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

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in cats

Objective

To determine if oral gabapentin decreases the minimum alveolar concentration (MAC) of isoflurane in cats.

Study design

Prospective, randomized, blinded, crossover, and experimental study.

Animals

A total of six healthy adult cats (three male, three female) aged 18-42 months, weighing 3.31 ± 0.26 kg.

Methods

Cats were randomly given oral gabapentin (100 mg cat^-1) or placebo 2 h before starting MAC determination, with the crossover treatment given at least 7 days apart. Anesthesia was induced and maintained with isoflurane in oxygen. Isoflurane MAC was determined in duplicate using an iterative bracketing technique and tail clamp method. Hemodynamic and other vital variables were recorded at each stable isoflurane concentration and were compared between gabapentin and placebo treatments at lowest end-tidal isoflurane concentration when cats did not respond to tail clamping. A paired t-test was used to compare normally distributed data, and a Wilcoxon signed-rank test was applied for non-normally distributed data. Significance was set at p < 0.05. Data are mean ± standard deviation.

Results

Isoflurane MAC in the gabapentin treatment was 1.02 ± 0.11%, which was significantly lower than that in the placebo treatment (1.49 ± 0.12%; p < 0.001), decreasing by 31.58 ± 6.94%. No significant differences were found in cardiovascular and other vital variables between treatments.

Conclusion and clinical relevance

Oral administration of gabapentin 2 h before starting MAC determination had a significant isoflurane MAC-sparing effect in cats with no observed hemodynamic benefit.

Application of different concentrations of sevoflurane with remifentanil in radical surgery for gastrointestinal tumors: Effects on intraoperative hemodynamics and postoperative anesthetic recovery

BACKGROUND

The combination of remifentanil and sevoflurane can provide patients with sufficient analgesic and sedative effects. Anesthesia for gastrointestinal tumor surgery not only needs to reach the required depth of anesthesia for surgery, but also needs to reduce the surgical stress to ensure rapid recovery after surgery.

AIM

To explore the application of different concentrations of sevoflurane with remifentanil in radical surgery for gastrointestinal tumors and the effects on intraoperative hemodynamics and postoperative anesthesia recovery.

METHODS

Eighty-six patients undergoing radical surgery for gastrointestinal tumors at our hospital from January 2020 to December 2021 were selected and divided into two groups by random number table method, with 43 cases in each group. Sevoflurane at a 1.0 minimum alveolar effective concentration (MAC) with remifentanil was adopted in group A, and 1.5 MAC sevoflurane with remifentanil was adopted in group B. The quality of anesthesia, intraoperative hemodynamics [mean arterial pressure (MAP) and heart rate (HR)], cerebral oxygen metabolism [cerebral oxygen uptake rate (CERO₂) and jugular venous oxygen content (SjvO₂)] at different time points, adverse events during anesthesia maintenance, and postoperative anesthesia recovery were recorded in the two groups.

RESULTS

During maintenance of anesthesia, the rate of adjustment of remifentanil pumping rate was lower in group A than in group B (32.56% vs 67.44%, P < 0.05). There was no significant difference in HR or MAP at each time point between the two groups (P > 0.05), and both HR and MAP were within the normal range. There was no significant difference in CERO₂ or SjvO₂ at each time point between the two groups (P > 0.05); CERO₂ at T2, T3, T4, T5, and T6 in both groups was lower than that at T1, and SjvO₂ was higher than that at T1 (P < 0.05). The incidence of hypotension during anesthesia maintenance in group A was lower than that in group B (P < 0.05). The times to open eyes on command, recovery of spontaneous breathing, extubation, and exit from the room during anesthesia awakening were shorter in group A than in group B (P < 0.05).

CONCLUSION

Both 1.0 MAC and 1.5 MAC sevoflurane can meet the demand for anesthesia maintenance in surgery for radical gastrointestinal tumors; however, 1.0 MAC sevoflurane can provide better quality of anesthesia maintenance with less effect on cerebral oxygen metabolism, which can significantly improve the quality of awakening and shorten the anesthesia awakening time, and is conducive to faster clinical turnaround.

