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Caring for the Down Horse
CHAPTER 36
Caring for the Down Horse Rachel Gardner
• Initial evaluation of the recumbent horse involves assessment of the entire situation, including the location of the horse and safety of the horse and all involved personnel. • A complete history should be taken that includes signalment, history of recent health or performance problems, recent treatments and onset (acute vs. chronic) of the recumbency. • Knowledge of diet and management practices, recent travel, and vaccination history are also important.
Clinical Examination • A physical examination, as complete as possible, and assessment of hydration should be performed if safe. • The limbs, head, and neck should be carefully palpated for evidence of pain or fracture. • A systematic neurologic exam should be performed, and if abnormalities are detected a neuroanatomic diagnosis should be formulated. • The general mentation of recumbent horses can be difficult to discern because of the stress of recumbency, inability to react normally, and potential exhaustion following prolonged struggling. • The neurologic exam should also include evaluation of the cranial nerves, skin sensation, cutaneous trunci reflex, patellar reflexes, and withdrawal reflexes. Tail and anal tone should be assessed, although anal tone may be altered in the down horse. Bladder tone and size may be evaluated via rectal examination (see Chapter 22, p. 339). • Muscle tone, including that of the eyelid and tongue, should be evaluated carefully, as weakness is a characteristic finding with botulism. • Practice Tips: ○ If the horse is able to rise into a dog-sitting position, then injury to the spinal cord caudal to T2, myopathy, or injury to the peripheral nerves of the hind limbs should be considered. ○ If the horse is unable to raise the head and respiratory pattern is abnormal, either a lesion in the proximal cervical spinal cord or diffuse neuromuscular disease is likely. ○ If the horse only lies on one side, then vestibular disease should be considered. • The eyes, or at a minimum the accessible eye, should be evaluated completely. 626
• When the recumbent physical and neurologic exams fail to elucidate a cause for the recumbency, attempts should be made to assist the horse to stand, which may make musculoskeletal injury or ataxia more apparent.
Diagnostic Testing • Initial diagnostic evaluation should include a complete blood count, serum biochemistry panel, and urinalysis. • Alterations in the leukogram may be suggestive of an inflammatory or infectious process, although it is important to distinguish these changes from those secondary to recumbency. • Evaluation of a blood smear may provide further evidence of toxemia, alterations in red blood cell morphology, evidence of neoplastic cells, or Anaplasma phagocytophilum. • Alterations in the serum biochemistry panel may provide evidence of a primary disease or changes secondary to recumbency. • Practice Tip: Significantly elevated creatine phosphokinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) concentrations occur with rhabdomyolysis, and generally to a lesser degree with recumbency alone (see Chapter 22, p. 358). • Electrolyte concentrations should be evaluated for the purposes of diagnosis of the primary cause of recumbency and for guiding therapy. Lactate concentrations can be used as a marker for tissue hypoxia, disease severity, and tissue perfusion. • Practice Tip: Measurement of blood ammonia may be indicated to evaluate for hepatic encephalopathy or primary hyperammonemia. Ammonia samples must be evaluated immediately or within 1 hour if kept on ice. • If central nervous system (CNS) signs are observed on examination or a neurologic cause of the recumbency cannot be ruled out based on exam findings, evaluation of cerebrospinal fluid (CSF) may be indicated. • Practice Tip: CSF is most easily and reliably obtained via atlanto-occipital (AO) puncture in the recumbent horse (see Chapter 22, p. 340). • Because general anesthesia is often required for AO sampling, this should only be performed on a stable patient in which a vertebral fracture is not suspected. • Practice Tip: Short-term general anesthesia using xylazine, diazepam, and ketamine provides 20 to 25 minutes of
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anesthesia time, which is adequate for the procedure (see Chapter 47, p. 744). If a short-acting anesthetic is used to remove the horse from the transporting van/trailer, then movement of the horse and CSF collection can be performed with a single anesthetic procedure. If the patient is unstable or if general anesthesia is not desired, lumbosacral (LS) puncture may be performed. This procedure is more challenging but may be assisted via the use of ultrasound to identify the LS space. Placing an object between the hind feet so that the limbs are positioned a normal distance apart may help ensure a successful centesis. Cytologic evaluation should be performed on fresh CSF samples. Samples may also be cultured or tested for specific antibodies/organisms. Radiography using handheld machines is useful to identify the presence and extent of fractures in the limbs, head, and neck. More robust fixed machines may be used to evaluate the caudal neck, ribs, thoracolumbar vertebrae, or pelvis. Computed tomography and magnetic resonance imaging require general anesthesia but may provide further diagnostic information regarding the head, cranial neck, and distal limbs (see Chapter 14, p. 107). Ultrasonography can be used to evaluate soft tissue structures, superficial bone integrity, and for the presence of body cavity effusions or hemorrhage (see Chapter 14, p. 81). Endoscopy can be used for evaluation of the upper airway, guttural pouches, and stylohyoid bones. An electrocardiogram is indicated in horses whose recumbency may be related to arrhythmias or in whom an arrhythmia is auscultated (see Chapter 17, p. 124). Myelography is indicated to evaluate for cervical spinal cord compression, although focal lateral sites of compression can be inapparent on routine myelography due to difficulty in obtaining diagnostic ventral-dorsal views in adult horses (see Chapter 22, p. 345). Muscle biopsy may be indicated if a myopathy is suspected (see Chapter 6, p. 24). Transcranial magnetic stimulation is used to measure abnormal nerve conduction along the descending motor tracts to determine the presence of spinal cord or peripheral nerve injury. Electromyography may help classify neuropathies, myopathies, or neuromuscular disorders. Electroencephalography can be used to complement the clinical examination in identifying functional disturbance in brain activity.
Differential Diagnoses for Recumbency • Accurate diagnosis is critical in forming a therapeutic plan and reasonable prognosis. • Practice Tip: A poor prognosis should not be assumed based on recumbency alone. • Differential diagnoses for recumbency are summarized subsequently although more complete descriptions of each problem are found in other parts of this book.
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Musculoskeletal Disorders
• Musculoskeletal disorders are one of the most common causes for recumbency. • Long bone, pelvic, or axial skeletal fractures may cause recumbency. Depending on the site, fracture stabilization may be adequate to assist the horse to rise. The prognosis is variable and depends on the site and severity of the fracture. • Laminitis commonly results in a disproportionate time in recumbency, and in severe cases can result in complete recumbency. Abaxial nerve blocks may help facilitate standing and further diagnostic evaluation. When severe enough to cause complete recumbency, the prognosis for laminitis is generally poor. • Generalized weakness, due to old age, chronic disease, severe degenerative joint disease, or cachexia, commonly results in recumbency. Treatment with anti-inflammatories; analgesics; and in the case of hind-limb degenerative joint disease, epidural administration of medications, may be sufficient to assist a patient to stand. The long-term prognosis tends to be poor unless the underlying problem is addressed with proper analgesics or appropriate nutrition. • Myopathies are a relatively common causes of recumbency in the horse. Exertional myopathies may be severe enough to cause recumbency in exhausted horses or horses that are cast for prolonged periods. • Horses with polysaccharide storage myopathy (PSSM) may also become recumbent following a severe episode (see Chapter 22, p. 360). Muscle sensitivity, firmness on palpation, and trembling may be observed; pigmenturia may be present. • Atypical myopathy results in peracute onset of clinical signs and has a poor prognosis. • Monensin intoxication results in skeletal and cardiac myopathy. Additional clinical findings include tachyarrhythmias, heart failure, and acute death. • Salinomycin toxicity may produce recumbency without cardiac failure. • White snakeroot ingestion may lead to recumbency due to severe myonecrosis. WHAT TO DO Musculoskeletal
• Treatment should include intravenous fluids to correct dehydration and provide diuresis as prophylaxis against pigment nephropathy. • If hypochloremia and alkalosis are present, 0.9% NaCl with supplemental potassium is recommended. • Analgesics (phenylbutazone or flunixin meglumine), intravenous dimethyl sulfoxide (DMSO), acepromazine, and methocarbamol may be used. • Recumbent PSSM horses should be treated with corn oil (6 oz/450 kg) via nasogastric tube or an intravenous lipid product. • If recumbency follows general anesthesia and malignant hyperthermia is a concern, treatment should include dantrolene or phenytoin.
