Understanding Respiratory Failure Causes and Management

Aug 5, 2024

Respiratory Failure Lecture Notes

Introduction

  • Topic: Respiratory Failure
  • Part of Clinical Medicine Section
  • Encouragement to support the channel: like, comment, subscribe, and visit the website for more resources.

Presentation of Respiratory Failure

  • Patients may present in various ways.
  • Common initial assessment: Oxygen saturation through pulse oximetry (SpO2).
  • Low SpO2 levels suggest hypoxemia (low oxygen in the bloodstream).

Key Definitions

  • Hypoxemia: Low oxygen in the bloodstream.
    • Measured via:
      • SpO2: Less than 90%
      • PaO2: Less than 60 mmHg

Causes of Hypoxemia

1. VQ (Ventilation-Perfusion) Mismatch

  • Poor ventilation to alveoli while blood flow (perfusion) is normal.
  • Causes of poor ventilation:
    • Alveolar filling (e.g., pneumonia, pulmonary edema, alveolar hemorrhage).
    • Alveolar collapse (atelectasis).
  • Consequence: Low oxygen concentration in blood (hypoxemia).
  • Patients typically exhibit:
    • Increased minute ventilation (high respiratory rate and work of breathing).
    • Potentially low or normal CO2 levels due to increased breathing.

2. Hypoventilation

  • Low minute ventilation (low respiratory rate or shallow breaths).
  • Consequence: Low O2 and potentially high CO2 levels.
  • Causes include:
    • CNS depression (e.g., drug overdose, stroke).
    • Neuromuscular dysfunction (e.g., Guillain-Barre syndrome, spinal cord injuries, myasthenia gravis).
    • Airway obstruction leading to hyperinflation and inability to take deep breaths (e.g., COPD exacerbations).

3. Severe Alveolar Filling or Collapse

  • Severe cases of VQ mismatch.
  • No ventilation occurs leading to severe hypoxemia.
  • Common in:
    • ARDS (Acute Respiratory Distress Syndrome).
    • Severe pneumonia or pulmonary edema.

4. Cardiac Shunts

  • Blood bypasses pulmonary arteries leading to low oxygen levels.
  • Causes include:
    • Atrial septal defect (ASD), patent foramen ovale (PFO), or ventricular septal defect (VSD).
  • Requires pulmonary hypertension for shunting to occur.

Diagnostic Process for Respiratory Failure

  • Assess patient for respiratory distress (high respiratory rate, accessory muscle use).
  • Obtain ABG to determine:
    • Type 1: Low PaO2 (<60 mmHg).
    • Type 2: Elevated PaCO2 (>45 mmHg).
  • Additional tests:
    • Imaging (chest x-ray, CT) to evaluate for pneumonia, edema, atelectasis, PE.

Treatment Approaches

Non-Invasive Ventilation

  • High flow nasal cannula for hypoxemic patients with pulmonary secretions.
  • BiPAP for hypercapnic respiratory failure and cardiogenic pulmonary edema.

Intubation

  • Endotracheal intubation for refractory respiratory failure.

Ventilator Management

  • Ventilator modes:
    • CMV (Controlled Mechanical Ventilation) for non-spontaneous breaths.
    • PSV (Pressure Support Ventilation) for spontaneous breathing.
  • Adjustments to manage PaCO2 and PaO2 based on tidal volume and respiratory rate.

Complications of Ventilation

  • High tidal volumes and plateau pressures can cause ventilator-induced lung injury.
  • Over-oxygenation can lead to VQ mismatching and lung damage.
  • Risk of ventilator-associated pneumonia (VAP) increases with prolonged intubation.

Conclusion

  • Respiratory failure is a complex topic with multiple causes and management strategies.
  • Understanding VQ mismatch, hypoventilation, and the importance of proper ventilation strategies is crucial.