Effects of PEEP on Respiratory Mechanics after Open Heart Surgery (14)

This probably explains the lack of recruitment at PEEP of 5 cm H20. In contrast, at PEEP of 10 cm H20, the initial values of end-inspiratory Pst,rs amounted to 24.6± 1.0 cm H20, which was probably sufficient to reopen collapsed alveoli (Fig 3). At PEEP of 15 cm H20, end-inspiratory Pst,rs in three patients ranged between 28 and 35 cm H20, and resulted in a further substantial increase in Vrec (Fig 3). Clearly, higher PEEP values than the recommended prophylactic PEEP (5 to 10 cm H20)* should be more effective in terms of recruitment. The adverse effects of high PEEP, however, on ventricular performance and cardiac output (and hence oxygen transport) are well recognized.
With increasing PEEP level, there was a progressive increase in EELV At low levels of PEEP, the changes in EELV occurred along a fixed static V-P relationship (up to 6 cm H20 in Fig 2, A). At higher levels of PEEP, however, there was an upward shift of the V-P curves, indicating that part of the increase in EELV reflected recruitment. Due to the persistent increase in EELV after runs 1 and 2, the EELV at any given level of PEEP was higher in run 3 than in runs 1 and 2. It should be noted that in all patients, the EELV at ZEEP was higher than the elastic equilibrium volume of the respiratory system because of presence of PEEPi (range, 0.3 to 5.0 cm HaO) (Fig 2).