Alexander Valverde

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.

Effect of a constant rate infusion of lidocaine on the quality of recovery from sevoflurane or isoflurane general anaesthesia in horses

REASONS FOR PERFORMING STUDY Lidocaine constant rate infusions (CRIs) are common as an intraoperative adjunct to general anaesthesia, but their influence on quality of recovery has not been thoroughly determined. OBJECTIVES To determine the effects of an intraoperative i.v. CRI of lidocaine on the quality of recovery from isoflurane or sevoflurane anaesthesia in horses undergoing various surgical procedures, using a modified recovery score system. HYPOTHESIS The administration of intraoperative lidocaine CRI decreases the quality of recovery in horses. METHODS Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min) or saline was administered for the duration of surgery or until 30 mins before the end of surgery under isoflurane (n = 27) and sevoflurane (n = 27). RESULTS Horses receiving lidocaine until the end of surgery had a significantly higher degree of ataxia and a tendency towards significance for a lower quality of recovery. There was no correlation between lidocaine plasma concentrations at recovery and the quality of recovery. CONCLUSIONS Intraoperative CRI of lidocaine affects the degree of ataxia and may decrease the quality of recovery. POTENTIAL RELEVANCE Discontinuing lidocaine CRI 30 mins before the end of surgery is recommended to reduce ataxia during the recovery period.

Epidural Analgesia and Anesthesia in Dogs and Cats

Current knowledge of drugs administered epidurally has allowed an effective way of providing analgesia for a wide variety of conditions in veterinary patients. Proper selection of drugs and dosages can result in analgesia of specific segments of the spinal cord with minimal side effects. Epidural anesthesia is an alternative to general anesthesia with inhalation anesthetics, although the combination of both techniques is more common and allows for reduced doses of drugs used with each technique. Epidural anesthesia and intravenous anesthetics can also be used without inhalation anesthetics in surgical procedures caudal to the diaphragm.

Alpha-2 agonists as pain therapy in horses.

Alpha-2 agonists, such as xylazine, clonidine, romifidine, detomidine, medetomidine, and dexmedetomidine, are potent analgesic drugs that also induce physiologic and behavioral changes, such as hypertension, bradycardia, atrioventricular block, excessive sedation and ataxia, all of which can potentially limit their systemic use as analgesics in some clinical cases. The use of medetomidine and dexmetomidine has been introduced for equine anesthesia/analgesia, and although not approved in this species, their increased specificity for alpha-2 receptors may offer some potential advantages over the traditional alpha-2 agonists. Similarly, other routes of administration and benefits of alpha-2 agonists are recognized in the human and laboratory animal literature, which may prove useful in the equine patient if validated in the near future. This review presents this relevant information.

Behavioural and cardiorespiratory effects of a constant rate infusion of medetomidine and morphine for sedation during standing laparoscopy in horses

REASONS FOR PERFORMING STUDY Standing surgical procedures are performed commonly in horses under sedation. This approach minimises the morbidity/mortality risks associated with general anaesthesia. The use of a medetomidine and morphine combination has not been investigated in horses despite the usefulness of each drug individually. OBJECTIVE To determine the efficacy of a medetomidine and morphine combination to produce standing sedation with minimal cardiorespiratory changes and adequate analgesia for exploratory laparascopy in mature horses. HYPOTHESIS The combination of medetomidine and morphine will induce reliable sedation with minimal cardiorespiratory changes. METHODS Medetomidine (5 microg/kg bwt i.v.) followed in 10 min by morphine (50 microg/kg bwt i.v.) and 10 min later by a constant rate infusion (CRI) of medetomidine and morphine (5 and 30 microg/kg bwt/h, respectively) was administered in 7 horses undergoing standing exploratory laparoscopy. Quality of sedation and cardiorespiratory function were assessed. RESULTS Sedation was satisfactory after the medetomidine and morphine bolus. The CRI of both drugs enhanced sedation and ataxia. Mean visual analogue scores on a scale of 10 varied between 7.8 and 8.8 and were similar between anaesthesiologists and surgeons. Heart rate, respiratory rate and packed cell volume (PCV) decreased significantly after medetomidine and, at some periods, during the CRI. Blood pressure only increased significantly at 5 min and arterial O2 decreased significantly at 10 min post medetomidine. PCV remained significantly lower and total protein decreased post morphine and CRI administration. Arterial CO2 increased towards the end of the CRI. Cardiac output did not change significantly over time. CONCLUSION AND CLINICAL RELEVANCE The combination of medetomidine and morphine results in reliable sedation and stable cardiorespiratory function in horses undergoing exploratory laparascopy.

