S&H Ch 104, 105, 107;Inflammation and Coagulation/Thrombosis MDRs;Cornell Coagulation and Platelet Videos

What is normal hemostasis a balance between?

• Normal hemostasis is a balance between prothrombotic and antithrombotic tendencies

  • Antithrombotic usually predominates so blood can circulate as a liquid

    • Achieved by intact endothelium separating the cellular and plasmatic components of blood from the prothrombotic substances in the subendothelium

    • Endothelium also produces several antithrombotic substances with either antiplatelet (e.g. prostacyclin, nitric oxide) or anticoagulant (e.g. antithrombin, thrombomodulin) activity

• If there is blood vessel damage there is a rapid switch from antithrombotic to prothrombotic

  • Clot formation traditionally considered two distinct processes, primary hemostasis and secondary hemostasis

Coagulation Cascade Diagram

Components of Primary Hemostasis

Platelet number

Platelet function

vWF

Signs of Dysfunction of Primary Hemostasis

Small spontaneous superficial and mucosal bleeds

Excessive postoperative/postprocedural bleeding

Diagnostic Test Options for Primary Hemostasis

Platelet count

Platelet indices (MPV, PCV)

BMBT

Platelet closure time

Platelet aggregometry

Platelet procoagulant assays

Viscoelastic testing

vWF:Ag

Therapeutic Strategies for Primary Hemostasis Disorders

Treat primary underlying disease (e.g. immunosuppression)

Platelet containing transfusions

Desmopressin

RBC containing transfusions

± antifibrinolytic drugs

Components of Secondary Hemostasis

Clotting factors

Cofactors (e.g. calcium, vitamin K)

Signs of Dysfunction of Secondary Hemostasis

Large volume spontaneous bleeds

Excessive postoperative/postprocedural bleeding

Diagnostic Test Options for Secondary Hemostasis

PT

aPTT
ACT

Viscoelastic testing

Thrombin generation

Individual factor analysis

Therapeutic Strategies for Secondary Hemostasis Disorders

Treat primary disease

Clotting factor containing transfusion

Cofactor replacement (e.g vitamin K, calcium gluconate)

± antifibrinolytic drugs

Components of Fibrinolysis

Plasmin

tPA

Signs of Dysfunction of Fibrinolysis

Large volume spontaneous bleeds

Excessive postoperative/postprocedural bleeding

Diagnostic Test Options for Fibrinolysis

D-dimers

Viscoelastic testing

Therapeutic Strategies for Fibrinolysis Dysfunction

Antifibrinolytic drugs

Plasma-based transfusion

What are the three overlapping phases of the cell based model of coagulation?

Initiation

Amplification

Propagation

Cell Based Model of Coagulation Diagram

What are the initiating trigger for hemostasis in the cell based model of coagulation?

Tissue factor laden cells are the major initiating trigger for hemostasis

• Analogous to the extrinsic pathway in secondary hemostasis

What occurs during the amplification phase of the cell based model of coagulation?

Small amount of thrombin made during the initiation phase which supports platelet activation during the amplification phase

What happens in the propagation phase of the cell based model of coagulation?

Most closely resembles the intrinsic and common pathways, supports massive thrombin generation

What are primary hemostatic disorders due to?

Reduced platelet number (thrombocytopenia) or abnormal platelet function (thrombopathia)

What are mechanisms of action of thrombocytopenia?

Decreased production

Increased destruction

Consumption

Sequestration

Non-pathological

What are differential diagnoses for thrombocytopenia due to decreased production?

Primary marrow disease

• Infectious

• Immune mediated

• Neoplastic

• Idiopathic

• Toxins/drugs

  • Radiation

What are differential diagnoses for thrombocytopenia due to increased destruction?

Primary ITP

Secondary ITP

• Septic focus

• Vector-borne disease associated (e.g. ehrlichiosis, anaplasmosis, RMSF, dirofilariasis)

• Neoplasia

• Vaccination

  • Drug recation

What are differential diagnoses for thrombocytopenia due to consumption?

Acute hemorrhage

Sepsis

Disseminated intravascular coagulation

Microagniopathies/ vasculitis

What are differential diagnoses for thrombocytopenia due to sequestration?

