Noninvasive ventilation with helmet continuous positive air pressure (CPAP) deserves to be embraced as an effective strategy in preventing self-induced lung injury, often a key factor in progression from the early milder expression of COVID-19 disease to classic severe acute respiratory distress syndrome, according to European physicians who have been through what they hope are the worst days of the pandemic in the Lombardy region of Northern Italy.
Courtesy Dr. Luciano Gattinoni
Dr. Luciano Gattinoni
Helmet CPAP is a relatively inexpensive, convenient, well-tolerated intervention. It allows patients to remain conscious and responsive to commands such as “Time to roll over,” which in turn frees up nursing staff. The purpose of helmet CPAP is to curb the huge inspiratory drive that’s a defining feature of this disease and which, unchecked, can lead to self-induced lung injury (SILI), Luciano Gattinoni, MD, explained at a webinar hosted by the European Society of Anaesthesiology.
“Paranoid attention to inspiratory effort – checking it and correcting it – is something where we can make the difference between death and life. It’s extremely important,” said Dr. Gattinoni, guest professor of anesthesiology and intensive care at the University of Gottingen (Germany).
He and his fellow panelists were in accord regarding the merits of helmet CPAP as the premier method of noninvasive ventilatory assistance. They also addressed the importance of monitoring for hypercoagulation, as well as what they’ve come to see as the essential role of pronation in what they define as Type H disease, and the need to have detailed respiratory physiotherapy protocols in place.
“COVID-19 doesn’t like physiotherapy,” explained Paolo Pelosi, MD, professor of anesthesiology and intensive care medicine at the University of Genoa (Italy).
Dr. Gattinoni is credited for identification of two polar phenotypes of what he considers to be a single COVID-19 disease. Early on, many patients present with an atypical form of acute respiratory distress syndrome (ARDS), distinguished by an often-unexpected degree of hypoxia accompanied by high pulmonary compliance and surprisingly little shortness of breath. Dr. Gattinoni and colleagues call this Type L disease, which stands for low elastane, low ventilation to perfusion ratio, low lung weight on CT, and low lung recruitability, which means the patient has a high proportion of aerated lung tissue. Over time, because of either the natural history of the disease or SILI, this may shift to Type H disease, marked by high elastane, high right-to-left shunt, high lung weight, and high recruitability.
“If the pulmonary compliance is above 60 [mL/cm H2O], I’m pretty sure it’s Type L. If it’s 30 [mL/cm H2O] or less, I’m pretty sure it’s Type H. Don’t ask me about 45-55 [mL/cm H2O]; it’s a grey zone,” Dr. Gattinoni said.
Giuseppe Foti, MD, said helmet CPAP in patients with COVID-19 should be free flow, not attached to a ventilator, and the gas flow should be set high – at least 50 L/min – in order to prevent CO2 rebreathing. Although noninvasive ventilation is well accepted for patients with chronic obstructive pulmonary disease or acute cardiogenic pulmonary edema, it hasn’t been extensively studied in the setting of ARDS. A notable exception is a single-center randomized trial in which 83 patients with ARDS at the University of Chicago were assigned to noninvasive ventilation delivered by helmet or face mask (JAMA. 2016 Jun 14;315[22]:2435-41). The endotracheal intubation rate was just 18% in the helmet group, compared with 62% in the face mask group. The 90-day mortality rate was significantly lower in the helmet group as well, noted Dr. Foti, director of the department of anesthesia and intensive care at Monza University Hospital in Milan.
Christian Putensen, MD, said he views intubation for mechanical ventilation as wise in moderate or severe ARDS with an arterial oxygen partial pressure/fraction of inspired oxygen (PaO2/FiO2) ratio below 150. But in milder, Type L COVID-19 disease, he also likes helmet CPAP. It spares the patient from the traumatic compressive stress to the lung induced by mechanical ventilation, which may cause alveolar edema and SILI.
There is, however, a caveat: “Watch carefully and do not delay intubation if you see helmet CPAP is not working; that is, if the blood gas analysis doesn’t improve, the respiratory rate increases, tidal volume increases, and there is still increased respiratory drive,” advised Dr. Putensen, an anesthesiologist at the University of Bonn (Germany).
There is no agreed-upon practical quantitative measure of respiratory drive. A clinical evaluation of the patient’s depth of inspiration is the best guide, he added.
Dr. Gattinoni said that, when helmet CPAP can’t control respiratory drive in a patient with early-stage disease, he feels the only way to interrupt this destructive process is through early intubation and what he termed “gentle mechanical ventilation,” not with a positive end expiratory pressure of 20 cm H2O, but more like 4-5.