I am performing [ideally] survival surgeries on male Sprague Dawley rats (PD45), and for some reason we are having issues with their breathing. We will be part way through a surgery, or just finished, and they will suddenly stop breathing. The surgeries are somewhat long (1.5-2 hours), but using Isoflurane we were under the impression that it shouldn't be a problem.
For reference, we are doing bilateral microinjections, and a bilateral cannulation procedure.
Spec for anesthetic: O2 flow rate knob set to 1, with Iso set between 2 and 3. We've done these surgeries before, and only recently have had issues where we've needed to resuscitate. Any insight/thoughts/methods would be greatly appreciated!
Thanks!
You have residual respiratory depression during insufficient anesthesia with a single agent in high concentration.
First, you need to start with 1-2 isoflurane (its MAC is 1.25!), but withdraw it slowly during surgery and stop it 15 to 30 min before end of surgery. Then, since isoflurane alone in such low concentration may be NOT so good anesthetic when you go below 1, you need to combine it with over 60% N2O and about 30% O2. If you do not have N2O, use some other injectable agent (for example ketamine, 20mg/kg). Why don’t you consult some local anesthesiologist to see which agent are available? We use to say “if you are good anesthesiologist it is possible to do good anesthesia even with saline”!
Thank you!
An additional question - do you think the length of the surgery may be an issue? We have them hooked up to a nose cone in the stereotax for 1.5-2 hours and we have been putting them in an induction chamber first to put them under initially (at an O2 flow rate of 2 and an ISO rate of 3). We have generally had the ISO higher for induction purposes at the beginning of surgery, and lowered it when breathing stabilized (to the O2 flow rate at 1 and ISO ~2). We are hesitant to use KET, as we are looking at neural markers that have been shown to be impacted by KET treatments (which is why we're using the ISO). Do you think it would be better to slowly put them into ISO and increase over time?
Thanks!
You don't hook them up by the incisors? What do you cannulate? Do you tracheotomise them, do you manipulate vagus? It runs both sides parallel - next to some tracheal arteries. If you cut vagus, they stop breathing after some time probably because they do not get feedback from the lungs. Even putting a thread around trachea to fix a tracheal cannula interrupts vagus and they stop breathing. You can carefully just detach vagus and put the thread below it, around the trchea.
I would not start with low concentration of ISO. It would be better to use other inhalation agent (halothane?) because MAC of ISO is variable. We used always pentobarbital without complications. See our microcirculation papers.
Yes, we hook them up by the incisors (within a nose cone that is hooked up to the gas lines)
So no tracheostomi? Hmmm...
You certainly HAVE TO HAVE tracheostomi for such long narcosis since rats tend to produce a lot of tracheal secretion and this is certainly the reason that they die. When you have an airway, you can suction it repeatedly as soon as you see that it start with shallow breathing. But then, of course, you have to dissect vagus both sides carefully and then fix your tracheal tube (plastic cannula, 16 gage or so). Do not bind the vagus with it! If the animals will survive, the tracheostoma will not be a problem.
Anyway, IF you still have respiratory depression “in addition”, try 100mg/kg thiopentol (Trapanal) i.p. to start. Then after about 20 min or when rat start reacting (its tail pinch is the test for the depth of anesthesia) every 20 min or so give 10mg/kg i.p. or iv or intra arterially (if you have cannulated one artery).
I'm late to the party, but my friend just had this problem during her surgery and I was trying to help her troubleshoot it so I found this thread.
If you decide to switch up your anesthetic drugs in the future, I've had really good success with using ketamine to induce (90mg/kg) and xylazine (10mg/kg). Once I'm ready to start surgery, I transfer them over to the iso system and start them at 0.5%/1LPM initially ramping up to a max of 1.5%/1LPM by the end of my 2-3 hour long surgery.
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