acute respiratory failure

Introduction

Rapid onset of life-threatening disorder in alveolar ventilation, arterial oxygenation &/or tissue oxygenation.

Etiology

• patients with chronic obstructive pulmonary disease
  • increases in volume, viscosity or purulence of secretions
  • increasing airway obstruction with inflammation
  • blunted respiratory drive
  • pharmaceutical agents
    • opiates
    • benzodiazepines
  • air pollution
• pneumonia
• pulmonary embolism
• left ventricular failure (congestive heart failure)
• pneumothorax
• aspiration or drowning
• drug overdose
• status asthmaticus
• acute neuromuscular disorders
  • myasthenia gravis*
  • Guillain-Barre syndrome*
  • hypophosphatemia (diaphragm dysfunction)
• carbon monoxide poisoning
• severe anemia
• cardiac tamponade

* most common causes of acute neurologic respiratory failure in ICU

Pathology

• ventilation-perfusion (VQ) mismatch
  • most common cause of hypoxemic respiratory failure
  • alveolar collapse (atelectasis)
  • alveolar filling with fluid
• inadequate alveolar ventilation resulting carbon dioxide retention
• increased carbon dioxide production
• decreased respiratory drive
• excessive work of breathing
  • auto-PEEP contributes to increased work of breathing during exacerbations of obstructive lung disease
• increased dead ventilation space
• neuromuscular weakness

Laboratory

• arterial blood gas
  • an acute drop in paO2 of 15 mm of Hg indicates acute respiratory failure
  • paO2 < 60 mm Hg or SaO2 of < 89% breathing ambient air
  • paO2/FiO2 < 200 mm Hg
  • any level of hypercapnia associated with a pH of < 7.30 should be considered acute respiratory failure
  • indicated if hypercapnia even if SaO2 normalizes with oxygen administration
• sputum for gram stain & culture

Diagnostic procedures

• electrocardiogram
• pulmonary function testing
  • FEV1
  • peak expiratory flow
• bedside vital capacity to assess impending respiratory failure in patients with neuromuscular disease
• maximum inspiratory & expiratory pressures & positional change in vital capacity helpful in assessing neuromuscular weakness

Radiology

• chest X-ray

Complications

• cardiac arrhythmias
  • generally multifocal supraventricular tachycardia
• left ventricular failure
• pulmonary emboli
• gastrointestinal hemorrhage from stress ulceration

Differential diagnosis

• the need for large amounts of supplemental oxygen suggests diagnosis other than obstructive lung disease (COPD, asthma)

Management

• maintenance of oxygenation & ventilation
  • maintain SaO2 >= 93%; target of 96% no better or worse than 93%
  • humidified high-flow oxygen delivered by nasal cannula
    • creates positive airway pressure
    • lower mortality at 90 days, more ventilator-free days, & less respiratory discomfort than BiPAP
  • bilevel positive airway pressure (BiPAP)
    • open fluid-filled or collapsed alveoli (atectasis)
    • COPD exacerbations, cardiogenic pulmonary edema, neuromuscular disease, obesity hypoventilation syndrome
  • endotracheal intubation & mechanical ventilation rate similar for BiPAP vs high-flow oxygen except for COPD exacerbations with hypercarbia
  • noninvasive positive-pressure ventilation vs high-flow oxygen does not prevent subsequent intubation or lengthen survival in immunocompromised patients
  • noninvasive positive-pressure ventilation (NPPV) delivered via helmet
    • confers lower risk for mortality & endotracheal intubation vs face mask NPPV
    • may be alternative to mechanical ventilation
  • for asthmatics with acute respiratory failure, endotracheal intubation recommended
• bedside ultrasonography for acute respiratory failure in critically ill patients prior to emergent needle aspiration for decompression of pneumothorax
• reversal of precipitating cause
  • treat infection
    • in the absence of evidence of acute pneumonia, use of broad-spectrum antibiotics is controversial
  • remove secretions
    • tracheal suction
    • postural drainage & percussion
    • beta2-adrenergic agonists (albuterol) increase ciliary clearance of particles
  • reverse airway constriction
    • beta2-adrenergic agonist (albulterol) nebulizer
    • anti-cholinergic (ipratropium, Atrovent) nebulizer
    • theophylline
• prevent complications
• ranitidine or other H2 blocker for GI prophylaxis
• Ted hose & SCD or heparin 5000 U sq BID for prophylaxis against pulmonary embolism
• prevent aspiration
• decrease carbohydrate calories & increase fat calories for severe hypercapnia resistant to mechanical ventilation
• daily rehabilitation does not reduce length of stay or improve functional status

More general terms

• respiratory failure
• sign/symptom

More specific terms

• acute hypercapneic respiratory failure
• acute respiratory distress syndrome; acute lung injury (ARDS, ALI)