The patient was 15.3kg and presented requiring re-sternotomy for LVOTO relief. An appropriate size oxygenator and tubing combination were selected, and the circuit primed with a blood, albumin, Hartmanns mix and 2500in heparin. Following a test-dose aprotinin was added to the circuit.
Prior to the initiation of cardiopulmonary bypass, the baseline ACT was within normal range. Following a heparin dose of 400iu/kg (6,000iu) the ACT was sub optimal for bypass at 367 seconds. After discussion with the anaesthetist a further 1,000 units of heparin was administered to the patient and ACT repeated. Subsequent ACT was again sub-optimal at 409 seconds. Further discussion took place with the anaesthetist and the two perfusionists for the case regarding the need for additional heparin doses. It was agreed that this was an adequate level of anticoagulation to proceed with bypass. The unit protocol states an ACT of 480 seconds is used for CPB.
On commencement of bypass the first ACT was below the required level at 254 seconds. A further 2,000 units of heparin was administered to the patient. ACT was repeated after adequate time to circulate through the system and was again low at 458 seconds. Therefore, a further dose of 1,500 units of heparin was administered. Repeated ACT showed this to be within the normal range for bypass, in excess of 500 seconds. At this point it was noted that venous levels were dropping dramatically, and it appeared that the venous filter was clotting off. A discussion took place between the perfusionist and the surgeon as to the course of action to be taken. It was decided the venous reservoir should be changed out before proceeding any further with the operation. Patient was prepared for coming off bypass by rewarming and filling the heart to achieve adequate cardiac output. The venous reservoir was changed out uneventfully, and cardiopulmonary bypass recommenced without any issues. Subsequent ACTs during the case were all in excess of 500 seconds. The operation was completed, and the patient weaned successfully. The patient recovered fully, and no untoward effects were noted.
Note: When the case was performed the unit had recently transitioned from using Haemochron celite tubes to Haemochron junior cartridges for ACT determination. This change in technique is widely known (and reported in the analyser information) to produce lower measurements for a sample of blood. This information was taken into account during the decision making.
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Learning Outcomes:
Following the case discussions were made regarding whether the patient was inadequately heparinised or whether another factor has caused the reservoir clot to develop e.g. suction, unknown patient factor, anti-thrombin III deficiency.
The case did deviate from the protocol, but it was felt appropriate in the context of the situation. This has stimulated a departmental review of practice particularly in view of introducing a new, different measuring technique and whether the protocol should be altered because of this.
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