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OBSTETRIC ANESTHESIA

The Effects of S(+)-Ketamine and Racemic Ketamine on Uterine Blood Flow in Chronically Instrumented Pregnant Sheep

Danja Strümper, MD^*,, Wiebke Gogarten, MD^*, Marcel E. Durieux, MD PhD^*,,, Kristian Hartleb, MS^*, Hugo Van Aken, MD PhD^*, and Marco A. E. Marcus, MD PhD^*,

*Department of Anesthesiology and Intensive Care Medicine, University Hospital Münster, Münster, Germany, the Department of Anesthesiology, Pain Therapy and Home Ventilation, University Hospital Maastricht, Maastricht, The Netherlands, and the Department of Anesthesiology, University of Virginia Health Sciences Center, Charlottesville, Virginia

Address correspondence and reprint requests to Danja Strümper, MD, Department of Anesthesiology and Intensive Care Medicine, University Hospital Münster, Albert-Schweitzer-Str. 33, 48153 Münster, Germany. Address email to struemper{at}anit.uni-muenster.de

Ketamine could be a useful maternal analgesic in obstetric surgery, as it might avoid the need for opioid administration and associated side effects in the newborn. Racemic ketamine passes the placental barrier and has oxytocin-like properties but does not seem to affect uterine blood flow (UBF). S(+)-ketamine was recently approved for clinical use, but its effects on UBF have not been evaluated. Therefore, we studied the effects of S(+)-ketamine on maternal and fetal hemodynamic variables. Equianalgesic doses of S(+)-ketamine (10 mg · kg^-1 · h^-1) or racemic ketamine (20 mg · kg^-1 · h^-1) were infused in 12 chronically instrumented pregnant sheep. Maternal and fetal vital signs, blood gases, and UBF were recorded over 120 min. Neither compound affected uterine perfusion or maternal and fetal hemodynamics. Whereas racemic ketamine increased maternal (+19%) and fetal (+11%) PCO₂ significantly, S(+)-ketamine was without effect. However, both compounds significantly decreased maternal (racemic, -0.05; S(+), -0.03) and fetal (racemic, -0.06; S(+), -0.02) pH. The effects of racemic ketamine and S(+)-ketamine on uterine perfusion are similar, and because of its limited effect on hemodynamics and respiration, S(+)-ketamine might therefore be of interest as an analgesic in the obstetric setting.

IMPLICATIONS: The effects of S(+)-ketamine on uterine perfusion and maternal/fetal hemodynamics are similar to those of the racemic mixture in chronically instrumented pregnant sheep. A decreased effect of S(+)-ketamine, as compared with the racemic mixture, on maternal and fetal PCO₂ levels was noted.