inclusion criteria (severe covid-19 status) * hospitalized with confirmed sars-cov-2 infection by polymerase chain reaction (pcr) or other validated tests as they become available within 30 days of enrollment. * in mild respiratory distress, defined as a p/f ratio of between 200 and 325 mm hg. * spontaneously breathing subjects receiving \> 4 liters/min of oxygen. * patients enrolled and able to start eno treatment after oxygen stabilization. * willing and able to provide written informed consent, or with a legal representative who can provide informed consent, or enrolled under international conference on harmonization (ich) e6(r2) 4.8.15 emergency use provisions as deemed necessary by the investigator (participants ≥ 18 years of age). * 18-89 years of age exclusion criteria * covid-19 patients with mild to no respiratory distress, defined as p/f ratio \> 325 mm hg. * covid-19 patients receiving supplemental oxygen equivalent to an fio2 of \> 0.90 (reduction of fio2 at this level or higher when eno is blended into gas source cannot be avoided). * covid-19 patients receiving supplemental oxygen with active ventilatory support, cpap, etc. * physician of record opposed to enrolling the patient due to perceived safety concerns; or any condition that does not allow the protocol to be followed safely. * subjects with past medical history of lung malignancy or pneumonectomy or lung transplant * subjects who have a history of malignancy or other irreversible disease/conditions with a 6-month mortality \> 50% * subjects that have experienced cardiac arrest with cpr for longer than 30 minutes * patients on extracorporeal membrane oxygenation (ecmo) + patients intubated on ventilator * patient groups at an increased risk to form methemoglobin. (e.g. congenital variants of met-hb) * patients with anemia, defined as a hemoglobin of \< 9 g/dl * individuals who are pregnant or breastfeeding * individuals with an acute disorder or history of chronic diseases of the heart, lungs, kidney, liver, or any other medical condition that in the opinion of the screening physician makes them unsuitable for study. * individuals taking nitrates. * individuals receiving pde-5 inhibitors, any drugs that are nitric oxide donors (e.g. prilocaine, sodium nitroprusside and nitroglycerine), drugs known to increase methemoglobin (e.g. lidocaine, prilocaine, benzocaine, or dapsone), drugs that interfere with nitrite metabolism (e.g. allopurinol) and drugs that may potentiate hypotension (e.g. antihypertensives, diuretics, meperidine). * individuals with an inherited or acquired blood coagulation disorder, congenital methemoglobinemia, or a familial hemoglobinopathy that impacts oxygen delivery (e.g. sickle cell). * individuals who might have difficulty with the placement of a face mask (e.g. claustrophobia, uncontrolled asthma, severe allergies, sensitive skin) and/or the inhalation of a product for approximately 6 hours.

