Many medical procedures involve the extraction and replacement of flowing blood or other biological fluid such as plasma from, and back into, a donor or patient. When the fluid is outside the patient it is conducted through machinery that processes the fluid. Examples of treatment processes include, but are not limited to, hemodialysis, hemofiltration, hemodiafiltration, blood and blood component collection, plasmapheresis, apheresis, and blood oxygenation.
The processes listed above, and others, may involve the movement of large amounts of fluid at a very high rate. For example, 500 ml of blood may be drawn out and replaced every minute, which is about 5% of the patient's entire supply. If a leak occurs in such a system, the patient could be drained of enough blood in a few minutes to cause loss of consciousness and even death. The lost blood and other fluids may pose other risks including economic and health risks. As a result, extracorporeal fluid circuits are normally used in very safe environments, such as hospitals and treatment centers, and attended by highly trained technicians and doctors nearby. Even with close supervision, a number of deaths occur in the United States every year due to undue blood loss from leaks.
Leaks can occur for various reasons, among them: extraction of a needle, disconnection of a luer, poor manufacture of components, cuts in tubing, and leaks in a catheter. However, in terms of current technology, the most reliable solution to this risk, that of direct and constant trained supervision in a safe environment, has an enormous negative impact on the lifestyles of patients who require frequent treatment and on labor requirements of the institutions performing such therapies.
Approaches for detecting leaks are described, for example in U.S. Pat. No. 5,674,390, which employs fluid detectors outside the fluid circuit to detect the presence of fluid after it has leaked. Another system that employs leak detectors external to a blood circuit is U.S. Pat. No. 7,040,142. U.S. Pat. No. 6,572,576 and U.S. Patent Publication No. 2008-0214979 (which was issued as U.S. Pat. No. 8,002,727 on Aug. 23, 2011) describe methods of detecting leaks in which flow is reversed to draw air into a positive pressure part of a leaking blood circuit (e.g., venous lines returning blood to the patient) so that air can be detected and the leak identified automatically.
Yet another method for detecting a leak in a fluid circuit, for example a vascular access, is to monitor the pressures in the arterial and venous lines and compare their levels and changes therein to leak profiles, thereby permitting machine detection of a leak. An example of such a system is described in U.S. Pat. No. 6,221,040. The former four U.S. patents and one patent publication, identified immediately above are hereby incorporated by reference in their entireties herein. In the provisional phase of this application, the above four patents and patent publication were attached as Appendices I, II, III, IV, and V.
Leak safe systems have also been proposed which rely on the detection of leaks by detecting fluid outside an expected flow path. For example, a resistance between two spaced dry electrodes may drop precipitously when wetted by blood or other fluid. The change in resistance may be detected by a galvanometer and used to generate an alarm signal.
There is a continuing need in the art for ultra-safe systems that can be used in a non-clinical setting and/or without the need for highly trained and expensive staff. Reliable mechanisms to preventing and detecting leaks of blood and other fluids are desirable. The detection of leaks involves a trade-off between sensitivity and the frequency of false detection.
If a system is overly sensitive, there is a high risk of many false alarms, which can lead to operator “alarm fatigue” which can cause operators to cancel alarms without duly investigating the cause. Such a response to alarm fatigue can subvert the function of sensitive leak detection.