1. Technical Field
The invention relates generally to medical equipment, and more particularly to an infusion system that operates to introduce fluid into a patient.
2. Background Information
It is often necessary or desirable to infuse a flowable material or fluid, which may be a liquid, a gas, or a combination thereof, into a patient. One example is the administration of parenteral fluids to a patient.
A typical infusion system includes an infusion device (or flow control device) for delivering the fluid and conduit means for conducting the flowable material from the infusion device to the patient. The conduit means typically comprises flexible tubing leading from the infusion device and a cannula, such as a needle or catheter, for insertion into the vascular system of the patient. In normal operation, the infusion device delivers the fluid through the tubing and the needle to the vascular system of the patient.
One problem with infusion systems of that type is a condition known as infiltraticn. Infiltration is a condition in which infused fluid finds its way into extravascular tissues rather than simply being released into the blood stream. Such a situation occurs when the needle is not in communicator with the interior of the vessel into which the fluid is to be infused. When that occurs, fluid is infused into the interstitial spaces between layers of tissues. Thus, the patient is deprived of proper intravenous drug administration and is further subjected to possible toxic or caustic effects associated with infused fluids being in direct contact with body tissues.
Infiltration is not the only possible type of anomaly associated with intravenous therapy which can cause the fluid to be improperly supplied to the patient. Other conditions which can cause abnormal infusion, i.e., the fluid to be improperly supplied to the patient, include venous inflammation and swelling at the infusion site (phlebitis), clotting, and a wide variety of obstructions of the conduit means, such as kinking of the tubing which supplies the fluid to the patient. Many of these affect fluid flow characteristics in a manner similar to infiltration and can, therefore, be detected by infiltration detection devices.
The goal of an infiltration detection system is to identify an abnormal infusion condition as early as possible without generating an excessive number of false alarms. Early detection allows the attending medical staff to rectify the problem before significant damage has been done by the infiltration and before the patient has been deprived of a significant amount of the intravenous therapy. On the other hand, if the detection system is too sensitive, false alarms will result. That is very undesirable since, from a clinical perspective, establishing a new intravenous site can be difficult and time consuming. During the time necessary to start the new IV, which can be hours in some cases, the patient is not receiving the desired treatment.
Bobo U.S. Pat. No. 4,648,869 discloses a significant advance in the field of infiltration detection systems and methods. According to the Bobo patent, an infusion system infuses a test pulse of fluid to a patient. The test pulse creates a pressure wave response which can be monitor and used to detect if abnormal infusion has occurred.
Butterfield U.S. Pat. No. 4,710,163 discloses an infiltration detection system which uses the test pulse-pressure wave response concept of the Bobo patent. However, the Butterfield system compares the pressure wave response with a reference pressure wave response which represents the normal response when there is no infiltration. Specifically, the area between two curves representing these responses is used to attempt to detect infiltration. Thus, the Butterfield approach has the disadvantage of requiring that a normal pressure wave response be first determined and then stored for later comparison.
In other words, those infusion systems include a pressure transducer coupled to a microprocessor and suitable firmware or other programming that operate to monitor fluid pressure for purposes of detecting infiltration or other abnormal infusion condition. Such testing is sometimes called site checking or performing a site check and the Bobo and Butterfield systems perform the site check by infusing a test pulse of fluid to the patient, the test pulse creating a pressure wave response which can be monitored to detect infiltration or other abnormal infusion conditions.
The test pulse may be initiated in various ways, such as manually by depressing a pushbutton, or automatically under program control. In any case, the microprocessor examines the resulting pressure wave response and activates an abnormal-infusion-condition alarm if an abnormal infusion condition exists. The alarm serves to alert the attending medical staff that an abnormal infusion condition may exist so that corrective action may be taken before significant consequences develop.
It has been found that patient activity can induce artifacts in the pressure existing in the infusion system. These artifacts can be sufficient to create a false alarm condition or possibly to even mask a correct alarm condition. False alarms can mean wasted time and extra expense, effort, and patient involvement, as well as increased stress on responding personnel and adverse affects on morale, and so they represent a problem that needs to be overcome.