone is recommended for use in small animals in combination with a local anesthetic of appropriate duration for procedures involving the hind end, although epidural morphine or hydromorphone may be more appropriate for procedures on the thorax and forelimbs. Side effects are few and can usually be easily managed, with the benefits outweighing any detrimental effects that might occur.

Chemical restraint and analgesia for diagnostic and emergency procedures.

Diagnostic or emergency procedures are a necessity; however, the accompanying stress, discomfort, and pain must be considered and alleviated. The requirement for restraint and analgesia varies with the individual animal and its condition. Safe protocols are suggested for specific patient concerns. Recommendations for stabilization are included to reduce the detrimental effects of the drugs used. Alternatives are presented when feasible for animals in less critical condition. Technique of administration and dose adjustment is covered, as is drug selection.

Dose effect and benefits of glycopyrrolate in the treatment of bradycardia in anesthetized dogs.

This study evaluated the effectiveness of glycopyrrolate (0.005 or 0.01 mg/kg body weight (BW)) in anesthetized dogs (n = 40) for reversal of bradycardia (< 65 beats/min). Following random intravenous (i.v.) treatment, heart rate was determined at 5 min and, if it was < or = 70 beats/min, the lower dose was repeated. A 2-way analysis of variance considered dose and animal size (< or = 10 kg, > 10 kg) effects (P < 0.05). Glycopyrrolate produced a significant increase in heart rate and infrequent tachycardia (< or = 150 beats/min), which was not dose-related. The size of the dog produced a significant effect on baseline heart rate (higher in small), rate following the first dose (lower in small), and requirement for retreatment (47% in small, 13% in large). In a separate group of anesthetized dogs (n = 20), the blood pressure effect of glycopyrrolate (0.01 mg/kg BW, i.v.) treatment of bradycardia (65-85 beats/min, weight-adjusted) was studied. A significant increase in systolic, diastolic, and mean blood pressure was produced. In conclusion, the effective dose of glycopyrrolate treatment is size-related and produces a beneficial effect on blood pressure.

Cardiovascular effects of epidurally administered oxymorphone and an oxymorphone-bupivacaine combination in halothane-anesthetized dogs.

OBJECTIVE: To evaluate cardiovascular effects of epidurally administered oxymorphone (OXY) and an OXY-bupivacaine combination (O/B) in halothane-anesthetized dogs. ANIMALS: 6 dogs. PROCEDURE: In a randomized crossover design study, dogs were anesthetized with halothane and given OXY, O/B, and saline solution (SAL). Eucapnia and end-tidal halothane concentration of 1.2% were established. Heart rate (HR), systemic and pulmonary arterial pressures, central venous pressure (CVP), and cardiac output were measured at baseline and 5, 15, 30, 45, 60, and 75 minutes after treatment. At 90 minutes, glycopyrrolate was administered IV, and measurements were repeated at 95 minutes. Cardiac index (CI), stroke volume, stroke index, systemic vascular resistance (SVR), and left ventricular work were calculated. End-tidal halothane concentration was decreased to 0.8% from 17 to 45 minutes and to 0.5% from 47 to 95 minutes for OXY and O/B, whereas for SAL, it was maintained at 1.5 and 1.2%, respectively. Samples were obtained at 0, 2, 5, 15, 30, 45, 60, and 95 minutes for measurement of serum opiate concentration and comparison with values after IM administration of OXY. RESULTS: HR decreased, but CVP and SVR increased in response to OXY and O/B. These changes were reversed after IV administration of glycopyrrolate, resulting in significant increase in CI, compared with that in response to SAL. Serum opiate concentration increased markedly and peaked within 15 minutes after OXY and O/B administration but did not differ from values after IM administration. CONCLUSIONS: Epidural administration of OXY results in rapid systemic uptake and decreased HR. Glycopyrrolate administration improves HR, resulting in improved CI at equipotent halothane concentrations.

