This invention relates to heart-lung machines, and more particularly to an automatic occlusion clamp that prevents retrograde blood flow through a centrifugal blood pump.
In a typical heart-lung machine of the type used in open-heart surgery, an extracorporeal blood circuit is established from the patient""s venous system through a venous reservoir, a blood pump and an oxygenator to the patient""s arterial system. This circuit takes over the function of the patient""s heart and lungs while the patient""s heart is stopped for the surgery.
The blood pump in the extracorporeal circuit is typically either a roller pump or a centrifugal pump. An advantage of the roller pump is that the blood line is always occluded at some point in the pump, so that there can be no retrograde blood flow in the circuit when the pump is stopped. A disadvantage is that a roller pump can convey air boluses through the line. Such air boluses need to be dealt with separately in order to avoid serious injury or death of the patient.
Centrifugal pumps, on the other hand, do not convey air boluses through the circuit. If an air bolus is applied to the intake of a centrifugal pump, the pump deprimes and needs to be reprimed and restarted. Because of this safety factor, centrifugal pumps are the preferred choice of many perfusionists.
A problem with centrifugal pumps is that they do not occlude the line, and that consequently, retrograde blood flow through the pump is possible when the pump is stopped, due to the pressure head in the patient""s arterial system. Such a retrograde flow drains blood from the patient and is medically unacceptable.
Retrograde flow through a centrifugal pump has been averted in the prior art by inserting into the extracorporeal circuit a one-way duckbill valve. The use of such a valve, though effective, does have two disadvantages: first, the shape of a duckbill valve causes turbulence at the exit end of the valve and thereby causes some hemolysis; and second, the duckbill valve, because it is part of the extracorporeal circuit, is a single-use item and therefore adds to the cost of patient disposables.
The present invention overcomes the above-described deficiencies of the prior art by providing an electrically or pneumatically operated occlusion clamp external to the blood line that is arranged to occlude the line, preferably between the centrifugal pump and the oxygenator, whenever the forward blood flow in the line essentially ceases. The clamp of this invention is designed to operate in a fail-safe mode, i.e. it will clamp the line shut in the event of a power failure. In combination with conventional devices that shut down the pump in the event of a low blood level condition in the venous reservoir and/or of the detection of an air bolus, the present invention provides a triple-action safety system.