Invasive mechanical ventilation

Abstract 

The majority of patients admitted to level 3 critical care facilities will need invasive ventilatory support. Over half of these will suffer from acute respiratory failure, with smaller proportions having exacerbations of chronic obstructive pulmonary disease (COPD), coma of various causes and neuromuscular diseases. Patients with respiratory failure can be divided into two groups on the basis of ventilation requirements. Those with acute respiratory distress syndrome (ARDS) have stiff lungs, while the major problem in COPD and asthma is increased airways resistance. In ARDS, the ‘recruitment’ and maintenance of open alveoli is important in order to improve oxygenation. In COPD and asthma, oxygenation is not usually a major problem but incomplete lung emptying is common, leading to gas trapping and increased intrathoracic pressures. Experimental and clinical studies show that ventilation can cause and exacerbate lung injury. Ventilation strategies which aim to reduce this damage have therefore been widely adopted. They are based on deliberate under-ventilation (using relatively low tidal volumes) with the acceptance of hypercapnia. Such strategies have been shown to improve clinical outcome in ARDS. Approximately 50% of patients needing prolonged ventilation will leave hospital with survival mostly determined by the severity of the original illness and the previous health status of the patient.

Keywords: acute lung injury, acute respiratory distress syndrome, chronic obstructive pulmonary disease, mechanical ventilation, tracheostomy, ventilator-induced lung injury