Effects of different spontaneous breathing modes on hemodynamics in patients after coronary artery bypass graft surgery

Objective

During mechanical ventilatory support the use of spontaneous breathing modes can be beneficial. Nevertheless the opportunity to combine different forms of assisted ventilation is not sufficiently investigated. We evaluated the effects of the combination of different modes of spontaneous ventilation on global end-diastolic volume and cardiac output in patients after elective coronary artery bypass graft surgery.

Design

A prospective, interventional study.

Setting

ICU of a university hospital.

Patients

Eight postoperative patients who underwent elective coronary artery bypass graft surgery.

Methods

After admission to the ICU each patient was ventilated using one of three ventilation modes for a time period of 30 min, followed by a 15-min equilibration period. All three respiratory settings were applied in randomly assigned order in every patient. A: biphasic positive airway pressure (BIPAP); B: BIPAP in combination with pressure support ventilation (BIPAP + PSV); C: pressure support ventilation (PSV). In every ventilator setting, all patients had spontaneous breathing efforts in at least 30% based upon minute ventilation (VE). The settings were adjusted to achieve a tidal volume (VT) of 6–8 ml/kg body weight. At the end of each 30-min period bolus thermodilution-derived cardiac output was obtained from thermodilution curves detected in the femoral artery. Three intermittent consecutive boli consisting of 10 ml ice-cold saline were randomly injected over the ventilatory cycle. The primary endpoints were the global end-diastolic volume and the cardiac output obtained by the PICCO monitor (Pulsion Medical AG, Munich, Germany).

Results

The mean tidal volume (VT) was 7.81 ± 0.31 ml/kg body weight. The mean airway pressure was A: 8.80 ± 1.36 mbar vs B: 8.72 ± 0.90 mbar vs C: 8.33 ± 1.73 mbar (P = not significant). No differences were found for GEDV (P = 0.99), stroke volume (P = 0.23) and cardiac output (P = 0.35). Respiratory parameters and indices of pulmonary gas exchange did not differ between the tested modes.

Conclusions

The combination of different modes of spontaneous breathing has no different effects on hemodynamic parameters of patients after elective coronary artery bypass graft surgery when the mean airway pressure did not change.