Amniotic fluid embolism: analysis of the national registry

Amniotic fluid embolism

PURPOSE OF REVIEW

To review the recent literature on amniotic fluid embolism and how it may influence the clinical management and further study of the condition. Morbidity and mortality from amniotic fluid embolism in the international context will be described, given the recent Confidential Enquiries into Maternal Deaths in the United Kingdom and other studies. With this rare condition we need to look for clues as to how to facilitate diagnosis and improve outcomes.

RECENT FINDINGS

Amniotic fluid embolism continues to be a leading cause of maternal death. There has been a decrease in mortality from amniotic fluid embolism in the UK from 5.1 to 3.7 per million maternities, but it is still the fifth greatest cause of direct maternal death. In France, 13% of deaths are caused by amniotic fluid embolism, the third highest cause. In Singapore, a study of postmortems found that over 30% of direct maternal deaths were caused by amniotic fluid embolism, the most common cause. Case-specific mortality may not be as high as previously thought. The early data from the UK Register of cases show only 16% mortality, although there is significant maternal and neonatal morbidity. Early diagnosis may be the best way to improve outcomes. Case reports suggest that plasma exchange techniques may be helpful after initial resuscitation.

SUMMARY

With a rare condition additions to the literature are sparse. Early consideration of the diagnosis after prompt resuscitation is needed. Further data are needed to advance beyond this.

Planning for hemorrhage. Steps an anesthesiologist can take to limit and treat hemorrhage in the obstetric patient

Obstetric hemorrhage continues to be a significant cause of maternal mortality and morbidity. Blood transfusion in such circumstances may be life saving but involves exposing the patient to additional risks. Limiting blood transfusion and using autologous blood when possible may reduce some of these risks. This article outlines the techniques that may be used to limit and more effectively treat hemorrhage in the obstetric patient, with particular attention paid to reducing the use of allogeneic blood transfusion.

Temporal and demographic trends in cerebral palsy--fact and fiction

The rate of cerebral palsy has not decreased in developed countries over the past 30 years, despite the widespread use of electronic fetal heart rate monitoring and a 5-fold increase in the cesarean delivery rate over the same period of time. However, neonatal survival has improved during these decades. These observations have lead to the hypothesis that increased survival of premature, neurologically impaired infants may have masked an actual reduction in cerebral palsy among term infants as a result of the use of electronic monitoring and the avoidance of intrapartum asphyxia. A review of the medical literature, as well as a demographic analysis of term and preterm birth rates in the United States, refutes this hypothesis on four grounds. First, cerebral palsy prevalence has been separately analyzed in term infants and shows no change over 30 years. Second, the prevalence of cerebral palsy is the same or lower in underdeveloped countries than in developed nations; in the former, the availability of emergency cesarean delivery based on electronic monitor data is limited or absent. Third, the increase in prevalence of cerebral palsy among low-birth-weight infants and the increase in cesarean sections based on presumed fetal distress were not simultaneous events-the former preceded the latter by a decade. Improved neonatal survival since the 1980s has been associated with a stable or decreasing rate of neurologic impairment and thus could not have obscured improvement from reduced term asphyxia. Finally, compared with the number of infants born by cesarean section for fetal distress, there are simply not enough infants born in the most vulnerable weight groups to make any impact on even a minimal improvement of outcome in the group delivered by cesarean section for presumed fetal distress. Except in rare instances, cerebral palsy is a developmental event that is unpreventable given our current state of technology.

Embolism during pregnancy: thrombus, air, and amniotic fluid

Pulmonary embolism is the primary cause of acute respiratory decompensation during pregnancy. Regardless of the nature of the embolism, a high index of suspicion, early diagnosis, and aggressive resuscitation need to be instituted to achieve a successful maternal and fetal outcome. Several clinical characteristics will assist practitioners to distinguish among the different forms of embolism and to institute specific measures of treatment.

[Amniotic fluid embolism during labor]

Amniotic fluid embolism is an unpredictable but dramatical complication of pregnancy that occurs when amniotic fluid enter into the maternal circulation. The classical clinical feature is acute respiratory distress, circulatory distress, seizures and coagulopathy. However there is no routine laboratory diagnosis, so that is a diagnosis of exclusion. We report here the case of a patient, on labor with an epidural analgesia who suddenly suffered from seizures, circulatory arrest, and haemorrhage. A symptomatic management was instituted and a caesarean section was performed. An haemostatic hysterectomy was required. The patient survived without any sequelae. Neurological outcome of the child is still reserved.

