Acute respiratory failure

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

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

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]

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

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

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

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

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