Non-conventional techniques of ventilatory support

Abstract

The non-conventional techniques for ventilatory support represent a new approach to the management of patients with respiratory failure. A large number of studies indicate that these techniques can maintain adequate gas exchange under conditions in which the traditional concepts of gas transport no longer hold. We have reviewed the group of techniques, collectively called high frequency ventilation (HFV), in which the tidal volumes are much less (1 to 5 ml per kg) than those observed during conventional mechanical ventilation. Although HFV has theoretical advantages in some clinical settings, it has been shown to be superior to conventional mechanical ventilation in but a few. HFV appears to provide adequate ventilation while still allowing access to tracheal and laryngeal surgical fields. It has been successful during pneumonectomy, and in the treatment of bronchopleural fistulae. The relevance of tracheal insufflation (TRIO) of oxygen and constant flow ventilation (CFV) to the human clinical setting is uncertain. TRIO may be useful to oxygenate patients who are difficult to intubate, or TRIO could be applied for ventilation of patients involved in mass casualties. Although CFV does not maintain normal levels of PaCO2 in humans, it can provide adequate oxygenation. It might be clinically applicable during thoracic surgery, in which movement of the abdominal and thoracic contents associated with conventional mechanical ventilation is undesirable. During CFV, the lung is kept motionless with sufficient airway pressures to maintain patency of airways and alveoli. CFV is useful as a tool for studying phenomena affected by breathing. The rationale for the use of an artificial lung during extracorporeal membrane oxygenation (ECMO) or extracorporeal carbon dioxide removal with low positive pressure ventilation (ECCO2R-LFPPV) in the treatment of acute respiratory failure is to provide temporary respiratory function while the pulmonary lesion is being treated or is resolving. The factors that most limit the usefulness of ECMO are not technical but relate to the ability of the lung to recover structurally and functionally after a severe insult. Poor survival figures in the published series of ECMO in adults reflect the gravity of illness prior to treatment. However, results in neonates have been quite encouraging. ECCO2R allows less exposure of blood to the extracorporeal circuit and avoids the reduction in pulmonary blood flow associated with ECMO. Although the reported survival of adults with severe acute respiratory failure treated with ECCO2R is extremely promising, it is important to point out that none of the published reports are controlled, randomized studies.(ABSTRACT TRUNCATED AT 400 WORDS)