Why You Must Fast Before Surgery: A UAE Spine Surgeon Explains the Real Risk

Most patients who are scheduled for surgery are told to fast beforehand, nothing to eat from midnight, sometimes nothing to drink except small sips of water up to two hours before. Many accept this instruction without fully understanding why it exists. It feels like a rule. It is actually a life-saving precaution, and understanding the anatomy and physiology behind it gives that instruction its proper weight.

Dr. Sherief Elsayed, Consultant Spine Surgeon in Dubai (About Dr Sherief Elsayed – Consultant Spine Surgeon), explains the real risk behind pre-operative fasting, and the emergency measure used when it fails.

The Problem: Aspiration Under Anaesthesia

General anaesthesia does something that cannot be replicated by any other medical intervention: it removes your ability to protect your own airway. In a conscious person, the reflexes that prevent food and liquid from entering the lungs are automatic and reliable. Swallowing, coughing, gagging, these protect the airway constantly without any conscious effort. Under general anaesthesia, these reflexes are suppressed or abolished entirely.

Dr. Sherief Elsayed explains what happens when this protective mechanism is absent: “Some of the medications that we use can make you throw up. And if you throw up and you don’t have good control of your airway because you’re under anaesthesia, for example, you will aspirate. You will breathe that vomit in and you’ll end up with a nasty pneumonia, which can be life threatening.”

Aspiration pneumonia, the pneumonia that results from inhaling stomach contents, is not an abstract complication. Stomach acid is highly corrosive to lung tissue. Aspirated material causes a severe chemical pneumonitis that can progress to respiratory failure. It is one of the genuinely dangerous anaesthetic complications, and pre-operative fasting is the primary strategy for preventing it.

Why Do Anaesthetic Drugs Cause Nausea and Vomiting?

Post-operative nausea and vomiting (PONV) is one of the most common side effects of general anaesthesia, affecting between 20 and 40 percent of patients without prophylaxis. Several mechanisms contribute:

Inhalational anaesthetic agents directly stimulate the chemoreceptor trigger zone in the brainstem, the area responsible for initiating the vomiting response.

Opioid pain medications used during and after surgery slow gastric emptying and stimulate the same brainstem centres.

Surgical manipulation of abdominal and spinal structures activates vagal reflexes that can trigger nausea.

Anxiety and pain in the peri-operative period independently increase PONV risk.

For spine surgery patients who are positioned face-down (prone) during the procedure, as is common in lumbar disc and decompression surgery, the risk of aspiration from vomiting is particularly significant. Vomit cannot drain away from the airway in the same way as in the supine position.

What the Pre-Operative Fast Actually Achieves

The stomach normally empties solid food within four to six hours and liquids within one to two hours of consumption. Pre-operative fasting is designed to ensure that the stomach is as empty as possible at the time anaesthesia is induced.

Standard fasting guidelines:

• Solid food, fatty foods, and milk: fast for six hours before surgery
• Light meals (toast, clear fluids without milk): fast for four to six hours
• Clear fluids (water, black tea or coffee without milk, fruit juice without pulp): can be taken up to two hours before surgery in most protocols
• Medications: taken with a small sip of water as directed by the anaesthetic team

These guidelines have been refined over decades of anaesthetic practice. They balance the risk of aspiration against the risk of dehydration and hypoglycaemia from excessively prolonged fasting. The blanket “nothing from midnight” instruction that was standard for many years has largely been replaced by more nuanced protocols that allow clear fluids closer to the procedure.

When Fasting Fails: The Cricoid Pressure Emergency

Despite pre-operative fasting, emergencies arise in which a patient must be anaesthetised when the stomach may not be empty, trauma cases, emergency surgery, or unanticipated delayed gastric emptying. In these situations, a specific technique is used to protect the airway during the most vulnerable period: the moment of intubation.

Dr. Sherief Elsayed describes what this looks like: “Now, if there’s an emergency, then while we’re intubating you, while we’re putting the tube down to seal off the airway and protect it from any vomit, this assistant will press very hard down on here, which closes the oesophagus while the tube goes down.”

This technique is called cricoid pressure, or the Sellick manoeuvre. The cricoid cartilage is the complete ring of cartilage at the base of the larynx. When firm pressure is applied downward over it, the oesophagus, which runs immediately behind the trachea at this level, is compressed against the vertebral body, closing it off and preventing stomach contents from travelling upward and entering the airway.

