Cardiovascular status during ketamine anesthesia in the fetal lamb.

To determine the effects of maternal ketamine anesthesia on fetal hemodynamic and cardiac function, a study was carried out on 8 chronically catheterized fetal lambs. Ketamine was administered intravenously to the mother every 15 min during 1 h. The fetal PO2 and pH remained within physiological limits whereas the PCO2 decreased from 44.35 +/- 1.36 to 37.32 +/- 4.75 Torr (p less than 0.05). The following changes of the fetal heart systolic time intervals were observed: a progressive lengthening of the preejection period (PEP) (from 52 +/- 10 to 63 +/- 11 ms, p less than 0.01), a shortening of the ejection time (ET) and a significant increase of the PEP/ET ratio (from 0.32 +/- 0.04 to 0.47 +/- 0.01, p less than 0.01). The two components of PEP, electromechanical delay and the isovolumetric contraction time were both prolonged. A progressive rise of fetal systolic and diastolic pressures was also noted (p less than 0.01). Fetal heart rate increased (145 +/- 33 to 190 +/- 28 beats/min, p less than 0.01) and cardiac beat-to-beat variability decreased (from 0.028 to 0.009, p less than 0.01) during the ketamine anesthesia. This study demonstrates that maternal anesthesia with ketamine can alter indices of fetal myocardial function and other cardiac parameters used in fetal and neonatal monitoring, without affecting tissular oxygenation.