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KEY QUESTIONS IN SURGICAL CRITICAL CARE - PART 9

Biến hiệu suất hệ thống cung cấp oxy Nồng độ oxy Giao cho bệnh nhân KHÔNG liên tục và phụ thuộc vào số lượng phút (MV), hoặc cụ thể hơn tốc độ dòng chảy cao điểm hít (PIFR). Khi Tăng PIFR hơn Sẽ cuốn theo không khí từ môi trường xung quanh và nồng độ oxy Giao cho GIẢM bệnh nhân sẽ, trừ khi tốc độ dòng chảy oxy tăng lên là | Respiratory System Variable performance oxygen delivery systems The oxygen concentration delivered to the patient is not constant and depends on the minute volume MV or more specifically the peak inspiratory flow rate PIFR . As the PIFR increases more air will be entrained from the surroundings and the oxygen concentration delivered to the patient will decrease unless the oxygen flow rate is increased. The following are two examples of systems commonly used after surgery Table 2.4 Table 2.4 The different systems for delivering variable concentrations of oxygen Hudson mask Nasal specs O2 flow l min O2 conc. O2 flow l min O2 conc. 2 24-38 1 25-29 4 35-45 2 29-35 6 51-61 4 32-39 8 57-67 10 61-73 Fixed-performance oxygen delivery systems Venturi masks These deliver a constant oxygen concentration independent of the patient s respiratory pattern MV and PIFR . The oxygen supply entrains air at a fixed rate via a jet built into the mask. The total flow rate is therefore higher than the PIFR and dilution of the oxygen supply does not occur. The jet entrainment devices are coloured coded and higher flow rates must be dialled when increased oxygen concentrations are required Table 2.5 . Table 2.5 The system for delivering a known concentration of oxygen Colour code O2 supply flow rate l min Delivered O2 conc. White 4 28 Yellow 8 35 Red 10 40 Green 15 60 SCC pp 76-78 186 Vivas Key Questions in Surgical Critical Care Q 14. How would you classify respiratory failure and what are the signs IA14. Respiratory failure occurs when the PaO2 and PaCO2 can no longer be maintained within normal limits. If untreated this leads on to cellular hypoxaemia and acidosis by decreasing the capacity for gaseous exchange. Respiratory failure may be split up into two types depending on the CO2 concentration present in blood. Patients may progress from one type to the other Type I ị PaO2 with normal or ị PaCO2 there may be respiratory alkalosis Pulmonary embolism Fibrosing alveolitis Pneumonia .