# Altitude Physiology Calculator

Use this calculator to determine the barometric pressure, gas expansion ratio and sea-level equivalent FiO2 at altitude.

The Altitude Physiology Calculator is only available on our mobile site mobile.nicutools.org. Enter the cabin altitude
Enter FiO2 required by the infant at sea level.

The calculated barometric pressure will be displayed in mmHg
The gas expansion ratio at this altitude will be displayed.
The FiO2 required to maintain a constant PaO2 at altitude (based on that required at sea-level) will be displayed.

Calculator Algorithm:

1. The Barometric Formula

P(h) = 760 x e-Mgh/RT

The barometric pressure at altitude h (in metres) is calculated from the Barometric Formula as above. Sea level pressure is estimated at 760 mmHg, and a sea level temperature of 290 Kelvin (15 C) is assumed.

M = the molar mass of the gas expressed in kg/mole = 0.0288
g = the acceleration due to gravity =9.81 m/s2
R = the gas constant = 8.3145 J/molK
T = temperature, Kelvin (see below)

2. Boyle’s Law

P1V1 = P2V2

The initial barometric pressure multiplied by the initial volume of gas equals the final barometric pressure multiplied by the final volume of gas.

Fa = F0 x (760-47) / (P(h) - 47)

The FiO2 required at any altitude (Fa) is calaculated from the sea-level Fio2 requirement multiplied by the sea-level barometric pressure and divided by the baraometric pressure at the given altitude. A pressure adjustment for the partial pressure of water at body temperature is included.

4. Temperature at altitude

Temperature is assumed to be 290 Kelvin (15C) at sea-level, and to drop by 6.6 Kelvin for every 1000m of additional altitude.

References:

Guidelines for Air & Ground Transport of Neonatal & Pediatric Patients. AAP 1999