Effects of intravenously administered glycopyrrolate in anesthetized horses.

The purpose of this study was to determine the heart rate (HR) and blood pressure (BP) effect of glycopyrrolate in anesthetized horses with low HR (< or = 30 beats/min). The horses were randomly treated with glycopyrrolate (2.5 micrograms/kg body weight (BW)) or saline, intravenously (i.v.) (n = 17). If HR failed to increase (by > 5 beats/min within 10 min), glycopyrrolate (same dose) was administered. Heart rate increased by > 5 beats/min in 3 out of 9 horses following the initial glycopyrrolate treatment. Overall changes in HR and mean BP were not significantly different, while systolic and diastolic BP increased significantly (P < 0.025 using a Bonferroni corrected paired t-test). On the 2nd treatment, 3 out of 7 horses given 2.5 micrograms/kg BW glycopyrrolate, and 4 out of 5 horses given 5.0 micrograms/kg BW (total dose) showed an increase in heart rate of > 5 beats/min, which was significant. A significant increase in BP was produced following treatment with 2.5 micrograms/kg BW, but not following 5.0 micrograms/kg BW. A final increase in HR, of > 5 beats/min, was associated with a significant rise in BP (P < 0.05 using an unpaired t-test). In conclusion, an increase in HR can occur with 2.5 to 5.0 micrograms of glycopyrrolate/kg BW, i.v., and results in improvement in BP in anesthetized horses.

Plasma concentrations and cardiovascular influence of lidocaine infusions during isoflurane anesthesia in healthy dogs and dogs with subaortic stenosis.

OBJECTIVE: To determine the plasma concentrations and cardiovascular changes that occur in healthy dogs and dogs with aortic stenosis that are given an infusion of lidocaine during isoflurane anesthesia. STUDY DESIGN: Phase 1, controlled randomized cross-over trial; Phase 2, before and after trial ANIMALS: Phase 1, 6 healthy dogs (4 female, 2 male) weighing 23.8 +/- 7.4 kg; Phase 2, 7 dogs (4 female, 3 male) with moderate to severe subaortic stenosis (confirmed by Doppler echocardiography) weighing 31.1 +/- 14.5 kg. METHODS: After mask induction, intubation, and institution of positive pressure ventilation, instrumentation was performed to measure hemodynamic variables. After baseline, measurement at an end-tidal isoflurane concentration of 1.9% (phase 1) or 1.85% (phase 2), a loading dose infusion of lidocaine at 400 microg/kg/min was given. Phase 1: Maintenance doses of lidocaine were administered consecutively (40, 120, and 200 microg/kg/min) after the loading dose (given for 10, 10, and 5 minutes, respectively) in advance of each maintenance concentrations. Measurements were taken at the end of each loading dose and at 25 and 35 minutes during each maintenance level. The same animals on a different day were given dextrose 5% and acted as the control. Phase 2: Dogs were studied on a single occasion during an infusion of lidocaine at 120 microg/kg/ min given after the loading dose (10 minutes). Measurements occurred after the loading dose and at 25 and 35 minutes. A blood sample for lidocaine concentration was taken at 70 minutes. Data were compared using a one-way ANOVA for phase 1, and between phase 1 and 2. Statistical analysis for phase 2 was performed using a paired t-test with a Bonferroni correction. A P value < or = .05 was considered significant. RESULTS: Phase 1: Plasma lidocaine concentrations achieved with 40, 120, and 200 microg of lidocaine/kg/min were 2.70, 5.27, and 7.17 microg/mL, respectively. A significant increase in heart rate (HR) (all concentrations), central venous pressure (CVP), mean pulmonary arterial pressure (PAP), and a decrease in stroke index (SI) (200 microg/kg/min) were observed. An increase in systemic vascular resistance (SVR) and mean PAP, and a decrease in SI also followed the loading dose given before the 200 microg/kg/min infusion. No other significant differences from the control measurements, during dextrose 5% infusion alone, were detected. Phase 2: Plasma lidocaine concentrations achieved were 5.35, 4.23, 4.23, and 5.60 microg/mL at 10, 25, 35, and 70 minutes, respectively. They were not significantly different from concentrations found in our healthy dogs at the same infusions. A significant but small increase in CVP compared with baseline was noted after the loading dose. There were no significant differences from baseline shown in all other cardiovascular data. There were no statistically significant differences in any measurements taken during the lidocaine infusion between the dogs in phase 1 and phase 2. Dogs with aortic stenosis tended to have a lower cardiac index than healthy dogs at baseline (88 v 121 mL/kg/min) and during lidocaine infusion (81 v 111 mL/kg/min). A small, statistically significant difference in systolic PAP was present at baseline. CONCLUSIONS: There does not appear to be any detrimental cardiovascular effects related to an infusion of lidocaine at 120 microg/kg/min during isoflurane anesthesia in healthy dogs or dogs with aortic stenosis. The technique used in this study resulted in therapeutic plasma concentrations of lidocaine. CLINICAL RELEVANCE: Methods shown in the study can be used in clinical cases to achieve therapeutic lidocaine levels without significant cardiovascular depression during isoflurane anesthesia.