[Amniotic fluid embolism: successful evolution course after uterine arteries embolization]

A 28-year-old woman, G3P3, who was otherwise healthy and had taken no medication and had no known allergy, was admitted to our hospital for delivery after a normal pregnancy. An epidural catheter was inserted for analgesia and labour was induced with oxytocin. Two hours later, she suffered a sudden cardiac arrest. She was immediately treated and, since a normal cardiac rhythm and a blood pressure of 90 mmHg has been obtained 30 minutes later, a 3750 g child was delivered by caesarean section. Soon after delivery, a life-threatening uterine haemorrhage appeared, due to DIC. Evolution was favourable, after bilateral uterine arteries embolization had been performed. The diagnosis of amniotic fluid embolism was established by the clinical course, the absence of local cause and the presence of a large number of amniotic cells in the mother's peripheral blood. Tryptase blood concentration was normal in the mother's blood.

Clinical experience with cell salvage in obstetrics: 4 cases from one UK centre

We present 4 cases in which cell salvaged blood was used in maternity patients, including three caesarean sections and one post-partum haemorrhage. All patients were monitored for a minimum of 24 h on either a general Intensive Care Unit (ICU) or specialised obstetric High Dependency Unit (HDU). Postoperative complications are discussed, with particular emphasis on whether the transfusion of cell salvaged blood was a contributory factor. Cell salvage in obstetrics is being used in a haphazard and individual manner and our only present outcome indicators are case reports. We consider the argument for and against cell salvage in obstetrics, and suggest guidelines to reflect current best practice in the use of the machine and filters.

A fatal case of amniotic fluid embolism with elevation of serum mast cell tryptase

A case of a 40-year-old female who died of amniotic fluid embolism is presented. This case showed typical histological findings of this syndrome. Postmortem serum of this case showed an elevated tryptase level (67.2ng/ml, normal levels <10ng/ml). Tryptase is a neutral protease of mast cells, and an important indicator of mast cell activation and degranulation. Thus, mast cell activation, a central feature of anaphylaxis, may have been involved in the pathogenetic mechanism of this case.

Fatal amniotic fluid embolism diagnosed histologically

Although the mortality of amniotic fluid embolism remains very high, there are more and more reports of patients surviving after prompt and aggressive therapy. However its pathogenesis is controversial, and, in some cases, an anaphylactic reaction to the amniotic fluid rather than the hemodynamic changes following mechanical obstruction by an embolus has been proposed as the underlying pathophysiological mechanism. In this paper we describe a case of amniotic fluid embolism with florid clinical features and a difficult and delayed diagnosis. On autopsy, clear-cut histological changes of amniotic fluid embolism were found.

Monitoring for suspected pulmonary embolism

It is fortunate that serious embolic phenomena are uncommon because, with the exception of neurosurgery in the sitting position and cardiac surgery, thoracic echocardiography and the precordial Doppler device, the most sensitive indicators of embolism, are seldom used. Vigilance is required of the anesthesiologist to recognize the rapid fall in end-tidal PCO2, the usual first indicator of a clinically significant PE. Any sudden deterioration in the patient's vital signs should include embolism in the differential diagnosis, particularly during procedures that carry a high risk of the complication.

Disseminated intravascular coagulation

Healthy pregnancy is accompanied by changes in the haemostatic system which convert it into a hypercoagulable state vulnerable to a spectrum of disorders ranging from venous thromboembolism to disseminated intravascular coagulation (DIC). This latter is always a secondary phenomenon triggered by specific disorders such as abruptio placentae and amniotic fluid embolism due to release of thromboplastin intravascularly or endothelial damage resulting from pre-eclampsia and sepsis. In modern obstetric practice the most common cause is haemorrhagic shock with delay in resuscitation leading to endothelial damage. The initial management of massive obstetric haemorrhage is the same whether associated with coagulopathy initially or not. Low-grade DIC, associated with pre-eclampsia, is monitored haematologically by serial platelet counts and serum fibrin degradation products (FDPs). Supportive measures and removal of the triggering mechanism are the key to successful management. Outcome depends primarily on our ability to deal with the trigger and not on direct attempts to correct the coagulation deficit.

