Ventilação mecânica: métodos convencionais

Abstract

Airway access for mechanical ventilation can be obtained by: orotracheal intubation, nasotracheal intubation, cricothyrotomy, ortracheostomy. Laryngeal mask and Combitube are devices that can be used in patients with difficult access to the airways (“not ventilate not intubate” situation). Mechanical ventilation is are source focused on healthcare of patients with compromised pulmonary gas exchange, whether caused by structural lung disease or conditions that result in alveolar hypoventilation. There are currently many options for ventilation support, but three of them are the most frequently used: volume controlled ventilation (VCV), pressure controlled ventilation (PCV) and pressure support ventilation (PSV). VCV guarantees tidal volume, but generates higher mean airway pressures, as a consequence of an initial peak pressure; PCV does not generate pressure peak, occurring lower medium pressures, but does not guarantee tidal volume. VCV and PCV allow assisted or controlled ventilation. PSV requires initial patient’s inspiratory stimulus, only functioning on assisted ventilation, and also does not guarantee tidal volume. For most patients VCV and PCV can be used at the beginning of assisted ventilation. There is no demonstration of superiority of one over the other, provided that their limitations are respected. Positive end expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) promote increases in functional residual capacity, resulting in improved blood oxygenation and reduced inspiratory effort. Both PEEP and CPAP promote these benefits through alveolar opening, when totally closed or only partially opened, and redistributing liquid eventually present in alveoli. The strategy of daily interruption of sedation helps reducing mechanical ventilation duration and intensive care unit length of stay. Patients on prolonged mechanical ventilation require gradual process of weaning from mechanical ventilation.