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SECTION I Special Problems
• Myopathy due to selenium deficiency may involve the masseter and/or pterygoid muscle groups. Diagnosis is by whole blood selenium concentrations or glutathione peroxidase activity. If selenium deficiency is suspected, an intramuscular injection of vitamin E/ selenium should be given while awaiting laboratory confirmation and is unlikely to cause harm if selenium levels are later determined to be adequate. If the diagnosis is correct, a second treatment 3 days later is recommended. • Immune-mediated myositis can occur following infection with Streptococcus equi or viral infection. Diagnosis is by historical findings and consistent histopathologic changes in muscle biopsies. Additional treatments include corticosteroids (prednisolone or dexamethasone) and penicillin. If the immune-mediated myopathy is severe and rapidly progressive, large doses (0.2 mg/kg) of dexamethasone may be required. • Anaplasma myopathy is best treated with tetracycline intravenously and has a good prognosis. • Subcutaneous fluid or gas crepitation is suggestive of clostridial myonecrosis. Specific treatments include anti-endotoxic medications, properly dosed penicillin, metronidazole, and surgical fenestration (see Chapter 35, p. 618).
EMG
Central Nervous System (CNS)
• CNS disorders are common causes for a down horse. CNS trauma may involve the brain, brainstem, or spinal cord. • Young horses are susceptible to CNS trauma following basisphenoid fracture from rearing and flipping over, resulting in head tilt, balance loss, blindness, recumbency, epistaxis, and/or hemorrhage from the ear. • Horses are prone to vertebral fracture and spinal cord injury after a fall. • A favorable prognosis is given if neurologic signs are secondary to edema/hemorrhage rather than direct neuronal damage. • Cervical compressive myelopathy (CCM) may cause recumbency from cervical stenosis exacerbated by acute trauma or severe flexion of the neck such as following a myelogram. • The history may include clumsiness or tripping, or neck stiffness in older patients. • If attempts are made to stand, symmetric ataxia may be apparent. • Intravertebral and intervertebral sagittal diameter ratios should be calculated on survey radiographs and may suggest vertebral canal stenosis (see Chapter 22, p. 346). • Osteoarthritis of the articular processes, most commonly C5-6 and C6-7 in older horses is suggestive, but not necessarily diagnostic, of the disease. CSF is typically normal. • Compression can also occur from other causes, including neoplasia, hematoma, abscess, granuloma, and cysts. CSF analysis varies. • Definitive diagnosis for cervical compressive myelopathy is by myelography.
WHAT TO DO Cervical Compressive Myelopathy
• Treatment depends on the cause of the compression and commonly includes high doses of dexamethasone in cases of acute onset or exacerbation of signs. • Surgical arthrodesis or decompression may be indicated. • The prognosis is guarded if significant improvement does not rapidly occur with treatment.
• Encephalomyelitis due to infection with the viral encephalitides can cause recumbency. • Eastern equine encephalitis (EEE) and Venezuelan equine encephalitis (VEE) are clinically indistinguishable and patients commonly show cerebral signs and remain afebrile. CSF analysis reveals mononuclear to mononuclear and neutrophilic pleocytosis, elevated protein, and xanthochromia. Antemortem diagnosis is by demonstrating rising serum titers. Treatment is supportive (see Chapter 22, p. 363), although dexamethasone may be helpful in early or progressive cases. • Equine herpesvirus-1 (EHV-1) causes respiratory disease, abortion, and neurologic disease. • Recumbency may occur because of severe CNS vasculitis. • Older adult horses in situations of high “stocking” density or increased movement are more commonly affected and outbreaks are common. • Affected horses are usually febrile and demonstrate a rapid onset of symmetric ataxia that may progress to recumbency. • Hind limbs are typically more affected and may result in “dog sitting.” • Urinary bladder paralysis and urine dribbling are common, and fecal retention may occur in recumbent patients. • CSF is commonly xanthochromic with an elevated protein level. • Treatment is largely supportive (see Chapter 22, p. 348). Moderate to high dose dexamethasone is recommended in rapidly progressive or severe cases. • Strict quarantine measures should be taken when EHV-1 is suspected, and all horses at risk should have temperature monitored at least twice daily. • Practice Tip: Any horse in which rabies or EHV-1 remains a differential diagnosis should be treated with strict biosecurity measures (see Chapter 53, p. 791). Human exposure should be limited and a list should be kept of all individuals who have had contact with the horse. Gloves should be worn and all specimens from the patient labeled with “Rabies Suspect.” Commercial vaccines are effective for prevention of rabies, but not EHV-1. • Practice Tip: Diagnosis may be confused with anaplasmosis because of paresis and recumbency with xanthochromic CSF. Botulism, moldy corn poisoning, atypical myopathy, and ionophore toxicity may also be causes of multiple horses developing recumbency but without fever.
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• Horses occasionally become recumbent because of equine protozoal myeloencephalitis (EPM) (see Chapter 22, p. 343). • Recumbency with EPM is more commonly associated with peracute or acute onset of signs and may be accompanied by vestibular signs, cranial nerve signs, or signs of lower motor neuron disease of the limbs. • Ataxia before recumbency is commonly asymmetric and horses remain afebrile. CSF analysis is typically normal. WHAT TO DO Equine Protozoal Myeloencephalitis
• Treatment is with antiprotozoal medications such as ponazuril, diclazuril, or a sulfadiazine-pyrimethamine combination in addition to supportive care. • Double doses of ponazuril are commonly used for the first week of therapy; treatment is recommended while awaiting laboratory confirmation of infection. • Corticosteroids and DMSO may be useful in the rapidly progressing case. • The prognosis is poor once recumbency occurs and in survivors, relapse following cessation of treatment may occur.
WHAT TO DO Vestibular Disease
• Treatment consists of supportive care and anti-inflammatory therapy (see Chapter 22, p. 351). • Otitis media and interna can cause similar signs or may occur concurrently with THO; therefore, antibiotic treatment with trimethoprim-sulfa, enrofloxacin, or chloramphenicol is often recommended. • If facial paralysis is present, frequent ophthalmic lubrication or tarsorrhaphy is recommended.
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• Denervation muscle atrophy, especially of type 1 (postural) muscle fibers due to equine motor neuron disease (EMND) (see Chapter 22, p. 355), results in excessive recumbency. • In subacute stages, horses may show signs of weakness, trembling, base-narrow stance, weight loss, and sweating before recumbency. • Ophthalmic evaluation reveals fundic lesions from lipofuscin accumulation in approximately 30% of cases. • Diagnosis is made by history and clinical findings, as well as demonstration of denervation muscle atrophy in a biopsy of the sacrocaudalis dorsalis muscle. WHAT TO DO Equine Motor Neuron Disease
• Affected horses should be administered 5000 to 7000 IU vitamin E daily, although the prognosis is poor for the uncommon down horse.
• Equine anaplasmosis, caused by infection with Anaplasma phagocytophilum, occasionally causes ataxia, which can progress to recumbency. • Horses are febrile and may exhibit depression, anorexia, edema, icterus, petechiae, and orchitis. • Diagnosis is by observation of inclusions in neutrophils, polymerase chain reaction (PCR) testing on whole blood, or rising serum titers. WHAT TO DO Equine Anaplasmosis
• Treatment consists of tetracycline and supportive care. • Response to treatment tends to be rapid, and the prognosis is good.
• Tetanus may result in skeletal muscle spasticity causing stiffness, trembling, spasm, and recumbency. • Masseter muscle stiffness, eyelid retraction, and flared nostrils are commonly present, and clinical signs are exacerbated by excitement. • Diagnosis is based on clinical signs in an unvaccinated horse with a history of soft tissue injury 1 to 3 weeks before. WHAT TO DO Tetanus
• Treatment is with antitoxin administration, which binds residual circulating endotoxin. • Intrathecal administration of antitoxin may be performed in early cases that remain ambulatory. • Supportive care in a quiet environment should be provided, and sedation should be used before performing procedures. • If a wound is present, it should be debrided to improve perfusion and oxygenation. • Concurrent vaccination is indicated, but the prognosis for recumbent horses is grave.
• Recumbency may occasionally occur secondary to hepatic encephalopathy or primary hyperammonemia.
