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What is A Ventilator And Why Is It So Important?

Forget rebreathers. With the pandemic still spreading, ventilators have arguably become one of the most essential pieces of life-support kit on the planet. We asked anesthesiologist and director of Karst Underwater Research (KUR) Andy Pitkin to brief us on these life-saving devices. Take a deep breath.



by Andrew Pitkin MBBS MRCP FRCA
Header photo by Sungmin Cho from Pixabay

The COVID-19 pandemic has highlighted one piece of medical equipment above all: the ventilator. What are these life-support devices, and how do they work? 

Until the 20th century, with a few exceptions, any patient unable to breathe for themselves was doomed to die. The large polio outbreaks that swept through the world in the 1930s and 40s prompted the design and manufacture of the first reliable means of respiratory support, the iron lung. Properly termed a negative pressure ventilator, and commonly referred to as a ‘tank’ ventilator, the iron lung and some smaller derivatives enclosing just the chest (‘cuirasse’ ventilators) were developed by Drinker1 and Emerson into the only equipment able to keep patients alive when their respiratory muscles had been paralyzed by the poliovirus. Well-funded hospitals in the USA were able to set up large wards full of iron lungs (Fig 1), but it was across the Atlantic, in the northern European country of Denmark, that the modern intensive care unit with its ubiquitous positive-pressure ventilators was born. 

Fig 1. At the height of the 1948 poliomyelitis epidemic 82 patients required ventilation in iron lungs at the same time in Los Angeles. Photo courtesy from “Patenting the Sun” by Jane S. Smith.

In the mid-1950s, Copenhagen, Denmark’s capital city, was ravaged by a severe polio epidemic that completely overwhelmed its handful of iron lungs and forced the physicians there to adopt methods borrowed from the operating room just to keep people alive. In desperation, the director of the infectious diseases hospital, the Blegsdamhospitalet, asked his anesthesiologist colleague Dr Bjorn Ibsen for help. Under Ibsen’s direction,  patients received tracheostomies and intermittent positive-pressure ventilation using a rebreathing system called a Waters circuit (Fig 2). 

Fig 2. A Waters circuit used for hand ventilation of poliomyelitis victims in the 1952 outbreak in Copenhagen, Denmark. A simpler system without the soda lime canister was used later, with the disadvantage that a higher flow rate of oxygen/nitrogen mixture was required to prevent excessive rebreathing of carbon dioxide. Illustration by InDepth.
Bjorn Ibsen. Photo courtesy of P.G. Berthelson.

Rebreather divers will easily recognize this as a pendulum rebreather system, but in this case the gas moved in and out of the patient’s lungs not through their own efforts, but by a medical student squeezing and releasing the bag (counterlung) 20 to 25 times per minute, 24 hours a day, for periods of up to several months. In the absence of enough mechanical ventilators, hundreds of medical students risked exposure to the much-feared polio virus to keep these patients, many of them children, alive (Fig 3). The success of positive-pressure ventilation in dramatically reducing mortality in Denmark rapidly spread throughout the world and the modern intensive care unit was born.

Fig 3. A patient with poliomyelitis being hand ventilated with a Waters circuit through a tracheostomy. Medical students were paid 30 shillings (about $100 today) for an 8-hour shift (with a 10-minute break for a cigarette in the middle!). Photo by Lassen HCA.

Human muscle power was soon replaced with mechanical power using either motorized bellows or a pressure-regulated gas source controlled by an automatic valve (like pressing the purge valve on a regulator’s second stage). The first classification by Mapleson2 divided ventilators into flow generators and pressure generators; both could be further subclassified into time-cycled, pressure-cycled and volume-cycled units, depending on what parameter the machine used to switch from inspiration (breathing in) to expiration (breathing out) and vice versa. An example of a flow generator is a typical bellows ventilator such as the Oxford Penlon unit (Fig 4), still used in some hyperbaric chambers because of its mechanical simplicity, and many anesthesia machines in operating rooms have similar ventilators built in. 

Fig 4. The venerable Penlon Oxford ventilator is a simple bellows system driven by a 60 psi compressed gas supply. A smaller set of bellows can be substituted for use in children. Photo courtesy of A. Pitkin.

Modern Ventilators

With advances in microelectronics in the 1970s it became feasible to integrate gas control valves with flow and pressure sensors to allow a single ventilator to work in a flow-generating mode as well as a pressure-generating mode, and many other modes became possible that could not be realized with a simple mechanical ventilator. Units such as the Siemens Servo 900 (Fig 5) and the Puritan Bennett 7200 were in the vanguard of this approach.

