The Servo Ventilator story

In 1965, Professor Sven Ingelstedt at the Department of Clinical physiology granted a request from the young doctor Björn Jonson to develop a new respirator. Sven's directive included a somewhat ambigious stipulation that would prove historic in retrospect. “Respirators are pressure or volume controlled. They should be flowcontrolled. Then we could do what we want! P.S. It is not possible to control flow!”

The core project team was later completed with the additions of anesthesiologist Dr. Lars Nordström and the ambitious electrical engineer Sven-Gunnar Olsson. Olson had been previously employed by Elema-Schönander, a company outside Stockholm famous for having invented the electrocardiogram inkjet printer (1948) and the implantable pacemaker (1958). The project was given a wide degree of freedom for experimentation in an environment that fostered cross-institutional teamwork and entrepreneurship.

The Servo Ventilator 900 became a world’s first and fulfilled Sven's directive – a ventilator that was indeed flow-controlled and could provide respiratory monitoring of vital parameters and gas delivery. The Servo 900 featured the Servo Control System, a small, silent, electronic device that enabled the clinician to reliably achieve set tidal volumes by delivering accurate flow to the patient, independent of changes in resistance and compliance from the patient ́s respiratory system.

The term Ventilator was introduced to emphasize that it involved new principles surpassing the old respirators. These new ventilator principles gave clinicians new options to provide optimized ventilation methods for each patient, from adults to infants.

The brain of the Servo Ventilator was the unique Servo control system, state of the art electronics that contributed to far greater flexibility in operation and choices for modes of ventilation. Pressure and flow sensors utilizing a very small compressible volume in the patient gas delivery circuit fed information back to the inspiratory and expiratory valve units several hundred times per second. Visual and audible alarms were immediately activated if pre-set limits for airway pressure and expiratory minute volume were exceeded.

Integrated monitoring capabilities of the Servo ventilator were a true clinical breakthrough. The Lung Mechanics Calculator 940 provided six different parameters and served as an aid in choosing the ventilator settings on a breath-by-breath basis. As an example, this calculator could assist in determination of optimal settings of the external PEEP-valve to achieve the best effect on end-expiratory lung volume and oxygenation.

The Servo ventilator also made recording and data export possible. This data export capability made the Servo the ventilator of choice for research in mechanical ventilation, a steadily increasing area of interest in scientific publications of the 1970s.

In the ICU, there was a need to continuously measure CO₂ as a surrogate for the arterial blood gas pressure PaCO_2. This was considered to be time-consuming and expensive. The CO₂ Analyzer 930 was the first commercial volumetric capnograph, and was based on measurement of IR light absorbtion in a small, fast mainstream sensor connected to the ventilator. This provided real-time breath-by-breath end-tidal CO₂ concentration, CO₂ tidal minute elimination, and deadspace calculations. It provided an invaluable contribution to guidance of ventilator settings and to the understanding of severity of pulmonary disease, gas distribution in the lungs, circulation and metabolism.

The successor to the Servo 900 came to be known as the Servo 900B. It introduced an Intermittent Mandatory Ventilation (IMV) mode synchronized to the patient's respiratory efforts. The patient was, in turn, encouraged to take over more and more of the respiratory workload. The result of this synchronized effort was that weaning process became less painful, both physically and mentally.

Additional features such as CPAP capability, extended setting ranges and the default “green settings” were implemented on the device's front panel.

Neonatal and pediatric possibilities gained notice. Hospitals around the world began to recognize that the Servo ventilator was not designed solely for adults. Unlike most ICU ventilators of the time, the Servo offered options for ventilation of children and newborn babies.

The Servo 900C was introduced in 1981 as the “Limitless Servo Ventilator System”. Like its predecessors, the 900C had been designed to be easy to learn, set, place, clean and service. It was the first ventilator on the market which could truly control airway pressure precisely throughout inspiration and expiration.

Electronic control of PEEP and eight different ventilation modes, also available in an accentuated infant patient range, were now available. CPAP could now be delivered through the ventilator with supervision of minute ventilation and CO₂ exchange.

Extensive training material (“The Servo University”) with application booklets, a demonstration simulator panel, a deck of patient cards, videos and a clear and consistent operating manual were integral parts of the limitless program.

