![]() ![]() ![]() The results indicated that positive effects were related not only to a high value of MDT but also to an abrupt cessation of end-inspiratory flow (EIF) that follows from shortening T I or using an increasing flow pattern. In one study, the T P was varied, but also the T I and SHAPE. In ARDS patients, a long T P reduces dead space and leads to reduced PaCO 2, without a clinically significant increase in intrinsic positive end-expiratory pressure (PEEP) or negative hemodynamic effects. The positive effects were more closely related to lnMDT than to MDT. It reduces dead space in healthy pigs and in pigs with acute lung injury. A longer T P prolongs MDT and enhances CO 2 elimination. The definition of MDT is recapitulated in Figure Figure1. T I, T P, and SHAPE affect mean distribution time (MDT), that is, time available for distribution and diffusion of inspired tidal gas with resident alveolar gas. SHAPE may be constant: that is, square flow, increasing or accelerating flow or decreasing that is decelerating flow. Characteristics of this pattern are the time for gas insufflation (T I), the postinspiratory pause time (T P) after T I, and the inspiratory flow wave pattern, denoted SHAPE. This suggests an optimal pattern of inspiratory gas delivery. So, adequate CO 2 elimination under well-controlled airway pressure and tidal volume (V T) is an important clinical issue, particularly in ARDS.Īccordingly, dead-space reduction plays a role in a rational lung-protection strategy. ![]() However, the decrease in minute ventilation induced by low V T can be difficult to offset by increasing respiratory rate and may induce hypercapnia. showed by dynamic CT that cyclic collapse and opening is reduced by lower V T, providing direct evidence that low V T ventilation may be lung protective by reducing this phenomenon. By using lower than traditional V T, both of the mentioned damaging mechanisms may be mitigated. Among efforts to provide lung-protective ventilation in ARDS, a reduction of tidal volume (V T) is a central issue. It may be caused by barotrauma related to high airway, alveolar, and transpulmonary pressures or by shear forces at lung collapse and opening during tidal breaths. Ventilator-induced lung injury is an important problem in the acute respiratory distress syndrome (ARDS). ![]()
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