Comparison Between Medetomidine and a Medetomidine-Vatinoxan Combination on Cardiorespiratory Variables in Dogs Undergoing Ovariectomy Anesthetized with Butorphanol, Propofol and Sevoflurane or Desflurane

The aim of this study was to compare the effects of a medetomidine-vatinoxan combination versus medetomidine alone on heart rate (HR) and mean arterial pressure (MAP) in a short-term surgery in dogs. Four groups of 10 dogs were administered as follows: medetomidine and sevoflurane; medetomidine and desflurane; medetomidine-vatinoxan and sevoflurane; and medetomidine-vatinoxan and desflurane. After administration, the increase in MAP soon stopped at 102-104 mmHg in the two groups administered medetomidine-vatinoxan, compared with significantly higher values of 143-126 mmHg achieved in the two groups administered medetomidine alone. The lowest MAPs in the two medetomidine-vatinoxan groups were 46-50 mmHg, while in the medetomidine groups, they were 58-79 mmHg. From 3 min onwards after administration, in the medetomidine-vatinoxan treatments, HR remained at values very close to those of pre-administration, between 83 and 118 beats min-1, while in the medetomidine treatments, it dropped to 36-43 beats min-1 and then slowly rose to reach 71-90 beats min-1. These results encourage the use of vatinoxan in clinical settings, particularly in anesthetic protocols for dogs when bradycardia and an increase in systemic pressure should be avoided. Further clinical studies are needed to manage the short periods of hypotension, as well as the slight reduction in sedative and pain-relieving medetomidine effects found, particularly when vatinoxan is in combination with desflurane rather than sevoflurane.

The effect of remifentanil infusion on sevoflurane minimum alveolar concentration-no movement (MACNM) and bispectral index in dogs

OBJECTIVE

To determine the effect of remifentanil infusion on the minimum alveolar concentration of sevoflurane preventing movement (SEVOMAC_NM) and bispectral index (BIS) in dogs.

STUDY DESIGN

Prospective, unmasked study.

ANIMALS

A total of 10 adult Beagle dogs weighing 9.0 ± 1.1 kg.

METHODS

Dogs were anesthetized with sevoflurane and baseline SEVOMAC_NM was determined. Remifentanil was infused at 5, 10 and 20 μg kg^-1 hour^-1, in sequence, with 20 minutes washout between infusions. Variables monitored throughout anesthesia included heart rate (HR), oscillometric blood pressure, end-tidal partial pressure of carbon dioxide, end-tidal sevoflurane concentration (Fe'Sevo) and BIS. SEVOMAC_NM after remifentanil infusion (SEVOMAC_NM-REMI) determination started 20 minutes after the start of each infusion. Venous blood samples were collected for plasma remifentanil concentration determination at baseline, SEVOMAC_NM-REMI determination time points, and 20 minutes after each infusion was stopped. A mixed model analysis was used to determine the effect of remifentanil infusion on response variables. The relationships between BIS and Fe'Sevo, plasma remifentanil concentrations and the percentage decrease in baseline SEVOMAC_NM were evaluated (p < 0.05).

RESULTS

The overall SEVOMAC_NM at baseline was 2.47 ± 0.11%. Addition of remifentanil at all infusion rates significantly decreased SEVOMAC_NM, but the medium and high doses resulted in significantly greater decreases in SEVOMAC_NM than the lower dose. There was no difference in SEVOMAC_NM percentage change between infusions 10 and 20 μg kg^-1 hour^-1. Plasma remifentanil concentrations were significantly different in all infusion rates. Baseline BIS value was 70 ± 1 and was lower than the BIS values recorded during all remifentanil infusions. BIS values were not significantly different among infusion rates. HR was lower and mean arterial pressure was higher during remifentanil infusions than at baseline.

CONCLUSIONS AND CLINICAL RELEVANCE

All remifentanil infusions decreased SEVOMAC_NM in dogs. Remifentanil infusion at any rate studied did not reduce BIS values.

Effects of Etco2 on the Minimum Alveolar Concentration of Sevoflurane that Blunts the Adrenergic Response to Surgical Incision: A Prospective, Randomized, Double-Blinded Trial

BACKGROUND

CO2 has anesthetic potency and effectively influences the circulatory system. We investigated the effects of Etco2 on the minimum alveolar concentration of sevoflurane that blunts the adrenergic response to surgical incision (MAC-BAR) in patients undergoing radical surgery for gastric carcinoma.

METHODS

Ninety patients undergoing radical gastric-carcinoma surgery under general anesthesia were enrolled and randomly assigned into 3 groups. After intubation, the Etco2 in group L (n = 30), group N (n = 30), and group H (n = 30) was adjusted to 25 mm Hg ≤ Etco2 <30 mm Hg, 30 mm Hg ≤ Etco2 < 40 mm Hg, and 40 mm Hg ≤ Etco2 < 45 mm Hg, respectively, by changes in controlled ventilation. Hemodynamics and depth of anesthesia were observed before and after skin incision. The MAC-BAR of sevoflurane for each group was determined using an up-and-down sequential-allocation technique.

