Down and out foals--what to do when referral is declined (Proceedings)

The majority of neonatal foals are born healthy and vibrant individuals; however, when a foal becomes ill, some disease processes can be severe and life threatening.  Such disease processes include sepsis, septic arthritis, hypoxic-ischemic encephalopathy and diarrhea, among others.  Due to the labor intensive nature of therapy, many ill foals would be best served in the hospital setting.  However, economic restrictions are always a consideration in veterinary medicine, and some clients may decline hospitalization and intensive care and yet request field treatment.  The purpose of this lecture is to propose management scenarios of various diseases in which the client refuses hospitalization but still requests therapy. 

Sepsis

Neonatal sepsis is a common disease entity afflicting foals.  Clinical manifestations and recognition can be quite obvious or elusive. Historical information such as a history of placentitis, vulvar discharge or dystocia should increase the suspicion of septicemia.  Sepsis should also be considered in foals that are typically less than 7-10 days of age that demonstrate signs of decreased nursing activity, generalized lethargy, intermittent or persistent fever, tachycardia, tachypnea, weakness and/or prolonged recumbancy.  Other physical exam findings such as hyperemic mucous membranes, petechia, anterior uveitis, respiratory distress or swollen joints also may support the suspicion of sepsis.       

Point-of-care devices that measure blood glucose and lactate should be utilized if available.  In a recent study, foals with hypoglycemia at admission were associated with sepsis, a positive blood culture, and the systemic inflammatory response syndrome (SIRS).1  Furthermore, foals with glucose concentrations < 50 mg/dL or > 180 mg/dL at admission were less likely to survive.1  The blood lactate at admission has also been associated with survival and bacteremia in another study; the mean lactate of foals that survived was 4.4 mmol/L whereas non-survivors had a lactate of 9.3 mmol/L.2

In addition, blood lactate at admission was higher for foals with bacteremia (7.55 mmol/L) or neonatal encephalopathy (8.5 mmol/L).  Semi-quantitative assessment of passive transfer of maternal antibodies should also be evaluated as failure of passive transfer is strongly associated with sepsis.  If readily available, CBC findings of leucopenia, neutropenia (with toxic neutrophils) and immature band neutrophils is highly supportive of septicemia.  Sepsis scores that predict the likelihood of septicemia based on various physical exam and clincopathologic data are also available.3

Definitive diagnosis of sepsis is based on culture of one or more microorganisms in blood culture bottles; however, the veterinarian must weigh the benefits of blood culture (specific identification of organism[s] and antimicrobial sensitivity) with the cost of blood culture ($50-100) in severely cost-restrictive situations.     

The obvious cornerstone of treatment of sepsis is appropriate antimicrobial administration.  According to several retrospective studies, gram-positive isolates were obtained in 40% (50/124) of cultures and gram negative isolates were obtained in 57% (71/124) of cultures.4,5  The most common gram-positive isolates identified were Streptococcus spp and Enterococcus whereas E. coli was the most common gram-negative isolate.4  Based on this information, the spectrum of activity of antimicrobial(s) selected to treat sepsis should be broad. 

The aminoglycosides (amikacin 25 mg/kg, IV, q 24 hours; gentamicin 6.6 mg/kg, IV, q 24 hours) are commonly administered for their efficacy against gram negative bacteria.  The beta-lactams such as penicillin (22,000 IU/kg, IV or IM depending on formulation), cefiofur (5 mg/kg, IV, q 12 hrs) or ampicillin (20-30 mg/kg, IV q 6-8 hrs) are commonly combined with one of the aminoglycosides to provide broad-spectrum antimicrobial activity.  Foals with sepsis should be treated for 10-14 days with injectable antimicrobials; some clinicians also provide another 7-10 days of oral antimicrobials once parenteral antimicrobials are complete.     

Intravenous catheters and nasogastric tubes may be necessary in the treatment of ill foals to provide IV treatments and nutritional support.  However, these devices can be a risky endeavor in the hands of the lay horse-owner.  Sterility is an important consideration with IV catheters and inappropriate feeding of a foal with gastric reflux or ileus is a concern with NG tubes.  In the foal that is hypoglycemic, a 1 liter bolus of sterile fluids combined with 20 mLs of 50% dextrose (1% dextrose solution) will provide enough glucose initially to the patient without causing profound hyperglycemia. 

If the foal is not able to nurse after this initial IV dextrose bolus, one must choose between continued IV administration of dextrose (4 mg/kg/min) or enteral feedings.  The veterinarian must decide if the foal will tolerate enteral feedings (i.e. presence of gastric reflux or colic signs, is the foal premature/dysmature, is there evidence of ischemic enteropathy).  Initially the foal should be administered 5-10% of the body weight every 1 to 2 hours (i.e. 5% in a 50kg foal fed every 2 hours; 0.05 x 50kg = 2.5 liters/day; divided into every 2 hour feedings = 200 mLs q 2hrs). 

