Cataract surgery is one of the most frequently performed medical procedures globally, offering a high success rate in restoring vision. Despite its routine nature, the procedure requires a non-negotiable step for patient safety: fasting, often referred to as NPO (nil per os, or nothing by mouth). Adhering to these guidelines is mandatory because the combination of food in the stomach and the medications used for sedation creates a unique, life-threatening risk that must be avoided.
How Sedation Affects Protective Reflexes
Cataract surgery typically involves conscious sedation, where intravenous (IV) medications are given to help the patient remain calm and comfortable. Sedative agents, such as midazolam or propofol, reduce anxiety and minimize head movement by depressing the central nervous system. This depression slows down several involuntary bodily functions, including the digestive system. Food or liquid remains in the stomach longer than usual. Crucially, these medications suppress the body’s natural defense mechanisms that protect the airway, such as the gag and swallowing reflexes. The temporary impairment of these reflexes means the patient loses the ability to cough or redirect stomach contents away from the lungs.
Understanding the Risk of Pulmonary Aspiration
The suppression of protective reflexes due to sedation directly leads to pulmonary aspiration. This occurs when stomach contents—including undigested food, liquids, and highly acidic gastric juices—are involuntarily regurgitated and inhaled into the lungs. Although the overall risk during cataract surgery is low, the consequences are severe enough to warrant the strict fasting rule.
If stomach contents enter the lungs, the delicate lung tissue cannot handle the corrosive nature of stomach acid. The immediate reaction is chemical pneumonitis, an acute inflammatory condition caused by the acid burning the lung lining. This rapidly causes severe breathing difficulties and lung damage. If the aspirated material contains bacteria, it can lead to aspiration pneumonia, a serious infection requiring intensive medical intervention.
Specific Timing and Rules for Fasting
To minimize the risk of pulmonary aspiration, specific, evidence-based fasting windows are mandated, which are often more liberal than the traditional “nothing after midnight” rule. For solid foods, the standard guideline advises patients to stop eating at least six hours before the scheduled procedure. This time frame allows the stomach to empty its contents, significantly reducing the volume of material available for regurgitation.
Clear liquids, such as water, black coffee, or apple juice without pulp, are typically allowed up to two hours beforehand. This shorter window is possible because clear liquids pass through the stomach quickly, helping prevent dehydration and patient discomfort. Patients taking essential morning medications should do so with only a tiny sip of water, which must be pre-approved by the medical team. Failure to follow these instructions means the safety protocol is breached, and the surgery will be postponed or canceled.