The effects of positive end-expiratory pressure on respiratory system mechanics and hemodynamics in postoperative cardiac surgery patients

Abstract

We prospectively evaluated the effects of positive end-expiratory pressure (PEEP) on the respiratory mechanical properties and hemodynamics of 10 postoperative adult cardiac patients undergoing mechanical ventilation while still anesthetized and paralyzed. The respiratory mechanics was evaluated by the inflation inspiratory occlusion method and hemodynamics by conventional methods. Each patient was randomized to a different level of PEEP (5, 10 and 15 cmH 2 O), while zero end-expiratory pressure (ZEEP) was established as control. PEEP of 15-min duration was applied at 20-min intervals. The frequency dependence of resistance and the viscoelastic properties and elastance of the respiratory system were evaluated together with hemodynamic and respiratory indexes. We observed a significant decrease in total airway resistance (13.12 ± 0.79 cmH 2 O l -1 s -1 at ZEEP, 11.94 ± 0.55 cmH 2 O l -1 s -1 (P<0.0197) at 5 cmH 2 O of PEEP, 11.42 ± 0.71 cmH 2 O l -1 s -1 (P<0.0255) at 10 cmH 2 O of PEEP, and 10.32 ± 0.57 cmH 2 O l -1 s -1 (P<0.0002) at 15 cmH 2 O of PEEP). The elastance (E rs ; cmH 2 O/l) was not significantly modified by PEEP from zero (23.49 ± 1.21) to 5 cmH 2 O (21.89 ± 0.70). However, a significant decrease (P<0.0003) at 10 cmH 2 O PEEP (18.86 ± 1.13), as well as (P<0.0001) at 15 cmH 2 O (18.41 ± 0.82) was observed after PEEP application. Volume dependence of viscoelastic properties showed a slight but not significant tendency to increase with PEEP. The significant decreases in cardiac index (l min -1 m -2 ) due to PEEP increments (3.90 ± 0.22 at ZEEP, 3.43 ± 0.17 (P<0.0260) at 5 cmH 2 O of PEEP, 3.31 ± 0.22 (P<0.0260) at 10 cmH 2 O of PEEP, and 3.10 ± 0.22 (P<0.0113) at 15 cmH 2 O of PEEP) were compensated for by an increase in arterial oxygen content owing to shunt fraction reduction (%) from 22.26 ± 2.28 at ZEEP to 11.66 ± 1.24 at PEEP of 15 cmH 2 O (P<0.0007). We conclude that increments in PEEP resulted in a reduction of both airway resistance and respiratory elastance. These results could reflect improvement in respiratory mechanics. However, due to possible hemodynamic instability, PEEP should be carefully applied to postoperative cardiac patients.

Effects of different PEEP levels on respiratory mechanics and oxygenation after coronary artery bypass grafting

“…Decreased lung compliance after CABG is well established, probably due interstitial edema, hemorrhage and vascular congestion that increases lung stiffness [11]. In cardiac surgery immediate postoperative period, static compliance is lower than normal, probably reflecting atelectasis [9].…”

“…Auler Jr et al [11] in a prospective trial that assessed effects of PEEP on respiratory mechanics and hemodynamics of CABG patients concluded that higher levels of PEEP promote reduction in airway resistance. Similar findings were found in our study, but with no statistical significance.…”

Pressão expiratória positiva na via aérea por máscara facial na hemodinâmica de pós-operatórios cardíacos

“…Aware of ventilatory 5 and hemodynamic changes of positive pressure during invasive mechanical ventilation (IMV) 6,7 and non-invasive ventilation (NIV) 8,9 , raises the possibility that EPAP may have hemodynamic effects, but these have not yet been studied. Moreover, it is known that the increase in expiratory resistance caused by EPAP may have consequences such as increased in the first or second day after surgery, during which the patient is allowed to remain with the pulmonary artery catheter, as needed.…”

“…In a study comparing the use of three levels of PEEP (0, 5 and 10 cmH 2 O) in RHS in patients with EF ≥ 45%, there were no statistical differences between groups, which led us to conclude that low levels of PEEP have no advantage over zero level of PEEP in improving gas exchange in patients RHS 31 . The effects of PEEP on respiratory mechanics and hemodynamics of patients after cardiac surgery resulted in reduced airway resistance and respiratory elastance, which may reflect an improved respiratory mechanics 6 . However, due to possibility of hemodynamic instability, PEEP should be carefully applied in RHS.…”

Factors Associated With Failure of Weaning From Long-term Mechanical Ventilation After Cardiac Surgery

“…20,21) A finding of low pulmonary compliance after cardiopulmonary bypass is well established, likely due to the tendency of interstitial edema, hemorrhage and vascular congestion to increase pulmonary stiffness. 22) Our study showed that although low static lung compliance was present, it was not sensitive enough to predict the weaning outcomes of our patients because they usually had normal pulmonary function before the surgery.…”