Fig 5. The Siemens Servo 900C, a ventilator I became intimately familiar with while training in intensive care in the early 1990s. Introduced in 1971, its use of electronically-controlled scissor valves to regulate gas flow based on input from pressure and flow sensors represented a major advance over earlier designs. Photo courtesy of Siemens Healthineers. Special thanks to Healthineers’ media team divers!

Modern intensive care ventilators have evolved into complex computer-controlled systems that operate with a degree of precision, flexibility and sophistication that would astonish Ibsen and his contemporaries (Fig 6). In the rare cases that adequate oxygenation and/or carbon dioxide clearance cannot be achieved with conventional ventilators, highly specialized options such as high frequency oscillatory ventilation (HFOV) and extracorporeal membrane oxygenation (ECMO) also exist.

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Fig 6. Simplified schematic of the pneumatic system of a modern intensive care ventilator. For simplicity, this diagram omits many important components, including non-return and safety valves, calibration and alarm systems. Diagram courtesy of A. Pitkin.

A patient with respiratory failure must be intubated with a breathing (endotracheal) tube in the windpipe (trachea) which connects to the ventilator, and to tolerate this they often need sedation and occasionally chemical paralysis to prevent them from “fighting” the ventilator, although most modern ventilators have useful support modes that synchronize the ventilator with the patient’s own respiratory efforts. An alternative to the endotracheal tube placed through the mouth, especially useful in the longer term, is to place a tube in the trachea through the front of the neck (tracheostomy), and this approach undoubtedly contributed to Ibsen’s success in Copenhagen as many polio patients had paralysis of the muscles of their throat and voicebox (larynx) and so were unable to protect their lungs from contamination by coughing. Both endotracheal tubes and tracheostomies bypass the normal humidification that occurs in the upper airways so humidification of the gas supplied to the patient is important to prevent drying out of the lining of the airways.

Current medical practice is to set tidal volumes at 6-8 ml/kg (ideal body weight) and adjust respiratory rate to achieve the desired carbon dioxide (CO2) clearance. Almost all modern ventilators can be time-cycled (most common), pressure- and volume-cycled. Patients are generally most comfortable when the partial pressure of CO2 in their blood (PaCO2) is just below normal but with severe respiratory failure it is frequently better to allow it to rise above normal as long as adequate oxygenation can be maintained rather than subjecting diseased lungs to a higher tidal volume or respiratory rate – this is called permissive hypercapnia.  Oxygenation is largely determined by the fraction of inspired oxygen (FiO2) and mean (average) airway pressure, the latter being influenced by a number of ventilator settings such as inspiratory/expiratory time ratio, positive end-expiratory pressure (PEEP) as well as patient factors such as lung compliance. For complex reasons it is common for other organ systems such as the heart and kidneys to fail in patients with respiratory failure, so for them to survive it requires a skilled team of doctors, nurses and other staff to monitor and intervene when problems occur. 

Bjorn Ibsen went on to establish the first real intensive care unit, which he called an ‘observation unit’, at the municipal hospital of Copenhagen where he was appointed chief of the anesthesiology department in 1954. He widened its scope to include any patient who needed respiratory or cardiovascular support for any reason, such as trauma, post-operative complications, sepsis and so on. One of the pioneering features was a multidisciplinary team approach that has stood the test of time and is still used today. Another was the idea that no matter what the original disease, the same principles of organ support apply. These ideas are so universally accepted now that it is hard for us to conceive of a time when they were not. 

Ventilators and the Covid-19 Virus

At the time of writing this, ventilators look like they could soon be in short supply and they cost tens of thousands of dollars. Why are they so complex and expensive? It is relatively easy to build a system of valves and sensors and an electronic control system that will function, but quite another to do so to the (justifiably) high standards of design quality, reliability, safety, ease of use and infection control that modern medicine demands. Getting any medical device approved by the US Food and Drug Administration (FDA) is very expensive and time-consuming, and similar regulatory processes exist in Europe and the rest of the world. Nevertheless, some would argue that medical device costs (like medications) are out of control, but essentially the price of sophisticated medical technology is a balance between its development costs and the price that the market will support. 

Dr. Andrew Pitkin at work.

The COVID-19 pandemic has spawned a number of projects to tackle the projected shortage of ventilators with homebuilt systems. Usefully, the Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom has published a set of specifications for a Rapidly Manufactured Ventilator System (RMVS), a minimum standard that such a ventilator has to meet to be useful, based on expert opinion3. These efforts are to be applauded, but use of such a ventilator would be close to a last resort, after all the ventilators in anesthesia machines in every operating room were in use. What is more, it doesn’t address the issue that patients with severe COVID-19 disease often have multiple organ involvement and it is the highly-skilled and cohesive medical and nursing teams to apply the principles that Ibsen and others pioneered that are the real limiting factor.


