Doris H. Dyson

Epidural morphine reduces halothane MAC in the dog.

Morphine, 0.1 mg · kg−1 was administered epidurally on two different occasions to ten dogs to determine the effect of two different volumes of saline dilution, 0.13 and 0.26 ml · kg−1, on the minimum alveolar concentration (MAC) of halothane as determined by subcutaneous electrical current applied to the fore and hind limbs in a random order. Following MAC determination with halothane alone, epidural morphine was administered and MAC was redetermined. Epidural morphine significantly reduced, P < 0.001, the MAC of halothane for fore and hind legs in both volume groups; from 1.04 ± 0.038 to 0.68 ± 0.034 and 0.60 ± 0.017 for fore and hind limbs, respectively, in the large volume group, and from 0.96 ± 0.038 to 0.66 ± 0.088 and 0.60 ± 0.030 for fore and hind limbs, respectively, in the small volume group. The reduction in MAC was significantly greater, P < 0.025, in the hind limb. This study indicates that epidural morphine reduces the halothane requirements in the dog in a segmental manner. The volume of administration was not shown to be critical. Epidural morphine, 0.1 mg · kg−1, diluted in 0.13 to 0.26 ml · kg−1 saline produces significant analgesia in the dog as far forward as the fore limb and will reduce the halothane requirement to permit surgery.RésuméNous avons observé en deux fois l’effet du volume de dilution (0,13 et 0,26 ml · kg−1 ) d’une dose de morphine péridurale (0,1 mg · kg−1) sur la modification de la concentration alvéolaire minimale (MAC) de l’halothane de dix chiens, mesurée par application d’un courant électrique sous-cutané aux pattes avant et arrière, en ordre variable. Peu importe le volume de dilution, le MAC diminuait de façon significative (P < 0,001) apr’es l’injection de morphine péridurale et ce, pour les pattes avant et arrière. Respectivement pour les membres antérieurs et postérieurs, le MAC passait de 1,04 ± 0,038 à 0,68 ± 0,034 et 0,60 ± 0,017 avec le grand volume de dilution et de 0,96 ± 0,038 à 0,66 ± 0,088 et 0,60 ± 0,030 avec le petit volume. En fait, la baisse du MAC était plus marquée aux membres postérieurs (P < 0,025) et cela semble indiquer un effet segmentaire de la morphine péridurale. Cependant, qu’on utilise 0,13 ou 0,26 ml · kg−1 de salin pour diluer 0,1 mg · kg−1 de morphine péridurale importe peu chez le chien, car la réduction du MAC de l’halothane et l’atteinte d’une analgésie englobant les membres antérieurs est la même.

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.

Perioperative Pain Management in Veterinary Patients

Pain exists; however, we can prevent it, and we can treat it. The fallacy that pain is protective and must be allowed to avoid risk for damage after surgery needs to be eradicated. Preoperative and postoperative analgesia is directed at aching pain, whereas sharp pain associated with inappropriate movements persists. Analgesia provides much more benefit than concern. This article provides suggestions for development of an analgesic plan from the point of admission to discharge. These guidelines can then be adjusted according to the patients needs and responses.

Cardiopulmonary effects of anesthetic induction with thiopental, propofol, or a combination of ketamine hydrochloride and diazepam in dogs sedated with a combination of medetomidine and hydromorphone.

OBJECTIVE To evaluate the cardiopulmonary effects of anesthetic induction with thiopental, propofol, or ketamine hydrochloride and diazepam in dogs sedated with medetomidine and hydromorphone. ANIMALS 6 healthy adult dogs. PROCEDURES Dogs received 3 induction regimens in a randomized crossover study. Twenty minutes after sedation with medetomidine (10 microg/kg, IV) and hydromorphone (0.05 mg/kg, IV), anesthesia was induced with ketamine-diazepam, propofol, or thiopental and then maintained with isoflurane in oxygen. Measurements were obtained prior to sedation (baseline), 10 minutes after administration of preanesthetic medications, after induction before receiving oxygen, and after the start of isoflurane-oxygen administration. RESULTS Doses required for induction were 1.25 mg of ketamine/kg with 0.0625 mg of diazepam/kg, 1 mg of propofol/kg, and 2.5 mg of thiopental/kg. After administration of preanesthetic medications, heart rate (HR), cardiac index, and PaO(2) values were significantly lower and mean arterial blood pressure, central venous pressure, and PaCO(2) values were significantly higher than baseline values for all regimens. After induction of anesthesia, compared with postsedation values, HR was greater for ketamine-diazepam and thiopental regimens, whereas PaCO(2) tension was greater and stroke index values were lower for all regimens. After induction, PaO(2) values were significantly lower and HR and cardiac index values significantly higher for the ketamine-diazepam regimen, compared with values for the propofol and thiopental regimens. CONCLUSIONS AND CLINICAL RELEVANCE Medetomidine and hydromorphone caused dramatic hemodynamic alterations, and at the doses used, the 3 induction regimens did not induce important additional cardiovascular alterations. However, administration of supplemental oxygen is recommended.