How cricoid pressure works:

1. An assistant places their fingers on the cricoid cartilage, identifiable as the prominent firm ring just below the thyroid cartilage (Adam’s apple)
2. When instructed, firm downward pressure is applied, typically 30 to 44 Newtons
3. This occludes the oesophagus, preventing passive regurgitation of stomach contents into the pharynx
4. The anaesthetist rapidly intubates, passes the endotracheal tube through the vocal cords and into the trachea
5. The cuff of the endotracheal tube is inflated, creating a complete seal and definitively protecting the airway
6. Only then is cricoid pressure released

This technique is used in rapid sequence induction, a specific anaesthetic protocol designed for patients with a full or potentially full stomach. It compresses two technically demanding manoeuvres, intubation and airway protection, into a single coordinated sequence performed in under 60 seconds.

What Aspiration Pneumonia Actually Looks Like

Understanding the consequence of failed airway protection reinforces why the pre-operative fast is not a bureaucratic inconvenience.

Pre-operative health optimisation extends beyond fasting. If you are preparing for spinal surgery and want to understand how your genetics may affect recovery, inflammation, and healing, Can a DNA Test Tell You How to Exercise and Eat Better  worth reading as part of your preparation.

Aspiration of gastric contents causes:

• Immediate bronchospasm and coughing (if any protective reflexes remain)
• Chemical pneumonitis from gastric acid, the pH of stomach acid is typically between 1 and 3, highly corrosive to lung tissue
• Patchy or lobar consolidation visible on chest X-ray within hours
• Fever, tachycardia, and respiratory distress
• In severe cases, progression to acute respiratory distress syndrome (ARDS)
• Secondary bacterial infection superimposed on the chemical injury

Treatment requires intensive care support, mechanical ventilation in severe cases, broad-spectrum antibiotics, and time. Recovery can take days to weeks. Severe aspiration pneumonia carries a meaningful mortality rate, particularly in older or medically compromised patients.

Practical Guidance for Patients Preparing for Spine Surgery in the UAE

For patients scheduled for spinal surgery with Dr. Sherief Elsayed or any Spine Surgeon in Dubai (Spinal Conditions – Diagnosis & Treatment in Dubai), the following practical points apply:

Follow the fasting instructions exactly. The specific times you are given have been calculated for your procedure. Do not assume that a light snack a few hours before is harmless, gastric emptying is variable and can be slowed by anxiety, medications, and specific foods.

Take prescribed medications as directed. Your anaesthetic team will advise which medications to continue taking on the morning of surgery, usually with a small sip of water. Do not withhold medications without guidance, and do not take additional medications not discussed with your team.

Tell your team about any nausea, vomiting, or reflux. Patients with gastro-oesophageal reflux disease (GORD), gastroparesis, or a history of difficult anaesthesia need specific pre-operative management. This history is important and should be disclosed.

Do not eat or drink anything after the specified cutoff time. If you inadvertently consume food or liquid within the fasting window, contact your surgical team immediately. Your procedure may need to be delayed rather than cancelled, but the decision requires medical assessment.

Understand that the rule protects you. The pre-operative fast is not a test of compliance. It is a clinical safety measure with real and serious consequences if ignored.

Why This Matters Beyond Spine Surgery

The principles of pre-operative fasting and airway protection apply to all procedures requiring general or deep sedation. For patients undergoing spinal procedures, the Spinal Conditions – Diagnosis & Treatment in Dubai (Spinal Conditions – Diagnosis & Treatment in Dubai) page outlines what to expect throughout the surgical process, not only spine surgery. Any patient undergoing dental procedures under general anaesthesia, bowel surgery, joint replacement, or emergency trauma surgery faces the same aspiration risk and benefits from the same protective protocols.

The article Dr. Sherief Elsayed Explains Which Post-Surgery Symptoms Need Urgent Care covers what to watch for after a procedure is complete, and fasting-related aspiration, if it occurs, would be one of the early warning signs to discuss with your clinical team.

Expert Summary

Pre-operative fasting exists because the normal reflexes that protect your airway are abolished by general anaesthesia, and vomiting under anaesthesia can cause life-threatening lung injury. The rule is simple, the biology behind it is well-established, and the consequences of ignoring it are serious.

When fasting has not been possible, in genuine emergencies, the anaesthetic team uses cricoid pressure and rapid sequence intubation to mechanically protect the airway during the vulnerable period of intubation. This is a skilled, co-ordinated technique that requires precision and speed. It is the safety net. Pre-operative fasting is the prevention. Both matter, and understanding why puts patients in a much stronger position as active participants in their own safe care. To discuss any concerns before your procedure, a Back Pain Doctor in Dubai (Back Pain Treatment in Dubai – Rapid Relief & Rehabilitation) or your treating surgeon’s team will be able to answer specific questions about your individual preparation.