Anaesthesia in neonates

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We have a lot of groups looking at neurodevelopment and so far we've been able to use Isofluorane for all of the studies, but one group are planning on doing Ca2+ imaging and the Isoflurane is thought to affect the imaging so they would like to look at using an injectable protocol.  They have proposed Medetomidine, Midazolam (+/- fentanyl) or Urethane, but I have no experience using these agents in neonates and wondered if anyone has experience they could share. In this case it is neonatal rats aged P6-11.  The imaging would be terminal and last between 10-30 minutes and is non-invasive.  There is a surgical set up which we may try and carry out under the same anaesthetic if possible.

Hypnorm works well, although you get some spontaneous movement unrelated to stimuli (painful or otherwise). There is paper in Laboratory Animals by Clowry and Flecknell. Other combinations tend to be lethal (see an older paper by Dannemann which also looked at hypothermia). I too have heard that medetomidine/midazolam/fentanyl is ok, but I have seen no controlled studies or data on this. Ketamine/medetomidine is lethal even at low doses, so I would want some reassurance that the “triple mix” is safe and effective.