Who said nil-by-mouth?

“Is the patient nil-by-mouth”?

A few months ago, I anaesthetised a patient for a routine operation. He was nervous, as many of them are, and had made the decision to forego his evening meal the night before surgery, and drink nothing after 6pm the previous day in order to be “extra safe” for his anaesthetic. When he told me, I responded with an outward smile and an inward eye-roll, popped out and came back with a glass of apple juice for him to drink, and a gentle explanation of how prolonged fasting is actually bad for his recovery.

Aspiration under anaesthesia is extremely rare in Europe, but it’s difficult to get accurate figures. Incidence for elective cases is around 1:5000 to 1:10,000. According to a UK Royal College of Anaesthetists audit, obstetrics is even lower with only 12 cases between 2013-2016, equating to around 5 cases per million pregnancies.

Traditionally, we anaesthetists have placed enormous importance on the patient being “NBM (nil-by-mouth) from midnight” irrespective of the time the operation takes place. This leads to extended fasting times for many, particularly our most vulnerable patients on emergency lists or with conditions needing frequent return to theatre. This often impacts significantly on their nutrition during the perioperative period and probably causes delayed recovery and harm.

Our perioperative fasting guidelines recommend six hours for solids and two hours for clear fluid. They are generally sensible, and the discussion in the paper is extremely informative, including a review of the physiology of stomach emptying. Despite this guideline being nearly fifteen years old I find it extremely frustrating that it’s not being adhered to, many local protocols come up with something different or accept some parts of it and not others. Did you know sparkling fluid is fine? That boiled sweets are ok and chewing gum is also allowed? It’s hard timing two hours, however, especially on an emergency list, so many places simply default to full fasting just in case the patient gets called for earlier.

When clear fluid enters the stomach, it is generally absorbed within around twenty minutes. It doesn’t increase the gastric volume significantly (unless you drink a lot in a short period) and also reduces the acidity of the stomach secretions. So, allowing our patients to keep hydrated up to when they’re called in for their operation is arguably safer than denying them fluids. The “sip til send” model, pioneered by NHS Tayside, is finally being adopted by hospitals up and down the country, and features in new guidelines from the Centre for Perioperative Care.

So, what about food? Six hours according to our guidelines, but does that mean I can safely have an enormous three-course meal six hours before my operation, but if I eat a biscuit five hours pre-op then I’m in mortal danger? I can feel when my stomach is full, and I promise after a big meal my stomach is definitely still full six hours later.

The patients at highest risk of aspiration are those with a high intragastric pressure, for instance due to bowel obstruction, gastroparesis, gastric outflow obstruction or renal failure. I worry that our strict blinkered adherence to six hours actually promotes a false sense of security when anaesthetising these high-risk patients, where we really do need to ramp them and get the tube in quickly. Cricoid pressure may even be useful for this cohort. I also think we sometimes lose focus on the overall risk and benefit to the patient, for instance, delaying a patient with a fractured hip because she had a biscuit with her tea may lead to her not getting done that day. This in turn increases her risk of death and disability, eclipsing any conceivable risk of aspiration from that biscuit.

I’m sure many of you will know people on the GLP-1 agonists, like Monjaro and Ozempic, along with many more who don’t like to admit that they have been using them. These medications are supremely effective, and many of the people I know who have used them say that they have transformed their lives. The annoying thing is they do slow down gastric emptying. And, at least, theoretically increase the likelihood of aspiration under anaesthesia. The drugs are really too new to get any robust population data on whether they really do increase the anaesthetic risk, but, so far, I’m not aware of a large increase in aspiration. Recent guidelines recommend not stopping the drugs before surgery as it’s difficult to titrate them back up, and stopping them may worsen diabetic control. Also, there is a possibility they may reduce perioperative strokes and cardiac events, so it’s likely to be safer to continue them. It’s probably advisable to increase the fasting time for solids on these drugs, but clear fluid should be unaffected.

For those of you who have read this far, what do I want you to take home from this? Changing ingrained culture is very difficult, and we can’t do it without your support and leadership. Encourage SipTilSend processes, inform the nursing staff of the guidelines and the importance of hydration. None of our patients should arrive in theatre thirsty. No resident doctor should have to prescribe IV fluids because the patient is nil by mouth. Your patient will recover faster; there will be fewer complaints to answer; the hospital will save money. It’s a win-win situation for everyone.

And I want you to stop saying “nil-by-mouth”.