Oxygen cylinder calculator for patient transport

Summary

This is a calculator for how many oxygen cylinders to take when transporting a patient. Choose a ventilator mode (IPPV or NPPV), high-flow (NHF) or oxygen therapy, enter the settings and the planned transport time, and it shows the number of cylinders needed and how many minutes one full cylinder lasts.

It first works out how much gas flows per minute, then, from the set oxygen concentration, how much of that has to come from the oxygen cylinder. That amount, multiplied by the transport time and a safety factor, is divided by the volume one cylinder can deliver to give the number of cylinders. The volume one cylinder can deliver comes from the cylinder's size and pressure.

No figures for any particular device model are built in. Values that differ between models (base flow, drive-gas consumption, how leak is displayed) are entered by the user from the operator's manual.

On a phone, the results appear below the inputs. To keep the results pinned to the bottom of the screen while you type, open the calculator on its own.

How it calculates

1. Total flow (gas delivered to the patient side)

Mode	Total flow
IPPV	tidal volume × respiratory rate + additional flow (leaks, etc.) + base flow
NPPV	tidal volume × respiratory rate + total leak
NHF	set flow
O₂ therapy (oxygen cylinder only)	oxygen flow
O₂ therapy (oxygen + air cylinders)	total flow (oxygen + air)

IPPV, NPPV and NHF assume a turbine- or blower-type device that draws in room air. The part of the total flow that air can supply comes from the room; only the part that raises the oxygen concentration comes from the cylinder.

For IPPV, base flow is added as if it flows throughout the whole breath. On models that supply it only during exhalation, the result comes out higher than the actual value.

For NPPV, total leak is the sum of the intentional leak through the exhalation port and the unintentional leak around the mask. On ventilators that display only the unintentional leak, add the exhalation port's flow (at the pressure in use; given in the mask's or exhalation port's manual) to that value before entering it. Entering the displayed value as it is makes the oxygen consumption come out lower than the actual value.

2. Oxygen consumption

Air is taken as 21% oxygen. The calculation uses the share of oxygen needed when oxygen (100%) and air (21%) are mixed to reach the set concentration.

• Oxygen consumption = total flow × (set concentration − 21) ÷ 79 + drive gas
• Drive gas is added only for gas-driven IPPV when a value is entered
• In O₂ therapy with an oxygen cylinder only, the whole flow is oxygen
• With oxygen + air cylinders, air consumption = total flow × (100 − set concentration) ÷ 79, and the air cylinders are worked out the same way

3. Usable volume per cylinder

• Usable volume = internal volume (L) × (fill pressure − change-out pressure) (MPa) × 10

1 MPa is treated as roughly 10 atmospheres, and the volume at atmospheric pressure is taken as proportional to pressure. Temperature changes and the deviation of compressibility at high pressure are ignored. A 500 L cylinder (internal volume 3.4 L) used from a full 14.7 MPa down to 1.0 MPa gives a usable volume of 466 L.

4. Cylinders and time

• Required volume = oxygen consumption × planned transport time × safety factor
• Cylinders = required volume ÷ usable volume, rounded up (at least one whenever oxygen is used)
• One full cylinder lasts = usable volume ÷ oxygen consumption
• Planning time per cylinder = usable volume ÷ (oxygen consumption × safety factor)

As an example, the default inputs (IPPV, tidal volume 450 mL, respiratory rate 15/min, base flow 3 L/min, FiO₂ 60%, 30-minute transport, safety factor 2.0, a full 500 L cylinder) give a total flow of 9.75 L/min, oxygen consumption of 4.81 L/min and a required volume of 289 L: one cylinder, and one full cylinder lasts 96 minutes.

Warnings shown

• FiO₂ (or the set oxygen concentration) is outside 21–100%
• The fill pressure is at or below the change-out pressure, so nothing is usable
• The fill pressure is above 14.7 MPa
• The last cylinder would be used beyond 85% (little margin if the transport runs longer)
• FiO₂ is 21% with no drive gas, so no oxygen is used

Assumptions and design

• The defaults follow Japanese cylinder standards (fill pressure 14.7 MPa; 500 L cylinder = 3.4 L internal volume; 1,500 L cylinder = 10 L internal volume). Internal volume and pressures can be changed
• The safety factor of 2.0, the change-out pressure of 1.0 MPa and the warning when the last cylinder is used beyond 85% are defaults, not standard or recommended values. Set them to match your facility's rules and the transport conditions
• Inputs are not saved, so that the previous person's values are not left on a shared device
• Everything is calculated in the browser; inputs are not sent anywhere
• Results are estimates. Actual consumption varies with the device, settings, circuit, leaks and the patient's condition