For example, ETTs have been developed that allow removal of subglottic fluids, thereby reducing the available volume of secretions entering the lungs. Manufacturers have redesigned their ETTs and cuffs in order to prevent aspiration of subglottic secretions. It is widely accepted that aspiration occurs for all HVLP ETTs to varying degrees and this has been consistently demonstrated in in vitro and clinical studies. These channels facilitate aspiration of subglottic secretions into the lungs. The excess material folds and causes involutions, causing channels to develop (Fig. Therefore, the cuff is only partially inflated, even when correct pressures are used. The fully inflated HVLP ETT cuff diameter is larger than the adult trachea, and this design prevents tracheal mucosal injury by allowing the pressure within the cuff to be equal to the tracheal wall pressure. Therefore, correctly achieving and maintaining the airway seal is critical in preventing VAP.Ĭonventionally, ETTs have high-volume, low-pressure (HVLP) cuffs. One study showed that the bacteria in subglottic secretions were identical to the causative agents of VAP in 70% of patients. High bacterial load, with chemical and enzymatic injury from gastric secretions, can overwhelm pulmonary defences leading to microbial colonisation of the lower respiratory tract and VAP. If the airway seal is compromised, aspiration of these secretions occurs. Gastric contents reflux into the oropharynx, mix with these secretions and accumulate above the cuff. After intubation, the ETT, oropharyngeal surfaces and secretions rapidly become colonised with pathogenic bacteria. However, the ETT subverts the patient's normal pulmonary defence mechanisms, including mucociliary clearance and the cough reflex. The inflated ETT cuff seals the airway, allowing ventilation to only occur though the tube lumen, and prevents movement of air and fluid around the ETT.
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