Intravenous-line air-detection system

A method for controlling the flow of a liquid from a intravenous fluid source through an intravenous line to a patient and detecting the presence of a bubble in the liquid, the method comprising:

• providing in the line a region having a first portion containing a measurement gas and a second portion containing a segment of the liquid flowing through the line, the sum of the first portion's volume and the second portion's volume being a constant volume, the region being part of an acoustically resonant system, the region being isolatable from pressure effects in the rest of the line by means of a first valve that controls flow from the source and a second valve that controls flow to the patient;
• closing the second valve and opening the first valve to permit flow from the source into the region;
• after liquid has flowed from the source into the region, closing the first valve so as to isolate the region from pressure effects in the line;
• determining the resonant frequency of the system at a first pressure of the measurement gas;
• after closing the first valve, changing the pressure of the measurement gas to a second pressure;
• determining the resonant frequency of the system at the second pressure;
• determining, based on the resonant frequency measured at the first pressure and the resonant frequency measured at the second pressure, whether the volume of the first portion has changed due to the change in pressure;
• and
• if no change in volume is detected due to the change in pressure, opening the second valve to permit flow to the patient, and if a change in volume is detected, generating a signal indicating the presence of a bubble in the liquid.

An apparatus for detecting the presence of a bubble in a liquid, the apparatus comprising:

• an acoustically resonant system having a region isolated from extraneous pressure effects, the region having a first portion containing a measurement gas and a second portion containing the liquid in which the presence of the bubble to be detected, the sum of the first portion's volume and the second portion's volume being a constant volume;
• means for detecting the resonant frequency of the system;
• means for changing the pressure of the measurement gas in the system;
• and
• signal generating means for generating a signal indicating the presence of a bubble in the liquid, wherein the signal generating means is in communication with the means for detecting the resonant frequency and the means for changing the pressure of the measurement gas, wherein the signal is generated based upon a first and a second resonant frequency determined by the means for detecting the resonant frequency when the means for changing the pressure has caused the measurement gas to have a first and second pressure, respectively.

An apparatus for controlling the flow of a liquid from a intravenous fluid source through an intravenous line to a patient and detecting the presence of a bubble in the liquid, the apparatus comprising:

• a region having a first portion containing a measurement gas and a second portion containing a segment of the liquid flowing through the line in which the presence of the bubble is to be detected, the sum of the first portion's volume and the second portion's volume being a constant volume, the region being part of an acoustically resonant system, the system having different frequencies of resonance for different volumes of the measurement gas in the first portion of the region, the region being isolatable from pressure effects in the rest of the line by means of a first valve that controls flow from the source and a second valve that controls flow to the patient;
• means for detecting the resonant frequency of the system;
• means for changing the pressure of the measurement gas;
• and
• a controller for controlling the valves, the resonance-detection means, and the pressure-changing means, for determining, based on the resonant frequencies measured at two different pressures, whether the volume of the first portion changes due to a change in pressure and for generating a signal indicating the presence of a bubble in the liquid if the first portion's volume does change due to a change in pressure.