Equine SIRS and Therapy

what is SIRS?

systemic inflammatory response syndrome - a complex, dysregulated inflammatory response initiated by a broad range of primary stimuli (typically acute and severe in presentation)

what are some primary stimuli of SIRS?

endotoxin exposure, severe trauma, burns, acute hemorrhage, some surgeries, some neoplasia

why are horses susceptible to endotoxemia?

enormous populations of gram-negative bacteria in their GIT; inflammatory or ischemic GIT disease damages the normal mucosal barrier of the intestine, allowing LPS to enter the circulation

what are the routes of LPS exposure?

1. GI origin (most common) — liver’s capacity to filter LPS is overwhelming and mucosal injury allows excessive LPS exposure to circulation

2. Focal infections — severe pneumonias, post-partum metritis, peritonitis

3. Systemic infections (sepsis) — gram-negative bacteremia (common in neonatal foals)

what organs are commonly affected by SIRS?

lamellae of the foot (laminitis risk), brain (altered mentation), heart (perpetuating cardiac effects), kidneys (AKI), GIT (further injury, ileus), liver (dysfunction)

what are the four clinical criteria of SIRS?

1. fever or hypothermia

2. tachycardia >52bpm

3. tachypnoea >20brpm or hypocapnoea

4. WBC changes: leukopenia, degenerative left sift

A horse needs two of the 4 criteria to be considered diagnostic for SIRS

what are some additional clinical signs of SIRS? (not diagnostic criteria)

• congested/hyperemia MM

• toxic line on MM

• prolonged CRT

• hypovolemic shock

• cardiac effects

• hemostatic dysfunction (coagulopathies, microthrombi formation)

how does SIRS progress to shock?

inflammatory cascade leads to cardiovascular dysfunction:

• increased vessel permeability → fluid extravasation

• transient vasoconstriction followed by profound vasodilation

what laboratory findings are associated with SIRS?

• elevated lactate (proxy for tissue oxygen delivery)

• leukopenia (neutrophil margination to tissues), usually with a left shift

• high PCV (fluid shifts, splenic contraction)

what are the 5 Fs when treating SIRS?

Fluids (restore circulatory volume)

Flunixin (address inflammatory dysregulation)

Feet (continuous icing to prevent laminitis)

Fragmin (dalteparin — anticoagulation therapy)

Flagyl (metronidazole — antimicrobial therapy in specific cases)

what are the dosing options for flunixin when treating SIRS?

half dose — anti-inflammatory benefit, less analgesic effect

full dose — most effective anti-inflammatory effect, provides analgesia, current standard of care

what are the requirements for cryotherapy to be effective against development of laminitis secondary to SIRS?

must be continuous to maintain foot temperature below 5-10°C, requires 24hr care environment (eg hospital), applied from hoof up to carpus/tarsus

continue while patient meets SIRS criteria

what are clear clinical indicates for systemic antimicrobials in horses with SIRS?

surgical colics, septic neonates, mares with metritis

colitis (may have fever and severe leukopenia), infectious colitis

what are the metronidazole indications for colitis?

antimicrobial-associated diarrhea (AAD), where clostridial species are implicated as the causative pathogen, evidence supports improved survival in acute equine colitis

what are the most reliable equine indicators of perfusion?

CRT - proxy for hypovolemia

Jugular refill - proxy for circulatory volume; delayed filling suggests reduced vascular volume

Temperature of extremities - palpate ears and limbs (proxy for peripheral circulation)

skin tent and sunken eyes not very reliable in adult horses

what laboratory assessments can be used to indicate perfusion?

PCV (not specific for dehydration alone), TP (assess with PCV, may be normal)

lactate (most useful) — proxy for oxygen delivery to tissues, assumes patient not anemic or severely hypoxemic, trends over time are particularly helpful

what clinical indicators should be monitored in response to fluid therapy?

HR, MM, CRT, jugular refill, temperature of extremities, urination! and USG, follow TP/PCV and lactate over first 6-24hrs

which electrolytes may be supplements in SIRS cases associated with GI disease?

potassium, calcium (never bolus), magnesium (regulates calcium hemostasis), dextrose

when should you refer a SIRS case?

• lack of response to initial therapy — persistent tachycardia despite fluid boluses, no urine production, worsening perfusion parameters

• development of complications — gastric reflux, signs of laminitis, severe coagulopathy, respiratory distress

• resource limitations — unable to provide 24hr monitoring, cannot deliver large fluid volumes, lack of intensive care facilities

• specific situations — all horses meeting SIRS criteria, horses requiring continual digital cryotherapy, cases needing advanced monitoring

how would you stabilize a SIRS case prior to referral?

initial fluid bolus (if safe to do so), IVC, flunixin

what are common pitfalls to avoid when managing a SIRS case?

• underestimating fluid requirements

• using inappropriate fluids

• inadequate monitoring

• delayed recognition (missing early SIRS signs)

• overlooking safety