Splenic torsion

Hypersplenism

Severe hypothermia

What are non-pathological causes of thrombocytopenia?

Inherited macrothrombocytopenia (e.g. CKCS)

What are causes of acquired intrinsic platelet dysfunction?

Platelet inhibitors

Uremia

Synthetic colloids

Myeloproliferative disease

Pit viper envenomation

Disseminated intravascular coagulation

Trauma-induced coagulopathy

What are secondary hemostatic disorders associated with?

Clotting factor deficiency or failure of their activation

What are differential diagnoses for acquired secondary hemostatic disorders?

Vitamin K deficiency

Vitamin K antagonism

Liver dysfunction

Citrate overdose

Severe hypothermia

Acidemia

Anticoagulants

Hemodilution

Disseminated intravascular coagulopathy

Trauma-induced coagulopathy

Angiostrongylus vasorum infection

What can disorders of accelerated fibrinolysis be associated with?

May occur associated with massive trauma (trauma-induced coagulopathy), acute liver dysfunction, and spontaneous hemoperitoneum

What are traditional hemostatic tests best suited for?

Detection of hypocoagulability

Buccal Mucosal Bleeding Time (BMBT)

• Most common method of assessing platelet function in small animals

• Normal BMBT is typically <3 minutes in dogs and <2 minutes in cats

• Crude indicator of primary hemostasis

  • Extraneous factors such as hematocrit and blood viscosity also influence the speed of clot formation

Platelet Closure Time

Obtained with an automated benchtop platelet function analyzer and provides similar infiromation to BMBT

How can platelet function be assessed?

With aggregometry or flow cytometry

• Whole blood multiple electrode impedance aggregometry is the option most conducive for clinical use

Prothrombin Time (PT)

Measured by adding tissue factor to a patient blood sample

Assesses the extrinsic and common pathways

Activated partial thromboplastin time (aPTT)

Assesses intrinsic and common pathways

Involves the addition of kaolin and a source of phospholipids to patient blood

Activated Clotting Time (ACT)

Modified aPTT with utility in situations where a high concentration of heparin is present (e.g. extracorporeal blood circuits used for hemodialysis)

PT and aPTT in Critically Ill Patients

• Prolonged PT with normal aPTT - issue with extrinsic and/or common pathways (e.g. factor VIII deficiency in hemophilia A, synthetic colloid administration)

• Common to see prolongation of both PT and aPTT in the critically ill Vitamin K-dependent factor deficiency (factors II, VII, IX, X)

  • Results in PT prolongation in excess of aPTT since factor VII has the shortest half-life of these factors

• Mild to moderate prolongation of aPTT is commonly seen in patients with systemic inflammation but doesn't normally correspond to increased bleeding risk

• Point-of-care aPTT results are more prone to inaccuracy than PT

• If abnormalities in these screening tests are identified, consider measurement of individual clotting factors on a case by case basis

How to you evaluate fibrinolysis?

Fibrin(ogen) degradation products and D-dimer assays

Animals with DIC usually have elevated D-dimers

• D-dimers are nonspecific indicators of clot turnover and should not be used as a sole indicator or DIC

What does viscoelastic monitoring provide information on?

The rate of clot formation, clot strength, and rate of fibrinolysis

What are viscoelastic variables that are indicators of rate of clot formation?

Reaction (R) time (TEG), Clot time (CT) (ROTEM), Clot time (CT) (VCM)

Kinetics (K) (TEG), Clot formation time (CFT) (ROTEM), Clot formation tests (CFT) (VCM)

Alpha (angle) (TEG), Alpha (ROTEM), Alpha (VCM)

What is reaction (R) time/clot time(CT)/clot time (CT) affected by?

Factors XII and XI

What is kinetics (K)/clot formation time (CFT)/clot formation tests (CFT) affected by?

Fibrinogen, factor XIII, and platelets

What is alpha (angle)/alpha/alpha affected by?

Fibrinogen, factor XIII, and platelets

What are viscoelastic indicators of clot strength?

Maximum amplitude (MA) (TEG), maximum clot firmness (MCF) (ROTEM), maximum clot firmness (MCF) (VCM)

Elastic shear modulus (G) (TEG)

What is maximum amplitude (MA)/maximum clot firmness (MCF)/maximum clot firmness (MCF) affected by?

