Is the failure of pulmonary gas exchange to maintain the normal arterial O2 and CO2 level. It is divided in to type I and II in relation to the presence or absence of hyper capnia ( Raised Pa CO2).

1- type I respiratory failure When there is hypoxia, (PaO2 less than 8 Kpa or 60mmHg), normal or low PaCO2 ( less than 6.6 Kpa or 50 mmHg). A-acute type I respiratory failure 1-acute asthma exacerbation 2-acute pulmonary oedema 3- lobar collapse 4- PE 5- pneumothorax 6- ARDS In these situations HCO3 will be normal and PH will be normal or slightly elevated,

B- chronic type I respiratory failure. 1- emphysema 2- early lung fibrosis 3- lymphangitis carcinomatosis 4- Brainstem lesion 5- right – left shunt In all theses situations PH and HCO3 will be normal

2- type II respiratory failure, there will be hypoxia and hypercapnia. A-acute type II 1- acute severe ashma 2-acute COPD exacerbation 3- upper airway obstruction 4- acute neuropathies/paralysis 5-narcotic drugs 6- flail chest injury. In all theses cases there will be low PH and normal HCO3.

B- chronic type II 1-COPD 2- Sleep apnea 3-kyphoscoliosis 4- myopathies 5- muscular dystrophies 6- ankylosing spondylitis In all these cases PH will be high and HCO3 will be high too.

C- acute on chronic, that include all chronic causes, with further pulmonary insult resulting in decompensation For example acute exacerbation of COPD, Here we have low PH and high HCO3.

Diagnosis CXR ABG Further investigations according to the cases.

Management Treat underline causes, each cases needs separate approach, O2 therapy needs to restore adequate arterial O2 level, with or without assisted ventilation. The consequence of untreated severe hypoxemia include systemic hypotension, pulmonary hypertension, polycythaemia, tachycardia and cerebral dysfunction ranging from confusion to coma. The delivery of O2 to the tissues depend on the following factors,

1- inspired O2 concentration 2- alveolar ventilation 3- ventilation – perfusion distribution. 4- Hb level 5- cardiac out put 6- distribution of capillary blood flow with in the tissues 7- concentrations of other agents like CO

Administration of O2 O2 should always prescribed in writing with clearly specified flow rate or concentration. 1- high concentration O2 (40-60 %) via high flow mask are useful in type I respiratory failure, and when it is used for prolonged period is better to be humidified by passing it over warm water. 2- low concentration O2 (24-28%) via venturi mask is accurate method to deliver controlled O2, this type of oxygen supply used in Type II respiratory failure.

If we need continuous flow Is better to use nasal cannulae, that allow the patient to eat and communicate while receiving O2 3- chronic O2 delivery to be used by patients at home through O2 cylinder or O2 concentrator, via a low concentration mask or a nasal cannulae. It is used in patients with chronic hypoxaemic lung disease ( end stage COPD, Pulmonary fibrosis).

Mechanically assisted ventilation In those patients when all medical treatment fail to improve the situation. 1- Non Invasive ventilation NIV ( C-PAP, Bi PAP) Used in conscious patient whom tolerating the device well. 2- invasive ventilation, when NIV fails or patient un conscious, or not tolerating NIV,

Doxapram by slow IV infusion as a respiratory centre stimulant, should only be used in those when NIV not available or patient not tolerating it. It has minor,and transient beneficial effect.

LUNG TRANSPLANTATION Is now an established treatment for carefully selected patients with advance lung disease not responding to medical treatment. Single lung transplant is indicated in elderly patients with emphysema or lung fibrosis, while this is contraindication in cystic fibrosis or bilateral bronchiectasis, in which bilateral transplant is the favored option. Heart and lung transplant indicated in patients with Eisenmenger’s syndrome and advanced pulmonary hypertention.

Indications for lung transplantation 1- lung parenchymal disease - Cystic fibrosis - Emphysema - Pulmonary fibrosis - Langerhans cell histocytosis - Lymphangioleiomyomayosis - Brochiolitis obliterance

2- pulmonary vascular disease - Primary pulmonary hypertention - Thromboembolic pulmonary hypertention - Veno-occlusive disease - Eisenmenger’s syndrome