Decreases in skin turgor may occur in the neonate, the very old horse, and animals with marked weight loss.
Exposure:
Mucous membranes may be tacky to dry with exposure secondary to swelling, trauma, neurologic dysfunction or other cause.
Capillary refill time (CRT):
Is assessed by rapid light touch of the observer's finger or thumb to the membranes resulting in blanching of the tissue, and the time to reestablish color is noted (see Figure 3.2).
Normal CRT is <2 seconds. A prolonged CRT may occur due to dehydration, toxemia/septicemia and/or decreased cardiac output. Prolongation usually reflects systemic problems but may also occur due to local disease processes.
D Peripheral arteries (pulses)
Peripheral pulses can be assessed at the head or on the limbs of a horse.
Caution must be used when palpating the hind limb arteries to avoid injury to the examiner. Figure 3.2 Normal mucous membrane color, blanching of mucous membranes with pressure for assessment of capillary refill time.
Sites for palpation:
Transverse facial arteryRuns horizontally on the lateral aspect of the head, behind the zygomatic arch, cranioventral to the ear.
Facial (submandibular artery)Can be palpated at the ventral aspect of the mandible, just cranial to the ramus, easy to palpate by “trapping” the somewhat movable artery between the skin and medial aspect of the mandible.
Maxillary arteryRostral to the infraorbital canal.This is a useful site in foals to palpate the pulse.
Posterior digital and abaxial sesamoid arteriesLocated at the caudolateral and caudomedial aspects of the pastern and fetlock, respectively.Palpable in all limbs.
Radial arteryLocated at the medial aspect of the carpus.
Median arteryLocated at the medial aspect of the forearm.
Great metatarsal arteryCaudolateral aspect of the hind limbs, runs vertically in the groove formed by the apposition of the canon and lateral splint (MT 3 and 4) bones.
Femoral arteryDeep palpation at the medial aspect of the thigh. Not a practical site for palpation in the adult horse.
Coccygeal arteryMore readily palpable in foals than adult horses.
Assessment of the pulse:
Pulse rateNormal rate is similar to the HR (24–50 pulses per minute).Assess the pulse while auscultating the heart to determine whether there are any heart beats without pulse generation (“dropped beats” or “pulse deficit”).
Pulse rhythmThe normal rhythm is regular. Slight irregularities may occur in the normal horse due to irregularities in the sinus firing (inherent or respiration associated).Rhythm assessment can be difficult when palpating the head arteries if there is head or chewing motions.
Pulse strengthThe normal pulse pressure is usually moderate in the healthy horse at rest; however, a very mild pulse may be present, especially in the distal limbs, when the horse is at rest.Decreased pulse strength may occur with peripheral vasoconstriction due to inactivity or cool ambient temperatures. May also be due to disease processes resulting in decreased perfusion or decreased cardiac output (e.g. hypovolemia, cardiac disease).Increased pulse strength occurs with increased peripheral vascular demand such as excitement, exercise or transportation. Examples of disease‐associated increases in pulse pressure include laminitis (may have increased pulse pressure in the distal limbs) and aortic valve regurgitation (common in older horses).
Pulse profileThe normal pulse profile consists of an initial rapid increase in the pulse pressure during systole, followed by a decreased pressure in very early diastole, then another increase in pressure due to the elastic‐recoil properties of the aorta and a subsequent decrease in pressure to baseline. The transition from the initial decrease to the second increase is termed the dicrotic notch. This second increase is typically palpable in the normal horse. An increase in pulse pressure above normal and a loss of the dicrotic notch occurs in horses with aortic valve regurgitation (see below).
E Peripheral veins
The jugular veins are the main veins assessed in the horse; however, all regions of the body should be observed and potentially palpated for vascular abnormalities.
The following are recommendations for jugular vein assessment:Examine the jugular veins for signs of inflammation (heat, pain, swelling) and obstruction (thrombosis/thrombophlebitis).Cranial neck and head swelling may occur, especially with acute venous obstruction.Note: IV injections of various drugs and compounds are commonly given to performance horses of most all disciplines, so careful evaluation of the jugular veins is important as partial to complete obstructions are commonplace.
Jugular vein waveforms
It is common to see fluid waves in the distal jugular vein (at the thoracic inlet) in the normal horse.
These waveforms are due to the presence of blood within the distal jugular vein, as the vein serves as a reservoir when the heart chambers are full and during systole.
The waveforms are generated in the blood column by the continuous flow of blood from the periphery to the jugular veins, carotid artery pulsation, and atrial & ventricular contractions.
These typically extend one‐third of the way up the neck when the horse is at rest and has its head and neck elevated.
The waveforms may extend one‐half of the way up the neck if the head and neck are held in a lower position or may go the length of the entire jugular vein if the head and neck are lowered such as when eating off the ground.
Occluding the jugular vein
Occlude each jugular vein in turn just caudal to the angle of the jaw (cranial jugular furrow) and milk the luminal blood distally toward the thoracic inlet; the vein should empty readily. Examine the vein for any spontaneous filling from the heart while the vein is still occluded (see jugular waveforms, above). Retrograde filling (jugular pulse) occurs with marked right AV valve regurgitation. A “true” jugular pulse is rare in the horse.
Next occlude the jugular vein distally at the thoracic inlet and observe the time for the vein to refill. The jugular vein will normally fill with blood over several seconds in the normal resting horse. Then release the vein and watch for rapid emptying.
F Heart
Cardiac silhouette
Refers to the region of the chest where the heart can be auscultated or palpated. An increased area of auscultation occurs due to cardiac enlargement or (caudal) displacement, thoracic masses or pulmonary/pleural disease.
Heart rate
The normal HR in the resting adult horse is 24–50 beats/min.
Some older, unfit horses may have a slightly