whilst gastric acid secretion is reduced due to loss of parietal cells, a gastric sleeve creates a high-pressure system while simultaneously weakening the anatomy designed to prevent backflow
the surgery transforms a large, highly distensible stomach pouch into a long, narrow, rigid tube with a capacity of only about 150 mL
the fundus (the top, stretchy part of the stomach) is entirely removed - without this reservoir to accommodate meals or normal secretions, eating or drinking causes an immediate, sharp spike in pressure inside the new sleeve. This high pressure easily forces fluids upward into the oesophagus as it is within a low-pressure chest cavity
normally, the oesophagus enters the stomach at a sharp, acute angle known as the Angle of His. This angle acts as a flap-valve: when the stomach fills, it presses against the esophagus to seal it shut. Creating a straight sleeve obliterates this acute angle, removing a major natural flap-valve mechanism.
the surgical dissection and stapling close to the gastro-oesophageal junction frequently sever the “sling fibres” of the stomach. These muscle fibres are vital for reinforcing the lower oesophageal sphincter (LOS). Without them, the resting pressure of the LOS drops, leaving a weaker valve.
if the sleeve is stapled too tightly or becomes twisted/kinked (often at the incisura angularis), it slows down gastric emptying. This stasis acts like a downstream blockage, leaving the contents no choice but to travel upward.
as the volume of fluid required to trigger reflux is much lower, what little acid is produced still ends up in the oesophagus and more importantly, the reflux fluid is frequently a mixture of digestive enzymes, pepsin, and highly alkaline bile traveling up from the small intestine. Bile reflux can irritate and inflame the oesophageal lining just as severely as pure hydrochloric acid, causing classic heartburn and GORD symptoms