Originally named Servo Pressure Control Ventilation, this delivery of constant inspiratory pressure with a decelerating flow pattern was able to prolong the time for gas exchange in the alveoli. It was expected to reduce the risk of barotrauma compared to traditional volume controlled ventilation.

Very high peak pressure was common before the current era of low tidal volume ventilation. Pressure Control also quickly gained popularity for use with uncuffed pediatric and neonatal patients.

Pressure Support was introduced to the intensive care world in the Servo 900C, less than 10 years after its inception. Pressure Support Ventilation became the new standard mode for weaning. It was an important step in allowing the patient to take increased control of the timing of the ventilatory support while the ventilator took over most of the respiratory work.

Servo engineers worked with several criteria to solve the timing problem, and finally concluded that the flow decay during a pressurized breath was likely the ideal variable to use. Breath termination at 25% of the peak flow was determined to be the most comfortable level of support. Research on the potential clinical benefits of Pressure Support immediately took off and became a major topic in scientific articles for many years to come.

Magnetic Resonance Imaging (MRI) was a novel and revolutionary imaging technique first emerging in the early 1980’s. The powerful electromagnet in the environment required by the technology was a challenge for the construction of the MR-suite and also for equipment that was brought in. Devices that could malfunction in a strong magnetic field could pose a serious risk.

Many patients in need of an MRI examination also required mechanical ventilation. The Servo 900C had few magnetic parts, and was the first ventilator that was released for use in this environment. It has later been followed by MR-versions of the latest Servo ventilator generations, including the Servo-u MR Conditional.

The Servo 300 series represented a significant technological advancement and a quantum leap into the microprocessor era as the first universal ventilator enabling treatment of all patient categories, from adults to tiny premature neonates. It included a completely new and unique gas delivery system with gas modules for air and oxygen and a small mixing chamber. The new sensitive flow-triggering system with rapid flow response gained substantial interest due to its ability to reduce work-of-breathing. Servo 300 also set a new benchmark for tidal volume delivery, delivering volumes as low as 2 ml.

With each new generation of Servo ventilators, each cycle of invention and innovation, there has been an inherent drive to develop ventilation modes that would meet the changing and challenging clinical needs of the future. The Servo 300 launched a set of volume-target modes :Pressure Regulated Volume Control (PRVC) and Volume Support (VS), modes where the key principle was to deliver the set volume at the lowest required inspiratory pressure targeted on a breath-by-breath basis.

Neonatal and pediatric ICUs quickly embraced volume-targeted ventilation as it became clear that this innovation would offer a long desired transition away from less precise and less predictable pressure-limited continuous flow ventilation modes.

Servo 300 was, for a time, available in a unique model designed to address a growing interest in nitric oxide (NO) therapy. NO was seen as a potent vasodilator to improve oxygenation in very severe patient groups including prematures with pulmonary hypertension.

NO delivery and monitoring were fully integrated into this special 300 model, and a third gas module provided precise NO dosing in full synchrony with breath delivery. Unfortunately, due to an exclusive patent held by a Swedish gas manufacturer for the medical use of NO for treatment of lung dysfunction, production of this then-unmatched Servo 300 NO delivery system was forced to be discontinued.

In the pioneering search for more gentle and patient-friendly ventilation, the next step was the Automode function, developed to form a bridge between controlled and spontaneous ventilation in the early weaning process. Automode incorporated three combinations of control and support modes, and was automatically switched back and forth seamlessly supervised by an adaptive apnea time algorithm. The benefits were clear: reduced sedation requirements, less operator intervention and less alarms. Weaning could be started earlier and patient activity was always rewarded without requiring intervention from the staff. The front of the Automode brochure progressively stated “Weaning begins with intubation."

Research with the goal of reducing ARDS incidence and mortality heralded the implementation of the Open Lung Tool which, by using breath-by-breath trends of parameters including dynamic compliance and CO₂ elimination, provided quantification of the effect of interventions - in particular alveolar recruitment maneuvers.

