Prediction of fetoplacental blood volume in isoimmunized pregnancy

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on Fetal Blood Components and Binding Proteins

BACKGROUND

Fetal blood and plasma volume and binding components are critical parameters in a fetal physiologically based pharmacokinetic model. To date, a comprehensive review of their changes during fetal development has not been reported.

OBJECTIVE

The objective of this work was to collate and analyze physiological information on fetal blood and plasma volume and binding component data during development and to provide a mathematical description of these parameters that can be integrated within a fetal physiologically based pharmacokinetic model.

METHODS

A comprehensive literature search was conducted on fetal blood and plasma volume and binding component parameters and their changes during growth from apparently healthy fetuses from uncomplicated pregnancies. Collated data were assessed, integrated, and analyzed to establish continuous mathematical functions describing their growth trends with fetal age and weight.

RESULTS

Data were available from 14 studies for blood, ten studies for hematocrit, 12 studies for albumin, and four studies for alpha-1-acid glycoprotein, while plasma and red blood cell volumes were described based on blood and hematocrit data. Fetal physiologically based pharmacokinetic parameters, including blood, plasma and red blood cell volumes, hematocrit, serum albumin, and acid glycoprotein were quantified as a function of fetal age and weight. Variability around the mean parameters at different fetal ages was also investigated. The growth of each of these parameters was different (with respect to direction and monotonicity).

CONCLUSIONS

Despite the limitations identified in the availability of some values, the collected data presented in this article provide a useful resource for fetal physiologically based pharmacokinetic modeling. Potential applications include predicting xenobiotic exposure and risk assessment in the fetus following maternally administered drugs or unintended exposure to environmental toxicants.

Prevention and management of RhD isoimmunization

An Rh-negative woman is at risk for developing Rh isoimmunization upon exposure to RhD antigens from her Rh-positive baby through fetal-maternal hemorrhage. The incidence of Rh isoimmunization and fetal hemolytic disease has decreased substantially since Rh immune globulin was introduced in 1968. When RhD sensitization does occur, careful follow-up of these mothers and judicious intervention can result in good outcomes for most pregnancies. Both Doppler assessment of middle cerebral artery peak systolic velocity and spectral analysis of amniotic fluid at 450 nm (DeltaOD 450) are useful in the diagnosis and management of fetal anemia.

Anesthesia for fetal surgery

Fetal surgery is a rapidly growing and evolving area. Fetal surgery is based on years of animal and clinical research. In contrast, anesthesia techniques for fetal surgery are based on clinical experience. The techniques that have emerged are safe for mother and fetus. In this review, the authors describe current techniques for anesthetic management of fetal surgery patients. General anesthesia is the primary technique used for hysterotomy based surgical correction of midgestation fetuses and ex utero interpartum corrections of end-gestation fetuses. Epidural analgesia, with general anesthesia as back-up, is the primary technique used for fetoscopic cases in which anesthetic care is required. Because of the myriad of anesthetic and surgical issues these cases generate, it is essential to have good communication and cooperation between surgeons and anesthesiologists from the preoperative period to the postoperative period. This will allow development of a cohesive anesthetic and surgical plan that can be used for the safe perioperative management of the fetal surgery patient.

A new method to determine the feto-placental volume based on dilution of fetal haemoglobin and an estimation of plasma fluid loss after intrauterine intravascular transfusion

OBJECTIVES

(1) To calculate the feto-placental volume (FPV), using the haematocrit (Ht) values and the percentages of fetal haemoglobin (HbF), before and after red blood cell transfusion. (2) To estimate the transfusion-induced loss of plasma fluid.

DESIGN

Retrospective analysis of data of 42 anaemic fetuses at the first transfusion [gestational age (GA) 19-36 weeks].

SETTING

Department of Obstetrics, Leiden University Medical Centre, The Netherlands.

SAMPLE

Fifteen hydropic and 27 non-hydropic fetuses.

METHODS

Donor blood volume (V(donor)) and Ht (Ht(donor)), fetal pre- and post-transfusion Ht values (Ht(initial), Htfinal) and percentages of HbF (HbF(initial) and HbF(final)) were used to calculate the FPV. The total red cell volume after transfusion (RCV(final)) and Ht(final) were used to estimate the plasma fluid loss.

MAIN OUTCOME MEASURES

Feto-placental blood volume and loss of plasma fluid.

RESULTS

The equations that use Htfinal over-estimate the FPV when the formula does not account for the difference between donor and post-transfusion Ht (FPV(Ht) = 21.36 * GA, - 390; r = 0.89). FPV is underestimated (FPV(Ht) = 9.90 * GA - 172; r = 0.84) when the blood volume increases with a volume less than the added donor blood volume. The calculation of FPV, using HbF percentages and the initial fetal RCV, is independent of volume changes (FPVHbF = 15.10 * GA - 279; r = 0.85). Comparing RCV(final) and Ht(final) values showed that 31.1 +/- 14.5% of the transfused volume was lost. Results of the hydropic fetuses did not differ from those of the non-hydropic fetuses.

CONCLUSIONS

FPV values based on Ht values are less reliable than those based on RCV and HbF findings. When, for practical reasons, Ht values have to be used, we propose an adapted equation for the calculation of the necessary volume of donor blood: V(donor) = FPV(HbF) * (Ht(final) - Ht(initial) / (Ht(donor) - 0.70 * Ht(final)).

Fetal transfusion therapy

Rapid advances are occurring in the diagnosis and treatment of the fetus with a red blood cell or platelet cytopenia. Noninvasive methods of monitoring the alloimmunized pregnancy, invasive methods such as amniocentesis and cordocentesis, and intrauterine transfusion therapy of both red cells and platelets, are being further refined to allow the prompt recognition and treatment of fetal cytopenias. Specialized centers have now accrued a large experience in the management of the fetus severely affected by alloimmunization. Advances in ultrasound, blood banking techniques, and genetic engineering technology have spurred the most recent advances. The indications for diagnosis, timing and frequency of invasive procedures for treatment, and technical considerations regarding preparation of blood products and volume of transfusion, are outlined in this review. Polymerase chain reaction (PCR) determination of fetal Rh(D) genotype by chorionic villus sampling or amniocentesis in the first or second trimesters is a recent clinically useful advance. The advent of hematopoietic stem cell transplantation and the potential for gene therapy are exciting advances in the treatment and prevention of hematopoietic diseases, including, but not limited, to the fetal cytopenias.

Acute fetal hemodynamic alterations after intrauterine transfusion for treatment of severe red blood cell alloimmunization

One of the compensatory hemodynamic mechanisms seen in the anemic human fetus is an increased cardiac output. With Doppler techniques, cardiac output was measured in 21 fetuses before and immediately after 38 intrauterine transfusions for severe red cell alloimmunization. Umbilical venous pressures were measured before and after transfusion; amniotic fluid pressure was also quantitated. After subtraction of amniotic pressure, umbilical venous pressure increased by 1.7 +/- 2.8 mm Hg (p less than 0.01). Left and right ventricular output declined by 19% and 22%, respectively (p less than 0.001). Four factors are known to affect cardiac output: heart rate, cardiac contractility, preload, and afterload. Fetal heart rate and mean acceleration, a measure of myocardial contractility, were unchanged after transfusion. A calculated mean increase in the fetoplacental volume of 18% in conjunction with an increase in umbilical venous pressure would indicate that cardiac preload was increased. We propose that intravascular intrauterine transfusion leads to an increased cardiac afterload, possibly by increasing blood viscosity. The fetal heart responds to the increased afterload by a decrease in stroke volume, leading to a fall in cardiac output.