Affected by platelets and fibrinogen

What does elastic shear modulus (G) indicate?

Indicates maximum clot strength

What is elastic shear modulus (G) affected by?

Platelets and fibrinogen

Elastic Shear Modulus (G) Equation

G = 5000 x MA/(100-MA)

What is a viscoelastic indicator of the rate of fibrinolysis?

Lysis (Ly/30/60) (TEG), Clot lysis (CL30/60) (ROTEM), Lysis index (Li30/45) (VCM)

What is lysis (Ly30/60)/clot lysis (Cl30/60)/lysis index (Li30/35) affected by?

Plasmin activity

What are monitoring options for aspirin?

PFA-100 (using collagen-epinephrine)

Platelet aggregometry (using arachidonic acid)

TEG-platelet mapping (using arachidonic acid)

What are monitoring options for clopidogrel?

PFA-100 (using ADP-collagen)

Platelet aggregometry (using ADP)

TEG-platelet mapping (using ADP

Monitoring Options for Warfarin

aPTT

INR

Monitoring Options for Unfractionated Heparin

Drug specific anti-Xa activity

PT

ACT

TF and kaolin activated TEG (RapidTEG)

Monitoring Options for Low Molecular Weight Heparin

Drug specific anti-Xa activity

Monitoring Options for Direct Oral Anticoagulants

Drug specific anti-Xa activity

PT

Platelet Counts in Thrombocytopenia

• Degree of thrombocytopenia can be a helpful indicator of the likely cause of the disease

  • Consumptive processes such as acute hemorrhage, sepsis, and vasculitis typically result in platelet counts between 50,000 and 90,000/ul

  • Increased destruction, decreased production, ehrlichiosis infections, and DIC typically lead to more severe thrombocytopenia (<20,000/ul)

• Platelet count alone is an imperfect means of assessing primary hemostatic competence

• Spontaneous and procedural bleeding is unlikely when platelet counts are >50,000/ul provided no other hemostatic dysfunction is present

Acquired Platelet Dysfunction

• May occur with NSAID toxicity

• Dose dependent coagulopathy, characterized as an acquired vWF and factor VIIIa deficiency, described in animals administered large volumes of synthetic colloids

• May be encountered in disease states such as uremia, pit viper envenomation, and trauma-induced coagulopathy

Acquired Clotting Factor Dysfunction

• Acquired secondary hemostatic disorders are associated with a reduced number or activity of clotting factors

• Hypoperfusion and massive transfusion of citrate phosphate dextrose adenine (CPDA)-containing blood products have been associated with severe acidemia that may impair clotting factor activity

• Clotting factor consumption (e.g. DIC) is another mechanism of secondary hemostatic dysfunction

• Calcium is an important cofactor for clotting factors

  • Acute hypocalcemia may occur associated with citrate toxicity (e.g. massive transfusion) and may contribute to a hypocoagulable tendency

Dilutional Coagulopathy

• Animals with acute hemorrhage will lose whole blood and consume clotting factors and platelets in response to hemorrhage

• Compensatory fluid shifts of clotting factor deficient fluid from the interstitium to the intravascular compartment may occur, in addition to the administration of synthetic replacement fluids devoid of clotting factors

Vitamin K Absence or Antagonism

• Vitamin K absence or antagonism is the most common reason for decreased clotting factor activity in small animals

  • Ingestion of anticoagulant rodenticides containing warfarin or coumadin

    • Inhibit vitamin K epoxide reductase, an enzyme needed for vitamin K recycling

    • Hydroquinone (reduced vitamin K) must be present for activation of the vitamin K-dependent coagulation factors (II, VII, IX, and X)

  • Vitamin K absence can also be caused by severe liver dysfunction and intestinal malabsorption

Liver Dysfunction Causing Coagulopathy

• Normal hemostatic function is related to liver function since clotting factors, endogenous anticoagulants (e.g. protein C) and fibrinolytic proteins are synthesized in the liver

• Hemostatic dysfunction typically occurs in the face of more advanced liver disease

  • Caused by reduced factor synthesis, vitamin K deficiency, and acquired platelet dysfunction