EMG
• Severe vestibular disease results in recumbency due to balance loss (see Chapter 22, p. 350). • Temporohyoid osteoarthropathy (THO) commonly results in vestibular signs. • Affected horses may have a history of unusual chewing behavior or an incident causing sudden head elevation. • Horses with acute onset of peripheral vestibular signs demonstrate nystagmus (fast phase away from the lesion) and a head tilt, and preferentially lie on the side of the lesion. • Circling and leaning toward the side of the lesion are observed if the horse is assisted to stand. • Strength is maintained and contralateral hypertonia may occur. Mentation remains normal and ipsilateral facial nerve paralysis commonly occurs. • Endoscopy of the guttural pouches, which can be difficult in the recumbent horse, or dorsoventral radiographs reveal enlargement and possible fracture of the proximal stylohyoid bone on the affected side.
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SECTION I Special Problems
• Acute cerebral signs, including behavior change, blindness, circling, seizures, and recumbency may be present. • Horses with hepatic encephalopathy have elevated liver enzyme concentrations, abnormal hepatic function tests, and icterus. • Horses with primary hyperammonemia commonly have a history of gastrointestinal disease, most commonly colic or diarrhea. • Definitive diagnosis is by measurement of elevated blood ammonia >150 μmol/L. • Concurrent metabolic acidosis and hyperglycemia are supportive findings. WHAT TO DO Hepatic Encephalopathy/Primary Hyperammonemia • • • • •
Treat liver disease, if present (see Chapter 20, p. 268). Sedate with phenobarbital or small doses of xylazine, if needed. Oral neomycin or oral magnesium sulfate may be administered. IV fluid therapy will likely be indicated. The prognosis for hepatic encephalopathy is poor; however, primary hyperammonemia has a more favorable prognosis.
• Bracken fern ingestion, moldy corn toxicity (ingestion of fumonisin B1), and adverse reactions to fluphenazine decanoate may also cause recumbency because of their toxic effects on the CNS. Inadvertent intracarotid injection of medications may result in hyperexcitability, collapse, seizure, or coma. WHAT TO DO
• In horses with caudal aortic thrombosis, the pelvic limbs are cold, associated muscles are firm on palpation, and no femoral pulse is present. • The prognosis is guarded for horses recumbent because of a peripheral nerve disorder or thrombosis, although recovery may occur if early and aggressive treatment is pursued in cases of EPM. • Recumbency due to botulism (see Chapter 22, p. 354) may be acute or chronic in onset. • Trembling occurs during standing as a result of weakness, and resolves during recumbency. • Dysphagia is a common presenting complaint and persists once down. • The history commonly includes feeding of poorly stored forages, especially round bales. • Diagnosis is based on history and clinical signs. • Diagnosis can be confirmed by the presence of botulism toxin in feed, serum, gastrointestinal (GI) contents, or wound contents, or the presence of spores in intestinal contents. WHAT TO DO Botulism
• Treatment consists of administration of specific or multivalent antiserum early in the course of the disease and supportive care. • Type B botulism can be prevented by vaccination with a type B toxoid. • The prognosis is poor in adult horses once recumbency has occurred, although recovery is possible with good nursing care and time.
Central Nervous System—General Guidelines
EMG
• General supportive and nursing care • Intravenous fluids • Anti-inflammatory treatment: • Corticosteroids • Nonsteroidal anti-inflammatory drugs (NSAIDs) • Mannitol or hypertonic saline • Intravenous DMSO • Vitamin E supplementation for antioxidant purposes
Peripheral Nervous and Neuromuscular Systems • Peripheral nerve disorders may cause recumbency secondary to: • Mechanical injury • Trauma • EPM • Neoplasia • Abscess • Caudal aortic thrombosis • Iatrogenic causes • Abnormalities of major peripheral nerves results in muscle weakness (paresis or paralysis), hyporeflexia or areflexia, hypotonia or atonia, and neurogenic atrophy. Examples include: • Femoral nerve paralysis secondary to EPM • Dystocia and obturator nerve paralysis following severe hind limb abduction.
Metabolic Disorders
• Disorders that lead to electrolyte abnormalities— hyponatremia, hypocalcemia, hyperkalemia—and may result in recumbency. • Hyperkalemia is most commonly observed during episodes of hyperkalemic periodic paralysis (HYPP) in Quarter Horses or Quarter Horse crosses, or it may occur secondary to uroperitoneum or renal failure. • Additional clinical signs include muscle stiffness, fasciculations, weakness, respiratory stridor, and death. • Cardiac arrhythmias may be present. • Preliminary diagnosis is based on clinical signs and serum potassium concentrations >6 mEq/L. Genetic testing is available to confirm diagnosis. WHAT TO DO Hyperkalemic Periodic Paralysis
• Slow IV administration of calcium borogluconate, NaHCO3, or dextrose solution (see Chapter 22, p. 357) • Long-term management includes: • Dietary management • Potassium-wasting diuretics such as acetazolamide
• Exhaustion from overwork, especially in hot, humid conditions, can cause recumbency.
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• Clinical signs include: ○ Severe sweating ○ Tachycardia ○ Tachypnea ○ Severe dehydration ○ Cardiac arrhythmias ○ Synchronous diaphragmatic flutter ○ CNS signs • Electrolyte abnormalities and serum biochemical abnormalities are frequently present. WHAT TO DO Exhaustion • • • • • •
Decrease body temperature. IV or oral fluid resuscitation Electrolyte replacement NSAIDs following fluid replacement Anti-endotoxic therapy (see Chapter 32, p. 567) Prognosis is good if the initial response to treatments is productive; however, delayed onset of myopathy, laminitis, and organ failure is possible.
• Hypoglycemia rarely causes recumbency in the adult horse. Practice Tip: When present, it is most commonly secondary to neoplastic disease/tumors.
Respiratory and Cardiovascular Disorders
WHAT TO DO Cardiovascular Collapse • • • • • •
Judicious administration of intravenous fluids Blood transfusion Intravenous aminocaproic acid NSAIDs Intranasal oxygen insufflation Quiet environment
• Severe shock (see Chapter 32, p. 565) may also cause recumbency, whether due to decreased perfusion or secondary to sepsis. Diagnosis is based on history and clinical signs of dark mucous membranes with prolonged capillary refill time, poor peripheral pulses, and cool extremities.
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Gastrointestinal Diseases
• Horses with abdominal pain may present down, but clinical examination and response to analgesics usually indicates that abdominal pain is the cause of the recumbency— an unwillingness to stand rather than inability to stand. • Horses with severe parasitism and starvation may be examined because of recumbency. Treatment is discussed in Chapter 50, p. 764, but the prognosis is poor for the down horse with these disorders. • Similarly, horses with neoplasia and/or organ failure may be examined because of recumbency. • Clinical examination, ultrasound exam, serum chemistries, complete blood count (CBC), and cytology of body fluids or tissue often reveal a cause. WHAT TO DO Down Horse Transport • Transport of the down horse is challenging and potentially dangerous. • In a quiet or depressed horse, transport may be carried out without the use of sedation/anesthesia; however, some degree of sedation is typically necessary. • The horse should be protected with padded leg wraps and a helmet, if available. • Horses can be moved on a flat surface with a coordinated effort by several people simultaneously pushing/pulling the horse in the same direction. Ropes can be tied to the down limbs to allow more distance between the limbs and people for safety. • More effectively, a horse can be moved using a Large Animal Rescue Glide1 (see Chapter 37, p. 638). The glide is a large sheet of durable, conformable plastic with handles and areas to hook ropes along the edges. The plastic slides easily over a variety of surfaces, and the edges can be folded to accommodate stall and trailer doorways. • An effective method for moving a recumbent horse is to place the UC Davis Large Animal Lift2 on the horse and use it to pull the horse onto the Large Animal Rescue Glide. The glide can then be pulled into the trailer and left under the horse to facilitate moving the horse off the trailer and into a hospital stall.
Basic Supportive Care • Management of the down horse includes treatment of the primary disease (when known or working cause) and intensive supportive care. • Bedding should be compressible, comfortable, and absorbent. It should be cleaned and aerated each time the horse is moved or turned. Wood shavings as a base-layer, with a thick covering of straw works well. Sheets or blankets may be placed on top to prevent abrasions, and the head should be slightly elevated. When the horse stands or is assisted with a sling, ensure that bedding is not slippery or excessively deep. • Positioning is critical in the down horse. Ideally, the horse should remain in sternal recumbency, propping with straw bales as necessary. The horse should be turned every 2 to 6 hours, even if it is able to remain in sternal recumbency. Turning helps prevent decubital ulcers, compressive myelopathy and neuropathy, and supports ventilation. 1
Large Animal Rescue Glide (L.A.R.G.E., Greenville, South Carolina). Large Animal Lift (Large Animal Lift Enterprises, Chico, California).