If the foal tolerates feedings over the first 6-12 hours, this amount can be increased to 10% of the body weight and over the next few days up to 20-25% of body weight.  The confounding problem here is if the client is trustworthy and reliable enough to feed the foal properly; this is up to the individual veterinarian to decide.  Good nursing care, including keeping the foal clean, dry and in sternal recumbancy is also necessary.  

Other variables to be aware of during the treatment of a septic foal is the development of a patent and/or infected urachus, identification of GI ileus or diarrhea, observation for respiratory distress and/or poor oxygenation, evidence of corneal ulcers, and evaluation for limb deformities.  The prognosis for survival of septic foals is variable with one report demonstrating a 70-80% survival rate in hospitalized foals.3

Field evaluation and treatment of the septic foal Client Observations Examination Findings Treatment Associated Processes Decreased nursing activity Fever, tachycardia, tachypnea

Antimicrobials

(± IV catheter) Infected or patent urachus Prolonged recumbency

- WBC,    - neutrophils

bands, toxic changes

Nutritional support

(± NG tube) Cardiopulmonary disorders Weakness FPT, - blood glucase ± Plasma transfusion GI ileus or diarrhea Lethargy + Lactate Nursing care Corneal ulcers Diarrhea Diarrhea Oxygenation Limb deformities  

± Blood culture

± sepsis score Electrolyte and fluid correction Fractured ribs

Septic arthritis

Septic arthritis can be a career-threatening disease that can affect young foals.  Septic arthritis can lead to permanent degenerative joint disease, irreversible cartilage damage and lameness if not treated expeditiously.  Septic arthritis can occur secondary to bacteremia with or without evidence of infection of other body systems.  Variables such as status of passive transfer of maternal antibodies, virulence of the organism and local joint factors (i.e. local blood perfusion) contribute to the development of septic arthritis. 

Clinical signs consistent with septic arthritis include a young (commonly neonatal) foal presented with lameness, periarticular edema and joint effusion of the affected joint.  Systemic manifestations may or may not be present.  In one study in which 57 individually infected joints were identified, the involved joints included the femoropatellar (n=17), tibiotarsal (15), metacarpophalangeal or metatarsophalangeal (10), radiocarpal (6), humero-ulnar (5), coxofemoral (2), scapulohumeral (1) and distal interphalngeal (1) joints.

Diagnosis of septic arthritis is based on arthrocentesis and examination of joint fluid which may reveal a high protein concentration (>2.5 gm/dL) and high leucocyte count (>30,000; >90% neutrophils).  The peripheral CBC may also be altered based on the presence or absence of generalized septicemia but a neutrophilia and hyperfibrinogenemia (>900 mg/dL) should alert the clinician to the possibility of septic physitis. 

Gram stain and bacterial culture of joint fluid is warranted with the knowledge that culture of synovial fluid with suspected infection yields positive results in only 64% of samples,7 even though infection is likely; gram staining or bacterial culture may not always be performed in the field setting.  Common organisms involved in septic arthritis include those involved in generalized septicemia such as E. Coli, Actinobacillus, Klebsiella sp, Pseudomonas sp, and Salmonella.

Field treatment of septic arthritis includes administration of broad-spectrum antimicrobials, local joint lavage and local antibiotic therapy (i.e. regional limb perfusion, interosseous perfusion).  Through-and-through needle lavage can be accomplished with large diameter (14-16 gauge) needles and heavy sedation or short-term anesthesia.  Typically this is performed daily to every other day for 3-5 treatments.  Intra-articular administration of antimicrobials such as the aminoglycosides may help maintain high drug concentrations locally. 

In addition, regional limb perfusion will attain high local drug concentrations for periods ≥ 24 hours.8 Concentration-dependent (amikacin, gentamicin) drugs are ideal but time-dependent (K-penicillin, ceftiofur, vancomycin, timentin, ampicillin) drugs have been utilized as well.  Enrofloxacin should be avoided because of its toxic effects on vascular tissues.8  No set standard in dosing has been established for regional limb perfusion but administration of 1/3 the systemic daily dose of drug combined with 10-35 mLs of isotonic fluids is routinely used in foals.8  Recently, the use of constant rate infusion bulbs has been published and demonstrated positive outcomes.9,10

The prognosis for survival in foals with septic arthritis is fair to good; however future athletic abilities may be compromised.  In one study, of the 69 foals hospitalized for septic arthritis, 84% (58/69) survived to discharge.  Of the 58 that survived, 48% (28/58) started a race compared to 66% of the control group.6  Other disease processes should also be taken into consideration when discussing prognosis. 

