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HEMOSTASIS IN CARDIAC SURGERY

Intraoperative Bleeding in Cardiac Surgery:   Operative Hemostasis is paramount

Surgicel                    Bone Wax                                         BioGlue                                                   Tisseel                    Floseal                       

                                                                          

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                                                  Activated Factor VII  -                                 RECOTHROM Thrombin                                  

                                                                            

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Bleeding Post Cardiac Surgery:
Acceptable rates of bleeding before surgical intervention may vary between surgeons, but are usually 2ml/kg/hr for the first 2 hours, 1ml/kh/hr for the next 3 hours and less than 0.5ml/kg/hr by 12 hours postoperatively.
Bleeding should always be on a downward trend.

Causes: Bleeding post cardiac surgery may be related to various abnormalities including
platelet related abnormalities, hypothermia post cardiopulmonary bypass, exposure to the extracorporeal circuit causing abnormalities of the intrinsic and extrinsic pathways, excessive thrombin generation and fibrinolytic activity.
Hypothermia slows enzymatic reactions of the coagulation cascade and impairs platelet function
Non- Surgical Bleeding may be related to the type of procedure, duration of cardiopulmonary bypass and drugs including inhibitors of thrombin and anti-platelet agents.
Excessive bleeding is suggested by clinical signs such as tachycardia, hypotension varying with respiration, a capillary refill of greater than 2 seconds, decrease urine output and a core-peripheral temperature difference of greater than 2 degrees.
Laboratory tests should include:
– Full blood count (FBC)
– Coagulation tests
– Blood gases
– Thromboelastography

Other investigations include a chest x-ray which may show widening of the mediastinum, pleural effusions and echocardiography (TOE/TTE) may demonstrate pericardial effusion and underfilled ventricles.

Emergency Resternotomy On Cardiac Intensive Care Unit: 
Resternotomy is usually carried out in theatre but may on occasions because of cardiac tamponade or excessive bleeding be carried out on CICU. Bleeding may be venous, atrial cannulation site, innominate , thymic , suprasternal, cardiac veins, mammary bed, bone marrow, left pulmonary artery, pacing wires sites and the raw surface of the myocardium.
Arterial bleeding may occur from the aortic cannulation site, aortomy, top ends, left atriotomy, vent sites (aortic, right superior pulmonary vein and left ventricular apex), vein/IMAsidebranch, mammary stump, coronary anastomosis, periosteal arteries.
The most common situations are:
• Cardiac tamponade
• Massive haemorrhage
• As part of resuscitation in the postoperative patient when diagnosis is uncertain.
Personnel
Staff should be familiar with the location and contents of the emergency resternotomy set.
• Have the nurse in charge, identify you a nurse, to act as your assistant (and yours alone).
• Call consultant cardiac anaesthetist
• Depending on the circumstances you may need a perfusionist – bear this in mind and call them earlier rather than later.
• Establish intravenous access with large bore intravenous catheters.
Anaesthetic Drugs
• Fentanyl
• Midazolan or propofol, the choice of which, and the dose, may be dependent on the circumstances.
• Paralyse – Atracurium is always in the CICU fridge
• Antibiotics – Any reopening should have teicoplanin 400-800mg
Other drugs
• Anticipate the need for going on bypass and have heparin drawn up
• Inotropes / vasoconstrictors
Fluids
• 2 drip stands, one each side of the bed
• Blood / HAES (Colloids)
• Pressure infusion devices and Fluid warming devices
• Clear the CVP line of any other infusions so that you have a clear port for administration of drugs and a ready means of flushing them in.
Airway
• 100% O2
• Beware of disconnection of ventilators in the mayhem
Think about:   • Hb • X match blood/blood products • ABG • K+ • Ca2+ • Gl • Coagulation studies • Hypothermia • Urine Output • Haemorrhagic controlling agents

Haemorrhage Control Agents:
Aprotinin:
Serine protease inhibitor - antifibrinolytic caused by plasmin inhibition
Aminocaproic and Tranexamic acid:
Synthetic lysine analogs bind to plasminogen –lysine binding sites, competitively inhibiting plasmin from binding to lysine residues on fibrin.
Fibrin glue: combination of fibrinogen, thrombin and factor XIII


Coagulation studies
 Tests of coagulation
test different parts and components of coagulation cascade
 Tests of fibrinolysis
 Qualitative assessment

PROTHROMBIN TIME
 Tests extrinsic and common pathway
 A source of tissue factor (thromboplastin) is added to citrated plasma
 Calcium chloride is added to overcome effect of citrate
 Time taken for clot to form is measured
 Normal value 11-15 seconds

Causes of prolonged PT
 Oral anticoagulation (warfarin)
 Liver disease-hepatocellular, obstructive-decreased absorption. of vitamin K
 Vitamin K deficiency
 Hypofibrinogenaemia
 Massive transfusion
 Inherited factor deficiency-VII, X,V
International Normalised Ratio (INR)

 Method to standardise PT between laboratories for monitoring anticoagulation with coumarins
 Ratio of PT: mean normal PT to the power of the ISI (International sensitivity index) of the thromboplastin used.
 Since sensitive thromboplastins ( ISI close to 1) are available, INR approximates the PT ratio.


