Ventilators

The worldwide outbreak of Covid-19 has countries scrambling to source ventilators, devices that could mean life or death for the most at-risk victims. The sophisticated machines cost as much as a new car and do more than pump air into the lungs; they can detect when a patient wants to breathe and aid the process, ensure the correct air pressure and oxygen mix, and minimize the side effects on fragile lung tissue.

It’s hard to quickly scale the manufacture of such specialized equipment, so governments and companies are getting creative. Ford, GM, and 3M are collaborating to upgrade respirators into ventilators with car parts. South Africa’s National Ventilator Project put out a bid for 10,000 new ventilators to be manufactured by the end of June. India’s Institutes of Technology are prototyping to meet an estimated need in the hundreds of thousands.

The improvisation is a throwback to the early days of ventilators, which saw repurposed sewer pipe and baking tins become turning points in medical history. The first intensive-care unit (ICU) was an act of pure desperation, with shifts of medical students serving as manual ventilators because there weren’t enough machines. Take a deep breath and read on.

2,000: Data points generated per patient per day in a modern ICU

12-20: Breaths per minute a ventilator delivers under normal circumstances

$25,000–$50,000: Cost of a modern ICU ventilator

$2,000: Cost of the original iron lung (about $30,000 today)

<$250: Cost for the parts of the open-source, hospital-grade Apollo Bag Valve Mask

$200-$500: Estimated price of a simplified ventilator Virgin Orbit has designed to run on a windshield-wiper motor

6 mL/kg: Typical “tidal volume” of oxygen delivered by a ventilator, based on a patient’s body weight

200,000: People in an average year with acute respiratory distress in the United States

33%: Share of people who survived a stay in an ICU on a respirator who later showed symptoms of post-traumatic stress disorder (PTSD), in a Johns Hopkins study of acute lung injuries

The first ventilators were mimics of nature. As humans, we breathe by expanding our chests, which creates negative pressure in the lungs, and pulls air in; when the pressure becomes positive, it’s forced out. An “iron lung” encases the body below the neck in a sealed chamber and uses bellows to vary the pressure in place of chest muscles. The first was patented in 1864. Several attempts followed, including one by Alexander Graham Bell, but the first useful breathing machine was built by Harvard professor Philip Drinker in 1929, after widespread electricity use provided a reliable source of power.

But it wasn’t very practical; Drinker himself described it as “rather cumbersome and complicated.” Biomedical engineer John Emerson managed to cut the cost in half—Drinker lost an intellectual-property lawsuit in part because so much of the underlying technology had been tried before—but didn’t change its nature: a giant canister that sealed in a human.

During World War II, Danish anesthesiologist Ernst Morch had designed a positive-pressure ventilator from “a piece of old Copenhagen sewer pipe, a piston and some castoff hardware.” After immigrating to the US, he turned it into a full-fledged device in 1954. At the same time, Forrest Bird, a former US army pilot who had built a high-altitude breathing device during the war, was also working on a prototype ventilator, beginning with baking tins and a doorknob and applying his war experience to the body: “In that lung are rudimentary air foils. It’s like a million airplane wings all down through the lungs,” Bird said (pdf). Bird’s little green box debuted in 1955 and became the first mass-produced positive-pressure ventilator, packing the power of an iron lung into the palm of a doctor’s hand.

“But that life may be restored to the animal, an opening must be attempted in the trunk of the trachea, into which a tube of reed or cane should be put; you will then blow into this, so that the lung may rise again and take air.”

—Belgian anatomist Andreas Vesaliu in his 1543 treatise De Humani Corporis Fabrica, writing about the mechanics of breathing used in today’s ventilators

The point of a ventilator is simple: push air into lungs. Covid-19, for example, causes liquid to build in the lungs, reducing the surface area that can absorb oxygen, so the ventilator compensates with a higher dose. In contrast, if a patient is under anesthesia that interferes with the mechanics of breathing, the ventilator fills in for the patient’s muscles. In less severe cases, a mask delivers the oxygen mixture; otherwise, a tube runs deep down the patient’s airway.

In the 60-plus years positive-pressure ventilators have been in use, they’ve been tuned to the subtleties of breathing in order to treat conditions while minimizing the damage machinated breathing can cause. Early ventilators merely pushed air into the lungs at a constant rhythm; modern versions have two basic modes (pdf): one that delivers a preset volume of oxygen, one that delivers a preset pressure, plus a dual mode. Doctors are still working out which methods are best for which patients.

