BACKGROUND The overwhelming demand for mechanical ventilators due to COVID-19 has stimulated interest in using one ventilator for multiple patients (multiplex ventilation). Despite a plethora of information on the Internet, there is little supporting evidence and no human studies. The risk of multiplex ventilation is that ventilation and PEEP effects are largely uncontrollable and depend on the difference between patient resistance, (R) and compliance (C). It is not clear whether volume control or pressure control is safer or more effective. We designed a simulation-based study to allow complete control over the relevant variables to determine the effects of various degrees of RC imbalance on tidal volume (VT), end-expiratory lung volume (VEE), and imputed pH. METHODS Two separate breathing simulators were ventilated with a ventilator using pressure control (PC) and volume control (VC) breaths. Evidence-based lung models simulated a range of differences in R and C (six pairs of simulated patients). Differences in VT, VEE, and imputed pH were recorded. RESULTS Depending on differences in R and C, differences in VT ranged from 1% (equal R and C) to 79%. Differences in VEE ranged from 2% to 109%. Differences in pH ranged from 0% to 5%. Failure due to excessive tidal volume (> 8 mL/kg) did not occur. Failure due to excessive VEE difference (> 10%) was evident in 50% of patient pairs. There was no difference in failure rate between VC and PC. CONCLUSIONS These experiments confirmed the potential for markedly different ventilation and oxygenation for patients with uneven respiratory system impedances during multiplex ventilation. Three critical problems must be solved to minimize risk: (1) partitioning of inspiratory flow from the ventilator individually between the two patients, (2) measurement of VT delivered to each patient, and (3) provision for individual PEEP. We provide suggestions for solving these problems.
Multiplex Ventilation: A Simulation-based Study of Ventilating Two Patients with One Ventilator.