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Báo cáo y học: " Equipment review: Tracheal gas insufflation"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học General Psychiatry cung cấp cho các bạn kiến thức về ngành y đề tài: Equipment review: Tracheal gas insufflation. | Nahum Critical Care 1998 2 43 http ccforum.com c CRITICAL CARE REVIEW Equipment review Tracheal gas insufflation Avi Nahum 47cc-2-2-043 Introduction Tracheal gas insufflation TGI is an adjunctive ventilatory technique that delivers fresh gas into the trachea either continuosly or only during a specific segment of the respiratory cycle phasic flow 1-4 . Two mechanisms are responsible for improving the efficacy of conventional tidal breaths during TGI 5-7 . First fresh gas introduced by the catheter during expiration flushes the series anatomic deadspace compartment proximal to its tip free of CO2. Consequently during the subsequent inspiration less CO2 is recycled back to the alveoli thus improving CO2 elimination. Second at high catheter flow rates turbulence generated at the tip of the catheter can enhance gas mixing in regions distal to the catheter tip thereby contributing to CO2 removal. Carbon dioxide elimination during TGI depends on catheter flow rate because fresh gas flushes a greater portion of the proximal deadspace at higher flow rates. Moreover at higher flow rates turbulence generated at the catheter tip may further enhance distal gas mixing. The volume of fresh gas introduced into the trachea during TGI depends on expiratory time TE and catheter flow rate Vc . At a certain TE X Vc fresh gas completely sweeps the proximal anatomic deadspace during expiration. At that point increasing Vc most likely does not dilute the CO2 residing in the series deadspace any further. This operational charactertistic of TGI and the fact that the decrease in the partial pressure of CO2 PaCO2 caused by a reduction in total physiologic deadspace fraction VD VT is much less at lower VD VT limits the decrement in PaCO2 afforded by TGI at high Vc 8 . Nevertheless at high Vc 10-15 1 min PaCO2 continues to decrease with increasing Vc but at a slower rate 8-10 . Once the series deadspace is flushed completely by the fresh gas during expiration the flow dependence of PaCO2 is .