Comparison of cardiovascular function and quality of recovery in isoflurane‐anaesthetised horses administered a constant rate infusion of lidocaine or lidocaine and medetomidine during elective surgery

REASONS FOR PERFORMING STUDY The effects of lidocaine combined with medetomidine or lidocaine alone on cardiovascular function during anaesthesia and their effects on recovery have not been thoroughly investigated in isoflurane-anaesthetised horses. OBJECTIVES To determine the effects of an intraoperative i.v. constant rate infusion of lidocaine combined with medetomidine (Group 1) or lidocaine (Group 2) alone on cardiovascular function and on the quality of recovery in 12 isoflurane-anaesthetised horses undergoing arthroscopy. HYPOTHESIS The combination would depress cardiovascular function but improve the quality of recovery when compared to lidocaine alone in isoflurane-anaesthetised horses. METHODS Lidocaine (2 mg/kg bwt i.v. bolus followed by 50 microg/kg bwt/min i.v.) or lidocaine (same dose) and medetomidine (5 microg/kg bwt/h i.v.) was started 30 min after induction of anaesthesia. Lidocaine administration was discontinued 30 min before the end of surgery in both groups, whereas medetomidine administration was continued until the end of surgery. Cardiovascular function and quality of recovery were assessed. RESULTS Horses in Group 1 had longer recoveries, which were of better quality due to better strength and overall attitude during the recovery phase than those in Group 2. Arterial blood pressure was significantly higher in Group 1 than in Group 2 and this effect was associated with medetomidine. No significant differences in cardiac output, arterial blood gases, electrolytes and acid-base status were detected between the 2 groups. CONCLUSIONS AND POTENTIAL RELEVANCE The combination of an intraoperative constant rate infusion of lidocaine and medetomidine did not adversely affect cardiovascular function in isoflurane-anaesthetised horses and improved the quality of recovery when compared to an intraoperative infusion of lidocaine alone.

Effect of remifentanil hydrochloride administered via constant rate infusion on the minimum alveolar concentration of isoflurane in cats

OBJECTIVE To evaluate the effects of increasing doses of remifentanil hydrochloride administered via constant rate infusion (CRI) on the minimum alveolar concentration (MAC) of isoflurane in cats. ANIMALS 6 healthy adult cats. PROCEDURES For each cat, 2 experiments were performed (2-week interval). On each study day, anesthesia was induced and maintained with isoflurane; a catheter was placed in a cephalic vein for the administration of lactated Ringers solution or remifentanil CRIs, and a catheter was placed in the jugular vein for collection of blood samples for blood gas analyses. On the first study day, individual basal MAC (MAC(Basal)) was determined for each cat. On the second study day, 3 remifentanil CRIs (0.25, 0.5, and 1.0 microg/kg/min) were administered (in ascending order); for each infusion, at least 30 minutes elapsed before determination of MAC (designated as MAC(R0.25), MAC(R0.5), and MAC(R1.0), respectively). A 15-minute washout period was allowed between CRIs. A control MAC (MAC(Control)) was determined after the last remifentanil infusion. RESULTS Mean +/- SD MAC(Basal) and MAC(Control) values at sea level did not differ significantly (1.66 +/- 0.08% and 1.52 +/- 0.21%, respectively). The MAC values determined for each remifentanil CRI did not differ significantly. However, MAC(R0.25), MAC(R0.5), and MAC(R1.0) were significantly decreased, compared with MAC(Basal), by 23.4 +/- 7.9%, 29.8 +/- 8.3%, and 26.0 +/- 9.4%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE The 3 doses of remifentanil administered via CRI resulted in a similar degree of isoflurane MAC reduction in adult cats, indicating that a ceiling effect was achieved following administration of the lowest dose.

