Vomiting

Vomiting (emesis) is the forceful ejection of solid and liquid gastrointestinal contents through the oesophagus, mouth and/or nostrils to the exterior. It is much more common in carnivorous than herbivorous species, although it is conten­ded that the basic mechanisms for the act are present in all species. A distinction is made between central and reflex vomiting. The former arises from direct stimulation of the vomiting centre in the medulla oblongata, and occurs in certain diseases of the brain, in uraemia resulting from nephritis and hepatitis and following the administration of apomorphine to the pig, dog and cat and, not infrequently, of morphine to the dog. The latter is caused by reflex stimulation of the vomiting centre as the result of irritation in various organs; it is observed in pharyngitis, oesophageal obstruction, foreign bodies in the stomach, gastric distension, pyloric hypertrophy, intestinal obstruction or distension, nephritis, pyometritis, peritonitis, hepatitis, etc.

The initial phenomena of vomiting consist of increased salivation, irregular, rapid and deep respiration, followed by retching, which arises from spasmodic contraction of all the muscles of respiration. The succeeding events consist of reflex mechanisms which prevent the vomitus from entering the respiratory tract. Following a deep inspiration the glottis is closed and the nasopharynx sealed off by elevation of the soft palate (see Fig. 90, p. 88). With the glottis still closed, expiration commences and is accom­panied by contraction of the abdominal muscles and diaphragm. In the next sequence the pyloric area of the stomach contracts, with relaxation of the fundic and cardiac areas and of the oesophagus. The increased abdominal pressure propels the stomach contents into the oesophagus, thereby creating antiperistaltic waves which carry them to the pharynx, from where they are ejected. Studies in the cat have shown the act of vomition is preceded by periods of retroperistalsis in the duodenum with reflux of duodenal contents into the flaccid stomach. This phase possibly occurs in other animals. When emesis occurs as a means of relieving an overloaded stomach, noted particularly in young puppies and kittens, retching is not observed and vomit­ing is projectile in character.

Except in the dog and cat, vomiting is always pathological, and in some species is of grave prognostic significance. In the horse, because of the long soft palate, vomited material is mainly regurgitated through the nostrils, and in other species through the mouth. In ruminant species, 'vomiting' in most instances is really regurgitation of rumen contents, not an emptying of the true stomach, although cattle and goats, and to a lesser extent sheep, manifest all the usual features of vomiting when they are poisoned by rhododendron or Convallaria majalis (lily-of-the-valley). Other causes of vomiting in cattle in­clude spoiled foods or highly acid silage and, in individual cases, diaphragmatic hernia, foreign body or papillomas in or near the oesophageal groove, impaction of the abomasum and ulcera­tion of the abomasum impinging on the pyloric sphincter. Dogs, cats and pigs vomit readily, and do so fairly frequently. In young pigs vomiting occurs as a feature in many systemic diseases, more consistently in vomiting and wasting disease and transmissible gastroenteritis. The bitch not uncommonly regurgitates recently ingested food in order to encourage its offspring to start eating solid food. It must be remembered, however, that persistent vomiting in the dog may indicate serious disease, e.g. pyloric obstruction or hyper­trophy, intestinal obstruction or occlusion, nephritis, pyometritis, peritonitis and hepatitis, as well as less serious conditions such as pharyn­gitis, mild catarrhal gastritis, etc. Many of the diseases which cause persistent coughing in the dog may give rise to mild emesis. The horse vomits only rarely and then with great difficulty and distress. In this species it is always an omi­nous sign, indicating very serious disease, includ­ing gastric impaction or distension with gas, or rupture of the stomach. Regurgitation of con­siderable quantities of greenish coloured fluid, which trickles from the nostrils, is seen to occur with little discomfort in grass sickness in the horse.

Retching is frequently observed without actual expulsion of stomach contents. In all conditions which predispose to reflex vomiting, retching can be induced artificially by strong pressure along the left jugular furrow, in the depth of which the oesophagus is situated. A similar response is obtained by applying pressure on each side, above and behind the larynx.

Points to note in regard to vomiting are its frequency (occurring once only or repeatedly) and the time at which it occurs in relation to the last meal, i.e. immediately after feeding or not until later at a time when food should normally have left the stomach.

The nature of the vomitus should be noted, attention being directed to the degree of diges­tion, amount and presence of abnormal consti­tuents, e.g. foreign bodies, blood, pus, parasites, faecal material, etc. Small quantities of blood, or toxic chemicals which have been ingested, can be detected by various chemical and other analytical methods, and bacteria, fungi and parasites by microscopical or cultural examination.

Proof that the vomited material has actually been derived from the stomach, and not from an oesophageal diverticulum, in the case of monogastric animals, is provided by demonstrating that the pH is acid by means of litmus or other suitable chemical indicator substance. The pre­sence of blood is suggested by a positive reaction to the orthotolidine test; conclusive proof de­pends upon a positive spectroscopic examination, although intact red blood cells may be demon­strated microscopically by examining suitably stained smears. In carnivorous animals receiving raw animal flesh as food the chemical test is not suitable.

Ova of parasites may be found in the vomitus, chiefly in the dog (ascarids, Spiroptera) (see Fig. 161a, p. 206). If sputum has been coughed up into the pharynx and swallowed, embryonated lungworm eggs may also be found in the vomitus (see Fig.158b, p.204).

Eructation

Eructation is the expulsion of gas from the stomach, via the oesophagus, to the exterior. It occurs when there is excessive gas formation or accumulation of air in the stomach. In ruminant species, moderate eructation is physiological and occurs from increase of gas pressure in the rumen initiating contraction in the dorsal sacs, the motion then passing to the oesophageal cardia and, in association with relaxation of the reticulum, depressing the upper level of the fluid in that organ. The gas is expelled when the cardia relaxes. The rate of the eructation contractions (normally 1-3 per minute) depends upon the pressure of gas in the rumen, and is independent of other cycles of ruminal motility.