The effect of low versus high tidal volume ventilation on inflammatory markers in animal model undergoing lung...

Mechanical ventilation (MV) with high tidal volume (Vt.) may induce or aggravate lung injury in critically ill patients. It might also cause an overwhelming systemic inflammation leading to acute lung injury (ALI), diffuse alveolar damage (DAD) and multiple organ failure (MOF) with subsequent high mortality. The objective of this study was to compare the effects of different Vt. on the inflammatory markers of the broncho-alveolar lavage (BAL) fluid and lung biopsy in a group of animal model (Beagle dogs).

A two-phased prospective study involving 30 Beagle dogs (15 dogs/phase), each phase divided into three groups (each 5 dogs/group). In the first phase each group received MV with Vt. of 8 (low), 10 (normal, control group), and 12 (high) ml/kg body weight (b.w.) respectively. BAL fluid was obtained at the time of induction of anesthesia immediately following tracheal intubation and one hour later following MV to count the macrophages, neutrophils and lymphocytes. In the second phase of the experiment, in addition to obtaining (BAL) fluid similar to the phase one, mini thoracotomy and lung biopsy obtained from the upper lobe of the right lung at same timings for histopathological examination study. Mann-Whitney-Wilcoxon test was used for statistical analysis of the data obtained.

BAL fluid analysis showed increase in the counts of macrophages and lymphocytes with Vt. of 12 ml/kg b.w. compared to the control group (10 ml/kg b.w.) (P < 0.05). in the second phase, similar findings obtained. The histopathological study of the lung tissue obtained in the second phase of the study from the group that received a high Vt. of 12 ml/kg b.w. showed significant inflammatory changes with presence of neutrophil infiltration and edema in the bronchial wall compared to the control group (10 ml/kg b.w.) (P < 0.05).

The use of high Vt. in ventilated animal lung model may increase the risk of inflammation and subsequent damage in healthy lungs, these findings may help physicians to avoid using high Vt. in short-term mechanically ventilated patients in the operating room setting.