Since the outbreak of SARS-CoV in 2002 and MERS-CoV in 2012, the emergence of SARS-CoV-2 marks the third introduction of a highly pathogenic and pandemic coronavirus into humans in the 21st century. SARS-CoV-2 is a beta coronavirus, and two other known beta CoVs are SARS and MERS. All these coronaviruses can lead to severe and potentially fatal respiratory infections, mainly caused by lung cell loss, pulmonary edema, and formation of hyaluronic acid. This then leads to ARDS causing death. Autopsy report showe confirm the lesions in both lungsas seen in ARDS [1,2]. Therefore, development of more effective mechanical strategies to reduce the mortality of ARDS is not only an urgent need in the current outbreak of novel coronavirus, but also a long-term need to reduce the mortality of viral pneumonia worldwide[3]. Heliox due to its unique properties may be an ideal gas in ARDS caused by SARS-COVID-2 in reuducing the work of breathing, improving compliance and inflammation and reducing morbidity and mortality[10]. During ventilation with heliox, lower driving pressures are necessary to distribute oxygen to the distal alveoli to improve oxygenation and CO2 diffusion . This will result in better gas exchange in ARDS[11]. Therefore, Heliox is a better lung-protective ventilation strategy for ARDS.
3.1 Animal models
In a study of neonatal piglets where ARDS was induced by saline lavage[12], three types of aeration therapy were evaluated, including oxygen-enriched air and heliox (60% oxygen/40% helium and 40% oxygen/60% helium). The results showed that the partial pressure of carbon dioxide(PaCO2), in the two heliox groups decreased on an average of 10.5 and 20.3 mm Hg. A modest improvement in oxygenation was observed with the 40% helium mixture. These results indicated that heliox improved oxygenation and elimination of carbon dioxide. Similar results were found in other animal models of ventilation in ARDS. Heliox significantly improved gas exchange, reduced the need for oxygen, and decreased PaCO2 compared with the pediatric swine ventilated with nitrogen[13,14].
3.2 Clinical study
Heliox has been clinically studied for more than 70 years to reduce airway resistance and improve ventilation. Two adult studies reported results in patients who were diagnosed to have bronchiolitis obliterans syndrome and acute respiratory failure following lung transplantation.and were treated with 60% heliox administered either via bi-level positive airway pressure(BiPAP) or high-frequency oscillatory ventilation (HFOV)[15]. This report showed that heliox ventilation increased pH and decreased PaCO2. In a randomized, controlled study of newborn respiratory distress syndrome[16], 51 newborns were randomly divided into two groups. Both groups received nasal continuous positive airway pressure (NCPAP). The first group received NCPAP plus Heliox21 while control group received NCPAP with standard medical air. The intervention group (n=27) received 80% heliox and the control group (n=24) received nasal continuous positive airway pressure with medical air. This study showed that NCPAP with heliox treatment significantly decreased the risk of intubation for mechanical ventilation (14.8% vs 45.8%; P=0.029, relative risk 0.32, 95% confidence interval 0.12–0.88) and decreased the requirement for surfactant (11.1% vs 43.5%; P=0.021, relative risk 0.26, 95% confidence interval 0.08–0.82). In clinical studies on the treatment of ARDS in adults and childrenit has been shown that a helium–oxygen mixture improves gas exchange, promotes elimination of CO2, and reduces the rate intubation r. Therefore, using a helium–oxygen mixture is a reasonable intervention for treating ARDS caused by COVID-19.