Many electrical devices are powered by passing a current through a load. A non-limiting example of such a device is a resistive heater attached to an intravenous (IV) liquid dispenser such as the ENFLOW® IV Fluid/Blood Warmer available from Vital Signs, Inc., located in Totowa, N.J. The resistive heater heats an IV fluid line by passing a current through a heating coil disposed proximate the IV fluid line. As the current passes through the coil, the temperature of the coil rises, heating an attached cartridge containing the IV fluid line.
Many common medical monitoring devices measure patient vital signs by monitoring low frequency electrical signals measured by various leads attached to the patient. The typical input to these monitoring devices is a low-pass filter. The low-pass filter is typically constructed of some combination of passive components such as resistors, capacitors, and inductors.
The inventor has observed that, in some instances, when a device, such as an IV fluid warmer or other electrical device, is coupled to a patient that is being monitored by a monitoring device as discussed above, transients generated when powering the device on or off may be undesirably picked up and displayed by the patient monitoring device. The inventor believes that this is due to a capacitive coupling of the electric device to the patient that facilitates transmission of the transients generated by powering the device on or off. For example, when an IV fluid warmer is powered on or off, transients are generated that travel through the IV fluid line via a capacitive coupling of the resistive heating element to the IV fluid line. Although these transients are generally short-lived, the inventor believes that transients that occur at low frequencies are filtered by the low-pass filter into lower amplitude rising signals that are visible on patient monitoring devices as the signals fall within the pass band of the physiological signals. As such, these low frequency signals are then measured by the patient monitoring device, resulting in erroneous data. Such erroneous data makes monitoring patient vital signs difficult for doctors and nurses and may cause false-alarms in the monitoring equipment. While shielding within the input of the patient monitoring device may block high frequency transients, such filtering is ineffective at blocking signals within the low frequency pass-band of signals allowed by the monitoring device.
As such, the inventor has provided an apparatus and system for powering electric devices coupled to a patient that reduces transients on patient monitoring devices.