Has a device ever saved your life?

Ventilators - what they do and what is being developed

Due to Covid-19, ventilators suddenly became the focus in spring 2020. What kind of devices are these today so sophisticated that they can save lives even in critical situations? Other designs, in turn, help people with lung disease to breathe in everyday life. The trend is towards systems that can automatically adapt to the patient's condition in order to relieve doctors and nurses.

Tim Schröder
Science journalist in Oldenburg

A healthy person hardly ever thinks about his or her own lung to. It goes without saying that you breathe. The lungs do their job - for decades - and in doing so they perform at their best. Ten to 15 times a minute to breathe we on and off again, around 12,000 liters per day. This corresponds to the amount of 75 full bathtubs.

Table of Contents

1. Different reasons for ventilation
2. Ventilators: support lung work
3. The compressed air cylinder was at the beginning of the ventilation
4. Early ventilation: Breathe gently with the iron lung
5. Precise breathing gas regulation on modern ventilators
6. Side effects of ventilation
7. Dangerous overstretching as a side effect
8. The goal for ventilators: Observe ventilation
9. The ventilator becomes an assistant
10. Intensiv devices should communicate
11. Ventilation of the future: back to the principle of the iron lung

On the way from the nose and mouth deep into the fine branches of the lungs, the air is humidified, warmed and freed of dirt particles. Pollen, grains of dust, fibers - almost everything sticks to the mucous membrane that lines the airways.

Different reasons for ventilation

How important that lung is, people become aware of when it fails to function, when an illness impedes the exchange of air. People who have been Shortness of breath speak of a feeling that must resemble drowning, of fear of death. Fortunately there is today Ventilatorswho are there when the lungs can no longer adequately supply the body with oxygen.

Severe pneumonia or Viral diseases how Covid-19 can mean that the breathing work has to be completely taken over by the machine. With other diseases, the patients still breathe themselves, but the breaths are not deep enough for a sufficient supply of oxygen. Such patients are supported by so-called breathing apparatus. Modern devices recognize in fractions of a second that the patient is beginning to inhale and then press additional air into the lungs in the right rhythm with gentle pressure.

Ventilators: support for lung work

To the people who have such a Respiratory support need, today count, for example, people who von Sleep apnea or COPD are affected. COPD is a condition often referred to as smoker's lung, but it can have a variety of causes.

COPD stands for chronic obstructive pulmonary disease - chronic obstructive pulmonary disease, whereby obstructive means something like "constricting" or "closed". About 90 percent of all people who have COPD have smoked. In some cases, secretion accumulates in the lungs, which makes breathing difficult and has to be coughed up.

In other forms of COPD, the lung tissue loses its elasticity. The lungs can be stretched when you inhale, but the lung tissue no longer fully contracts when you exhale. The Respiratory Equipmentsupported the lung then at their hard work.

At a Sleep apnea the airways in the throat and pharynx are narrowed. The reason is usually too little tension in the muscles in this area, so that the tissue slackens and the upper ones respiratory tractconstricts. Affected people have trouble breathing, especially at night. You have to press against the resistance. Often the blockage only opens after several breaths with a bang that sounds like a very loud one snorer sounds.

Either COPD patients as well as from Sleep apnea affected people wear at night Breathing masksthat are attached to the head with a ribbon. Since the mask can slip while sleeping, it occasionally happens that it no longer fits perfectly and air hisses through a gap. Modern breathing apparatus automatically recognize this pressure difference and can adapt both the pressure and the oxygen content of the breathing air to the losses.

The compressed air cylinder was at the beginning of the ventilation

What progress the Ventilation technology has made over the course of around 100 years, can be recognized primarily from the devices that are now in the Intensive care can be used. You can take over the work of breathing completely or help the patient to breathe and then adjust their pressure precisely to the performance of the lungs. The devices precisely dose the breathing gas and humidify and warm the air before it flows into the lungs.

Such functions were at the beginning of the artificial respiration not to think. The Lübeck watchmaker Heinrich Dräger developed one of the first breathing apparatus in the world - to revive people with gas poisoning: 1907 he received a patent for the Pulmotor - a device for "blowing fresh air or oxygen into the lungs".

