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less than 2 seconds, there is 90% survival, a survival rate of 53% if CRT ranges between 2.5 - 4 seconds, while only 12% survive if CRT is greater than 4 seconds.
CORROBORATION WITH THE ENTIRE CLINICAL PICTURE
Although mucous membranes are telling of
the ability of the heart to pump blood and the dispersal of oxygenated blood to the periphery,
it is not the only physical parameter used to evaluate the health of a horse. No one parameter should be used to evaluate the metabolic status of a horse whether it be the fitness of the horse to accommodate the stress under which it performs or its status during a crisis of illness. For an exercising horse, if only one parameter could be evaluated, it would be the heart rate. Evaluation of the heart rate and its recovery following exercise encompasses more physiological parameters that any other single measurement.
Heart rate is also a prognostic parameter useful to assess a horse with colic. Elevations in heart rate occur because of pain, dehydration, endotoxemia, and shock. The higher the heart rate, the worse the prognosis. A colicky horse has a 90% survival rate if the heart rate remains below 60 beats per minute (bpm). At heart rates between 60-80 bpm, a horse has 50% likelihood of survival, and at 80–100 bpm, only a 25% survival rate. Heart rate exceeding 100 bpm correlates poorly with survival – only 10%. The temperature of a horse’s limbs,
ears, and muzzle also reflect peripheral blood perfusion; cold extremities and ears and
cold, clammy skin are signs that corroborate cardiovascular shock and poor survivability.
With regards to an exercising horse, it is appropriate to gather a full clinical “picture” of a horse’s physical status to use in conjunction with evaluation of the mucous membranes. Other important evaluations of an exercising horse include auscultation (with a stethoscope)
of the abdomen in all quadrants to appreciate quality and frequency of gut sounds, palpation of muscle tone in the croup and hamstrings, and assessment of anal tone reflex. Jugular filling gives a relative impression of blood pressure,
as does the quality of the peripheral pulses of other large blood vessels such as those monitored on the face or along the lower limbs. A more subjective, but equally important, factor is
the horse’s demeanor. Does the horse appear engaged in its surroundings, or does he seem “checked out?” Does the horse want to eat and drink? Does the horse wag its head side to side when asked to trot? Does the horse ‘snirl’ its nostrils and/or have a dull, glazed expression?
OTHER DISEASE REFLECTIONS
Because mucous membranes are sensitive and informational, they are an alert for other disease syndromes that are apparent with
visual inspection. Blisters, vesicles, or ulcers may form subsequent to inflammation or
due to a systemic disease process. Examples
of pathologic conditions that cause blistering
of the mucous membranes of the mouth, in particular, include vesicular stomatitis virus (VSV) or blister beetle toxicity. While VSV is accompanied by blisters or ulcers within the tissues of the mouth, nose, and bordering skin, ingestion of even a portion of a blister beetle hidden in alfalfa hay creates inflammation
and necrosis along the entire internal mucosal lining into the bowel and is not isolated only to the oral or external tissues. VSV also can elicit vesicles on the mammary gland or prepuce or penis, while crusty vesicles develop due to some infections with equine rhinopneumonitis virus.
Mucous membranes possess some absorptive capacity that may be useful in administering medications, yet this characteristic may
be harmful if membranes come in contact
with toxic substances. Nonsteroidal anti- inflammatory drug toxicosis (as for example
with phenylbutazone or flunixin meglumine or ketoprofen) may create oral ulcers concurrent with the development of gastric ulcers. Caution should be taken when applying caustic or irritant substances like leg paints and blisters or when painting a fence with chew-stop products; a horse might lick or touch any of these with his mouth, setting up an adverse reaction that may be difficult to interpret without diligent sleuthing to discover the source of the problem. Ingestion of certain toxic alkaloid-containing plants also can elicit mouth blisters.
Vasculitis describes an illness associated with leakage of blood vessels. Collection of red blood cells in the surrounding tissues is often visible as tiny red spots on the mucous membranes. Such blood spots (petechiation) develop from a vasculitis event such as occurs with equine viral arteritis (EVA), equine rhinopneumonitis virus, or due to purpura hemorrhagica, which is an allergic response subsequent to previous infection with Streptococcus equi bacteria.
Typically, a systemically sick horse demonstrates other abnormal physical signs associated with many of these illnesses, such as an elevated fever and poor appetite related to pain with eating. Slobbering and excess salivation often accompany mouth pain or irritation. There may be localized swelling or edema, or hives related to some systemic illness. Mechanical problems, such as foxtails and weed seeds that embed in the gum margins cause an abnormal appearance to the mucous membranes, sometimes accompanied by an unwillingness to eat. When inflammatory conditions involve the mucous membranes of the eye, the horse will be troubled by associated swelling, engorgement of blood vessels, and other signs of ocular inflammation, such as tearing and pain.
Cancer, most commonly squamous cell carcinoma, is a disease process that often develops directly in mucous membranes. The most likely locations for this cancer are the ocular membranes such as the sclera or the third eyelid, the penis or prepuce of a male horse, on the vulva of a mare, or around a non- pigmented anus. Squamous cell carcinoma
can be invasive over time, but external cancer lesions are managed well with cryosurgery
to freeze affected cancerous tissue. Mucous membranes lining the stomach and other internal organs are also prone to squamous cell carcinoma. Because this internal form of cancer is more insidious and lurking, it is not readily identified until a horse shows clinical signs of major systemic effects, often beyond the scope of treatment options.
NEXT TIME
In the next installment, we will look at the Significance of Gut Sounds. Stay tuned!
VETERINARY VIEWS
Elevations in heart rate occur due to pain, dehydration, endotoxemia, and shock, and the higher the heart rate, the worse the prognosis.
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