It is known that a lower cbt reduces the dose needed for general anesthesia. Does anybody know if there is literature about that or even a table?
Have never seen a table or formula for that, but it gets a little more complicated as propofol also lowers core body temperature per se by inhibiting vasoconstriction and promoting core-to-periphery blood flow. It all amounts however to the same practice - titrate the dose, and do it slowly.
I am unaware of any study that has formally assessed this. With the volatile (inhalational) anesthetics it is known that anesthetic dose requirements decrease by around 4% per degree celsius decline in temperature (for an example in rats - see Eger, Anesthesia and Analgesia 1987). It is likely that a reduction of similar magnitude occurs with propofol, but I agree with Philip - dose titration is important (bearing in mind though that if an EEG parameter is used for titration, then hypothermia alone can cause EEG slowing). Two issues are important though:
a. There are some differences in the molecular mechanisms of action of propofol (mostly GABA A agonist) versus volatiles (GABA A, but also effects on 2 pore K channels, ? NMDA effects etc).
b. More importantly, propofol is usually formulated as a lipid emulsion. The ability of the body to metabolise or store the lipid declines rapidly with decreasing body temperature. Thus, when mild therapeutic hypothermia is performed on ICU (eg after a cardiac arrest), propofol infusions are usually stopped (to prevent lipid accumulation) and are replaced by another agent (eg midazolam) that is not formulated in lipid.
Hello Oliver,
I have included interesting article from Shintaku 2014 *attached as pdf, where propofol is compared to other anesthesia. Even as propofol was presented as inhibiting sympathetic tone effect on temperature was not observed in this study. Interestingly, and I applaud this group for this is that they have presented mouse as (nocturnal animal) and claimed that all experiments were conducted between 1:00 p.m. and 4:00 p.m, which is in mouse's less active period. All anesthetics therefore act at less active period and might be directly compared. Have a good read article is quite interesting also for other aspects.