Oxygen & Mixed Gas Therapy

Objectives - Calculate oxygen cylinder duration, operate oxygen and mixed gas therapy devices, and calculate FiO2 delivered through the nasal cannula.

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Administration of Oxygen and Mixed Gas Therapy

Therapeutic Respiratory Gases

Therapeutic respiratory gases include:

• Air
• Oxygen
• Carbogen
• Heliox
• Nitric oxide

Compressed Air

Compressed air is a colorless, tasteless, odorless gas that supports life and is non-flammable.

Clinical applications:

• Dilute 100% O2 to produce FiO2 from 22% to 99% for therapeutic administration
• Serve as driving gas for devices when oxygen is not desired for that purpose

Compressed air is produced from filtered ambient air.

Oxygen

Oxygen is a colorless, tasteless, non-flammable gas that is slightly heavier than air at STPD.

STPD means:

• Standard temperature: 0 degrees C or 273 K
• Pressure: 760 mmHg
• Dry: no water vapor

Clinical application:

• Driving gas for breathing devices when FiO2 greater than 21% is desired for life support

Additional oxygen facts from the source material:

• Fractional distillation: gaseous oxygen becomes liquefied when temperature drops to -297 degrees F
• FiO2 of air is 20.95% and remains constant to an altitude of 60 miles above mean sea level
• PO2 varies with barometric pressure: O2 = Pb x FiO2
• Oxygen supports and accelerates the rate of combustion, making fire burn faster and hotter
• Oxygen cylinder color: green

Carbon Dioxide

Carbon dioxide is a colorless, slight acid-taste, non-flammable gas that does not support combustion or animal life.

Clinical application:

• Clinical research

Additional carbon dioxide facts:

• Carbonic acid forms when CO2 is dissolved in water
• Carbonic acid is corrosive to metals
• At sea level, CO2 concentration is very low, about 0.03%
• CO2 cylinder color: grey

Carbogen

Carbogen is CO2 mixed with oxygen.

Clinical application:

• Carbogen added to mechanically ventilated patients serves as an alternative to adding mechanical dead space

Two mixtures used in medicine:

Carbogen cylinder color: grey/green.

Helium

Helium is a colorless, tasteless, non-flammable inert gas. It does not support life or combustion.

Additional helium facts:

• Second lightest element on the periodic table
• Extremely rare gas
• Occurs naturally in the atmosphere in very small amounts: 0.000524%
• Helium cylinder color: brown

Heliox

Heliox is a mixture of helium and oxygen.

Heliox promotes laminar flow within the airways by two factors:

• Lower density
• Higher viscosity

Laminar flow is determined with the Reynolds number gas mixture formula:

Re = inertial forces / viscous forces
Re = (v r p) / eta

Where:

Heliox Mixtures

• 80/20
• 70/30
• 60/40

Heliox Delivery Methods

• Non-rebreather mask
• Non-invasive positive pressure ventilators
• Mechanical ventilator

Heliox cylinder color: brown/green.

Upper-Airway Indications

Resistance to breathing occurs in the upper and large airways, causing large increases in work of breathing. The source material lists approximately 80%.

Indications include:

• Vocal cord or trachea inflammation
• Tumors or foreign bodies in the trachea or main stem bronchi
• Croup
• Bronchial cancer
• Large airway obstruction

Lower-Airway Indications

Use of a less dense gas, such as a helium-oxygen mixture, can increase medication particle deposition.

Indications include:

• Acute asthma
• COPD: ongoing research, promising

Heliox Goals

• Increased peak flows
• Decreased respiratory rate
• Decreased work of breathing
• Decreased use of accessory muscles
• Decreased respiratory rate after initiating Heliox

Nitric Oxide

Nitric oxide is:

• Colorless
• Tasteless
• Metallic odor
• Non-flammable
• Does not support life
• Exists in very small amounts in the atmosphere
• Also referred to as nitrogen monoxide and inhaled nitric oxide

Nitric oxide is a vasodilator.

Clinical applications:

• Treatment of persistent pulmonary hypertension of the newborn (PPHN)
• Non-FDA application: acute and primary pulmonary hypertension in adults
• Non-FDA application: revascularization perfusion after lung transplants

Dose delivered: parts per million (PPM).

