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Anesthesia in Lab Animals

Isoflurane For Animal Anesthesia: How to Safely Use

What Is Isoflurane?

Isoflurane, also known by the brand names, Forane and Terrel, is an inhalation anesthetic used in animal research to induce general anesthesia.[1]

Structure of isoflurane

Figure: The structure of Isoflurane.

Inhalation anesthetics are medicines or anesthetic agents that induce and maintain general anesthesia via inhalation through a mask. General anesthesia is a combination of medicines for inducing a sleep-like state in animals during research activities. In this condition, animals are present in an induced coma, resulting in loss of reflexes and any bodily sensations. 

Isoflurane is often combined and used with other anesthetic agents to induce anesthesia in animals. The drug causes airway irritation and has a certain smell which makes it difficult for animals to inhale the anesthesia.

Thus, other anesthetic agents (often nitrous oxide) are used to induce anesthesia, and isoflurane is later administered to maintain the condition. The drug is always delivered to animals in conjunction with air or pure oxygen.[1]

Isoflurane is volatile, colorless, clear, and liquid at room temperature and pressure. Here’s a chart presenting all the physical properties of the medicine:[1]

Physical Property Values
Molecular Weight
184.5g/mol
Density
1.496 g/mL
Boiling Point
48.5 °C
MAC (Minimum Alveolar Concentration)
1.15 vol %
Vapor Pressure
238 mmHg & 31.7 kPa (at 20 °C); 295 mmHg & 39.3 kPa (at 25 °C); 367 mmHg & 48.9 kPa (at 30 °C); 450 mmHg & 60.0 kPa (at 35 °C)
Water Solubility
13.5 mM (at 25 °C)
Blood: Gas Partition Coefficient
1.4
Oil: Gas Partition Coefficient
98

In this article, you will learn the mechanism of action of the Isoflurane drug, its effects on animals, how to use it, and safety tips to observe when using the anesthetic.

How To Deliver Isoflurane and How It Works

Isoflurane is administered to animals using an anesthetic machine. Follow the guidelines below to administer anesthesia in the animals:[2]

  • Allow oxygen flow in the machine. Check if there’s sufficient oxygen in the tank by checking the pressure gauge.
  • Check the level of isoflurane in the vaporizer.
  • Place the animal in an induction chamber.
  • Turn on the vaporizer to a concentration of 3.5 to 4.0%. Turn the oxygen knob in the machine to 1.0 to 2.0 liters.
  • Once you observe that the animal has lost its reflexes and is in a coma state, remove it from the induction chamber and place a nose cone over the animal’s nose.
  • At this concentration of anesthesia, the animal can awake from pain stimuli. Therefore, it’s essential to allow the anesthesia to deepen a bit.
  • After achieving the correct depth of anesthesia, lower the level of isoflurane to 1.5-2.0% and oxygen to 0.8-1.0 liters.
  • After the procedure is complete, turn the isoflurane off and allow the animal to have pure oxygen for a few minutes. After some time, turn off oxygen, remove the animal from the chamber, remove the mask, and stimulate the animal by picking it up and setting it down.[2]

Mechanism of Action

The exact action mechanism of isoflurane isn’t known till now. However, certain studies suggest that the drug likely binds to cell receptors, like GABA, glycine, and glutamate.[1] However, it produces different effects during its interaction with different receptors.

For example:

  • In electrophysiology studies of neurons and recombinant receptors, isoflurane acts as a positive allosteric modulator of the GABA receptor.
  • The drug potentiates glycine receptor activity, resulting in decreased motor function.
  • Isoflurane inhibits the conduction of potassium channels and inhibits receptor activity at NMDA glutamate receptors.[1]

Other than this, Isoflurane can also affect intracellular molecules. For example, it hinders the flow of Ca2+ (calcium ions) across the membrane, which inhibits plasma membrane calcium ATPases (PMCAs) and affects membrane fluidity. Moreover, the molecule can also bind to the NADH dehydrogenase and D subunit of ATP synthase.[1]

Furthermore, it’s also known that isoflurane causes a decrease in gap junction channel opening times and an increase in gap junction channel closing times, which results in reduced junctional conductance.[3]

Effects Of Isoflurane on Animals

Below are some effects observed in animals while or after administering isoflurane.

  • Increasing the depth of Isoflurane in animals may cause an increase in hypertension and respiratory depression.[4]
  • Isoflurane can elevate carboxyhemoglobin levels in some animals by producing carbon monoxide when it reacts with desiccated carbon dioxide (CO2) absorbents. Thus, it’s recommended that a clinician replace any suspected desiccated CO2 absorbent before administering Isoflurane.[4]
  • The risk of neurodegeneration is increased when isoflurane is used in combination with drugs like nitrous oxide and benzodiazepines (such as midazolam).[1]
  • According to a report, isoflurane can also cause hepatic injury ranging from mild transient increases of liver enzymes to fatal hepatic necrosis.
  • At deeper levels of anesthesia, isoflurane increases cerebral blood flow.
  • Electroencephalography shows burst suppression, spikes, and isoelectric periods associated with deep anesthesia.[4]
  • In animals, in addition to respiratory depression, hypotension and arrhythmias have been observed.