Through a stepwise approach that included a decremental PEEPtitration, the PEEP setting could now be personalized to achieve improved oxygenation with ventilation at the lowest possible driving pressure and with a homogenous lung volume. The Open Lung Tool would also indicate when lungs were not recruitable, suggesting that other approaches should be considered and evaluated.

In December 1999, a new dimension of ventilation technology was presented in the journal Nature Medicine. A group lead by Dr. Christer Sinderby at the University of Montreal described how progress in signal acquisition and processing of the electrical activity of the diaphragm (Edi) meant that these signals could be used to allow the patient's own respiratory center to assume full control of the timing and magnitude of the respiratory support provided by the ventilator.

Establishment of full patient-ventilator synchrony and use of intrinsic lung-protective reflexes provided new hopes and possibilities for adult and pediatric intensive care ventilation for the 21st century. The vision in this article outlined reduction of ventilator-related complications, facilitation of weaning in order to decrease ICU and hospital length of stay. Visionary Servo engineers grasped the potential of this technology and immediately developed a practical working implementation, which was initially deployed on a Servo 300-based prototype.

As the culmination of unprecendented cooperation with clinicians worldwide, Servo-i became first ventilator designed as a mobile and modular platform, designed to easily bring new clinical functionality and upgrades to already-installed ventilator fleets.

The innovative modular system approach included three main configurations - Infant, Adult and Universal. New levels of flexibility in placement, handling and support during intrahospital transport were offered through a comprehensive range of smart accessories and uninterrupted connectivity. The user interface now allowed clinicians to choose between touch screen, a main rotary dial and direct access knobs, all providing secure control of the most vital settings. The clear flatscreen display provided up to five color-coded high-resolution waveforms with diagnostic quality.

The new one-piece Expiratory Cassette met increasing customer demands related to reliability and re-processing, and introduced a brand new technology seen for the first time in Servo ventilators: Time-of-flight Ultrasound. Its ultra-fast flow measurement was virtually independent of gas composition and humidity. The success of the ultrasonic flowmeter also lead to the development of an Ultrasonic Oxygen Sensor, meant to function over the lifetime of the ventilator.

The technology was later found to be effective for detection of the low density Heliox gas mixture when Heliox was latter was implemented as the third supply gas for the Servo-i.

Servo-s, with its tagline of "Simplicity makes sense", took the cutting edge technology from its big brother Servo-i and consolidated it into a straightforward and cost-effective package. The simplified Servo-s was appropriate for a variety of hospital ventilatory care settings, and in combination with the quiet and compact Compressor Mini was able to deliver high-quality ventilation independent of central wall gas.

The user-friendly simplicity, state-of-the-art performance and reliability for both adult and pediatric patients made the Servo-s an instant success in the emerging BRIC economies (Brazil, Russia, India and China) searching for high-value medical devices when modernizing their healthcare systems.

The introduction of NAVA in Servo-i was nothing short of a sensation! Featuring plug-in HW and SW modules as well the an Edi catheter with the secondary function of a nasogastric feeding tube, the NAVA Servo-i brought neurally controlled ventilation to an already-respected and popular ventilator.

Recent scientific papers had demonstrated the deleterious effects of patient-ventilator asynchrony, as well associated problems due to increased sedation and VIDD (ventilator-induced diaphragm dysfunction). Since those findings and the introduction of NAVA in Getinge ventilators, NAVA has been shown to address these problems by both shortening the time of mechanical ventilation
^[1]and increasing the number of ventilator-free days^[1][2][3] by providing personalized ventilation that is both lung- and diaphragm-protective.

As NAVA when compared to traditional ventilation modes is independent of leaks, the application of non-invasive ventilation (NIV NAVA) was a natural step to take as a paradigm shift in treatment to patient groups that had been traditionally treated with more invasive modes. NIV NAVA's continuously growing application in neonates has been tremendous. Its success is based on findings that it may prevent intubation entirely ^[4][5], or allow early extubation
^[6][7][8] when compared to conventional NIV modes which are not sufficiently synchronized.