Nitric oxide cylinder color: teal/black.

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Storage, Transport & Delivery of Medical Gas

Medical gas storage methods include:

• Liquid storage
• Compressed cylinders
• Concentrators

Liquid Oxygen Storage

Most large hospitals use liquid bulk oxygen storage.

Important points:

• A small volume of liquid O2 equals a large volume of gaseous O2
• 1 liter of liquid O2 equals 860 liters of gaseous O2
• Liquid O2 must be stored at -118 degrees C or it will revert to gaseous state

Central gas piping in hospitals incorporates pressure-reducing valves that regulate and maintain outlet pressure at 50 psig.

Patient room wall outlets supply oxygen and air at 50 psig. Respiratory equipment operates at 50 psig and can be connected directly to wall outlets.

Compressed Gas Cylinders

Since the 1890s, steel cylinders have been used to store and transport compressed gases. Their use continues today for transporting patients on oxygen.

U.S. Department of Transportation (DOT) regulations specify that high-pressure medical gas cylinders be made of seamless construction from high-quality steel, chromium-molybdenum alloy, or aluminum.

Cylinder Testing and Inspection

Cylinders must be tested at regular intervals to ensure they remain safe for filling to their specified pressure.

The cylinder exterior is inspected for signs of damage:

• Dents
• Rust
• Corrosion
• Deep scarring

The interior is inspected by pressure testing at least five-thirds greater than its 2015 psig service pressure, or 3358 psig.

Tank Color Codes

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Safety Indexed Connector Systems

Safety indexed connector systems ensure the correct gas is delivered to patients using the correct equipment.

Examples:

• American Standard Safety System (ASSS)
• Pin Index Safety System (PISS)
• Diameter Index Safety System (DISS)

American Standard Safety System (ASSS)

ASSS restricts use of regulators attached to large cylinders, such as H or K oxygen cylinders.

It uses nut size and thread design to restrict regulator use to the specific gas the regulator is designed for and calibrated to.

Pin Index Safety System (PISS)

PISS governs attachment of specific gas regulators to small cylinders, such as D and E cylinders.

Regulators are designed for specific gas through a series of pin placements on the regulator. Pin placement must match the pin holes drilled in the yoke of the cylinder.

Diameter Index Safety System (DISS)

DISS connectors are threaded and have a unique diameter for each gas to prevent erroneous connection.

DISS connections are used with low-pressure gas systems: less than 300 psi, usually 50 psi for respiratory and anesthesia equipment.

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Compressed Gas Regulators

Regulators reduce cylinder pressure to 50 psi working pressure.

Types:

Attaching a Regulator

1. Obtain the appropriate pressure regulator for the intended tank.
2. For PISS tanks, use a tank valve key.
3. For ASSS tanks, use a brass non-spark-producing wrench.
4. Before attaching the regulator, crack open the cylinder valve briefly.
5. The burst of gas removes debris and dust that may be lodged in the outlet valve.
6. Position the regulator on the tank and tighten in place.
7. Turn the tank on and check for leaks.
8. Attach the delivery device and put it into use.

Newer O2 cylinders are equipped with regulators to reduce pressure and display tank contents in psi.

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Flow Metering Devices

Flow metering devices include:

• Thorpe tube
• Bourdon gauge
• Flow restrictor

Thorpe Tube Flow Meter

A Thorpe tube consists of a glass tube with graduated markings indicating flow in L/min.

Gas entering the flow meter creates a pressure differential to lift the float.

Thorpe tube flow meters are affected by gravity, such as when a cylinder is lying on its side. Most are scaled from 0 to 16 L/min.

Pressure-Compensated Thorpe Tube

Pressure-compensated Thorpe tube:

• Needle valve is distal to the float
• Reads accurately with backpressure, such as kinked oxygen tubing
• If O2 tubing is occluded, the float drops to zero

Non-Compensated Thorpe Tube

Non-compensated Thorpe tube:

• Needle valve is proximal to the float
• Does not read accurately with backpressure
• If O2 tubing is occluded, the float remains at the same liter flow
• Not common

Confirming Compensation

1. Connect the flowmeter to a wall source.
2. Set flow to 5 L/min.
3. Confirm the ball rises to 5 L/min.
4. Occlude the outlet with a finger.
5. Confirm the ball drops to zero if functioning properly.