inclusion criteria (severe covid-19 status) * hospitalized with confirmed sars-cov-2 infection by polymerase chain reaction (pcr) or other validated tests as they become available within 30 days of enrollment. * in mild respiratory distress, defined as a p/f ratio of between 200 and 325 mm hg. * spontaneously breathing subjects receiving \> 4 liters/min of oxygen. * patients enrolled and able to start eno treatment after oxygen stabilization. * willing and able to provide written informed consent, or with a legal representative who can provide informed consent, or enrolled under international conference on harmonization (ich) e6(r2) 4.8.15 emergency use provisions as deemed necessary by the investigator (participants ≥ 18 years of age). * 18-89 years of age exclusion criteria * covid-19 patients with mild to no respiratory distress, defined as p/f ratio \> 325 mm hg. * covid-19 patients receiving supplemental oxygen equivalent to an fio2 of \> 0.90 (reduction of fio2 at this level or higher when eno is blended into gas source cannot be avoided). * covid-19 patients receiving supplemental oxygen with active ventilatory support, cpap, etc. * physician of record opposed to enrolling the patient due to perceived safety concerns; or any condition that does not allow the protocol to be followed safely. * subjects with past medical history of lung malignancy or pneumonectomy or lung transplant * subjects who have a history of malignancy or other irreversible disease/conditions with a 6-month mortality \> 50% * subjects that have experienced cardiac arrest with cpr for longer than 30 minutes * patients on extracorporeal membrane oxygenation (ecmo) + patients intubated on ventilator * patient groups at an increased risk to form methemoglobin. (e.g. congenital variants of met-hb) * patients with anemia, defined as a hemoglobin of \< 9 g/dl * individuals who are pregnant or breastfeeding * individuals with an acute disorder or history of chronic diseases of the heart, lungs, kidney, liver, or any other medical condition that in the opinion of the screening physician makes them unsuitable for study. * individuals taking nitrates. * individuals receiving pde-5 inhibitors, any drugs that are nitric oxide donors (e.g. prilocaine, sodium nitroprusside and nitroglycerine), drugs known to increase methemoglobin (e.g. lidocaine, prilocaine, benzocaine, or dapsone), drugs that interfere with nitrite metabolism (e.g. allopurinol) and drugs that may potentiate hypotension (e.g. antihypertensives, diuretics, meperidine). * individuals with an inherited or acquired blood coagulation disorder, congenital methemoglobinemia, or a familial hemoglobinopathy that impacts oxygen delivery (e.g. sickle cell). * individuals who might have difficulty with the placement of a face mask (e.g. claustrophobia, uncontrolled asthma, severe allergies, sensitive skin) and/or the inhalation of a product for approximately 6 hours.

inclusion criteria (severe covid-19 status) - hospitalized with confirmed sars-cov-2 infection by polymerase chain reaction (pcr) or other validated tests as they become available within 30 days of enrollment. - in mild respiratory distress, defined as a p/f ratio of between 200 and 325 mm hg. - spontaneously breathing subjects receiving > 4 liters/min of oxygen. - patients enrolled and able to start eno treatment after oxygen stabilization. - willing and able to provide written informed consent, or with a legal representative who can provide informed consent, or enrolled under international conference on harmonization (ich) e6(r2) 4.8.15 emergency use provisions as deemed necessary by the investigator (participants ≥ 18 years of age). - 18-89 years of age exclusion criteria - covid-19 patients with mild to no respiratory distress, defined as p/f ratio > 325 mm hg. - covid-19 patients receiving supplemental oxygen equivalent to an fio2 of > 0.90 (reduction of fio2 at this level or higher when eno is blended into gas source cannot be avoided). - covid-19 patients receiving supplemental oxygen with active ventilatory support, cpap, etc. - physician of record opposed to enrolling the patient due to perceived safety concerns; or any condition that does not allow the protocol to be followed safely. - subjects with past medical history of lung malignancy or pneumonectomy or lung transplant - subjects who have a history of malignancy or other irreversible disease/conditions with a 6-month mortality > 50% - subjects that have experienced cardiac arrest with cpr for longer than 30 minutes - patients on extracorporeal membrane oxygenation (ecmo) + patients intubated on ventilator - patient groups at an increased risk to form methemoglobin. (e.g. congenital variants of met-hb) - patients with anemia, defined as a hemoglobin of < 9 g/dl - individuals who are pregnant or breastfeeding - individuals with an acute disorder or history of chronic diseases of the heart, lungs, kidney, liver, or any other medical condition that in the opinion of the screening physician makes them unsuitable for study. - individuals taking nitrates. - individuals receiving pde-5 inhibitors, any drugs that are nitric oxide donors (e.g. prilocaine, sodium nitroprusside and nitroglycerine), drugs known to increase methemoglobin (e.g. lidocaine, prilocaine, benzocaine, or dapsone), drugs that interfere with nitrite metabolism (e.g. allopurinol) and drugs that may potentiate hypotension (e.g. antihypertensives, diuretics, meperidine). - individuals with an inherited or acquired blood coagulation disorder, congenital methemoglobinemia, or a familial hemoglobinopathy that impacts oxygen delivery (e.g. sickle cell). - individuals who might have difficulty with the placement of a face mask (e.g. claustrophobia, uncontrolled asthma, severe allergies, sensitive skin) and/or the inhalation of a product for approximately 6 hours.

