Ventilating Two Subjects with One Ventilator: Achievable but not Advisable

Abstract

Background: The world is in the midst of the COVID-19 viral pandemic and the number of patients requiring mechanical ventilation may exceed the number of ventilators available. New information is being sought on the feasibility of using one ventilator on multiple patients should the need arise. In this study, we hypothesized that two rabbits could be simultaneously mechanically ventilated using a simple, readily available, dual circuit. Methods: Two pairs of New Zealand White rabbits (n=4) were anesthetized and hooked up to a simple dual circuit and ventilated in the Airway Pressure Release Ventilation mode. Arterial and venous lines were placed for arterial blood gases, hemodynamic monitoring and fluid administration. Following one hour of ventilation, a surfactant washout was performed and mechanical ventilation resumed. Animals were euthanized after an additional one hour of ventilation. Results: Both Pairs of rabbits had a similar pre-injury PaO2/FiO2 ratio. Following injury, all rabbits had a decline in PaO2/FiO2 with 2 maintaining a PaO2/FiO2 ratio consistent with moderate ARDS, 1 consistent with mild and 1 return to normal. Both Pairs of rabbits had a similar pre-injury PaCO2. Rabbits in Pair 1 maintained similar arterial carbon dioxide (PaCO2) levels following ARDS. Pair 2 showed an increase in PaCO2 with ARDS due to the much higher PaCO2 in the rabbit with the more severe lung injury.Conclusion: A dual ventilator circuit can be constructed from materials in any respiratory therapy department. Using this dual circuit, two animals with ARDS can be oxygenated and ventilation sufficiently to meet current standards.

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“…A concomitant rise in both peak inspiratory and peak plateau pressure was noted in this study. It has earlier been noted that a marked difference in the peak inspiratory and peak plateau pressure reflects an obstruction of the airway by secretion or kinking of the tube [8] The ideal peak plateau pressure should be <30cmH 2 O to prevent volutrauma i.e lung injury secondary to over distension of the alveoli [9] In the healthy lungs, there is a direct relationship between the peak inspiratory pressure and the peak plateau pressure. If there is however a rise in the values of the peak inspiratory pressure without a commensurate rise in the peak plateau pressure; a kinked endotracheal tube, the presence of secretions or bronchospasm should be suspected [10].…”