Cardiac arrest, a situation in which the heart stops providing circulation of blood through the body, occurs in roughly 1 out of every 30,000 pregnancies. This means that it’s very unlikely to happen to you, but it’s also worth discussion, at least for the sake of putting you at ease with the knowledge that healthcare providers have ways for managing cardiac arrest and that pregnant women who suffer cardiac rest have a fairly good chance of surviving.
Reversible causes of cardiac arrest during pregnancy often are grouped as the “4 Ts” and the “4 Hs”, as they consist of the following:
- Thrombosis: This means formation of blood clots, such as a pulmonary embolism or a myocardial infarction due to a clot in an artery that supplies the myocardium, the muscle tissue of the heart
- Tension pneumothorax: This is a condition in which the air pressure that is usually lower in the cavity that surrounds the lung rises, due to an injury, and keeps rising, each time that the person inhales. This can interfere with the blood returning to the heart through the venous system.
- Toxins: Various toxins can cause cardiac arrest
- Cardiac tamponade: This is when the pericardium, the fibrous sac surrounding the heart, fills with fluid to such an extreme that pressure rises so high around the heart that the heart is unable to relax enough to fill with blood.
- Hypoxia: This is when body tissues do not have enough oxygen to support normal functions
- Hypovolemia: This means that there is not enough volume of fluid outside of body cells, including not enough volume of blood.
- Hypothermia: This is when the body’s core temperature drops below 35 °
- Hyperkalemia, hypoglycemia, and othermetabolic abnormalities. To me, this means that there are not 4 Hs, but 5 Hs and an O or an M. Hyperkalemia means that the concentration of potassium in your blood is too high, which means above 5.0 mEq/L to 5.5 mEq/L (depending on the clinical laboratory). Hypoglycemia means that the concentration of the sugar glucose in your blood is below a certain level. Generally, this means below 70 mg/dL although sometimes during pregnancy it means below 63 or even 60 mg/dL. Other metabolic abnormalities can include abnormalities in a range of things, such as chloride, calcium, BUN and creatinine (indicators of kidney function) and acid/base abnormalities).
To the above lists, many clinical guidelines recommend adding eclampsia and intracranial hemorrhage. Eclampsia is a severe pregnancy complication in which preeclampsia (characterized by high blood pressure and protein in the urine or other signs of organ dysfunction) worsens to the point that seizures occur. Intracranial hemorrhage is bleeding in the brain.
The three main causes of cardiac arrest in pregnancy are obstetric hemorrhage, pulmonary embolism (an embolus generated from a blood clot in a vein, usually a deep vein, lodges in the lung and obstructs blood flow), and sepsis (infection throughout the body) leading to metabolic acidosis and septic shock. Examples of conditions causing obstetric hemorrhage include ectopic pregnancy (pregnancy develops outside the uterus lining, usually in a fallopian tube) that advances to cause rupture of a fallopian tube, uterine atony (the uterus doesn’t squeeze strongly enough to close placental blood vessels after delivery), abruptio placentae (the placenta detaches too early from the uterus), placenta previa (the placenta blocks the cervix and is susceptible to bleeding), placenta accreta (placenta is attached too deeply into the uterus, so hemorrhage develops when it detaches).
Another situation that can affect the heart during pregnancy is aortocaval compression syndrome. This happens when the mass of uterus during late pregnancy obstructs the aorta (the large artery that carries blood from the heart’s left ventricle) and/or the inferior vena cava (IVC, the large vein that returns blood from the lower body to the heart’s right atrium). Usually, on account of pressure on the IVC disrupting return of venous blood to the heart, this leads to reduction in cardiac output, meaning that the woman’s blood pressure drops. But, in severe cases it can lead to actual cardiac arrest. The uterus is likely to put pressure on the IVC if you sleep on your back during the late stages or pregnancy and since the IVC is positioned slightly to the right side of the body, the solution to aortocaval compression is to sleep on your left side. This improves venous return to the heart and consequently improves the cardiac output (the volume of blood that the heart pumps out each minute).
