Apparatus and method for monitoring air emboli during extracorporeal

Abstract

Disclosed is a method and apparatus for detecting the presence of an embolism, such as air, during extracorporeal circulation in tubing carrying blood or other fluid such as would be present in the use of an artificial kidney machine. Electrodes are placed near the tubing to monitor the impedance thereof as well as the impedance of the fluid passing therethrough. An oscillator is attached to the electrodes and puts out a signal, the frequency of which is proportional to the basic impedance of the tubing and fluid. When an air bubble or the like passes the electrodes, the impedance will change causing a change in the frequency of the signal of the oscillator. The difference between the normal frequency and the changed frequency is indicative of the size of the embolism. Means are provided so that if a single embolism is large enough to cause damage to the patient or if a number of smaller emboli accumulate to the point of potentially causing damage to the patient, an alarm may be sounded or other remedial measures, such as system shutdown, could be taken. In addition, should the basic impedance of the fluid change, means are provided to prevent a false indication of an embolism.