Effects of inhaled nitric oxide combined to mechanic ventilation on the patients with acute respiratory dysfunction in postoperative heart surgery: comparative study among pressure controlled ventilation and volume controlled ventilation

Introduction

Pressure-controlled ventilation (PCV), is related to a better distribution of the inhaling flow and lower pressure peaks, when compared to volume-controlled ventilation (VCV). Nitric oxide (NO) promotes redistribution of blood flow to the ventilated areas and decreases the pulmonary shunt effect improving oxygenation.

Objectives

To evaluate the effects of 10 ppm of inhaled nitric oxide, combined to two ventilation modalities - pressure-controlled ventilation and volume-controlled ventilation - on the respiratory function of 40 patients undergoing heart surgery with extracorporeal circulation and respiratory dysfunction characterized by PaO₂/FiO₂ ratio <200 in postoperative heart surgeries.

Method

The patients were randomized into four groups: PCVNO group, pressure controlled ventilation with NO; PCVWNO group, pressure-controlled ventilation without NO; VCVWNO group, volume-controlled ventilation without NO; and VCVNO group, volume-controlled ventilation with NO. Evaluations were performed at times zero (baseline), 60, 120, 240 and 360 min. NO was administered in all times for groups I and IV.

Results

There were no significant changes in hemodynamic parameters, peak inspired pressure and oxygenation among the groups. There was a significant difference in the four groups for the following parameters throughout the different times: systolic pulmonary pressure (SPP); diastolic pulmonary pressure (DPP); mean pulmonary pressure (MPP); systolic systemic pressure (SSP); mean blood pressure (PBP); transpulmonary gradient (TPG); pulmonary/systemic vascular resistance index (PVRI/SVRI); ratio of partial arterial oxygen pressure and fractional inspired oxygen concentration (PaO₂/FiO₂); partial arterial carbon dioxide pressure (PaCO₂); oxygen consumption index (VO₂I); pulmonary shunt (Qs/Qt); oxygen extraction rate (O₂ER); alveolar-arterial oxygen gradient (A-aO₂)G; and pulmonary compliance (Cst) expressed by hemodynamic and oxygenation improvement.

Conclusions

No significant differences were observed for hemodynamic and respiratory parameters and those related to respiratory mechanics, when volume-controlled ventilation (VCV) was compared to pressure-controlled ventilation (PCV). NO inhalation did not show significant improvement in blood oxygenation of the studied patients. Ventilation time seems to have had a favorable influence on the clinical course. Ideal PEEP was calculated for all patients prior to the study