Mechanical Ventilation With Room Air Is Feasible In A Moderate Acute Respiratory Distress Syndrome Pig Model - Implications For Disaster Situations And Low-Income Nations

Introduction:Patients with respiratory failure are usually mechanically ventilated, mostly with fraction of inspired oxygen (FiO(2)) > 0.21. Minimizing FiO(2) is increasingly an accepted standard. In underserved nations and disasters, salvageable patients requiring mechanical ventilation may outstrip oxygen supplies.Study Objective:The hypothesis of the present study was that mechanical ventilation with FiO(2) = 0.21 is feasible. This assumption was tested in an Acute Respiratory Distress Syndrome (ARDS) model in pigs.Methods:Seventeen pigs were anesthetized, intubated, and mechanically ventilated with FiO(2) = 0.4 and Positive End Expiratory Pressure (PEEP) of 5cmH(2)O. Acute Respiratory Distress Syndrome was induced by intravenous (IV) oleic acid (OA) infusion, and FiO(2) was reduced to 0.21 after 45 minutes of stable moderate ARDS. If peripheral capillary oxygen saturation (SpO(2)) decreased below 80%, PEEP was increased gradually until maximum 20cmH(2)O, then inspiratory time elevated from one second to 1.4 seconds.Results:Animals developed moderate ARDS (mean partial pressure of oxygen [PaO2]/FiO(2) = 162.8, peak and mean inspiratory pressures doubled, and lung compliance decreased). The SpO(2) decreased to <80% rapidly after FiO(2) was decreased to 0.21. In 14/17 animals, increasing PEEP sufficed to maintain SpO(2) > 80%. Only in 3/17 animals, elevation of FiO(2) to 0.25 after PEEP reached 20cmH(2)O was needed to maintain SpO(2) > 80%. Animals remained hemodynamically stable until euthanasia one hour later.Conclusions:In a pig model of moderate ARDS, mechanical ventilation with room air was feasible in 14/17 animals by elevating PEEP. These results in animal model support the potential feasibility of lowering FiO(2) to 0.21 in some ARDS patients. The present study was conceived to address the ethical and practical paradigm of mechanical ventilation in disasters and underserved areas, which assumes that oxygen is mandatory in respiratory failure and is therefore a rate-limiting factor in care capacity allocation. Further studies are needed before paradigm changes are considered.