The Pulmotor was oxygenated from a Pressure bottle dined and had a Valve, which alternately generated positive and negative airway pressure (video about the operation of a Pulmotor from 1920). At that time there was no talk of gently adjusting the pressure to the lungs. The problem is that too much pressure can injure the lungs. Above all, the small alveoli, where the gas exchange between air and blood takes place, can tear. The more alveoli are destroyed, the less area is available for gas exchange.

Early ventilation: Breathe gently with the iron lung

“This is a much gentler breathing machine Iron lungthat occurred in Europe especially in the 1950s during the Polio epidemics was used, ”says Steffen Leonhardt, who holds the chair for medical information technology at RWTH Aachen University. At that time, many children fell ill with poliomyelitis, which is why one spoke of polio. In acute stages, the respiratory muscles of some of those affected stopped working. The iron lung saved the lives of many (video from 2018 about a patient in the USA who uses such a device).

The iron lung consists of one large hermetically sealed metal cylinderin which the patient lies down. Only the head looks out. The device creates a negative pressure that lifts the chest and allows air to flow into the lungs. "This form of ventilation is more natural and gentler," says Steffen Leonhardt. "However, the patient's body could neither be observed nor treated, which is why positive pressure ventilation became established in the following decades." With success: Today around 400,000 patients in Germany are ventilated with intensive medical care every year. In the early 1960s there were only a few dozen.

Contributed to success modern valves that help the patient to breathe - initially mechanical valves. They were reliable and efficient, but had the disadvantage that they reacted very slowly to the patient. If the patient tried to breathe, it took around 300 milliseconds for the valves to respond.

In many cases this was too long because during this time the patient already had a feeling of Shortness of breath hired. The aim of the developer was therefore initially to create this so-called Trigger latency between the start of inhalation and the response of the valves. This goal was achieved with the development of microelectronically controlled devices since the 1980s - today the trigger latency is only around 20 milliseconds.

Precise breathing gas regulation on modern ventilators

In general, modern devices are true High performance machinesthat measure the tidal volume precisely and, above all, work gently. The trend of the time is above all the "patient-friendly ventilation". This should be so gentle that the lungs are not damaged. Modern devices have algorithms that help to cautiously start ventilation, especially during the acute phase of an illness.

Is the Patient on the mend, the challenge is to wean him off ventilation. Because over time, the respiratory muscles get used to the support of the machine - like a muscle that you no longer train. The weaningThe aim of weaning is to stimulate the patient so that he can take on the full work of breathing again.

Modern breathing equipment drive from Algorithm controlled weaning programs from. These test regularly and very gently whether the patient is already able to breathe completely or partially by himself - and thus get him used to artificial breathing again. These algorithms mean that patients can now be disconnected from the ventilators up to two days earlier.

Side effects of ventilation

One of the most important parameters of the Ventilation is today the PEEP value (positive end-expiratory pressure), the positive end expiratory pressure. A valve ensures that at the end of each exhalation there is still enough air in the lungs that the alveoli remain open and do not collapse. In the case of severe lung diseases, such a collapse can lead to the collapsed tissue no longer opening and being lost for breathing.

But despite all the development steps, ventilation remains a challenge because it brings complications. "Ventilation is like a drug: it has significant side effects," say experts. There is no question that when patients are admitted with an acute lung disease, artificial ventilation is worth gold because it saves lives. But there are also problems.

At intensive care interventions becomes a Tube inserted into the windpipe through which the breathing gas flows in and out. The rest of the trachea is closed with a balloon so that controlled ventilation can be provided through the tube. But despite the balloon barrier, germs that are normally held back by the glottis can penetrate the lungs. And the longer the patient is ventilated, the greater the risk of infection.