Bourdon Gauge

A Bourdon gauge can be calibrated to measure pressure or flow.

Key points:

• Not affected by gravity
• Accurate if the cylinder is on its side
• Can be inaccurate with high resistance or occluded O2 tubing, similar to a non-compensated Thorpe tube

Flow Restrictor

Flow restrictors use a series of holes in a disk calibrated to deliver different flow rates when connected to 50 psi.

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Air-Oxygen Blender

An air-oxygen blender blends 50 psi air and O2 to deliver a specific FiO2.

Input connections:

• Oxygen: 50 psig
• Air: 50 psig

Outlet:

• Blended gas at 50 psig
• Flowmeters can be attached to deliver specific FiO2

Typical uses:

• Oxygen delivery devices for pediatric and neonatal patients
• Mechanical ventilators

Blender Setup Procedure

1. Gather equipment: flowmeter, oxygen hose, air hose, and oxygen blender.
2. Connect oxygen and air hoses for gas service.
3. Connect to wall gas outlets or tank cylinders.
4. Attach the flowmeter to the blender outlet.
5. Connect the O2 device to the flowmeter.

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Oxygen Cylinder Duration

When a therapist cannot be present while a patient is on an oxygen device powered by cylinders, it is necessary to calculate cylinder duration.

Formula Components

• Cylinder pressure
• Conversion factor, which converts cylinder pressure to cylinder volume
• Delivery device liter flow
• Safety factor, used to leave a reserve amount or time so the therapist can change the tank before it runs empty and the patient no longer receives O2

Oxygen Tank Factors

Oxygen Cylinder Duration Formula

[(Pressure - 500) x tank factor] / flow = duration in minutes

Oxygen Duration Example

A patient is receiving 5 L/min by nasal cannula from an E cylinder with 2000 psig.

[(2000 - 500) x 0.28] / 5
(1500 x 0.28) / 5
420 / 5 = 84 minutes

Duration: 84 minutes, or 1 hour and 24 minutes.

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Heliox Cylinder Duration and Delivery

Heliox H-Cylinder Duration

Heliox tank factor or K-factor:

Formula:

(Cylinder pressure x tank factor) / flow = duration in minutes

Heliox Duration Example

An H tank of Heliox has 2200 psi and is delivering Heliox by non-rebreather mask at 10 L/min.

(2200 x 2.50) / 10
5500 L / 10 L/min = 550 minutes
550 / 60 = 9.17 hours

Heliox Delivery with Oxygen Flowmeters

If an oxygen flowmeter is used to deliver Heliox, the flow delivered is greater than what the float indicates.

It is better to use the appropriate Heliox-calibrated flowmeter.

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Oxygen Concentrators

Molecular Sieve Method

Molecular sieves are composed of inorganic sodium aluminum silicate pellets.

They remove:

• Nitrogen
• Carbon dioxide
• Water vapor

Oxygen concentration:

• 92% to 95% at flow less than 2 L/min
• 85% to 93% at flow greater than 5 L/min

This is the most common type.

Vacuum Method

The vacuum method draws ambient air through a semipermeable plastic membrane.

Oxygen concentration:

• Approximately 40%

This method is not commonly used.

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High-Yield Review

Therapeutic Gases

• Oxygen cylinder color: green.
• CO2 cylinder color: grey.
• Carbogen cylinder color: grey/green.
• Helium cylinder color: brown.
• Heliox cylinder color: brown/green.
• Nitric oxide cylinder color: teal/black.
• Heliox promotes laminar flow through lower density and higher viscosity.
• Nitric oxide is delivered in PPM and is used for PPHN.

Delivery Systems and Calculations

• Hospital wall outlets commonly supply oxygen and air at 50 psig.
• ASSS is for large cylinders such as H and K.
• PISS is for small cylinders such as D and E.
• DISS is used with low-pressure gas systems.
• Pressure-compensated Thorpe tubes drop to zero when occluded.
• Bourdon gauges are not affected by gravity.
• Oxygen cylinder duration uses [(Pressure - 500) x tank factor] / flow.
• Heliox flow through an oxygen flowmeter is greater than the indicated flow.