Effects of PEEP on Respiratory Mechanics after Open Heart Surgery (12)

Application of 10 cm H20 of PEEP reduced substantially the degree of atelectasis which, however, was rapidly reinstated after removal of PEEP. In all three inflation runs, Vrec at PEEP of 5 cm h2o was small and not statistically significant (Fig 3). At PEEP of 10 cm H20, Vrec amounted to 165 ±57 ml during inflation run 1, but less during inflation runs 2 and 3 (104 ±35 ml and 121 ±41 ml, respectively). In the three patients studied at PEEP of 15 cm H20, the Vrec amounted to 446 ±123 ml during inflation run 1 and slightly less during runs 2 and 3.
At ZEEP, EELV increased by the end of run 1 by 109 ±44 ml, and after run 2 by an additional 32 ±30 ml (Fig 1). This increase in EELV probably reflects in part an increase in volume due to persistent recruitment of collapsed alveoli, ie, alveoli that have been recruited with increasing PEEP and that remain open upon return to ZEEP. The changes observed in Vrec and AEELV during each individual run (Fig 3) are considerably smaller than the cumulative changes. Assuming that the volumes of EELV in Figure 1 reflect entirely recruitment of previously collapsed lung units, at PEEP of 5 and 10 cm H20 during inflation runs 2 and 3, the cumulative Vrec at PEEP of 5 cm H20 should amount to 116 ± 40 ml and 216 ± 29 ml, respectively. At PEEP of 10 cm H20, the corresponding values would be 245± 29 ml and 264 ± 48 ml.