Morbidity and mortality associated with anesthetic management in small animal veterinary practice in Ontario.

During 1993, 66 small animal practices participated in a prospective study to evaluate the incidence and details of anesthetic-related morbidity and mortality. Considering a total of 8,087 dogs and 8,702 cats undergoing anesthesia, the incidences of complications were 2.1% and 1.3%, respectively. Death occurred in 0.11% and 0.1% of cases, respectively. Logistic regression models were developed and showed that a significant odds ratio (OR) of complications in dogs was associated with xylazine (OR, 91.5); heart rate monitoring (OR, 3.2); American Society of Anesthesiologists (ASA) 3, 4, or 5 classification (OR, 2.5); isoflurane (OR, 2.4); butorphanol (OR, 0.35); technician presence (OR, 0.26); acepromazine (OR, 0.24); ketamine (OR, 0.21); and mask induction (OR, 0.2). Complications in cats were associated with ASA 3, 4, or 5 classification (OR, 5.3); diazepam (OR, 4.1); intubation (OR, 1.7); butorphanol (OR, 0.45); and ketamine (OR, 0.17). Cardiac arrest in dogs was associated with xylazine (OR, 43.6) and ASA 3, 4, or 5 classification (OR, 7.1). Cardiac arrest in cats was associated with ASA 3, 4, or 5 classification (OR, 21.6) and technician presence (OR, 0.19). This paper reports the incidences of complications and cardiac arrest in small animal practice and identifies common complications and factors that may influence anesthetic morbidity and mortality. This information may be useful in comparing anesthetic management practices.

End tidal halothane concentration and postoperative analgesia requirements in dogs: a comparison between intravenous oxymorphone and epidural bupivacaine alone and in combination with oxymorphone.

The purpose of this study was to compare the effects of epidural bupivacaine (BUP) and oxymorphone/bupivacaine (O/B) and intravenous (i.v.) oxymorphone (IVO) on halothane requirements during hind end surgery and postoperative analgesia in 24 dogs. Dogs were randomly assigned to treatment groups: O/B--oxymorphone (0.1 mg/kg) in 0.75% bupivacaine (1 mg/kg for a total volume of 0.2 ml/kg); BUP--0.5% bupivacaine (1 mg/kg for a total volume of 0.2 ml/kg) with i.v. oxymorphone (0.05 mg/kg) postoperatively; and IVO--oxymorphone (0.05 mg/kg) pre- and postoperatively. Heart rate (HR), respiratory rate, arterial blood pressure, end-tidal carbon dioxide and halothane, and arterial blood gases were recorded prior to treatment and every 15 minutes thereafter. Once surgery had begun, end-tidal halothane concentrations were decreased as low as possible while still maintaining a stable anesthetic plane. Data were analyzed using ANOVA with P < 0.05 considered significant. End-tidal halothane requirements did not differ significantly among treatments. Respiratory depression was increased and HR was decreased in the O/B and IVO groups. Postoperative analgesic requirements were significantly less in dogs receiving O/B.

