Fluid Management in Obstetric Patients

Abstract

In pregnancy, hemodynamic and cardiovascular changes occur that prevent blood loss during delivery. In fact, there is an increase in blood volume, during the first trimester [1]. The volume of blood continues to expand rapidly in the second trimester before reaching a plateau in the last trimester. At the same time, the increase in Red Blood Cell (RBC) mass occurs more slowly, leading to a relative anemia and hemodilution [2], with the latter peaking by 30-32 weeks of gestation. Dilutional anemia is therefore common, especially between 28 and 34 weeks gestation, when hemoglobin concentrations are lowest. The accretion in RBC mass results in an 18-25% increase in the first months of pregnancy, followed by a drop after childbirth due to hemorrhage [3][4][5]. The increase in red cell volume provides for the extra oxygen demands of the mother and fetus. The lower end of the normal range for hemoglobin in pregnancy is 11-12 g/dL. These physiological responses have considerable advantages during pregnancy: improved placental perfusion, decreased risk of thrombosis and an adequate blood supply despite the bleeding that occurs with childbirth [6][7][8].The White Blood Cell (WBC) count increases in pregnancy beginning in the first trimester, as a result of selective marrow erythropoiesis. This causes a left shift, with granulocytosis and more immature white cells in the circulation. The normal WBC count for pregnancy is 5000-12,000 WBC/mm 3 , although values as high as 15,000 WBC/mm 3 are not uncommon [9].

Volume Replacement Following Severe Postpartum Hemorrhage

“…Women may lose up to 20% to 25% of their blood volume before displaying symptoms of hypovolemia (Table ), and clinical symptoms of hypovolemia follow a predictable sequence (Table ), although the speed of the blood loss, the woman's original hematocrit, the extent of her blood volume expansion, and her hydration status will affect the individual response. The severe loss of blood leads to inadequate tissue oxygenation, a release of epinephrine and norepinephrine, and increased vasoconstriction . This catecholamine response increases the heart rate, vascular tone, and myocardial contractility to compensate for the decreased volume …”

“…To reverse hypovolemia through fluid volume expansion during or following a PPH, rapid intravenous infusion of a crystalloid fluid such as Lactated Ringer's solution or 0.9% normal saline, at a volume approximately 3 times the estimated blood loss, has been recommended . Crystalloids are effective in restoring volume; however, they contribute to hemodilution and decreased oxygen‐carrying capacity and are not effective in preventing or correcting a coagulopathy.…”

“…In the past, volume replacement with crystalloid fluid was followed by a transfusion of packed red blood cells (PRBCs) . Other blood products were used only when laboratory values suggest the presence of a coagulopathy because neither crystalloid fluid nor PRBCs prevent or correct coagulopathy .…”