14- Resp failure

• Respiratory Failure

  Impairment in gas exchange that causes hypoxemia with or without hypercapnia (PaO2 < 60 mmHg or PaCO2 > 55 mmHg)
• Types of Respiratory Failure


  • Type 1
  • Type 2
• Type 1 Respiratory Failure

  • PaO2 low, PaCO2 normal or low
• Type 2 Respiratory Failure

  • PaO2 low, PaCO2 high
• Major Mechanisms

  • Type 1: V/Q mismatch - Right-to-left shunts

  Type 2: Alveolar hypoventilation
• Causes of Type 1 Respiratory Failure

  • Pneumonia
  • Pneumothorax
  • PE
  • Pulmonary edema
  • Pulmonary fibrosis
  • ARDS
• Causes of Type 2 Respiratory Failure

  • COPD
  • Acute severe asthma
  • Bronchiectasis
  • Cystic fibrosis

  Chest wall deformities

  • Respiratory muscle weakness (e.g. GBS, MG)

  Respiratory center depression (e.g. sedatives/drug overdose)

  • Sleep apnea
• Clinical Assessment - Signs

  • Tachypnea, tachycardia, sweating, use of accessory muscles of respiration, intercostal recession, inability to speak complete sentences, decreased consciousness, pulsus paradoxus, asynchronous respiration, signs of CO2 retention (asterixis, bounding pulse, warm peripheries, papilledema)
• Pulse Oximetry

  Normal range 95 - 100%, gives no indication of CO2 retention
• Forced Vital Capacity (FVC)


  Used as a guide to deterioration in acute neuromuscular problems, FVC < 20 ml/Kg → ICU admission, FVC < 10 ml/Kg → intubation and ventilation
• FEV1

  Useful to assess patients with acute asthma attacks
• ABG in Type 1 RF

  • May show respiratory alkalosis
• ABG in Type 2 RF

  • Respiratory acidosis, chronic Type 2 RF: ↑HCO3 due to renal retention → pH partially/completely normal
• PaO2/FIO2 ratio

  Used to define respiratory impairment in ARDS
• Capnography

  Continuous breath-by-breath analysis of the expired [CO2], confirms tracheal intubation, recommended for all mechanically ventilated patients to detect acute airway problems
• Management

  Treatment of the underlying cause

  Control of secretions and airway obstruction (e.g. bronchodilators)

  Correction of abnormalities that may weaken the respiratory muscles e.g. hypokalemia

  Administration of supplemental O2 via face mask or nasal cannula

  Respiratory Support (ventilation) when above measures fail
• Fixed-performance mask (Venturi Mask)


  Should be used in COPD patients to deliver continuous controlled O2 therapy because their respiratory center is driven by hypoxia rather than hypercapnia
• Non-invasive ventilation

  CPAP used for acute type 1 RF

  BiPAP used for acute COPD exacerbation with persistent decompensated respiratory acidosis despite 1 hour of controlled O2 therapy
• Contraindications to Non-invasive ventilation

  • Facial burns/trauma/surgery, vomiting, fixed upper airway obstruction, undrained pneumothorax, intestinal obstruction
• Indications for Mechanical Ventilation

  • Acute respiratory failure with signs of severe distress, rising PaCO2 > 60 mmHg, extreme hypoxemia < 60 mmHg

  Acute ventilatory failure e.g. MG, GBS

  Prophylactic post-operative in high-risk patients

  Trauma: Chest injury and lung contusion

  Severe LVF

  Coma with breathing difficulty (drug overdose)
• Complications of Mechanical Ventilation

  • Fall in cardiac output

  Ventilator-associated pneumonia

  Acute brain edema

  Barotrauma – overdistension and alveolar rupture may present with tension pneumothorax and surgical emphysema

  Trauma to the upper airway

  Intestinal ileus

  Increased ADH and reduced ANP leading to salt and water retention