Comparison of two injectable anaesthetic protocols in Egyptian fruit bats (Rousettus aegyptiacus) undergoing gonadectomy

Egyptian fruit bats have gained increasing interest being a natural reservoir for emerging zoonotic viruses. Anaesthesia is often required to allow safe handling of bats. We aimed to compare the sedative and cardiopulmonary effects of two balanced anaesthetic protocols in bats undergoing gonadectomy. Group DK (n = 10) received intramuscular dexmedetomidine (40 µg/kg) and ketamine (7 mg/kg), whereas group DBM (n = 10) received intramuscular dexmedetomidine (40 µg/kg), butorphanol (0.3 mg/kg) and midazolam (0.3 mg/kg). Induction time and cardiopulmonary parameters were recorded. If anaesthetic plan was inadequate, isoflurane was titrated-to-effect. At the end of surgery venous blood gas analysis was performed and atipamezole or atipamezole-flumazenil was administered for timed and scored recovery. In DBM group heart rate and peripheral oxygen saturation were significantly higher (p = 0.001; p = 0.003 respectively), while respiratory rate was significantly lower (p = 0.001). All bats required isoflurane supplementation with no significant differences between groups. Induction and recovery times showed no significant differences. In group DK a better recovery was scored (p = 0.034). Sodium and chloride were significantly higher in DBM group (p = 0.001; p = 0.002 respectively). Both anaesthetic protocols were comparable and can be recommended for minor procedures in bats.

Ferret Sedation and Anesthesia

Providing safe anesthetic events in ferrets can be achieved if fundamental principles in anesthesia are followed. Each phase of the anesthetic, event including preanesthetic, maintenance, and postanesthetic phase, have certain considerations. The anesthetic supervisor or veterinarian providing management should have a firm understanding of the species-specific anatomy, physiology, and common indications of general anesthesia along with perspective of their own experience with ferrets. Ensuring these guidelines are followed will facilitate safe administration of general anesthesia in this species.

Sedation and Anesthesia in Rodents

Sedation and anesthesia in rodent species are complex due to their wide species variation, small size, and metabolism. This review article covers recent advances in sedation and anesthesia as well as an updated drug formulary for sedation protocols. Setup, equipment, monitoring, maintenance, and recovery are reviewed as well as species-specific anatomy.

Drug class effects on respiratory mechanics in animal models: access and applications

Assessment of respiratory mechanics extends from basic research and animal modeling to clinical applications in humans. However, to employ the applications in human models, it is desirable and sometimes mandatory to study non-human animals first. To acquire further precise and controlled signals and parameters, the animals studied must be further distant from their spontaneous ventilation. The majority of respiratory mechanics studies use positive pressure ventilation to model the respiratory system. In this scenario, a few drug categories become relevant: anesthetics, muscle blockers, bronchoconstrictors, and bronchodilators. Hence, the main objective of this study is to briefly review and discuss each drug category, and the impact of a drug on the assessment of respiratory mechanics. Before and during the positive pressure ventilation, the experimental animal must be appropriately sedated and anesthetized. The sedation will lower the pain and distress of the studied animal and the plane of anesthesia will prevent the pain. With those drugs, a more controlled procedure is carried out; further, because many anesthetics depress the respiratory system activity, a minimum interference of the animal's respiration efforts are achieved. The latter phenomenon is related to muscle blockers, which aim to minimize respiratory artifacts that may interfere with forced oscillation techniques. Generally, the respiratory mechanics are studied under appropriate anesthesia and muscle blockage. The application of bronchoconstrictors is prevalent in respiratory mechanics studies. To verify the differences among studied groups, it is often necessary to challenge the respiratory system, for example, by pharmacologically inducing bronchoconstriction. However, the selected bronchoconstrictor, doses, and administration can affect the evaluation of respiratory mechanics. Although not prevalent, studies have applied bronchodilators to return (airway resistance) to the basal state after bronchoconstriction. The drug categories can influence the mathematical modeling of the respiratory system, systemic conditions, and respiratory mechanics outcomes.

Local Anesthetics: Pharmacology and Special Preparations

Local anesthetics are the only class of drugs that can block transduction and transmission of nociception. Physical properties, mechanism of action, and pharmacokinetics of this class of drugs are reviewed in this article. The clinical use, such intravenous administration of lidocaine, and local and systemic toxic effects are covered. A review of current studies published in the human and veterinary literature on lidocaine patches (Lidoderm) and liposomal bupivacaine (Experal and Nocita) are discussed.