Clinical Applications of Gas Therapies

Clinical Applications of Helium-Oxygen Therapy

• Utilized for exacerbation of asthma, post-extubation stridor, refractory croup, and severe airway obstruction in chronic bronchitis and emphysema.

Helium-Oxygen Mixtures

• Available concentrations: 80% Helium/20% oxygen, 70% Helium/30% oxygen, 60% Helium/40% oxygen.
• Actual flow is impacted by the low density of helium; standard flowmeters are not accurate.
• Correction factors for flow rates:
  • 80:20 mixture: 1.8 × liter flow
  • 70:30 mixture: 1.6 × liter flow
  • 60:40 mixture: 1.4 × liter flow

Carbon Dioxide/Oxygen Therapy

• Used for various disorders like singultus.
• Common gas mixtures: 5% CO2/95% O2 and 7% CO2/93% O2.

Nitric Oxide (NO) Therapy

• Administered for persistent pulmonary hypertension in newborns.
• Highly reactive, forming nitrogen dioxide (NO2) or nitric acid (HNO3).
• Delivered via I-NOvent with the potential for rebound vasoconstriction; cautious weaning is crucial.

Hyperbaric Oxygen Therapy

• Defined as exposure to pressure greater than one atmosphere while breathing 100% oxygen.
• Physiological effects include reduction of trapped gas bubbles and increase in plasma supersaturation with oxygen (up to 1500 mmHg).
• Conditions that benefit: gas gangrene, radiation necrosis, carbon monoxide/cyanide poisoning, decompression sickness, and severe acute anemia.

Equipment for Hyperbaric Oxygen Therapy

• Monoplace chamber accommodates one patient; multiplace chamber allows more than one patient and healthcare provider.
• Increased ability of white blood cells to fight infections and promoted neovascularization to poorly perfused tissues.

Indications for Oxygen Therapy

• Hypoxemia classifications:
  • Acute care: PaO2 < 60 mmHg or SaO2 < 90%.
  • Sub-acute/home care: PaO2 < 55 mmHg or SaO2 < 88%.
  • Patients with cor pulmonale or congestive heart failure may require oxygen therapy at PaO2 of 56-59 mmHg.

Oxygen Delivery Systems

• High-flow systems provide all inspiratory flow needs without air entrainment.
• Low-flow devices partially meet inspiratory gas flow; include nasal cannula, simple masks, and partial/non-rebreathing masks.

Low-Flow Oxygen Delivery Devices

• Nasal Cannula: Delivers 1-6 LPM; effective FIO2 up to 44%.
• Simple Mask: Delivers 35-55% FIO2; requires minimum flow rate of 5 LPM.
• Transtracheal Catheter: Surgically inserted for continuous O2, using less flow than nasal cannula but carries certain risks.

High-Flow and Environmental Oxygen Devices

• Anesthesia bag-mask systems provide 100% FiO2 but require gas source.
• Environmental devices like incubators, head boxes (oxyhoods), and mist tents help regulate oxygen concentration and temperature for infants.

Gas Densities

• Densities: O2 (1.429 g/L), Air (1.29 g/L), CO2 (1.98 g/L), He (0.1785 g/L), N2O (1.98 g/L), NO (1.34 g/L).
• Understanding gas densities is essential for the layering effect within oxygen enclosures and accurate oxygen analysis.

Indications for Oxygen Therapy

• Hypoxemia defined as PaO2 < 60 mmHg or SaO2 < 90% in acute care settings.
• For sub-acute/home care, PaO2 < 55 mmHg or SaO2 < 88% indicates hypoxemia.
• In sub-acute/home care, PaO2 of 56-59 mmHg or SaO2 < 89% associated with:
  • Cor pulmonale
  • Congestive heart failure
  • Erythrocythemia with hematocrit > 56

Oxygen Delivery Systems

• High-Flow Systems: Deliver all inspiratory flow needs; no air entrainment.
• Low-Flow Devices: Provide partial inspiratory gas flow; air entrainment occurs.

Low-Flow Oxygen Delivery Devices

• Nasal Cannula: Delivers 1 to 6 LPM, achieving up to 44% FiO2; FIO2 varies with tidal volume and respiratory rate.
• Nasal Catheter: More invasive than nasal cannula, positioned in the oropharynx.
• Reservoir Cannula: Maintains a higher FiO2 at lower flows using a small reservoir.
• Transtracheal Catheter: Surgically inserted for long-term oxygen delivery; requires less flow than nasal cannula but poses infection risks.
• Simple Mask: Delivers 35-55% FiO2, requires minimum flow of 5 LPM.
• Partial Rebreathing Mask: Rebreathes some exhaled gas, achieving up to 70% FiO2.
• Non-Rebreathing Mask: Provides up to 100% FiO2; incorporates one-way valves to prevent CO2 rebreathing.
• HiOx80 Disposable Mask: Delivers high FiO2 (>80%) at low flow rates without entrainment.

High-Flow Oxygen Delivery Systems

• High-Flow Nasal Cannula: Achieves high FiO2 and washes out CO2; requires humidification.
• Venturi Mask: Delivers a precise FiO2 using air entrainment ratios.
• Anesthesia Bag-Mask Systems: Provide 100% FiO2; unable to function without a gas source.

Oxygen Enclosures or Environmental Devices

• Incubator: Controls temperature and FiO2 for infants; frequent care may disrupt O2 regulation.
• Head Box/Oxyhood: Encloses the head, requires careful O2 analysis due to layering effects.
• Mist Tents (Croupettes): Used for aerosol therapy; O2 concentration control can be challenging.

Hyperbaric Oxygen Therapy

• Exposure to pressure > 1 atmosphere while breathing 100% oxygen.
• Physiological effects include decreased gas bubble sizes (Boyle's Law), improved O2 transport, and enhanced white blood cell function.
• Conditions benefiting from therapy include gas gangrene, radiation necrosis, and decompression sickness.
• Types of chambers include monoplace (one patient) and multiplace (multiple patients).

Helium-Oxygen Therapy

• Low density of heliox improves gas movement around obstructions.
• Used for acute asthma exacerbations, post-extubation stridor, and severe airway obstruction.
• Available concentrations include 80% He / 20% O2, and flow rates must be adjusted due to low density.

Carbon Dioxide/Oxygen Therapy

• CO2/O2 mixtures (e.g., 5/95% or 7/93%) used historically for various disorders such as singultus.

Nitric Oxide Therapy

• Used for treating pulmonary hypertension in neonates.
• Inhaled nitric oxide poses risks such as NO2 formation and rebound vasoconstriction. Delivered using I-NOvent device.