• Chronic hepatopathies are less likely to exhibit hyperfibrinolytic tendency, but hypocoagulability is common with more severe disease

• Hypercoagulability has been identified in some animals with liver disease (e.g. congenital portosystemic shunts) and could lead to serious adverse effects (e.g. portal vein thrombosis)

• Spontaneous hemorrhage is less common in animals with liver disease but there is considerable concern for bleeding if these animals undergo invasive procedures

Disseminated Intravascular Coagulation

• A precipitating trigger (e.g. inflammation, sepsis, heat stroke) incites systemic activation of coagulation, resulting in massive thrombin generation and widespread clot formation

• Two major detrimental effects of extensive thrombosis

  • Microthrombosis may lead to tissue hypoperfusion and resultant tissue dsyfunction

  • Massive thrombosis leads to clotting factor consumption and fibrinolysis activation leading to a bleeding tendency

• Early in the disease course, hypercoagulability and DIC will be asymptomatic (nonovert) and may be missed by conventional laboratory diagnostic tests

• As consumption continues, more pronounced bleeding tendency will be appreciated (overt DIC)

• Bleeding characteristics may have features of both primary and secondary hemostatic dysfunction

• Potential hemostatic abnormalities in DIC include thrombocytopenia, prolongation of PT and aPTT, hypofibrinogenemia, elevated D-dimers, and reduced antithrombin activity

Trauma-Induced Coagulopathy

• In people, an early-onset endogenous hemostatic dysfunction, termed trauma-induced coagulopathy (TIC) occurs in severely injured patients with shock

• Mechanisms

  • Increased generation of activated protein C by high concentrations of thrombin-thrombomodulin and endothelial damage favoring an anticoagulant and hyperfibrinolytic state

• Limited evidence to suggest this occurs in traumatized dogs and cats

• Good evidence that an iatrogenic resuscitation-associated coagulopathy occurs in both people and animals secondary to dilution with synthetic fluids, combined with the presence of acidosis, hypothermia, and hypocalcemia

Hyperfibrinolylsis

• Identified in some disease state, especially trauma-induced coagulopathy (TIC) and acute liver disease

• Dogs with more severe hemodynamic compromise, assessed by a higher plasma lactate concentration and greater volume of plasma administered, were more likely to demonstrate a hyperfibrinolytic tendency

What are the three categories of treatment options for coagulopathy?

Administration of transfusion products

Hemostatic agents

Therapies aimed at addressing the primary disease process

Administration of Transfusion Products for Coagulopathies

• Product used depends on the nature of the hemostatic dysfunction (e.g. platelet replacement for primary hemostatic disorders, clotting factor replacement for secondary hemostatic disorders)

Hemostatic Agents for Coagulopathies

• Desmopressin - facilitates vWF release from the endothelium

• Lysine analog antifibrinolytic drugs (e.g. epsilon aminocaproic acid, tranexamic acid)

  • Not recommended in DIC since they may worsen clotting factor consumption due to clot persistence

What are the three pillars of patient blood management?

Detection and treatment of hemorrhage

Reduction in further blood loss

Harnessing patient specific physiologic reserves

How do primary hemostatic defects manifest?

Surface or mucosal bleeding

How do disorders of secondary hemostasis present?

Body cavity hemorrhage, hematomas, subcutaneous, intramuscular, or joint hemorrhage

Generalized Bleeding

Occurring in multiple parts of the body

Localized Bleeding

Confined to one particular area

Differentials for Hemorrhage

Disorders of primary or secondary hemostasis

Hyperfibrinolysis

Traumatic tissue damage

Intra- or postoperative complications

Rupture of mass lesions

DIC can result in uncontrolled severe bleeding, has a high mortality rate

• Most common cause of DIC in the ICU is sepsis

Common Acquired Primary Causes of Bleeding in the ICU

Immune-mediated thrombocytopenia

Bone marrow disease

Uremia

Hyperviscosity syndrome

Antiplatelet medications (clopidogrel)

Nonsteroidal antiinflammatory medications

DIC

Splenic Sequestration

Common Acquired Secondary Causes of Bleeding in the ICU

Liver failure

Anticoagulant medications (direct thrombin inhibitors, factor X inhibitors, warfarin)