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EMG
• Cardiovascular collapse, especially when acute, may result in recumbency. • Hemorrhage, whether external or internal, may result in cardiovascular collapse. • Internal bleeding occurs most commonly in the abdomen, although bleeding into the thorax and uterus may occur. • Initial diagnosis is based on history, mucous membrane pallor, tachypnea, tachycardia, abdominal discomfort or respiratory compromise, and low blood pressure. • Further diagnosis is achieved by ultrasound examination and/or abdominocentesis or thoracocentesis.
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EMG
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SECTION I Special Problems
• Practice Tip: Turning is ideally achieved by placing in sternal recumbency and pushing the body over the limbs; however, this is difficult in a full-sized horse. The advantage of this technique is that it allows the atelectic “down-side” lung to become inflated before being placed in lateral recumbency with the opposite lung down. • Alternatively, with the horse in lateral recumbency, ropes may be tied to the down limbs and pulled by individuals on the opposite side of the horse while one person assists the head. Caution should be used because horses typically struggle when the procedure is first performed. • Many recumbent horses can bear some weight and spend considerable time upright with the assistance of a sling. Decreasing recumbent time minimizes the effects of prolonged recumbency and some muscle mass can be maintained. • The sling also provides the clinician with the opportunity to better evaluate the patient. • Horses with abnormal mentation are poor candidates to sling, and fractious or nervous horses may require light sedation or tranquilization. The sling must be properly adjusted to prevent pressure sores and the horse should be monitored closely while in the sling. • The amount of time the horse stands in the sling should be gradually increased, if well tolerated. Horses with botulism should not be assisted to stand with a sling unless necessary because of complications of recumbency. • Practice Tip: Excessive movement of horses with botulism depletes acetylcholine stores. • Use of a sling: • To use a sling safely in a stall environment, a cross-beam and hoist capable of supporting at least 2000 to 4000 lb (900 to 1800 kg) should be available, depending on the size of the horse, sling, and hoist. The UC Davis Anderson sling provides the most support in the most stable and balanced manner (see Chapter 37, p. 638). The sling consists of a rectangular overhead support, which provides level support, abdominal support, and additional leg supports alleviating excessive pressure on the abdomen and thorax/sternum. Disadvantages of this sling are that it is expensive and can be difficult to place on the horse, especially in a down patient without sedation or anesthesia. • The Liftex sling3 is simpler to use, containing an abdominal support, as well as tail and chest supports. It is less expensive and easier to place on the recumbent patient. • The UC Davis Large Animal Lift is the most affordable and lightweight of the slings. It is intended to be used for lifting and moving horses, rather than providing ongoing support for a horse unable to stand unassisted, although it can be used in this manner. The device is relatively simple to place on a recumbent horse and can be used with a tractor or winch for lifting. • Practice Tip: There should be even “tension” on the bar or it may bend as the horse is being lifted. If a horse needs continued support for standing, the Anderson sling may be placed over the UC Davis Large Animal Lift once the horse has been lifted to a standing position, then the Large Animal Lift can be removed. • On an especially quiet horse, the individual may be lifted using the sling and positioned in a bovine float tank.4 The horse must be monitored closely, and there is a risk of injury when confined to the tank.
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• The Enduro NEST,5 recently developed by Enduro Medical Technology, supports the horse with a sling containing an abdominal support and leg supports. The sling is supported by a selfcontained metal frame providing customized support or for lifting the horse. A horse can be placed under, and recover from, general anesthesia safely while being continuously supported in a standing position. The device can be used in a fixed position to provide variable limb support or is mobile to assist a weak, injured, or neurologic horse to walk. Self-trauma and decubital ulcers can be minimized with attention to good nursing care—bedding and skin care. • Leg wraps are recommended to protect the distal limbs and shoes should be wrapped to alleviate sharp edges. • Well-fitting head bumpers help prevent head trauma, which commonly occurs during failed attempts to get into sternal recumbency. • Horses should be groomed frequently and damp areas from sweat or urine should be dried thoroughly because wet skin is more prone to pressure sores and ulceration. • Wounds should be kept clean and dry, and antibiotics or topical medications used if necessary. Ophthalmic care of the recumbent horse includes: • Lubrication with an artificial tear ointment should be performed bilaterally at least q3-4h. • Corneas should be stained at least q24h to monitor for corneal ulceration. • Corneal ulcers should be treated aggressively and a temporary tarsorrhaphy considered if necessary. Nutritional support is an integral and challenging aspect of supportive care (see Chapter 51, p. 768). • Horses that are not dysphagic should be positioned in sternal recumbency and offered water, long-stem forage, and grain. • Horses are more likely to eat when standing, so feed and water should always be offered at a comfortable height when horses are assisted to stand. • Horses that are dysphagic or inappetent for several days require enteral or parenteral nutritional support. • Enteral feeding may be provided by nasogastric tube, and the tube can be left indwelling or passed several times daily. • Enteral diets may be formulated using complete feeds or alfalfa meal, or a commercial equine enteral diet may be used. • Feedings should be divided into 4 to 6 small meals per day while the horse is sternal or standing. • In horses with adequate gastrointestinal function, maintenance fluids may be administered by nasogastric tube. • In horses with gastrointestinal dysfunction in which enteral feeding is not possible, parenteral nutrition with dextrose, amino acids, and lipid solutions should be considered. • Maintenance fluid requirements must also be met using intravenous fluids in horses on parenteral nutrition. Intravenous catheter care is challenging because of an unavoidably contaminated environment and frequent movement at the catheter site (see Chapter 3, p. 9). • Polyurethane, over-the-wire jugular catheters are recommended because they are less likely to cause thrombosis than over-theneedle catheters. • Routine catheter care—i.e., flushing the catheter with heparinized saline q6h is recommended.
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Liftex Large Animal/Equine Sling (Liftex Corporation, Philadelphia, Pennsylvania). 4 Aqua Cow Rise System (Aqua Cow/North America, Saint Johnsbury, Vermont).
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Enduro N.E.S.T. (Enduro Medical Technology, South Windsor, Connecticut).
• A neck wrap of elastic tape with dry gauze placed over the base of the catheter is recommended to prevent friction and gross contamination, and should be replaced daily or more often if soiled. • The vein and the catheter insertion sites should be inspected at least two times a day for evidence of skin swelling, heat, or thickening of the vein. If any abnormalities are detected, the catheter should be removed and the tip cultured. • In the event of a compromised jugular vein, hot-packing the catheter site and vein several times a day, followed by topical application of DMSO/furacin sweat, ichthammol or Surpass6 are recommended to minimize thrombophlebitis. Antibiotic therapy is typically indicated. • Urinary catheterization is necessary in horses with neurologic disorders that cause an atonic bladder, such as EHV-1, and in horses not urinating appropriately. • Some down horses, especially mules, may choose not to urinate even with normal bladder and spinal cord function. • Catheterization may be performed several times a day or the catheter may remain indwelling. • Indwelling catheters are useful for keeping the bedding and patient dry and helping to prevent decubital ulceration. • An indwelling Foley catheter should be placed under aseptic conditions and urine collected using a closed system. IV tubing
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and empty sterile IV fluid bags placed deep in the bedding below the level of the bladder can be easily and inexpensively used to collect urine. • Securing the catheter and/or tubing to the skin on the ventral body wall (males) or tail (mares) using elastic tape or suture, respectively, alleviates pressure on the catheter when the horse struggles or is turned. • The urinary collection system should be monitored for obstructions and urine collection bags emptied at least several times a day. • Practice Tip: The most common complication of urinary catheterization is cystitis due to ascending bacterial infection. • Cytologic and dipstick evaluation of urine is easy and inexpensive, and should be performed every few days. If cystitis is suspected, a urine culture and colony count should be performed and antibiotic therapy instituted. • Large colon impactions are common in down horses because of poor gastrointestinal motility. • It is essential to monitor fecal production closely in these horses. • Easily digestible feeds should be offered and mineral oil administered by nasogastric tube. • Manual evacuation of the rectum may be necessary, especially in horses with EHV-1.
References 6
Surpass (Boehringer Ingelheim Metmedica, Inc., St. Joseph, Missouri).
References can be found on the companion website at www.equine-emergencies.com.