Tips Or Guidelines on How to Safely Handle Isoflurane

  • Inspect vaporizers thoroughly before administering anesthetic gas.
  • Always wear a lab coat, eye protection, and disposable nitrile gloves while working with isoflurane.[5]
  • It’s highly recommended to start inducing isoflurane at a concentration of 0.5%.
  • To accurately control the concentration of delivered anesthetics, it’s essential to use well-calibrated vaporizers.
  • Do not allow carbon dioxide adsorbents to dry out. Because it can lead to the formation of carbon monoxide in rebreathing circuits and the possibility of elevated carboxyhemoglobin levels, which is fatal to the animal.[4]
  • Use surgical stimulation to reverse the respiratory depression – both tidal volume and respiratory rate decrease. The technique is even effective at deeper levels of isoflurane anesthesia.[5]
  • While performing intra-abdominal operations at normal levels of isoflurane, ensure that adequate muscle relaxations are achieved in animals.
  • Do not use the anesthesia on horses intended for food.
  • Use muscle relaxants (especially nondepolarizing relaxants) less than usual with isoflurane. Upon delivering the usual amount of the drug, Isoflurane will prolong recovery from myoneural blockade compared to other common anesthetics.[4]
  • To prevent the accumulation of anesthetic vapor, the operating rooms should have adequate ventilation.
  • In the case of overdosing on animals, instantly stop drug administration. Ensure the airway is clear and start an assisted or controlled ventilation with pure oxygen.
  • Workers that are supposed to be handling isoflurane and in contact with the anesthesia should be given UCSC-approved anesthetic gas training before starting animal work.[6]
  • Store Isoflurane in a tightly sealed bottle in a cool well-ventilated area at a temperature ranging between 15-30°C.[6]

Related Read: Is Sevoflurane A Better Anesthetic Agent?

What Can You Do If Exposed (Make Contact) To Isoflurane?

Exposure to isoflurane may cause several problems, which include:[7]

  • Cough or sore throat
  • Irritation of the eyes, skin, and respiratory tract
  • Asphyxia
  • Headache, drowsiness, dizziness
  • Unconsciousness
  • Certain other health issues in pregnant animals

There are certain steps you can follow to reduce contact with the drug. For example:[7]

  • Maintain anesthetic equipment in proper working condition.
  • Use the smallest amount of isoflurane in procedures.
  • Reduce WAG (waste anesthetic gas) release by using an induction box with a sliding lid instead of a hinged lid in the vaporizer system.
  • The nose/face cone on the animal should be tightly sealed while delivering isoflurane. If the nose/face cone is not equipped with a diaphragm, a latex glove can be used to create one.
  • Use open-drop jars only for brief procedures that don’t last longer than 1 minute. And while opening the jars, ensure that the jars are at arm’s length.
  • In open-drop jars, use the smallest concentration of isoflurane to achieve the desired results.
  • Never perform procedures involving volatile chemicals in a standard biosafety cabinet or laminar flow hood.[7]

Benefits and Limitations of Isoflurane

The advantages of Isoflurane are:[8]

  • The drug provides dose-dependent muscle relaxation.
  • The induction of general anesthesia is faster.
  • The anesthetic has less metabolism and poses less organ toxicity if given in optimum quantity.
  • Compared to some other anesthetics, such as halothane, isoflurane causes less reduction in cardiac output and less sensitization to the arrhythmogenic effects of catecholamines.

The limitations of Isoflurane include:[8]

  • The drug has a certain sweet smell and causes irritability in the airway during administration.
  • Increase in the depth of the anesthesia may cause certain health risks to animals. Thus when performing the procedure, a drug and medication expert and continuous monitoring are required.
  • When the fresh gas flow is high, the anesthetic can be rapidly inhaled by animals which can be risky.
  • Without an anesthesia expert, the anesthetic machine can’t be used because of the unfamiliarity of other personnel with the machine.
  • The anesthesia can cause certain undesirable health issues such as respiratory and myocardial depression and an increased risk of diabetes insipidus.

Conclusion

Isoflurane is an inhalation anesthetic used to induce and maintain general anesthesia. The drug induces muscle relaxation and a coma state in the animal to perform surgical procedures.

The anesthesia is administered to animals using an anesthetic machine. However, there are some precautions that you need to follow while working with isoflurane, such as its proper handling and storage, wearing personal protective equipment, and performing the procedure in a well-ventilated area.

However, if you ever come in contact with the drug, immediately seek a doctor’s attention, change your clothes, and wash the contacted area thoroughly. If any kind of irritation persists, go for a proper examination of the affected area.

If you work with rodents and need isoflurane anesthesia for regular surgical procedures, then here’s our high-quality, effective, and certified isoflurane.

References

  1. Isoflurane. Retrieved from https://en.wikipedia.org/wiki/Isoflurane
  2. Anesthetic Machine (Isoflurane) Operation. Retrieved from https://research.charlotte.edu/sites/research.charlotte.edu/files/media/files/iacuc/policies/Isoflurane-machine-operation-SOP.pdf
  3. Isoflurane. Retrieved from https://go.drugbank.com/drugs/DB00753
  4. Isoflurane. Retrieved from https://www.drugs.com/vet/isoflurane.html
  5. Isoflurane Veterinary. Retrieved from https://www.drugs.com/pro/isoflurane-veterinary.html
  6. Isoflurane. Retrieved from https://ehs.ucsc.edu/lab-safety-manual/specialty-chemicals/Isoflurane.html
  7. Safe Use of Isoflurane in Animal Research. Retrieved from https://animalcare.umich.edu/announcements/safe-use-isoflurane-animal-research
  8. Advantages and disadvantages of potent volatile inhalation anesthetic agents (sevoflurane or isoflurane) for prolonged sedation during mechanical ventilation. Retrieved from https://www.uptodate.com/contents/image/print?imageKey=ANEST%2F132152&topicKey=ANEST%2F127762&source=see_link
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