INHALATION ANESTHESIA IN DUMERIL'S MONITOR (VARANUS DUMERILI) WITH ISOFLURANE, SEVOFLURANE, AND NITROUS OXIDE: EFFECTS OF INSPIRED GASES ON INDUCTION AND RECOVERY

Abstract Induction and recovery from inhalation anesthesia of Dumerils monitors (Varanus dumerili) using isoflurane, sevoflurane, and nitrous oxide (N2O) were characterized using a randomized crossover design. Mean times to induction for isoflurane in 100% oxygen (O2), sevoflurane in 100% O2, sevoflurane in 21% O2:79% nitrogen (N2; room air), and sevoflurane in 66% N2O:34% O2 were 13.00 ± 4.55, 11.20 ± 3.77, 10.40 ± 2.50, and 9.40 ± 2.80 min, respectively, at 26°C (n = 10). Mask induction with sevoflurane was significantly faster than with isoflurane. There was no significant difference between the induction time for sevoflurane in O2 or in room air, but sevoflurane combined with N2O resulted in significantly faster inductions than were obtained with sevoflurane in 100% O2. All treatments resulted in a significantly higher respiratory rate than in undisturbed animals. There were no significant differences in respiratory rate among lizards receiving O2, isoflurane in 100% O2, sevoflurane in room air, and sevoflurane combined with N2O, but animals receiving sevoflurane in O2 had a lower respiratory rate than those receiving pure O2. The sequence of complete muscle relaxation during induction was consistent and not significantly different among the four treatments: front limbs lost tone first, followed by the neck and the hind limbs; then the righting reflex was lost and finally tail tone. There were no significant differences in recovery times between isoflurane and sevoflurane or between sevoflurane in 100% O2 and sevoflurane combined with N2O. Similar recovery times were observed in animals recovering in 100 and 21% O2.

The cardiopulmonary effects of anesthetic induction with isoflurane, ketamine-diazepam or propofol-diazepam in the hypovolemic dog.

OBJECTIVE To evaluate and compare the cardiopulmonary effects of induction of anesthesia with isoflurane (Iso), ketamine-diazepam (KD), or propofol-diazepam (PD) in hypovolemic dogs. Study design Prospective randomized cross-over trial. ANIMALS Six healthy intact, mixed breed, female dogs weighing 20.7 +/- 4.2 kg and aged 22 +/- 2 months. Methods Dogs had 30 mL kg(-1) of blood removed at a rate of 1.5 mL kg(-1) minute(-1) under isoflurane anesthesia. Following a 30-minute recovery period, anesthesia was reinduced. Dogs were assigned to one of three treatments: isoflurane via facemask using 0.5% incremental increases in the delivered concentration every 30 seconds, 1.25 mg kg(-1) ketamine and 0.0625 mg kg(-1) diazepam intravenously (IV) with doses repeated every 30 seconds as required, and 2 mg kg(-1) propofol and 0.2 mg kg(-1) diazepam IV followed by 1 mg kg(-1) propofol increments IV every 30 seconds as required. Following endotracheal intubation all dogs received 1.7% end-tidal isoflurane in oxygen. Cardiopulmonary variables were recorded at baseline (before induction) and at 5 or 10 minute intervals following endotracheal intubation. RESULTS Induction time was longer in Iso (4.98 +/- 0.47 minutes) compared to KD (3.10 +/- 0.47 minutes) or PD (3.22 +/- 0.45 minutes). To produce anesthesia, KD received 4.9 +/- 2.3 mg kg(-1) ketamine and 0.24 +/- 0.1 mg kg(-1) diazepam, while PD received 2.2 +/- 0.4 mg kg(-1) propofol and 0.2 mg kg(-1) diazepam. End-tidal isoflurane concentration immediately following intubation was 1.7 +/- 0.4% in Iso. Arterial blood pressure and heart rate were significantly higher in KD and PD compared to Iso and in KD compared to PD. Arterial carbon dioxide partial pressure was significantly higher in PD compared to KD and Iso immediately after induction. CONCLUSIONS AND CLINICAL RELEVANCE In hypovolemic dogs, KD or PD, as used in this study to induce anesthesia, resulted in less hemodynamic depression compared to isoflurane.