Effect of heparin on activated partial thromboplastin time in patients undergoing gynecologic or obstetric surgery

The exaggerated prolongation of the activated partial thromboplastin time (APTT) by heparin prophylaxis for postoperative thromboembolism may cause bleeding complications. We examined the effects of various doses of unfractionated heparin on the APTT in patients who underwent a gynecologic or obstetric operation. A total of 68 patients who underwent a gynecologic operation (n = 47) or a cesarean section (n = 21) with risk factors for thromboembolism received a continuous intravenous infusion of unfractionated heparin (110-285 IU/kg/day) after surgery until the patient was mobilized the next day. A group of 61 postoperative patients who did not receive heparin served as controls. The APTT was measured in these 129 patients preoperatively and on postoperative day 1. A clinical deep vein thrombosis occurred in only 1 patient, who was in the control group. No bleeding complications occurred in any patient. The percent change in the APTT was significantly correlated with the dose of heparin administered (p < 0.001). Compared with the control group, the mean APTT was not prolonged in the patients who received heparin at 110-149 IU/kg/day. It was prolonged significantly in the patients who received heparin at greater than 150 IU/kg/day. An exaggerated prolongation of the APTT, defined as an APTT greater than 150% of the preoperative value, was found in 0 of 32 patients in the 110-149 IU/kg/day group, 1 of 28 patients (3.6%) in the 150-199 IU/kg/day group and 2 of 8 patients (25%) in the 200-285 IU/kg/day group. The continuous postoperative administration of intravenous heparin at less than 200 IU/kg/day does not result in an exaggerated prolongation of the APTT.

Tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in amniotic fluid and blood plasma: implications for the mechanism of amniotic fluid embolism

Tissue factor (TF) is known to be present in a high concentration in amniotic fluid. The main question of this study is whether tissue factor pathway inhibitor (TFPI), a natural inhibitor of TF, is present in amniotic fluid. The study group consisted of 28 women with normal pregnancy course, and at the first stage of termed labour. Fifteen non-pregnant women were the control group. TF and TFPI were studied by an immunoenzymatic method (ELISA). The level of TFPI in amniotic fluid was 38.7% of that in blood plasma (16.81+/-5.34ng/ml versus 43.41+/-18.70ng/ml, P<0.001), while the level of TF in amniotic fluid was 44.8 times higher than in blood plasma (9995.93+/-8533.11pg/ml versus 252.66+/-28.84pg/ml, P<0.001).

CONCLUSIONS

(i) It was found, for the first time, that amniotic fluid contains TFPI (ii) It is reasonable to assume that the intrusion of amniotic fluid into the blood-stream may influence the plasmatic TFPI-TF equilibrium resulting in intravascular blood coagulation.

Amniotic fluid embolus: a review of the research literature

The diagnosis of Amniotic Fluid Embolus (AFE) is often missed clinically leading to the incorrect attribution of a major post-partum haemorrhage, which may accompany AFE, to uterine atony. This paper reviews the research on AFE with particular emphasis on the clinical presentation and diagnosis; both before and after death. It begins by dealing with the difficulty of defining AFE due to confusion about the underlying pathophysiological events. As this paper will demonstrate, the theory that AFE is an embolic event is no longer valid. A description of the clinical manifestations is provided so that these can be explained by the contemporary theory of AFE as an 'anaphylactoid' reaction. Finally, the difficulties of diagnosis, particularly laboratory diagnosis, will be discussed. The research indicates that it is not possible to accurately diagnose AFE, either, pre or post mortem, by any currently available laboratory tests. Because of better diagnosis it is now known that AFE in not uncommon and, if it is diagnosed early, a much higher rate of intact survival can be achieved than was previously thought possible.

Amniotic fluid embolus: a review of the literature

PURPOSE

To review the literature since 1979 to determine the natural history, etiology, diagnosis and potential treatment of amniotic fluid embolus (AFE).

SOURCE

English language articles and books published between June 1976 and June 1998 were identified by a computerized medline search using the title or text word amniotic fluid embolus. This same search strategy was repeated and updated to October 1999 by an independent individual using both Medline and Embase. The search was also expanded to include Science Citation Index listing Morgan's 1979 review article. All relevant publications were retrieved and their bibliographies were scanned for additional sources.

PRINCIPAL FINDINGS

Randomized controlled trials are not possible with amniotic fluid emboli. The majority of the literature consists of clinical reports combined with occasional limited reviews. Knowledge obtained from these reports suggests that amniotic fluid emboli present as a spectrum of disease that ranges from a subclinical entity to one that is rapidly fatal. Because cases are sporadic and the diagnosis is often unconfirmed, little progress has been made towards understanding its etiology or defining the risk factors. Present management is empirical and directed towards the maintenance of oxygenation, circulatory support and the correction of coagulopathy.

