Oxygen Delivery Devices

Objectives - Describe indications for oxygen therapy; administer oxygen utilizing low-flow and high-flow therapy devices; describe flow rate and FiO2 range for each oxygen device; perform a two-point calibration on an oxygen analyzer.

---

Indications for Oxygen

Documented Hypoxemia

Confirmed by ABG:

• PaO2 less than 60 mmHg or SaO2 less than 90% on room air (21% FiO2)
• PaO2 or SaO2 below desirable range for specific clinical situations, such as pneumonia

Acute Care Situations in Which Hypoxemia Is Suspected

Examples include:

• Cor pulmonale
• Congestive heart failure
• Severe trauma (severe blood loss)
• Acute myocardial infarction

Short-Term Therapy or Surgical Intervention

• Post-anesthesia recovery

---

Contraindications for Oxygen

With few exceptions, no specific contraindication to O2 therapy exists when indications are present.

Certain delivery devices are contraindicated:

• Nasal cannulas and nasopharyngeal catheters in pediatric and neonatal patients with obstruction

---

Hazards of Oxygen

• PaO2 greater than or equal to 60 mmHg: ventilatory depression may occur rarely in spontaneously breathing patients with elevated PaCO2 (COPD)
• With FiO2 greater than 0.5: absorption atelectasis, O2 toxicity, or depression of ciliary or leukocyte function may occur
• Increased FiO2 can worsen lung injury in patients with paraquat poisoning or patients receiving bleomycin
• During laser bronchoscopy or tracheostomy: minimal FiO2 should be used to avoid intratracheal ignition
• Fire hazard increased in the presence of high FiO2
• Bacterial contamination can occur when nebulizers or humidifiers are used

Infant-Specific Hazards of Oxygen

• Premature infants: PaO2 greater than 80 mmHg may contribute to Retinopathy of Prematurity (ROP). Retina do not vascularize completely, leading to detached retina and blindness
• Certain congenital heart lesions such as hypoplastic left heart syndrome: high PaO2 can compromise the balance between pulmonary and systemic blood flow (duct dependent babies)
• O2 flow directed at the face may stimulate an alteration in respiratory pattern

---

Low-Flow vs High-Flow Devices

---

Low-Flow Oxygen Devices

Flow is generally less than 10 L/min. FiO2 is variable and dependent upon the patient:

• Tidal volume and respiratory rate (minute volume / min vol)
• Increased Vt or RR decreases delivered FiO2 in low-flow devices
• Inspiratory flow rate
• Air entrainment around the device — increased air entrainment decreases FiO2

Flow Deficit Example

• Patient inspiratory flow rate = 20 L/min
• O2 device set at 8 L/min
• Flow deficit = 12 L/min

The remaining 12 L/min comes from room air entrainment.

Low-Flow Device Summary

---

Nasal Catheter

• Widely used as the standard low-flow oxygen delivery system until the late 1960s
• Made of soft pliable PVC tube approximately 12 inches long with a series of small holes at the distal end
• Adult catheter sizes: 12 and 14 Fr
• Pediatric catheters: 8 and 10 Fr
• Flow rates: 1 to 5 L/min
• FiO2 ranges from 22% to 35%
• Inserted blindly through the nose after length is estimated by measuring from the nose to the ear

Contraindications:

• Nasal septum deviation
• Mucosal congestion
• Nasal polyps (abnormal growth of tissue projecting from a mucous membrane)

The nasal cannula and other less-invasive devices have replaced the nasal catheter.

---

Nasal Cannula

• Most widely used device for administering low-flow oxygen to infants, children, and adults
• Easily applied and well tolerated by most patients
• Flow rates: 0 to 6 L/min
• Must be humidified above 4 L/min

Rule of Fours

Each liter of flow equals approximately a 4% increase in FiO2:

20% + (O2 L/min x 4) = estimated FiO2

---

Simple Mask

Also called a face mask.

