Differential Ventilation Using Flow Control Valves as a Potential Bridge to Full Ventilatory Support during the COVID-19 Crisis

Background During the COVID-19 pandemic, ventilator sharing was suggested to increase availability of mechanical ventilation. The safety and feasibility of ventilator sharing is unknown. Methods A single ventilator in pressure control mode was used with flow control valves to simultaneously ventilate two patients with different lung compliances. The system was first evaluated using high-fidelity human patient simulator mannequins and then tested for 1 h in two pairs of COVID-19 patients with acute respiratory failure. Patients were matched on positive end-expiratory pressure, fractional inspired oxygen tension, and respiratory rate. Tidal volume and peak airway pressure (PMAX) were recorded from each patient using separate independent spirometers and arterial blood gas samples drawn at 0, 30, and 60 min. The authors assessed acid-base status, oxygenation, tidal volume, and PMAX for each patient. Stability was assessed by calculating the coefficient of variation. Results The valves performed as expected in simulation, providing a stable tidal volume of 400 ml each to two mannequins with compliance ratios varying from 20:20 to 20:90 ml/cm H2O. The system was then tested in two pairs of patients. Pair 1 was a 49-yr-old woman, ideal body weight 46 kg, and a 55-yr-old man, ideal body weight 64 kg, with lung compliance 27 ml/cm H2O versus 35 ml/cm H2O. The coefficient of variation for tidal volume was 0.2 to 1.7%, and for PMAX 0 to 1.1%. Pair 2 was a 32-yr-old man, ideal body weight 62 kg, and a 56-yr-old woman, ideal body weight 46 kg, with lung compliance 12 ml/cm H2O versus 21 ml/cm H2O. The coefficient of variation for tidal volume was 0.4 to 5.6%, and for PMAX 0 to 2.1%. Conclusions Differential ventilation using a single ventilator is feasible. Flow control valves enable delivery of stable tidal volume and PMAX similar to those provided by individual ventilators. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Differential ventilation using flow control valves as a potential bridge to full ventilatory support during the COVID-19 crisis: From bench to bedside

ABSTRACTBackgroundIt has been projected that there will be too few ventilators to meet demand during the COVID-19 (SARS CoV-2) pandemic. Ventilator sharing has been suggested as a crisis standard of care strategy to increase availability of mechanical ventilation. The safety and practicality of shared ventilation in patients is unknown. We designed and evaluated a system whereby one mechanical ventilator can be used to simultaneously ventilate two patients who have different lung compliances using a custom manufactured flow control valve to allow for individual adjustment of tidal volume and airway pressure for each patient.MethodsThe system was first evaluated in a simulation lab using two human patient simulators under expected clinical conditions. It was then tested in an observational study of four patients with acute respiratory failure due to COVID-19. Two separately ventilated COVID-19 patients were connected to a single ventilator for one hour. This intervention was repeated in a second pair of patients. Ventilatory parameters (tidal volume, peak airway pressures, compliance) were recorded at five minute intervals during both studys. Arterial blood gases were taken at zero, thirty, and sixty minutes. The primary outcome was maintenance of stable acid-base status and oxygenation during shared ventilation.ResultsTwo male and two female patients, age range 32-56 yrs, participated. Ideal body weight and driving pressure were markedly different among patients. All patients demonstrated stable physiology and ventilation for the duration of shared ventilation. In one patient tidal volume was increased after 30 minutes to correct a respiratory acidosis.ConclusionsDifferential ventilation using a single ventilator and a split breathing circuit with flow control valves is possible. A single ventilator could feasibly be used to safely ventilate two COVID-19 patients simultaneously as a bridge to full ventilatory support.Summary StatementNot applicable.

Selective positive end-expiratory pressure and intracardiac dimensions in dogs

Effects of differential ventilation with general vs. selective right (R) and left (L) positive end-expiratory pressure (PEEP) on left (LV) and right ventricular (RV) end-diastolic dimensions were compared in seven pentobarbital-anesthetized dogs. All three modes of PEEP reduced LV cross-sectional area: general PEEP more than RPEEP and RPEEP more than LPEEP. General PEEP and, to a lesser degree, RPEEP decreased both the LV anteroposterior diameter and LV septum-free wall diameter, whereas LPEEP reduced the LV septum-free wall diameter only. Cardiac output was unaffected by LPEEP, whereas general PEEP (20 cmH2O) reduced cardiac output by 48%, and RPEEP (20 cmH2O) reduced it by 23%. RV septum-free wall diameter was not changed by any mode of PEEP. In conclusion, cardiac output was better maintained with selective PEEP than with general PEEP because LV filling was less impeded with selective PEEP. During LPEEP LV assumed a different configuration than during RPEEP and general PEEP, probably reflecting a different pattern of heart-lung interaction.