Blood product management during paediatric Cardio Pulmonary Bypass (CPB)

Principles

• Blood and blood product transfusion can have serious adverse effects.

• There is some good evidence that an Hct < 0.3 results in a worse neurological outcome in paediatric patients undergoing Cardio Pulmonary Bypass (CPB).

• The most common coagulation defect post CPB is a defect of platelet function and/or an absolute decrease in platelet number.

• There is limited need for FFP to treat coagulopathy in children post CPB.

• Neonates and infants have an immature coagulation system. Adult normal values do not apply for some tests.

• There are some patients who are more likely to bleed post CPB and in these patients there should be a lower threshold for coagulation factor administration.

• Antifibrinolytic treatment limits blood loss - aprotinin may be superior to high dose tranexamic acid in neonates.

• Coagulation tests should be performed after initial coagulation component treatment including TEG if available.

• TEG is a valuable POCT that provides rapid analysis on the clotting and fibrinolytic state of the patient. In patients at high risk of bleeding a heparinase TEG should be done during patient rewarming on CPB to guide blood product administration. Laboratory coagulation tests often take longer than 60 minutes to obtain, limiting their value in guiding which products to administer in the patient with ongoing bleeding.

• The role of recombinant factor VIIa is unclear but it can be effective in cases of ongoing bleeding without surgical solution and with relatively normal coagulation tests.

• If the patient is not bleeding, minor coagulation abnormalities should not be treated. Major abnormalities may need treatment.

• In the presence of aprotinin TEG results can be unreliable.

• Repeat any tests that are inconsistent with the patient condition.

Practice

Aim for a Hct on CPB of 0.3 in all patients on CPB

This may be slightly less in an older child having a straightforward procedure as it may be possible to avoid transfusion entirely in these patients. However the HCT should NEVER be less than 0.26.

In neonates, cyanotic patients, and those who have been very polycythemic preoperatively  (Hct > 0.6) a Hct > 0.35 should be targeted when coming off CPB and some of these patients may benefit from running their Hct on CPB at this level. The surgeon needs to be made aware of the Hct during rewarming so that the patient comes off bypass with an acceptable Hct.

Post bypass MUF is performed on most patients for 15-20 minutes. This removes excess water and haemoconcentrates the patient causing a rise in the haematocrit (usually 5-10 points above the Hct coming off bypass). MUF also allows for the transfusion of blood products without haemodiluting the patient.

Blood component therapy in the operating rooms (OR)

1. Platelets

   Patients < 5 kilograms undergoing CPB will usually undergo a platelet transfusion of 10-20 mL/kg while MUFing post bypass. Ideally these platelets should be single donor platelets ie one or more neonatal units or a single adult platelet pheresis unit. Aim is a platelet count > 100 E+9/L.

   Older patients undergoing redo surgery, DHCA, or prolonged CPB may also require platelet transfusion as will those who have been on aspirin pre-operatively.

   Platelets can have a serious negative inotropic effect on the heart immediately post CPB. In patients with poor myocardial function they need to be given very slowly and often accompanied by calcium boluses +/- a temporary increase in inotropes. It is advisable to delay platelet transfusion for 5-10 minutes after coming off CPB and starting to MUF in patients with poor ventricular function.

2. Cryoprecipitate

   Patients < 5 kilograms and those undergoing DHCA may develop low fibrinogen during CPB resulting in bleeding. Treatment is cryoprecipitate transfusion 10 mL/kg. For patients > 15 kg: 1 unit up to 25 kg then 1 unit per 25kg.

   Aim is to achieve a fibrinogen level > 1.5 g/L.
   Cryoprecipitate can be added to the bypass circuit during rewarming.

3. Fresh Frozen Plasma

   Fresh frozen plasma is not commonly indicated but if required is dosed at 10 mL/kg. As above neonates, long CPB times and hypothermia can deplete clotting factors. Patients who have been on warfarin pre-operatively will require FFP.
   Aim is INR < 1.5 and APTT < 60 seconds.
   FFP can be added to the bypass circuit during rewarming.

4. Prothrombinex (PCC Prothrombin Complex Concentrate)
   Can be used as an alternate to FFP though contains little Factor VII. It comes as a powder that needs reconstituting. It is available from blood bank for patients undergoing CPB.
   It is useful for patients who do not tolerate the volume load of FFP.
   Initial dose is 25 U/kg.

5. Activated Factor VII

   Ongoing bleeding without repairable surgical cause and with a relatively normal coagulation profile may be treated with activated factor VIIa. Initial dose is 30 micrograms/kg repeated every 10 minutes until bleeding stops or total dose is 90 micrograms/kg. In exceptional circumstances > 90 micrograms/kg may be given.

Notes

Do not treat coagulation results in isolation, i.e. if the patient is not bleeding then the coagulation does not have to be normalised.

Minimise bleeding by controlling systolic blood pressure and atrial filling pressures.

Avoid excessive volumes of blood component transfusion post CPB which can lead to atrial overdistension and exacerbate bleeding from atrial suture lines.

Patients should have a FBC and coagulation screen taken with their post protamine ACT. If they are at increased risk of bleeding they will also have a TEG done at this stage.

See the Paediatric CPB TEG algorithm for intepretation and treatment of coagulation defects diagnosed with TEG.