• Covers the nose and mouth and is held in place by an elastic band around the head
• Ambient air drawn in around the mask mixes with oxygen delivered to the mask, resulting in an approximate FiO2
• Used when a nasal cannula is not appropriate, such as nasal obstruction
• Flow rates: 5 to 10 L/min
• FiO2: 30% to 60%
• Humidified: up to 15 L/min

Safety Hazards (All Enclosed O2 Mask Systems)

• CO2 accumulation and re-breathing of exhaled gases can occur at flow rates less than 5 L/min
• All masks must be run at greater than 5 L/min to wash out exhaled CO2
• Hypoxic rebound when the mask is removed
• Asphyxiation secondary to aspiration
• Patient compliance: difficulty eating, drinking, speaking on phone, and hygiene
• Claustrophobia due to masks covering both the nose and mouth simultaneously

---

Non-Rebreathing Mask (NRB)

• Incorporates reservoir bag and two one-way valves between the reservoir bag and mask
• Prevents exhaled gas from entering the reservoir bag
• Opens during inhalation to provide 100% oxygen
• One exhalation port
• During inhalation, the valve on the mask closes, reducing room air entrainment
• Not humidified
• FiO2: 60% to 80%
• Flow rates: 10 to greater than 15 L/min
• Must meet or exceed the patient inspiratory flow demand
• Maintain inflated reservoir greater than 50%
• Only device used to deliver Heliox

---

Trans-Tracheal Catheter

• Oxygen delivered through a small catheter inserted transdermally
• Application: long-term oxygen therapy
• Flow rate less than 6 L/min
• FiO2: 22% to 35%
• Trachea acts as a reservoir to provide efficient use of O2 and reduced O2 flow
• Hazards: site infections and mucus plugging

Small bore oxygen tubing connectors are used with this device.

---

High-Flow Oxygen Devices

Characteristics:

• Flow rate exceeds the patient inspiratory flow rate
• Delivers fixed FiO2
• Increased flow rates minimize dilution with room air

Indications for high-flow oxygen:

• Patient with high work of breathing
• Accessory muscles in use
• Increased tidal volume and/or respiratory rate

High-flow device types in this lesson:

• Large volume nebulizer (LVN)
• Air entrainment mask (Venturi mask)
• HF nasal cannula (Vapotherm)

---

Large Volume Nebulizer (LVN)

• FiO2: 30% to 100%
• Jet nebulizer that also delivers aerosolized water
• Uses large bore tubing to minimize flow resistance and prevent occlusion by condensate
• Can be heated: hot plate, doughnut/yoke collar, or immersion heater

Delivery devices:

For LVN use in bland aerosol and humidification therapy, see Humidification Delivery.

---

Venturi Mask (Air-Entrainment Mask)

Also called Venti mask.

• Comprised of an aerosol mask with air entrainment adapters attached to small bore oxygen tubing
• FiO2: 24% to 60%
• Total flow can exceed 100 L/min due to air entrainment
• Each adapter or dial is for a specific FiO2

Indications

• Patients with increased minute volume requiring high flow to match or exceed inspiratory flow rate
• If total flow to the mask is less than the patient inspiratory flow demand, delivered FiO2 will decrease
• Occlusion of entrainment ports increases FiO2 while decreasing total flow — avoid obstructing air entrainment ports
• Mouth breathing or blocked nasal passage
• Tracheostomy patient transports through a trach collar
• COPD patients who require FiO2 0.24 to 0.35 (24%–35%)

Total flow: combination of delivered oxygen flow rate plus entrained air flow rate, calculated for each FiO2.

Air-Oxygen Entrainment Ratios

Remember: as air entrainment decreases, FiO2 increases. Do not obstruct air entrainment ports.

Calculating Air-Oxygen Entrainment Ratios

Air : O2 = (100 - % O2) : (% O2 - 21)

FiO2 = 24%:

Air: (100 - 24) / (24 - 21) = 76 / 3 = 25 : 1

FiO2 = 40%:

Air: (100 - 40) / (40 - 21) = 60 / 19 = 3 : 1

Calculation is possible only up to 60% maximum.