INR in clinical practice
 Target ratio of 2-2.5 for DVT prophylaxis with warfarin
 2-3 for DVT, PE , TIA (transient ischaemic attacks)
 3-4.5 for prophylaxis of recurrent DVT, PE, prosthetic heart valves.
 Probably INR 2-3 for a mechanical aortic valve and 3-4 for mitral
 1.5 considered safe for surgery


APTT
 Tests intrinsic and common pathway
 Plasma incubated with phospholipid and kaolin to activate contact factors
Calcium chloride is then added.
Time to clot formation recorded
 Normal value 35-40 seconds
 Sensitivities of different phospholipids vary no method of standardizing available, so local therapeutic ranges needed.
 Used to monitor heparin therapy
 Target ratio of 2-4 used for treatment of DVT or PE

Prolonged APTT
 Heparin therapy
 Sample contamination by heparin
 Liver disease
 DIC
 Hypofibrinogenaemia
 Massive transfusion
 Inherited factor deficiency


PT/APTT Correction
 Patient’s plasma mixed with normal plasma and test repeated
 If test normal suggests factor deficiency
 If still prolonged, suggests presence of an inhibitor eg. Antibody or heparin
 Important- Normal APTT test will not detect factor deficiencies of up to 50%

Thrombin Time
 Tests the key reaction in coagulation cascade FIBRINOGEN → FIBRIN
 A solution of thrombin is added to platelet poor plasma and the time taken to form clot measured
 Very sensitive to low levels of heparin
 Heparin is the commonest reason for prolonged TT

Causes of prolonged TT
 Hypofibrinogenaemia
DIC
Fibrinolytic therapy
Massive transfusion
Inherited deficiency (rare)
 Dysfibrinogenaemia
inherited (rare)
acquired (liver disease)
 Raised FDP levels-DIC, liver disease
 Heparin

Reptilase test
 Snake venom added to plasma
 Converts fibrinogen to fibrin
 Unaffected by heparin
 If RT is normal and TT is prolonged, suggestive of heparin


Platelets
 Normally 150-400 x 10 9/l
 Bleeding time
a standard incision made on forearm
BP cuff inflated around upper arm to 40 mm Hg
Incision dabbed with filter paper every 30 seconds until bleeding stops
Normal value 2-9 minutes

Bleeding Time
Whole blood clotting time
 Bedside test of intrinsic and common pathways ( spontaneous coagulation in a glass tube without external reactive substance e.g. tissue fluid)
 1 ml blood added to each of 3 glass tubes at body temp.
 The first is tilted every 15 seconds until clotted, then the second, third etc.
 The time until the third is clotted is about 9-12 minutes

Other coagulation studies
 Specific factor assays
eg. Factor VIII assay
• Tests to assess fibrinolysis
 Fibrinogen assay
 normal value 1.5-4.0 g/dl
 Thrombin time
 Fibrinogen Degradation Products (FDP)
normally < 10mg/l, D-dimer normally <500ng/ml (D-dimer specific for plasminogen mediated breakdown of fibrinogen)
 Plasminogen assay
Clot lysis times needs bullet point stuff formatted



Point of care monitors

Activated Clotting Time
 Commonly used to monitor heparin anticoagulation in cardiac surgery
 Similar to whole blood except that celite or diatomaceous earth is added to blood for quicker result
 Automated device used to detect fibrin formation with a small bar magnet in the test tube
Hemochron- ACT Device
ACT
 The tube is placed in the device and rotated slowly
 The magnet starts to rotate when fibrin forms and activates the detector
 Normal value is 100-140 seconds
 Values of 480s times preheparin value adequate for cardiopulmonary bypass is this in the perfusion protocol
 ACT checked after protamine reversal to ensure near baseline values after CPB

Thromboelastography
 Thromboelastograph monitors hemostasis as a whole dynamic process instead of revealing information of isolated conventional coagulation screens
 Measures viscoelastic properties of blood as it is induced to clot under a low shear environment resembling sluggish venous flow could we have a hyperlink to instructions on using and interpreting TEG

Sonoclot
 Another qualitative analysis of coagulation
 Generates a qualitative graph known as ‘’sonoclot signature’’
 provides qualitative information as well on clot formation time, rate of fibrin polymerisation, clot retraction and fibrinolysis

Platelet Function Analyser Can we have one
 Detects acquired and inherited platelet disorders from a 1 ml sample of blood
 Simulates an invivo situation by aspirating blood thru’ a steel capillary tube and creating a shearing force
 This activates platelets
 Blood passed thru’ a collagen coated membrane with a central aperture- collagen either coupled with adrenaline or ADP
 Time for closure of the hole (Closure time) due to aggregation is noted