Overview of anticoagulation
What does Aspirin do and how does it work?
under normal conditions thromboxane is responsible for the aggregation of platelets that form blood clots
prostaglandins function prostaglandins are local hormones produced in the body and have diverse effects including
the transmission of pain information to the brain
modulation of the hypothalamic thermostat
Mechanism of ASA inhibits the production of prostaglandins and thromboxanes through irreversible inactivation of the cyclooxygenase enzyme within platelets
acts as an acetylating agent where an acetyl group is covalently and irreversibly attached to a serine residue in the active site of the cyclooxygenase enzyme.
this differentiates aspirin different from other NSAIDs which are reversible inhibitors
Unfractionated Heparin (SQ)
binds and enhances ability of antithrombin III to inhibit factors IIa, III, Xa
HIT (heparin induced thrombocytopenia)
molecular name: enoxaparin
trade name: Lovenox, Clexane
has advantage of not requiring lab value monitoring
LMWH acts in several sites of the coagulation cascade, with its principal action being inhibition of factor Xa
reversed by protamine sulfate
trade name: Arixtra
has advantage of not requiring lab value monitoring
indirect factor Xa inhibitor (acts through antithrombin III)
studies show decreased incidence of DVT when compared to enoxaparin in hip fx and TKA patients
Risk highest bleeding complications
not to be used in conjunction with epidurals
Mechanism of anticoagulation inhibits vitamin K 2,3-epoxide reductase
prevents reduction of vitamin K epoxide back to active vitamin K
vitamin K is needed for gamma-carboxylation of glutamic acid for factorsII (prothrombin), VII (first affected), IX, X protein C, protein S
target level of INR (international normalized ratio) is 2-3 for orthopaedic patients
not achieved for 3 days after initiation
vitamin K (takes up to 3 days)
fresh frozen plasma (acts immediately)
difficult to dose requires the frequent need for INR lab monitoring
can have adverse reaction with other drugs including
others in the same class include apixaban (Eliquis) and edoxaban (Savaysa or Lixiana)
mechanism of action of these drugs can be deduced from the name.
direct Xa inhibitor
no current antidote- why you have to wait with surgery
andexanet alpha being investigated
8-hours (12-hours for apixaban)
urgent surgical procedures delayed until half-life spanned from last dose
reversible direct thrombin (factor IIa) inhibitor
idarucizumab (FDA approved Oct 2015)
an antifibrinolytic that promotes and stabilizes clot formation
studies have shown that TXA reduce perioperative blood loss and transfusion in THA and TKA
synthetic derivative of the amino acid lysine
competitively inhibits the activation of plasminogen by binding to the lysine binding site
at high concentrations, is a non-competitive inhibitor of plasmin
has roughly 8-10 times the antifibrinolytic activity of ε-aminocaproic acid
10-20 mg/kg initial bolus dose followed by repeated doses of the initial TXA dose every 3 hours for 1-4 doses
10-20mg initial bolus followed either by an infusion of 1-10 mg/kg/hr for 4-30 hours
topical application is as effective as IV
sprayed onto open wound at completion of procedure
no detectable TXA in the bloodstream after topical application
<5% of the drug is metabolized
biological half-life in joint fluid is 3h, present in tissues for up to 17h
systematic review shows no increase in thromboembolic events
relatively few adverse reactions have been reported in the arthroplasty literature
Tranexamic acid (TXA) works through the competitive inhibition of plasminogen activation.
TXA (Lysteda) is an antifibrinolytic that promotes and stabilizes clot formation. It competitively inhibits the activation of plasminogen by binding to the lysine binding site. TXA is effective in reducing the need for blood transfusions while not increasing the risk of VTE and renal complications. However, it is still advised that patients with cardiac stents and previous thromboembolic events including ischemic stroke not be administered TXA.
Herbal supplements that affect bleeding:
gingko, ginseng, and garlic have been found to increase the rate of bleeding
related to effect on platelets
proper history taking can avoid complications
Increased warfarin effect (increase INR)omega-3 fish oil
affects platelet aggregation and vitamin K dependent coagulation factors
Reduced warfarin effect (reduces INR)
direct warfarin antagonist (reduces INR)
St John's wort
increases catabolism of warfarin (reduces INR)
where do Anticoagulants act on the clotting cascade?
what are the criteria vis MSIS for an infected periprosthethic joint?
What are the mechanism of actions for heparin, aspirin, warfarin, rivoxaban, dabigatran
the big Atran--
Warfarin inhibits vitamin K 2,3-epoxide reductase, thereby limiting the production of vitamin K-dependent clotting factors (II, VII, IX, X) as well as Protein C and Protein S.
Aspirin inhibits the production of prostaglandins and thromboxanes through irreversible inhibition of cyclooxygenase (COX, 1 and 2) and thus inhibits platelet aggregation.
Rivaroxaban is a direct inhibitor of factor Xa.
Dabigatran is a direct thrombin inhibitor.
