Restrictor Calculator for Multi-Patient Ventilation

How do I use this page?

IMPORTANT: Attaching two patients to a single ventilator is not recommended. Use the information below with discretion.



This tool guides the selection of ventilator settings and flow restrictors for two patients on a single ventilator. Given the tidal volume and end expiratory pressure requirements for each patient, it guides selection of appropriate ventilator settings and then computes the corresponding resistances to be added to the inspiratory and expiratory circuits. The resulting pressure, flow, and volume responses are plotted against time at the bottom. Click the "info" links in the top right corner of any box for detailed guidance on that step.

Further information:
More on the University of Bath's response to Covid-19
BathRC-web v1.2 © University of Bath 2020; based on this paper and this dataset
More information on differential multiventilation (the method this tool supports) at differentialmultivent.org
Ventilation circuit parameters Info
  • These represent the compliance and resistance of a single leg of the ventilation circuit, i.e. inspiration or expiration, for a single patient, including any common section beyond a T/Y-connector.
  • These values encompass the tubes, one way valves, filters, connectors, and anything else in the circuit, but do not include the patient, nor the restriction to be added for tuning purposes.
  • It is assumed that the inspiration and expiration legs are identical (i.e. they contain the same number and type of valves, filters, tubes, etc.).
  • Component resistances are additive for components in series in a circuit. Typical component resistances identified in experiments are:
    • 12 cmH2O/(L/s) for a one-way valve,
    • 3 cmH2O/(L/s) for an HME filter,
    • 11 cmH2O/(L/s) for a constricted (clamped) tube,
    • <1 cmH2O/(L/s) for a 1 metre stretch of tube with connectors at either end.
  • A typical compliance value from experiments with 22 mm corrugated tube is 0.5 mL/cmH2O per metre of tube (includes air compressibility combined with tube deformation).
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Patient 1 Info
  • Arnal et al. (2018) found median values for normal lungs of:
    • Compliance C = 0.054 L/cmH20
    • Inspiration resistance, Ri = 13 cmH20/(L/s)
    • Expiration resistance, Re = 12 cmH20/(L/s)
  • For ARDS patients, they found:
    • a median compliance of C = 0.039 L/cmH20
    • a lower quartile of C = 0.032 L/cmH20
    • little change in resistance
Arnal, J-M, Aude Garnero, Mathieu Saoli, and Robert L Chatburn. (2018) Parameters for Simulation of Adult Subjects During Mechanical Ventilation. Respiratory Care, Vol 63, No. 2.

* End expiration lung pressure is not exactly the same as ventilator PEEP; the two converge for long expiration times, but ventilator PEEP is lower than the lung end expiration pressure due to resistances in the ventilation circuit and nonzero flow rates at the end of expiration. Hide






Patient 2 Info
  • Arnal et al. (2018) found median values for normal lungs of:
    • Compliance C = 0.054 L/cmH20
    • Inspiration resistance, Ri = 13 cmH20/(L/s)
    • Expiration resistance, Re = 12 cmH20/(L/s)
  • For ARDS patients, they found:
    • a median compliance of C = 0.039 L/cmH20
    • a lower quartile of C = 0.032 L/cmH20
    • little change in resistance
Arnal, J-M, Aude Garnero, Mathieu Saoli, and Robert L Chatburn. (2018) Parameters for Simulation of Adult Subjects During Mechanical Ventilation. Respiratory Care, Vol 63, No. 2.

* End expiration lung pressure is not exactly the same as ventilator PEEP; the two converge for long expiration times, but ventilator PEEP is lower than the lung end expiration pressure due to resistances in the ventilation circuit and nonzero flow rates at the end of expiration. Hide






Ventilator Settings and Restrictor Requirements Info
  • These figures are generated according to the parameters entered above.
  • In figure 1 the x- and y-axes represent, respectively, the ventilator pressure and duration for the inspiration phase.
  • In figure 2 the x- and y-axes represent, respectively, the ventilator pressure and duration for the expiration phase.
  • The contours on the two graphs show the restrictor coefficients required for each patient on the inspiration circuit (Fig 1) and expiration circuit (Fig 2) in order to meet their respective tidal volume and end expiratory pressure requirements.
  • The green indicator dots are positioned by changing the values in the boxes beneath the figures or by clicking on the figures themselves, to select the desired ventilator settings.
  • The resulting restrictor resistance requirements are displayed in the red and blue boxes beneath. Four restrictors need to be added, one to each of the individual inspiratory and expiratory circuits for each of the two patients.
  • The "ventilation response" section of the page shows graphs of the pressure, flow, and volume for each patient against time for this configuration.
  • Summary information appears at the bottom of the page.
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Inspiration restrictor requirements



Expiration restrictor requirements


Where do the restrictors go?
Four restrictors are needed: one for each patient's inspiration line and one for each patient's expiration line. There may also be a need for a bypass circuit for the ventilator to function correctly (not pictured).
Ventilation response
Summary Info
  1. Patient tidal volume and lung end expiration pressure requirements as entered at the top of this form.
  2. Ventilator settings, calculated from the values chosen beneath Figs. 1 and 2.
  3. Restrictor resistances, computed to meet the requirements of (I) and (II).
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I. Patient tidal volume / lung end expiration pressure requirements



II. Ventilator settings


III. Restrictor resistances