Principles of Intravenous, Inhalation and Chamber Induction

Intravenous Anaesthesia

Advantages  Useful when maintained with inhalant agents. Fast acting and quick recovery. Does not cause thrombophlebitis if injected outside the vein. Works with many common pre-medications.

Disadvantages  Possibility of respiratory and cardiovascular depression (as with other anaesthetic agents). Mild hypotension and transient apnoea may occur. If induction is not smooth evidence of excitations may occur (paddling of limbs, nystagmus, focal muscle twitching). Rare occasions of vomiting during recovery. 

Side Effects

Potential for toxic effects caused by the preservative, benzyl alcohol. Respiratory - laboured breathing. Cardiovascular - hypotension, bradycardia, tachycardia, membrane cyanosis, arrythmias  Musculoskeletal - fasciculations, tenseness paddling, movements Central Nervous System - excitation, opisthotonus, seizures, excessive depression Gastrintestinal: emesis, retching, salivation

Propofol Group (image/jpeg)

Inhalation Anaesthesia

IsoFlo (POM-V) is an inhalation vapour, as a liquid, containing 100% isoflurane per ml. Isoflurane should be administered using an accurately calibrated vaporiser in an appropriate anaesthetic circuit along with oxygen or oxygen/nitrous oxide mixtures. The MAC (Minimum Alveolar Concentration) of IsoFlo os approx 1.15%.

Isoflurane

Advantages  Recovery from isoflurane anaesthesia is usually smooth and rapid.  Can be used in a wide range of species. The ease and rapidity of alteration of the depth of anaesthesia and its low metabolism may be considered advantages for special groups as young, old or impaired organ function. Compatible with most pre-medictaion drugs.

Disadvantages  Has little to no analgesic properties. Has a pungent smell and irritant to airways.

Side Effects

Can cause depression of the cardiovascular and respiratory systems.  The metabolism of IsoFlo in birds and small mammals can be affected by decreases in body temperature that may occur secondary to a high surface area to bodyweight ratio.

Chamber Induction Technique

Img 1005 (image/jpeg)

It is best to use a chamber that is as small as possible without squashing the patient. Use of a clear plastic chamber allows for constant observation of the animals during induction. An entry and exit port are built into the chamber. The entry port allows connection of an anaesthetic breathing circuit to the chamber for the delivery of inhalant agent and oxygen via an anaesthetic machine. Exit port allows the connection of a scavenging system.

How to Use a Chamber Induction

First fill the chamber with 02. Place the patient inside the closed chamber. The inhalant agent is delivered via an anaesthetic machine. It is necessary to use a high percentage of volatile anaesthetic in a timely fashion. Once the patient has lost the righting reflex, flush the chamber with 02 to remove excess inhalant agent via the scavenging pipeline.  Open the chamber and remove the patient quickly before re-sealing the chamber. Use a face mask to deliver further inhalant agent to maintain anaesthesia until a suitable plane has been obtained and the patient can be intubated. It is also to maintain anaesthesia via inhalant agent delivery by face mask, but this has health and safety implications for staff working in the area.

Chamber Induction

Advantages Does not require restraint of the patient.

Disadvantage Depending on the size of the chamber it can take a relatively long time to build up a high concentration of inhalant agent inside the chamber.  Can be aversive to animals - may cause injury. Movement can be limited depending on the size of the chamber and the animal. Significant environmental contamination occurs when the chamber is opened to remove the animal.

Side Effects of Chamber Induction

Rabbits tend to hold their breath when exposed to inhalant agents when conscious and this can lead to hypoxia. Injury can occur if the animal becomes excited and can move freely in the chamber.