Effect of fentanyl and lidocaine on the end-tidal sevoflurane concentration preventing motor movement in dogs

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.

The Determination of the Minimum Anaesthetic Concentration of Halothane in the Rock Dove (Columba livia) Using an Electrical Stimulus

This study aims to determine the minimum anaesthetic concentration (MAC) of halothane in the Rock Dove using electrical stimulus. Seven Rock Doves are anaesthetised with halothane, and the MAC is determined using the bracketing method. An electrical stimulus (two single pulses and two five-second stimuli, all separated by five-second pauses; 30 Hz, 30 V, 7.5 ms) is applied to the legs via subcutaneous electrodes. A maximum of eight periods of electrical stimulation, each with a preceding 15 min stable phase, is applied to each bird. If the non-reflexive movement occurred following stimulation, the end-tidal halothane (Fe’Hal) is increased by 10% before the next stimulus delivery. If no movement occurred, Fe’Hal is decreased by 10%. The MAC is the average of the highest concentration that allowed movement and the lowest that prevented movement. Physiological variables and ventilatory settings are recorded every five minutes. The current delivered is calculated offline. The mean ± SD MAC of halothane is 1.62 ± 0.29%, calculated from five birds. During the entire anaesthesia, all birds had cardiac arrhythmias —with three having sporadic recurrent periods of prolonged ventricular standstill followed by marked sinus tachycardia. The mean recorded voltage and calculated current and resistance are 27.6 ± 2.7 V, 20.3 ± 7.3 mAmp and 1.6 ± 0.9 kΩ, respectively. The advantage of halothane for prolonged anaesthesia in Rock Doves may be limited when noxious stimulation is used, due to the development of severe ventricular arrhythmias.

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.

Intravenous lidocaine as adjuvant to general anesthesia in renal surgery

The role of intraoperative intravenous lidocaine infusion has been previously evaluated for pain relief, inflammatory response, and post-operative recovery, particularly in abdominal surgery. The present study is a randomized double-blinded trial in which we evaluated whether IV lidocaine infusion reduces isoflurane requirement, intraoperative remifentanil consumption and time to post-operative recovery in non-laparoscopic renal surgery. Sixty patients scheduled to undergo elective non-laparoscopic renal surgery under general anesthesia were enrolled to receive either systemic lidocaine infusion (group L: bolus 1.5 mg/kg followed by a continuous infusion at the rate of 2 mg/kg/hr until skin closure) or normal saline (0.9% NaCl solution) (Group C). The depth of anesthesia was monitored using the Bispectral Index Scale (BIS), which is based on measurement of the patient’s cerebral electrical activity. Primary outcome of the study was End-tidal of isoflurane concentration (Et-Iso) at BIS values of 40–60. Secondary outcomes include remifentanil consumption during the operation and time to extubation. Et-Iso was significantly lower in group L than in group C (0.63% ± 0.10% vs 0.92% ± 0.11%, p < 10^–3). Mean remifentanil consumption of was significantly lower in group L than in group C (0.13 ± 0.04 µg/kg/min vs 0.18 ± 0.04 µg/kg/min, p < 10^–3). Thus, IV lidocaine infusion permits a reduction of 31% in isoflurane concentration requirement and 27% in the intraoperative remifentanil need. In addition, recovery from anesthesia and extubation time was shorter in group L (5.8 ± 1.8 min vs 7.9 ± 2.0 min, p < 10^–3). By reducing significantly isoflurane and remifentanil requirements during renal surgery, intravenous lidocaine could provide effective strategy to limit volatile agent and intraoperative opioids consumption especially in low and middle income countries.

Effects of neoadjuvant chemotherapy on minimum alveolar concentration values of sevoflurane and desflurane in patients with hepatocellular carcinoma complicated with jaundice

The effects of neoadjuvant chemotherapy on the minimum alveolar concentration (MAC) values of sevoflurane and desflurane in patients with hepatocellular carcinoma (HCC) complicated with jaundice were investigated. Eighty patients with HCC complicated with jaundice were selected. Forty patients underwent the neoadjuvant chemotherapy and were grouped into the desflurane group (Group D) and the sevoflurane group (Group S). Patients in all chemotherapy groups received 2 cycles of chemotherapy prior to surgery and underwent surgical treatment 3 weeks after chemotherapy. The remaining 40 patients in the control group were divided into the desflurane group (Group C1) and the sevoflurane group (Group C2). Changes in MAP, HR and BIS at different time points before and after anesthesia induction and skin incision were compared among the groups. Results showed that there were no significant differences in MAP, HR and BIS before anesthesia induction (T0) (P>0.05); at each time point from T1 to T6, MAP, HR and BIS of Group D were significantly lower than those of Group C1 (P>0.05). Furthermore, MAP, HR and BIS of Group S were significantly lower than those of Group C2 (P>0.05). The MAC^Mean of sevoflurane and desflurane were compared among all patient groups using the mean method. MAC^Mean values of Group D were significantly lower than those of Group C1 (P<0.05). Notably, MAC^Dixon values of sevoflurane and desflurane were compared among all patient groups using the Dixon method and the differences were statistically significant (P<0.05). Logistic regression analyses were conducted, respectively, which revealed that the MAC of sevoflurane and desflurane were associated with whether patients received the neoadjuvant chemotherapy. MAC^Log of sevoflurane and desflurane were decreased in patients receiving the neoadjuvant chemotherapy. The results suggested that neoadjuvant chemotherapy can reduce MAC values of sevoflurane and desflurane in HCC patients complicated with jaundice and may improve these patients' sensitivity to sevoflurane and desflurane.

State of the art analgesia-Recent developments pharmacological approaches to acute pain management in dogs and cats: Part 2

There has been considerable interest in the area of acute pain management over recent years, focusing on pain assessment, pharmacological and non-pharmacological interventions. The evidence base for our clinical decision making and treatment of patients is ever increasing and becoming more robust. There is still a tendency to base some aspects of pain management on poor quality evidence and this requires further input in years to come. With new literature come new ideas and this review will detail the current knowledge base behind pharmacological management of acute pain in dogs and cats. The known mechanisms of action of each analgesic and its evidence will be considered. The second part of this review will consider the non-traditional analgesics, describing their component drugs individually, thereby focusing on their mechanisms of action and the current evidence for their use in acute pain management.

Minimum alveolar concentration: Key concepts and a review of its pharmacological reduction in dogs. Part 2

OBJECTIVE

To outline the major components of the minimum alveolar concentration (MAC) and review the literature regarding pharmacological manipulation of the MAC of halothane, isoflurane, sevoflurane, enflurane, and desflurane in dogs. The pharmacological agents included are alpha-2 agonists, benzodiazepines, propofol, opioids, lidocaine, acepromazine, non-steroidal anti-inflammatory agents (NSAIDs), maropitant, and NMDA antagonists. Part 2 of this review will focus on the effect of opioids, lidocaine, NSAIDs, maropitant, acepromazine, and NMDA antagonists 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

Opioids, lidocaine, NSAIDs, maropitant, acepromazine, and NMDA antagonists have been shown to reduce the MAC of inhaled anesthetics in dogs and allow for clinically important decreases in inhalant anesthetic use. Thus, the use of these agents potentially decrease the adverse cardiovascular and pulmonary effects associated with the use of high concentrations of inhaled anesthetics.

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.