Dangerous overstretching as a side effect

Another form of complication is lungs overextension. It is known that the lung tissue changes in the course of the Ventilation can harden. Then you have to ventilate with a higher pressure. The risk for Lung damage increases. When it comes to complications that occur in connection with artificial ventilation, experts also generally speak of ventilation-induced lung injury (ventilator-induced lung injury, or VILI), which is caused directly by mechanical ventilation. Lung diseases can also be exacerbated by ventilation.

The GAU is the acute one Lung failurewhich can occur in severe infections. Whole areas of the lungs collapse in the process. Although parts of the lungs are still ventilated, there is no longer enough oxygen to pass into the blood. In the opposite direction, the carbon dioxide cannot escape from the blood. In short: acute lung failure is a gas exchange problem that, although treated by artificial respiration, can also be triggered.

The goal for ventilators: Observe the ventilation

"Basically, we still know far too little today about how well a patient's breathing actually works," says Steffen Leonhardt. “The breathing apparatus sensors measure the pressure and the flow rate at the outlet. However, we do not know how much oxygen passes into the blood and whether all areas of the lungs are actually ventilated. "

But now there are technical processes that bring more clarity. especially the electrical impedance tomography (EIT)which has been on the market for a few years.

In this procedure the patient is given a Electrode belt placed around the chest and back. This measures the electrical resistance of the lungwhich changes with the expansion of the alveoli. The advantage: The EIT provides a grid image in which the lungs are divided into a checkerboard pattern of 36 fields. In the picture you can see in detail in which areas the alveoli are opened and ventilated and in which they are not.

Another new technology is on the rise: the oesophageal pressure measurement. The idea: if the lungs expand, they press against the gullet, the esophagus. This pressure also shows how well the lungs are being stretched - far more precisely than a pressure measurement on the chest could ever be. The first esophageal sensors are currently being tested.

The ventilator becomes an assistant

And there is another trend at the moment; the development away from a pure ventilator towards an assistance system that uses measured values ​​to independently adapt ventilation to the patient. "Today the nimbus still applies that the treating doctor alone changes the settings of a breathing apparatus based on measured values," says Matthias Schwager, group leader at the VDE testing and certification institute in Offenbach. “But they are already Ventilators in development that is more and more of an assistant device that automatically adapt ventilation to the patient's condition. "

So far rely Intensive care physician on their experience and on oxygen values, which are measured about three times a day in the patient via blood samples, or on the values ​​of clips that measure the oxygen saturation on the finger. But there are good reasons for more automation: In crises like that Corona pandemic devices must also be operated by inexperienced colleagues.

Oxygen measurement using a blood sample does not generate values ​​in real time. And the finger clip provides uncertain statements when the fingers are poorly supplied with blood. Matthias Schwager: "That is why there are already concepts according to which ventilators are coupled with other devices - for example with the devices for monitoring cardiac activity - or completely different new systems."

Intensiv devices should communicate

In development are for example arterial catheterswhich can be used to permanently measure the oxygen content of the blood. It is also conceivable in the future Stress hormones and Inflammation values to measure, to provide the ventilator with information about the overall condition of the patient. The release of stress hormones can be a reaction to a reduced oxygen supply.

In the standardization bodies of ISO / IEEE is currently on Standard 11073Service-oriented Device Connectivity (SDC) worked, according to which the devices in the intensive care unit, which are still working separately today, should exchange data with each other and cooperate in the future. "The patient is then part of a closed circuit in which measured values ​​from his body are supplied to the devices so that they can adjust the parameters in real time." Standard DIN EN 60601–1–10: 2016–04 the first requirements for the development of such "physiological closed control loops" have already been formulated.

Ventilation of the future: back to the principle of the iron lung

Steffen Leonhardt looks for that future yet another completely different form of ventilation, the Resume the principle of the iron lung would. "In a project we are currently dealing with the question of whether one could stimulate the diaphragm to move in a targeted manner by stimulating the neurons - after all, it contributes a large part to the work of breathing."

If this actually succeeds at some point, it would be a sensible step back to gentle ventilation, in which the air is not pumped into the lungs with excess pressure, but is sucked into the lungs through the natural work of the muscles. Either way, we can expect interesting developments in ventilation technology over the next few years.

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