A comparative study of the mortality rate of rats receiving a half lethal dose of fat intravenously: under general anaesthesia versus under spinal anaesthesia.

Background: There is no data that demonstrates what anaesthesia is suitable for patients who have a high risk of fat embolism syndrome (FES). We investigated the mortality rates of rats that received a half lethal dose (LD(50)) of fat by intravenous injection after induction of general or spinal anaesthesia.

Methods: An LD(50) of fat for rats was determined by using a toxicological method. Three hundred and seventy five rats were randomly assigned to receive general anaesthesia (group GA, n=125), or spinal block (group SA, n=125), or no anaesthesia (group C, n=125). The rats were injected with the LD(50) of fat at 20 min after anaesthesia induction. The mortality rates were recorded at 2, 8, 12, and 24h after fat injection.

Results: The LD(50) of fat was 0.706 ml/kg and its 95% CI was 0.622 ml/kg-0.801 ml/kg. The mortality rate was lower in the group GA than in the group SA (p<0.01), whilst there was no statistical difference between the group SA and the group C (p=0.442).

Conclusion: It is feasible to assess the efficacy of various treatments for FES by comparing the mortality rates of animals after injection of an LD(50) of fat. The mortality rate of rats was lower when FES was induced under general anaesthesia than under spinal anaesthesia which implies that general anaesthesia is superior to spinal anaesthesia for patients who have a high risk of FES.