An air medical transport team is called to the Post Anesthesia Care Unit (PACU) of a local referring center for a 39 year-old G2P2 mother with hypotension and shock one hour after an emergent caesarean section.
She was delivered at 34 weeks gestation secondary to fetal compromise. On bed rest the past two weeks for pregnancy induced hypertension (PIH), the patient presented to the emergency department by EMS with focal seizures and vaginal bleeding. Obstetrical exam was suspicious for a placental abruption.
Upon arrival at the patient’s bedside, the flight crew finds the patient intubated and mechanically ventilated, although with some difficulty. She has a right internal jugular central venous catheter and has been given two units of packed red blood cells (PRBC’s) and four liters of crystalloid.
Her last recorded vital signs include a heart rate of 122 beats per minute and regular, a blood pressure of 88/52 and an oxygen saturation of 85 percent. She is receiving pressure-control ventilation with high peak inspiratory pressures and positive end expiratory pressure (PEEP).
Clinical examination shows dilated and sluggish pupils, flat neck veins, coarse lung sounds bilaterally with poor chest excursion and dark red blood coming from the nose, gums and vagina.
Notable abnormalities in laboratory studies were a serum potassium of 5.8 mEq/L, an anion gap of 26 mEq/l, a serum hemoglobin of 7.1 g/dl, a prothrombin time (PT) of 34 seconds, a partial thromboplastin time (PTT) of 76 seconds and a fibrinogen level of 94 mg/dl. An arterial blood gas obtained on a FiO2 of 1.0 revealed pH of 7.16, PaCO2 of 52 mmHg, PaO2 of 57 mmHg, oxygen saturation 88 percent, bicarbonate (HCO3) 18 mEq/L and BE of negative6 mmol/L. A serum lactate drawn with the blood gas was 5.7 mmol/L.
What is quite apparent given this patient’s presentation is that she is hypoxic, in profound shock, is acidotic and coagulopathic. The question to be answered this month is why? What mechanism caused this pregnant female, who initially presented only a few hours previously with focal seizures and hypertension, to progress to this life-threatening condition?
The diagnosis
What makes this particular problem so difficult is that it is solely discovered by clinical suspicion. There is no one laboratory or diagnostic test that will confirm it. Even more confusing is that recent literature refers to it with different names: Amniotic Fluid Embolus (AFE) and more recently, Anaphylactoid Syndrome of Pregnancy. Regardless of how the clinician labels it, the results can be quickly devastating if not aggressively managed.
Pathophysiology and clinical presentation
The initiating event is not clearly understood and is still being studied3. It is commonly thought that there is an introduction of products within the amniotic fluid (that fluid surrounding the fetus during development, composed of hair, skin cells, inflammatory mediators, procoagulants and possibly meconium) into maternal vasculature.
Entrance may typically occur as a result of placental or uterine trauma4; or iatrogenically following a cesarean section or placement of an intrauterine catheter2. When this occurs, endogenous inflammatory mediators (such as cytokines, histamine, leukotrienes, bradykinin complement – and platelet- activating factors) initiate remarkable pathophysiological events2.
These alterations in normal maternal physiology produce the hallmark clinical presentation of this syndrome: hypoxia and respiratory distress, shock and consumptive coagulapathy4.
Once the “immunologically active4” fluid enters the mother’s pulmonary vasculature, it is believed to cause profound pulmonary vasoconstriction, bronchospasm, dyspnea and ultimately, hypoxia and respiratory acidosis.
Increased pulmonary vascular resistance leads to right heart failure. The effects of right heart failure and release of inflammatory mediators result in left heart failure, pulmonary edema and systemic hypotension.
Extravasation of vascular fluid also occurs. Immune system activation of the coagulation cascade leads to coagulapathy, bleeding and Disseminated Intravascular Coagulation (DIC)4. Prolonged hypoxia also may lead to altered mentation, encephalopathy and seizure activity.
