In the past, emergency responders would have used bag-valve-mask (BVM) ventilation until arrival at an intensive care unit (ICU) and transfer of the patient to a large and complicated ventilator, explained Anne-Marie Willems, Application Specialist at WEINMANN Emergency. However, BVM requires one person to hold a mask tightly over the patient’s mouth while another squeezes a rubber bag to force oxygen or air into the lungs. As there is no measurement or control to limit the pressure being applied, it can be a risky procedure on people with lung problems.

BVM has now been replaced generally by mechanical ventilators, and developments in technology have made these devices light and small enough to be used in the pre-hospital environment, carried in ground and air ambulances. They can also carry out pre-programmed automatic ventilation patterns that are simply selected by the doctor or paramedic to suit the casualty’s condition.

 While some applications are non-invasive, requiring just a mask, many air medical patients have serious injuries, hence the need for transport, and so they need to be anesthetized and a breathing tube inserted into their airway, which is then connected to the ventilator. Causes can include:

• Cardiac arrests, where the patient has been resuscitated and a pulse restored
• Head trauma, where the patient’s consciousness is too low
• Spontaneous brain bleed; or an evolving brain injury, where being anesthetized protects the brain
• Impaired respiratory mechanics, such as neuromuscular disease
• Poor gas exchange, such as pneumonia
• Coma or upper airway obstruction, where the patient’s ability to breathe has to be maintained.

There are a number of ventilation patterns that can be used:

• With bilevel positive airway pressure (BiPAP), a slightly pressurized airflow is blown into the airways. The continual positive pressure helps to open the airways, allowing more air to get in and out of the lungs. It can be used as a fully controlled ventilation mode but does allow spontaneous breathing (which has physiological benefits) at any time
• Airway pressure release ventilation (APRV) is a pressure-controlled mode of ventilation that delivers an almost continuous positive pressure with intermittent, time-cycled short releases at a lower pressure
• Positive end-expiratory pressure (PEEP) maintains a positive pressure in the airway at exhalation that helps to prevent collapse of distal alveoli, the small sacs in the lung that enable the exchange of oxygen and carbon dioxide between inhaled air and the bloodstream
• Continuous positive airway pressure (CPAP), as the name implies, constantly maintains a level greater than atmospheric pressure in the upper respiratory tract.

Helicopter operations

Emergency medical services (EMS) operations are complicated by never knowing what is waiting after arrival on scene and by tight limits on space in the cabin and the amount of weight onboard. These have been design drivers for WEINMANN Emergency with its range of transport

EMS operations are complicated by never knowing what is waiting after arrival on scene and by tight limits on space in the cabin and the amount of weight onboard

ventilators (MEDUMAT Transport, MEDUMAT EasyCPR, MEDUVENT Standard, MEDUMAT Standard2), and its helicopter customers include Johanniter Luftrettung (St John Air Ambulance) in Germany, Rega in Switzerland, and Great North Air Ambulance Service and Thames Valley Air Ambulance in the UK.

Thames Valley Air Ambulance, which is celebrating its 25th anniversary this year, has seven MEDUVENT Standard turbine-driven ventilators. It became an independent healthcare provider in 2018. In October 2022, it gained its own air operator certificate and acquired an Airbus Helicopters EC135 T2+. From its base at RAF Benson in southern England, the helicopter can reach anywhere in the coverage area of Oxfordshire, Berkshire and Buckinghamshire within 15 minutes’ flying time. In addition, there are five critical care response vehicles, two of which are on call at any one time and can reach anywhere within 40 minutes. A typical medical crew consists of a doctor and a paramedic. It is a charity that receives no local or national government funding, relying on donations from the public, so this is quite an achievement.

Dr Asher Lewinsohn is an anesthetic and intensive care consultant and also a HEMS Pre-Hospital Doctor with Thames Valley Air Ambulance. He led on the project to select a replacement for the previous paraPAC ventilators. Not only had technology moved on but, as Thames Valley Air Ambulance activities expanded, it was encountering a wider range of medical emergencies requiring ventilation. Consistent feedback from other unit doctors and paramedics was that size and ease of use were key parameters. Dr Lewinsohn also wanted a system that was better than the previous model and could provide ventilation that was as close to ICU standards as possible.

 Physically, the MEDUVENT Standard measures just 8.1in x 5.4in x 5.1in (206mm x 137mm x 130mm), with a weight (including battery) of 4.6lb (2.1kg). That allows it to be carried in the standard medical equipment bags used by ambulance crews on every mission, without the need for a new bag or increased carry weight. When used on the helicopter, it is fitted to a custom bracket to make it safe in-flight.

Dr Lewinsohn said using the MEDUVENT Standard gives him much more precise control and it is very consistent in the care that can be delivered when compared with the older paraPacs. He can work properly with pressures and volumes more accurately, adjusting them if necessary to keep the patients safe and maintain a high standard of care at all times. There is also a chest compression synchronized ventilation (CCSV) mode used during cardiopulmonary resuscitation (CPR), in which a pressure-controlled mechanical breath is synchronized with the manual compression to increase pressure in the lungs (a unique WIENMANN facility on the MEDUVENT Standard, said Willems). A hygiene filter protects the patient, crew and the device from viral and bacterial contamination as well.