Balanced Anesthesia and Constant-Rate Infusions in Horses

Balanced anesthetic techniques are commonly used in equine patients, and include the combination of a volatile anesthetic with at least one injectable anesthetic throughout the maintenance period. Injectable anesthetics used in balanced anesthesia include the α2-agonists, lidocaine, ketamine, and opioids, and those with muscle-relaxant properties such as benzodiazepines and guaifenesin. Administration of these injectable anesthetics is best using constant-rate infusions based on the pharmacokinetics of the drug, which allows steady-state concentrations and predictable pharmacodynamic actions. This review summarizes the different drug combinations used in horses, and provides calculated recommended doses based on the pharmacokinetics of individual drugs.

Determination of cardiac output in neonatal foals by ultrasound velocity dilution and its comparison to the lithium dilution method.

OBJECTIVE To compare cardiac output (CO) measured by use of lithium dilution (LiDCO) and ultrasound velocity dilution (UDCO) in conditions of high, intermediate, and low CO in anesthetized foals. DESIGN Original prospective study. SETTING University teaching hospital. ANIMALS Six foals 1-3 days of age (38-45 kg). INTERVENTIONS Neonatal foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. The CO was measured by use of LiDCO and UDCO techniques. Measurements were obtained from each foal at baseline and during low, intermediate, and high CO states. Measurements were converted to cardiac index (cardiac index=CO/body weight) values for statistical analysis. Agreement between the 2 methods was determined using Bland and Altman analysis and concordance correlation coefficients. MEASUREMENTS AND MAIN RESULTS LiDCO determinations of CO ranged between 4.0 and 14.0 L/min resulting in cardiac index ranging between 75.5 and 310 mL/kg/min. There was no significant effect of blood pressure variation on bias or relative bias (P=0.62 and 0.93, respectively). The mean bias and relative bias of UDCO (+/-SD) compared with LiDCO were -20.1+/-39.2 mL/kg/min and -7.7+/-23.4%, respectively. Concordance correlation coefficient between LiDCO and UDCO was 0.833. CONCLUSIONS When compared with LiDCO, the UDCO technique has acceptable clinical utility for measuring CO in healthy anesthetized newborn foals.

Evaluation of the efficacy and safety for use of two sedation and analgesia protocols to facilitate assisted ventilation of healthy dogs.

OBJECTIVE To determine the effectiveness and safety of 2 sedative-analgesic protocols to facilitate assisted ventilation in healthy dogs. ANIMALS 12 healthy dogs. PROCEDURES Dogs were randomly assigned to 2 groups. Mean dosages for protocol 1 were diazepam (0.5 mg/kg/h [n = 3 dogs]) or midazolam (0.5 mg/kg/h [3]), morphine (0.6 mg/kg/h [6]), and medetomidine (1.0 microg/kg/h [6]). Mean dosages for protocol 2 were diazepam (0.5 mg/kg/h [n = 3]) or midazolam (0.5 mg/kg/h [3]), fentanyl (18 microg/kg/h [6]), and propofol (2.5 mg/kg/h [6]). Each dog received the drugs for 24 consecutive hours. All dogs were mechanically ventilated with adjustments in minute volume to maintain normocapnia and normoxemia. Cardiorespiratory variables were recorded. A numeric comfort score was assigned hourly to assess efficacy. Mouth care, position change, and physiotherapy were performed every 6 hours. Urine output was measured every 4 hours. RESULTS Use of both protocols maintained dogs within optimal comfort ranges > 85% of the time. The first dog in each group was excluded from the study. Significant decreases in heart rate, oxygen consumption, and oxygen extraction ratio were evident for protocol 1. Cardiac index values in ventilated dogs were lower than values reported for healthy unsedated dogs. Oxygen delivery, lactate concentration, and arterial base excess remained within reference ranges for both protocols. CONCLUSIONS AND CLINICAL RELEVANCE Use of both protocols was effective for facilitating mechanical ventilation. A reduction in cardiac index was detected for both protocols as a result of bradycardia. However, oxygen delivery and global tissue perfusion were not negatively affected.