Anaesthesia by intravenous emulsified isoflurane in mice

An emulsion of isoflurane in Intralipid for intravenous (iv) injection was formulated and its anaesthetic properties determined in mice. The major advantage of iv delivery of volatile agents is to accelerate the induction of anaesthesia by circumventing the anesthetic circuitry and the lung's functional residual capacity. Isoflurane was added to Intralipid in varying concentrations. The ED50 (n = 34) and LD50 (n = 20) were determined by a single iv bolus injection. Anaesthesia was also induced and maintained for 30 min (n = 5) by continuous infusion and the time to emergence was measured. The ED50 and LD50 were 0.7 +/- 0.2 microliter and 2.4 +/- 0.2 microliter of isoflurane equivalent respectively. An average infusion rate of 1.6 +/- 0.4 microliters.min-1 of isoflurane equivalent was required for maintenance following which the average emergence time was 193 +/- 35 secs. The only negative effect was local skin ulceration with an inadvertent interstitial injection. We conclude that iv induction and maintenance with emulsified isoflurane in Intralipid can be carried out with safety and reproducibility in the mouse. Further larger animal studies are warranted assessing the haemodynamic, toxicological, physiochemical and pharmacokinetic characteristics of these and other similar preparations.