Supplemental Oxygenation

PHT5341C - Supplemental Oxygenation

Role of Supplemental Oxygen

  • Supplemental oxygen is critical in managing cardiac and pulmonary conditions.

  • Addresses oxygen desaturation, a key factor compromising tissue perfusion and organ function.

The Oxyhemoglobin Dissociation Curve

  • Illustrates how small drops in arterial oxygen (PaO2) can lead to steep declines in oxygen saturation and significant clinical consequences.

  • Aim:

    • To demonstrate how supplemental oxygen can improve oxygenation.

    • To reduce symptom burden.

    • To enhance exercise tolerance, especially when the body's oxygen demand increases.

Physiological Consequences of Hypoxemia

  • Definition of Hypoxemia: Reduced oxygen levels in the blood.

  • When partial pressure of oxygen (PaO2) falls below approximately 55-60 mmHg, compensatory mechanisms activate:

    • Increased minute ventilation:

    • Minute ventilation calculated as (respiratory rate) x (tidal volume).

    • Increased heart rate:

    • Raises cardiac output to support oxygen delivery.

  • Initial adaptive responses can lead to:

    • Increased myocardial strain.

    • Respiratory muscle fatigue.

    • Progressive clinical deterioration.

Local Mechanisms in Response to Hypoxemia

  • Reflexive Regional Pulmonary Vasoconstriction:

    • Occurs in alveolar areas with low oxygen levels, constricting small pulmonary arterioles and redirecting blood flow to well-ventilated regions, optimizing gas exchange and arterial oxygenation.

  • Chronic or widespread hypoxia (e.g. interstitial lung diseases, advanced COPD):

    • Generalized vasoconstriction increases pulmonary vascular resistance, impairing gas exchange and adding a chronic workload to the right ventricle.

Cor Pulmonale

  • Definition: Right-sided heart failure due to sustained pulmonary hypertension secondary to lung diseases or chronic hypoxemia.

  • Implications include:

    • Clinical management considerations.

    • Impact on functional capacity and exercise tolerance.

Systemic Signs and Symptoms from Hypoxemia

  • Early compensatory symptoms include:

    • Dyspnea

    • Palpitations

    • Headache

    • Cognitive slowing

    • Impaired judgment

  • As hypoxemia progresses:

    • Further cognitive decline.

    • Motor incoordination.

    • Decreased exercise tolerance.

    • Severe cases can lead to loss of consciousness.

    • Increased myocardial oxygen demand in patients with existing cardiovascular disease (e.g. angina).

Impact of Supplemental Oxygen

  • Immediate changes observed when supplemental oxygen is administered:

    • Reduction in breathlessness, especially in patients with low PaO2 or SpO2 at rest/exertion.

    • Improved exercise tolerance, even with moderate/severe hypoxemia.

    • Physiological strain reduction, including:

    • Decreased minute ventilation due to reduced hyperventilation drive.

    • Enhanced respiratory muscle function, particularly concerning diaphragm and accessory muscles.

    • Alleviation of hypoxic pulmonary vasoconstriction, improving pulmonary hemodynamics and reducing right heart strain.

Clinical Reasoning in Oxygen Therapy

  • As a physical therapist (PT), anticipate appropriate responses to supplemental oxygen:

    • If no improvement in breathlessness or activity tolerance, question if oxygenation is the primary issue.

    • Consider potential alternate issues such as cardiac dysfunction or acid-base disturbances.

    • Reassess, consult the medical team, or recommend further medical evaluation if symptoms persist despite oxygen therapy.

Formal Indications for Continuous Oxygen Therapy

  • Criteria by the Centers for Medicare and Medicaid Services for long-term oxygen treatment:

    • PaO2 < 55 mmHg or SpO2 < 88% while breathing room air warrants therapy.

    • In some cases with systemic consequences, PaO2 56-59 mmHg or SaO2 89-90% may also qualify.

    • This is valid only if there are signs of chronic hypoxia like pulmonary hypertension or cor pulmonale.

  • Important Note: Supplemental oxygen is classified as a drug, requiring a prescription.

Titrating Oxygen in Different Settings

  • Oxygen delivery can be adjusted based on patient activity needs and prescribed orders:

    • General orders to maintain SpO2 above a certain percentage allow for titration during mobility or exercise.

    • Specific orders (e.g. flow rates) legally bind the PT to those rates without exceeding them.

Monitoring SpO2 During Activity

  • Continually assess SpO2 during patient activity and respond to desaturation by:

    • Determining if the patient is above the designated saturation threshold.

    • Responding to distress symptoms (dyspnea, pallor, dizziness).

    • Interventions include:

      • Positioning.

      • Breathing techniques.

      • Airway clearance strategies (coughing).

    • After intervention, monitor SpO2 to determine stabilization or need for further action.

Adjustments Based on Medical Orders

  • If patient saturation falls below the prescribed threshold:

    • If the patient is already on oxygen:

    • Check the order for titration.

      • If allowed, adjust the flow rate accordingly.

    • If a fixed rate is specified, consult the medical team for changes if further desaturation occurs.

    • If no orders exist, consult the medical team for the initiation of oxygen delivery.

Oxygen Delivery Devices

  • Devices aim to increase FiO2 (fraction of inspired oxygen):

    • Room air: Approximately 20-21% oxygen.

Nasal Cannula

  • Most frequently used oxygen delivery device.

  • Provides modest FiO2 increase (24-44%) based on flow rate:

    • Estimated calculation: FiO2 = 20% + (4% x flow rate in L/min).

    • Example: At 3 L/min, FiO2 is ~32%.

  • Humidification recommended for >3 L/min to prevent dryness.

Simple Face Mask

  • Alternative for higher concentrations (35-50% FiO2).

  • Requires minimum flow rate of 5 L/min to avoid CO2 rebreathing.

Venturi Mask

  • Allows precise FiO2 delivery using color-coded adapters (24-50% FiO2).

  • Useful for CO2 retention at risk patients (e.g., COPD).

High-Flow Nasal Cannula

  • For required flow rates exceeding 6 L/min (max for standard cannula).

  • Can deliver up to 100% FiO2 at 60 L/min.

  • Systems like Vapotherm and Airvo offer heated humidification, improving comfort and airway function.

Non-Rebreather Mask and Manual Ventilation System

  • Non-Rebreather Mask:

    • Delivers high concentrations (90-100% FiO2) at 10-15 L/min.

    • Features a one-way valve and a reservoir bag.

  • Manual Ventilation Devices (e.g., Ambu bag):

    • Used in emergencies to provide 100% FiO2 with an oxygen source.

    • Can assist in patient transport and ambulation.

Key Clinical Responsibilities

  • Measure baseline vital signs and oxygen saturation before activity.

  • Return patient to pre-activity oxygen settings after interventions:

    • Oxygen therapy based on arterial blood gases must be respected.

  • Monitor for hypoxemia signs and communicate if current oxygen plans seem insufficient.

  • Understanding the physiological rationale and procedures with supplemental oxygen leads to better patient outcomes.

Conclusion

  • The combination of physiological knowledge and clinical practice supports effective management for patients with cardiopulmonary needs.

Acknowledgment

  • Thank you for attending the presentation on supplemental oxygen.

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