RESULTS

To obtain 7 crossovers, 25, 26, and 26 patients were used in group L, group N, and group H, respectively. The MAC-BAR of sevoflurane using the up-and-down method for group H was significantly lower than that for group L (2.3% [95% confidence interval {CI}, 2.2-2.4] vs 2.9% [95% CI, 2.7-3.0]; difference, -0.6% [95% CI, -0.7 to -0.4], P < .001) and group N (2.3% [95% CI, 2.2-2.4] vs 2.8% [95% CI, 2.8-2.9]; difference, -0.5% [95% CI, -0.7 to -0.4], P < .001), while no significant difference was found between group L and group N (P = 1.000).

CONCLUSIONS

Higher Etco2 levels (Etco2 values equal to 40 mm Hg or higher) can effectively decrease the MAC-BAR of sevoflurane in patients undergoing radical surgery for gastric carcinoma.

Determination of the minimum alveolar concentration of sevoflurane that blunts adrenergic responses and the effect of a constant rate infusion of ketamine in sheep

Minimizing sympathetic stimulation under anesthesia prevents activation of the neuroendocrine stress response. The minimum alveolar concentration blunting adrenergic responses in 50% of the population when exposed to a noxious stimulus is defined as MAC-BAR. The purpose of this study was to determine the MAC-BAR of sevoflurane (MAC-BAR_sevo) in sheep and the MAC-BAR sparing effects of ketamine. Thirteen healthy Dorset-cross adult ewes, 4 ± 1 year old and weighing 74 ± 9 kg, were enrolled in a randomized blinded crossover study design. Ewes were anesthetized twice for MAC-BAR_sevo determination. After face mask induction with sevoflurane, sheep received intravenous ketamine at 1.5 mg/kg and a constant rate infusion of 1.5 mg/kg/h or an equivalent volume of saline (placebo). After 8 day washout, the other treatment was administered. A bracketing technique was used for MAC-BAR_sevo determination and values were collected in duplicate. The mechanical stimulus (sponge forceps) was applied at the coronary band for 1 min and blood was collected for ketamine plasma concentrations. The MAC-BAR_sevo values of each treatment were compared using a paired t-test. Mean MAC-BAR_sevo of the ketamine and placebo were 2.73 ± 0.23% and 2.77 ± 0.31%, respectively and no significant difference was found (p = .638). Average ketamine plasma concentrations was 1.54 ± 0.18 μg/mL maintained through the study. Ketamine at 1.5 mg/kg, followed by 1.5 mg/kg/h, did not decrease the MAC-BAR_sevo in sheep. Further studies to determine the effect of higher doses of ketamine on inhalational anesthetic agents and their potential adverse effects are warranted.

Anesthetic management of a dog with severe subaortic stenosis and mitral valve disease complicated with atrial fibrillation undergoing ovariohysterectomy

The anesthetic management in patients with subaortic stenosis and mitral valve disease should involve intensive monitoring and the anesthesiologist's main concern is to ensure oxygen delivery and tissue perfusion. Since anesthetic procedures in such patients are rare, there is no previous report about the anesthetic management. A 5.5-year old, 32-kg Boxer, suffering a severe heart disease due to a final stage subaortic stenosis and mitral insufficiency, was anesthetized for an ovariohysterectomy to remove an ovarian tumor that was producing high-volume ascites. Methadone (0.3 mg kg^-1) was administered intramuscularly (IM) for pre-anesthetic medication, etomidate (1.3 mg kg^-1) and midazolam (0.2 mg kg^-1) were used for the induction of anesthesia and after endotracheal intubation, anesthesia was maintained with sevoflurane vaporized in oxygen and air. Fentanyl (5-10 μg kg^-1 h^-1) and paracetamol (15 mg kg^-1) were administered to improve analgesia. Previous persistent atrial fibrillation was refractory to medication (digoxin, diltiazem, and pimobendan) and continued during the anesthetic procedure. Dobutamine (1.5-5 μg kg^-1 minute^-1) helped to maintain mean arterial blood pressure above 60 mmHg. Epidural morphine (0.1 mg kg^-1) and incisional bupivacaine (2 mg kg^-1) were administered at the end of surgery to provide postoperative analgesia. Anesthesia was otherwise uneventful, and recovery was considered excellent.

