Effects of PEEP on Respiratory Mechanics after Open Heart Surgery (15)

Effects of PEEP on Respiratory Mechanics after Open Heart Surgery (15)The values of PEEPi were much lower than those commonly observed in mechanically ventilated patients with chronic obstructive pulmonary disease (up to 22 cm H20). Nevertheless, PEEPi in our patients had to be taken into account for the correct measurements of the Cst,rs. In the two patients with the highest PEEPi (4.6 and 5.0 cm H20), the difference between the corrected and uncorrected Cst,rs was 22 and 24 percent at initial ZEEP. There are no previous measurements of PEEPi in postoperative open heart surgery patients, and the nature of PEEPi exhibited by our patients is not clear. It should be noted, however, that nine of our patients had a smoking history. Furthermore, our baseline ventilation included an end-inspiratory pause of 10 percent of the total cycle duration, which, according to a previous report should have promoted the development of PEEPi.
In conclusion, the main findings of this study are as follows: (1) In postoperative open heart surgery patients, high values of PEEP appear to be potentially useful for reopening atelectatic lung units. (2) In the immediate period after open heart surgery, static compliance of the respiratory system is lower than normal, probably reflecting the presence of atelectasis. (3) The application of prophylactic PEEP of 5 cm H20 results in virtually no recruitment of collapsed alveoli. By contrast, PEEP of 10 cm H20 elicits significant alveolar recruitment. However, at PEEP of 10 cm H20, not all of the atelectatic alveoli are recruited because higher values of PEEP caused a further substantial increase in Vrec. Although high levels of PEEP are effective in terms of recruitment, there may be adverse circulatory effects and hence high levels of PEEP are contraindicated.