Effects of dexamethasone on cardiovascular functions in acute phase in meconium-injured rabbits

Because cardiovascular functions and their control mechanisms may be influenced by meconium aspiration and by treatment, cardiovascular parameters including heart rate variability (HRV) were evaluated after meconium instillation and treatment with dexamethasone.

Adult rabbits were anesthetized, paralyzed, and artificially ventilated. Meconium suspension (25 mg/mL, 4 mL/kg) was instilled intratracheally to induce respiratory failure. Thirty minutes later, animals received i.v. dexamethasone (0.5 mg/kg; dexa group, n = 6) or were left without treatment (control group, n = 5). All animals were ventilated for an additional 5 h. Mean heart rate (MHR), mean blood pressure (MBP), central venous pressure (CVP), and time and spectral analyses of HRV were registered and evaluated. Blood gases were measured and right-to-left pulmonary shunts (RLS) calculated.

Immediately after meconium instillation, MBP, CVP, and RLS increased and MHR decreased (P < 0.05). MHR and MBP were restored within several minutes, while CVP and RLS remained high until the end of experiment. Thirty minutes after meconium instillation, slightly but non-significantly higher spectral powers in all frequency bands of HRV were found (P > 0.05). Dexamethasone treatment enhanced oxygenation (P < 0.05) and slightly reduced PaCO(2) (P > 0.05), increased parasympathetic activity expressed by mean squared successive difference and decreased spectral power in the very low frequency band (P < 0.05) compared to controls, but had no significant effect on MHR, MBP, CVP, and RLS.

Single-dose i.v. dexamethasone showed a trend to improve gas exchange, however, increased parasympathetic activity, what should be considered in use of corticosteroids in the treatment of meconium aspiration syndrome.