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Today we will discuss one of the most critical devices utilised by anesthetists and throughout the anesthetic communities—the oxygen delivery devices. From anesthesia circuits, nasal prongs, and basic face masks to ventilators in the ICU environment, these devices are integral to guaranteeing optimal oxygen delivery. It is important to understand these devices in determining the oxygen flow, the needed fraction of inspired oxygen (FiO2), and categorizing these devices according to patient requirements.
Significance of Oxygen Therapy
Oxygen is crucial to life, and its administration becomes important in the management of hypoxemia, which may occur because of hypoventilation, ventilation-perfusion (V/Q) mismatch, atelectasis, or anesthetic-induced respiratory depression. Oxygen therapy is important for:
- The management of hypoxemia and enhancement of tissue oxygenation
- Carbon monoxide poisoning
- Maintaining survival during low atmospheric pressure environments, e.g., mountaineering
- Aiding patients undergoing anesthesia who cannot breathe on their own
The World Health Organization (WHO) has indicated that an FiO2 of 80% is acceptable, though in the majority of ICU environments, 50-60% FiO2 is usually acceptable. Oxygen delivery can be administered via simple face masks, nasal cannulas, or invasive ventilatory assistance based on a patient’s ventilatory needs.
Classification of Oxygen Delivery Systems
Oxygen delivery systems can be classified into two general categories:
- Normobaric Oxygen Therapy – Oxygen is delivered at atmospheric pressure.
- Hyperbaric Oxygen Therapy – Oxygen is administered at greater-than-atmospheric pressures.
Additional Classification Based on Patient Dependency
- Low Dependency Systems: Supplemental oxygen alone is adequate to correct hypoxemia in spontaneously breathing patients.
- Medium Dependency Systems: Patients need further assistance like Continuous Positive Airway Pressure (CPAP) or High-Flow Nasal Cannula (HFNC).
- High Dependency Systems: Patients need mechanical ventilation or Non-Invasive Positive Pressure Ventilation (NIPPV).
Low Dependency Oxygen Delivery Systems
Low dependency systems are subdivided into:
Low Flow Devices:
- Nasal Cannula: Supplies variable oxygen concentration (FiO2 varies with respiratory rate and tidal volume).
- Simple Face Mask: Supplies more FiO2 than a nasal cannula but less accurately.
- Reservoir Masks:
- Partial Rebreather Mask: Permits some rebreathing of exhaled gases, which raises FiO2.
- Non-Rebreather Mask: Fitted with one-way valves to avoid rebreathing, providing increased FiO2 levels.
High Flow Devices:
- Venturi Mask: Offers a constant and reliable FiO2 irrespective of patient effort.
- High-Flow Nasal Cannula (HFNC): Provides warm, humid oxygen at high flow rates (max. 60 L/min), facilitating improved oxygenation and comfort.
Determinants of Delivered FiO2
Several factors affect the actual FiO2 that a patient inhales:
- Equipment Factors: Oxygen flow rate, mask volume, quality of fit, and effectiveness of mask seal.
- Patient Factors: Respiratory rate, tidal volume, peak inspiratory flow rate, and intrinsic respiratory disease.
- Other Factors: Whether or not humidification is present, patient compliance, and external air entrainment.
Conclusion:
Knowledge of oxygen delivery devices is essential to maximize patient care, especially in ICU and anesthesia environments. Selecting the appropriate oxygen therapy modality according to patient requirements and levels of dependency ensures proper oxygenation, reduces complications, and improves overall treatment outcomes.
Stay updated, stay ready, and keep moving forward in the specialty of anesthesiology and critical care!
