02 cylinder

Components of Oxygen Delivery Systems

Bourdon Gauge

  • A pressure gauge that measures the amount of oxygen delivered by a flow system. It operates by measuring pressure within the system, which is then converted to a flow reading through a pressure-reducing regulator and a fixed orifice. This design makes it gravity-independent.

  • Connected to a regulator, the flow should be set to 8 liters per minute (lpm).

  • Step 1: Connect a bourdon gauge regulator and turn the flow up to 8 lpm.

  • Step 2: Turn the tank on its side; observe that the flow remains steady, confirming system integrity, as its function is not affected by gravity.

  • Step 3: Occlude the oxygen flow; the gauge indicates pressure, not actual flow being delivered to the patient (it reflects pressure build-up but no actual gas movement through the outlet).

Thorpe Tube

  • A flow meter that accurately measures gas flow using a float within a tapered tube. It utilizes a bobbin or ball float that rises in a tapered tube due to the force of the gas flow against gravity. This makes it gravity-dependent, requiring an upright position for accurate readings.

  • Step 4: Connect a Thorpe tube flow-meter and set the flow to 8 lpm.

  • Step 5: When the tank is turned on its side, the float ball goes to the top, indicating an inaccurate reading due to the effect of gravity on the float.

  • Step 6: Occlude the oxygen flow; the Thorpe tube's float drops to zero, accurately indicating that no flow is being delivered.

  • Step 7: The Thorpe tube displays true flow and is preferred for accurate measurements when oriented upright.

Oxygen Flow Ranges

  • The normal liter flow range for a nasal cannula (NC) is 1-6 lpm, providing a fraction of inspired oxygen (FiO2) of approximately 24\%-44\%.

  • A simple mask typically delivers oxygen at 6-10 lpm, yielding an FiO2 of about 35\%-50\%.

  • A non-rebreather mask delivers oxygen at 10-15 lpm, achieving the highest possible FiO2 through a mask, typically 60\%-90\%, by utilizing a reservoir bag and one-way valves.

Room Air and Oxygen Delivery

Composition of Room Air

  • Room air contains approximately 21\% oxygen.

Factors Affecting FiO2

  • For every one liter per minute (lpm) of oxygen flow increase (via nasal cannula), the fraction of inspired oxygen (FiO2) increases by approximately 3\% from room air (21\%$). This approximation is most accurate for flows between 1-6 lpm.

Flow-Meter Types and Cylinder Orientation

Preferred Flow-Meter Types

  • If a cylinder needs to be placed on its side, a Bourdon flow-meter type is preferred as it functions independently of gravity.

Safety Relief Valves

E Tank Safety Relief Valve

  • The safety relief valve for an E tank is known as the Pressure Indicator Safety System (PISS).

H Tank Safety Relief Valve

  • The safety relief valve for an H tank is known as the American Standard Safety System (ASSS).

Practice Duration of Gas and Liquid Delivery Systems

  • Understanding how long different gas sources will last at various flow rates is crucial for interventional preparation.

E Cylinder Duration

  • An E cylinder with 800 psi at a flow of 3 lpm nasal cannula will last:

    • The general formula for cylinder duration is: Duration (minutes) = (Cylinder PSI x Cylinder Factor) / Flow Rate (L/min).

    • The cylinder factor for an E cylinder is approximately 0.28 L/PSI.

    • So, Duration (minutes) = (800 PSI x 0.28 L/PSI) / 3 L/min = 224 / 3 \approx 74.67 minutes, or approximately 1 hour and 15 minutes.

    • To calculate duration in hours: Duration (hours) = (Cylinder PSI x 0.28) / (Flow Rate x 60).

Liquid Oxygen Tank Duration

  • A liquid oxygen tank with 1.5 lbs. of O2 at a flow of 3 lpm nasal cannula will provide gas for a specific duration based on the liquid oxygen equation:

    • An approximate conversion factor for liquid oxygen is 1 lb of liquid O2 = 344 L of gaseous O2.

    • Duration (minutes) = (Weight of O2 (lbs) x 344 L/lb) / Flow Rate (L/min).

    • So, Duration (minutes) = (1.5 lbs x 344 L/lb) / 3 L/min = 516 / 3 = 172 minutes, or 2 hours and 52 minutes.

    • To calculate duration in hours: Duration (hours) = (Weight of O2 (lbs) x 344) / (Flow Rate x 60).

H Cylinder Duration

  • An H cylinder with a PSI of 1500 at a flow of 15 lpm will have a calculated duration based on the appropriate formula for the tank size and operating pressure:

    • The cylinder factor for an H cylinder is approximately 3.14 L/PSI.

    • Duration (minutes) = (Cylinder PSI x 3.14 L/PSI) / Flow Rate (L/min).

    • So, Duration (minutes) = (1500 PSI x 3.14 L/PSI) / 15 L/min = 4710 / 15 = 314 minutes, or 5 hours and 14 minutes.

    • To calculate duration in hours: Duration (hours) = (Cylinder PSI x 3.14) / (Flow Rate x 60).

3 lb Liquid Oxygen Cylinder Duration

  • A 3 lb liquid oxygen cylinder at a flow of 12 lpm will have a limited operational time based on similar calculations referencing liquid weight and flow rates:

    • Using the conversion factor of 1 lb liquid O2 = 344 L gaseous O2.

    • Duration (minutes) = (Weight of O2 (lbs) x 344 L/lb) / Flow Rate (L/min).

    • So, Duration (minutes) = (3 lbs x 344 L/lb) / 12 L/min = 1032 / 12 = 86 minutes, or 1 hour and 26 minutes.

    • To calculate duration in hours: Duration (hours) = (Weight of O2 (lbs) x 344) / (Flow Rate x 60$$).