Patient-ventilator Asynchrony in Conventional Ventilation Modes During Short-term Mechanical Ventilation After Cardiac Surgery

Effects of Mechanical Ventilation on Controlled Volume, Controlled Pressure and Pressure Support in the Immediate Postoperative Period of Cardiac Surgery on Pulmonary Electrical Impedance and Patient-ventilator Asynchrony: a Parallel Clinical Trial

This study evaluates the effects of VCV, PCV and PSV ventilatory modes during the immediate postoperative period on the variables resulting from regional and global pulmonary electrical impedance and diaphragmatic mobility, as well as perform ventilator synchrony analysis in PSV mode by mechanical ventilator. Half of the participants will receive VCV followed by PSV for weaning, while the other half will receive PCV followed by PSV for weaning.

In the immediate postoperative period of cardiac surgery, patients are found under mechanical ventilatory support. Commonly, they are ventilated in controlled and assisted-controlled volume (VCV) or pressure (PCV) modes, with weaning at pressure support (PSV).

Systematic reviews indicate that there is no difference between the VCV and PCV ventilatory modes for some clinical outcomes or that the existing evidence is insufficient. The distribution of regional ventilation and diaphragmatic mobility can be measured from the use of electrical impedance tomography (EIT) and diaphragmatic ultrasonography (US) to clarify the physiological changes and / or mechanisms of adaptation of the organism submitted to controlled modes cycled at volume or at pressure and spontaneously flow cycled mode.

Besides EIT and US measures, gasometric, hemodynamic and respiratory data will also be recorded. The statistical analysis will be considered α≤0.05 for a statistically significant difference.

Inclusion Criteria:

• IMC 18.5-29.9 kg/m²
• Two thoracic tubes (one mediastinal and one left-sided pleural)
• under mechanical ventilation after surgery
• submitted to intraoperative extracorporeal circulation

Exclusion Criteria:

• Over 2h of cardiopulmonary bypass
• Over 12h of post-operative mechanical ventilation
• Post-operative bleeding above 500 ml in the first hour or above 300 ml in the first two hours
• History of special conditions (neuromuscular and chronic pulmonary disease, thoracic deformity, abdominal distension).