The initial assessment of a pregnant woman in cardiac arrest should include the evaluation of the airway, breathing, and circulation (ABCs). The airway should be secured and the patient should be placed on supplemental oxygen. If the patient is not breathing, ventilation should be provided with a bag-valve-mask (BVM). The presence of a pulse should be assessed using a carotid or femoral pulse. Treatment begins with basic life support, meaning that cardiopulmonary resuscitation (CPR) is initiated immediately. The chest compressions should be performed on the lower half of the sternum, at a rate of at least 100 compressions per minute, with a depth of at least (5 cm), while ventilation with a BVM should be at a rate of 8-10 breaths per minute.
The treatment also immediately expands to advanced cardiac life support (ACLS), which will include the administration of medications, such as epinephrine and vasopressin, aimed at restoring blood pressure and cardiac function. Also, if the treatment will include defibrillation (shocking the heart with electrical current), if the cardiac arrest is associated with a shockable rhythm, meaning ventricular tachycardia (VT) or ventricular fibrillation (VF). On the other hand, in cases of non shockable rhythms —meaning as asystole (known colloquially as “flatline”) or pulseless electrical activity (PEA, the heart generates voltage patterns on the heart monitor, but the patterns are not linked to the pumping of blood, as there is no mechanical response to the activity)— management will include only medications, since shocking the heart will not be helpful. In women with non shockable rhythms, medications are considered successful, if either they cause return of spontaneous circulation (ROSC) or they convert the heart to a shockable rhythm (VT or VF) and then defibrillation leads to ROSC.
One important consideration providing ACLS to pregnant women is the positioning of the patient. The supine position (back down), which is the standard position for non-pregnant patients, may compromise uterine perfusion and fetal oxygenation due aortocaval compression syndrome that we discussed above. So the patient is put on her left side to improve uterine and fetal perfusion.
Once ROSC is achieved, the resuscitation team must make a rapid decision on whether to lower the woman’s body temperature. Although we noted above that hypothermia, meaning unintentional hypothermia, is a potential cause of cardiac arrest, hypothermia also is induced on purpose in certain cases, following resuscitation from cardiac arrest. Specifically, guidelines of the American Heart Association (AHA) recommend such treatment —officially called targeted temperature management— when a cardiac arrest patient suffers any abnormality of consciousness after ROSC. In such cases, within 4 hours of achieving ROSC (preferably as soon as possible after ROSC), doctors bring the core body temperature of the patient down to a range of 32-34 °C and maintain that temperature for at least 24 hours, with the patient sedated. While pregnancy is a relative contraindication to induced hypothermia, it is not an absolute contraindication and hypothermia (targeted temperature management) improves survival dramatically, and prevents brain damage dramatically in cases of cardiac arrest when there is any indication of abnormalities of consciousness after resuscitation from cardiac arrest.
During pregnancy, rescuers must use a 15 degree tilt to the left side for administration of chest compressions to avoid aortocaval compression syndrome. Other than this, various factors can complicate resuscitation in pregnant women. These include increased oxygen requirements, splinting of the diaphragm by the pregnant abdomen when the patient is on her left side, increased risk of aspiration of stomach contents (due to pressure in the abdomen causing reflux of stomach contents), and ongoing risk of obstetric hemorrhage. Pregnant women need early intubation (tube inserted for breathing) and early supplemental oxygen. Doctors will perform aggressive fluid resuscitation, although this is done with extra caution in women with preeclampsia.
As for fetal consideration, doctors generally perform emergency delivery of the baby by caesarean section, if there is no ROSC after 4 minutes of CPR being performed correctly and when CPR continues for more than 4 minutes in a woman that has reached more than 20 weeks gestation. Delivery of the baby and the placenta should be completed within 5 minutes of initiating CPR. Such a delivery can be very chaotic, but the primary purpose of rushing to delivery the baby is to improve the mother’s chances of survival. This is because delivery improves delivery of blood the maternal heart, improves cardiac output, and reduces oxygen consumption. The delivery also helps with chest compressions and ventilation. While delivery also improves the baby’s chances of surviving, this consideration is secondary to that of the mother’s survival.