Meconium perhaps leads to chemical pneumonitis as it is a potent activator of inflammatory mediators which include cytokines, complement, prostaglandins and reactive oxygen species.Meconium is a source of pro-inflammatory cytokines, including tumour necrosis factor (TNF) and interleukins (IL-1, IL-6, IL-8), and mediators produced by neutrophils, macrophages and epithelial cells that may injure the lung tissue directly or indirectly. For example, proteolytic enzymes are released from neutrophilic granules and these may damage the lung membrane and surfactant proteins. Additionally, activated leukocytes and cytokines generate reactive nitrogen and oxygen species which have cytotoxic effects. Oxidative stress results in vasoconstriction, bronchoconstriction, platelet aggregation and accelerated cellular apoptosis. Recently, it has been hypothesised that meconium is a potent activator of toll-like receptor (TLRs) and complement, key mediators in inflammation, and may thus contribute to the inflammatory response in MAS.Meconium contains high amounts of phospholipase A2 (PLA2), a potent proinflammatory enzyme, which may directly (or through the stimulation of arachidonic acid) lead to surfactant dysfunction, lung epithelium destruction, tissue necrosis and an increase in apoptosis. Meconium can also activate the coagulation cascade, production of platelet-activating factor (PAF) and other vasoactive substances that may lead to destruction of capillary endothelium and basement membranes. Injury to the alveolocapillary membrane results in leakage of liquid, plasma proteins, and cells into the interstitium and alveolar spaces. Surfactant inactivation
Surfactant is synthesised by type II alveolar cells and is made of a complex of phospholipids, proteins and saccharides.
Usually dogs are known to understand when its time to eat in their bailey chair, and this helps prevent issues. Bailey chairs can be made and are sold. Also, a simple chair turned upside down can be successfully used for this purpose. In two unrelated incidents in Latvia and Australia megaesophagus developed in dogs that had eaten certain brands of dog food, however no agent that could have caused the disorder has been found in lab tests of the food. Diagnosis
An important distinction in recognizing megaesophagus is the difference between when a dog regurgitates or vomits. When a dog regurgitates there is usually not as much effort involved as when a dog vomits. Often when regurgitating, the dog will tip its head down and the liquid and/or food will almost appear to "spill out" of its throat.One of the primary dangers to a dog with megaesophagus is aspiration pneumonia. Because the food stays lodged in the throat, it can often be inhaled into the lungs causing aspiration pneumonia. One way to avoid this is to make sure that every time the dog eats or drinks anything, that the dog sits for at least 10 minutes afterward or is held in a sitting up or begging position. This disorder has a guarded prognosis, however, a successful management technique is vertical feeding in a Bailey Chair. Affected breeds
Cats
Affected breeds:

American Shorthair
Persian (cat)
Siamese (cat)

Horses
Megaesophagus is rare in horses. It is more frequently reported in Friesian horses than in other breeds.