The Effect of Maternal Catecholamines on the Caliber of Gravid Uterine Microvessels

Abstract

taken for S a O 2 to fall from 90% to 40% was 35 seconds (range, 32 to 43) in pregnancy and 45 seconds (range, 38 to 56) in nonpregnancy. The relationship between starting P E O 2 and time to fall to <90% S a O 2 was linear, which indicates apnea tolerance is directly proportional to the starting P E O 2 . Increasing time spent in preoxygenating subjects led to a plateau effect, with less benefit on tolerance to apnea due to using oxygen.Apnea tolerance is markedly reduced during pregnancy with a ceiling effect that the time spent preoxygenating has on apnea tolerance. Two minutes of tidal breathing of 100% oxygen can provide 3.5 to 6 minutes of time before SaO 2 reaches <90% in a nonlaboring, full-term normal pregnancy. Addition preoxygenation probably will provide only 12 seconds longer apnea time.

Intrapartum interventions that affect maternal and neonatal outcomes for vaginal birth after cesarean section

“…Labor pain causes sympathetic hyperactivity, and increases plasma epinephrine and norepinephrine levels. 27 Epinephrine decreases uterine contractility, while norepinephrine increases uterine contractility. Severe pain, such as that with induced labor, may cause a surge in epinephrine that cannot be offset by an equal increase in norepinephrine, and may precipitate uncoordinated uterine contractions and dystocia.…”

Modern techniques to optimize neuraxial labor analgesia

“…The CSE technique does, however, increase the incidence of fetal bradycardia and heart rate abnormalities immediately following block placement compared to epidural alone (relative risk [RR] = 1.3) [9]. The proposed mechanism for fetal bradycardia is a sudden decrease in circulating epinephrine after rapid onset of analgesia with CSE, resulting in uterine hypertonus and transiently diminished uteroplacental flow [10,11]. The risk of fetal bradycardia is increased in advanced labor with high pain levels [12], and may also increase with higher doses of intrathecal opioids [13].…”

The Lesson

“…Scant information is available regarding the potential impact of resuscitation drugs on the fetus; however, the vasoconstrictive effects of high doses of α-adrenergic agents on uteroplacental circulation have been demonstrated in animal studies. 10 Use of these drugs in resuscitation is essential because rapid restoration of maternal circulation offers the best chance for survival for both mother and fetus.…”