Assessment of 3 audible monitors during hypotension in anesthetized dogs.

Severe hypotension was produced in 8 dogs during halothane anesthesia. Three monitors detecting respiratory rate, Doppler signal and pulse rate were compared to direct blood pressure measurements. Deep anesthesia was most consistently detected using the respiratory monitor. The signal fade of the Doppler device was best at detecting hypotension from blood loss. Changes in heart rate were not useful.

Cardiopulmonary and gastrointestinal motility effects of xylazine/ketamine-induced anesthesia in horses previously treated with glycopyrrolate.

OBJECTIVE: To assess the usefulness of glycopyrrolate (GLY) in preventing the decrease in cardiac index (CI) usually caused by xylazine (XYL)/ketamine (KET)-induced anesthesia in horses. ANIMALS: 6 healthy horses. PROCEDURE: Horses were treated with saline solution or 2.5 micrograms of GLY/kg of body weight, administered i.v. 15 minutes later, XYL (1 mg/kg) was administered i.v., followed 5 minutes later by KET (2 mg/kg) administration. The horses were positioned in left lateral recumbency, insufflated with 15 L of oxygen/min, and maintained for 30 minutes on the infusion of 0.05 mg of XYL and 0.1 mg of KET/kg/min. Mean, systolic, and diastolic arterial blood pressures, mean pulmonary arterial and central venous pressures, heart rate, CI, and arterial and mixed venous blood gas tensions were recorded up to 40 minutes after anesthesia induction. Intestinal motility was assessed by auscultation of 4 abdominal quadrants for 24 hours after induction. Data were analyzed by Wilcoxon's rank-sum test for nonparametric observations, and by ANOVA for repeated measures and Scheffé's test for continuous parametric variables. RESULTS: Horses given GLY had significantly higher heart rate; mean, systolic, and diastolic arterial blood pressures; CI; oxygen delivery; and mixed venous oxygen tensions, with significantly less tissue oxygen extraction, compared with saline-treated horses. Both groups had complete loss of intestinal motility associated with general anesthesia. CONCLUSIONS: GLY significantly reduced the cardiovascular dysfunction attributable to general anesthesia with XYL and KET. The return of intestinal motility was delayed by 3 to 6 hours without causing any serious side effects.

Cardiorespiratory effects of a 5HT2 antagonist (R51703) in awake and anesthetized dogs.

To investigate cardiorespiratory effects of an experimental 5-hydroxytryptamine receptor antagonist (R51703) with sedative properties, intramuscular doses of the drug were studied in 6 awake dogs of mixed breed, and in 6 anesthetized beagles. Two doses (0.2 and 0.4 mg/kg) of R51703 and a saline control were studied in the awake dogs using a randomized crossover trial. Subsequently, the higher dose of R51703 was included as a component of halothane anesthesia to determine whether the halothane sparing effect of R51703 produced a beneficial alteration of hemodynamic function. Data were obtained at equipotent halothane/R51703 (H/R) and halothane/saline (H/S) doses equivalent to 1.0, 1.5 and 2.0 MAC. In awake dogs, heart rates tended to be lower in dogs sedated with R51703, significantly so at 30 min for both doses, and at 90 and 120 min for the 0.2 and 0.4 mg/kg doses, respectively (P < 0.05). The cardiac index (CI) was lower at 60 min with both doses compared to the saline control group. Both doses of R51703 reduced mean blood pressure at 30, 90 and 120 min, and diastolic pressure at 30 and 90 min after administration; however, systolic blood pressure (SBP) was not altered. Overall, the cardiovascular alterations were minimal in conscious dogs and there was no evidence of respiratory depression. In the anesthetized dogs, at equipotent MAC, CI tended to be lower with H/R than with H/S, though the difference was not significant. Heart rate and stroke volume index also tended to be lower in the dogs treated with R51703, while systemic vascular resistance tended to be higher: these changes were not significant. Mean and SBP were higher at each MAC multiple in the H/R group. It was concluded that the halothane sparing effect of R51703 did not substantially improve hemodynamic function compared to the use of halothane alone at equipotent doses.

