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How human lives can be saved by measuring respiratory flow

First aid at the site of an accident can save many lives. Initial assistance is very often given by non-experts. In order to help these first-aiders in what are difficult circumstances, Karl Küfner GmbH & Co. KG from Albstadt and the HSG-IMIT (Institut für Mikro- und Informationstechnik) from Villingen-Schwenningen have developed a respiratory flow sensor for first-aiders which gives visual and acoustic information during resuscitation.

In Europe, around 500,000 people die of sudden cardiac arrest every year. According to the European Resuscitation Council, the majority of them could be saved by improved first-aid measures. In emergency situations, rapid oxygen supply is necessary to prevent permanent damage to vital organs. "Unfortunately, first-aiders often fail to deliver resuscitation because they are afraid of making mistakes. They frequently do not know exactly what to do, and feedback on whether they have acted properly in dangerous situations is usually not provided," says Rolf Bronner, head of Küfner GmbH's medical technology division.

However, successful treatment of cardiac arrest depends largely on the quality of care provided on the scene in the first minutes. Küfner therefore commissioned the HSG-IMIT to develop a first-aid assistant to help untrained first-aiders provide rapid and effective emergency treatment at accident scenes. "The rescue-iFil is easy to use; it does not need to be connected to a power supply and can therefore be used on scene," says Rolf Bronner.

Increased safety by providing assistance to the first-aider

The rescue-iFil device enables direct user management of chest compressions. © Karl Küfner GmbH & Co. KG

The central element of the device is a respiratory flow sensor that analyses, records, assesses and regulates air flow and flow velocity. This is achieved with a flow tube that determines the volume of passive air flow generated by way of chest compressions. The device records the respiratory parameters of both the first-aider and of the accident victim, and checks that the cardiac massage is being carried out effectively. It provides the first-aider with visual and acoustic information on the progress of the resuscitation. Measurement of flow velocity, airway pressure and the temperature of the victim's breath all play an important role in the process. The rescue-iFil device uses these parameters to calculate a respiration curve and subsequently determine whether the victim's airways are blocked or not and what intensity of cardiac massage is required.

Direct monitoring of the respiratory flow with sensors that are placed near the victim's mouth presented a huge challenge for the developers and microsystems engineers due to the high levels of humidity and associated condensation of fluids produced when breathing. "As the breath is warmer and moister than the area around it, water droplets form and hinder measurements with conventional sensors," explains Dr. Sophie Billat, head of the Thermal Sensor research team at the HSG-IMIT. The problem was solved by using a free-standing thermal sensor system in the main flow, which delivers an accurate mass flow signal even in the presence of condensation or water droplets on the sensor.

This micro-electromechanical system (MEMS) not only includes a thermal sensor membrane for measuring air flow, but also a second membrane that can be used for the dynamic temperature measurement of breathing gas and for moisture detection. "Additional condensate heaters can be used for heating the sensor and vaporising droplets or for keeping the sensor above the dew point," explains Sophie Billat.

Innovative solution for hygienic applications

Mechanical protection of the sensor needs to be guaranteed and it also needs to comply with medical hygiene regulations. The rescue-iFil therefore consists of two components - an inexpensive single-use tube that is discarded after use, and a reusable electronics system.

Advantages for patients, first-aiders and doctors

The respiratory flow sensor of the rescue-iFil enables direct measurement of respiration. © Karl Küfner GmbH & Co. KG

The rescue-iFil is the first patient-centred respiratory flow sensor that enables the direct and synchronous measurement of respiratory flow, temperature and pressure. It opens up new diagnostic possibilities and considerably improves first-aid measures. It makes on scene emergency management more efficient, and the exact instructions provided during cardiac massage will improve the treatment given in the first minutes. "The use of the rescue-iFil can significantly increase the likelihood of survival," says Rolf Bronner.

The device gives first-aiders a simple feedback system during the resuscitation process and improves the quality of first-aid measures. In addition, the device is also of great help to emergency doctors. When they arrive at the scene, the device helps them to rapidly determine pulmonary status, reproduce the resuscitation history and carry out the steps required for the safe transport of the victim to hospital. A prototype is already in use and the company expects to place the device on the market in 2016.

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