Severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), the virus that causes coronavirus disease 19 (COVID-19), primarily affects the respiratory system. A high percentage of patients with COVID-19 who are admitted to an intensive care unit develop severe acute hypoxemic respiratory failure and acute respiratory distress syndrome (ARDS), and ultimately require mechanical ventilation. For patients with COVID-19, noninvasive mechanical ventilation (NIV) with face masks or high-flow nasal oxygen may avert the need for tracheal intubation. However, the use of these NIV methods can increase the risk of viral aerosolization and therefore requires the patient to be placed in an isolation room to prevent airborne spread of disease. This also makes it very difficult or impossible for such patients to be transported while NIV methods are in use and may result in the patient being intubated and mechanically ventilated for transport.
For many years, helmet-based methods to provide NIV support have been used as part of a respiratory failure management strategy in China and European countries. Helmet-based continuous positive airway pressure (H-CPAP) significantly reduces aerosolization and exposure risk to health care personnel compared with face masks or high-flow nasal therapies. Given the resource challenges due to the COVID-19 pandemic, H-CPAP could be a lifesaving, easy-to-perform respiratory management tool for appropriately selected COVID-19 patients with respiratory failure and may avoid the need for intubation or an intensive care unit (ICU) stay. H-CPAP may also be an option when patients with COVID-19 undergo interfacility transport. The following summarizes the evidence for helmet use to deliver NIV support to patients during a respiratory pandemic such as COVID-19.
Patel BK, Wolfe KS, Pohlman AS, Hall JB, Kress JP. Effect of noninvasive ventilation delivered by helmet versus face mask on the rate of endotracheal intubation in patients with acute respiratory distress syndrome: a randomized clinical trial.JAMA. 2016;315:2435-2441.
The authors of this single-center trial of patients admitted to the ICU with ARDS who required NIV randomized patients to receive oxygen therapy either by face mask or H-CPAP and determined whether NIV via a helmet could reduce the rate of intubation and improve other patient outcomes. This was the first such trial to compare the use of H-CPAP with traditional oxygen delivery methods in this patient population.
The primary outcome was the proportion of patients who required tracheal intubation, and the secondary outcomes included 28-day invasive ventilator-free days, the duration of ICU and hospital length of stay, and hospital and 90-day mortality. Patients were randomly assigned to continue face mask NIV or switch to a helmet for NIV support for a planned enrollment of 206 patients (103 patients per group).
A total of 83 patients (55% men, median age = 59 years; 44 to helmet and 39 to face mask) were enrolled and included in the analysis. The trial was stopped early based on predetermined efficacy criteria. The rate of intubation was 61.5% (n = 24) in the face mask group and 18.2% (n = 8) in the helmet group (absolute difference = −43.5%, P < 0.001). The number of ventilator-free days was also significantly higher in the helmet group (28 vs. 12.5, P < 0.001). There were 15 patients (34.1%) who died at 90 days in the helmet group compared with 22 (56.4%) in the face mask group (absolute difference = −22.5%, P = 0.02).
The authors concluded that among patients with ARDS, H-CPAP significantly reduced intubation rates and 90-day mortality, and given the small single-center study, larger multicenter studies were needed to replicate these findings.
Aliberti S, Radovanovic D, Billi F, et al. Helmet CPAP treatment in patients with COVID-19 pneumonia: a multicentre cohort study.Eur Respir J. 2020;56:2001935.
The authors of this prospective, multicenter, observational study evaluated the outcomes of adult COVID-19 patients with pneumonia-related hypoxemic respiratory failure who were admitted to 1 of 3 high-dependency units (HDUs) in Italy and underwent H-CPAP over a 7-week period in 2020. The primary outcome was CPAP failure defined as the occurrence of either intubation or death due to any cause during HDU stay. The secondary outcomes included weaning from CPAP to oxygen therapy (CPAP success) and all-cause in-hospital and 30-day mortality.
A total of 157 patients (74.5% males, median age = 64 years) with hypoxemic respiratory failure and a median Pao 2/fraction of inspired oxygen (Fio 2) ratio of 142.9 underwent H-CPAP. Hypoxemia generally improved when treatment was initiated, with median values of the Pao 2/Fio 2 ratio significantly improving (205.6, P < 0.0001) after 6 hours when H-CPAP was used. However, an increase of at least 30% was found only in 52% of patients undergoing H-CPAP. Eighty-seven (55.4%) patients improved during their HDU stay, were weaned to oxygen therapy, and were transferred to the general ward. H-CPAP failure was observed in 70 (44.6%) patients; 34 (21.7%) were intubated, and 36 (22.9%) died during the HDU stay. Among the 34 patients who were intubated in HDU and transferred to the ICU, 9 (26.5%) died. The all-cause in-hospital and 30-day mortality rates were 28.7% and 28.0%, respectively.
This prospective cohort study was the first to evaluate outcomes in COVID-19 patients undergoing H-CPAP. The authors concluded that the application of H-CPAP in COVID-19 patients can be considered to prevent or potentially delay tracheal intubation. However, the authors point out that prognostic criteria that discriminate responders to H-CPAP therapy cannot be determined from their study.
Ferreyo BL, Angriman F, Munshi L, et al. Association of noninvasive oxygenation strategies with all-cause mortality in adults with acute hypoxemic respiratory failure: a systematic review and meta-analysis.JAMA. 2020;324:57-67.