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Caring for the Down Horse Rachel Gardner
• Initial evaluation of the recumbent horse involves assessment of the entire situation, including the location of the horse and safety of the horse and all involved personnel. • A complete history should be taken that includes signalment, history of recent health or performance problems, recent treatments and onset (acute vs. chronic) of the recumbency. • Knowledge of diet and management practices, recent travel, and vaccination history are also important.
Clinical Examination • A physical examination, as complete as possible, and assessment of hydration should be performed if safe. • The limbs, head, and neck should be carefully palpated for evidence of pain or fracture. • A systematic neurologic exam should be performed, and if abnormalities are detected a neuroanatomic diagnosis should be formulated. • The general mentation of recumbent horses can be difficult to discern because of the stress of recumbency, inability to react normally, and potential exhaustion following prolonged struggling. • The neurologic exam should also include evaluation of the cranial nerves, skin sensation, cutaneous trunci reflex, patellar reflexes, and withdrawal reflexes. Tail and anal tone should be assessed, although anal tone may be altered in the down horse. Bladder tone and size may be evaluated via rectal examination (see Chapter 22, p. 339). • Muscle tone, including that of the eyelid and tongue, should be evaluated carefully, as weakness is a characteristic finding with botulism. • Practice Tips: ○ If the horse is able to rise into a dog-sitting position, then injury to the spinal cord caudal to T2, myopathy, or injury to the peripheral nerves of the hind limbs should be considered. ○ If the horse is unable to raise the head and respiratory pattern is abnormal, either a lesion in the proximal cervical spinal cord or diffuse neuromuscular disease is likely. ○ If the horse only lies on one side, then vestibular disease should be considered. • The eyes, or at a minimum the accessible eye, should be evaluated completely. 626
• When the recumbent physical and neurologic exams fail to elucidate a cause for the recumbency, attempts should be made to assist the horse to stand, which may make musculoskeletal injury or ataxia more apparent.
Diagnostic Testing • Initial diagnostic evaluation should include a complete blood count, serum biochemistry panel, and urinalysis. • Alterations in the leukogram may be suggestive of an inflammatory or infectious process, although it is important to distinguish these changes from those secondary to recumbency. • Evaluation of a blood smear may provide further evidence of toxemia, alterations in red blood cell morphology, evidence of neoplastic cells, or Anaplasma phagocytophilum. • Alterations in the serum biochemistry panel may provide evidence of a primary disease or changes secondary to recumbency. • Practice Tip: Significantly elevated creatine phosphokinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) concentrations occur with rhabdomyolysis, and generally to a lesser degree with recumbency alone (see Chapter 22, p. 358). • Electrolyte concentrations should be evaluated for the purposes of diagnosis of the primary cause of recumbency and for guiding therapy. Lactate concentrations can be used as a marker for tissue hypoxia, disease severity, and tissue perfusion. • Practice Tip: Measurement of blood ammonia may be indicated to evaluate for hepatic encephalopathy or primary hyperammonemia. Ammonia samples must be evaluated immediately or within 1 hour if kept on ice. • If central nervous system (CNS) signs are observed on examination or a neurologic cause of the recumbency cannot be ruled out based on exam findings, evaluation of cerebrospinal fluid (CSF) may be indicated. • Practice Tip: CSF is most easily and reliably obtained via atlanto-occipital (AO) puncture in the recumbent horse (see Chapter 22, p. 340). • Because general anesthesia is often required for AO sampling, this should only be performed on a stable patient in which a vertebral fracture is not suspected. • Practice Tip: Short-term general anesthesia using xylazine, diazepam, and ketamine provides 20 to 25 minutes of
•
• •
•
•
• • •
•
anesthesia time, which is adequate for the procedure (see Chapter 47, p. 744). If a short-acting anesthetic is used to remove the horse from the transporting van/trailer, then movement of the horse and CSF collection can be performed with a single anesthetic procedure. If the patient is unstable or if general anesthesia is not desired, lumbosacral (LS) puncture may be performed. This procedure is more challenging but may be assisted via the use of ultrasound to identify the LS space. Placing an object between the hind feet so that the limbs are positioned a normal distance apart may help ensure a successful centesis. Cytologic evaluation should be performed on fresh CSF samples. Samples may also be cultured or tested for specific antibodies/organisms. Radiography using handheld machines is useful to identify the presence and extent of fractures in the limbs, head, and neck. More robust fixed machines may be used to evaluate the caudal neck, ribs, thoracolumbar vertebrae, or pelvis. Computed tomography and magnetic resonance imaging require general anesthesia but may provide further diagnostic information regarding the head, cranial neck, and distal limbs (see Chapter 14, p. 107). Ultrasonography can be used to evaluate soft tissue structures, superficial bone integrity, and for the presence of body cavity effusions or hemorrhage (see Chapter 14, p. 81). Endoscopy can be used for evaluation of the upper airway, guttural pouches, and stylohyoid bones. An electrocardiogram is indicated in horses whose recumbency may be related to arrhythmias or in whom an arrhythmia is auscultated (see Chapter 17, p. 124). Myelography is indicated to evaluate for cervical spinal cord compression, although focal lateral sites of compression can be inapparent on routine myelography due to difficulty in obtaining diagnostic ventral-dorsal views in adult horses (see Chapter 22, p. 345). Muscle biopsy may be indicated if a myopathy is suspected (see Chapter 6, p. 24). Transcranial magnetic stimulation is used to measure abnormal nerve conduction along the descending motor tracts to determine the presence of spinal cord or peripheral nerve injury. Electromyography may help classify neuropathies, myopathies, or neuromuscular disorders. Electroencephalography can be used to complement the clinical examination in identifying functional disturbance in brain activity.
Differential Diagnoses for Recumbency • Accurate diagnosis is critical in forming a therapeutic plan and reasonable prognosis. • Practice Tip: A poor prognosis should not be assumed based on recumbency alone. • Differential diagnoses for recumbency are summarized subsequently although more complete descriptions of each problem are found in other parts of this book.
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Musculoskeletal Disorders
• Musculoskeletal disorders are one of the most common causes for recumbency. • Long bone, pelvic, or axial skeletal fractures may cause recumbency. Depending on the site, fracture stabilization may be adequate to assist the horse to rise. The prognosis is variable and depends on the site and severity of the fracture. • Laminitis commonly results in a disproportionate time in recumbency, and in severe cases can result in complete recumbency. Abaxial nerve blocks may help facilitate standing and further diagnostic evaluation. When severe enough to cause complete recumbency, the prognosis for laminitis is generally poor. • Generalized weakness, due to old age, chronic disease, severe degenerative joint disease, or cachexia, commonly results in recumbency. Treatment with anti-inflammatories; analgesics; and in the case of hind-limb degenerative joint disease, epidural administration of medications, may be sufficient to assist a patient to stand. The long-term prognosis tends to be poor unless the underlying problem is addressed with proper analgesics or appropriate nutrition. • Myopathies are a relatively common causes of recumbency in the horse. Exertional myopathies may be severe enough to cause recumbency in exhausted horses or horses that are cast for prolonged periods. • Horses with polysaccharide storage myopathy (PSSM) may also become recumbent following a severe episode (see Chapter 22, p. 360). Muscle sensitivity, firmness on palpation, and trembling may be observed; pigmenturia may be present. • Atypical myopathy results in peracute onset of clinical signs and has a poor prognosis. • Monensin intoxication results in skeletal and cardiac myopathy. Additional clinical findings include tachyarrhythmias, heart failure, and acute death. • Salinomycin toxicity may produce recumbency without cardiac failure. • White snakeroot ingestion may lead to recumbency due to severe myonecrosis. WHAT TO DO Musculoskeletal
• Treatment should include intravenous fluids to correct dehydration and provide diuresis as prophylaxis against pigment nephropathy. • If hypochloremia and alkalosis are present, 0.9% NaCl with supplemental potassium is recommended. • Analgesics (phenylbutazone or flunixin meglumine), intravenous dimethyl sulfoxide (DMSO), acepromazine, and methocarbamol may be used. • Recumbent PSSM horses should be treated with corn oil (6 oz/450 kg) via nasogastric tube or an intravenous lipid product. • If recumbency follows general anesthesia and malignant hyperthermia is a concern, treatment should include dantrolene or phenytoin.