---

High-Flow Nasal Cannula (HFNC)

Vapotherm — high flow nasal cannula (HFNC):

• Alternative to mask or CPAP oxygen therapy
• Patient comfort increases compliance
• Oxygen FiO2: 21% to 100%
• Delivered flow rates:
  • Adults: 5–40 L/min
  • Neonates/children: 1–8 L/min
• Heated (active) humidity incorporated with HFNC
• Nasal delivery: prongs less than half inner diameter of nares

High velocity gas produces more pronounced clinical effects.

Exhalation effects:

• CO2 washout
• Dead space
• Alveolar ventilation efficiency
• Breathing efficiency

Positive pressure effects:

• Mean airway pressure
• Gas exchange
• Work of breathing
• Increased O2 concentration

Optimal humidification effects (compared to cool, dry gas):

• Mucous clearance
• Airway conductance
• Pulmonary compliance

---

Oxygen Analyzers

Oxygen analyzers measure and monitor delivered FiO2.

Oxygen analyzers are necessary when specific FiO2 delivery must be known or is critical.

Examples: neonatal oxygen hoods, infant incubators, mechanical ventilators, high flow O2 devices, and others.

• Perform 2-point calibration prior to each use
• O2 error range is no greater than +/- 2% (if out of range, replace analyzer sensor or send for repair)

Types of Oxygen Analyzers

Common:

• Electrochemical
• Galvanic
• Polarographic (Clark)
• Paramagnetic
• Zirconium cell
• Raman scattering
• Mass spectrometry

Specialized:

• Galvanic fuel cell

Galvanic Fuel Cell

• Cell runs continuously
• Energy and accuracy depletes over time
• Cap off sensor when not in use
• Slow response time
• Accuracy +/- 2% or replace cell

Operation:

• Chemical reaction creates electrical current
• Gold cathode (+), lead anode (-) immersed in electrolyte gel
• PiO2 measured then converted to read as FiO2

Polarographic (Clark) Electrode

• Operates continuously or intermittently
• Fast response time
• Accuracy +/- 2% or replace cell

Operation:

• Battery powered source (9 Volt)
• Platinum cathode (+), silver anode (-)
• PiO2 measured then converted to read as FiO2

Electrochemical O2 Analyzer Comparison

---

Analyzer Calibration Procedure

1. Assemble: Connect cable to O2 cell, then attach to analyzer unit. Turn on unit to verify lights and audible alarms.
2. Two-point calibration (21% and 100%):
   • Calibrate to room air — press "21%" then "unlock"
   • Calibrate to 100% — place sensor in plastic bag and bleed oxygen into bag. Press "100%" then "unlock"
3. Set high/low alarms: Press "set", then "up arrow" for high alarm. Press "set", then "down arrow" for low alarm.
4. Place analyzer in line with gas source with Briggs adaptor.
5. Ventilator use:
   • Place adaptor pre-heater (cool)/humidifier (dry)
   • Recalibrate with altitude changes
   • Set O2 alarm (if available/default): high 10% above FiO2, low 10% below FiO2

---

High-Yield Review

Indications for Oxygen Therapy

• Documented hypoxemia confirmed by ABG: PaO2 less than 60 mmHg or SaO2 less than 90% on room air (21% FiO2); or below desirable range for specific clinical situations
• Acute care when hypoxemia is suspected: cor pulmonale, congestive heart failure, severe trauma, acute MI
• Short-term therapy or post-anesthesia recovery

Low-Flow Devices

• Variable approximate FiO2; flow generally less than 10 L/min
• FiO2 depends on minute ventilation (Ve = respiratory rate x tidal volume)
• Increasing minute ventilation increases air entrainment and decreases FiO2

High-Flow Devices

• Fixed known FiO2; flow generally greater than 10 L/min
• Total flow exceeds patient inspiratory demand
• Increasing flow minimizes room air dilution

Device Flow and FiO2 Ranges

Oxygen Analyzer Calibration

• 2-point calibration at 21% and 100% before each use
• Accuracy within +/- 2%