Long term ventilation in neurogenic respiratory failure.

Respiratory failure, often acutely precipitated by aspiration and/or infection, is a common cause of death in advanced nervous system disease. Importantly, chronic respiratory failure, or symptoms relating to respiratory limitation, may occur before generalised disability. For such patients, providing ventilatory support, usually at night, has long been known to improve daytime symptoms, sleep quality, and prognosis in stable or slowly progressive neurological disease. The increased availability and convenience of modern non-invasive ventilation (NIV) has led to a dramatic change in the management of chronic neurogenic ventilatory failure. Respiratory symptoms, such as cough, choking, dyspnoea, recurrent infection, and respiratory failure may develop for a number of reasons. In respiratory failure the principal problem is usually muscle weakness leading to respiratory pump failure. Although respiratory rate may increase, there is alveolar hypoventilation because of a fall in tidal volume and the arterial PCO2 rises (type 2 respiratory failure). Other factors, such as paralytic scoliosis in the younger patient, significant upper airway obstruction in conditions involving the bulbar muscles, or truncal obesity may further compromise respiratory function. A secondary fall in residual lung volume, micro-atelectasis from ineffective sigh function, basal lung collapse, and a poor cough result in impaired alveolar gas exchange and hypoxaemia. This is easily corrected by oxygen supplementation. Hence the importance of even minor falls in oxygen saturation in neurological disease and the potential danger of treating the oximeter reading rather than the patient. Alveolar hypoventilation usually initially occurs at night. Eventually, nocturnal hypoventilation is sufficiently severe that respiratory failure persists while the patient is awake. It is important to recognise patients at risk of respiratory failure. Apart from providing NIV, which reduces both morbidity and mortality, 4 5 other treatments may be needed to improve cough efficiency, avoid aspiration or prevent infection. The decision to assist ventilation in acute neurological disorders is usually straightforward. It is not uncommon, however, that mechanical ventilation is initiated as a result of a respiratory crisis despite warning features. In this situation, both an accurate diagnosis and an estimate of prognosis is essential for careful consideration of the possible benefits and disadvantages of ventilatory support.