Resp Care
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In order to use tracheal gas insufflation (TGI) in a safe and effective manner, it is important to understand potential interactions between TGI and the mechanical ventilator that may impact upon gas delivery and carbon dioxide (CO2) elimination. Furthermore, potentially serious complications secondary to insufflation of cool, dry gas directly into the airway and the possibility of tube occlusion must be considered during use of this adjunct modality to mechanical ventilation. Regardless of the delivery modality (continuous TGI, expiratory TGI, reverse TGI, or bidirectional TGI), conventional respiratory monitoring is required. ⋯ Therefore, depending on the gas delivery technique used, it is important to carefully monitor these ventilatory parameters for TGI-induced changes and understand the potential need for adjustments to ventilator settings to facilitate therapy and avoid problems. Optimally, gas insufflated by the TGI catheter should be conditioned by addition of heat and humidity to prevent mucus plug formation and potential damage to the tracheal mucosa. Finally, patients must be closely monitored for increases in peak inspiratory pressure from obstruction of the tracheal tube and should have the TGI catheter removed and inspected every 8-12 hours to assess for plugs.
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Over the past 50 years, a variety of techniques have been developed that have in common the insufflation of gas into the central airway to facilitate carbon dioxide (CO2) clearance. These include continuous insufflation of oxygen, transtracheal jet ventilation, high frequency jet ventilation, transtracheal oxygen administration, intratracheal pulmonary ventilation, and tracheal gas insufflation (TGI). Continuous insufflation of oxygen is a technique used to enhance CO2 removal in the presence of apnea. ⋯ However, other techniques, such as TGI, are used as an adjunct to positive pressure ventilation. Intratracheal pulmonary ventilation provides positive pressure ventilation while bypassing the upper airway. Although some of these techniques are promising adjuncts to mechanical ventilation and may help reduce ventilator-associated lung injury, much remains to be learned about their role in the care of patients with acute lung injury.
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As an adjunct to mechanical ventilation, tracheal gas insufflation (TGI) injects gas flow into the trachea to flush carbon dioxide (CO2) from the anatomical and mechanical dead space, but the addition of TGI flow from a catheter may cause problems related to increased flow velocity at the catheter tip. Forward momentum and turbulence beyond the tip oppose expiratory flow and may cause or increase intrinsic positive end-expiratory pressure. If the catheter is placed within the endotracheal tube (ETT), the catheter itself acts as a resistive element to exhalation. ⋯ A recently developed bidirectional catheter allows the option of delivering TGI flow cephalad, towards the lungs or in both directions. Unfortunately, to be convenient, the use of specially designed catheters or ETTs requires the anticipation of TGI use. A complete system for the safe and convenient use of TGI in ventilated patients is not as yet available, but concerns about the safety and convenience of TGI delivery have been addressed with recent advances in catheter/tube design.
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Traditional ventilator management of acute respiratory distress syndrome (ARDS), emphasizing normalization of blood gases, promoted high rates of conventional barotrauma. Research revealed a broader range of ventilator-induced lung injury, physiologically and histopathologically indistinguishable from ARDS itself. It is now known that overdistention and cyclic inflation of injured lung can exacerbate lung injury and probably promote systemic inflammation, effects minimized by low tidal volumes/plateau pressures and by application of positive end-expiratory pressure. ⋯ There may thus be disparate goals in ARDS management: rapid institution of a restrictive ventilatory strategy, and avoidance of significant acidosis. We review data pertaining to ARDS physiology, ventilator-induced lung injury, lung-protective ventilatory strategies, and the physiology of respiratory acidosis. Tracheal gas insufflation is considered as a means to reconcile the clinical goals of ventilatory reduction and control of acidosis.
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Numerous reports of patient, lung model, and animal use of tracheal gas insufflation (TGI) have appeared in the literature over the past 10 years. However, no commercial TGI system is available. As a result, extreme care must be exercised if attempts are made to provide TGI. ⋯ However, this requires that the TGI system be integrated with the mechanical ventilator. In addition, appropriate system monitoring should be available, including measurement of total positive end-expiratory pressure, peak inspiratory pressure, and tidal volume, and there should be a method of identifying increased carinal pressure and deactivating the TGI system if an obstruction occurs proximal to the point of TGI injection. As a result of the potential complications of TGI, this technique cannot be recommended for routine use until commercial systems are available.