Acute respiratory failure



Background

Acute Respiratory Failure

Two types (mechanism)

  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 hypercapnia, metabolic acidosis)
  2. Hypoxemia
    1. Alteration in diffusion
    2. Hypoventilation
    3. Pulmonary shunt
    4. V/Q mismatch

Hypercarbic?


Symptoms & Signs

Hypoxemia

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

Hypercapnia

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

Approach to patient with Dysponea

  • Start with ABCD (exclude acute 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)

ABG’S Diff. Diagnosis:

  • Hypoxemia with normocapnia – Lung failure (ARDS, CCF, LRTI, P.E.)
  • Hypoxemia with Hypercapnia – Pump failure due to NMD/Chest wall deformities, Lung failure due to COPD, Asthma

Acute upper airway obstruction

Causes

  • Infection – Croup, Bacterial epiglottitis
  • Neoplasm – Subglottic Hemangioma, tracheal/endobronchial neoplasm, mediastinal tumors
  • Trauma
  • Foreign body aspiration
  • Anaphylaxis
  • Neurogenic disease (recurrent nerve pathology

Symptoms

  • Stridor – Inspiratory stridor in extrathoracic obstruction, expiratory stridor in intrathoracic 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

Symptoms

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

Management

Mx depends on clinical state:

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

COPD/Asthma

Please see COPD

Hypoxemic Respiratory failure

Pulmonary oedema

Overflow of lung capillary fluid to alveolar space.

Cardiogenic pulmonary edema

Examination:

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

Management

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

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.

ARDS

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

Causes

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

Management

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

Pneumonia

See Pneumonia


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