Perhaps not every patient can understand why a patient needs to fast before receiving anesthesia. Anesthesia for most of the lay person in my country means receiving gas. However over the years anesthesia can be either general anesthesia (GA), regional anesthesia (RA) or even monitored anesthesia care (MAC) where the patient is sedated just enough to tolerate the procedure but is still able to breathe on their own, respond to the call of their name while their vital signs are being monitored throughout. Vital signs indicate your blood pressure, oxygen saturation, heart rate, and end-tidal carbon dioxide (the carbon dioxide that you breathe out and it is an indication that you are still breathing i.e there is ventilation). Of course different cases will require different types of monitoring but the one mentioned are basic monitoring that is compulsory for all patients receiving anesthesia.
I hope you can follow what I am saying so far and let's get to why you need to fast before anesthesia. The simple answer is that we do not want you to aspirate the contents of your vomitus. To aspirate is simply to inhale so imagine if you had some food particles left in your stomach and you vomited and the content went into your lungs, it could be disastrous and may lead to death. I am serious when I say death as there are cases reported of people dying from aspiration pneumonia. Do remember that under anesthesia you might be unable to protect your own breathing passage and the contents from the stomach is very likely to go into your lungs.
So how does it cause death? It is because the aspirated contents cause a condition called aspiration pneumonia where there is inflammation in the lungs due to the inhaled contents. Those are foreign particles to the lungs and once the lungs are inflamed they will not be able to function optimally. As we all know we use our lungs to breathe where oxygen goes in and carbon dioxide goes out and all these exchange takes place at the thin and tiny lung units called alveoli which have tiny blood vessels around them (since our blood is the one that is carrying the oxygen around the body). Thus if there is inflammation, the exchange of gaseous would be impaired, and there is insufficient oxygen to supply to the body. In the body, the brain consumes the most oxygen as compared to other organs and when the supply is inadequate it could cause brain damage. Scary isn't it? It is a nightmare for an anesthetist to have their patient aspirate and we often take precautions to prevent it and it is also a risk we often discuss and highlight to patients.
You might be at a higher risk for aspiration if you are pregnant (because of the hormone progesterone causing the lower esophageal sphincter to be more relaxed, esophageal = food pipe, sphincter = ring shape "door"), obese (the gastric (stomach) pressure is higher), have underlying gastro-esophageal reflux disease basically you often have water brash which is due to backflow of stomach acid into your food pipe. You could taste the acidity in your mouth. Cases where the patient is unable to fast like dire emergencies or patients with underlying conditions that make gastric emptying time slower like in diabetics or post-trauma (eg. motor vehicle accident).
For elective cases, meaning that you came for a scheduled, well-planned procedure, you must fast at least 6 hours for solids (food) and 2 hours for clear fluids. Do note it is clear fluids meaning you can take plain water, pulp-free juice like apple juice, tea and coffee without milk. A simple rule is you could see through the liquid in a clear plastic cup. If you had a heavy meal then you should be fasted for at least 8 hours. Fasting guidelines are available for different countries. The European and American fasting guidelines differ mainly at the part involving children. In Malaysia we follow the American fasting guidelines which is:
8 hours for heavy meal/ fatty food/ fried food
6 hours for light meal (toast or cereal) / non-human milk
4 hours for breast milk
2 hours for clear fluids (Alcohol is a NO NO! It slows the transit time of gastric contents)
What about chewing gum? you are allowed to chew them and to spit them out right before you are given anesthesia. If the gum is accidentally swallowed then it would be treated as solid food and you need to wait another 6 hours (the procedure gets delayed). Those on feeding tubes or percutaneous endoscopic gastric tube (also a feeding tube but this one goes directly at your stomach through your skin bypassing your food pipe) then the fasting regime might differ and you should ask your healthcare provider.
I did encounter patients who were so afraid of aspiration pneumonia that they told me they fasted for more than the prescribed fasting time. Actually fasting more than required will not bring additional benefits and in fact might cause harm. Fasting for too long can cause dehydration, and it can also make patient's "hangry" (hungry and angry). Most of the Enhanced Recovery After Surgery (ERAS) advocate for minimal fasting and early feeding post-surgery if conditions permit.
The most important duty you have as a patient is to adhere to the advice given by your healthcare provider on when to fast. The instructions may differ based on your condition, local institutional practice and depending on what time your procedure is going to take place. NEVER LIE or conceal your condition or LIE about fasting time as it can cost you your life. I did encounter patients who lied throughout my practice, usually about their last smoking status. Interestingly the Scandinavian fasting guideline mentioned 2 hours for chewing gum and tobacco products.
Remember that your anesthetist will do everything they can to prevent aspiration from occurring so please listen to instructions and be truthful when you are asked what time did you fast.
That's all for today's sharing.
