A histological study of experimental amniotic-fluid and meconium embolism in dogs

Maternal death following cardiopulmonary collapse after delivery: amniotic fluid embolism or septic shock due to intrauterine infection?

PROBLEM

The amniotic fluid embolism (AFE) syndrome is a catastrophic complication of pregnancy frequently associated with maternal death. The causes and mechanisms of disease responsible for this syndrome remain elusive.

METHOD OF STUDY

We report two cases of maternal deaths attributed to AFE: (1) one woman presented with spontaneous labor at term, developed intrapartum fever, and after delivery had sudden cardiovascular collapse and disseminated intravascular coagulation (DIC), leading to death; (2) another woman presented with preterm labor and foul-smelling amniotic fluid, underwent a Cesarean section for fetal distress, and also had postpartum cardiovascular collapse and DIC, leading to death.

RESULTS

Of major importance is that in both cases, the maternal plasma concentration of tumor necrosis factor-alpha at the time of admission to the hospital and when patients had no clinical evidence of infection was in the lethal range (a lethal range is considered to be above 0.1 ng/mL).

CONCLUSION

We propose that subclinical intraamniotic infection may be a cause of postpartum cardiovascular collapse and DIC and resemble AFE. Thus, some patients with the clinical diagnosis of AFE may have infection/systemic inflammation as a mechanism of disease. These observations have implications for the understanding of the mechanisms of disease of patients who develop cardiovascular collapse and DIC, frequently attributed to AFE. It may be possible to identify a subset of patients who have biochemical and immunological evidence of systemic inflammation at the time of admission, and before a catastrophic event occurs.

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.

Amniotic fluid embolism

The statement that amniotic fluid embolism is the most dangerous and untreatable condition in obstetrics appears to be true. It must be suspected in any patient who collapses or bleeds excessively during labour or the immediate post-partum period. Attempts should be made to secure a definitive diagnosis in life by examination of blood obtained from the right side of the heart and the sputum for elements of amniotic fluid. Lung scanning is a useful aid to diagnosis. The principal factors that have been implicated in the clinical syndrome of amniotic fluid embolism are anaphylaxis, vascular obstruction by particulate matter, vascular spasm due to prostaglandins and possibly some other vasoactive substances, and the possibility that all the changes could be explained by disseminated intravascular coagulation as a primary event. Further work is required to elucidate the relative contributions of these various factors. Due to the suddeness of the catastrophe and the very high mortality, haemodynamic data in humans is virtually non-existent. With improved methods of resuscitation it is to be hoped that the mortality rate will be reduced and that such data will become available. In this way it might become possible to apply the results of animal research and indicate the most effective method of treatment.

Amniotic fluid embolism: a review of the literature with two case reports

Amniotic fluid embolism (AFE) is a rare but dramatic obstetric complication. In this study, the pathogenesis of AFE and the disorders of coagulation and fibrinolysis and postmortem gross pathologic and histologic findings resulting from it are reviewed. The 2 case histories examined in this report exemplify different clinical courses of amniotic fluid embolism. In the first case, there was a predominant activation of the coagulation system, with a fatal outcome. In the second case, generalized fibrinolysis dominated, and the woman survived. Finally, the authors wish to emphasize that the administration of fibrinogen is an incorrect approach to the management of this syndrome. A combination of Macrodex and heparin might be effective in preventing the formation of microthrombi, but increased fibrinolysis has to be treated by a sufficiently high dose of fibrinolytic inhibitors.