Like its predecessors, SARS-CoV and Middle Eastern respiratory syndrome (MERS)-CoV, SARS-CoV-2 is a coronavirus that can be transmitted to humans and cause significant respiratory disease. 1 As of April 24 th 2020, there are over 2.85 million reported SARS-CoV-2 positive patients globally, resulting in at least 198,000 deaths. 2 The disease associated with SARS-CoV-2 infection is now known as COVID-19.
Although most SARS-CoV-2 infections cause very mild symptoms, approximately 5% of patients develop acute respiratory distress syndrome (ARDS) with some patients progressing to multiorgan dysfunction. This disease has been reported to have a case fatality ratio (CFR) of 1-4%. 3 In just over a month, COVID-19 has become the leading cause of death in the United States of America in 2020, overtaking both heart disease and cancer. 4 Currently many hospitals around the world are struggling to meet the needs for mechanical ventilators and expand intensive care unit (ICU) capacity. 5 The reserve capacity for ventilators is necessary given the expected surge in hypoxemic patients presenting with progressive COVID-19, and an uncertain future when our seasons change. 5 The aim of this stand-alone editorial is to examine the role of helmet delivered continuous positive airway pressure (CPAP) noninvasive ventilation (NIV) as an adjunct to mechanical ventilation in patients requiring respiratory support in COVID-19.
The recent Surviving Sepsis Campaign: Guidelines on the Management of Critically Ill Adults with Coronavirus Disease 2019 consensus statement agrees that; following admission for COVID-19, each patient may progress at a variable rate to either recovery, with minimal oxygen requirements and no ventilatory support, or a worsening of the disease process and the need for an escalation in NIV and mechanical ventilation. 6 When COVID-19 progression is identified, the current critical care management recommendation is to initiate early endotracheal intubation and mechanical ventilation. 6 This recommendation aims to avoid emergent intubation in a rapidly decompensating patient should worsening hypoxemia develop if intubation is delayed. This recommendation is also aimed at source control, decreasing the risk of cross contamination from droplet and aerosolized viral particles to other patients and health care workers (HCW). 6 All persons under investigation (PUI) for COVID-19 and all COVID-19 positive patients should wear a mask. 6, 7 It is also recommended that all HCWs should wear droplet and contact personal protective equipment (PPE) to provide a mechanical barrier to droplet spread and ideally be greater than 2 meters from the patient. 6, 7 Additional airborne PPE is required during any aerosol generating medical procedures (AGMP) in these patients. 6, 7 These recommendations are based on reports that 11% of critically ill patients in Wuhan required High Flow Nasal Cannula (HFNC) and this increased the risk of viral aerosolization and droplet transmission . 3, 6, 8, 9 While HFNC poses significant risks for providers, patient mortality associated with mechanical ventilation is also significant. Mortality among COVID-19 patients over 65 years of age in the Seattle was at least 62%. 10 A recent report from the experience in New York found the mortality associated with intubation and mechanical ventilation in 5700 patients hospitalized with COVID-19 was 76% in the those aged 18 to 65 years and 97% in patients over 65 years of age. 11 The usual features of typical ARDS, recently termed the H-type, in COVID-19 patients are a progressive deteriorating lung compliance requiring increased inspired oxygen concentration(FiO 2 ), high positive end expiratory pressure (PEEP), prone ventilation, sedation with paralysis and inotropic support. 12 There is growing evidence that a subset of COVID-19 patients present with atypical ARDS which has recently been termed to L-Type ARDS: severe hypoxemia but well-preserved pulmonary mechanics, good lung compliance and low lung congestion. 12, 13 (Table 1) The respiratory support requirements for COVID-19 patients with L-type atypical respiratory ARDS physiology may require different respiratory support principles than that usually provided to patients presenting with the typical H-Type classic ARDS. 14 As a result, several have advocated a ventilation strategy focused on the principle where less is more. [12] [13] [14] [15] Mechanical ventilation should be delivered with low tidal volumes, low plateau pressure and a low PEEP level, 15 albeit with a higher inspired fraction of oxygen (FiO 2 ). 14 It is postulated that the hypoxemia in this subset of COVID-19 patients with more compliant lungs may be due to a large shunt secondary from the loss of the protective mechanism of lung perfusion regulation and the loss of pulmonary hypoxic vasoconstriction and microthrombi in pulmonary vascualtrure. 12, 16 As a result of the coagulopathy seen in this disease, anticoagulation in the treatment algorithms is an important therapeutic modality in COVID-19. 17 The fact that many of these COVID-19 patients with L-Type ARDS with good lung compliance show improved oxygen saturation during prone positioning, may be related to improved lung perfusion and the force of gravity affecting pulmonary blood flow. 12