Another patient group that may benefit are adults with acute exacerbation of COPD, in which NIV NAVA has been shown to reduce NIV complications, and may be effective in managing the patient's status. ^{[9][10][11][12][13]}

Every new generation of Servo Ventilator has had high expectations of transforming how ventilators are perceived within healthcare settings. Servo-u successfully introduced a highly intuitive all-touch user interface with context-based guidance and workflows, recommendations and shortcuts. The objective of this user experience design was to make implementation of advanced ventilation strategies easier to implement in daily practice through enhanced user confidence.

New important monitoring parameters, such as VT/PBW and Driving Pressure were implemented, both continuously visualized in the Servo Compass interface. New options for personalized lung protection and weaning for treatment of all patient categories, from neonates to adults were added. A comparative study of ventilator usability showed higher levels of patient safety and a superior user experience with the Servo. ^[14]

Servo-n was purpose-designed as an all-in-one neonatal ventilator to help provide vulnerable neonates with the support they needed while protecting the lungs, respiratory muscles and other developing organs. ^[15] Dedicated exclusively to neonatal ICU’s and engineered to build confidence for parents and caregivers, it includes aesthetic details like the pediatric-friendly green ladybug casing and a unique Family View.

Compensation for variable leakage in all invasive modes, an optional hot-wire flow sensor as well as the integrated option to run High Flow oxygen therapy had been added. NAVA and NIV NAVA are standard modes, the continuous Edi signal playing an essential role in monitoring and managing apnea of prematurity in order to prevent desaturation and bradycardia.^[15][16][17]

The Servo-air was the first turbine-driven Servo Ventilator with powerful “hot-swappable” battery backup, making it easy to move around the hospital without requiring wall gas or power outlets. With its plethora of Servo legacy functions and gentle and sensitive non-invasive ventilation(NIV) modes, Servo-air was and is ideally suited for intensive and intermediary care as well as intra-hospital transportation. Servo-air proudly carries the Servo Ventilator heritage further in terms of quality, reliability, performance, ease of use and low cost of ownership.

High-frequency oscillatory ventilation (HFOV) has become an established rescue mode for neonates with refractory respiratory failure or severe respiratory distress syndrome (RDS). Some key requirements for its integration into the Servo-n were to make it powerful through active exhalation and at the same time offer the patient reduced work of breathing ^[18]. The patented technology implemented is based on inertia and relies on rapid flow control and synchronization of the inspiratory and expiratory valves, managed by the legendary Servo Control System. This offers both pressure controlled and volume-targeted HFOV modes. The patient-centric solution is also supported by optional monitoring of the babies neural respiratory drive (Edi), which means that respiratory monitoring during this rescue mode is no longer guesswork.

Esophageal manometry had, in the 2010s, experienced something of a scientific renaissance, but was found to be difficult to implement in routine clinical use outside of a research setting. To make this technology more accessible and easy to understand and to improve accuracy, a diagnostic view was developed for the Servo-u that presented esophageal (Pes) and transpulmonary (PL) pressure waveforms with key parameters for assessment of controlled and spontaneous ventilation. In addition, an automatic occlusion maneuver was invented to validate balloon positioning and filling.

This new tool for personalized lung protection has been used extensively during the Covid-19 pandemic, and it has been reported that it is now poised to be implemented in routine clinical practice.

Every patient comes with special challenges. Whether it’s a 300-gram newborn or an adult, an individual suffering from acute respiratory failure or chronic pulmonary disease, their needs and complexities will differ. That is why we are committed to developing innovative, personalized ventilation solutions that help protect the lungs and diaphragm, speed up weaning and support better outcomes.

The Servo ventilator isn’t just an engineering marvel. It’s a philosophy. A mindset, intrinsic in our DNA. It’s this conviction that has driven our pursuit in discovering new techniques for the treatment of critically ill patients. We are constantly evolving and reinventing our therapies and innovative solutions with the aim of helping wean the patient off the ventilator as quickly and safely as possible. The goal is better patient outcomes while simultaneously conserving medical resources. It’s an ambition that has remained with us from the very start, and it’s a way of thinking predominant in everything we do today. Innovation, reliability, enduring quality - doing more with less. Qualities we build into everyone of our Servo ventilators produced today. It’s these same qualities that will define tomorrow’s Servo ventilators, in today’s unpredictable world. It’s how we’ve written our history. And it’s how we’ll shape our future.