Anticoagulant rodenticides

Consumptive processes

Extracorporeal therapies

Dilutional

Hypothermia (<34*C)

Acidemia (pH<7.2)

Hypocalcemia (ionized Ca <1 mmol/L)

Vitamin K1 deficiency

Common Causes of Fibrinolysis in the ICU

Acute traumatic coagulopathy

Liver disease

Neoplasia

Breed predisposition (Greyhounds)

Common Vascular Causes of Bleeding in the ICU

Infectious diseases (e.g. sepsis, rickettsial diseases)

Cushing’s disease

Hyperviscosity. syndromes

Drug-induced

Neoplasia

Trauma

Surgical bleeding

Ruptured Mass

Diagnostic Approach for Patients Exhibiting Cutaneous and Mucosal Bleeding

• Automated platelet count in conjunction with a blood smear is the first diagnostic test of choice to rule out a severe thrombocytopenia

• If platelet count is normal, platelet function testing can be performed

  • Requires fresh platelets that are tested ideally within 2.5 hours of collection

  • May not identify the specific reason for platelet dysfunction

• Buccal mucosal bleeding time could be considered as a simple bedside test of platelet function

  • Disadvantages

    • Operator dependent variability

    • Lack of ability to detect mild defects in platelet function

    • Unreliable prediction of surgical bleeding

• Platelet mapping viscoelastic test (VET) assays can quantify the degree of platelet dysfunction due to clopidogrel or aspirin administration

  • Insensitive for the diagnosis of platelet dysfunction and a severe decrease in platelet count and function must be present to affect the VET

Diagnostic Approach for Patients with Bleeding Consistent with Dysfunction of Secondary Hemostasis

Coagulation testing, consisting of activated clotting time (ACT), prothrombin time (PT), activated partial thromboplastin time (PTT), D-dimers, and VETs, should be considered

What results of coagulation testing are reflective of coagulopathy?

Prolonged clotting times >1.5-2 times the patient baseline or reference value

What is one of the most reliable predictors of massive transfusions in human patients?

An international normalized ratio (PT standardized to thromboplastin reagent) >1.5

What are prolongations of PT and PTT associated with in human and veterinary patients?

Blood loss and increased mortality

Sensitivity of Coagulation Tests

• Not much evidence that the standard plasma-based coagulation tests accurately reflect a clinical coagulopathy or are useful in guiding transfusion therapy in bleeding patients

• Standard coagulation tests are an insensitive indicator of clotting factor deficiency with 60-70% of the factor level decrease necessary for prolongation of PT and PTT

• ACT is less sensitive than PTT with less than 10% of factor activity necessary for the ACT prolongation

  • ACT, unlike PTT< may be affected by severe thrombocytopenia and may be increased in patients with platelet counts of less than 10,000/uL

• VET is a more sensitive diagnostic modality for identifying hemostatic abnormalities in bleeding patients

  • Advantage is its ability to evaluate the interaction of cellular components and coagulation factors, which is more indicative of in vivo hemostasis

  • VET-guided transfusion protocols have been documented to result in less blood product use, decreased morbidity, and possibly decreased mortality than protocols based on standard tests of hemostasis

• Imaging is useful for quantifying the degree and extent of the hemorrhage as well as identifying potential anatomic targets to address

What is the ideal resuscitative fluid for significant blood loss?

Whole fresh blood (WFB)

When is isotonic crystalloid therapy the recommended resuscitation fluid?

• Isotonic crystalloid therapy is the recommended resuscitation fluid for the initial treatment of patients suffering from hemorrhagic shock, especially when blood product therapy is not immediately accessible

  • Recommendations for resuscitation have recently shifted, with current guidelines favoring the administration of conservative volumes of crystalloids to avoid dilution of blood cells and coagulation factors, hypothermia, and acidosis, and to prevent formed clot dislodgement

What can be used for low volume fluid resuscitation?

