Comparison of the effects of low-dose vs. high-dose aminophylline on lung function in experimental meconium aspiration syndrome

Due to missing information on appropriate dosing of aminophylline in meconium aspiration syndrome (MAS), this study compared effects of high-dose and low-dose aminophylline on lung function of animals with MAS. Meconium-instilled rabbits were treated by low-dose (LD, 1.0 mg/kg), or high-dose (HD, 2.0 mg/kg) aminophylline at 0.5 and 2.5 h after meconium instillation, or were left untreated. Within 5 h of oxygen ventilation, HD-aminophylline improved gas exchange, reduced pulmonary shunts and ventilatory pressures, and decreased edema formation and lung neutrophils. LD-aminophylline enhanced lung function to a lower extent than HD-aminophylline, and failed to reduce lung edema and the number of lung neutrophils. Both treatments decreased lung peroxidation, with a stronger effect of HD-aminophylline on lipid oxidation and of LD-aminophylline on protein oxidation. Tracheal reactivity to histamine decreased after HD-aminophylline, while lung tissue reactivity was more reduced after LD-aminophylline. Although LD-aminophylline showed some anti-inflammatory potential, HD-aminophylline improved most of the parameters more effectively.

Combination of budesonide and aminophylline diminished acute lung injury in animal model of meconium aspiration syndrome

Combination of low-dose budesonide and low-dose aminophylline may improve lung function in reduced adverse effects compared with high-dose monotherapy. Adult rabbits intratracheally received 4 ml/kg of saline or meconium (25 mg/ml). Meconium-injured rabbits were treated at 0.5 and 2.5 h after meconium instillation by intravenous aminophylline (1.0 mg/kg), by intratracheal budesonide (0.125 mg/kg) followed by intravenous aminophylline (1.0 mg/kg), or were untreated. Although aminophylline improved some respiratory parameters, budesonide+aminophylline more effectively reduced intrapulmonary shunts and improved gas exchange, without significant cardiovascular effects. Combined treatment reduced lung edema and number of lung neutrophils to a higher extent than aminophylline alone. Both treatments reduced lung peroxidation and in vitro airway reactivity to histamine, with a better effect after aminophylline alone. Combination of budesonide and aminophylline enhanced respiratory parameters more effectively, having fewer side effects than aminophylline alone. However, no additive effect of budesonide was observed on lung peroxidation and in vitro airway reactivity.

Dexamethasone treatment improved lung functions in meconium-instilled rabbits, but influenced cardiovascular variables

BACKGROUND

In this study, the effects of single and repetitive dexamethasone administration on lung functions in meconium-instilled rabbits were compared. In addition, short-term adverse effects of dexamethasone on blood pressure, heart rate, and heart rate variability were evaluated.

METHODS

Artificially ventilated adult rabbits intratracheally received 4 ml/kg of meconium suspension (25 mg/ ml). When respiratory failure developed, animals received single-dose of dexamethasone (0.5 mg/kg i.v.) 0.5 h after meconium instillation (Dex1), two doses of dexamethasone (each 0.5 mg/kg i.v.) 0.5 and 2.5 h after meconium instillation (Dex2) or were left without treatment (Mec). Animals were oxygen-ventilated for 5 h after the first dose of treatment.

RESULTS

Dexamethasone treatment significantly improved gas exchange and reduced right-to-left pulmonary shunts, central venous pressure, and lung edema, whereas trend to more pronounced improvement in some parameters was observed after two doses of dexamethasone. There were no significant between-group differences in blood pressure, however, decreased heart rate and increased heart rate variability were observed particularly after repetitive dexamethasone administration.

CONCLUSION

Intravenous dexamethasone, especially when given in two doses, improved lung functions, but influenced cardiovascular variables in meconium-instilled rabbits (Tab. 2, Fig. 3, Ref. 34). Full Text (Free, PDF) www.bmj.sk.

Intratracheally administered corticosteroids improve lung function in meconium-instilled rabbits

Local administration of corticosteroids may diminish acute lung injury associated with meconium aspiration. Budesonide was given intratracheally in 2 doses of 0.25 mg/kg each by means of inpulsion effect of high-frequency jet ventilation 0.5 and 2.5 hours after meconium instillation to oxygen-ventilated adult rabbits. Within 5 hours after the first dose, budesonide significantly improved gas exchange and decreased right-to-left pulmonary shunts, central venous pressure, and ventilatory pressures. In addition, budesonide reduced the meconium-induced lung edema formation, airway hyperreactivity to histamine, count of neutrophils in bronchoalveolar lavage fluid associated with higher total white blood cell and neutrophil counts in the blood, and diminished oxidative modifications of proteins and lipids in lung tissue compared to non-treated meconium-instilled group. The intratracheally administered corticosteroid budesonide effectively improved pulmonary functions and alleviated changes associated with inflammation in meconium-instilled rabbits.

