UNFAVORABLE MECHANICAL EFFECTS OF HEAT AND MOISTURE EXCHANGERS IN VENTILATED PATIENTS

Objective:To investigate the mechanical effects of artificial noses. S etting: A general intensive care unit of a university hospital. Patien ts: 10 patients in pressure support ventilation for acute respiratory failure. Interventions: The following three conditions were randomly t ested on each patient: the use of a heated humidifier (control conditi on), the use of a heat and moisture exchanger without filtering functi on (HME), and the use of a combined heat and moisture exchanger and me chanical filter (HMEF). The pressure support level was automatically a dapted by means of a closed-loop control in order to obtain constancy, throughout the study, of patient inspiratory effort as evaluated from airway occlusion pressure at 0.1 s (P-0.1). Patient's ventilatory pat tern, P-0.1, work of breathing, and blood gases were recorded. Measure ments and main results: The artificial noses increased different compo nents of the inspiratory load: inspiratory resistance, ventilation req uirements (due to increased dead space ventilation), and dynamic intri nsic positive end-expiratory pressure (PEEP). The additional load impo sed by the artificial noses was entirely undertaken by the ventilator, being the closed-loop control of P-0.1 effective to maintain constanc y of patient inspiratory work by means of adequate increases in pressu re support level. Conclusions: The artificial noses cause unfavorable mechanical effects by increasing inspiratory resistance, ventilation r equirements, and dynamic intrinsic PEEP. Clinicians should consider th ese effects when setting mechanical ventilation and when assessing pat ients' ability to breathe spontaneously.