CONCLUSION

Amniotic fluid embolus continues to be a life-threatening but potentially reversible complication unique to pregnancy. It cannot be predicted nor prevented. Review of the literature reveals that there are no standardized investigational methods or protocols to confirm the diagnosis in suspected cases.

Successful application of extracorporeal membrane oxygenation and intra-aortic balloon counterpulsation as lifesaving therapy for a patient with amniotic fluid embolism

A woman in labor was noted to have amniotic fluid embolism. Extracorporeal membrane oxygenation and intra-aortic balloon counterpulsation were performed post partum, and the vital signs became stable. The ensuing recovery was uneventful. We conclude that extracorporeal membrane oxygenation and intra-aortic balloon counterpulsation should be considered to save the life of a patient with amniotic fluid embolism and left ventricular failure unresponsive to medical therapy.

Amniotic fluid embolism: the UK register

Amniotic fluid embolism is rare but is a significant cause of maternal death. No clear risk factors seem to be identifiable from previous cases. A register has been established in the UK to look at possible therapies.

Administration of autologous fetal membranes: Effects on the coagulation in pregnant mini-pigs

OBJECTIVE: A hallmark of the so-called amniotic fluid embolism is the induction of coagulation defects. Entry of meconium-free autologous amniotic fluid into the circulation, however, is innocuous. Little is known about the true causative agent or agents. The purpose of this study was to assess the effects of homogenized autologous fetal membranes (FM) on the coagulation system in the mini-pig model. DESIGN: Laboratory study. SETTING: University institute animal laboratory. SUBJECTS: Six near-term pregnant, Göttingen-bred mini-pigs. INTERVENTIONS: After induction of general anesthesia, FM were col-lected from all animals by cesarean section. Animals received 2 g FM (shredded and suspended in lactated Ringer's solution) via an ear vein. MEASUREMENTS: Blood samples were taken from a central vein before administration (baseline), immediately after administration, every 10 mins until 90 mins after administration, and every 20 mins until 150 mins after administration. The following parameters were measured: platelets, partial thromboplastin time, prothrombin time index, fibrinogen, factors II, V, VII, VIII, IX, X, XI, antithrombin III, and protein C. The values relative to baseline in the FM group were compared with a historical control group by rank order test. A p <.05 was considered significant. MAIN RESULTS: In the FM group (compared with the control group), platelets were lower; partial thromboplastin time was prolonged; fibrinogen was lower; prothrombin time index was lower (ie, prothrombin time was prolonged); protein C and antithrombin III were lower; and activity levels of factors V and VII were lower. The levels of factors II, VIII, IX, X, and XI showed a trend toward lower activity in the FM group, but the differences were not statistically significant. CONCLUSIONS: FM can activate coagulation in mini-pigs. The laboratory parameter changes seen are typical for disseminated intravascular coagulation. However, the full clinical picture of amniotic fluid embolism and disseminated intravascular coagulation could not be elicited despite the high dose of FM used.

Fetal heart rate observations in the brain-damaged infant

The objective of this study was to describe the fetal heart rate patterns and underlying pathophysiologic changes in the brain-damaged fetus. Fetuses with brain damage from hypoxic ischemic encephalopathy do not manifest uniform fetal heart rate patterns. However, these fetuses do show distinct fetal heart rate patterns that permit categorization based on their admission heart rate, subsequent changes in their baseline rate; and neonatal findings. Based on the observations of infants brain damaged in utero because of hypoxic ischemic encephalopathy, the intrapartum fetal management will depend on the admission fetal heart rate pattern, and the subsequent changes in the baseline rate.

Non-haemorrhagic obstetric shock

The causes of non-haemorrhagic obstetric shock (pulmonary thromboembolism, amniotic fluid embolism, acute uterine inversion and sepsis) are uncommon but responsible for the majority of maternal deaths in the developed world. Clinically suspected pulmonary thromboembolism should be treated initially with heparin and objective testing should be performed. If the diagnosis is confirmed, heparin is usually continued until delivery, following which anticoagulation in the puerperium is achieved with either warfarin or heparin. Amniotic fluid embolism is a rare complication of pregnancy, occurring most commonly during labour. The management of amniotic fluid embolism involves maternal oxygenation, the maintenance of cardiac output and blood pressure, and the management of any associated coagulopathy. Acute uterine inversion arises most commonly following mismanagement of the third stage of labour. The shock in uterine inversion is neurogenic in origin, although there may also be profound haemorrhage. The management of this condition includes maternal resuscitation and replacement of the uterus either manually, surgically or by hydrostatic pressure. Genital tract sepsis remains a significant cause of maternal death, the most common predisposing factor being prolonged rupture of the fetal membranes. The management of septic shock in pregnancy includes resuscitation, identification of the source of infection and alteration of the systemic inflammatory response.