In Thames Valley Air Ambulance daily operations, which run from 07:00 hrs to 02:00 hrs (with the helicopter flying in daylight hours), up to six ventilators can be in use at different times between the helicopter and critical care response vehicles, so the seventh is kept as a standby spare in case of problems.

Battery life is 10 hours but Thames Valley Air Ambulance missions by helicopter or car are much shorter than that and so a ventilator might be used for about an hour in each case. Nevertheless, it goes on charge at the end of each shift so it is at full power for its next use. End of shift also sees all the other used items in the kit bags replaced and made ready for the next shift or crew.

It is thanks to the charity being an independent healthcare provider that it can make its own evidence-based decisions based on operational experience in its local environment

This is all part of Thames Valley Air Ambulance’s constant focus on active patient safety and its world-class care policy, Dr Lewinsohn added. It is thanks to the charity being an independent healthcare provider that it can make its own evidence-based decisions based on operational experience in its local environment, which includes the ventilator upgrade, he said.

Fixed-wing operations

Dr Sebastian Gautsch, Medical Director with FAI rent-a-jet, based at Albrecht Dürer Airport in Nürnberg, Germany, said that, as a general classification, the company carries ventilated patients suffering from similar problems to those flown by helicopter, but the cabin environment is entirely different. First, there is the pressure of cabin altitude in cruise: cabin altitude is inevitably higher than sea level and so has a lower oxygen content – typically 10,000ft for an airliner; for the Challenger it is 6,500ft and for the Global Express 5,680ft. While the slightly reduced oxygen levels do not affect healthy individuals, if the patient has a compromised respiratory function, low cardiac output, anemia, or a combination of these conditions, ventilation may become necessary to improve oxygenation.

A further complication is managing the pressure changes during climb and descent, which may occur several times during a long transfer if refueling stops have to be made. Air within cuffs or endotracheal tubes and tracheal cannulas will expand at cruising altitude, meaning that cuff pressures have to be diminished in order to prevent pressure-related injuries of the trachea. On descent, the cuff will have to be filled with additional air to prevent leakage. In addition, aircraft vibration, movements and turbulence have to be taken into account as they could upset the ventilation patterns, so sedation may be used to help, or increased in some cases.

Another unique aspect of fixed-wing operations, because of their longer flight times, is advance preparation to ensure adequate therapeutic effects and to minimize potential complications

For FAI, the Hamilton-T1 turbine ventilator is fit as standard. Weighing 6.5kg, it has two batteries, each with a four-hour life, but these are only used during ground transfers as the T1 can be powered by the aircraft’s electrical system when onboard.

Dr Gautsch said that continuous monitoring of heart rate, blood pressure, oxygen saturation, and respiratory rate are standard procedures but become more important in the aircraft; for ventilated patients, regular monitoring of blood gas levels is also essential. Another unique aspect of fixed-wing operations, because of their longer flight times, is advance preparation to ensure adequate therapeutic effects and to minimize potential complications. That means precise calculation of the amounts of required medications and oxygen supply for each sector of the flight.

Nico Raab, Head of Medical Department at FAI, explained that some repatriation companies have regular seasonal markets, e.g. for ski injuries in winter. However, each FAI mission can be at short notice to anywhere in the world. And the aircraft does not always return to base – it can be tasked for the next mission from wherever it might be, remaining in the field for some time.

FAI has been in operation for over 30 years, with an unusual business model that combines VIP charters with air ambulance work. It also specializes in air support in hostile areas for the world’s largest NGOs, such as the International Committee of the Red Cross (ICRC), the United Nations World Food Programme (WFP), and government agencies. The business is supported by more than 250 full-time staff, plus 80 physicians, nurses and paramedics.

It has a fleet of 16 aircraft, of which four Learjet 60s and five Bombardier Challenger 604s are dedicated to medevac operations, each with a permanently installed Spectrum Aeromed intensive care base with power and oxygen. For very long missions, this equipment can be temporarily fitted to a Bombardier Global Express from the charter side of the business. All three types can carry an additional non-ICU patient on a stretcher, with room for two more seated patients on the Challenger and up to eight on the Global Express. A typical medical crew consists of a flight doctor and a flight paramedic or nurse.

Extracorporeal membrane oxygenation (ECMO) support temporarily draws blood from the body to allow artificial oxygenation of the red blood cells and removal of carbon dioxide

The Challenger carries additional equipment for extracorporeal membrane oxygenation (ECMO) support, which temporarily draws blood from the body to allow artificial oxygenation of the red blood cells and removal of carbon dioxide. This is used for patients with profound heart and/or lung failure.

That sort of extended operation means that relief flight and medical crews have to be pre-positioned ahead of the aircraft. Typically, up to three ICU patients can be carried in succession without needing to replenish supplies. Because East Asia is a common destination, Dubai World Central airport and Al Bateen Executive Airport in Abu Dhabi are FAI hubs, where many crew changes take place and spare materials are held. They have also been used to transfer patients from one aircraft to another (‘wing-to-wing’).