Today I tried to induce and maintain the anesthetic state for a mouse using isoflurane vapor. Initially I followed the protocol that I composed with the dose below:
+ Induction: flow rate = 1000 mL/min - 4% isoflurane
+ Maintenance: flow rate = 500 mL/min - 1.75% - 2.5% isoflurane
However, the mouse was still moving and even woke up while it was inhaled with anesthetic agent. At that time, I decided to increase the dose like this:
+ Induction: the same as above
+ Maintenance:
- Stage 1: 1000 mL/min - 3.5% isoflurane (in 2 minutes)
- Stage 2: 1000 mL/min - 2.5% isoflurane (until it ends)
The total time of maintenance was 1 hour simulated to the previous surgery. After that I removed the mouse and let it recover. Unluckily, there were some muscle contractions that quite strong and then the mouse’s heart stopped beating and it died in a short time. During the maintenance time, I tried to count the heart beat of it, it’s 176 bpm. Finally, I could not save the mouse.
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In our animal facilities, we don't have the mixture of oxygen and air, I just use only the 100% Oxygen as a carrier gas to supply for the vaporizer. So is it a problem?
Can anyone help me in this case? Thank you in advance.
---Huy Vu---
Hello Vu Huy
I think all what happed will be explained through the coming problems :
1- Due to their high metabolic rate and likelihood of hypoglycaemia, rats and
mice need only be starved a matter of 40 – 60 min (mice) to 45 – 90 min (rats)
prior to anaesthetic induction.
2- These species will breath - hold during gaseous induction, to the point where
they become very cyanotic. In rabbits, the ‘ shock ’ organ is the lungs, and
during intense stress the pulmonary circulation can go into spasm, making the
hypoxia due to breath - holding even worse, even to the point of collapse and
cardiac arrest!
3- Volatile agents
However, their disadvantages
include the fact that there is a drying effect on the airways of the patient
when using inhalational anaesthetic agents that can cause dehydration during
long procedures. They also create problems if used as an induction agent, as
many species will breath - hold during this procedure.
Isofl urane
This is now becoming the most widespread volatile agent used for induction
and maintenance of general anaesthesia in small mammals as well as in dogs
and cats. A pre - anaesthetic medication incorporating an analgesic is usually
administered as isofl urane has no post - anaesthetic analgesic qualities and it is
irritant to the mucous membranes of many animals. Inspired concentrations
required for induction of anaesthesia vary from 2.5 – 4%. Breath - holding still
occurs, but the practice of supplying 100% oxygen to the patient for 2 min
prior to anaesthetic administration helps minimise hypoxia. After this pre -
oxygenation, gradually introduce the isofl urane, fi rst 0.5% for 2 min, then
assuming regular breathing, increase to 1% for 2 min and so on until anaesthetic
levels are reached allowing a smooth induction. Surgical anaesthesia can
usually be
4- Intermittent positive pressure ventilation
This may be necessary in some individuals who breath - hold during induction.
If intubation is not possible
5- Note the use of
a pulse oximeter probe, oesophageal stethoscope, intravenous catheter and supplemental heating is important.
Using a face mask for rodents such as this rat is often necessary owing to
the difficulty of intubation.
So I think that the Monitoring was deficient
6- Maintaining core body temperature is vitally important in all patients to
ensure successful recovery from anaesthesia, but is particularly important in
small mammals. This is primarily due to their increased surface area in relation
to their volume, so allowing more heat to escape per gram of animal.
Anaesthetic gases have a rapidly cooling effect on the oral and respiratory
membranes, and so patients maintained on gaseous anaesthetics will cool
down quicker than those on injectable ones: a situation that worsens as the
duration of anaesthesia increases.
7- Intra - , pre - and postoperative fl uid therapy is very important in small mammals,even for routine surgery. Again, as with the issue of maintaining core bodytemperature, the small size and relatively large body surface area in relationto the volume of these patients means that they will also dehydrate muchfaster, gram for gram, than a larger cat or dog. Studies have shown that theprovision of maintenance volumes of fl uids to small mammals during and immediately after routine surgery improved anaesthetic safety levels by as much as 15% in some cases, with greater improvement if the surgery was
being performed on severely debilitated animals. It is therefore to be strongly
recommended that all small mammal patients receive fl uids during and after
an anaesthetic whether it is routine or not.
8- Gaseous anaesthesia, particularly
with isofl urane, tends to result in more rapid recovery than the injectable
anaesthetics, but all forms of anaesthesia recovery are improved by maintaining
body temperature and fl uid balance during and after anaesthesia.
Reference:
Anaesthesia for Veterinary Nurses
Second edition, Edited by Liz Welsh
Chapter 12, Rabbits, Ferrets and Rodent Anaesthesia ( by Simon Girling)
Pages : 317- 335
Hi Rizk, thanks for your elaborative explanation.
Can you please tell us how to stop respiration for a few seconds in rat on isoflurane anaesthesia? I require avoiding respiratory artefact in my experiment. When I stop the ventilator the rat starts breathing spontaneously.