title: Use of a single ventilator to support 4 patients: laboratory evaluation of a limited concept.
abstract: BACKGROUND
  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(2)O. Tests were repeated with pressure targeted breaths at 15 cm H(2)O. 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.
authors: Department of Surgery, University of Cincinnati, Cincinnati, OH, USA. richard.branson@uc.edu
authors: Richard D
authors: RD
authors: Branson
authors: Thomas C
authors: TC
authors: Blakeman
authors: Bryce Rh
authors: BR
authors: Robinson
authors: Jay A
authors: JA
authors: Johannigman
mesh_terms: D006801:Humans; D008170:Lung Compliance; D054527:Mass Casualty Incidents; D016544:Patient Simulation; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial / Q000295:instrumentation / Q000379:methods*; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D013990:Tidal Volume