An evaluation of the influence of medetomidine hydrochloride and atipamezole hydrochloride on the arrhythmogenic dose of epinephrine in dogs during halothane anesthesia.

Alterations in the arrhythmogenic dose of epinephrine (ADE) were determined following administration of medetomidine hydrochloride (750 micrograms/M2) and a saline placebo, or medetomidine hydrochloride (750 micrograms/M2), followed by specific medetomidine reversal agent, atipamezole hydrochloride (50 micrograms/kg) 20 min later, in halothane-anesthetized dogs (n = 6). ADE determinations were made prior to the administration of either treatment, 20 min and 4 h following medetomidine/saline or medetomidine/atipamezole administration. Epinephrine was infused for 3 min at increasing dose rates (2.5 and 5.0 micrograms/kg/min) until the arrhythmia criterion (4 or more intermittent or continuous premature ventricular contractions) was reached. The interinfusion interval was 20 min. There were no significant differences in the amount of epinephrine required to reach the arrhythmia criterion following the administration of either treatment. In addition, the ADE at each determination was not different between treatment groups. In this study, the administration of medetomidine to halothane-anesthetized dogs did not alter their arrhythmogenic response to infused epinephrine.

Cardiopulmonary effects of hypercapnia during controlled intermittent positive pressure ventilation in the horse.

The cardiopulmonary effects of eucapnia (arterial CO2 tension [PaCO2] 40.4 +/- 2.9 mm Hg, mean +/- SD), mild hypercapnia (PaCO2, 59.1 +/- 3.5 mm Hg), moderate hypercapnia (PaCO2, 82.6 +/- 4.9 mm Hg), and severe hypercapnia (PaCO2, 110.3 +/- 12.2 mm Hg) were studied in 8 horses during isoflurane anesthesia with volume controlled intermittent positive pressure ventilation (IPPV) and neuromuscular blockade. The sequence of changes in PaCO2 was randomized. Mild hypercapnia produced bradycardia resulting in a significant (P < 0.05) decrease in cardiac index (CI) and oxygen delivery (DO2), while hemoglobin concentration (Hb), the hematocrit (Hct), systolic blood pressure (SBP), mean blood pressure (MBP), systemic vascular resistance (SVR), and venous admixture (QS/QT) increased significantly. Moderate hypercapnia resulted in a significant rise in CI, stroke index (SI), SBP, MBP, mean pulmonary artery pressure (PAP), Hct, Hb, arterial oxygen content (CaO2), mixed venous oxygen content (CvO2), and DO2, with heart rate (HR) staying below eucapnic levels. Severe hypercapnia resulted in a marked rise in HR, CI, SI, SBP, PAP, Hct, Hb, CaO2, CvO2, and DO2. Systemic vascular resistance was significantly decreased, while MBP levels were not different from those during moderate hypercapnia. No cardiac arrhythmias were recorded with any of the ranges of PaCO2. Norepinephrine levels increased progressively with each increase in PaCO2, whereas plasma cortisol levels remained unchanged. It was concluded that hypercapnia in isoflurane-anesthetized horses elicits a biphasic cardiopulmonary response, with mild hypercapnia producing a fall in CI and DO2 despite an increase in MBP, while moderate and severe hypercapnia produce an augmentation of the cardiopulmonary performance and DO2.

Intraosseous cannulation and drug administration for induction of anesthesia in chickens.