Ventilators also control positive end-expiratory pressure (PEEP), residual air pressure that prevents lungs from collapsing, a metric that varies on the patient’s condition; they can also be set to sense when a patient wants to breathe and assist with each breath rather than fully controlling breathing. Airway pressure, flow, and oxygen volume are displayed with waveforms that respiratory therapists learn to read.

1674: British chemist John Mayow demonstrates the principle that will eventually create machines to help patients breathe, using an animal bladder inside a bellows.

1864: Alfred Jones patents the first ventilator.

1927: Philip Drinker and Louis Agassiz Shaw Jr., an industrial hygienist and physician respectively, invent the Drinker respirator and coin the term “iron lung.”

1931: American engineer John Haven Emerson improves upon Drinker and Shaw’s design, making the iron lung cheaper.

1949: Emerson creates the first anesthetic ventilator to help patients breathe when anesthetized during surgery.

1952: The first intensive care unit opens in Copenhagen, Denmark in order to provide ventilator support to people with polio.

To be put on a mechanical ventilator today, you have to be intubated first. After doctors put the patient to sleep, they insert a device called a laryngoscope into the mouth, then the throat. They gently push the epiglottis, a flap of tissue that sits over the larynx, out of the way so they can then insert the endotracheal tube down the throat and into the trachea, or windpipe. A small balloon on the tube inflates, creating a seal in the lungs into which the ventilator will add and remove air. Once everything’s secure and in the right place, the laryngoscope comes out, while the endotracheal tube stays in. The other end is attached to the ventilator machine to help the patient breathe.

Though getting put on a ventilator can save someone’s life, it doesn’t guarantee their survival. Over time, the highly oxygenated air it delivers can start to damage the lungs and other organs like the heart. And the tube itself can cause new infections. Multiple studies (pdf) have found that many Covid-19 patients don’t survive ventilation. Those that do (especially if they were on a ventilator for weeks) face long-term damage to the lungs, kidneys, heart, or liver; psychological effects including memory loss, confusion, and post-traumatic stress disorder; and weeks or months of physical therapy to rebuild muscles and nerves that atrophied or were damaged by the sedatives.

These negative effects are part of the reason that doctors are considering less-invasive ventilation for some Covid-19 patients as they learn more about the surprising features of the virus. Some patients are doing better than their critically low blood oxygen levels would suggest; one doctor’s patients “looked a lot more like they had altitude sickness than pneumonia,” according to Stat News. Some hospitals have sent home “borderline” patients with portable, nose-fed oxygen-concentrating machines and oximeters. The problem with using less invasive forms of breathing assistance, though, is that Covid-19 is highly contagious. “[A]fter insertion, intubation is better at preventing the spread of coronavirus in the air than a tube or mask that doesn’t isolate the patient’s respiratory system,” Tim Fernholz and Michael J. Coren report for Quartz.

According to Dr. Kathryn Dreger, a healthy lung is made of such delicate tissue that touching it feels like putting your fingers in “a bowl of whipped cream.”

Having a 10-inch (25-cm) tube stuck down your throat is an experience that would be deeply uncomfortable, should you be awake and conscious of it. Doctors ensure that people on ventilators are treated with drugs that can sedate them, ease the discomfort, and help the ventilator do its job. Some of those drugs include:

• Succinylcholine, muscle relaxant

Many of these drugs are currently in short supply in the US. Pharmacists can help healthcare teams come up with suitable workarounds, though they’re not always ideal.

During the Covid-19 crisis, some designers, including experts in bioengineering and biodesign, are going back to the ventilator’s beginnings with cheap homemade prototypes, in the hopes that they will be good enough to do some good.

All this feeling a little stressful? Try a deep breathing exercise. Start from about 1:00 to get to the good stuff.

In 1952, a polio outbreak in Copenhagen meant that nearly a dozen patients each day suffered respiratory failure in a city with a single iron lung. In Nature, Hannah Wunsch writes that anesthesiologist Bjørn Ibsen came up with a scrappy workaround: Medical students manually ventilated patients around the clock by the hundreds, using bags to pump air into their lungs through tracheotomy tubes—a first, desperate attempt at extended positive-pressure ventilation. Students worked in six-hour shifts for months, saving an estimated 120 lives, reducing the mortality rate from 87% to 31%, and giving birth to the intensive-care unit on the fly.

The Quartz Daily Obsession will be off tomorrow to practice our deep breathing.