Blog with interesting cases and/or problems related to anesthesia with discussion based on best evidence in the literature.

April 8, 2010

A fatal enigma

A 31 year old G2P1 was admitted for induction of labor. At 2 cm dilation the Obstetrician ruptured her amniotic sac and gave the ok for her to receive an epidural. The obstetrical nurse called the anesthesiologist covering the OB unit who came up to place the epidural. However, during the interim, another patient who was experiencing more pain and was further along in her labor was given priority. The anesthesiologist went into her room and began placing the epidural. Shortly thereafter, (aproximately 10 to 15 minutes after having her amniotic sac ruptured) the husband of the first patient notified the nurse that his wife was having difficulty breathing. The nurse went into the room, found the patient unresponsive, and a code blue was called. Another anesthesiologist responded, the patient was intubated, and CPR began when a pulse was not detected. She was immediately transported to the OR and a cesarean section was performed emergently. The neonate was born live, resuscitated and suffered no permanent sequelae. However, after following ACLS protocol and performing a TEE with a cardiologist, the mother was pronounced dead.

In this previously otherwise healthy parturient who developed sudden dysnpnea followed by rapid cardiovascular collapse resistant to ACLS and CPR a diagnosis of amniotic fluid embolism is likely. However, amniotic fluid emobolism (or anaphylactoid syndrome of pregnancy) AFE is quite rare estimated to occurr in only 1 in 80,000 deliveries in some series, while a recent study put the estimate closer to 1 in 20, 464 deliveries. In any case, AFE is a syndrome that seems to lie outside any cut and dry diagnostic criteria, occurrs only very rarely, seems to be completely unpreventable, and is generally not amenable to treatment. It is usually a diagnosis of exclusion and venous thromboembolism and pulmonary embolism are likely to present in a similar fashion at least initially. Another possibility is cardiovascular collapse from an allergic reaction to some medication. If the patient had recived an epidural, then this would have to be considered in the differential (high spinal vs. local anesthetic toxicity). In this women's case, no thrombus was visualized on TEE, the only medication she was receiving was pitocin which had been running for some time with no ill affect, and therefore, the liklihood that she suffered from AFE is probable.

Cardiac arrest in a term parturient is especially challenging because of the altered physiology and anatomy. Recommendations for resuscitation of the parturient have been given by the American Heart Association (AHA). These recommendations take into account that the gravid uterus receives up to 30% of the cardiac output (only about 2% in the nonpregnant patient), and that aortocaval compression can decrease cardiac output by up to 25%. Consequently, some slight modifications need to be made when performing CPR in the term parturient. Placing the patient in the left lateral position for CPR is recommended, and cesarean delivery should be initiated within 4 minutes of arrest if initial resuscitation efforts fail. An excellent article on peripartum cardiac arrest was published in this month's "Anesthesiology News". (Wang S, Lourim JF and Sanborn RH, Lesson 285: Cardiopulmonary Resuscitation During Pregnancy and Perimortem Cesarean Delivery. April 2010. Anesthesiology News)

There are plenty of reviews in the literature on what AFE consists of, but briefly, the constellation of symptoms known as AFE are thought to be caused by fetal tissues and amniotic fluid that enters the maternal circulation via uterine veins. There are two phases: 1) SOB and hypotension to cardiac arrest, 2) hemorrhagic phase likely due to DIC.

This 31 year old parturient did not have many of the common risk factors for AFE. In fact, she had only one; her labor was being induced with pitocin. Others include advanced maternal age, precipitous labor, advanced maternal age, cesarean section or instrumental vaginal delivery, placenta previa and abruption, grand multiparity (> or = 5 live births or stillbirths), cervical lacerations, fetal distress, and eclampsia.

Despite the name: amniotic fluid embolism, it is unlikely that a large embolus of fetal tissues literally blocks the pulmonary vasculature. Animal studies suggest that pulmonary hypertension results from fetal material in the pulmonary vasculature. On the otherhand, hemodynamic measurements in humans seem to indicate that cardiovascular collapse results from left ventricular failure. Therefore, it has been proposed to marry this conflicting data, that early on pulmonary hypertension causes right ventricular failure which is then followed in 15 to 30 minutes by left ventricular failure.

Severe pulmonary hypertension also results in severe V/Q mismatch leading to hypoxemia. This in fact is typically the first clinical manifestatin that there is a problem. Later, pulmonary edema develops from left ventricular failure which also contributes to hypoxemia. Finally, if the pateint survives the initial hours, hypoxemia can persist due to noncardiogenic pulmonary edema from a capillary leak syndrome. Fortunately, in these patients who survive, the noncardiogenci pulmonary edema is short lived unlike ARDS, which is protracted.

Finally, some case reports have found evidence that the complement system is involved where decreased complement levels have been measure in some patients. This corresponds to the systemic manifestations of this syndrome.

Presentation may also include such nonspecific signs as chills, nausea, vomiting and seizure activity. Unfortunately, the presentation is often fulminant and death can occur in many cases within an hour of initial symptoms. In up to 80% of these patients, a severe DIC is found. DIC can begin within only 10 minutes after initial symptoms are manifested. On the other hand, its onset may be delayed by several hours.

Management of these patients can be quite difficult. First, the mortality rate can be as high as 80%. The patient suffers in severe cases from hypoxemia from multiple etiologies that may not respond easily to high oxygen delivery. Furthermore, the patients suffer from severe hypotension that may be from vasodilation, third spacing and biventricular dysfunction. Fluids needs to be given along with vasopressors and ionotropes and potentially pRBCs with component therapy for potential coagulopathy. Because these patients can develop both cardiogenic and noncardiogenic pulmonary edema, great care and careful monitoring is required to maintain the patient in the very narrow therapeutic window of sufficient left ventricular volume and volume overload.

There are case reports of novel interventions that have proved helpful. Nitric oxide started at 40 ppm was administered in one case to treat severe pulmonary hypertension that caused righ ventricular failure and left ventricular diastolic dysfunction from a dilated right ventricle. Another case report describes an RVAD to treat right ventricular failure. In another case, a 45 year old female undergoing elective c-section for placenta previa suffered an AFE. TEE was instituted and showed significant and persistent pulmonary vasoconstriction. Cardiopulmonary bypass, heparin, epinephrine and high dose steroids were used in the management with successful outcome. In other case, ECMO along with intra-aortic balloon counterpulsation were performed to stabilize a patient who suffered from AFE during an otherwise routine labor. Activated recombinant factor VII has also been used successfully to control bleeding in a patient with AFE and DIC.

Obviously, the above novel therapies are enormously expensive with large inherent risks. But, given that this patient population is one that is typically otherwise healthy, younger, and likley to be depended upon for the caring of a new infant, heroic efforts are likely rational particularly if they are potentially lifesaving.

In summary, AFE is not predictable nor is it preventable. A high clinical suspicion and rapid and aggressive management is required given that the mortality rate from this syndrome is estimated to be up to 90% in some estimates. Early moblization of subspecialties such as cardiothoracic surgery, cardiology, pulmonary and hematology may be indicated depending the available resources at your hospital.

1 comment:

moheyeldin farghaly said...

thank you it is a very nice post