Definition

Respiratory Failure

Definition:

• Inadequate gas exchange causing low oxygenation or high carbon dioxide levels.

Types:

• Hypoxemic Respiratory Failure:
  • Low oxygen (PaO2 < 8 kPa).
  • Normal/low carbon dioxide (PaCO2).
• Hypercapnic Respiratory Failure:
  • High carbon dioxide (PaCO2 > 6 kPa).
  • Low oxygen (PaO2 < 8 kPa).

Categories:

• Acute: Sudden onset, often in patients with no or minor respiratory issues.
• Acute on Chronic: Acute deterioration in those with pre-existing respiratory failure.
• Chronic: Develops over days or longer in patients with existing respiratory diseases.

Hypoxemic Respiratory Failure (Type 1)

• PaCO2: Normal/low.
• Occurs in conditions like pneumonia, ARDS, pulmonary edema, and severe asthma exacerbation.
• Mechanism: Ventilation/perfusion mismatch (V/Q mismatch).

Hypercapnic Respiratory Failure (Type 2)

• PaCO2: High.
• Causes: Alveolar hypoventilation due to pulmonary diseases (e.g., COPD), neuromuscular disorders (e.g., myasthenia gravis), or sedative drugs.

Aetiology

Common Causes of Respiratory Failure

Type I Respiratory Failure Causes:

• Chronic Obstructive Pulmonary Disease (COPD)
• Pneumonia
• Pulmonary Edema
• Pulmonary Fibrosis
• Asthma
• Pneumothorax
• Pulmonary Embolism
• Pulmonary Hypertension
• Cyanotic Congenital Heart Disease
• Bronchiectasis
• Acute Respiratory Distress Syndrome (ARDS)
• Respiratory Illness with HIV Infection
• Kyphoscoliosis
• Obesity

Type II Respiratory Failure Causes:

• COPD
• Severe Asthma
• Drug Overdose, Poisoning
• Myasthenia Gravis
• Polyneuropathy
• Poliomyelitis
• Muscle Disorders
• Head and Neck Injuries
• Obesity
• Pulmonary Edema
• Adult Respiratory Distress Syndrome
• Hypothyroidism

Risk Factors

Risk Factors for Respiratory Failure

Patient Characteristics:

• Advanced Age
• Pre-existing Lung Diseases (e.g., COPD, interstitial lung disease)
• Smoking
• Obesity
• Weakened Immune System
• Certain Medical Conditions (e.g., heart failure, kidney failure)

Medication and Substance Use:

• Sedative or Opioid Use
• Prolonged Mechanical Ventilation
• Exposure to Environmental Pollutants

Pathophysiology

Types of Respiratory Failure:

Hypoxemic Respiratory Failure:

• Decrease in oxygen levels (PaO2 < 8 kPa) in arterial blood.
• Causes include ventilation-perfusion mismatch and shunting.
• Impaired gas exchange leads to tissue hypoxia.

Hypercapnic Respiratory Failure:

• Inability to eliminate carbon dioxide (PaCO2 > 6 kPa) from arterial blood.
• Can result from alveolar hypoventilation.
• Leads to elevated blood carbon dioxide levels and respiratory acidosis.

(Note: Both types disrupt the balance of oxygen and carbon dioxide, impacting tissue oxygenation and acid-base equilibrium.)

Differential Diagnosis

Differential Diagnosis of Respiratory Failure:

• Pneumonia
• Pulmonary edema
• Pulmonary embolism
• Acute exacerbation of COPD
• Congestive heart failure
• Neuromuscular diseases

Epidemiology

Respiratory Failure in the UK

• Specific UK epidemiological data for respiratory failure is limited.
• It’s a significant cause of hospital admissions.
• More prevalent in people with pre-existing lung diseases and those in intensive care.
• Incidence and prevalence vary with underlying causes and studied populations.

Clinical Presentation

Signs and Symptoms of Respiratory Failure:

Common Symptoms:

• Severe shortness of breath (dyspnea).
• Rapid, shallow breathing.
• Bluish lips and fingertips (cyanosis).
• Confusion, fatigue, restlessness.
• Decreased consciousness.

Severe Cases:

• Respiratory arrest.

Presentation: Identifying Underlying Cause:

• Thorough history and examination.