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Chapter 36
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SECTION I Special Problems
• Myopathy due to selenium deficiency may involve the masseter and/or pterygoid muscle groups. Diagnosis is by whole blood selenium concentrations or glutathione peroxidase activity. If selenium deficiency is suspected, an intramuscular injection of vitamin E/ selenium should be given while awaiting laboratory confirmation and is unlikely to cause harm if selenium levels are later determined to be adequate. If the diagnosis is correct, a second treatment 3 days later is recommended. • Immune-mediated myositis can occur following infection with Streptococcus equi or viral infection. Diagnosis is by historical findings and consistent histopathologic changes in muscle biopsies. Additional treatments include corticosteroids (prednisolone or dexamethasone) and penicillin. If the immune-mediated myopathy is severe and rapidly progressive, large doses (0.2 mg/kg) of dexamethasone may be required. • Anaplasma myopathy is best treated with tetracycline intravenously and has a good prognosis. • Subcutaneous fluid or gas crepitation is suggestive of clostridial myonecrosis. Specific treatments include anti-endotoxic medications, properly dosed penicillin, metronidazole, and surgical fenestration (see Chapter 35, p. 618).
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Central Nervous System (CNS)
• CNS disorders are common causes for a down horse. CNS trauma may involve the brain, brainstem, or spinal cord. • Young horses are susceptible to CNS trauma following basisphenoid fracture from rearing and flipping over, resulting in head tilt, balance loss, blindness, recumbency, epistaxis, and/or hemorrhage from the ear. • Horses are prone to vertebral fracture and spinal cord injury after a fall. • A favorable prognosis is given if neurologic signs are secondary to edema/hemorrhage rather than direct neuronal damage. • Cervical compressive myelopathy (CCM) may cause recumbency from cervical stenosis exacerbated by acute trauma or severe flexion of the neck such as following a myelogram. • The history may include clumsiness or tripping, or neck stiffness in older patients. • If attempts are made to stand, symmetric ataxia may be apparent. • Intravertebral and intervertebral sagittal diameter ratios should be calculated on survey radiographs and may suggest vertebral canal stenosis (see Chapter 22, p. 346). • Osteoarthritis of the articular processes, most commonly C5-6 and C6-7 in older horses is suggestive, but not necessarily diagnostic, of the disease. CSF is typically normal. • Compression can also occur from other causes, including neoplasia, hematoma, abscess, granuloma, and cysts. CSF analysis varies. • Definitive diagnosis for cervical compressive myelopathy is by myelography.
WHAT TO DO Cervical Compressive Myelopathy
• Treatment depends on the cause of the compression and commonly includes high doses of dexamethasone in cases of acute onset or exacerbation of signs. • Surgical arthrodesis or decompression may be indicated. • The prognosis is guarded if significant improvement does not rapidly occur with treatment.
• Encephalomyelitis due to infection with the viral encephalitides can cause recumbency. • Eastern equine encephalitis (EEE) and Venezuelan equine encephalitis (VEE) are clinically indistinguishable and patients commonly show cerebral signs and remain afebrile. CSF analysis reveals mononuclear to mononuclear and neutrophilic pleocytosis, elevated protein, and xanthochromia. Antemortem diagnosis is by demonstrating rising serum titers. Treatment is supportive (see Chapter 22, p. 363), although dexamethasone may be helpful in early or progressive cases. • Equine herpesvirus-1 (EHV-1) causes respiratory disease, abortion, and neurologic disease. • Recumbency may occur because of severe CNS vasculitis. • Older adult horses in situations of high “stocking” density or increased movement are more commonly affected and outbreaks are common. • Affected horses are usually febrile and demonstrate a rapid onset of symmetric ataxia that may progress to recumbency. • Hind limbs are typically more affected and may result in “dog sitting.” • Urinary bladder paralysis and urine dribbling are common, and fecal retention may occur in recumbent patients. • CSF is commonly xanthochromic with an elevated protein level. • Treatment is largely supportive (see Chapter 22, p. 348). Moderate to high dose dexamethasone is recommended in rapidly progressive or severe cases. • Strict quarantine measures should be taken when EHV-1 is suspected, and all horses at risk should have temperature monitored at least twice daily. • Practice Tip: Any horse in which rabies or EHV-1 remains a differential diagnosis should be treated with strict biosecurity measures (see Chapter 53, p. 791). Human exposure should be limited and a list should be kept of all individuals who have had contact with the horse. Gloves should be worn and all specimens from the patient labeled with “Rabies Suspect.” Commercial vaccines are effective for prevention of rabies, but not EHV-1. • Practice Tip: Diagnosis may be confused with anaplasmosis because of paresis and recumbency with xanthochromic CSF. Botulism, moldy corn poisoning, atypical myopathy, and ionophore toxicity may also be causes of multiple horses developing recumbency but without fever.
Chapter 36
• Horses occasionally become recumbent because of equine protozoal myeloencephalitis (EPM) (see Chapter 22, p. 343). • Recumbency with EPM is more commonly associated with peracute or acute onset of signs and may be accompanied by vestibular signs, cranial nerve signs, or signs of lower motor neuron disease of the limbs. • Ataxia before recumbency is commonly asymmetric and horses remain afebrile. CSF analysis is typically normal. WHAT TO DO Equine Protozoal Myeloencephalitis
• Treatment is with antiprotozoal medications such as ponazuril, diclazuril, or a sulfadiazine-pyrimethamine combination in addition to supportive care. • Double doses of ponazuril are commonly used for the first week of therapy; treatment is recommended while awaiting laboratory confirmation of infection. • Corticosteroids and DMSO may be useful in the rapidly progressing case. • The prognosis is poor once recumbency occurs and in survivors, relapse following cessation of treatment may occur.
WHAT TO DO Vestibular Disease
• Treatment consists of supportive care and anti-inflammatory therapy (see Chapter 22, p. 351). • Otitis media and interna can cause similar signs or may occur concurrently with THO; therefore, antibiotic treatment with trimethoprim-sulfa, enrofloxacin, or chloramphenicol is often recommended. • If facial paralysis is present, frequent ophthalmic lubrication or tarsorrhaphy is recommended.
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• Denervation muscle atrophy, especially of type 1 (postural) muscle fibers due to equine motor neuron disease (EMND) (see Chapter 22, p. 355), results in excessive recumbency. • In subacute stages, horses may show signs of weakness, trembling, base-narrow stance, weight loss, and sweating before recumbency. • Ophthalmic evaluation reveals fundic lesions from lipofuscin accumulation in approximately 30% of cases. • Diagnosis is made by history and clinical findings, as well as demonstration of denervation muscle atrophy in a biopsy of the sacrocaudalis dorsalis muscle. WHAT TO DO Equine Motor Neuron Disease
• Affected horses should be administered 5000 to 7000 IU vitamin E daily, although the prognosis is poor for the uncommon down horse.
• Equine anaplasmosis, caused by infection with Anaplasma phagocytophilum, occasionally causes ataxia, which can progress to recumbency. • Horses are febrile and may exhibit depression, anorexia, edema, icterus, petechiae, and orchitis. • Diagnosis is by observation of inclusions in neutrophils, polymerase chain reaction (PCR) testing on whole blood, or rising serum titers. WHAT TO DO Equine Anaplasmosis
• Treatment consists of tetracycline and supportive care. • Response to treatment tends to be rapid, and the prognosis is good.
• Tetanus may result in skeletal muscle spasticity causing stiffness, trembling, spasm, and recumbency. • Masseter muscle stiffness, eyelid retraction, and flared nostrils are commonly present, and clinical signs are exacerbated by excitement. • Diagnosis is based on clinical signs in an unvaccinated horse with a history of soft tissue injury 1 to 3 weeks before. WHAT TO DO Tetanus
• Treatment is with antitoxin administration, which binds residual circulating endotoxin. • Intrathecal administration of antitoxin may be performed in early cases that remain ambulatory. • Supportive care in a quiet environment should be provided, and sedation should be used before performing procedures. • If a wound is present, it should be debrided to improve perfusion and oxygenation. • Concurrent vaccination is indicated, but the prognosis for recumbent horses is grave.
• Recumbency may occasionally occur secondary to hepatic encephalopathy or primary hyperammonemia.