The high mortality associated with intubation and mechanical ventilation in COVID-19 patients, coupled with the concerns over provider risk from aerosolization via traditional forms of NIV have led to the following questions: "Do many mild to moderate COVID-19 patients undergo endotracheal intubation too early in order to limit aerosolized and droplet viral particles; and does this potentially delay or worsen some patient's recovery ?" 8 , and, "What is the role of helmet based CPAP via NIV for respiratory support in COVID-19 patients to limit the spread of aerosolized viral particles and potentially avoid endotracheal intubation?" 18, 19 The main reason for early endotracheal intubation over initiating NIV support in patients with COVID-19 is to limit possible aerosolization of COVID-19 particles from HFNC and NIV as was reported in the early Chinese experience. 6 Airway procedures in these patients are all classified as medical aerosol generating procedures (MAGPs). These MAGPs include; NIV and HFNC bag-mask ventilation, endotracheal intubation or tube suctioning, bronchoscopy, transport, tracheostomy tube change, and high-frequency oscillatory ventilation, etc. 6, 20, 21 We do know that NIV can play a significant role in respiratory support. A recent systematic review and metanalysis concluded that NIV can improve survival in the acute care settings when it is applied early for respiratory failure, however the benefit is lost when it is used too late in respiratory deterioration. 18 Continuous positive airway pressure (CPAP) is a mode in NIV used to treat hypoxemic acute respiratory failure (hARF). This mode of respiratory support delivers a constant positive airway pressure during both inspiration and expiration. 22, 23 Helmet CPAP is an important and evidence-based airway adjunct. 18, 19, 24, 25 While it is not intended to replace endotracheal intubation and mechanical ventilatory support in the critically ill patient, it can be used for more patients than intubation and confines aerosolized viral particle spread within the helmet. Determining which patients will undergo rapid progression from mild respiratory disease, or the L-type better compliance form of respiratory failure, to overt H-Type ARDS in COVID-19 is often not clear in the early course of the disease. 13, 14 Recent literature suggests that although only 10-14% of COVID-19 patients need ICU, 60-70% of those will develop progressive ARDS and 20-25% will require endotracheal intubation and ventilation. 6, [26] [27] [28] Helmet CPAP, as used in Italy, can play a significant role in helping to determine patient severity.
It provides good respiratory support in the moderately ill patient in the earlier stages of the disease. 19 These patients can still breath well on their own but remain significantly hypoxic despite conventional treatment. The helmet can be fitted at this stage. It provides a significant increase in inspired oxygen with up to 10 cm H 2 0 CPAP through adaption with a traditional CPAP machine or wall oxygen regulated by a simple device. It further enables patient self-proning to improve oxygenation, which limits the need for multiple personnel to perform this in the intubated patient The helmet allows for a safe means of containing droplet and aerosolization of virus particles by the use of a heat moisture exchange (HME) filter on the inspiratory and expiratory limb of the helmet. The comfort of the helmet also limits the need for sedation and subsequent inotropic support when compared to endotracheal intubation. With the use of the helmet, the need for rapid early intubation can often safely be delayed while a patient is observed carefully for any improvement in disease or deterioration in their condition. This may enable endotracheal intubation to be avoided in a subset of patients.
Previous data supports the use of helmet CPAP as a safe and effective evidence-based approach to respiratory failure. An independent metanalysis, inclusive of four randomized clinical trials in Italy, found helmet CPAP to be a beneficial mode of respiratory support when used for the correct indication. influenced by type of ARF and ventilation mode (P <0.00001). 29 The authors in this study concluded that NIV with a helmet was associated with reduced hospital mortality and endotracheal intubation requirement. The helmet was as effective as the mask in gas exchange with no additional advantage.