Differential diagnoses
Possible differential diagnoses for patients with AFE or Anaphylactoid Syndrome of Pregnancy include2,4:
- Pulmonary Embolism
- Hemorrhagic shock
- Septic shock
- Anaphylaxis
- Complications of pregnancy and labor such as:
o PIH
o Eclampsia
o Abruptio Placentae / Placenta Previa
o Traumatic cesarean section / uterine rupture - Cardiomyopathy
- Acute Myocardial Infarction
Pertinent laboratory studies
Laboratory studies that may support this diagnosis include those that assess adequacy of tissue oxygenation (serum lactate and / or SvO2), adequate respiration and ventilation (arterial blood gas), blood counts (complete blood count (CBC)) and coagulation (DIC profile including at minimum: prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and D-dimer).
The clinician might expect to see a patient suffering from respiratory and / or metabolic acidosis, anemia and coagulapathy. Expect a large base deficit and high lactate levels, possibly reduced hemoglobin and hematocrit levels, increased clotting times and reduced fibrinogen with increased products of coagulation.
Management
Management is entirely supportive4. Hypoxia is treated with oxygenation and mechanical ventilation. Hypotension and hypoperfusion are treated first with crystalloid and vasopressor therapy, followed by appropriate blood products based upon degree of anemia and coagulapathy (eg, packed red blood cells (PRBC) for hemorrhage; fresh frozen plasma (FFP), cryoprecipitate and factor replacement for DIC; platelets for thrombocytopenia).
Improvement of cardiac contractility is aided with the use of inotropic support1,2,3. Serial lactate, SvO2 and blood gas measurements may guide therapy. Arterial lines and pulmonary artery catheters are considered adjunctive aids to guide therapy1,4 .
Case progression
Bedside stabilization started with ventilator manipulation, including adjustments in minute ventilation and inspiratory to expiratory (I:E) ratio to increase mean airway pressures. A pressure transducer was attached to the distal lumen of the central venous catheter and initial central venous pressure (CVP) was six mmHg. Five percent Albumin was started per the anesthesiologist at the bedside for intravascular volume repletion and the transport team started and titrated Dopamine.
The patient also received an additional unit of PRBCs, two units of cryoprecipitate and one unit of FFP to treat hemorrhage and coagulapathy. Following these initial therapies, the patient’s blood pressure rose to 98/52 (mean arterial pressure of 67 mmHg). ScvO2 measurement (see endpoints discussion) was 64 percent. Transport took place without incident. The patient spent 10 days in the medical intensive care unit (ICU), receiving high-frequency ventilation, factor administration, and continuous veno-venous hemofiltration (CVVH). She was discharged home, completely neurologically intact. Her 8-pound 4-ounce baby girl was also healthy.
Conclusion
Considering morbidity and mortality statistics reported for this disorder, this patient is extremely fortunate. Incidence ranges from 1 case in 8,000 to 1 in 80,000 pregnancies.
The large disparity in incidence is due to inaccurate or missed diagnoses. Mortality is as high as 80 percent with many deaths during the first hour of symptom onset4.
For this reason alone, it is important for transport personnel to suspect this in any gravid patient presenting with acute hypoxia and shock. This is truly a situation in which speed and skill will make a difference in outcome.
References
1. Davis D. Amniotic Fluid Embolism: Exploring this Rare but Typically Fatal Condition. AWHONN Lifelines 7(2). April / May 2003. pp. 126-131.
2. De Jong MJ and Fausett MB. Anaphylactoid Syndrome of Pregnancy: A Devastating Complication Requiring Intensive Care. Critical Care Nurse 23(6). December 2003. pp. 41-48.
3. Gilmore DA, Wakim J, Secrest J and Rawson R. Anaphylactoid Syndrome of Pregnancy: A Review of the Literature with Latest Management and Outcome Data. AANA Journal 71(2). April 2003. pp. 120-126.
4. Moore J and Baldisseri MR. Amniotic Fluid Embolism. Critical Care Medicine 33(10) (Suppl.). 2005. pp. S279-S285.
