Mechanical ventilation with traditional large tidal volume versus low tidal volume in patients with acute lung injury : pulmonary and hemodynamic study

Abstract EN

This study was carried out in the ICU of Assuit University Hospital.

A total of 30 patients who fulfilled the criteria of acute lung injury (ALI) and ARDS with lung injury score of 2.5 were enrolled in the study.

The patients were randomly classified into 2 groups namely traditional tidal volume group which was managed with TV of 10- 12ml/kg, and lower tidal volume group which was managed with TV of 6ml/kg.

The patients were mechanically ventilated using SIMV mode.

In the traditional group of patients, the plateau pressure was kept >40 cm H20, respiratory rate was adjusted to maintain PaC02 of35-45 mmHg.

PEEP level was > 5cmH20.

In the lower tidal volume group, the PaC02 was allowed to increase (permissive hypercarbia), unless the pHwas severely affected < 7.2, to allow lowering of the plateau pressure to 25 — 30 cmH20.

PEEP was used according to the calculation of optimal PEEP.

In both groups of patients, the Fi02 was adjusted to maintain Pa02 60mmHg, and arterial oxygen saturation > 90%.

Traditional or protective mechanical ventilation was maintained until the patient was extubated or died.

The following parameters were studied for 17 days including: hemodynamic (HR, MAP, CVP, MPAP, PCWP, and CI), arterial blood gases and oxygenation parameters (pH, PaC02, HC03, Pa02, Pv02, QS/QT, Pa02/Fi02); lung mechanics (PP, PIP, CST).

The present results demonstrated that the mean value of HR was mildly decreased in the traditional tidal volume group while it was increased in the lower tidal volume group throughout all days of the study.

An initial decrease in MAP, which was followed by an increase, was found in the traditional tidal volume group.

But lower tidal volume group demonstrated a continuous rise in MAP.

Both groups of patients demonstrated an increase in CVP, MPAP and PCWP levels in most of investigated days especially in lower tidal volume group.

Reasonable values of CI were observed in both groups.

The mean value of PaC02 was found to be increased in the lower tidal volume group in the early period of the study resulting in a lower PH.

The greater rise in HC03 found in later period resulting in methiogation of the increase in pH.

In the conventional TV group of patients, the PH, PaC02 andHC03 were within its normal limits.

The conventional tidal volume group revealed more elevation in Pa02 levels than lower tidal volume group in the earlierperiodof the study.

Later on, the Pa02 levels in the lower tidal volume group were increased to greater levels than traditional tidal volume group.

Similar effects were obtained concerning Pa02 / Fi02 levels in both groups.

The shunt] fraction was mildly improved in both studied groups especially in lower TV group, but still ;/1 did not achieve its normal levels.

In both groups there was an increase in the levels of thA Pv02 during most investigated days of mechanical ventilation.

Better respiratory mechanic^ were found in lower tidal volume group.

The plateau pressure was less, the peak inspiratory! pressure was also less, and static compliance was greater in this group as compared with traditional tidal volume group.

In conclusion, the consequences of application of this lung protective strategy resulted in modest effects regarding the investigated hemodynamics due to modest increments in PaC02.

Lower tidal volume group of patients demonstrated better oxygenation parameters and better improvement in lung mechanics.

Further studies may be needed to investigate the combined use of other ventilatory strategies, for example: prone I positioning in addition to the one applied in this work to obtain better results regarding the f studied oxygenation.