Specific Clues:

• Paroxysmal nocturnal dyspnoea.
• Orthopnoea (in pulmonary edema).

Signs:

• Vary with the cause.
• May include restlessness, confusion, tachycardia, cyanosis.
• Polycythemia in chronic cases.

Cor Pulmonale (Right Heart Failure): Associated with Pulmonary Hypertension:

• May cause hepatomegaly and peripheral edema.

Investigations

Diagnostic Investigations for Respiratory Failure:

• Arterial Blood Gas Analysis: Confirms diagnosis and assesses oxygen and carbon dioxide levels.
• Chest X-ray (CXR) or CT Scan: Identifies the cause of respiratory failure and evaluates lung structure.
• Full Blood Count (FBC): Detects anemia contributing to tissue hypoxia and polycythemia indicating chronic hypoxemic respiratory failure.
• Renal and Liver Function Tests: Provides clues to etiology and identifies complications. Abnormal electrolytes can worsen organ dysfunction.
• Serum Creatine Kinase and Troponin I: Excludes recent myocardial infarction and indicates myositis.
• Thyroid Function Tests (TFTs): Useful for assessing chronic hypercapnic respiratory failure related to hypothyroidism.
• Spirometry: Evaluates chronic respiratory failure.
• Echocardiography: If a cardiac cause of acute respiratory failure is suspected.
• Electrocardiogram (ECG): Evaluates cardiovascular causes and detects dysrhythmias due to severe hypoxemia or acidosis.
• Right Heart Catheterization: Consider if there is uncertainty about cardiac function, volume replacement, and systemic oxygen delivery.
• Pulmonary Capillary Wedge Pressure: Helpful in distinguishing cardiogenic from non-cardiogenic edema.
• Microbiological Studies: For infectious etiologies.
• Histopathology of Lung Aspirate: May be needed for further evaluation.

Management

Management of Respiratory Failure:

• Prompt hospital admission in an intensive care unit for acute respiratory failure; some chronic cases can be managed at home based on severity, cause, comorbidities, and social factors.
• Immediate resuscitation might be necessary.
• Address the underlying cause of respiratory failure.
• Maintain appropriate oxygen delivery to tissues (PaO2 ≥ 60 mm Hg or SaO2 > 90%).Be cautious with prolonged high-concentration oxygen use in chronic cases to prevent hypercapnia.
• Assisted Ventilation:
  • Mechanical Ventilation:
    • Supports gas exchange, decreases PaCO2, and rests respiratory muscles.
    • Used in acute hypoxemic respiratory failure.
    • Can be challenging to wean chronic cases off mechanical ventilation.
  • Non-Invasive Ventilation (NIV):
    • Alternative to invasive ventilation.
    • Improves survival and reduces complications in selected acute cases.
    • Mainly used for COPD exacerbation, cardiogenic pulmonary edema, and immunocompromised patients.
  • Extracorporeal Membrane Oxygenation (ECMO):
    • Neonatal, pediatric, and some adult severe cases.
    • NICE recommends caution due to potential serious side-effects.
• Strategies to support oxygenation must consider risks of lung injury, oxygen toxicity, transfusion complications, and cardiac stimulation.
• Address hypercapnia and respiratory acidosis by treating underlying causes and/or providing assisted ventilation.

Prognosis

Respiratory Failure Prognosis

• Depends on cause, severity, treatment, and overall health.
• Prompt recognition and management improve outcomes.
• Severe cases have higher risks: organ dysfunction, long hospital stays, mortality.
• Mortality varies based on cause, diagnosis speed, and treatment efficacy.

Complications

Complications of Respiratory Failure

• Pulmonary: ARDS, pulmonary embolism, fibrosis, mechanical ventilation-related issues.
• Cardiovascular: Cor pulmonale, hypotension, arrhythmias, reduced cardiac output.
• Gastrointestinal: Hemorrhage, gastric distention, ileus, stress ulcers.
• Polycythemia: Elevated RBC count due to chronic hypoxia.
• Infections: Pneumonia, sepsis, urinary tract infections.
• Renal: Acute kidney injury, electrolyte and acid-base imbalances.
• Nutritional: Malnutrition, complications from nutrition.
• Mechanical Ventilation: Ventilator-associated pneumonia, barotrauma, ventilator-induced lung injury.
• Close monitoring and interventions are essential for prevention and management.