Amniotic fluid embolism: a case report and review

A 41-year old primigravida underwent caesarean section because of foetal distress following prostin induction of labour. Intraoperative coagulopathy, haemorrhage and hypotension necessitated a hysterectomy. Subsequently, she developed respiratory and renal failure, requiring mechanical ventilation and haemodialysis. She made a full recovery. The likely diagnosis was amniotic fluid embolism (AFE), a rare complication of pregnancy with a variable presentation, ranging from cardiac arrest and death through to mild degrees of organ system dysfunction with or without coagulopathy. The differential diagnosis includes pre-eclamptic toxaemia/pregnancy-induced hypertension, anaphylaxis and pulmonary embolism. There is no diagnostic test for AFE; the finding of foetal elements in the maternal circulation is non-specific. Historically, AFE was thought to induce cardiovascular collapse by mechanical obstruction of the pulmonary circulation. It is now thought that a combination of left ventricular dysfunction and acute lung injury occur, with activation of several of the clotting factors. An immunological basis for these effects is postulated. There is no specific therapy and treatment is supportive. The mortality of the condition remains high.

Anaphylaxis during caesarean section in a patient with undiagnosed placenta accreta: it never rains but it pours!

Published guidelines exist for the management and investigation of suspected anaphylactic reactions associated with anaesthesia. We report a woman who had a life-threatening anaphylactic reaction during caesarean section under spinal anaesthesia, complicated by undiagnosed placenta accreta. We discuss the particular problems of the case and the practical difficulties of testing survivors of anaphylaxis: despite following the recommendations, we have been unable to identify the cause.

Amniotic fluid embolism

Amniotic fluid embolism occurs rarely but is one of the leading causes of maternal mortality in the United States. The risk of death associated with this syndrome is 60% to 80% with half of survivors suffering long-term neurologic disability. The pathophysiology of amniotic fluid embolism is poorly understood. A review of the largest case series to date concluded that the physiologic and hematologic manifestations bear a greater resemblance to septic and anaphylactic shock than to any embolic phenomenon. Care of the patient who suffers amniotic fluid embolism is supportive. To date, no therapeutic interventions have been found to improve survival.

Amniotic fluid embolism and isolated disseminated intravascular coagulation

PURPOSE

Disseminated intravascular coagulation (DIC) is a well-known complication of an amniotic fluid embolus. However, clinical experience has shown that, in some patients, clinical hemorrhage may be the initial presentation. Mortality in this subset of patients is high. This report describes a patient with a suspected amniotic fluid embolus who survived and in whom the initial presentation was post partum hemorrhage.

CLINICAL FEATURES

During the post delivery repair of a fourth degree perineal tear a 29 yr old prima gravida was noted to have excessive vaginal bleeding despite a well contracted uterus. Laboratory investigations revealed a decrease in hemoglobin from 126 g x l(-1) to 86 g x l(-1) and a severe disseminated intravascular coagulopathy (PT 27.5 sec, APPT 149 sec, direct fibrinogen < 0.6 g x l(-1), FDP > 640 g x l(-1)). Treatment included massive blood component therapy and, eventually, total abdominal hysterectomy. The patient subsequently recovered without sequelae. In the absence of any other explanation, the coagulopathy was considered to be secondary to amniotic fluid embolus.

CONCLUSION

Amniotic fluid embolus remains an important cause of maternal mortality. Clinical reports, reviews of the literature, and the development of the national registry have all contributed to our understanding of this syndrome. Contrary to earlier beliefs, not all patients present with sudden cardiorespiratory collapse. As the present case illustrates, a less common presentation is the development of an isolated DIC in the peripartum period without antecedent hemodynamic or respiratory instability. Therefore, anesthesiologists must maintain a high index of suspicion for the disorder in order to facilitate early recognition and treatment.

