“Here comes the sleepy juice” said the anaesthetist as he prepped me for surgery and injected me full of a milky looking blend to make sure I couldn’t see, hear or feel anything that would happen over the course of the next two hours. As a scientist I couldn’t help but wonder what exactly the ‘sleepy juice‘ was, but I had passed out before I was able to form this question out loud.
Intravenous anaesthesia is often made up of a cocktail of different substances, each with their own specific purpose. The active component of the milky concoction was likely to be a molecule called propofol whose job is to induce amnesia and ensure that there is no memory of the period of time that propofol is in the body. It usually comes as a mixture of 1% propofol and 10% soybean oil. The rest of the components include egg phospholipid as an emulsifier, glycerol as a tonicity-adjusting agent (to balance osmotic pressure), and aqueous sodium hydroxide to adjust the pH. It is believed to interact with the GABAA receptor – a ligand gated ion channel found in nerve cells that is involved in virtually all brain functions. The inhibitory action of propofol drastically slows the progression of signals through the nervous system meaning that the patient is not be able to think, create any memories, move, or see or hear anything. Most importantly they are not able to feel any pain during the operation! Incidentally, propofol was the drug allegedly used to kill Michael Jackson.
The levels of anaesthesia in the body is closely monitored by specialists called anaesthetists whose job is to make sure the anaesthetics don’t wear off during the procedure. In general the duration of action of intravenous anaesthetics is between 5 and 10 minutes after which the patient will spontaneously regain consciousness. To stop this from happening the level of anaesthetic in the body is maintained, either by via a suspension of propofol in a drip that enters the body through an intravenous catheter, or by the inhalation of a gaseous anaesthetic such as sevoflurane (so named due to its highly fluorinated structure). Historically, volatile solvents such as chloroform and diethyl ether have been used as anaesthetics, which can explain why you might feel a little light headed after mistakenly inhaling too much during a day in the organic teaching labs!
*This article will also appear in the autumn semester edition of ‘Resonance,’ the University of Sheffield Chemistry Departmental magazine.