Use of a single ventilator to support 4 patients: Laboratory evaluation of a limited concept

Abstract

INTRODUCTION: A mass-casualty respiratory failure event where patients exceed available ventilators has spurred several proposed solutions. One proposal is use of a single ventilator to support 4 patients. METHODS: A ventilator was modified to allow attachment of 4 circuits. Each circuit was connected to one chamber of 2 dual-chambered, test lungs. The ventilator was set at a tidal volume (V T) of 2.0 L, respiratory frequency of 10 breaths/min, and PEEP of 5 cm H 2O. Tests were repeated with pressure targeted breaths at 15 cm H 2O. Airway pressure, volume, and flow were measured at each chamber. The test lungs were set to simulate 4 patients using combinations of resistance (R) and compliance (C). These included equivalent C and R, constant R and variable C, constant C and variable R, and variable C and variable R. Results. When R and C were equivalent the V T distributed to each chamber of the test lung was similar during both volume (range 428-442 mL) and pressure (range 528-544 mL) breaths. Changing C while R was constant resulted in large variations in delivered V T (volume range 257-621 mL, pressure range 320-762 mL). Changing R while C was constant resulted in a smaller variation in V T (volume range 418-460 mL, pressure range 502-554 mL) compared to only C changes. When R and C were both varied, the range of delivered V T in both volume (336-517 mL) and pressure (417-676 mL) breaths was greater, compared to only R changes. CONCLUSIONS: Using a single ventilator to support 4 patients is an attractive concept; however, the V T cannot be controlled for each subject and V T disparity is proportional to the variability in compliance. Along with other practical limitations, these findings cannot support the use of this concept for mass-casualty respiratory failure. © 2012 Daedalus Enterprises.