One of the most common complaints relating to anaesthesia is being left without food and drink for extended periods of time waiting for surgery. Being left without food or drink became one of the issues on the medical wards in the Mid Staffs scandal and it makes people miserable. I know if I miss lunch I start non-specifically hating everyone and generally getting irritable, so I can see why our patients get upset.
In the UK, despite much guidance for 6hrs for solids and 2hrs fasting for clear fluid, the phrase ‘nil by mouth from midnight’ is routinely used as a safe default , even when their surgery might not be until later in the morning, or even late afternoon. Our patients themselves have also become so used to this principle that they are often too frightened to follow the (up to date) fasting instructions we give them and still make themselves NBMFM, or even way before, just to be extra safe.
Why do we fast our patients before an operation? At the start of anaesthesia we give opiates, general anaesthetic drugs and medication that paralyses the muscles in your body. With a full stomach, the likelihood of acidic content regurgitating and being inhaled into the lungs increases when we abolish the body’s own defensive reflexes. The average person’s stomach is usually empty six hours after a normal sized meal (although when I have a large curry I know for a fact my stomach is still full the next morning, particularly when beer is also involved). Clear fluid is usually absorbed much more rapidly.
The European Society of Anaesthesia has produced some really sensible and excellent guidelines on preoperative fasting recently. You can view them here: ESA fasting guidelines. All the evidence I quote here is referenced from there.
The way clear fluid is managed preoperatively is my biggest bugbear. Our patients arrive in theatre very nervous, with a dry mouth and cold peripheries. Their previously beautiful veins shrivel to mere capillaries, and being dehydrated only makes this state worse. The evidence quoted in the fasting guidelines above suggest that in most instances a moderate amount of clear fluid is absorbed from the stomach in about 30minutes. In addition, the stomach itself produces an appreciable volume of acidic fluid continually, and being allowed to drink clear fluid reduces the acidity of the stomach content. Chewing gum has little effect on gastric volume, and neither does eating boiled sweets – they get rapidly dissolved into sugar solution and absorbed in the same way as clear fluid.
So, even if you anaesthetise a patient who an hour ago had a carton of Ribena, their stomach content is likely to be the same volume, and less acidic than someone who didn’t. In addition, they are likely to be less miserable than someone who’s been fasted for 8 hours or more, and they are less likely to do acid damage to their lungs if they inhale their vomit.
Preoperative carbohydrate loading has become one of the pillars of enhanced recovery, and it looks like patients do better if we give them some calories before operating on them. Minimising fasting time preoperatively and starting food soon after an operation changes the body’s physiology from a catabolic fasting state, where the body’s reserves are being broken down for energy, to a more anabolic state. There is now reasonably good evidence for the overall enhanced recovery principles not only being better for our patients, but also reducing length of stay in hospital, making it more cost effective too.
Many people (me included) find it difficult to face a new day without their morning coffee. The good news is that coffee and tea count as clear fluid as long as you don’t add milk. The European guideline committee wanted to add coffee/tea with a little milk as an allowable drink, but this was vetoed by a single member of the working party. Again evidence shows that if milk is added to a clear drink so it makes up less than 1/5th of the volume it acts as a clear fluid and gets absorbed quickly. When it forms a larger proportion it curdles and gets handled by the stomach as a solid. So a latte gets handled as a solid, but an americano with a dash of milk is a liquid. I suppose the guidelines err on the side of caution, and to avoid confusion it might be better to avoid milk altogether.
Allowing your patients to drink clear fluids up to two hours before surgery is not only safe, but probably safer than starving them excessively. We currently generally say patients ‘may’ have a drink of clear fluid two hours before surgery, but I think we should change this to ‘should’. Patients are still frightened to do so and need encouragement that it’s not only right, but better. Interestingly the surgical division at Mid Staffs has been doing this for years, and I’m really proud of our orthopaedic/trauma wards who are now actively giving our patients apple juice at 0630 on their day of surgery rather than hanging up the NBM sign.