The effect of remifentanil on the minimum alveolar concentration (MAC) and MAC derivatives of sevoflurane in dogs

Remifentanil is an ultra-short-acting µ-opioid receptor agonist. The purpose of this study was to determine the relationship of the minimum alveolar concentration (MAC) of sevoflurane and other MAC derivatives, including the MAC for blocking adrenergic responses (MAC-BAR) and the MAC at which tracheal extubation is occurred (MAC-extubation), with or without remifentanil infusion. Six healthy adult beagle dogs were randomly anesthetized three times for determining the MAC-BAR (SEV_MAC-BAR), MAC (SEV_MAC), and MAC- extubation (SEV_{MAC-extubation}) of sevoflurane under infusion of saline and remifentanil at rates of 0.15, 0.30, 0.60, 1.20, and 2.40 µg/kg/min. The ratio of the SEV_MAC-BAR and SEV_MAC and that of the SEV_{MAC-extubation} and SEV_MAC were not significantly different at baseline and during treatment. The MAC-BAR₉₅ and MAC₉₅ decreased in a dose-dependent manner until reaching 1.20 µg/kg/min, and the MAC-extubation₅ decreased in a dose-dependent manner until reaching 0.60 µg/kg/min. The percentage reduction of SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-extubation} increased in a dose-dependent manner during remifentanil infusion. The heart rate significantly decreased in the MAC-BAR and MAC groups, and the systolic and mean arterial pressures increased after remifentanil infusion compared with the baseline values. Remifentanil infusion caused reduction of the SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-extubation} in a dose-dependent manner, and ceiling effects were observed in the dogs. Higher doses of remifentanil and sevoflurane were necessary for blocking the sympathetic response to the supramaximal stimulus to prevent movement and extubation in dogs.

Minimum alveolar concentration: Key concepts and a review of its pharmacological reduction in dogs. Part 1

OBJECTIVE

To outline the major components of the minimum alveolar concentration (MAC) and review the literature in regard to pharmacological manipulation of the MAC of halothane, isoflurane, sevoflurane, enflurane, and desflurane in dogs. The pharmacologic agents included are alpha-2 agonists, benzodiazepines, propofol, maropitant, opioids, lidocaine, acepromazine, non-steroidal anti-inflammatory agents, and NMDA antagonists. Part 1 will focus on summarizing the relevance, measurement, and mechanisms of MAC and review the effects of alpha-2 agonists, benzodiazepines, and propofol on MAC.

DATABASES USED

PubMed, Google Scholar, CAB Abstracts. Search terms used: minimum alveolar concentration, MAC, dog, canine, inhaled anesthetic potency, isoflurane, sevoflurane, desflurane, enflurane, and halothane.

CONCLUSIONS

Many drugs reduce the MAC of inhaled anesthetics in dogs, and allow for a clinically important decrease in inhalant anesthetic use. A decrease in MAC may decrease the adverse cardiovascular and pulmonary effects associated with the use of high concentrations of inhaled anesthetics.

Interaction between maropitant and carprofen on sparing of the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs

Maropitant, a neurokinin-1 receptor antagonist, may provide analgesic effects by blocking pharmacological action of substance P. Carprofen is a non-steroidal anti-inflammatory drug commonly used for pain control in dogs. The purpose of this study was to evaluate the effect of a combination of maropitant and carprofen on the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs. Six healthy adult beagle dogs were anesthetized with sevoflurane four times with a minimum of 7-day washout period. On each occasion, maropitant (1 mg/kg) alone, carprofen (4 mg/kg) alone, a combination of maropitant (1 mg/kg) and carprofen (4 mg/kg), or saline (0.1 ml/kg) was subcutaneously administered at 1 hr prior to the first electrical stimulation for the sevoflurane MAC-BAR determination. The sevoflurane MAC-BAR was significantly reduced by maropitant alone (2.88 ± 0.73%, P=0.010), carprofen alone (2.96 ± 0.38%, P=0.016) and the combination (2.81 ± 0.51%, P=0.0003), compared with saline (3.37 ± 0.56%). There was no significant difference in the percentage of MAC-BAR reductions between maropitant alone, carprofen alone and the combination. The administration of maropitant alone and carprofen alone produced clinically significant sparing effects on the sevoflurane MAC-BAR in dogs. However, the combination of maropitant and carprofen did not produce any additive effect on the sevoflurane MAC-BAR reduction. Anesthetic premedication with a combination of maropitant and carprofen may not provide any further sparing effect on anesthetic requirement in dogs.

Sparing effect of robenacoxib on the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs

Robenacoxib is a newer nonsteroidal anti-inflammatory drug approved for dogs and cats. This study was designed to evaluate the effect of robenacoxib on the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs. Sevoflurane MAC-BAR was determined by judging dogs’ response to a noxious electrical stimulus (50 V, 50 Hz and 10 msec) for 10 sec in 6 beagle dogs on two occasions at least a 7-day interval. In each occasion, saline (0.1 ml/kg) or robenacoxib (2 mg/kg) was administered subcutaneously at 1 hr prior to the MAC-BAR determination. Robenacoxib significantly decreased the sevoflurane MAC-BAR (3.44 ± 0.53% for saline vs. 2.84 ± 0.38% for robenacoxib, P=0.039). These results suggest that subcutaneous robenacoxib provides a clinically relevant sparing effect on anesthetic requirement.