04/19/2021 Chicago
Helmet use to deliver non-invasive ventilation, or NIV, has become more common in the United States because of COVID-19. A University of Chicago pulmonary medical doctor shares tips and suggestions for helmet use to treat patients who have COVID as well as others in respiratory distress.
Dr. John P. Kress is a professor of medicine and director of the Medical Intensive Care Unit at the University of Chicago Medicine, a not-for-profit academic medical health system. Kress participated in a University of Chicago study published in 2016 on helmet use in patients with respiratory failure. It showed the benefits of helmet NIV in lowering mortality rates and hospital stays. But the one helmet that they used at that time was not easy to operate, so there was little demand for it, and European helmet manufacturers had no big interest in marketing their product here.
Since COVID, the FDA has issued Emergency Use Authorization, or EUA, approval for two helmets to deliver NIV that are easier to use and more comfortable for patients. The new generation helmet neck rings come in many different sizes and doesn’t need to be cut to size. An inflatable pillow goes around the neck to improve the seal. Helmets also have better access to patients’ faces to suction their mouths, give oral fluids, and perform oral care.
Like other treatments, as technology advances, the use increases gradually. Back in the 1990s, Kress said, people were skeptical of using BiPAP, a type of ventilation delivered via face mask, because they weren’t familiar with it.
There are two ways to use a helmet, Kress said:
Connect the helmet to a ventilator and use pressure support mode to deliver bi-level positive airway pressure.
Use the helmet to deliver continuous positive airway pressure, or CPAP, by connecting gas flow from the wall, not a ventilator.
A helmet used during pressure support ventilation (PSV) can create challenges like patient-ventilator asynchrony, which is different from problems caused when tracheal tubes are used, Kress said.
“The helmet has high compliance, and so when the pressure from the ventilator is given during inhalation, what it initially does, is it inflates the helmet and moves the helmet up, with the neck ring being the most compliant part of the helmet. It (air) doesn’t go into the patient’s lungs, because the patient’s lungs are typically much less compliant than the helmet,” Kress said.
In a pressure support mode, the ventilator continues to give the pressure until it’s programmed to stop, he said, which for most ventilators is 25 percent of the maximum flow. “That’s a long time when the maximum flow is very high because the helmet is so compliant,” Kress said.
Two things have been shown in previous work by other helmet NIV experts to improve the synchrony between the patient, the ventilator, and the helmet, Kress said.
Adjust the onset time on the ventilator from the default of 200 milliseconds to 50 milliseconds, which means the breath gets pushed in quicker.
Increase the offset time, which is typically a percentage of the maximum flow, from a standard 25 percent or 35 percent to 50 percent. That makes the breath end quicker, Kress said.
“That more rapid delivery and short time of inhalation before the breath ends has been shown in previous work – and we did it in our study – to improve synchrony substantially,” Kress said.
Additionally, you can reduce the compliance of the helmet a little bit to help with synchrony, he said, by reducing the amount of movement upward. Sometimes the helmet “looks like a bobblehead going up and down,” he said. If you put something on top to hold it in place, the helmet won’t be as compliant, and you see less dyssynchrony.
Using straps under the armpits can reduce the tendency of the helmet to bob up and down, he added, and some helmets come with straps on the top of the hood.
For patients with hypoxemic respiratory failure, the key to helmet CPAP use is the fresh gas flow of at least 50 liters per minute, Kress said, to make sure you wash out the exhaled carbon dioxide. “What we usually do is just hook the helmet directly up to high-flow nasal cannula apparatus, which can give whatever FIO2 you want, at 60 liters a minute, which will for certain effectively wash out carbon dioxide. Then … you put a PEEP (positive end-expiratory pressure) valve on the expiratory limb.”
When it comes time to wean a patient from the positive pressure of the helmet, Kress suggests you can open the front access port of the helmet – new helmet designs have a large access port to reach the patient’s face easily – and put a high-flow nasal cannula on the patient. Disconnect the gas flow from the helmet and hook it up to the high-flow nasal cannula to see if the patient is ready to come off positive pressure. “It buys you a little bit of time when transitioning from one to the other,” Kress said, and it’s much easier than taking off the entire helmet and neck ring.
Caution, don’t connect the helmet to the ventilator and set it to CPAP mode. Because if you do that, the patient will rebreathe CO2. Only ventilator high flow modes can be used with the helmet interface.
Recent helmet studies of COVID patients found an improved ability to stay off the mechanical ventilation, Kress said.
“I think the key thing that makes the helmet different from a high-flow nasal cannula is the need for PEEP,” he said.
“One thing interesting was that there has been this description written about, since COVID became such a problem, is the different phenotypes of COVID,” Kress said. One phenotype of COVID is seen with conventional acute respiratory distress syndrome, or ARDS, which is airspace filling, very stiff lungs, and the lungs are amenable to PEEP with recruitments, he said.
