Mechanical ventilation with controlled pressure and controlled volume in septic patients with acute respiratory distress syndrome

Introduction

It is known that mechanical ventilation with the adoption of high tidal volumes (V_T = 10–15 ml/kg) has a relationship with the increase of the death rate in patients with acute respiratory distress syndrome (ARDS) [1]. Since then, different ventilatory strategies have been investigated adopting small tidal volumes; however, there is no agreement about which of them would cause a minimal pulmonary aggression to the preexisting injury.

Objective

To compare two methods of mechanical ventilation employed in septic patients with ARDS (controlled volume and controlled pressure), both adopting permissive hypercapnia, evaluating the hemodynamic and respiratory effects of those patients.

Methods

Research previously approved by the Hospital's Medical Ethics Committee, prospective and randomized, performed in the intensive care unit of the Hospital of UNICAMP. Seven patients were ventilated with controlled volume and nine patients with controlled pressure (Bird 8400^® Sti ventilator for both groups), the tidal volume variation being between 6 and 8 ml/kg, accepting PaCO₂ until 80 mmHg with pH > 7.2. The ideal positive end expiratory pressure was calculated based on the higher compliance level through the method of progressive positive end expiratory pressure. The selected patients were submitted to the Murray scale [2] with LIS ≥ 2.5, and the Sepsis-related Organ Failure Assessment [3] and Acute Physiology and Chronic Health Evaluation II scale were applied to evaluate their gravity on the moment of the protocol inclusion. Hemodynamic and respiratory monitoring was carried out by Swan–Ganz catheter, gasometry (arterial and venous) and capnometry sampling, twice a day during three subsequent days.

Results

There were no parameter differences between both mechanical ventilation groups. There was a significant difference for both groups, from the first to the second day of collection, only on the following parameters: pH rise and reductions of PaCO₂ and RVP.

Conclusion

All septic patients with ARDS studied, when ventilated with low V_T (6–8 ml/kg), both in controlled volume and controlled pressure, did not present differences in the lung function nor in the hemodynamic state.

Table 1 Patient characteristics at entry

Table 2 Results of the variable analyzed for both groups (controlled volume and controlled pressure) over three subsequent days