The role of respiratory medicine in intensive care
Modern intensive care medicine began in the 1920s with the introduction of the iron lung for the treatment of respiratory failure associated with polio. This expands the lungs with each breath by applying a suction (negative) pressure around the trunk. The next important step was the availability of artificial airway tubes and positive-pressure ventilators, which deliver air directly into the patient’s airways. These developed from the requirements of modern surgery to facilitate better control of anaesthesia during operations. Intensive care medicine benefitted from the new ventilation techniques, which at first were applied exclusively to surgical patients.
By the mid 20th century intensive care medicine consisted primarily of mechanical ventilation via an endotracheal or tracheostomy tube. In the USA, intensive care became an integral part of respiratory medicine but in most European countries, anaesthetists (anaesthesiologists) became responsible for most general medical and postoperative intensive care units. However, this pattern did not develop uniformly across Europe. In some countries a new specialty of intensive care medicine developed, while in some others training in intensive care was incorporated in the curriculum of several specialties, including anaesthetics (anaesthesiology), internal medicine, surgery and paediatrics. Within the medical specialties more specialised care facilities were developed to care for patients with failure of a single bodily system, e.g. coronary care, respiratory care and, latterly, stroke units. In some countries, the representation of respiratory medicine in intensive care is still relatively low, even though acute respiratory failure is one of the three main issues in modern intensive care medicine, along with circulatory failure and severe infection.
The increasing focus of respiratory medicine on patients with chronic respiratory disease has led to the development of respiratory intermediate care units, which specialise in treating respiratory insufficiency as a single-organ problem. Therapeutic techniques were developed that could be performed outside fully equipped intensive care units, including specialised physiotherapy, respiratory therapy, mechanical support systems for the expectoration of secretions, and improved oxygen delivery systems.
The introduction of noninvasive ventilation (NIV) about 20 years ago was a major advance. A face-mask or other device is used to deliver air without the need for intubation and its attendant risks such as infection. Initially, NIV was applied to patients with chronic ventilatory insufficiency caused by diseases that do not originate from the lung, i.e. neuromuscular disorders such as the postpolio syndrome and muscular dystrophies, and severe deformation of the thorax and vertebral column such as scoliosis (figure 1). In these patients, ventilation is inadequate due to failure of the ‘ventilatory pump’, which results in hypercapnia (high arterial carbon dioxide pressure); this is readily corrected by use of NIV applied intermittently (usually during sleep), resulting in a tremendous improvement of quality of life and survival. Long-term domiciliary NIV is now used routinely to treat these conditions.
With better understanding of the pathophysiology of severe chronic obstructive pulmonary disease (COPD) (which results in hypercapnia due, in part, to relative weakness of the respiratory muscles), the use of NIV has been extended to patients with advanced COPD and hypercapnic respiratory failure, particularly during acute exacerbations (AE-COPD). These patients are a large group, and in many hospitals NIV is now used routinely to treat patients with hypercapnic, acidotic AE-COPD outside traditional intensive care units, in high-dependency units or in the general respiratory ward setting. For many such patients, this avoids the need for intubation and its complications, in particular infection and difficulty in weaning from the ventilator. Long-term home NIV is also used in some patients with COPD and chronic hypercapnia (figure 1), but the optimal indications and selection criteria are the subject of ongoing research. In intensive care units NIV is also often used during tracheal intubation prior to commencing full assisted ventilation, during weaning from mechanical ventilation and after failure of extubation.
Increasing numbers of elderly patients undergo major surgery or need intensive care because of comorbidities or for other reasons. Improvements in ventilation strategies and the consequent reduction of ventilator-associated lung injury, in combination with advances in intensive care medicine, have allowed much longer periods of ventilation. In the past, unless patients were extubated after 3 days they usually died, but now intubation and ventilation for weeks or months is feasible. However, weaning from mechanical ventilation becomes more difficult with every additional day of ventilation. During prolonged mechanical ventilation, patients experience progressive wasting of skeletal muscles and may also develop a peripheral neuropathy, both of which can affect the muscles of the ventilatory pump. Respiratory physicians in many countries have established, or are now involved in, specialised weaning centres. Relevant teaching courses have been developed for physicians, nurses, physiotherapists and respiratory therapists.