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• Severe vestibular disease results in recumbency due to balance loss (see Chapter 22, p. 350). • Temporohyoid osteoarthropathy (THO) commonly results in vestibular signs. • Affected horses may have a history of unusual chewing behavior or an incident causing sudden head elevation. • Horses with acute onset of peripheral vestibular signs demonstrate nystagmus (fast phase away from the lesion) and a head tilt, and preferentially lie on the side of the lesion. • Circling and leaning toward the side of the lesion are observed if the horse is assisted to stand. • Strength is maintained and contralateral hypertonia may occur. Mentation remains normal and ipsilateral facial nerve paralysis commonly occurs. • Endoscopy of the guttural pouches, which can be difficult in the recumbent horse, or dorsoventral radiographs reveal enlargement and possible fracture of the proximal stylohyoid bone on the affected side.
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SECTION I Special Problems
• Acute cerebral signs, including behavior change, blindness, circling, seizures, and recumbency may be present. • Horses with hepatic encephalopathy have elevated liver enzyme concentrations, abnormal hepatic function tests, and icterus. • Horses with primary hyperammonemia commonly have a history of gastrointestinal disease, most commonly colic or diarrhea. • Definitive diagnosis is by measurement of elevated blood ammonia >150 μmol/L. • Concurrent metabolic acidosis and hyperglycemia are supportive findings. WHAT TO DO Hepatic Encephalopathy/Primary Hyperammonemia • • • • •
Treat liver disease, if present (see Chapter 20, p. 268). Sedate with phenobarbital or small doses of xylazine, if needed. Oral neomycin or oral magnesium sulfate may be administered. IV fluid therapy will likely be indicated. The prognosis for hepatic encephalopathy is poor; however, primary hyperammonemia has a more favorable prognosis.
• Bracken fern ingestion, moldy corn toxicity (ingestion of fumonisin B1), and adverse reactions to fluphenazine decanoate may also cause recumbency because of their toxic effects on the CNS. Inadvertent intracarotid injection of medications may result in hyperexcitability, collapse, seizure, or coma. WHAT TO DO
• In horses with caudal aortic thrombosis, the pelvic limbs are cold, associated muscles are firm on palpation, and no femoral pulse is present. • The prognosis is guarded for horses recumbent because of a peripheral nerve disorder or thrombosis, although recovery may occur if early and aggressive treatment is pursued in cases of EPM. • Recumbency due to botulism (see Chapter 22, p. 354) may be acute or chronic in onset. • Trembling occurs during standing as a result of weakness, and resolves during recumbency. • Dysphagia is a common presenting complaint and persists once down. • The history commonly includes feeding of poorly stored forages, especially round bales. • Diagnosis is based on history and clinical signs. • Diagnosis can be confirmed by the presence of botulism toxin in feed, serum, gastrointestinal (GI) contents, or wound contents, or the presence of spores in intestinal contents. WHAT TO DO Botulism
• Treatment consists of administration of specific or multivalent antiserum early in the course of the disease and supportive care. • Type B botulism can be prevented by vaccination with a type B toxoid. • The prognosis is poor in adult horses once recumbency has occurred, although recovery is possible with good nursing care and time.
Central Nervous System—General Guidelines
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• General supportive and nursing care • Intravenous fluids • Anti-inflammatory treatment: • Corticosteroids • Nonsteroidal anti-inflammatory drugs (NSAIDs) • Mannitol or hypertonic saline • Intravenous DMSO • Vitamin E supplementation for antioxidant purposes
Peripheral Nervous and Neuromuscular Systems • Peripheral nerve disorders may cause recumbency secondary to: • Mechanical injury • Trauma • EPM • Neoplasia • Abscess • Caudal aortic thrombosis • Iatrogenic causes • Abnormalities of major peripheral nerves results in muscle weakness (paresis or paralysis), hyporeflexia or areflexia, hypotonia or atonia, and neurogenic atrophy. Examples include: • Femoral nerve paralysis secondary to EPM • Dystocia and obturator nerve paralysis following severe hind limb abduction.
Metabolic Disorders
• Disorders that lead to electrolyte abnormalities— hyponatremia, hypocalcemia, hyperkalemia—and may result in recumbency. • Hyperkalemia is most commonly observed during episodes of hyperkalemic periodic paralysis (HYPP) in Quarter Horses or Quarter Horse crosses, or it may occur secondary to uroperitoneum or renal failure. • Additional clinical signs include muscle stiffness, fasciculations, weakness, respiratory stridor, and death. • Cardiac arrhythmias may be present. • Preliminary diagnosis is based on clinical signs and serum potassium concentrations >6 mEq/L. Genetic testing is available to confirm diagnosis. WHAT TO DO Hyperkalemic Periodic Paralysis
• Slow IV administration of calcium borogluconate, NaHCO3, or dextrose solution (see Chapter 22, p. 357) • Long-term management includes: • Dietary management • Potassium-wasting diuretics such as acetazolamide
• Exhaustion from overwork, especially in hot, humid conditions, can cause recumbency.
Chapter 36
• Clinical signs include: ○ Severe sweating ○ Tachycardia ○ Tachypnea ○ Severe dehydration ○ Cardiac arrhythmias ○ Synchronous diaphragmatic flutter ○ CNS signs • Electrolyte abnormalities and serum biochemical abnormalities are frequently present. WHAT TO DO Exhaustion • • • • • •
Decrease body temperature. IV or oral fluid resuscitation Electrolyte replacement NSAIDs following fluid replacement Anti-endotoxic therapy (see Chapter 32, p. 567) Prognosis is good if the initial response to treatments is productive; however, delayed onset of myopathy, laminitis, and organ failure is possible.
• Hypoglycemia rarely causes recumbency in the adult horse. Practice Tip: When present, it is most commonly secondary to neoplastic disease/tumors.
Respiratory and Cardiovascular Disorders
WHAT TO DO Cardiovascular Collapse • • • • • •
Judicious administration of intravenous fluids Blood transfusion Intravenous aminocaproic acid NSAIDs Intranasal oxygen insufflation Quiet environment
• Severe shock (see Chapter 32, p. 565) may also cause recumbency, whether due to decreased perfusion or secondary to sepsis. Diagnosis is based on history and clinical signs of dark mucous membranes with prolonged capillary refill time, poor peripheral pulses, and cool extremities.
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Gastrointestinal Diseases
• Horses with abdominal pain may present down, but clinical examination and response to analgesics usually indicates that abdominal pain is the cause of the recumbency— an unwillingness to stand rather than inability to stand. • Horses with severe parasitism and starvation may be examined because of recumbency. Treatment is discussed in Chapter 50, p. 764, but the prognosis is poor for the down horse with these disorders. • Similarly, horses with neoplasia and/or organ failure may be examined because of recumbency. • Clinical examination, ultrasound exam, serum chemistries, complete blood count (CBC), and cytology of body fluids or tissue often reveal a cause. WHAT TO DO Down Horse Transport • Transport of the down horse is challenging and potentially dangerous. • In a quiet or depressed horse, transport may be carried out without the use of sedation/anesthesia; however, some degree of sedation is typically necessary. • The horse should be protected with padded leg wraps and a helmet, if available. • Horses can be moved on a flat surface with a coordinated effort by several people simultaneously pushing/pulling the horse in the same direction. Ropes can be tied to the down limbs to allow more distance between the limbs and people for safety. • More effectively, a horse can be moved using a Large Animal Rescue Glide1 (see Chapter 37, p. 638). The glide is a large sheet of durable, conformable plastic with handles and areas to hook ropes along the edges. The plastic slides easily over a variety of surfaces, and the edges can be folded to accommodate stall and trailer doorways. • An effective method for moving a recumbent horse is to place the UC Davis Large Animal Lift2 on the horse and use it to pull the horse onto the Large Animal Rescue Glide. The glide can then be pulled into the trailer and left under the horse to facilitate moving the horse off the trailer and into a hospital stall.
Basic Supportive Care • Management of the down horse includes treatment of the primary disease (when known or working cause) and intensive supportive care. • Bedding should be compressible, comfortable, and absorbent. It should be cleaned and aerated each time the horse is moved or turned. Wood shavings as a base-layer, with a thick covering of straw works well. Sheets or blankets may be placed on top to prevent abrasions, and the head should be slightly elevated. When the horse stands or is assisted with a sling, ensure that bedding is not slippery or excessively deep. • Positioning is critical in the down horse. Ideally, the horse should remain in sternal recumbency, propping with straw bales as necessary. The horse should be turned every 2 to 6 hours, even if it is able to remain in sternal recumbency. Turning helps prevent decubital ulcers, compressive myelopathy and neuropathy, and supports ventilation. 1
Large Animal Rescue Glide (L.A.R.G.E., Greenville, South Carolina). Large Animal Lift (Large Animal Lift Enterprises, Chico, California).