Single-dose versus two-dose dexamethasone effects on lung inflammation and airway reactivity in meconium-instilled rabbits

Two doses of the corticosteroid dexamethasone may alleviate meconium-induced acute lung injury more effectively than a single dose. Meconium-instilled rabbits intravenously received dexamethasone (0.5 mg/kg) at one dose 0.5 hours after meconium instillation or at two doses 0.5 hours and 2.5 hours after meconium instillation or were left without treatment, and were oxygen-ventilated for additional 5 hours. At the end of experiment, lungs and trachea were excised. Two doses of dexamethasone effectively diminished meconium-induced lung edema, tracheal hyperreactivity to histamine, neutrophil count in bronchoalveolar lavage fluid, and decreased oxidative modifications of proteins and lipids in lung homogenate compared with the non-treated group. Single-dose dexamethasone also reduced lung edema, lung neutrophils, and tracheal hyperreactivity to histamine, but these effects were weaker than those after two-dose dexamethasone. We conclude that two-dose dexamethasone is superior to single-dose dexamethasone in prevention lung injury in meconium-instilled rabbits.

Aminophylline treatment in meconium-induced acute lung injury in a rabbit model

Administration of methylxanthines may diminish meconium-induced acute lung injury. Meconium-instilled rabbits intravenously received aminophylline (2.0 mg/kg) at two doses 0.5 h and 2.5 h after meconium instillation or were left without treatment, and were oxygen-ventilated for additional 5 h. At the end of experiment, lungs and trachea were excised. Within 5 h after the first dose of treatment, aminophylline significantly improved gas exchange and decreased right-to-left pulmonary shunts, central venous pressure, and ventilatory pressures. Moreover, aminophylline reduced meconium-induced lung edema formation, airway hyperreactivity to histamine, count of neutrophils in bronchoalveolar lavage fluid associated with higher total white blood cells and neutrophils in the blood, and diminished oxidative modifications of proteins and lipids in lung tissue compared with the non-treated meconium-instilled group. In a rabbit model of the meconium aspiration syndrome, aminophylline treatment enhanced pulmonary functions and alleviated oxidative injury and changes in airway reactivity related to lung inflammation.

Cardiopulmonary and inflammatory changes in adult rabbits with meconium aspiration

BACKGROUND

Pulmonary inflammation and vasoconstriction are important pathogenetic factors in neonatal meconium aspiration syndrome (MAS).

OBJECTIVES

Study was performed to evaluate cardiopulmonary and inflammatory changes in adult rabbits after meconium administration.

METHODS

Animals were anesthetized and ventilated with room air. Initial values of cardiopulmonary parameters were recorded and blood samples taken. Three animals were then sacrifice and used as controls. The others were administered saline (4 ml/kg, n = 4) or meconium (25 mg/ml, 4 ml/kg, n = 5) and were further ventilated with 100% oxygen. When respiratory failure developed, parameters were recorded and animals were ventilated for additional 5 hours. Rabbits were then sacrifice and lungs excised. Right lungs were dried to determine wet/dry weight ratio and left lungs were lavaged with saline. Differential leukocyte count in the blood and lavage fluid sediment, and total blood leukocyte count were evaluated.

RESULTS

Instillation of meconium significantly decreased lung compliance, ventilation efficiency index and gas exchange, and increased right-to-left pulmonary shunts in comparison with saline group. No significant differences between groups were observed in mean blood pressure, heart rate, and central venous pressure. Meconium caused higher fluid and polymorphonuclear accumulation in the lungs, linked with decreased neutrophil and increased eosinophil counts in the blood.

CONCLUSIONS

Adult rabbits may be used for experimental testing of drugs influencing lung inflammation and vasoconstriction in MAS (Tab. 1, Fig. 4, Ref. 16).

Lung lavage using high-frequency jet ventilation in rabbits with meconium aspiration

AIM

To determine the efficacy of the expulsion effect of high-frequency jet ventilation (HFJV) on meconium clearance from the airways in comparison with conventional suctioning in adult rabbits with meconium aspiration.

METHODS

Experiments were carried out on tracheotomized, anaesthetized and paralysed adult rabbits. A suspension of human meconium in saline (25 mg ml(-1), 4 ml kg(-1)) was instilled into the tracheal cannula. When respiratory failure developed, saline lavage (10 ml kg(-1) in 3 portions) was performed during conventional ventilation or by means of the inpulsion and expulsion regime of HFJV. Animals were further ventilated for 2 h with either conventional ventilation or HFJV.

RESULTS

There was no significant difference between groups in the amount of meconium recovered by lavage. Compared to conventional ventilation, the application of HFJV enhanced the elimination of carbon dioxide, increased lung compliance and diminished right-to-left shunts after 30 min of ventilatory treatment. Oxygenation also improved during HFJV, although this was not a consistent finding during the ventilation period.

CONCLUSION

HFJV improved gas exchange, lung compliance and reduced right-to-left pulmonary shunts, but saline lung lavage by HFJV was not found to be more efficient than lavage during conventional ventilation in rabbits with meconium aspiration.