Equine Endotoxemia Flashcards
What does MODS/MOF stand for?
Multiple Organ Dysfunction Syndrome
What is the most common cause of death for patients admitted to a contemporary intensive care unit? (ICU)
Multiple Organ Dysfunction Syndrome
What does ARDS stand for?
Acute respiratory distress syndrome
What does DIC stand for?
Disseminated intravascular coagulation
What does SIRS stand for?
Systemic inflammatory response syndrome
What are indications of diagnosis for SIRS (at least 2 required)?
- Leukopenia, Leukocytosis, or >10% bands
- Hyperthermia or hypothermia
- Tachycardia
- Tachypnea
- Evidence of sepsis in foals
What is endotoxemia?
presence of endotoxin in circulation
- cell wall/Gram neg bacteria (LPS or lipopolysaccharide)
How does endotoxemia happen?
pathogen recognitions by the receptor leads to an inflammatory response that can not be sufficiently contained.
What are the 3 structural domains of lipopolysaccharide (LPS)?
- Polysaccharide O region outer portion (accounts for serologic differentiation among bacterial species)
- Core acidic polysaccharide (connects the two)
- Lipid A region (hydrophobic) inner most portion (unique)
What structure is most responsible for the toxic effect of endotoxemia?
Lipid A portion
What is the role of LPS in endotoxemia?
activates cellular population acting as a virulence factor.
- Histamine, tumor necrosis factor, bradykinin, beta-endophins, O2 derived free radicals, platelet activating factor, IL-1 and IL-2, myocardial depressant factor, etc.
What are preventative mechanisms to endotoxemia and how do they work?
- Mucosal epithelial cells/physical barrier
- restrict bacterial transmural movement across bowel wall.
- Secrete lysozyme, enzymes, and antibodies
- Removal endotoxin from portal blood by liver
- Intravascular Macrophages
- other cells: endothelial, platelets, lymphocytes and neutrophils
- Monocytes
- Kupffer cells (hepatic macrophages) become effective scavengers of endotoxin
- Circulating anti-endotoxin antibodies directed against core region
- bind endotoxin and remove it from circulation
What are the Stages of Endotoxemia?
- Endotoxins breach physical barrier (digestive, respiratory, reproductive, endocrine, integument, immune system, urinary, toxicities)
- Endotoxins stimulate macrophages
- TNF and IL1 act on neutrophils and endothelial cells
- Compromised organ perfusion
- Recovery
How does endotoxemia present in the GI tract?
- Colic ‘Abdominal pain’
- usually level of pain indicates the severity
- Colitis (inflammation LI)
- dmg to GI walls and subsequent bacterial translocation
- Sand colic
How does Carbohydrate Overload cause endotoxemia?
- Bacterial overgrowth in colon
- Degeneration of colonic mucosa which allows endotoxins to gain access to the portal circulation
Which drugs can induce colitis and thus endotoxemia?
- Antibiotics
- NSAIDS: Banamine and Phenylbutazone
What respiratory conditions can lead to endotoxemia and how?
- Pleuropneumonia
- infection b/w pleural space and lungs (most commonly bacterial)
- Thoracotomy to provide drainage
- Choke (esophageal obstructions)
What conditions of the integument can lead to endotoxemia?
- bacterial infections: clostridium myositis
What conditions of the reproductive tract can lead to endotoxemia?
- retained placenta (most common) (needs special attention immediately)
- Uterine rupture
- Severe metritis
What conditions of the Urinary tract can lead to endotoxemia?
- infection
- obstruction
(uncommon)
How can Equine metabolic syndrome lead to endotoxemia?
- lipotoxicity: excessive conversion of glucose to fat
- disruption of insulin receptors progress until insulin resistance
- associated with oxidative stress and inflammation
- EMS horses have increased IL6, IL10, TNFalpha –> affects inflammatory response by prolonging cytokine expression in circulating leukocytes
How can Cushings disease lead to endotoxemia?
it is due to pituitary par intermedia dysfunction -> ACTH overstimulates adrenal glands -> cortisol synthesis -> Hyper-cortisolemic state = functions as immunosupressant
How do endotoxins stimulate macrophages?
- LPS bind to LBP (binding protein) which then binds to CD14 cell surface intravascular macrophages and monocytes (in circulation).
- Activation of PRRs by PAMPs trigger the production of pro and anti-inflammatories. (also initiate adaptive immune response)
- LBP-CD14 interaction with TLR 4 (activates)
- > MyD88 pathway (TNF and IL1, proinflammatory)
- > TRIF and TRAM (anti-inflammatory)
- Results in pro and anti-inflammatory mediators
LPS only leads to the MYD88 pathway
What are PAMP’s?