Describe Transaminic Acid:
Factor Ia is fibrin. The enzyme that breaks down fibrin is plasmin. Tranexamic acid (TXA) is an antifibrinolytic that prevents the activation of plasmin from the inactive zymogen plasminogen.
Tranexamic acid competitively inhibits the activation of plasminogen to plasmin by binding to specific sites on both plasminogen and plasmin. Tranexamic acid has roughly eight times the antifibrinolytic activity of an older analogue, e-aminocaproic acid. It is used during joint replacement surgery to reduce blood loss and the need for transfusion.
Watts et al. review strategies for minimizing blood loss and transfusion. They recommend 1g of TXA prior to incision, and 1g at wound closure. They also recommend giving fluids for symptoms of anemia, rather than transfusion, as even high risk patients do well with sufficient intravascular volume even with low hemoglobin levels.
what are the half-lives of anticoagulation medications as it relates to surgery?
Warfarin, which is dosed daily, can take 72 to 96 hours to reach therapeutic levels. It has a plasma half-life of 36 to 42 hours. Low-molecular heparins have a plasma half-life of 4 to 5 hours, and fondaparinux has a half-life of 17 to 21 hours. Warfarin will not affect the International Normalized Ratio (INR) until 2 to 3 days after it is given. Patients on chronic warfarin therapy should have treatment stopped 3 to 5 days before elective surgery to allow the INR to normalize.
Xarelto is 8-12 hours. have to hold urgent surgery for those on it.
What herbal supplements affect platelets
The three G's
what is the clotting cascade's final product?
converts soluble fibrinogen to insoluable fibrin
Review the genetic components of hypercoagulability:
List the risk factors for thromboembolic disease:
what are the recommendations on preventing VTE on arthroplasty?
Miller's brief review of pharmacologic treatment for SVT prophylaxis:
Surgical Care Improvement Project (SCIP) quality measures require DVT prophylaxis.
Irreversibly binds and inactivates COX in platelets, thereby reducing thromboxane A2
Weakest: Use of IPCD encouraged
Low bleeding risk: Should be considered for patients at higher risk for bleeding.
Prevents vitamin K γ-carboxylation in liver
Inhibits factors II, VII, IX, X, and proteins C and S
Vitamin K and fresh frozen plasma can reverse
Multiple reactions with drugs and diet
Must be monitored with international normalized ratio (INR; goal, 2–3)
Activates antithrombin III (ATIII), which then inactivates factor Xa and thrombin
Protamine sulfate can reverse
Short half-life: 2 hours
High bleeding rate in arthroplasty
Binds platelets—heparin-induced thrombocytopenia
Low-molecular-weight heparin (LMWH)
Reversibly inhibits factor Xa through ATIII and factor II
Protamine sulfate can reverse•
No monitoring needed
Less heparin-induced thrombocytopenia
Higher risk for bleeding than with warfarin
Fondaparinux (akin to oral heparin)
Irreversibly but indirectly inhibits factor X through ATIII
Higher risk for bleeding than with LMWH
Direct Xa inhibitor
Higher risk for bleeding than with LMWH
Direct thrombin (IIa) inhibitor
Intramuscular and oral (dabigatran) versions
Inferior vena cava (IVC) filter use: controversial
Should be considered in following conditions:
Contraindication to prophylaxis
Prior complication of prophylaxis
How do you assess cardiac risk factors prior to surgery?
American College of Cardiology/American Heart Association (ACC/AHA) elements for assessing risk
Clinical risk factors in perioperative cardiac risk
Unstable/severe angina, recent MI (<6 weeks)
Worsening or new-onset CHF
Atrioventricular (AV) block
Symptomatic ventricular dysrhythmia: bradycardia (<30 beats/min), tachycardia (>100 beats/min)
Severe aortic stenosis or symptomatic mitral stenosis
Prior ischemic heart disease
Renal insufficiency (creatine >2 mg/dL)
Functional exercise capacity—measured in metabolic equivalents (METs) MET: 3.5 mL O2 uptake/kg/min
Perioperative risk elevated if unable to meet 4-MET demand
Walk up flight of steps or hill (= 4 METs)
Heavy work around house (>4 METs)
Can patient walk four blocks or climb two flights of stairs?
Please quantify surgery specific risks by procedure:
High risk (>5% risk of death/MI)
Aortic, major or peripheral vascular procedures
Intermediate risk (1%–5% risk of death/MI)
Orthopaedic, ENT, abdominal/thoracic or procedures
Low risk (<1% risk of death/MI)—usually do not need further clearance
Ambulatory surgery, endoscopic or superficial procedures
What are cardiac recommendations prior to surgery?
Twelve-lead ECG if:
CAD and intermediate-risk procedure
One clinical risk factor and intermediate-risk procedure
Noninvasive evaluation of left ventricular function if:
---Three or more clinical risk factors and intermediate- risk procedure
---Dyspnea of unknown origin
---CHF with worsening dyspnea without testing in 12 months
β-Blockers and statins should be continued around the time of surgery.
Acetylsalicylic acid (ASA) should be stopped 7 days prior to surgery.
