Acute respiratory failure

Acute Respiratory Failure

Two types (mechanisms)

  1. Lung failure-mismatch in blood gas exchange (ARDS/NRDS, CCF, Status Asthmaticus, pneumonia, P.E.)
  2. Pump failure (NMD, COPD, Chest wall deformities)

Blood gas

Manifestation on blood gas:

  1. Hypercapnia- four mechanisms:
    1. ↑CO2 production (high carbohydrates, pyrexia)
    2. ↓ gas exchange (COPD/PE)
    3. ↓ in respiratory mechanics
    4. Altered control of ventilation (chronic ⇑CO2, metab. acidosis)
  2. Hypoxaemia:
    1. Alteration in diffusion
    2. Hypoventilation
    3. Pulmonary shunt
    4. V/Q mismatch


Symptoms & Signs


SOB, tachycardia, Confusion, restlessness, cyanosis, palpitations, arrhythmias


Drowsiness, confusion, convulsions, arrhythmias, meiosis, hypotension, coma

Approach to patient with Dyspnoea

  • Start with ABCD (exclude upper airway obstruction)
  • Evaluate need of airway intervention - NIV vs Intubation
  • Administer O2, get vitals, ECG
  • V/ABG’s, baseline bloods(FBC, U&E, CRP, Troponin etc)

Blood gases Diff. Diagnosis:

  • ↓PaO2 with normal CO2 – Lung failure (ARDS, CCF, LRTI, P.E.)
  • Hypoxaemia with Hypercapnia – Pump failure due to NMD/Chest wall deformities, Lung failure due to COPD, Asthma

Acute upper airway obstruction


  • Infection – Croup, Bacterial epiglottitis
  • Neoplasm – tracheal/endobronchial, mediastinal tumours, subglottic haemangioma
  • Trauma
  • Foreign body aspiration
  • Anaphylaxis
  • Neurogenic disease (recurrent nerve pathology)


  • Stridor – Inspiratory stridor in extra-thoracic obstruction, expiratory stridor in intra-thoracic obstruction
  • Cyanosis
  • LOC

If you suspect epiglottitis, avoid throat examination – can provoke complete obstruction.

If Foreign body obstruction use Heimlich’s manoeuvre.

ARF due to NMD/Chest wall deformities


  • Rapid shallow breathing
  • Paradoxical breathing
  • Alternating breathing
  • Inability to cough


Mx depends on clinical state:

  • If stable vitals: deliver O2, CXR to find cause, moniter
  • If unstable: call anaesthesiology on call, consider airways intervention


Please see COPD

Hypoxaemic Respiratory failure

Pulmonary oedema

Overflow of lung capillary fluid to alveolar space.

Cardiogenic pulmonary oedema


  • Low flow state with wet crackles
  • JV distension
  • Cardiomegaly (CXR or displaced apex beat)


  • CPAP
  • Nitrates (10 microgram/min)
  • Diuretics
  • Inotropes


  • If arterial SBP 70-100 mmHg Dobutamine (2-20 micgm/kg/min) = ↑ contractility, ↓ peripheral resistance
  • If signs of cardiogenic shock dopamine 5-15 micgm/kg/min increases contractility and promoted diuresis


  • Non cardiogenic pulmonary oedema
  • Severe hypoxaemia
  • New bilat. pulmonary infiltrates
  • Lung damage which ↑ permeability of capillary endothelium


  • Infection (mostly gram neg. bacteria)
  • Trauma
  • DIC
  • Aspiration of gastric contents
  • Foreign body/toxic gases inhalation
  • Acute radiation pneumonitis


  • Oxygen (main problem is hypoxaemia)
  • Mechanical ventilation via ET tube as soon as possible (low tidal volume- 6ml/kg with PEEP 5-15 cm H2O)
  • Methylprednisolone 2mg/kg


See Pneumonia

Content by Dr Abhishek Sharma 11/12/2014. Last review Dr ÍOS 19/04/23.