Clotting Times Flashcards
what is activated clotting times?
length of time required for whole blood to clot when exposed to an activate particle
what are the particles that blood is exposed to in ACT
kaolin
celite
glass
other negatively charged surface
what is the activator for the ACT test
celite
contact activating is used for which factor
F12
Hagemann
what are ACTs used for (3)
- assess the status of the pt’s overall hemostatic mechanism
- monitor the anticoagulant effect of various drugs used to modify the ability of a pt’s blood to form a clot
- determine the pt’s hemostatic status following reversal of heparin with protamine
historically, ACT are used to
manage heparin anticoagulation
minimum standard of care for heparin management is based on
the Lee and White test tube based procedure
First activated whole blood clotting time was described by who
Hattersley (1966)
- activate factor XII
- used to accelerate clot formation
ACT testing is required when….
CPB
minimum standard of care for monitoring anticoagulation
ACTs performed when (regarding in surgery).
- prior to bypass (baseline)
- every 20 to 30 minutes on bypass
- following reversal with protamine
ACTS are also performed (outside of surgery)
- ECMO: done every 2-4 hrs
- ICU/CCU: every 4-6 hrs during therapeutic heparinization
- IR
- VAD
- hemodialysis
- cardiac catheterization: following anticoagulant admin and prior to pulling the sheath
what is the earliest activator used for ACT test
Celite
what is prolonged ACT results caused by?
- factor deficiency: congenital and acquired
- hemodilution (CPB)
- rapid consumption of clotting factors (DIC)
- warfarin (Coumadin)
- heparin
- hypothermia
- very low platelet count (need platelets to make a clot)
- abnormal platelet function/platelet inhibitors (aspirin, plavix)
what is normal ACT result
80-120
what can cause shortened ACT results?
- activation during sample collection: intro of tissue activator, venous access through a hematoma, slow syringe fill
- delay in initiation of test following specimen collection: 60 sec for unanticoagulated sample, 120 sec for heparinized sample
i-Stat device for ACTs
- synthetic substrate that reacts with thrombin
- does not measure clot formation
what does heparinase ACT confirm
presence of heparin in a blood sample while performing HR-ACT
what does heparinase ACT look at
- presurgical assessment for presence of heparin
- confirm heparin reversal following protamine
- confirm heparin rebound
- identify the presence of heparin in a pt with post-operative bleeding
effect of CPB on hemostasis
- HEMODILUTION
- HYPOTHERMIA
- factor 7/tissue factor activation
- contact activation
- kinin generation
- complement activation & systemic inflammatory response
- shear stress (platelet activation)
- fibrinolysis
- anticoagulation/reversal
anticoagulant
ability to prolong coagulation
antithrombotic
ability to inhibit thrombus formation
detrimental effects of inadequate heparin dosing during CPB
- activation of the coagulation proteins, platelets, and inflammatory system
- generation of excess thrombin
- increased post-operative bleeding
- increased risk to patient associated with transfusion
Heparin management with the HMS plus
- heparin dose response (HDR)
- heparin protamine titration (HPT)
- high range ACT (HR-ACT)
heparin dose response (HDR)
- simultaneous evaluation of pt’s in-vitro response to multiple heparin doses
- projects dose of heparin required to increase pt’s ACT to the user defined target
- identify pt’s who are resistant to heparin
if you have a HDR result of less than 80
resistance to heparin
if you have a HDR more than 120
HIT?
high slope in HDR means…
sensitivity
mechanisms for heparin resistance
- AT3 deficiency
- IV nitroglycerine
- elevated levels of heparin binding proteins
congenital AT3 deficiency for heparin resistance is how common in population
rare <0.5%
aquired AT3 deficiency for heparin resistance is how common in population comes from
- pre-operative heparin
- renal failure
- liver disease
- increased consumption
- during CPB
pediatric AT3 deficiency for heparin resistance has what characteristics
- decreased AT3 synthesis
- higher RBC mass
how do you get IV nitroglycerine heparin resistance
high dose with levels of >350 ug/min
elevated levels of what heparin binding proteins can be a mechanism for heparin resistance
- PF4
- extracellular proteins
- growth factors
- enzymes
- factor VIII/vWF
what does an HMS plus HR-ACT tell us
- global picture of patient’s function coagulation status
- accepted test to indicate heparin effect
- information regarding individual patient response to heparin
what are some limitations of ACT during CPB
- not specific to heparin (hemodilution, hypothermia, congenital deficiencies, lupus anticoagulant)
- insufficient for determining protamine dose
- questionable as sole indicator of heparin reversal
what does HMS plus heparin protamine test (HPT) tell us
- heparin concentration (specific and quantitative)
- maintain constant heparin concentration
- basis for determining appropriate protamine dose
- quantitative verification of heparin neutralization
if there is too much protamine, what will you see in the ACT level?
rise of ACT level
results of good anticoagulation management (8)
- minimize thrombin generation
- preserve clotting factors
- reduced platelet activation
- decrease post-op bleeding
- decrease blood product utilization
- fewer surgical reps
- fewer complications
- improved pt outcomes
anticoagulation management is part of a multimodality approach to (3)
- minimize peri-operative blood transfusion
- improve outcomes in cardiac surgery
- STS/SCA guidelines