Twenty-four chickens were randomly assigned to one of three treatments (ketamine, 30 mg/kg; thiopental, 20 mg/kg; saline, 0.8 mL). Baseline data (heart rate, respiratory rate, systolic blood pressure, and cloacal temperature) were recorded before ulnar intraosseous cannulation and administration of drug treatment and for 30 minutes after administration. One investigator, unaware of the treatment administered, assessed the reaction to cannulation, number of attempts per cannulation, reaction to injection, time to induction and recovery, and quality of induction and recovery. Respiratory rate increased significantly (p < .05) from baseline after thiopental. Other parameters did not vary within groups or between groups. Most birds did not react or had a mild reaction to cannulation and injection, and on average fewer than two attempts were necessary. Quality of recovery was significantly (p < .05) better after thiopental. Time to recovery was significantly (p < .05) shorter after thiopental. No major histopathologic changes were noted in bone marrow samples from the injection site. This study demonstrates that the intraosseous route may be used to induce anesthesia in chickens, and that minimal changes in the variables studied were produced by ketamine and thiopental.

Comparison of medetomidine and fentanyl-droperidol in dogs: sedation, analgesia, arterial blood gases and lactate levels.

Medetomidine and fentanyl-droperidol (Innovar-vet) were assessed over a three hour period in 80 healthy dogs. Following physical examination, electrocardiogram (ECG), arterial blood sample analysis, and dynamometer pressure threshold (analgesia score), the dogs were randomly assigned to one of four treatments: Miv--medetomidine (750 micrograms/M2) administered intravenously (IV), Mim--medetomidine (1000 micrograms/M2) administered intramuscularly (IM), Iiv--Innovar-vet IV (0.05 mL/kg) or Iim--Innovar-vet IM (0.1 mL/kg). All assessments were carried out by a single individual unaware of the treatment used. Objective assessments included temperature, heart and respiratory rates, analgesia score, arterial blood gases, acid-base and lactate levels. Subjective evaluation included degree of sedation, response to various clinical procedures, noise responsiveness, posture, and the incidence of side effects. Onset and duration of effect were also recorded. The ECG strips were assessed for arrhythmias. Data was analyzed using a 3-way analysis of variance for continuous variables and a Chi-square analysis of frequencies. A p value < or = 0.05 was considered significant. Medetomidine-treated animals had a decreased respiratory rate, longer duration of analgesic effect, increased incidence of bradycardia, vomiting and twitching, were less noise responsive and shivered less throughout the study. An increased incidence of second degree heart block with Miv (15 min), a delayed onset and recovery with Mim and increased lactate levels following Iiv (15 min) were observed. No differences were found in other measurements and good to excellent chemical restraint was produced with all treatments in 65% or more cases.

Analgesia after lateral thoracotomy in dogs. Epidural morphine vs. intercostal bupivacaine.

One of two analgesic treatments was randomly assigned to 40 dogs undergoing lateral thoracotomy. Group E (20 dogs) received an epidural injection of morphine (0.1 mg/kg) before surgery. Group I (20 dogs) received injections of bupivacaine around five intercostal nerves when the thorax was about to be closed. All dogs were given an opioid as part of their preoperative medication (meperidine or butorphanol), followed by thiopental for induction and halothane or methoxyflurane for maintenance of anesthesia. Scores were assigned for pre-operative demeanor and response to restraint and injection. Alertness, undisturbed pain behavior, and response to palpation of the wound were assessed 3, 6, 12, and 24 hours after surgery. Dogs that appeared uncomfortable were given analgesics. Blood for evaluation of arterial blood gases was obtained at 3 and 6 hours after surgery. The person scoring the dogs was blinded to the treatment given. There were no statistically significant differences between the groups. Group E contained more "nervous" dogs (12 vs. 6) and more dogs in group E received postoperative analgesics (8 vs. 2). Both techniques appeared to provide adequate analgesia for most dogs.