Neonatal diarrhea

Diarrhea in foals is a common clinical presentation and may range from mild and transient to severe and life-threatening.  While the obvious sign of loose feces is an indication of disease, other physical exam parameters that should be considered are attitude (alert vs. lethargic), nursing activity (decreased or normal), hydration status, and evaluation of the temperature, pulse and respiratory rate.  Evaluation of a CBC and biochemistry profile may also help decide the severity of disease and the need for intervention.  Evidence of a neutropenia, left shift, toxic neutrophils along with electrolyte derangements, hypoproteinemia and azotemia suggest that the diarrhea requires close monitoring and treatment. 

Depending on the situation, clients may request that diagnostics be performed in efforts to identify a specific cause of the diarrhea.  Fecal analysis that attempt to detect Salmonella (cultures), Rotavirus (ELISA), Clostrdium (culture, ELISA), and Lawsonia (PCR) are available, but, at times, may all be negative.  Other non-infectious cases of diarrhea such as foal-heat diarrhea, dietary intolerance, sand ingestion, asphyxia-associated enteropathy, and gastric ulceration should also be investigated. 

In a recent retrospective study involving 223 foals with diarrhea, at least one infectious agent was identified in 55% (122/233) of foals.11  Agents identified included Rotavirus in 20% (47) of foals, followed by C. perfringens in 18% (42), Salmonella spp in 21% (28), parasites in 7% (16 foals; P. equorum-10; Strongylus spp-6; Giardia-3; Trichostrongylus-1, S. westeri-1), coronavirus in 1% (3) and Cryptosporidium in 1% (3) of foals evaluated.   

If possible, evaluation of a biochemistry profile will provide valuable information of electrolytes, dehydration, protein concentration and acid-base status (indirect).  Blood gas analysis should be considered if severe academia is suspected.  Point-of-care measurement of blood lactate can also be used as a reflection of patient hydration and perfusion.  Fluid therapy is essential in rehydration of foals with significant diarrhea. 

Typically an IV catheter is necessary to administer sterile isotonic fluids and will also provide a means to administer equine plasma or synthetic colloids if hypoprotenemia is severe.  Intermittent bolus IV fluid therapy (at times accomplished by the client) may be necessary to adequately rehydrate a foal in the field setting.  A starting point consists of 1 liter IV boluses of isotonic fluids (i.e. LRS or normosol) every 4 hours in a 50 kg foal.  This can be increased in volume or frequency if adequate hydration is not obtained. 

Measurement of urine specific gravity can be used as a gauge of hydration if available.  The use of antimicborials for the treatment of diarrhea in horses is somewhat controversial but in neonatal foals, broad-spectrum antimicrobials are indicated to prevent bacterial translocation across the gut and possible bacteremia/septicemia.  Metronidazole (15 mg/kg, PO or IV, TID) is indicated for Clostridial diarrhea.  The prognosis for survival of diarrhea is variable but tends to be fair to good with appropriate therapy.  In the study investigating infectious causes of diarrhea, 87% of foals (191/223) survived to discharge; however, no information is available in regard to diarrheic foals treated in the field setting. 

Disclaimer

It is important for the veterinarian to advise clients that certain disease processes would have the best chance of survival with hospitalization and intensive care.  If the burden of treatment is left to “field treatment” it is up to the individual veterinarian to decide if the care is worth their time and also advise their clients of potential complications that may occur with field management such as IV catheter infection, decreased sterility and lack of medical supervision, among other complications. 

References

Hollis AR et al. Blood Glucose Concentrations in Critically Ill Neonatal Foals. J Vet Intern Med 2008;22:1223-27. 

Corley KTT et al.  Arterial lactate concentration, hospital survival, sepsis and SIRS in critically ill foals. Eq Vet J 2005;37:53-9.  

Brewer BD et al. Development of a scoring system for the early diagnosis of equine neonatal sepsis. Eq Vet J 1988:20:18-22.  

Russell CM et al. Blood culture isolates and antimicrobial sensitivities from 427 critically ill foals. Aust Vet J 2008;86:266-71. 

Marsh PS et al. Bacterial isolates from blood and their susceptibility patterns in ill foals: 543 cases (1991-1988). JAVMA 2001:218:1608-10. 

Smith LJ et al. What is the likelihood that Thoroughbred foals treated for septic arthritis will race? Eq Vet J 2004;36:452-56.

Hunt RJ. Lameness in foals. In: Ross , Dyson eds. Diagnosis and management of lameness in the horse. St Louis: Saunders, 2003; 1084-93.

Rubio-Martinez et al. Antimicrobial regional limb perfusion in horses. JAVMA 2006;228:706-712.

Meagher DT et al. Evaluation of a balloon constant rate infusion system for treatment of septic arthritis, septic tenosynovitis, and contaminated synovial wounds: 23 cases (2002-2005). JAVMA 2006;228:1930-34.

Lescum et al.  Treatment with continuous intrasynovial antimicrobial infusion for septic synovitis in horses: 31 cases. JAVMA 2006;228:1922-9.

Frederick J et al.  Infectious agents detected in the feces of diarrheic foals: 233 cases (2003-2008). JVIM 2009;23:1254-60.