The authors of this systematic review and meta-analysis compared the association of noninvasive oxygenation strategies with mortality and tracheal intubation in adults with acute hypoxemic respiratory failure. The authors included 25 studies with 3,804 patients with acute hypoxemic respiratory failure in their analysis. Of the 25, 3 trials (330 patients) specifically compared H-CPAP with standard oxygen therapy and found that H-CPAP had a significantly lower risk of tracheal intubation (relative risk= 0.26; 95% confidence interval, 0.14-0.46) and death (relative risk = 0.40; 95% CI, 0.24-0.63) compared with standard oxygen therapy. However, no clinical trial has compared H-CPAP with high-flow nasal cannula; separate clinical trials that directly compared H-CPAP and high-flow nasal cannula with a common comparator, face mask NIV, could be used to generate indirect evidence for the relative benefit associated with H-CPAP versus high-flow nasal cannula. Thus, the certainty of the evidence supporting H-CPAP compared with other modes of noninvasive oxygen support is low because of the limited number of available published clinical trials and the small number of participants. The authors point out that future clinical trials that compare strategies should not focus on which is best but rather on identifying the types of patients who may benefit from any one particular noninvasive therapy.
Tverring J, Akesson A, Nielsen N. Helmet continuous positive airway pressure versus high-flow nasal cannula in COVID-19: a pragmatic randomized clinical trial (COVID HELMET).Trials. 2020;21:994.
Although individual studies and a systematic review found significant reductions in hospital mortality when using H-CPAP in patients with hypoxemic respiratory failure, the evidence to make recommendations regarding H-CPAP is not clear. H-CPAP has gained broad use in the setting of the COVID-19 pandemic, and it is the hypothesis of these authors that H-CPAP can reduce the need for intubation in these patients compared with high-flow nasal cannula without having a negative effect on survival.
The authors are investigating the use of H-CPAP with the assumption that it will increase the number of days alive and ventilator free within 28 days compared with the use of high-flow nasal cannula in patients admitted to Helsingborg Hospital, Sweden, suffering from COVID-19 and acute hypoxic respiratory failure. The treatment (H-CPAP) arm provides helmet-delivered CPAP with a start-up air flow of 40 L/min and a positive end-expiratory pressure of 5 cm H2O. Titration parameters are an oxygen flow and Fio 2 to achieve a target oxygen saturation of 92%, with a maximum allowable positive end-expiratory pressure of 20. The control (high-flow nasal cannula) arm delivers high-flow oxygen via nasal cannula using the Optiflow nasal high-flow interface driven by the AIRVO-2 humidification system (Fisher and Paykel; Auckland, New Zealand), with start-up air flow of 30 L/min and maximum air flow of 60 L/min. Oxygen flow and Fio 2 are titrated to achieve a target oxygen saturation of 92%.
The goal was to recruit 120 patients from an intermediate-level COVID-19 cohort ward and randomize them 1:1 to either H-CPAP or high-flow nasal cannula. All patients had COVID-19 and peripheral oxygen saturation less than 92% despite conventional low-flow oxygen therapy of at least 6 L/min for at least 15 minutes. Patients were excluded if they had a need for direct admission to the ICU for mechanical ventilation, were unconscious or drowsy, had a pneumothorax, had a high carbon dioxide pressure in a venous blood gas, had moderate to severe chronic obstructive pulmonary disease stage, opted not to participate, or could not comprehend the study content and give informed consent.
The study started recruiting adult patients on June 3, 2020, and ended recruitment on April 12, 2021. This study had the potential to clarify the role of H-CPAP in the setting of COVID-19 and provide a first direct comparison between H-CPAP and high-flow nasal cannula. However, the study was terminated because only 2 patients could be recruited. The reasons for termination included too few eligible patients at study start, patients received high-flow nasal cannula before intermediate care ward admission, noninvasive ventilation was considered a step-up therapy to high-flow nasal cannula at the study center, and full-face masks replaced the helmet interface as the local noninvasive ventilation standard. Although this study could have answered key questions regarding H-CPAP, it was unable to do so because of the lack of eligible patients.
In summary, the application of H-CPAP may represent a valid noninvasive method to support a patient's respiratory status and may serve as a bridge to definitive care. H-CPAP is relatively easy to use and may have physiological and biological advantages over alternative noninvasive strategies. Although patients are undergoing H-CPAP, it is not possible to measure minute ventilation, and the helmet itself may facilitate CO2 rebreathing. This requires careful monitoring to ensure the patient is adequately ventilated. Future evidence is needed to quantify the benefits of H-CPAP compared with other methods of respiratory support and identify those patients who are predicted to derive the most benefit from this method. At the present time, that evidence is lacking. Nevertheless, given that H-CPAP decreases air leaks compared with face mask interfaces and can potentially reduce viral transmission when used to treat patients with COVID-19, this method would be advantageous in the close confines of a transport vehicle where providers are in close proximity to the patient for prolonged periods of time. Until further evidence is available, the precise role of H-CPAP in the setting of hypoxemic respiratory failure has yet to be determined.
Biography
Russell D. MacDonald, MD, MPH, FCFP, FRCPC, is the former medical director at Ornge Transport Medicine; the current medical director at Toronto Paramedic Services; a professor in the Faculty of Medicine at the University of Toronto; and an attending staff member at Sunnybrook Health Sciences Centre in Toronto, Ontario, Canada. He can be reached atrussell.macdonald@toronto.ca.