Microliter Flow Sensors for Accurate Drug Administration

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Medical procedures and therapies are frequently faced by the same challenge: accurately measuring and regulating lowest flow rates down to the microliter per hour range. In a majority of these cases, the result of the therapy, as well as the well-being or even the survival of the patient strongly depend on the reliable and continuous drug administration in such low flow regimes.

While a range of countermeasures have been assessed and introduced, there is still room for development and for innovative technologies to be established. One novel development with incredible potential is a single-use liquid flow sensor that can measure the lowest flow rates and detect usual failure modes rapidly and reliably.

Ambulatory Infusion Pumps

Ambulatory infusion pumps are gaining in popularity in ambulatory and home care settings for the continuous delivery of extremely-concentrated medication over several days. Herein, flow rates range from single milliliters up to a few hundred milliliters per hour (ml/h). Portable ambulatory infusion treatments have been able to greatly decrease the length of hospitalization with its related costs, while at the same time significantly improving patient quality of life. For instance, in the case of chemotherapy, it has been demonstrated that continuous drug administration has an advantageous pharmacodynamic impact on toxicity and efficacy, compared to old-style bolus injections every 24 hours.

A standard elastomeric pump consists of a pressurized reservoir exerting continuous force on the medication, an IV administration set including a pressure drop element (for example, a thin capillary used as a restrictor) which establishes the required flow rate, and an injection port or IV catheter. These pumps are often purely mechanical and engineered as single-use devices for pain management, infusional chemotherapy, or chelation therapy. Their characteristic pressure profile is usually concave, i.e. the generated flow rate at the beginning and at the end of the therapy is greater than in the middle.

The actual flow rates of elastomeric pumps are mostly influenced by two parameters: the differential pressure between the outlet and inlet of the restrictor and the resistance of the restrictor itself. While the inlet pressure is defined by the pressure profile of the pump’s reservoir, the outlet pressure is influenced by several factors: the patient’s specific vein back pressure, the type of the injection site, as well as the difference in height between reservoir and injection site. The resistance of the restrictor is impacted by the viscosity of the medication which in turn is established by the solution’s molecular composition and its temperature. In order to greatly increase temperature stability despite changing ambient temperatures, medical device manufacturers usually recommend to tape the restrictor to the patient’s skin at all times.

The presently established solutions, as described above, have a series of recognized shortcomings.

The required flow rate accuracy according to global standards is ±15% under highly specific conditions. During a normal daily routine, it is hard for a patient to follow the handling instructions that ensure the specified performance. In consequence, the real life flow rates frequently stray drastically from the planned values. While greater flow rates may result in an increased toxicity of the therapy, lower flow rates will decrease the treatment’s efficacy. Both deviations will prevent an ideal therapeutic outcome. Furthermore, medication not administered because of lower flow rates and thus leftover in the reservoir, may require dedicated waste management.

Particularly at low flow rates, clogging of the very thin restrictor or at the injection site is hard to detect rapidly and reliably without a liquid flow sensor. In several cases, it takes hours for an occlusion to get detected by the nursing staff or patient. This again will prevent an ideal therapeutic outcome.

The effects illustrated above can at present neither be monitored for direct feedback or remote support nor can they be recorded for later analysis by the clinical staff.

Therefore, many ambulatory infusion pump manufacturers are developing smart versions of their current products. One probable solution is the seamless integration of a single-use liquid flow sensor, like the LD20 from Sensirion, into the infusion set.

Liquid flow sensor LD20 for drug delivery


Pediatrics and Neonatology

In Pediatrics and Neonatology, the little and vulnerable patients receive plenty of special care and attention, not only from the clinicians, nursing staff, and their parents, but also from the medical industry.

In this context, flow rates of 1 ml/hour or even lower are typical because of the patients’ low body weights. Consequentially, the known and intrinsic issues of the existing infusion technology (flow-discontinuation, start-up delays, and dependence on hydrostatic pressure) may have even more harmful effects on the therapy outcome.

Administration of life-saving drugs with a short half-life, for instance adrenalin, must not be discontinued or delayed by the infusion technology in question. However, this happens often due to the compliance of the tubing and syringe plunger, the movement, and vertical displacement of syringe pumps while transporting the patient, or the loading of a new syringe into the pumping device.

The fluidic balance of a child or a neonate has to be tracked and calculated on an everyday basis. The sum of any fluid ingested or injected, be it nutrition or drugs, and the excreted fluid is not only vital to the well-being of the child but also limited. Single-use liquid flow sensors, integrated into infusion sets, will enable medical devices not only to track the administered flow rates accurately, but also to detect the above mentioned typical failure modes rapidly and reliably.

Measuring lowest flow rates in neonatology

Measuring lowest flow rates in neonatology.

Continuous urine flow measurements to prevent acute kidney injury

Continuous urine flow measurements to prevent acute kidney injury (AKI).

Continuous Urine Flow Measurements

Continuous Urine Flow Measurements of critically ill patients require flow rates to be measured in the range of single milliliters up to 100 milliliters per hour. Acute Kidney Injury (AKI) is a usual complication (occurrence 20% - 30%) in critically ill patients in the ICU. The early detection and correct diagnosis of AKI presently receives much attention in medical research and development. Patient mortality and the risk to develop a prolonged kidney disease significantly increase with AKI onset.

Currently, AKI can be diagnosed using laboratory data, including a variation in serum creatinine or in the excretion of waste products of the kidney’s nitrogen metabolism. Research revealed that the urine output of a catheterized patient is more sensitive than biochemical markers to variations in renal function. It displays a faster response than variations to the biochemical composition of the urine.

The standardized RIFLE (risk, injury, failure, loss, end-stage) classification is used by clinicians to boost the specificity and sensitivity of their AKI diagnosis. This classification states that a decrease in urine output below 0.5 ml per kilogram body weight per hour for over six hours is a first sign for an increased risk of acute renal failure.

The main issue faced today, when defining the urine output of a patient, is that it has to be measured and recorded manually at systematic intervals by the ICU’s nursing staff. Only then can a further trend analysis be done. The possibility of automatically and constantly measuring and recording urine outputs would allow a timelier diagnosis and allow clinicians to recognize or even avert AKI onset. In this case too, the LD20 single-use liquid flow sensor can solve this problem.

Common to all of the medical fields and applications described above, is that by using a single-use liquid flow sensor, significant measurement data and vital signs could be attained and stored automatically in the electronic patient data management system (PDMS). This solves the problem of time-consuming, inaccurate, and tedious hand written medical charts and allows the well-timed detection of adverse effects. The data would additionally be easily available for a retrospective analysis. Most of all, it would free-up time of the nursing staff to be spent on other tasks which still need personal care.

Download the Brochure for More Information

All of these medical applications can be transformed or for the first time enabled by using the LD20 - the single-use liquid flow sensor from Sensirion.

About Sensirion Inc

Medical devices must meet the highest standards in terms of quality and reliability. Doctors, nurses, and patients benefit daily from applications in the field of medical technology that are getting smarter by the day.

The use of proven Sensirion sensor solutions contributes to this and offers the possibility of making applications safer, more reliable and more convenient. Our many years of experience in the field of medical technology make us the preferred experts for leading medical-technology companies.

  • Home Care Devices (Ventilation)
  • Critical Care Devices (Ventilation)
  • Anesthesia
  • Point-of-Care Diagnostic
  • Drug Delivery / Infusion
  • Catheters
  • Smart Inhalers
  • Metabolic measurements
  • E-Health / M-Health

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Last updated: Mar 10, 2023 at 11:53 PM


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