Lung pathology after high frequency jet ventilation combined with low rate intermittent mandatory ventilation in a canine model of meconium aspiration

Abstract

The microscopic appearance of lungs subjected to six hours of conventional ventilation (CV), standard high frequency jet ventilation (HFJV), and HFJV combined with low rate intermittent mandatory ventilation (CHFJV) was studied in 22 mongrel puppies. A lung injury model was created by insufflating 4 ml/kg of a 20% mixture of meconium into the trachea. The animals were initially ventilated at the same mean airway pressure (Paw). Subsequently, if PCO2 fell below 20 torr, peak and mean airway pressures were reduced. A scoring system was devised which assigned 0-3 points for each of eight lung injury parameters, and a total lung injury score (TLIS) was calculated. CHFJV resulted in significantly less bronchopneumonia and edema, when compared to CV. A consistent, though not significant, trend toward lesser injury scores in CHFJV animals was noted for several other parameters. Six of eight lungs exposed to CV had TLIS greater than 5 compared to only 1 of 9 ventilated by CHFJV. (P = 0.02). It is concluded that CHFJV may have a protective effect on the lung, perhaps because effective gas exchange is achieved with a lower pressure amplitude and at lower Paw.

Combined effects of high‐frequency ventilation and surfactant treatment in experimental meconium aspiration syndrome

“…The clinical manage-ment of severe MAS usually requires mechanical ventilation with high peak inspiratory pressures (PIP) and a high fraction of inspired oxygen (FiO 2 ) to maintain adequate blood oxygenation (6). In some experimental studies on MAS in piglets and young mongrel dogs, less severe pathologic alterations (7,8) and better oxygenation at lower PIP (9) were found in animals ventilated with various modes of high-frequency ventilation in comparison with controls treated with CV. However, a similar more recent study has failed to confirm these observations (10).…”

Toxicity of prolonged high dose inhaled PGE1 in ventilated neonatal pigs

“…Moderate to severe diffuse/mutifocal alveolar edema was observed in both the control and IPGE 1 groups suggesting that the alveolar alterations may be secondary to effects of mechanical ventilation with high FiO 2 (30,(44)(45)(46). The commonest abnormality observed in the IPGE 1 group was the presence of moderate-severe focal tracheal or bronchial epithelial flattening, loss of cilia and ulceration in two animals.…”

“…Representative sections were obtained from all pulmonary lobes (12 sections per animal) and trachea (five sections per animal), processed routinely for paraffin embedding, and stained with hematoxylin/eosin. Lung histomorphology was assessed by a single pathologist masked to group assignment using a scoring system adapted from those described in literature (30)(31)(32)(33). Lung injury was characterized on the basis of both severity of injury and extent of injury.…”

Meconium Aspiration Syndrome in Animal Models: Inflammatory Process, Apoptosis, and Surfactant Inactivation

“…Finally, an area of opportunity that has not been fully explored is combining treatment with ventilatory assistance with other options. In this regard, it has been observed that the use of standard high-frequency jet ventilation or in combination with low-rate intermittent mandatory ventilation can decrease the level of bronchopneumonia and edema in the lung affected by the MAS in the canine model [ 118 ]. Moreover, the combination with surfactant can reduce the presence of lung lesions in the pig model [ 32 , 102 , 119 ].…”