“But then there’s this other curious group of COVID patients that don’t seem to fall into that biological, physiological category, that is high compliance, … and those patients don’t seem to benefit much from PEEP,” he said.
Kress referenced a study by D.L. Grieco and colleagues of COVID patients using helmet NIV vs. high-flow nasal oxygen. The study didn’t make a distinction between the two COVID phenotypes, but overall, there was a benefit for the helmet group with PEEP.
“PEEP will improve airspace lung recruitment,” Kress said, but “not everybody with COVID has that.”
Helmets are an important component to manage patients, Kress said, particularly COVID patients who have airspace flooding that’s visible on the X-ray.
Kress said he had a few patients who were going to be intubated, so they tried the helmet and had remarkable improvement.
“You put the helmet on, and the patient’s respiratory rate goes from 40 to 16, their saturation on 100 percent high flow nasal cannula goes from 88 to 97 percent and their FI02 goes from 100 percent to 60, and that happens in 30 minutes. Those are the patients for whom the helmet is most clearly beneficial,” Kress said.
But Kress warns to watch the patient carefully.
“In the first 30 to 60 minutes (of helmet use), if there isn’t a substantial improvement, you should think twice and identify this person as somebody who isn’t going to benefit,” he said.
“I think the biggest error people make, and they make the error with noninvasive mask ventilation, too, BiPAP, is they put the BiPAP on, the patient is clearly not performing well – high energy expenditure with breathing, saturation may be in quotes acceptable, but the patient is failing.”
With a helmet or face mask, the patient’s ability to communicate is impaired. You can’t hear them as well, he said, and their saturation may be OK because you’re giving 100 percent oxygen. “But if the patient is working extremely hard to breathe, the saturation is largely irrelevant. And that person needs an advance in the care to perhaps an endotracheal tube,” he said. “Those patients have a very poor prognosis.
“Not everybody is going to benefit from the helmet. Some patients will need to be intubated,” Kress said. “In hindsight, some won’t benefit. Some won’t benefit from being intubated. Unfortunately, those people usually die.”
Kress has had some patients use a helmet for a week or longer.
He also uses sedation from time to time for patients using helmet ventilation. Intubated patients traditionally were routinely sedated the moment you put the endotracheal tube in, which Kress doesn’t think is necessary in some cases but has been practice for many years.
“With the helmet, we don’t begin with the idea focused on sedation but rather focused on alleviating the patient’s breathlessness,” he said. If a person is short of breath and distressed, and the helmet improves that, sedation may not be needed.
Kress may use dexmedetomidine to alleviate distress, but if it’s not effective, those patients usually aren’t going to tolerate the helmet very well, and it’s risky to use other medications, he noted.
Another recent study from A. Sforsa and colleagues showed a small group of patients with hypercapnic cardiopulmonary edema benefited from helmet treatment.
Kress agreed that helmets could benefit hypercapnic hypoxemic patients. “If they have both problems, typically the hypercapnia is an epiphenomenon, meaning when your lungs are stiff from airspace flooding, you are going to be more inclined, in all comers, to have trouble. Because when your lungs are stiff and airspace filled, the energy expenditure with breathing is increased. It’s harder to breathe. If your lungs are wet like a sponge, it’s harder to breathe and eliminate carbon dioxide. And so the CO2 rise is usually a reflection not of bronchospasm or things of that sort but rather energy expenditure, because you’re breathing with your lungs being so flooded. And so the ability to eliminate carbon dioxide is impaired.
“So it’s not uncommon to see patients with pulmonary edema of any type also have rising CO2, especially when you’re looking at people that are debilitated, weak, or essentially just running out from an endurance standpoint,” Kress said.
Helmets sometimes are used for patients with chronic obstructive pulmonary disease, or COPD, as well. However, COPD patients generally benefit so well from BiPAP there isn’t as much positive impact from the helmet, he said.
“But the incremental benefit, in my opinion, is driven more from the benefits of PEEP and airspace recruitment, which is, frankly, why, a decade ago, when we first started thinking about the idea of the helmet for ARDS, we chose to target that population because it seemed like they’d be more amenable to benefiting.”
Currently, Dr. Bhakti Patel, John Kress, and the team at the University of Chicago Medicine are doing research to evaluate the efficacy of helmet NIV in reducing the duration of invasive mechanical ventilation in order to minimize ventilator needs during the COVID-19 pandemic.
Watch a recorded on April 15 2021 video interview with Dr. John P Kress who shared his experience on the use of respiratory assist helmets for reducing the need for invasive mechanical ventilation in COVID-19 patients suffering from ARDS.