inclusion criteria (severe covid-19 status) - hospitalized with confirmed sars-cov-2 infection by polymerase chain reaction (pcr) or other validated tests as they become available within 30 days of enrollment. - in mild respiratory distress, defined as a p/f ratio of between 200 and 325 mm hg. - spontaneously breathing subjects receiving > 4 liters/min of oxygen. - patients enrolled and able to start eno treatment after oxygen stabilization. - willing and able to provide written informed consent, or with a legal representative who can provide informed consent, or enrolled under international conference on harmonization (ich) e6(r2) 4.8.15 emergency use provisions as deemed necessary by the investigator (participants ≥ 18 years of age). - 18-89 years of age exclusion criteria - covid-19 patients with mild to no respiratory distress, defined as p/f ratio > 325 mm hg. - covid-19 patients receiving supplemental oxygen equivalent to an fio2 of > 0.90 (reduction of fio2 at this level or higher when eno is blended into gas source cannot be avoided). - covid-19 patients receiving supplemental oxygen with active ventilatory support, cpap, etc. - physician of record opposed to enrolling the patient due to perceived safety concerns; or any condition that does not allow the protocol to be followed safely. - subjects with past medical history of lung malignancy or pneumonectomy or lung transplant - subjects who have a history of malignancy or other irreversible disease/conditions with a 6-month mortality > 50% - subjects that have experienced cardiac arrest with cpr for longer than 30 minutes - patients on extracorporeal membrane oxygenation (ecmo) + patients intubated on ventilator - patient groups at an increased risk to form methemoglobin. (e.g. congenital variants of met-hb) - patients with anemia, defined as a hemoglobin of < 9 g/dl - individuals who are pregnant or breastfeeding - individuals with an acute disorder or history of chronic diseases of the heart, lungs, kidney, liver, or any other medical condition that in the opinion of the screening physician makes them unsuitable for study. - individuals taking nitrates. - individuals receiving pde-5 inhibitors, any drugs that are nitric oxide donors (e.g. prilocaine, sodium nitroprusside and nitroglycerine), drugs known to increase methemoglobin (e.g. lidocaine, prilocaine, benzocaine, or dapsone), drugs that interfere with nitrite metabolism (e.g. allopurinol) and drugs that may potentiate hypotension (e.g. antihypertensives, diuretics, meperidine). - individuals with an inherited or acquired blood coagulation disorder, congenital methemoglobinemia, or a familial hemoglobinopathy that impacts oxygen delivery (e.g. sickle cell). - individuals who might have difficulty with the placement of a face mask (e.g. claustrophobia, uncontrolled asthma, severe allergies, sensitive skin) and/or the inhalation of a product for approximately 6 hours.

inclusion criteria: - hospitalized with confirmed sars-cov2 infection by polymerase chain reaction (pcr) or other validated tests as they become available. - in respiratory distress, defined as p/f ratio of < 200 mmhg. - 18-89 years of age. - patients that are intubated and mechanically ventilated with a device approved/certified for the blending-in of other medical gases into the ventilator circuit. - patients to be enrolled and to be able to start treatment within 36 h of being intubated.

inclusion criteria: - hospitalized with confirmed sars-cov2 infection by polymerase chain reaction (pcr) or other validated tests as they become available. - in respiratory distress, defined as p/f ratio of < 200 mmhg. - 18-89 years of age. - patients that are intubated and mechanically ventilated with a device approved/certified for the blending-in of other medical gases into the ventilator circuit. - patients to be enrolled and to be able to start treatment within 36 h of being intubated.