Cardiology consultation should be considered for patients taking other agents (clopidogrel, prasugrel).
Risk of stent thrombosis balanced with that of surgical bleed
What are measures of shock recovery?
Lactate—indirect marker of tissue hypoperfusion
Best measures of adequate resuscitation:
Clinical measure of organ function: urine output more than 30 mL/h
Laboratory measure: serum lactate less than 2.5 mg/dL
Review the types of shock and their clinical presentation:
High spinal cord injury (also anesthetic accidents)
Loss of sympathetic tone and of vasomotor tone of peripheral arterial bed
Bradycardia, hypotension, warm extremities
Treatment: vasoconstrictors and volume
Septic shock (vasogenic)
Number one cause of ICU death
Bacterial toxins stimulate cytokine storm.
Examples: gram-negative lipopolysaccharides, toxic shock superantigen
Inflammatory mediators cause endothelial dysfunction and peripheral vasodilation
Identification and treatment of infections
Prompt resection of dead tissue
Bad pump: Extensive MI, arrhythmias
Blocked pump (obstructive shock)
Massive “saddle” pulmonary embolism
Beck triad: hypotension, muffled heart sounds,
neck vein distension
Decreased systolic BP with inspiration
Most common shock of trauma
Volume loss from bleeds or burns
“Third spacing” also a cause
Neuroendocrine response: save heart and brain
BP may be normal
Pale, cold, clammy extremities
Percentage of blood loss key to symptoms/signs:
Class I: up to 15% blood volume loss
Vital signs can be maintained.
Pulse below 100 beats/min
Class II: 15%–30% blood volume loss
Tachycardia (>100 beats/min), orthostatic,
Increased diastolic BP
Class III: 30%–40% blood volume loss
Decreased systolic BP
Confusion, mental status changes
Class IV: more than 40% blood volume loss
Life threatening; patient is obtunded
Narrowed pulse pressure
IImmeasurable diastolic BP
First, ABCs of resuscitation: then, bleeding must be stopped.
Blood products make better resuscitation fluids than saline.
How to address perioperative pulmonary issues around surgery:
Higher in cases that involve thorax such as scoliosis
Highest in patients with prior disease
Spinal/epidural anesthesia favored over general
Medical treatment should be maximized around surgery.
Symptomatic COPD: anticholinergic inhalers (ipratropium; May require corticosteroids
Presence of wheezes or shortness of breath: β-agonist inhalers (albuterol)
Perioperative oral steroids safe
Systemic glucocorticoid should be considered if forced expiratory volume in 1 minute (FEV1) or peak expiratory flow rate (PEFR) is below 80% predicted values/personal best.
Like the associated cough, the workup is usually nonproductive.
Deep breathing/incentive spirometry—equally effective
Postoperative pneumonia takes up to 5 days to manifest.
Productive cough, fever/chills, increased WBC count
Radiograph: pulmonary infiltrates
Smoking cessation improves outcomes
Patients should stop 6–8 weeks preoperatively.
Nicotine supplements do no harm to wound.
Fewer pulmonary complications
Smokers have six times more pulmonary complications.
Fewer wound healing issues and wound infections
Lower nonunion rate
Shoulder, neck, and thoracic pain in smokers
Prompts careful evaluation of lung fields
Superior sulcus tumor (Pancoast tumor)
Intrinsic atrophy of hand—C8–T1
Pulmonary failure due to edema (see Fig. 1.56A)
Complement pathway activated
Increased pulmonary capillary permeability
Intravascular fluid floods alveoli
Hypoxia, pulmonary HTN
Right heart failure
Blunt chest trauma, aspiration, pneumonia, sepsis
Shock, burns, smoke inhalation, near drowning
Orthopaedic: Long-bone trauma
Tachypnea, dyspnea, hypoxia, decreased lung compliance
Pao2/fio2 ratio below 200
Radiographs: diffuse bilateral infiltrates, “snowstorm”
CT: ground glass appearance
Treatment: Aggressive supportive care
Prompt diagnosis and treatment of musculoskeletal infections:Prompt treatment of long-bone fractures
Ventilation with positive end-expiratory pressure (PEEP)
Describe Fat Emboli Syndrome:
Petechial rash: fat to skin
Neurologic symptoms: fat to brain
Mental status changes: confusion, stupor
Rigidity, convulsions, coma
Pulmonary collapse: fat showers lung
ARDS: hypoxia, tachypnea, dyspnea
Associated with long-bone fractures
Characterize the common blood disoders as it relates to surgery:
Common inherited bleeding disorders:
Vonwillebrands disease AD (Vonwillebrands factor)
Hemophilia Ax-linked recessive
Hemophilia B. Christmas
Von Willebrand disease: autosomal dominant
Most common genetic coagulation disorder
Von Willebrand factor dysfunction
Binds platelets to endothelium
Carrier for factor VIII
Hemophilia A (VIII): X-linked recessive
Hemophilia B (IX) Christmas disease: X-linked recessive