Pathogen associated molecular patterns
What are PRRs?
Pathogen recognition receptors
Where are PRRs present?
on phagocytic cells
What are the chemical events of stage 2 Endotoxemia?
- Early: Macrophages stimulates TXA2 and other vasoconstrictors (pulmonary constriction -> increase pulmonary arterial pressure)
- Later: Synthesis of cytokines: TNF, IL1 (amplification of endotoxin signal. Endogenous pyrogen, cortisol epinephrine, procoagulant activity and vasodilator nitric oxide.
VASOCONSTRICTION THEN VASODILATION
What happens during stage 3 of endotoxemia when TNF and IL1 act on neutrophils and endothelial cells?
- Cytokine induce margination of neutrophils to epithelial cells (accounts for leukopenia)
- Neutrophils empty granular content onto endothelium
- Endothelial cells activate procoagulant activity
- platelets contribute to procoagulant effect
- Endothelial dmg due to hypercoagulative state-intravascular coagulation
- Abnormal vascular tone -> Hyperdynamic shock (initial) (pulmonary vasoconstriction, tachypnea, hypoxia) and then Hypodynamic shock (later) (vasodilation)
What happens during stage 4 of endotoxemia?
Compromised organ perfusion:
- Vasodilation
- Vascular leakage and injury
- Intravascular cellular plugging
- Coagulation
- Systemic arterial hypotension (less O2 delivered)
When does Multiple Organ Failure occur?
if two or more organs are involved
How does recovery occur in endotoxemia?
LPS induce IL10 which results in deactivation mononuclear phagocyte and inhibits pro-inflammatory cytokine
What is the clinical status of endotoxemia?
(may not be related to primary condition)
- Alteration in cardio pulmonary rate
- Abnormal mucous membrane color and CRT
- Fever or Hypothermia
- Fecal consistency changes
- Organ failure
What signs are expected in the early stages of endotoxemia?
Tachypnea, pale mucous membranes
- (~90mins) depression, restlessness, inappetance, fever - (~2hrs) peak tachycardia, congested mucous membranes and prolonged CRT; "Toxic line". - Decreased GIT sounds
What signs are expected 4-6 hours into endotoxemia?
a secondary phase:
- Tachycardia and tachypnea, fever
- circulatory failure and coagulopathy dominate
- Dehydration (dry MM, skin tenting (ski turgor), sunken eye)
What signs are expected in the later stages of endotoxemia? (after 4-6 hours)
- decreased rectal temp
- Oliguria or anuria
- rapid weak pulses
- muscle tremors
- hemostatic dysfunction (petechia, ecchymoses on MM, hypercoagulability
What signs are expected past 24 hours of endotoxemia?
ventral edema and laminitis
What are some species differences in endotoxin recognition and response to receptors?
- Horses have high sensitivity to LPS when compared to other species
- Specially equine monocytes, when challenge with E.coli LPS
- Equine-specific cellular response to flagellin
- Flagellin induces pro-inflam. response NEUTROPHILS by the ligand TLR5, does not activate MONOCYTES as expression of TLR5 is low in these cells.
- MM are white or injected
- CRT may be normal
- Strong pulses, tachycardia
- Tachypnea
- Fever
What state of endotoxemia are these clinical signs indicative of?
Hyperdynamic state
- MM congested, dark, toxic line
- CRT prolonged >2sec
- Pulses are weak
- Tachycardia or tachypnea
- Cold extremities
- Normo or hypothermic
What state of endotoxemia are these clinical signs indicative of?
Hypodynamic state
What are the clinical signs of the hyperdynamic state of endotoxemia?
- MM are white or injected
- CRT may be normal
- Strong pulses, tachycardia
- Tachypnea
- Fever
What are the clinical signs of the Hypodynamic state of endotoxemia?
- MM congested, dark, toxic line
- CRT prolonged >2sec
- Pulses are weak
- Tachycardia or tachypnea
- Cold extremities
- Normo or hypothermic
What indicators of endotoxemia can you find during a physical exam?
- Increased heart rate (>48bpm) and respiratory rate (>12bpm)
- Toxic mucous membranes
- Cold extremities
- Poor pulses
- +/- fevers (>102.4 F)
What tests can you run to diagnose endotoxemia? What results would you expect?
