History of Air Detection in IV Therapy
Electronic infusion devices were first introduced in the late 1960’s. At that time, the only available safety product to potentially prevent air from being infused was a 0.2 micron particulate filter. However, these were not widely used as there were major issues with air block and potential for occlusion and tubing rupture as pumps at that time could generate 100 psi or greater pressure. Addition of an electronic “eye” to detect drops falling in the drip chamber was a safety advance enabling clinicians to know when the infusion source was empty and likely to start infusing air. The primary use of the electronic eye was to control the infusion rate. Initial devices were programmed to “count” drops/minute just as clinicians do to convert to mL/hour.
In the mid 1970’s, the first infusion pump with an optical air detector was introduced. The IV tubing downstream of the pumping cassette was threaded into the detector. Nurses left a small loop of tubing above the detector and would typically pull the tubing while it was still in the detector to move the air from the detector. Small amounts of air were then trapped at the top of the pumping cassette. These optical detectors were limited in use to clear fluids and were problematic in other ways. For example, the detectors could be contaminated by fluid spills. It was also not possible to start or restart the pump if air was present or if the tubing was not installed in the detector.
With the addition of ultrasonic sensors, features were eventually added to some pumps such as the ability to set air detection levels. Typical settings are 50, 100 and 250 microliters. How the size detection limit was originally determined is unknown and was likely based more on the capability of the detection system than any scientifically-validated assessment of what has the potential to cause harm.
In cases where it was widely known and acknowledged that tolerance of air in line should be zero, final filters with air venting capability could be added. Since the pumps could not determine if a filter was being used and single air mass detection (if present on the device) cannot be turned off; the alarms remained active even when filters were in use. Filters are generally placed below the infusion pump as placing them above the pump is problematic for several reasons. Pulling fluids through a filter, especially at high flow rates can cause significant inaccuracy as well as upstream occlusion alarms. Given the limitations of filters – incompatibility with many meds and fluids, air vent weeping when used with very low surface tension fluids, severe restriction of flow rates and siphoning and/or bolusing depending on the position of the filter in relationship to the level of the patient – the use of filters has largely fallen out of favor except with nutrition lines.
None of the infusion pumps currently marketed have the ability to actively remove the air, only to detect and alarm. Detection without active remove has many shortcomings. Any alarm during an infusion stops the infusion, so life support and critical medication delivery are interrupted. No infusion pump has been marketed to alarm for air but continue infusion for some predetermined period to advance the air to a visible point. Air removal from these devices typically requires stopping the pump, opening the door, removing the tubing, manually aspirating the air and resetting the pump. Requiring a significant amount of time and effort. (https://youtu.be/FmK8BBMXgcM). As a consequence, air masses may end up being ignored and ultimately enter the patient.