NARCOBIT: a newly developed inhalational anesthesia system for mice

Use of an Integrated Low-Flow Anesthetic Vaporizer, Ventilator, and Physiological Monitoring System for Rodents

Low-flow digital vaporizers commonly utilize a syringe pump to directly administer volatile anesthetics into a stream of carrier gas. Per animal welfare recommendations, animals are warmed and monitored during procedures requiring anesthesia. Common anesthesia and physiological monitoring equipment include gas tanks, anesthetic vaporizers and stands, warming controllers and pads, mechanical ventilators, and pulse oximeters. A computer is also necessary for data collection and to run equipment software. In smaller spaces or when performing field work, it can be challenging to configure all this equipment in limited space. The goal of this protocol is to demonstrate best practices for use of a low-flow digital vaporizer using both compressed oxygen and room air, along with an integrated mechanical ventilator, pulse oximeter, and far infrared warming as an all-inclusive anesthesia and physiological monitoring suite ideal for rodents.

Use of a Low-flow Digital Anesthesia System for Mice and Rats

A traditional vaporizer depends on flowing gas and atmospheric pressure for passive anesthetic vaporization. Newly developed direct injection vaporizers utilize a syringe pump to directly administer volatile anesthetics into a gas stream. Unlike a traditional vaporizer, it can be used at very low flow rates, making it ideal for use on mice and rats. The equipment's capability to use low flow rates could result in a substantial cost savings due to the reduced need for anesthetic agents, compressed gas, and charcoal scavenging filters(1). A lower flow rate means less waste of anesthetic gas and likely reduces the risk of anesthetic exposure to laboratory personnel. Thus, the high levels of precision and safety associated with direct injection vaporizers, along with a reduced need for anesthetic agents, compressed gas, and charcoal filters are beneficial for research requiring small animal anesthesia. The goal of this protocol is to demonstrate the use of a syringe-driven direct injection vaporizer as part of a digital, low-flow anesthesia system. The direct injection vaporizer is capable of accurately delivering anesthesia at very low flow rates compared to a traditional vaporizer, making it a promising alternative for controlled gas anesthetic delivery to rodents.

Molecular and Integrative Physiological Effects of Isoflurane Anesthesia: The Paradigm of Cardiovascular Studies in Rodents using Magnetic Resonance Imaging

To-this-date, the exact molecular, cellular, and integrative physiological mechanisms of anesthesia remain largely unknown. Published evidence indicates that anesthetic effects are multifocal and occur in a time-dependent and coordinated manner, mediated via central, local, and peripheral pathways. Their effects can be modulated by a range of variables, and their elicited end-effect on the integrative physiological response is highly variable. This review summarizes the major cellular and molecular sites of anesthetic action with a focus on the paradigm of isoflurane (ISO) - the most commonly used anesthetic nowadays - and its use in prolonged in vivo rodent studies using imaging modalities, such as magnetic resonance imaging (MRI). It also presents established evidence for normal ranges of global and regional physiological cardiac function under ISO, proposes optimal, practical methodologies relevant to the use of anesthetic protocols for MRI and outlines the beneficial effects of nitrous oxide supplementation.

More effective induction of anesthesia using midazolam-butorphanol-ketamine-sevoflurane compared with ketamine-sevoflurane in the common marmoset monkey (Callithrix jacchus)

The common marmoset has been increasingly used for research in the biomedical field; however, there is little information available regarding effective methods of anesthesia in this species. This study retrospectively analyzed 2 regimens of anesthesia induction: intramuscular injection of ketamine followed by inhalation of 5% sevoflurane, and intramuscular injection of midazolam, butorphanol and ketamine followed by inhalation of 5% sevoflurane. Anesthetic depth did not reach the surgical anesthesia stage in 7 out of 99 animals receiving the former regimen, whereas there were only 2 such animals out of 273 receiving the latter regimen. The latter regimen, when followed by maintenance anesthesia with 3% sevoflurane inhalation, was successfully used in various nociceptive procedures. These results indicate that the injection of a combination of midazolam, butorphanol and ketamine followed by inhalation of a high concentration of sevoflurane is effective for anesthesia induction in marmosets.

Comparison of newly developed inhalation anesthesia system and intraperitoneal anesthesia on the hemodynamic state in mice

KNI-472 is the first anesthetic system for mice and rats to incorporate a ventilator. It consists of a newly developed syringe pump-type vaporizer and gas monitor that can deliver accurate concentrations of anesthetic gas at an extremely low airflow. In this study, we compared the hemodynamic effects of isoflurane anesthesia using KNI-472 and intraperitoneal pentobarbital anesthesia. In the isoflurane anesthetic group, Institute of Cancer Research (ICR) mice were anesthetized with 5% isoflurane, followed by endotracheal intubation. Subsequently, they were ventilated mechanically, and anesthesia was maintained with 2% isoflurane for a 60-min period using KNI-472. In the pentobarbital anesthetic group, the ICR mice were anesthetized by an intraperitoneal injection of sodium pentobarbital (70 mg/kg). In isoflurane anesthesia, the heart rate (HR) and mean blood pressure (MBP) were stable. In contrast, in pentobarbital anesthesia, MBP decreased in the first stage after the initiation of anesthesia, after which it gradually increased. The intra-group variability in the estimated skin blood flow (SBF) was higher in the pentobarbital anesthesia than that in the isoflurane anesthesia. The PaO(2) and PaCO(2) values at 15 min after the initiation of pentobarbital anesthesia revealed hypoxia and hypercapnia compared with isoflurane anesthesia. In this study, isoflurane anesthesia using KNI-472, unlike pentobarbital anesthesia, did not induce changes in MBP, SBF, or blood gases. The changes induced by pentobarbital anesthesia were attributed to a change in the depth of anesthesia with time. These results indicate that inhalation anesthesia using KNI-472 is suitable in research on the hemodynamic state in mice.