HEMOSTASIS IN CARDIAC SURGERY
Intraoperative Bleeding in Cardiac Surgery: Operative Hemostasis is paramount
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
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.
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.
• 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
• Anticipate the need for going on bypass and have heparin drawn up
• Inotropes / vasoconstrictors
• 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.
• 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:
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
Tests of coagulation
test different parts and components of coagulation cascade
Tests of fibrinolysis
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
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
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
Sample contamination by heparin
Inherited factor deficiency
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%
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
Inherited deficiency (rare)
acquired (liver disease)
Raised FDP levels-DIC, liver disease
Snake venom added to plasma
Converts fibrinogen to fibrin
Unaffected by heparin
If RT is normal and TT is prolonged, suggestive of heparin
Normally 150-400 x 10 9/l
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
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
normal value 1.5-4.0 g/dl
Fibrinogen Degradation Products (FDP)
normally < 10mg/l, D-dimer normally <500ng/ml (D-dimer specific for plasminogen mediated breakdown of fibrinogen)
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
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
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
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