In non-ventilated patients- Mean change in the worst (highest) level of oxygenation (oxygen flow in litres/min). This will be assessed by the nursing documentation in the participant's electronic record of the flow rate of oxygen delivered and the delivery method (ie nasal prongs; Hudson mask; or non-breather mask). In ventilated patients- Mean change in the worst (lowest) PaO2 /FiO2 ratio (in mmHg). This will be assessed by nursing documented PaO2 and FiO2 levels in the patient chart.[Worst recorded level of oxygenation during the 7 days of intervention.];Feasibility will be assesses by the following measures:• The primary assessment of our ability to blind treatment of the HDIVZn in a 250-ml saline preparation• Drug availability from supplier; storage and timely delivery to a patient• Good clinical practice documentation of drug prescription on Cerner (an electronic medical record); delivery to ICU by project research officer; double signing by nursing staff• Appropriate preparation of drug- onsite refrigeration storage; preparation with SOPs; maintenance of sterile conditions; protocol compliance; breaches; and variation; documentation processes including patient retention and follow-up rates• Determine the per-patient cost to estimate subsequent pivotal trial costs• Assess the process for efficient and effective data entry and analysisThese will be assessed by our research investigators on a regular basis and data collected in the case report forms.[During 7 days of intervention]

In non-ventilated patients- Mean change in the worst (highest) level of oxygenation (oxygen flow in litres/min). This will be assessed by the nursing documentation in the participant's electronic record of the flow rate of oxygen delivered and the delivery method (ie nasal prongs; Hudson mask; or non-breather mask). In ventilated patients- Mean change in the worst (lowest) PaO2 /FiO2 ratio (in mmHg). This will be assessed by nursing documented PaO2 and FiO2 levels in the patient chart.[Worst recorded level of oxygenation during the 7 days of intervention.];Feasibility will be assesses by the following measures:• The primary assessment of our ability to blind treatment of the HDIVZn in a 250-ml saline preparation• Drug availability from supplier; storage and timely delivery to a patient• Good clinical practice documentation of drug prescription on Cerner (an electronic medical record); delivery to ICU by project research officer; double signing by nursing staff• Appropriate preparation of drug- onsite refrigeration storage; preparation with SOPs; maintenance of sterile conditions; protocol compliance; breaches; and variation; documentation processes including patient retention and follow-up rates• Determine the per-patient cost to estimate subsequent pivotal trial costs• Assess the process for efficient and effective data entry and analysisThese will be assessed by our research investigators on a regular basis and data collected in the case report forms.[During 7 days of intervention]