Intravenous infusion therapy assisted by a smart infusion pump provides controlled drug delivery throughout a prolonged period of time and offers assistance to hospital staff. However, pumps fall short when it comes to reliable failure detection, as they lack technology to directly measure flow rates of drugs inside tubing. This results in two major problems – failures can remain undetected and over-sensitive pumps that generate lots of false alarms. The ECRI Institute named alarm fatigue and infusion pump medication errors as No. 1 and No. 2 on their list of top 10 health technology hazards for 2014.

Typical failures during infusion therapy include occlusion, air-in-line, free flow, cross-flow in multiple-infusion settings, and infiltration or extravasation. While all of the above failure modes are well-known to hospital staff, infusion pumps can only detect the first three at best.

© Mark Eaton |
Improved technology

Sensirion’s CMOSens is a tiny flow sensor chip integrated into a variety of packages that has offered improved diagnostics and automation for the semiconductor industry. The technology can be applied to infusion applications and medical devices to increase patient safety and support hospital staff.

The measurement method is based on a micro-thermal principle where a microscopic heating element introduces a negligible amount of heat into the bypassing liquid. The shape of the heat cloud is monitored by two temperature sensors and is directly related to the flow rate inside the fluidic channel. By using this principle, Sensirion’s liquid flow sensors can constantly measure low flow rates that are typical for medical applications. Every sensor is fully calibrated and provides a linearized, digital output. CMOSens technology is scalable and allows sensor solutions to be technically and economically feasible. The sensor chip is packaged into a plastic housing that features all mechanical, electrical, and fluidic connections.

Integrated into an infusion set, Sensirion’s disposable liquid-flow sensor communicates the flow rate inside the tubing in real-time. Occlusion can be detected within a few seconds by noticing a decrease in the flow rate, even in ultra-flow ranges, speeding response time compared to the 45-minute wait before an alarm is triggered by the infusion pump. Drops in primary infusions due to cross-flow errors from secondary lines can be detected quickly so that corrections can be made without impacting therapy. A bubble-detection feature identifies air inside the infusion tubing, and the sensor is sensitive enough to detect small changes in the flow rate. It can measure the patient’s heartbeat and detect the regular peaks in the infusion flow rate produced by the oscillating back pressure of the patient’s venous pulse.

Detecting the heartbeat on the flow rate is a direct indication of an intact connection of the infusion cannula to the vein of the patient, and the absence of the pulsation indicates an interrupted connection. Possible causes may include kinked, disconnected, ruptured tubing, or a dislodged infusion cannula, which may in turn lead to infiltration. By evaluating the sensor signal, Sensirion’s solution offers the possibility of detecting infiltration quickly and preventing harmful patient consequences.

Infiltration and extravasation

Infiltration and extravasation describe the leaking of IV fluid into the tissue surrounding the vein. With infiltration, the IV fluid is a non-vesicant agent leading to irritations, while extravasation describes the efflux of vesicant agents that can damage the tissue. Potent chemotherapy drugs, for example, are such vesicant agents. Tissue damage can involve nerves, tendons, and joints, and can continue for months after the initial incident. If treatment is delayed, surgical debridement, skin grafting, and even amputation may be required.

The frequency of complications caused by extravasation is hard to establish clearly, varying between hospitals and tending to be underreported. However, the estimated incidence rate published in literature is between 0.1% and 6.0% for patients receiving chemotherapy.

The leakage of IV fluid into the surrounding tissue can be caused by many reasons, including damage to the vein’s backside during catheter insertion. However, one of the most common reasons is the puncture of the vein wall by mechanical friction of the catheter needle, which is typically preceded by an occlusion. With a traditional infusion pump, the occlusion may remain undetected until the pressure in the tubing reaches a certain threshold, triggering an alarm through a pressure sensor many minutes, and sometimes closer to an hour, later. Detecting occlusion quickly and consequently stopping the infusion pump can prevent the rupture of the vein and the subsequent leakage.

Medical device manufacturers familiar with the art of infusion therapies are aware of the technology challenges inherent to smart infusion pumps. Integrating a liquid flow sensor into infusion tube sets can take infusion therapies a step forward and allows for controlled drug delivery on a broader scale. Failures that have gone unnoticed can be detected or even prevented, increasing patient safety and well-being, reducing workload and stress for hospital staff, and saving costs in the healthcare system.