  1. Drinker P, McKhann CF. The use of a new apparatus for prolonged administration of artificial respiration. JAMA 1929; 92: 1658-61.
  2. Mapleson WW. The effect of lung characteristics on the functioning of artificial ventilators. Anaesthesia 1962;17:300-14.
  3. accessed April 17th, 2020.

Additional Resources

Karst Underwater Research

Andrew Pitkin learned to dive in 1992 in the cold murky waters of the United Kingdom and started cave and technical diving in 1994. His first exposure to exploration was in 1995 when he was one of a team of divers who were the first to reach the bottom of the Great Blue Hole of Belize at 408 fsw (123 msw). Subsequently he has been involved in numerous cave exploration projects in Belize, Mexico and Florida.
From 1996-2000 he was employed at the Royal Navy’s Institute of Naval Medicine, running a hyperbaric facility, treating decompression illness, participating in research into outcome after decompression illness, submarine escape and testing of new military underwater breathing systems. He is one of a handful of civilians to be trained by the Royal Navy as a diving medical officer.  
He moved to Florida in 2007 and is currently on the faculty of the College of Medicine at the University of Florida in Gainesville. With Karst Underwater Research he has participated in numerous underwater cave exploration and filming projects. Like many explorers, he spends much of his spare time developing and building innovative equipment for exploration purposes.

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The Price of Helium is Up in the Air

With helium prices on the rise, and limited or no availability in some regions, we decided to conduct a survey of global GUE instructors and dive centers to get a reading on their pain thresholds. We feel your pain—especially you OC divers! InDEPTH editor Ashley Stewart then reached out to the helium industry’s go-to-guy Phil Kornbluth for a prognosis. Here’s what we found out.




Helium Technical Diving

By Ashley Stewart. Header image by SJ Alice Bennett.

Helium is one of the most abundant elements in the universe, but here on Earth, it’s the only element considered a nonrenewable resource. The colorless, odorless, and tasteless inert gas is generated deep underground through the natural radioactive decay of elements such as uranium and thorium in a process that takes many millennia. Once it reaches the Earth’s surface, helium is quickly released into the atmosphere—where it’s deemed too expensive to recover—and rises until it ultimately escapes into outer space. 

Luckily for divers who rely on the non-narcotic and lightweight gas for deep diving (not to mention anyone who needs an MRI scan or who uses virtually any electronic device), some helium mixes with natural gas underground and can be recovered through drilling and refinement.

Yet the world’s helium supply depends primarily on just 15 liquid helium production facilities around the globe, making the industry uniquely prone to supply chain disruptions, which this year caused the industry’s fourth prolonged shortage since 2006. The shortage has caused many technical dive shops around the world to raise prices, limit fills, or stop selling trimix altogether, according to an InDEPTH survey of GUE instructors and affiliated dive centers.

Longtime helium industry consultant Phil Kornbluth, however, expects the shortage will begin to ease gradually now through the end of the year, and for supply to increase significantly in the future.

Photo courtesy of Extreme Exposure

While a majority of the world’s helium is produced in just a few countries, a new gas processing plant in Siberia is expected to produce as much as 60 million cubic meters of helium per year, about as much as the US—the world’s largest helium producer—was able to produce in 2020. The Siberian plant ran for three weeks in September, but experienced major disruptions over the past year, including a fire in October and an explosion in January, that delayed its planned opening until at least 2023.

Meanwhile, according to Kornbluth, the U.S. Bureau of Land Management in Texas closed down from mid-January to early June due to safety, staff, and equipment issues, wiping out at least 10% of the market supply. The plant reopened in June and is back to normal production as of July 10. The supply of helium was further reduced as two of Qatar’s three plants closed down for planned maintenance, a fire paused production at a plant in Kansas, and the war in Ukraine reduced production of one Algerian plant.

With the exception of the plant in Siberia, Kornbluth said virtually all of the recent disruptions to the helium supply chain have been resolved and should yield some relief. And the future looks promising. Once the Siberian plant is online, it’s expected to eventually boost the world’s helium supply by one-third. While sanctions against Russia could prevent some buyers from purchasing the country’s helium, Kornbluth expects there will be plenty of demand from countries that as of now are not participating, like China, Korea, Taiwan, and India, though there could be delays if those countries have to purchase the expensive, specialized cryogenic containers required to transport bulk liquid helium. “Sanctions are unlikely to keep the helium out of the market,” Kornbluth said.

Meanwhile, there are at least 30 startup companies exploring for helium, and there are other projects in the pipeline including in the U.S., Canada, Qatar, Tanzania, and South Africa. “Yes, we’re in a shortage and, yes, it’s been pretty bad, but it should start improving,” Kornbluth told InDEPTH. “The world is not running out of helium anytime soon.” 


