Study Notes – Respiratory Failure in the ICU

Purpose of ICU

• ICU exists to closely monitor unstable patients or those at risk of rapid deterioration.

• Provides resources, expertise, and rapid interventions.

• Core role: Monitoring and managing the patient’s ability to breathe.

Definition of Respiratory Failure

• Failure of the respiratory system to maintain gas exchange.

• Results in impaired O₂, CO₂, or both → threatens cellular function.

Classification

1. Type 1 (Hypoxemic)

   • PaO₂ < 60 mmHg

   • Impaired oxygenation → tissues not perfused adequately.

2. Type 2 (Hypercapnic)

   • PaCO₂ > 50 mmHg with pH < 7.30

   • CO₂ retention → acidosis.

   • Example: COPD patients may live with elevated CO₂ but maintain normal pH (compensated).

3. Mixed Respiratory Failure

   • Combination of impaired O₂ and CO₂.

4. Acute, Chronic, or Acute-on-Chronic

   • Classified by time course.

Complications

• Impaired gas exchange → multi-organ dysfunction and failure.

• Mortality often linked to multi-organ failure.

Causes of Respiratory Failure

Four main pathophysiologic categories:

1. Impaired Ventilation (Hypoventilation)

   • CNS depression (narcotics, sedatives, anesthesia, ↑ ICP, stroke).

   • Nerve impairment (SCI, phrenic/vagus injury, Guillain-Barré, myasthenia gravis, ALS, neuromuscular blockade).

   • Muscle fatigue, chest wall injury, atrophy.

2. Impaired Gas Exchange

   • Alveolar-capillary membrane damage (toxic gases, aspiration, pneumonia, sepsis, ARDS).

   • Fluid in alveoli/interstitium (pulmonary edema – cardiogenic/non-cardiogenic).

   • Alveolar collapse (atelectasis, pneumothorax, pleural effusion).

   • Leads to pulmonary shunt (perfusion without ventilation).

3. Airway Obstruction

   • Airway wall changes (edema, fibrosis, constriction – asthma, COPD).

   • Internal blockage (foreign body, secretions, mucus plug).

   • External compression (tumors, enlarged lymph nodes, edema).

4. Ventilation–Perfusion (V/Q) Mismatch

   • Shunt: Perfusion without ventilation (e.g., collapsed alveoli, pneumonia, ARDS).

   • Dead space: Ventilation without perfusion (e.g., PE, shock, emphysema, COPD).

Clinical Presentation

• Early signs: Dyspnea, tachypnea, accessory muscle use, diaphoresis, restlessness, confusion, anxiety.

• Later signs: Cyanosis, arrhythmias, hypotension, altered LOC → coma.

• Other findings: Crackles/wheezes, fever, sputum, chest pain, symptoms of underlying disease.

Diagnostics

• ABG (gold standard):

  • PaO₂ < 60

  • PaCO₂ > 50

  • pH < 7.30

  • O₂ Sat < 90%

• Additional tests:

  • CXR, ECG, echo, bronchoscopy

  • Labs: CBC, electrolytes, lactate

  • Cultures (sputum, blood, urine)

Management

Goals: Support oxygenation & ventilation + treat underlying cause.

1. Supportive Oxygenation

   • Maintain PaO₂ > 60 mmHg, O₂ sat > 90%.

   • Non-invasive: NC, NRB mask, HFNC, CPAP, BiPAP.

2. Supportive Ventilation

   • Maintain PaCO₂ < 50 mmHg, pH > 7.30.

   • Mechanical ventilation indications:

     • Apnea/respiratory arrest

     • RR > 30, sustained

     • Altered LOC

     • Muscle fatigue (“tuckering out”)

     • Hemodynamic instability

     • Refractory hypoxemia/hypercapnia despite non-invasive support

     • pH < 7.25

   • Ventilator goals:

     • Correct hypoxemia (FiO₂, PEEP)

     • Correct acidosis (adjust tidal volume × RR = minute ventilation)

     • Rest respiratory muscles

   • Additional strategies: Proning, pulmonary vasodilators, ECMO.

3. Treat Underlying Cause

   • Pneumonia → antibiotics

   • COPD exacerbation → bronchodilators, steroids

   • PE → anticoagulation

   • Pleural effusion/pneumothorax → chest tube

   • Sepsis → source control + fluids + antibiotics.