Oxygen is widely used in patients with advanced respiratory disease, both in hospital and, on a long-term basis, in the patient’s home. Indications include both the relief of symptoms and prolongation of survival. In general, oxygen is only likely to be beneficial when the level of oxygen in the arterial blood (arterial oxygen tension (PaO2)) is low; it is not a general panacea for breathlessness, as this often results from factors other than shortage of oxygen. Therefore, accurate assessment is essential before oxygen is prescribed; this includes confirmation of hypoxaemia when the patient is breathing air and demonstration of improvement when breathing oxygen.
Several different methods for administering oxygen are available (figure 2). The optimal method for an individual patient depends on the nature and severity of the underlying condition, as well as the situation in which oxygen is to be used. In very ill patients in hospital with severe hypoxaemia (e.g. in acute respiratory distress syndrome, extensive pneumonia or severe acute asthma), high-flow oxygen, via a face mask or in conjunction with assisted ventilation, may be required. However, in patients with exacerbations of severe COPD, uncontrolled high-flow oxygen can result in progressive retention of carbon dioxide (hypercapnia) and respiratory acidosis, which itself may be life-threatening. In this situation, therefore, it is necessary to restrict the concentration or flow of oxygen being breathed. Low-flow oxygen can be delivered comfortably via small nasal cannulae (figure 2a and 2b), but this does not give precise control of the inspired oxygen concentration. The latter can be controlled by use of a mask that operates on the Venturi principle, where the concentration of oxygen breathed by the patient is relatively independent of the oxygen flow rate. Such masks allow only a small increase of inspired oxygen concentration – for example to 24% or 28%, compared to the 21% present in room air – but in COPD this is usually sufficient to relieve life-threatening hypoxaemia, while at the same time minimising the risk of serious hypercapnia.
Long-term oxygen at home has been shown to improve the life-expectancy of patients with severe hypoxaemia resulting from advanced COPD. To achieve this, oxygen treatment needs to be given for as long as possible each day (minimum: average 15 out of 24 hours). It is delivered most conveniently by an oxygen concentrator (which, as the name implies, concentrates the oxygen from room air) or by using a large tank of liquid oxygen, from which a small cylinder can be refilled as required. Patients who show worsening oxygenation (‘desaturation’) during exercise may benefit from breathing oxygen during exertion; this can be supplied by a refillable small liquid oxygen tank or by a portable concentrator.
However, even severely hypoxaemic patients may not show desaturation during exercise and so prescription of ambulatory oxygen should be preceded by specialist assessment and the demonstration of both desaturation when breathing room air and improved performance when breathing oxygen.
Physiotherapy is particularly helpful as an aid to clearing bronchial secretions, for example in acute exacerbations of COPD and in patients with chronic production of infected sputum, as in CF and bronchiectasis. Various techniques are used, including postural drainage and forced expiration; often, these are taught to patients who continue to use them regularly at home. Other important aspects of physiotherapy, including exercise and muscle training, are employed as part of pulmonary rehabilitation (see chapter 29).
Intermittent positive pressure ventilation
The traditional method of mechanically assisting the ventilation of seriously ill patients in hospital is by intermittent positive pressure ventilation (IPPV), in which the patient’s airway is connected to a ventilator that blows air (usually with supplementary oxygen) into the lungs, with the ventilator set to deliver a specified volume or pressure. The air is delivered into the trachea via an endotracheal tube, or if ventilation needs to continue for a prolonged period, via a tracheostomy tube. Modern ventilators are highly sophisticated and allow a range of modes and patterns of ventilation, including total ventilation, in which the machine does all the work, and various ‘assist’ modes, in which the ventilator detects and then supplements each inspiratory effort.
Over the past 20 years, noninvasive ventilation (NIV) has increasingly been used. It offers several advantages: in particular, the need for sedation is avoided; the patient retains the ability to cough and communicate; and the risk of further infection associated with intubation of the airway is minimised. Ventilation is achieved by delivering air (with or without supplementary oxygen) via a tight-fitting face mask applied to the nose, or nose and mouth (the range of patient ‘interfaces’ is the same as is used for delivering continuous positive airway pressure (CPAP) for treating obstructive sleep apnoea syndrome (OSAS) – see below). In most respiratory departments, NIV is now first-line management for patients requiring ventilatory assistance for acute exacerbations of COPD. It is also increasingly used for long-term nocturnal domiciliary ventilation in certain groups of patients with chronic hypercapnia. It is particularly suitable and effective for chronic respiratory failure due to severe respiratory muscle weakness (e.g. various muscular dystrophies or motor neurone disease/amyotrophic lateral sclerosis) or severe deformity of the chest wall (e.g. scoliosis). Long-term domiciliary NIV is also used in some patients with severe COPD, but its indications in this condition require further investigation.
Continuous positive airway pressure
CPAP is a simpler form of ventilatory support, which is used with one of two aims. CPAP delivered by a conventional ventilator is used in the management of very ill patients with severe hypoxaemia, as applying a continuous inflating pressure to the airway (in addition to the fluctuating pressure required to ventilate the lungs) increases lung volume, which is beneficial in improving oxygenation.
In its alternative, and now much more common, application, CPAP is used as the treatment of choice in most patients with symptomatic obstructive sleep apnoea syndrome (OSAS) in order to overcome the narrowing or obstruction of the upper airway (pharynx), which is the prime mechanism of OSAS. In this situation, applying a positive pressure at the nose or mouth (or both) during sleep stabilises the upper airway; maintaining airway patency in this way prevents the recurrent apnoeas and the accompanying hypoxaemia and sleep disturbance which they cause. The pressure delivered is adjusted either manually or automatically to the level necessary to maintain the patency and stability of the airway and the patient is encouraged to use this treatment every night, usually indefinitely. Although some individuals experience discomfort or intolerance, the majority find that the improvement in daytime alertness, which is often dramatic, more than compensates for this. A variety of patient interfaces is available by which the pressure is delivered, via the nose or mouth or sometimes both (figure 3 – see also chapter 23).
In a minority of patients with nonsmall cell bronchial carcinoma, radical radiotherapy is used with the aim of achieving a cure. This approach is only appropriate for patients with small peripheral tumours, with no evidence of spread, and in whom surgical resection is not an option. The direction of the radiation beam can be focused more precisely by use of stereotactic methods of three-dimensional imaging.
More commonly, radiotherapy is used, sometimes in combination with chemotherapy, in both small and nonsmall cell bronchial carcinoma, with the aim of achieving a partial or, occasionally, complete response, and also as palliative treatment to improve symptoms, particularly haemoptysis or pain due to bone invasion or metastasis.
Surgical treatment is used for both malignant and nonmalignant respiratory disease. It is the treatment of choice for primary nonsmall cell bronchial carcinoma, and gives the best prospect of cure when the tumour appears technically resectable, there is no evidence of metastasis and the patient is fit for the procedure. Depending on the extent and position of the cancer, resection may involve removal of a whole lung (pneumonectomy), one or more lobes (lobectomy) or, less commonly, a lung segment (segmentectomy).
Surgical treatment options for other respiratory conditions include: removal of benign tumours or of giant bullae; lung volume reduction surgery for selected patients with severe hyperinflation of the lungs due to emphysema; resection of lung abscess, severe localised bronchiectasis or lung affected by drug-resistant TB; and pleural surgery for empyema, persistent pneumothorax or extensive pleural thickening. The ultimate form of surgical treatment is lung transplantation, which is performed for a variety of end-stage lung diseases, most commonly nowadays for advanced CF.
Further information can be found in chapter 32.