(910) Effects of magnesium sulfate on the heart rate of preterm fetal sheep with intraamniotic inflammation

Objective: The specific findings of fetal heart rate (FHR) patterns after drug administrations under intraamniotic inflammation have not been clarified. This study aimed to investigate the effects of fetal magnesium sulfate (MS) injection on the heart rate of preterm fetal sheep with intraamniotic inflammation during increasing and decreasing levels of serum MS concentration.

Study Design: We used chronically instrumented pregnant sheep at 113–119 d (term=145 d) of gestation without (Group 1, n=4: MS group, and n=4: control group) and with (Group 2, n=4: MS group, and n=4: control group) intraamniotic inflammation induced by lipopolysaccharide injection (40 mg/body) into the amniotic cavity. MS was injected intravenously for 2 h into fetal sheep in MS groups at a dose of 1200 µg/h for 30 min and followed by 200 µg/h for 90 min. Physiological saline was used in the control groups. Changes in FHR, FHR variabilities, fetal blood pressure (FBP), and fetal arterial blood gas (FABG) values were measured before and at 1, 2, 4, and 6 h after initiating fetal MS administration; 1 and 2 h were defined as increasing fetal MS level phase (phase 1) and 4 and 6 h were defined as decreasing fetal MS level phase (phase 2). Fetal serum MS concentration and fetal interleukin-6 were also evaluated. We used the Friedman test to evaluate the changes of each parameter, compared to those before administration.

Results: In Group 1, no significant difference was observed in FHR in MS group. In Group 2, fetal MS injection significantly decreased FHR in phase 1 (2 h: p=0.044) and phase 2 (4h: p=0.007 and 6h: p=0.007). FBP and FABG values in MS groups and FHR, FBP, and FABG values in control groups did not significantly change.

Conclusion: Fetal MS injection decreased FHR even in the decreasing fetal MS level phase under intraamniotic inflammatory condition. Effects of fetal MS administration on FHR in both physiological and intraamniotic inflammatory condition will be discussed, considering short-term variabilities and long-term variabilities in FHR.