Critical Care Obstetrics part 6 provides expert clinical guidance throughout on how you can maximize the chances of your patient and her baby surviving trauma. In this stimulating text, internationally recognized experts guide you through the most challenging situations you as an obstetrician are likely to face, enabling you to skillfully:Recognize conditions early-on which might prove life threatening, Implement immediate life-saving treatments in emergency situations, Maximize the survival prospects of both the mother and her fetus | Pregnancy-Induced Physiologic Alterations may be necessary to achieve optimal birthweight. Indeed interventions designed to interfere with this increase in blood pressure in the latter half of pregnancy such as antihypertensive medications have repeatedly been shown to be associated with low birthweight 109 110 . The mechanism by which low blood pressure leads to stillbirth is not well understood. One possible explanation is that in women with a low baseline blood pressure a further drop in systemic pressure such as may occur when a woman rolls over onto her back during sleep with resultant supine hypotension may result in a drop in placental perfusion below a critical threshold resulting in fetal demise. Central hemodynamic changes associated with pregnancy To establish normal values for central hemodynamics Clark and colleagues 41 interrogated the maternal circulation by invasive hemodynamic monitoring. Ten primiparous women underwent right heart catheterization during late pregnancy 35-38 weeks and again at 11-13 weeks postpartum Table . When compared with postpartum values late pregnancy was associated with a significant increase in heart rate 17 stroke volume 23 and cardiac output 43 as measured in the left lateral recumbent position. Significant decreases were noted in SVR -21 pulmonary vascular resistance -34 serum colloid osmotic pressure -14 and the colloid osmotic pressure to pulmonary capillary wedge pressure gradient -28 . No significant changes were found in the pulmonary capillary wedge or central venous pressures which confirmed previous studies 40 . Hemodynamic changes during l abor Repetitive and forceful uterine contractions but not Braxton-Hicks contractions have a significant effect on the cardiovascular system during labor. Each uterine contraction in labor expresses 300-500 mL of blood back into the systemic circulation 111 112 . Moreover angiographic studies have shown that the change in shape of the uterus during contractions leads to .