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.

Anesthesia for patients with stable end-stage renal disease.

Patients with stable, end-state renal disease should be premedicated with an opioid and induced with minimal doses of an ultrashort barbiturate or isoflurane. Supplemental systemic or epidural analgesics can be administered if necessary. Urine output should be monitored in the perioperative period. If oliguria exists, fluids and perhaps a diuretic such as furosemide, mannitol, or dopamine should be administered.

Response of hypotensive dogs to dopamine hydrochloride and dobutamine hydrochloride during deep isoflurane anesthesia

OBJECTIVE To evaluate the dose-related cardiovascular and urine output (UrO) effects of dopamine hydrochloride and dobutamine hydrochloride, administered individually and in combination at various ratios, and identify individual doses that achieve target mean arterial blood pressure (MAP; 70 mm Hg) and cardiac index (CI; 150 mL/kg/min) in dogs during deep isoflurane anesthesia. ANIMALS 10 young clinically normal dogs. PROCEDURES Following isoflurane equilibration at a baseline MAP of 50 mm Hg on 3 occasions, dogs randomly received IV administration of dopamine (3, 7, 10, 15, and 20 microg/kg/min), dobutamine (1, 2, 4, 6, and 8 microg/kg/min), and dopamine-dobutamine combinations (3.5:1, 3.5:4, 7:2, 14:1, and 14:4 microg/kg/min) in a crossover study. Selected cardiovascular and UrO effects were determined following 20-minute infusions at each dose. RESULTS Dopamine caused significant dose-dependent responses and achieved target MAP and CI at 7 microg/kg/min; dobutamine at 2 microg/kg/min significantly affected only CI values. At any dose, dopamine significantly affected UrO, whereas dobutamine did not. Target MAP and CI values were achieved with a dopamine-dobutamine combination at 7:2 microg/kg/min; a dopamine-related dose response for MAP and dopamine- and dobutamine-related dose responses for CI were identified. Changes in UrO were associated with dopamine only. CONCLUSIONS AND CLINICAL RELEVANCE In isoflurane-anesthetized dogs, a guideline dose for dopamine of 7 microg/kg/min is suggested; dobutamine alone did not improve MAP. Data regarding cardiovascular and UrO effects indicated that the combination of dopamine and dobutamine did not provide greater benefit than use of dopamine alone in dogs.

Impact of dopamine or dobutamine infusions on cardiovascular variables after rapid blood loss and volume replacement during isoflurane-induced anesthesia in dogs

OBJECTIVE To determine the cardiovascular effects of dopamine and dobutamine infusions during nor-movolemia, hypovolemia (HV) through blood loss of 10 mL/kg (HV(10)), further loss to 25 mL/kg (HV(25)), and volume replacement (VR) in isoflurane-anesthetized dogs. ANIMALS 7 healthy young dogs. PROCEDURES Dogs were anesthetized with isoflurane 2 times (3 weeks apart). Cardiovascular measurements were obtained for each volume state. The cardiac index (CI) determined by the lithium dilution technique was compared with CI assessed by the arterial pulse contour technique. At each volume state, random treatment with dobutamine or dopamine was assessed (CI by the arterial pulse contour technique). Ten-minute treatments with 3 and 6 microg of dobutamine/kg/min or 7 and 14 microg of dopamine/kg/min (low and high doses, respectively) were administered sequentially. Differences from baseline were determined for volume, drug, and dose effects. RESULTS Significant proportional changes in blood pressure (BP), stroke index (SI), and CI were evident with changes in volume state. Systemic vascular resistance (SVR) decreased after VR. Dobutamine induced little change in BP; increased heart rate (HR), SI, and CI; and decreased SVR (high dose). Dopamine increased BP and SI, did not change CI, and increased SVR (high dose). The arterial pulse contour technique underestimated changes in CI associated with volume changes. CONCLUSIONS AND CLINICAL RELEVANCE Isoflurane eliminates clinically obvious compensatory increases in HR during HV. Dopamine is suitable for temporary management of blood loss in isoflurane-anesthetized dogs. Dobutamine increased CI without an associated improvement in BP. The arterial pulse contour monitor should be recalibrated when volume status changes.