Cell salvage in obstetrics: an evaluation of the ability of cell salvage combined with leucocyte depletion filtration to remove amniotic fluid from operative blood loss at caesarean section

During 27 elective caesarean sections, operative blood loss was collected and processed using the Haemonetics Cell Saver 5 and filtered by Pall RC 100 leucocyte depletion filtration. The efficiency of removal of amniotic fluid, and the degree. of contamination with fetal red cells were assessed in the resulting 'cleaned' blood. Cell saver processing effectively removed alpha-fetoprotein from the red cells of 14 patients whose amniotic fluid was removed by separate suction and from nine of the 13 patients whose amniotic fluid was aspirated into the cell saver along with operative blood loss. Cell saver processing and leucocyte depletion filtration completely removed trophoblastic tissue and white cells, but fetal squames were still clearly present in 10, and possibly in 14 samples after processing and fully removed in only two specimens. Amorphous debris was present in all samples after processing. The maximum mass of fetal red cells contaminating any patient's total salvaged blood was 19 ml (range 2-19 ml). Had this been re-transfused into a rhesus-incompatible mother it would have required 2500 i.u. (500 microg) anti-D immunoglobulin to prevent rhesus-immunization of the mother. Contamination of processed caesarean section blood with fetal red cells and fetal squames is defined and its clinical implications discussed, with an overview of the development and current status of cell salvage. Autotransfusion by cell salvage with leucocyte depletion filtration should be considered in life-threatening obstetric haemorrhage and offered to Jehovah's Witnesses.

Meconium and amniotic fluid embolism: effects on coagulation in pregnant mini-pigs

OBJECTIVE

A hallmark of amniotic fluid embolism is the induction of coagulation defects. Little is known about the nature of these defects or the causative agent or agents. The purpose of this study was to assess the effects of meconium containing (native) meconium-amniotic-fluid infusion (MAFI) and meconium-free (centrifuged) amniotic-fluid infusion (AFI) on the coagulation system in the mini-pig model.

DESIGN

Laboratory study.

SETTING

University institute animal laboratory.

SUBJECTS

Near-term pregnant Göttingen bred mini-pigs in three groups (control, MAFI, AFI) of six animals each.

INTERVENTIONS

After induction of anesthesia, amniotic fluid was collected by cesarean section in all animals. Depending on the group, animals received either Ringer's solution (control), native amniotic fluid (MAFI), or centrifuged amniotic fluid (AFI) via an ear vein.

MEASUREMENTS AND MAIN RESULTS

Blood samples were taken from a central vein before infusion (baseline), immediately after infusion, every 10 mins until 90 mins after infusion, and finally, every 20 mins until 150 mins after infusion. The following parameters were measured: Platelets, partial thromboplastin time, prothrombin time, fibrinogen, factors V, VII, VIII, antithrombin III, and protein C. The values relative to baseline in the MAFI and AFI groups were compared with control by rank order test. A p<.05 was considered statistically significant. Compared with the control group, platelets were lower in the MAFI group (p<.005), PTT was prolonged in both the MAFI and AFI groups (p<.005), fibrinogen was lower in both the MAFI and AFI groups (p<.05), prothrombin index was lower (i.e., prothrombin time was prolonged) in the MAFI group (p<.05), and protein C was lower in the MAFI group (p<.005).

CONCLUSIONS

Both MAFI and, to a much lesser extent, AFI cause an activation of coagulation in mini-pigs. The changes induced by meconium-free AFI are probably not sufficient to explain the high mortality of the condition.

The effect of amniotic fluid on the human omental artery in vitro

OBJECTIVE

The aim of the study was to determine the effect of amniotic fluid on the in vitro contractility of the human omental artery.

STUDY DESIGN

Amniotic fluid and a segment of omentum were obtained from each of 5 patients at the time of planned cesarean delivery at normal term gestation for the indication of previous cesarean delivery. The omental artery was cleaned and cut into 3-mm rings, which were placed in 10-mL organ chambers for isometric tension recording. The chambers were filled with Krebs-Henseleit solution bubbled with 5% carbon dioxide in air and maintained at 37 C, pH 7.4. The rings were then equilibrated at 1 g passive tension for 90 minutes. The amniotic fluid was centrifuged for 10 minutes at 3000 rpm to remove all debris. Increasing volumes of supernatant (10-2000 microL) were added to the omental artery rings at baseline tone or after contraction with U46619 (10(-7) mol/L) or potassium chloride (60 mmol/L) to detect contractile and relaxant effects, respectively. Time-solvent control preparations were also run in parallel.

RESULTS

Amniotic fluid had no effect on the basal tone of omental artery rings. Amniotic fluid had no effect on the tension in rings previously contracted with either U46619 or potassium chloride.

CONCLUSIONS

Amniotic fluid has no direct effect on isolated human omental artery. The catastrophic hemodynamic changes associated with the syndrome of amniotic fluid embolism are not due to a direct effect of circulating amniotic fluid on vascular tone but rather may be due to secondary responses

[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.