Amniotic fluid embolism: analysis of the national registry

[Evaluation of the blood quality collected by cell-saver during cesarean section]

OBJECTIVE

To determine the quality of blood salvaged and processed during Caesarean section with a cell-saver.

STUDY DESIGN

Laboratory study.

PATIENTS

The study included 20 patients of ASA physical class 1 or 2 undergoing a scheduled Caesarean section.

METHODS

A separate suction device was used from the beginning surgery until the delivery of the fetus, to remove most of the amniotic fluid coming from the surgical field. Thereafter using an Haemolite 2Plus (Haemonetics), the blood was separated and washed with 2 L of normal saline solution. Blood quality was assessed through detection of fetal cells and measuring out of alpha-fetal-protein, tissue factor. A Kleihauer test was also performed.

RESULTS

Cell-saver processing removed most of alpha-fetal-protein and tissue factor while fetal cells were rarely seen. The Kleihauer test could not be performed because of haemolized blood samples. However, the results were very heterogeneous and after washing some salvaged units contained very high concentrations of alpha-fetal-protein or tissue factor.

CONCLUSIONS

These preliminary results show that intra-operative autologous transfusion is not fully safe during Caesarean sections. In addition, there is an immunological risk if a significant part of fetal red blood cells are reinfused into maternal circulation. Therefore, additional studies are needed to better assess this risk.

Acute respiratory failure in pregnancy. An analysis of 19 cases

We studied 19 peripartum patients with acute respiratory failure associated with pregnancy. Although it is an uncommon event, noncardiogenic pulmonary edema is the most common cause of respiratory failure in the peripartum period. This acute lung injury syndrome was observed to be associated with a variety of complications of pregnancy including premature labor, the use of tocolytics, infection, hypertension, leukoagglutinin reactions, aspiration, abruptio placentae, and amniotic fluid embolism. From 1989 through 1992 there were 10,852 deliveries and 19 patients with noncardiogenic pulmonary edema at our institution. Analyzing these cases has led us to favor the hypothesis that the respiratory failure associated with the various complications of pregnancy primarily represents the fatal and nonfatal cases of amniotic fluid embolism that Steiner and Lushbaugh initially believed undoubtedly to exist. Moreover, we suggest, as have others, that the nonspecific symptom complex of inflammation, coagulopathy, and cardiopulmonary failure represents the release of soluble mediators into the maternal circulation. It is not clear what the predominant mediator is, but we have focused on platelet activating factor. It is also not established whether the mediator(s) is of amniotic fluid origin or a result of maternal anaphylactoid-type of response to a fetal or amnioplacental antigen. In conclusion, monitoring maternal oxygenation either directly or indirectly by oximetry should be considered routinely in the peripartum period, especially in complicated pregnancies, to detect at an early stage "asymptomatic" or preclinical cases of noncardiogenic pulmonary edema, in hopes of then modifying management to prevent their progression.

The ability of the Haemonetics 4 Cell Saver System to remove tissue factor from blood contaminated with amniotic fluid

The purpose of this study was to determine whether functionally active tissue factor could be removed from blood contaminated with amniotic fluid (AF) after processing through a Haemonetics 4 Cell Saver System (Haemonetics Corporation, Braintree, MA). In Phase I, AF was collected from 29 women undergoing cesarean section. Nine experiments were performed. Forty-milliliter aliquots of pooled AF were mixed with 125 mL of packed red blood cells and processed in the Cell Saver. In Phase II, all the blood and AF lost at cesarean section was collected and processed through the Cell Saver. Pre- and postwash specimens were collected and analyzed for total tissue factor concentration and the concentration of functionally active tissue factor. In Phase I, total tissue factor concentration was reduced by 89%, and the concentration of active tissue factor was reduced to 0 after processing. In Phase II, no tissue factor was detected after processing through the Cell Saver. We have demonstrated the ability of the Haemonetics 4 Cell Saver System to remove tissue factor activity from blood contaminated with AF.

IMPLICATIONS

Hemorrhage after childbirth may require massive transfusion. If the patient's own blood can be collected and given back to the patient, this may avoid the use of regular banked blood. Amniotic fluid, which may mix with blood lost after delivery, contains tissue factor, a substance that may activate the coagulation system and cause further bleeding. The authors found that the Haemonetics 4 Cell Saver System (Haemonetics Corporation, Braintree, MA), which collects and washes blood, can remove tissue factor from blood contaminated with amniotic fluid.

Amniotic fluid embolism causing severe left ventricular dysfunction and death: case report and review of the literature

Hemodynamic instability in amniotic fluid embolism has previously been demonstrated only by right heart catheterization. We present detailed documentation obtained by echocardiography and cardiac catheterization of a 35-year-old woman who developed amniotic fluid embolism and died from severe left ventricular dysfunction and wide QRS complex tachycardia despite intensive medical therapy (inotropes) and mechanical (intraaortic balloon pump) support.

Amniotic fluid embolism, anaphylaxis, and tryptase

It has been recently suggested that amniotic fluid embolism is an anaphylactic reaction to fetal antigens. This hypothesis can be readily tested by obtaining serum tryptase levels within a few hours of the appearance of symptoms in affected patients.

Clinical role of amnio-infusion

Amnio-infusion is a simple, yet beneficial, technique for improving pregnancy outcome. Antepartum amnio-infusion has been shown to be beneficial as an aid to enhancing ultrasonographic fetal imaging and may have a role in the administration of antibiotic therapy or the prevention of pulmonary hypoplasia. There are considerable data to support the intrapartum use of amnio-infusion in the presence of oligohydramnios, variable decelerations or meconium. Numerous prospective clinical trials have shown a significant benefit of amnio-infusion in reducing the rate of emergency caesarean section for fetal distress and complications related to meconium when used for these indications. Additional research is needed to clarify further its intrapartum role in patients with premature rupture of membranes or chorio-amnionitis.

Amniotic fluid embolism

AFE, although rare, remains a significant cause of maternal mortality. Even with improvements in supportive care, the prognosis remains poor for mother and fetus. The guidelines presented may help the physician to recognize this condition when it occurs and give some direction for therapy.

Amnioinfusion

Abnormal amniotic fluid volume may be both the result and the cause of complications at various stages of pregnancy. This review focuses on evidence from randomised trials of the effectiveness of amnioinfusion. Attempts to prevent the development of pulmonary hypoplasia by means of transabdominal amnioinfusion to correct severe oligohydramnios in the middle trimester of pregnancy have not been evaluated by randomised trials. Long-term transcervical amnioinfusion for prelabour rupture of the membranes has shown promising results in prospective studies, but has also not been subjected to randomised evaluation. Transcervical amnioinfusion during labour is a relatively simple procedure. Normal saline is infused through an intrauterine catheter, preferably one with a catheter-tip pressure transducer. Once an adequate volume of amniotic fluid has been achieved, it is maintained by means of a slow continuous infusion or repeated bolus infusions. Amnioinfusion has been used to prevent or treat fetal heart rate (FHR) decelerations thought to be due to oligohydramnios. In several rather small randomised trials, amnioinfusion has been associated with a reduction in FHR decelerations, caesarean sections, low Apgar scores, low umbilical arterial pH values and postpartum endometritis. Amnioinfusion has also been used to dilute thick meconium-staining of the amniotic fluid. In trials for this indication, amnioinfusion has been associated with similar benefits, and in addition a reduction in meconium presence below the vocal cords, meconium aspiration syndrome and the need for neonatal ventilation. Larger trials are needed to determine whether amnioinfusion is associated with an effect on perinatal mortality, and whether complications such as umbilical cord prolapse are increased.