Heart-Protective Mechanical Ventilation in Postoperative Cardiosurgical Patients.

BACKGROUND

This study compared the hemodynamic effects and gas exchange under several different ventilator settings-with regard to tidal volume, respiratory rate, and end-expiratory pressure-in patients after coronary artery bypass grafting (CABG).

METHODS

Prospective interventional cohort study with a controlled group in a single cardiosurgical ICU involving 119 patients following on-pump CABG surgery. During the 1st postoperative hour, the intervention group patients were ventilated with Vt 10 ml × kg, RR 14/min, PEEP 5 cmHO ("conventional ventilation"). During the 2nd hour, RR was reduced to 8/min ("reduced RR ventilation"). At 3 hrs, Vt was decreased to 6 ml × kg, RR returned to 14/min, and PEEP increased to 10 cmHO ("low Vt-high PEEP ventilation").

RESULTS

Patients in the "low Vt-high PEEP" ventilation period showed significantly lower alveolar ventilation and thoraco-pulmonary compliance than during "reduced RR" ventilation. Mean airway pressure and Vds/Vt peaked during low Vt-high PEEP ventilation; however, driving pressure was lower. Vt decrease and PEEP increase did not lead to oxygenation improvement and worsened CO elimination. Hemodynamically, the study revealed significant cardiac output decrease during low Vt-high PEEP ventilation. In 23.2% of patients, catecholamine therapy was initiated.

CONCLUSIONS

In postoperative cardiosurgical patients, MV with Vt 6 ml × kg and PEEP 10 cm HO is characterized by worsened oxygenation and elimination of CO and a less favorable hemodynamic profile than ventilation with Vt 10 ml × kg and PEEP 5 cmHO. . (i) Patients after CABG may be especially sensitive to low tidal volume and increased PEEP as it negatively affects hemodynamic profile by means of the right heart preload decrease and afterload increase. (ii) Mechanical ventilation settings aiming to minimize mean airway pressure reduce the negative effects of positive inspiratory pressure and are favorable for hemodynamics.