MS is commonly used in neonatal and pediatric intensive care patients for analgesia and sedation. MS has been shown to attenuate and/or abolish metabolic and endocrine responses to pain and stress. The systemic and cerebrovascular effects of continuous infusion of therapeutic doses of MS was investigated in 1-3 day old newborn piglets post-surgical instrumentation. The study piglets were given 100μg/kg MS over 5 minutes followed by a continuous infusion of MS at 100μg/kg/hr for 4 hours. The control animals received equivalent volume bolus and infusion of 5% dextrose. Blood samples from the sagittal sinus vein and femoral artery were collected at baseline(0), at 0.5, 1, 2, 3, and 4 hours of infusion, and for 2 hours post infusion, for the determination of pH and respiratory gases. Hemodynamic parameters were recorded at the same time intervals. Compared to baseline (BL), the study piglets had significantly higher respiratory rates(p<0.05-p<0.01) during the MS infusion and 2 hours post infusion. They also had significantly higher(p<0.05-p<0.01) systemic mean arterial blood pressure during and post infusion. Compared to control animals, the MS group exhibited significantly lower (p<0.05-p<0.01) fractional oxygen extraction [C(a-v)O2/CaO2] by the brain while systemic PaO2 and O2 content (CaO2) remained unchanged from BL and compared the control group. In the MS group, mean sagittal sinus vein BP increased significantly (p<0.05-p<0.01) compared to BL and to the control group during, and at 1 hour post infusion. Although sagittal sinus vein PO2 remained unchanged from the BL in both MS and control groups, sagittal sinus vein PO2 was significantly higher(p<0.05-p<0.01) in the MS group during and post infusion compared to the control group. This study shows that continuous infusion of therapeutic doses of MS in the newborn piglet has both hemodynamic and metabolic effects. These effects may be due to increased vascular resistance and possible changes in brain blood flow and metabolism.