To find out how the helium shortage is affecting divers, InDEPTH surveyed Global Underwater Explorers’ (GUE) instructors and dive centers and received 40 responses from around the world. 

The survey’s highest reported helium price was in Bonaire—a Dutch island in the Caribbean that imports its helium from the Netherlands—where helium costs as much as US$0.14 Liter(L)/$4.00 cubic foot (cf) and is expected to rise. At that price, a set of trimix 18/45 (18% O2, 45% He) in double HP100s (similar to D12s) would cost around $360.00 and trimix 15/55 would cost $440.00.

“We have enough to support both open circuit and CCR, but in the near future, if the situation remains, we may be forced to supply only CCR divers,” Bonaire-based GUE instructor German “Mr. G.” Arango told InDEPTH. “We have enough for 2022, but 2023 is hard to predict.”

Not far behind Bonaire was the Philippines, where helium costs around US$0.13 L/$3.68 cf—if you can even get it. Based on the responses to our survey, Asia is experiencing the greatest shortages. Supply is unavailable in some parts of the Philippines, limited in South Korea, and unavailable for diving purposes in Japan as suppliers are prioritizing helium in the country for medical uses, according to four instructors from the region. In Australia, it’s relatively easy to obtain.

Four US-based instructors reported that helium prices are increasing significantly and supply is decreasing. Helium remains “very limited” in Florida and prices in Seattle increased to $2.50 from $1.50 per cubic foot ($0.09 L from about $0.05 L) in the past six months, and there was a period when the region couldn’t get helium as suppliers were prioritizing medical uses. In Los Angeles, prices have reached as high as $2.80 cf (nearly $0.10 L) and one instructor reported helium is only available for hospitals and medical purposes, even for long-term gas company clients who are grandfathered in. Another Los Angeles-based instructor said direct purchases of helium had been limited to one T bottle per month, down from three. 

“Currently, we are only providing trimix fills for our CCR communities,” GUE instructor Steven Millington said. “Possibly this will change, but the current direction for active technical divers is CCR. I agree (and already see) that open circuit technical diving in some regions will go the way of the dinosaur.”

In Western Europe, helium is becoming more difficult and expensive to acquire, 10 instructors in the region told us. Instructors in the United Kingdom, Spain, Italy, and Germany reported longer wait times, high price increases, and limited supply. 

Meanwhile, Northern Europe appears to be a bright spot on the map with comparatively reasonable prices and general availability. In Norway, two instructors reported helium is easy to obtain, with no lead time from suppliers. Likewise in Sweden and Finland, though one Finnish instructor told us that in the past year prices have increased significantly.

Three instructors in Northern Africa and the Middle East said helium is easy to get, but is becoming more expensive. The price of Sofnolime used in rebreathers is increasing in Egypt as helium becomes more expensive and more difficult to obtain. Lebanon has minimal lead times, but helium is among the most expensive in all of the responses we received at US$0.10 L/$2.83 cf.

Helium is generally easy to obtain in Mexico, though prices are increasing dramatically and instructors are starting to see delays. In Brazil, prices in São Paulo quadrupled in the past 12 months and by 30% in Curitiba. Suppliers there aren’t accepting new customers and existing customers are having difficulty obtaining supply. Supply is mostly constrained in Canada, with the exception of one outlier: an instructor who has a longstanding account with the gas company and pays less than US$ 0.035 L/$1.00 cf. “I have been hearing of helium shortage every year for the last decade,” instructor Michael Pinault of Brockville Ontario told InDEPTH, “but I have never not been able to purchase it.”

Many instructors around the world said that helium shortages and skyrocketing prices are, no surprise, fueling a shift to CCR for individual divers and exploration projects. “CCR is saving our exploration projects,” GUE instructor Mario Arena, who runs exploration projects in Europe, said. “These projects would be impossible without it.”

Please let us know what helium prices and availability are in your area: InDEPTH Reader Helium survey

Additional Resources

US Geological Survey: Helium Data Sheet: Mineral Commodity Summaries 2021

NPR: The World Is Constantly Running Out Of Helium. Here’s Why It Matters (2019)

The Diver Medic: The Future of Helium is Up in the Air,” Everything you wanted to know about helium, but were too busy analyzing your gas to ask—talk by InDEPTH chief Michael Menduno

InDepth Managing Editor Ashley Stewart is a Seattle-based journalist and tech diver. Ashley started diving with Global Underwater Explorers and writing for InDepth in 2021. She is a GUE Tech 2 and CCR1 diver and on her way to becoming an instructor. In her day job, Ashley is an investigative journalist reporting on technology companies. She can be reached at:

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