Comparative study between target-controlled-infusion and continuous-infusion anesthesia in dogs treated with methotrimeprazine and treated with propofol and remifentanil

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.

Total Intravenous Anesthesia With Propofol Associated or Not With Remifentanil, Ketamine, or S-Ketamine for Laparoscopic Ovariectomy in Female Dogs

Total intravenous anesthesia (TIVA) has been gaining ground in the routine of small animals. This study aimed to evaluate the hemodynamic effects produced by continuous infusion of propofol isolated or associated with ketamine, S-ketamine, or remifentanil in dogs submitted to video laparoscopic ovariectomy. Thirty-two female dogs were randomly assigned to 4 groups (n = 8): G,1 propofol (0.6 mg/kg/min); G2. ketamine (2 mg/kg followed by 100 µg/kg/min) and propofol (0.4 mg/kg/min); G3, S-ketamine (1 mg/kg followed by 50 µg/kg/min) and propofol (0.4 mg/kg/min); and G4, remifentanil (1 µg/kg followed by 0.2 µg/kg/min) and propofol (0.4 mg/kg/min). All dogs were submitted to the same pre-anesthetic protocol with acepromazine (0.1 mg/kg) and meperidine (4 mg/kg) intramuscularly, followed by anesthetic induction with propofol (4 mg/kg). All animals were mechanically ventilated. Heart rate (HR), respiratory rate (f), SpO₂, systolic, diastolic and mean arterial blood pressures (SAP, DAP and MAP, respectively), EtCO₂, cardiac output (CO), blood glucose and rectal temperature were evaluated in 7 time-points (M0-M7). HR increased throughout the anesthesia in all groups, except for G4, which showed inferior values. In all groups, EtCO₂ increased from M1 to M7. SAP was higher in G1 in relation to G2 in M2 and M3, and G4 in all time points. G4 also obtained the lower values for DAP and MAP, although not inferior to 60 mmHg. CO was unchanged through time and among groups. No groups had hyperglycemia, although glucose levels varied with time. It was concluded that all TIVA protocols showed satisfactory results and hemodynamic stability.

Intravenous anaesthesia in goats: A review

Intravenous anaesthesia is gradually becoming popular in veterinary practice. Traditionally, general anaesthesia is induced with intravenous drugs and then maintained with inhalation agents. Inhalation anaesthetic agents cause more significant dose-dependent cardiorespiratory depression than intravenous anaesthetic drugs, creating a need to use less of the inhalation anaesthetic agents for maintenance of general anaesthesia by supplementing with intravenous anaesthesia drugs. Better still, if anaesthesia is maintained completely with intravenous anaesthetic drugs, autonomic functions remain more stable intra-operatively. Patient recovery from anaesthesia is smoother and there is less pollution of the working environment than happens with inhalation anaesthetic agents. Recently, a number of drugs with profiles (pharmacokinetic and pharmacodynamic) suitable for prolonged intravenous anaesthesia have been studied, mostly in humans and, to a certain extent, in dogs and horses. There is currently very little scientific information on total intravenous anaesthesia in goats, although, in the past few years, some scholarly scientific articles on drugs suitable for partial intravenous anaesthesia in goats have been published. This review article explored the information available on drugs that have been assessed for partial intravenous anaesthesia in goats, with the aim of promoting incorporation of these drugs into total intravenous anaesthesia protocols in clinical practice. That way, balanced anaesthesia, a technique in which drugs are included in anaesthetic protocols for specific desired effects (hypnosis, analgesia, muscle relaxation, autonomic stabilisation) may be utilised in improving the welfare of goats undergoing general anaesthesia.

Bispectral index and the clinically evaluated anaesthetic depth in dogs

OBJECTIVE

This study investigated whether the bispectral index (BIS monitor) corresponded with the clinical assessment of anaesthetic depth in dogs.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Sixty-five dogs undergoing anaesthesia for surgery.

METHODS

Dogs were assigned to one of three different anaesthetic techniques. A three point scale was devised to determine the clinical depth of anaesthesia (CDA); CDA 1 represented light, CDA 2 surgical and CDA 3 excessive depth of anaesthesia. BIS values were recorded and CDA assessed at specific times and points throughout surgery. Data were statistically analysed using mixed model regression.

RESULTS

Clinical depth of anaesthesia was assessed as CDA 1 on 68, 2 on 748 and 3 on four occasions. The BIS recorded for CDA 1 differed significantly from that for CDA 2 (p<0.001). However, individual BIS values measured at light and surgical levels of anaesthesia overlapped considerably. The sensitivities and specificities calculated for BIS to diagnose CDA 1 compared to CDA 2 in the three anaesthetic protocols were 28-86% and 55-85%. The accompanying positive predictive value was 0.08-0.29 and the negative predictive value was 0.95-0.97. End-tidal isoflurane concentrations (anaesthetic techniques 1 and 3) and propofol infusion (technique 2) at CDA 1 was significantly lower than those at CDA 2 (p=0.001).

CONCLUSIONS

Although BIS values overall distinguished between CDA scores, the calculated specificities, sensitivities and predictive values were low, and there were anomalous results in individual cases.

CLINICAL RELEVANCE

The use of the BIS as the sole method to determine anaesthetic depth in dogs is imprudent.

Survey of the current use of pharmacokinetic model-driven drug delivery in small animal anaesthesia and analgesia in Italy

Veterinary surgeons in Italy were surveyed about their current practice with regard to the use of propofol and intravenous opioids during anaesthesia and for treatment of acute pain in small animals. Questionnaires were e-mailed to all 171 members of the Italian Society of Veterinary Regional Anaesthesia and Pain Medicine. Information was requested on the type of practice the veterinarians worked in, the administration techniques used and the perceived benefit of pumps with target-controlled infusion (TCI) capability implementing small animal pharmacokinetic models. A total of 168 responses were received (response rate 98.2 per cent). Of the respondents, 121 (72.0 per cent) worked in a first-opinion private practice, 25 (14.9 per cent) worked in a 24/7 private practice, 11 (6.5 per cent) worked in a referral private practice, eight (4.8 per cent) worked in a university hospital, two (1.2 per cent) were not currently practising with small animals and one (0.6 per cent) had retired. Of the 130 (78.8 per cent) practising respondents who reported using a syringe pump, eight (4.8 per cent) used a TCI system, 31 (18.8 per cent) used manual TCI, 40 (24.2 per cent) used a bolus-elimination-transfer scheme and 51 (31 per cent) used a constant-rate infusion. As a result, 79 of 165 (47.9 per cent) practising respondents used a pharmacokinetic model-driven method of drug delivery. The majority of respondents (81.2 per cent) believed that the use of pumps with TCI capability would improve practice and patient care.