Large randomized controlled trials are needed to provide more robust evidence. 29 Patients presenting with mild-to-moderate COVID-19 or the L-type ARDS, initially supported with HFNC low (CPAP) or NIV must be observed very closely for any clinical deterioration due to disease progression. 6, 12, 14, 34 One of the early signs of disease progression is the use of excessive inspiratory work being generated by the patient. If observed, the patient should undergo endotracheal intubation because any increased work of breathing and the generation of excessive negative intrathoracic pressure to move air has been shown to cause a self-inflicted lung injury (SILI). 14, 35 Determining patient breathing effort during progression of respiratory disease is not always easy. To more precisely quantify patient breathing work effort, esophageal manometry although not commonly used, may be needed in these patients to measure the generation of changes in intrathoracic pressure . 34 Esophageal pressure changes of 5 to 10 cmH 2 O may be well tolerated. However, if an esophageal pressure change greater than 15 cmH 2 O is generated, the risk of self-inflicted lung injury (SILI) is increased and endotracheal intubation should be performed promptly. 14 If endotracheal intubation is delayed in this situation, and a further sudden clinical deterioration occurs, it can be associated with hypoxemia, cardiovascular collapse and an emergent endotracheal intubation may be required, which puts the HCW team at risk during the MAGP. 6, 7, 36 Naturally it is not practical to monitor respiratory effort with manometry in a pandemic situation.
It remains unclear that delaying intubation in the COVID-19 patient who ultimately requires intubation has any benefit. However, the data discussed above is promising that some patients may benefit, and others may avoid intubation at all. The current surviving sepsis campaign recommendations for COVID-19 discuss the use of helmet NIV and CPAP compared with mask NIV. 6 Helmet CPAP is certainly a therapeutic option that has been used in Italy for over a decade, and has been used extensively during the COVID-19 pandemic. 8, 19, 37 However, in the current surviving sepsis campaign recommendations, consensus could not be reached on its safety or efficacy in COVID-19, especially in those patients that ultimately require endotracheal intubation and mechanical ventilatory support. 6
The first helmet prototypes were developed in 1991 by Maurizio Borsari. One of the problems with CPAP helmets available in other parts of the world is that they are not all FDA approved and most U.S. physicians are unfamiliar with the helmet. (Figure 1 ) However, the concept and fitting of the mask is relatively simple. Patients typically can sit up or lie down on some pillows. It is likely that the CPAP helmet NIV, is best used in the early phase of the disease or during recovery after extubation. The CPAP helmet consists of a transparent plastic hood that surrounds the patient's head. The helmet does not have any pressure points on the face, thereby reducing patient discomfort and improving device tolerance without the risk of skin necrosis. 25 The helmet allows the patient to see, read, talk, and interact more easily than other NIV respiratory devices. It is available in various sizes that can fit small children and adults. 23 It has a soft latex free collar constructed of silicon-polyvinyl chloride that creates a pneumatic seal around the patient's neck. The presence of two or more inlet and outlet ports enable connections of standard respiratory inspiratory and expiratory limb tubing. A high efficiency particulate (HEPA) filter is placed on the expiratory limb of the circuit to minimize exhaled aerosolized viral particles. 8 Additionally, there is a distal variable CPAP valve. The extra ports allow a sealed site for the insertion of a naso-gastric tube, or the administration of a nebulizer. This port also enables the patient to drink from a straw. A monitor controls the gas flow in the helmet (n= 30-60 liters to prevent rebreathing and CO 2 retention), temperature and FiO 2 . The presence of a zip in the helmet allows easy access if needed. The noise level in the CPAP helmet is equal 100 dB which can be reduced with a HME filter on the helmet gas inspiratory limb. 38 Helmet CPAP requires a fairly cooperative patient with an intact neuromuscular system but tolerance appears to be excellent especially in those patients who feel claustrophobic with a tight fitting CPAP face mask. Armpit straps can be replaced with a counterweight system that results in better patient comfort and humidification can be added to the system. 8 Occasionally, it may be necessary to reduce anxiety with the administration of very light sedation.
Patients in a CPAP helmet must be monitored closely. An inability to maintain a PaO 2 /FiO 2 ratio of 150 during use, with no reduction in respiratory rate and an increasing FiO 2 requirement, defined as an FiO 2 > 80% after one hour of initiating helmet CPAP therapy, are considered indications for endotracheal intubation and mechanical ventilation. (Table 1) The challenge in COVID-19 patients is to identify those patients most likely to benefit from CPAP helmet NIV, and to monitor them closely for any signs of worsening respiratory therapy that would require an escalation to endotracheal intubation and mechanical ventilation. 37 Patients with COVID-19 are all recommended to receive regular respiratory therapy to help mobilize inspissated respiratory secretions associated with this disease. 37
In this critical time of unparalleled medical challenges of caring for vast numbers of COVID-19 hypoxemic patients requiring respiratory support, any alternative respiratory support device with evidence of extensive use in other parts of the world deserves consideration. We submit that the helmet delivered NIV pressure support device could be a low-cost addition to the ventilatory options for COVID-19 patients. 