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Update in Intensive Care and Emergency Medicine - part 4

Từ một quan điểm thực tế, tiềm năng về huyết động học ý nghĩa của tự động PEEP có thể dễ dàng xác định bằng cách đánh giá xem 30 - 45 giây gián đoạn thông khí áp lực dương dẫn đến tăng huyết áp và cung lượng tim [34]. Mặc dù này cơ động thường cũng có kết quả trong một PAOP thấp hơn, | Pulmonary Artery Occlusion Pressure Measurement Significance and Clinical Uses 121 pressure ratio are more reliable than the nadir PAOP technique in patients with auto-PEEP due to airflow obstruction. From a practical standpoint the potential hemodynamic significance of auto-PEEP can be easily determined by assessing whether a 30- to 45-second interruption of positive-pressure ventilation leads to an increase in blood pressure and cardiac output 34 . Although this maneuver usually also results in a lower PAOP an unchanged PAOP does not exclude the presence of hemodynamically significant auto-PEEP because a large increase in venous return could offset the reduction in juxtacardiac pressure. Active expiration When the abdominal expiratory muscles remain active throughout expiration the resultant increase in juxtacardiac pressure causes the end-expiratory PAOP to overestimate transmural pressure Fig. 4 . Although initially described in spontaneously breathing patients with COPD this problem also occurs in the absence of obstructive lung disease and in mechanically ventilated patients 35 . Since the pressure generated by the abdominal expiratory muscles is transmitted directly to the pleural space and is not buffered by the lungs active exhalation typically causes the end-expiratory PAOP to overestimate transmural pressure to a much greater extent than does the application of PEEP 36 . With active exhalation it is common for the end-expiratory PAOP to overestimate transmural pressure by more than 10 mmHg 5 36 . Failure to appreciate the effect of active exhalation on A Before Paralysis 30 20 10 0 Fig. 4. Effect of vigorous respiratory muscle activity on end-expiratory wedge pressure arrow . 122 J. J. Marini and J. W. Leatherman the measured PAOP may result in inappropriate treatment of hypovolemic patients with diuretics or vasopressors on the basis of a misleadingly elevated PAOP. When respiratory excursions in the PAOP tracing are due entirely to inspiratory muscle .