- Complete blood count
- Leukopenia, neutropenia and a left shift
- Arterial blood gas analysis
- Hypoxemia and metabolic acidosis
- Look at levels of glucose, lactate, platelets, fibrinogen
- Limulous Ameobocyte lysate assay
- Direct measurement of circulating endotoxins
What different methods of a Limulous Ameobocyte lysate assay can be used for endotoxemia?
- Gel Clot assay (proteins coagulate in presence of endotoxins, minimum detection limit = 0.01EU/ml)
- Turbidi-metric testing (measuring a light beam passing through, MDL of 0.005EU/ml)
- Chromogenic Limulus Amebocyte Lysate (MDL of 0.10 EU/ml)
What happens during the systemic inflammatory response syndrome?
lack of ID infection or bacteria in the bloodstream
very similar criteria to endotoxemia
At least what may appear before SIRS?
at least two of the main criteria appear before SIRS
- changes in temp, HR & RR combine with hematology changes (WBCs)
- leukocytosis (leukopenia greater than 10%)
Why is it important to catch endotoxemia early?
- Early treatment
- Prevention of MOD
- Prevent laminitis
How can Endotoxemia be prevented?
- Vacine: S. typhimurium mutant (partial protection and little support, not beneficial in foals)
- Repeated LPS exposure (diminish pro inflammatory and clinical response -> reduce gene expression and production of TNFalpha, reduce fever, tachycardia, tachypnea, and pain response.
- Endotoxin tolerance subside after 14-21 days
What are the goals of treatment of endotoxemia?
- circulatory support
- removal of causes
- neutralization of circulating endotoxin
- inhibition of endotoxin induced inflammation
- prevent laminitis
While treating endotoxemia, how does one provide cardiovascular support?
Improving intravascular volume
- Balanced polyionic solution
- LRS or normosol. Volume and rate depend on degree of hypovolemia (severe at 10-20mls/kg/hr). Minimum at admitions of 10L/hr first hr or more.
- Hypertonic saline (7.5% NaCl) (always follow with balance IV fluids)
- Plasma (protein loss)
In what cases can the cause of endotoxemia be removed?
- Surgical colic
- Pleuropneumonia
- Retained placenta
- Peritonitis
How is Endotoxemia treated?
- PAMPs antibody:
- Anti-microbial Therapy
- LPS neutralizing agent
- Endoserum: commercial anti-endotoxin serum from hyper-immune horses. (recomended any stage but fallen from favor)
- Inhibition of synthesis of endotoxin induced mediator
- Pentoxifylline: phosphodiesterase inhibitor
- Dimethyl Sulfoxide: DMSO
- Ketamine: Dissociative anestheic agent
- Lidocaine CRI
- Ethyl pyruvate
How does the PAMPs antibody help treat endotoxemia?
- IgM and IgG bind to neutralize LPS in other species
- Hyperimmune anti-LPS core antigen plasma decrease the mortality rate significantly
How does the Anti-microbial therapy help treat endotoxemia?
- Can worsen clinical presentation cause lower LPS when kill bacteria
- Rapid death of Gram negative
How does a LPS neutralizing agent help treat endotoxemia?
- Polymixin B: cationic polypeptide antibiotic (interacts directly with lipid A forming stable molecular complex. Decr. TNFalpha and residual LPS activity. Can cause renal toxicity
- External removal of LPS by binding polymixin B filters
what is used to inhibit the synthesis of an endotoxin induced mediator help treat endotoxemia?
- NSAIDs most accepted flunixin meglumin (prevent incr in both TXA2 and PGI2)
- Glucocorticoid (very controversial) (immunosuppression, laminitis)
How does Pentoxifylline: phosphodiesterase inhibitor help treat endotoxemia?
- dose dependant inhibition of TNFalpha and IL6 activity in horses with endotoxemic shock
- combine with flunixin meglumine was more effective in treating the hemodynamic effect of LPS in horses
- rapidly eliminated after IV infusion, need CRI
How does Dimethyl Sulfoxide: DMSO help treat endotoxemia?
- decrease the expression of cytokines IL6, TNFalpha, Macrophage inflammatory protein 1-alpha
How does a Ketamine: Dissociative anestheic agent help treat endotoxemia?
- posessed a cytokine-modulating activity on LPS-induced TNFalpha and IL-6 formation in equine macrophage
How does Lidocaine CRI help treat endotoxemia?
- significantly decreased severity of clinical signs
- inhibited significantly TNFalpha activity in peritoneal fluid
How does Ethyl pyruvate help treat endotoxemia?
- down regulated TNFalpha, IL6 and COX2 expression on horses challenged with LPS
What should treatment of endotoxemia begin with and why?
Aggressive supportive care
- other treatments show limited beneficial effects
