There are many causes of respiratory failure but by far the most common is chronic bronchitis and emphysema. In this type II respiratory failure the PaC02 is elevated and the Pao2 is reduced. It is important to realize that whereas hypercapnia is intoxicating, hypoxaemia is potentially lethal. The primary aim of the management of respiratory failure is to improve the Poo2 by continuous oxygen therapy. This nearly always leads to a rise in the Paco2 (see p. 728). Small increases in Paco2 can be tolerated but not if the pH falls dramatically. The pH should not be allowed to fall below 7.25; under such circumstances, increased ventilation must be achieved either by the use of a respiratory stimulant or by artificial ventilation. A fixed-performance mask (Venturi mask) for the administration of oxygen. This style of mask is used when only low concentrations of oxygen can be given. It should be compared with the variableperformance face mask. Initially, 24% oxygen is given, which is only slightly greater than the concentration of oxygen in air but, because of the shape of the oxygen-haemoglobin dissociation curve, this small increase in oxygen is valuable. Gradually, the concentration of inspired oxygen can be increased if there is no dramatic rise in the Paco2.
Additional measures
These include:
REMOVAL OF RETAINED SECRETIONS. The patient should be encouraged to cough to remove secretions. Physiotherapy is helpful. If this fails, bronchoscopy and/or aspiration via an endotracheal tube may be necessary. A tracheostomy is only rarely required.
RESPIRATORY STIMULANTS. Doxapram, 0.5- 4 mg min-‘ by slow i.v. infusion, may help in the short term to arouse the patient and to stimulate coughing, with clearance of some secretions.
ASSISTED VENTILATION (see p. 728). This is occasionally used for patients with chronic bronchitis and emphysema with severe respiratory failure when there is a definite precipitating factor and the overall prognosis is reasonable. This can be a difficult ethical problem.
Corticosteroids, antibiotics and bronchodilators should also be administered
Further management at home
Two controlled trials (chiefly in men) have indicated that the continuous administration of oxygen at 2 litres min’ via nasal prongs to achieve an oxygen saturation of greater than 90% for large proportions of the day and night can prolong life. Survival curves from these two studies are shown. Only 30% of those not receiving long-term oxygen therapy survived for more than 5 years. A fall in pulmonary artery pressure was achieved if oxygen was given for 15 hours daily, but substantial improvement in mortality was only achieved by the administration of oxygen for 19 hours daily. These results suggest that long-term continuous domiciliary oxygen therapy will benefit patients who have:
• Chronic bronchitis and emphysema with an FEV, of less than 1.5 Iitres
• A Pao2 on air on two occasions 3 weeks apart of less than 7.3 kPa (55 mmHg) with or without hypercapnoea.
• Carboxyhaemoglobin of less than 3%, i.e. patients who have stopped smoking
The provision of 19 hours of oxygen daily at a flow rate of 1-3 litre min “, using a 28% oxygen mask to increase the arterial oxygen saturation to over 90%, needs 20 oxygen cylinders per week. This is extremely expensive. Oxygen concentrators are cheaper and are now available through the health service in the UK for patients who fulfill the above criteria.
ADDITIONAL THERAPY. Pulmonary hypertension can be partially relieved by the use of oral l3-adrenoceptor stimulants such as salbutamol (4 mg three times daily), but whether this is useful in the long term is unknown. The sensation of breathlessness can be reduced by the use of either promethazine 125 mg daily or dihydrocodeine 1 mg kg-l by mouth. Reduced breathlessness and increased exercise tolerance also result from the combined administration of dihydrocodeine and oxygen delivered from a portable cylinder.
EXERCISE TRAINING. A modest increase in exercise capacity with diminution in the sense of breathlessness and improved general well-being can result from exercise training. Regular training periods can be instituted at home; climbing stairs or walking fixed distances combined with regular clinic visits for encouragement. Breathing exercises are probably of less value. Quality of life though not life expectancy or decline in lung function can be improved by a multidisciplinary approach emphasizing physiotherapy, exercise, education and smoking cessation.
PROGNOSIS
In general, 50% of patients with severe breathlessness die within 5 years, but even in the severe group stopping smoking helps the prognosis.
