Why The “No Eating or Drinking Before Surgery” Rule is a Serious One

Photo by Sharon McCutcheon on Unsplash

We’ve all gone under the knife at some point in our lives. In the days leading up to the surgery, the surgeon would schedule appointments with the anesthesiologist and also give us a list of dos-and-dont’s. As patients, we don’t think much about these and some of us are even flippant about it —

“yeah, yeah, doc, no eating or drinking 12 hours before surgery, I know the drill”.

Noncompliance can delay your surgery, or can cost your life (no hyperbole intended). Let’s break it down.

Explaining brain chemistry as an electrical gradient

Let’s take a step back and understand that the nerve cells or neurons communicate through a complex interplay of chemical messengers and electrical signals. The cells have receptors on their surfaces and they can bind other molecules called ligands — think of the lock and key, or the baseball and the mitt analogy. When this binding occurs, a channel is opened up into the cell and positive or negatively charged ions can enter or leave. The interior and exterior of the cell have a gradient in electrical charge or at a “resting potential”. The neuron is more likely to conduct a message when it is positively charged inside the membrane relative to the outside. Let’s remember this!

Glutamate is an organic molecule that binds to a voltage-sensitive receptor. After binding, the receptor’s channel allows the entry of positively charged sodium and calcium ions and the exit of positively charged potassium ions. The interior of the cell is now less negative than it was earlier. This triggers “depolarization” and induces signal transmission along the adjacent nerve cell. Later, the reverse happens — sodium out, potassium in, and the establishment of the resting potential.

Another organic molecule called gamma-aminobutyric acid or GABA binds to receptors on the neuron, called the GABA A and GABA C. Like before, a channel is opened up and negatively charged chloride ions move across the membrane of the neuron. The addition of negative charge decreases the resting potential of the cell, resulting in an inhibitory effect. This is how, propofol, a common anesthetic, works.

When GABA binds to another type of receptor called the GABA B receptor, the net result is the shunting of positively charged potassium out of the cell. Therefore, this makes the interior of the membrane more negative relative to the exterior and conduction does not occur.

General anesthesia, sedation, and a burrito

It’s lunch time. You’re starving and bite into your burrito with gusto. Unfortunately, you swallow hurriedly and a bit of hot cheese goes down your windpipe. Your gag reflex kicks in and you bend over and cough until the food comes out. This happens because the stimulus activates several nerves and fires off the information to the brain. The brain receives the information and triggers the gag reflex. It just saved your lungs from receiving a barrage of cheese.

When you are sedated with anesthesia, the nerves don’t fire like we explained before, and the gag reflex is diminished. If you had a stomach full of liquid or food, the contents might be brought up to the mouth and leak into your windpipe, down to your lungs. It’s not pretty.

The real dangers of aspiration under anesthesia

1. “Arterial hypoxaemia”- Food causes blockage of oxygen intake and your body has oxygen starvation. May cause immediate death.
2. “Acidosis and hypercapnia”- Food in the stomach is acidic and causes imbalances in the lung’s acid-base balance. The lungs’ ability to remove carbon dioxide is impaired. Particles of food can cause tissue damage and inflammatory responses.
3. Aspiration pneumonia- Aspirated food serves as a catalyst for certain types of bacteria (like Fusobacterium or Bacteroides) to grow in the lungs, leading to a serious infection. Respiratory failure is also a possibility.

Therefore, it is crucial that we follow our doctor’s advice on the time window of limiting food and drink intake before surgery. Death by inhaled burrito is not the most romantic way to go, believe me.

References:

1. Institute of Medicine (US) Forum on Neuroscience and Nervous System Disorders. Glutamate-Related Biomarkers in Drug Development for Disorders of the Nervous System: Workshop Summary. Washington (DC): National Academies Press (US); 2011. 2, Overview of the Glutamatergic System. Available from: https://www.ncbi.nlm.nih.gov/books/NBK62187/
2. Allen MJ, Sabir S, Sharma S. GABA Receptor. [Updated 2021 Feb 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526124/
3. Sanivarapu RR, Gibson J. Aspiration Pneumonia. [Updated 2021 Jun 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470459/
4. Engelhardt T, Webster NR. Pulmonary aspiration of gastric contents in anaesthesia. Br J Anaesth. 1999;83(3):453–460. doi: 10.1093/bja/83.3.453. PMID: 10655918.

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