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• Cardiovascular collapse, especially when acute, may result in recumbency. • Hemorrhage, whether external or internal, may result in cardiovascular collapse. • Internal bleeding occurs most commonly in the abdomen, although bleeding into the thorax and uterus may occur. • Initial diagnosis is based on history, mucous membrane pallor, tachypnea, tachycardia, abdominal discomfort or respiratory compromise, and low blood pressure. • Further diagnosis is achieved by ultrasound examination and/or abdominocentesis or thoracocentesis.
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SECTION I Special Problems
• Practice Tip: Turning is ideally achieved by placing in sternal recumbency and pushing the body over the limbs; however, this is difficult in a full-sized horse. The advantage of this technique is that it allows the atelectic “down-side” lung to become inflated before being placed in lateral recumbency with the opposite lung down. • Alternatively, with the horse in lateral recumbency, ropes may be tied to the down limbs and pulled by individuals on the opposite side of the horse while one person assists the head. Caution should be used because horses typically struggle when the procedure is first performed. • Many recumbent horses can bear some weight and spend considerable time upright with the assistance of a sling. Decreasing recumbent time minimizes the effects of prolonged recumbency and some muscle mass can be maintained. • The sling also provides the clinician with the opportunity to better evaluate the patient. • Horses with abnormal mentation are poor candidates to sling, and fractious or nervous horses may require light sedation or tranquilization. The sling must be properly adjusted to prevent pressure sores and the horse should be monitored closely while in the sling. • The amount of time the horse stands in the sling should be gradually increased, if well tolerated. Horses with botulism should not be assisted to stand with a sling unless necessary because of complications of recumbency. • Practice Tip: Excessive movement of horses with botulism depletes acetylcholine stores. • Use of a sling: • To use a sling safely in a stall environment, a cross-beam and hoist capable of supporting at least 2000 to 4000 lb (900 to 1800 kg) should be available, depending on the size of the horse, sling, and hoist. The UC Davis Anderson sling provides the most support in the most stable and balanced manner (see Chapter 37, p. 638). The sling consists of a rectangular overhead support, which provides level support, abdominal support, and additional leg supports alleviating excessive pressure on the abdomen and thorax/sternum. Disadvantages of this sling are that it is expensive and can be difficult to place on the horse, especially in a down patient without sedation or anesthesia. • The Liftex sling3 is simpler to use, containing an abdominal support, as well as tail and chest supports. It is less expensive and easier to place on the recumbent patient. • The UC Davis Large Animal Lift is the most affordable and lightweight of the slings. It is intended to be used for lifting and moving horses, rather than providing ongoing support for a horse unable to stand unassisted, although it can be used in this manner. The device is relatively simple to place on a recumbent horse and can be used with a tractor or winch for lifting. • Practice Tip: There should be even “tension” on the bar or it may bend as the horse is being lifted. If a horse needs continued support for standing, the Anderson sling may be placed over the UC Davis Large Animal Lift once the horse has been lifted to a standing position, then the Large Animal Lift can be removed. • On an especially quiet horse, the individual may be lifted using the sling and positioned in a bovine float tank.4 The horse must be monitored closely, and there is a risk of injury when confined to the tank.
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• The Enduro NEST,5 recently developed by Enduro Medical Technology, supports the horse with a sling containing an abdominal support and leg supports. The sling is supported by a selfcontained metal frame providing customized support or for lifting the horse. A horse can be placed under, and recover from, general anesthesia safely while being continuously supported in a standing position. The device can be used in a fixed position to provide variable limb support or is mobile to assist a weak, injured, or neurologic horse to walk. Self-trauma and decubital ulcers can be minimized with attention to good nursing care—bedding and skin care. • Leg wraps are recommended to protect the distal limbs and shoes should be wrapped to alleviate sharp edges. • Well-fitting head bumpers help prevent head trauma, which commonly occurs during failed attempts to get into sternal recumbency. • Horses should be groomed frequently and damp areas from sweat or urine should be dried thoroughly because wet skin is more prone to pressure sores and ulceration. • Wounds should be kept clean and dry, and antibiotics or topical medications used if necessary. Ophthalmic care of the recumbent horse includes: • Lubrication with an artificial tear ointment should be performed bilaterally at least q3-4h. • Corneas should be stained at least q24h to monitor for corneal ulceration. • Corneal ulcers should be treated aggressively and a temporary tarsorrhaphy considered if necessary. Nutritional support is an integral and challenging aspect of supportive care (see Chapter 51, p. 768). • Horses that are not dysphagic should be positioned in sternal recumbency and offered water, long-stem forage, and grain. • Horses are more likely to eat when standing, so feed and water should always be offered at a comfortable height when horses are assisted to stand. • Horses that are dysphagic or inappetent for several days require enteral or parenteral nutritional support. • Enteral feeding may be provided by nasogastric tube, and the tube can be left indwelling or passed several times daily. • Enteral diets may be formulated using complete feeds or alfalfa meal, or a commercial equine enteral diet may be used. • Feedings should be divided into 4 to 6 small meals per day while the horse is sternal or standing. • In horses with adequate gastrointestinal function, maintenance fluids may be administered by nasogastric tube. • In horses with gastrointestinal dysfunction in which enteral feeding is not possible, parenteral nutrition with dextrose, amino acids, and lipid solutions should be considered. • Maintenance fluid requirements must also be met using intravenous fluids in horses on parenteral nutrition. Intravenous catheter care is challenging because of an unavoidably contaminated environment and frequent movement at the catheter site (see Chapter 3, p. 9). • Polyurethane, over-the-wire jugular catheters are recommended because they are less likely to cause thrombosis than over-theneedle catheters. • Routine catheter care—i.e., flushing the catheter with heparinized saline q6h is recommended.
3
Liftex Large Animal/Equine Sling (Liftex Corporation, Philadelphia, Pennsylvania). 4 Aqua Cow Rise System (Aqua Cow/North America, Saint Johnsbury, Vermont).
5
Enduro N.E.S.T. (Enduro Medical Technology, South Windsor, Connecticut).
• A neck wrap of elastic tape with dry gauze placed over the base of the catheter is recommended to prevent friction and gross contamination, and should be replaced daily or more often if soiled. • The vein and the catheter insertion sites should be inspected at least two times a day for evidence of skin swelling, heat, or thickening of the vein. If any abnormalities are detected, the catheter should be removed and the tip cultured. • In the event of a compromised jugular vein, hot-packing the catheter site and vein several times a day, followed by topical application of DMSO/furacin sweat, ichthammol or Surpass6 are recommended to minimize thrombophlebitis. Antibiotic therapy is typically indicated. • Urinary catheterization is necessary in horses with neurologic disorders that cause an atonic bladder, such as EHV-1, and in horses not urinating appropriately. • Some down horses, especially mules, may choose not to urinate even with normal bladder and spinal cord function. • Catheterization may be performed several times a day or the catheter may remain indwelling. • Indwelling catheters are useful for keeping the bedding and patient dry and helping to prevent decubital ulceration. • An indwelling Foley catheter should be placed under aseptic conditions and urine collected using a closed system. IV tubing
Chapter 36
Caring for the Down Horse
633
and empty sterile IV fluid bags placed deep in the bedding below the level of the bladder can be easily and inexpensively used to collect urine. • Securing the catheter and/or tubing to the skin on the ventral body wall (males) or tail (mares) using elastic tape or suture, respectively, alleviates pressure on the catheter when the horse struggles or is turned. • The urinary collection system should be monitored for obstructions and urine collection bags emptied at least several times a day. • Practice Tip: The most common complication of urinary catheterization is cystitis due to ascending bacterial infection. • Cytologic and dipstick evaluation of urine is easy and inexpensive, and should be performed every few days. If cystitis is suspected, a urine culture and colony count should be performed and antibiotic therapy instituted. • Large colon impactions are common in down horses because of poor gastrointestinal motility. • It is essential to monitor fecal production closely in these horses. • Easily digestible feeds should be offered and mineral oil administered by nasogastric tube. • Manual evacuation of the rectum may be necessary, especially in horses with EHV-1.
References 6
Surpass (Boehringer Ingelheim Metmedica, Inc., St. Joseph, Missouri).
References can be found on the companion website at www.equine-emergencies.com.
EMG