1. Acute respiratory failure

2. Of all patients requiring mechanical ventilation for ARF
A sudden life threatening deterioration of pulmonary gaseous exchangeindicaing failure of lungs to ventilate or oxygenate blood
Of all patients requiring mechanical ventilation for ARF
62% survive to be weaned fron the ventilator
43% survive to be discharged from hospital
30% are still alive after discharge

3. Classifiction Broadly classified into:
Oxygenation or Hypoxaemic or normocapnic respiratory failure – characterised by hypoxemia and normal or low PaCO2. thorax and lungs can move air normally but there is a V/Q mismatch [normal ventilation but decreased perfusion]
Hypercapnic or ventilatory failure – there is both hypoxemia and hypercapnia. V/Q mismatch [normal perfusion but reduced ventilation]
Combined ventilatory and oxygenation failure – there is hypoventilation and inadequate alveolocapillary membrane for adequate gaseous exchange. May/ may not include poor pulmonary circulation. Results in profound hypoxia

5. Causes of ventilatory failure
Extrapulmonary:
Neuromuscular disorders
Multiple sclerosis
Myasthenia gravis
Gullain Barre syndrome
Poliomyelitis
Spinal cord injuries affecting nerves to the intercostal muscles
CNS dysfunction
Cerebrovascular accident
Cerebral edema
Increased ICP
Meningitis
Chemical depression
Opioid analgesics, sedatives, anaesthetic agents, drug overdose
Kyphoscoliosis, massive obesity, sleep apnea, external obstruction/constriction, airway obstruction [oedema, laryngospasm, foreign body]

6. Intrapulmonary Airway disease – COPD, Asthma V/Q mismatching:
Pulmonary embolism
Pneumothorax
ARDS
Amyloidosis
Pulmonary edema
Near drowning
Interstitial fibrosis

7. Oxygenation failure Low atmospheric oxygen concentration Pneumonia
High altitudes
Smoke inhalation
Carbon monoxide poisoning
Pneumonia
Abnormal hemoglobin
Pulmonary embolism
Pulmonary oedema
Interstitial pneumonitis-fibrosis
ARDS
Mechanical obstruction
CCF
Hypovolaemic shock
Hypoventillation

9. Pathophysiology There is always hypoxemia in ARF
It may be normocapnic or hypercapnic
Triggers of ARF include:
Pneumonia, fever, infections of the tracheobronchial tree
Increased volume and viscosity or pulmonary secretions
Decreased ability to clear secretions
Bronchospasm
Oxygen therapy at high FiO2
Trauma
CVS disorders
pneumothorax

11. Clinical features
Restlessness, fatigue, headache, dyspnoea, air hunger, tachycardia, increased blood pressure.
With profound hypoxemia – confusion, lethargy, central cyanosis, tachycardia, tachypnea, diaphoresis, respiratory arrest

12. Diagnosis ABG – PaO2 <50-60mmHg, PaCO2 >50mmHg, pH<7.25
Correct underlying cause, intubate and manage on mechanical ventilator
Bronchodilators, antibiotics, diuretics, digoxin can be used depending on underlying cause