Hypertonic saline

• May be a crystalloid of choice in polytrauma patients with suspected traumatic brain injury

Synthetic Colloids for Hemorrhagic Shock Resuscitation

Synthetic colloids have been used for hemorrhagic shock resuscitation but are not superior to crystalloids and can inhibit platelet function as well as induce a coagulopathy

Administration of Blood Products for Hemorrhagic Shock

• Administration of blood products in a 1:1:1 unit ratio of packed red blood cells (pRBCs):fresh frozen plasma (FFP): platelet concentrates, as well as additional fibrinogen concentrates in cases of severe hypofibrinogenemia, has proven beneficial in bleeding human trauma patients

  • This protocol has resulted in the lowest mortality rate when compared to other ratios

• No evidence for an ideal ratio in veterinary medicine

  • Fresh platelet concentrates are routinely not available so reasonable to use a combination of FFP and pRBCs

  • Consider high ratios of FFP to pRBCs on a volume basis in veterinary patients with active bleeding

Target Hematocrit/Hemoglobin

• Target hematocrit/hemoglobin concentration is controversial

  • Some recommend a higher hemoglobin threshold of 10 g/dl as a goal in actively bleeding humans and patients with comorbidities that may benefit from higher oxygen content

  • Conservative transfusion triggers that use a hemoglobin of 7 g/dl have been shown to be superior in some groups of bleeding patients

Hypotensive Resuscitation

• Strategy to minimize further blood loss and hemodilution from nonsanginous fluid administration

• Refers to maintaining mean arterial pressure (MAP) in the range of 60 mm Hg for up to 90 minutes

• Typically culminates in the definitive management of hemostasis with surgery

• TBI is a contraindication, must reestablish a MAP of 90 mmHg to preserve cerebral perfusion

Triad of Death

Acidemia + Hypothermia + Coagulopathy

How is the triad of death prevebted in bleeding ICU patients?

• Prevention achieved with special focus on active rewarming and refraining from the administration of large quantities of crystalloids which results in dilutional anemia and coagulopathy

• Correction of the underlying cause of acidemia should be attempted

  • Bicarbonate administration to correct acidemia has not been shown to improve outcome in acidemic, critically ill patients

Vitamin K for Control of Bleeding

• Intake may be inadequate and its absorption and recycling may be compromised in patients with intrahepatic and posthepatic cholestasis

• Administration at 0.5-1 mg/kg subcutaneously every 24 hours should be considered for coagulopathy associated with liver disease and biliary obstruction

Desmopressin (DDAVP) for Control of Bleeding

• Synthetic analog of L-arginine-vasopressin

• Most commonly used in bleeding patients to release von Willebrand factor and factor VIII from Weibel-Palade bodies in endothelial cells

• Enhances the density of platelet surface glycoprotein receptors, increasing their adhesion potential

• Dose of 1 mcg/kg subcutaneously should be considered in patients with evidence of platelet dysfunction

  • Could be repeated every 24 hours for up to 3 days, but there is about a 30% reduction in efficacy compared to initial administration

Antifibrinolytic Drugs for Control of Bleeding

• Currently the mainstays of treatment of patients with severe bleeding due to acute traumatic coagulopathy, liver disease, and surgical bleeding associated with a number of procedures

• Aminocaproic acid and tranexamic acid

  • Act by competitively inhibiting the lysine-binding sites on plasminogen, which prevents the conversion of plasminogen to plasmin in addition to direct inhibition of plasmin action

  • Higher doses might be needed in veterinary patients than in humans

  • In patients with severe traumatic hemorrhage, should be administered as soon as possible and preferably within 3 hours of the traumatic event

Structure of Hemoglobin

• Hemoglobin is composed of four polypeptide chains (globins) each attached to a heme molecule

  • Heme is made up of a tetrapyrrole with a central iron molecule

  • Oxygen binds to the central iron molecule in the ferrous (Fe++) form

  • Each hemoglobin molecule carries four oxygen molecules

Pathophysiology of Carbon Monoxide Toxicity

• CO is absorbed rapidly through the lungs at the level of the alveolus

• Quantity of gas absorbed is dependent on minute ventilation (respiratory rate x tidal volume), duration of exposure, and concentrations of CO and oxygen in the environment

• Once absorbed in the blood and circulated throughout the body, a small amount of CO is oxidized to CO2, some remains as gas in solution, and some binds to proteins including Hb, myoglobin, and cytochromes in mitochondria

What are the two main mechanisms of CO toxicity?

Impaired oxygen delivery to tissues (hypoxia via dyshemoglobinemia)

Direct cellular toxicity