This part of Lab 1 will serve as a review of the gas laws used in the practice of respiratory care and include application of these laws in clinical scenarios.
Use the universal gas law to determine the new pressure, volume, or temperature.
Derive a cylinder duration factor when given the volume of a tank in liters.
Solve cylinder duration problems when given the psig of a tank and the usage flow rate.
The universal gas law explains the behavior of gases when mass remains constant. In the following formula, P stands for pressure, V for volume, and T for temperature. Pressure and volume units must be the same on both sides of the equation. Temperature is absolute temperature using Kelvin's scale. To change Celsius to Kelvin, add 273 degrees to the Celsius temperature. Common temperatures in the following problems will be body temperature (37 degrees Celsius) and room temperature (21 degrees Celsius).
The universal gas law above is a combination of 3 gas laws: Boyle's, Charles, and Gay-Lussac's.
Boyle's Law states that pressure and volume are inversely proportional when temperature remains constant. An increase in pressure will decrease the volume. .
P1V1 = P2V2
If P1 = 100 and V1 = 10, what will V2 equal if the pressure doubles? Set up the problem and solve for V2.
How does Boyle's Law apply to taking a breath?
Charles' Law states that pressure is directly proportional to temperature when the volume remains constant.
P1/T1 = P2/T2
What is the new pressure if P1 = 2200 psig, T1 = 21 degrees C, and T2 = 100 degrees C?
Gay-Lussac's Law states that volume is directly proportional to temperature when the pressure remains constant.
V1/T1 = V2/T2
What is the new volume if V1 = 1000 milliliters (mL), T1 = 21 degrees C, and T2 = 37 degrees C?
The following diagram arranges the gas characteristics with the law's name. B stands for Boyle's Law which describes the relationship between pressure and volume.
There are 3 sizes of tanks commonly used in respiratory care: E, G, and H-K. Each tank has a cylinder duration factor used to calculate how long the gas in the tank will last. Based on Boyle's Law, the factors are in liters/psig units.
One cubic foot of oxygen equals 28.3 Liters. Each tank is filled to 2200 psig. The cylinder duration factor is the tank's volume in liters over the pressure when the tank is full. An oxygen E tank contains 22 cu.ft. of gas or 22 x 28.3 = 622.6 liters. 622/2200 = 0.28 for the cylinder duration factor. What are the factors for the other two sizes of tanks?
To use the cylinder duration factor, multiply the factor times the psig and divide by the Liters per Minute (LPM) of use. If an E cylinder is being used at a flow rate of 10 LPM and the tank contains 800 psig, how long will it last?