Authors: William Freeman, MD (Emergency Medicine Resident Physician, WashU School of Medicine); Emma Altieri, MD (Obstetrics and Gynecology Resident Physician, WashU School of Medicine); James Li, MD (Assistant Professor of Emergency Medicine, WashU School of Medicine)
Editor: Alex Blau, DO (EMS Physician, ChristianaCare Health System)
Case 1:
You are called as transport from OSH ED for a 32 year-old G3P2 at 28 weeks gestation who presented to the emergency department due to headache. Her pregnancy is complicated by a history of eclampsia in a prior pregnancy. On arrival, she was found to have persistently elevated blood pressure to 170/90. After receiving IV antihypertensive treatment, she was given a 4 g MgSO4 bolus and started on an infusion. Transport is arranged to the nearby tertiary care facility with in-house neonatology and obstetrics coverage. With minutes left in the transport, her O2 sats drop precipitously and she becomes unresponsive and loses pulses. CPR is initiated.
Case 2:
You are called to the site of a high-velocity MVC, where one of the patients is a pregnant woman of viable gestational age. An EMS physician is on-scene as the patient’s lower extremity was trapped due to significant vehicle intrusion and she required a prolonged extraction. On removal from the vehicle, she is bleeding profusely and is pale, mumbling, and not following commands. Her vitals demonstrate tachycardia, tachypnea, and hypotension. There are no additional signs of life threatening injuries other than her mangled lower extremity. Shortly after the tourniquet is applied to her leg she becomes unresponsive and loses pulses. CPR is initiated.
In cases of maternal cardiac arrest such as those above, what considerations are there when comparing maternal cardiac arrest to our standard patient population?
Physiologic Considerations
Due to the physiologic changes that occur in pregnancy, different factors may contribute to cardiac arrest when compared to non-pregnant individuals. The gravid uterus, particularly in later stages of gestation, results in compression of the great vessels that run through the abdominal cavity. Compression of the inferior vena cava (IVC) results in decreased venous return (preload) to the right heart, while pressure on the aorta increases peripheral resistance (afterload), thus increasing the amount of work the left ventricle must perform. Pulmonary physiology is also negatively impacted by pregnancy. The increased space occupied by the gravid uterus decreases the residual capacity of the lungs, and the increased metabolic demand required to support a growing fetus results in faster onset of hypoxemia in pregnant individuals. These cardiovascular and pulmonary factors, among others, may contribute to more rapid decompensation among pregnant patients.
Given the physiologic adaptations of pregnancy, certain interventions should be prioritized for critically ill pregnant individuals in order to help prevent cardiac arrest. Rapid recognition and correction of hypoxemia with supplemental oxygen or other interventions is paramount to optimize maternal and fetal wellbeing. One can consider starting patients on higher oxygen concentrations such as 15 L non-rebreather and de-escalating, rather than slowly up-titrating as needed. For patients with hemodynamic instability, placing the patient in the left lateral decubitus positioning may help facilitate aortocaval decompression and optimize cardiovascular function. Finally, placement of IV/IO access above the diaphragm, while routine, will specifically avoid any aortocaval obstruction caused by the gravid uterus. This is most relevant when IO placement is indicated and suggests favoring humeral placement.
Cardiac Arrest Care
In the case of cardiac arrest, the adage “what is best for mother is best for baby” is excellent advice. Most care in maternal cardiac arrest does not deviate from normal ACLS and BLS protocols. There are no changes to chest compressions, airway indications, and pad placement, nor to defibrillation parameters. Choice of vasopressors, antiarrhythmics and other medications should not be affected by concern for fetal teratogenicity. Fetal monitoring is of low priority and may in fact impede high quality resuscitation and so should not be performed.
Taking the physiology of pregnancy into account does lead to some alterations or considerations to routine cardiac arrest care. Due to aortocaval obstruction, left uterine displacement (LUD) should occur throughout the duration of chest compressions in order to optimize maternal hemodynamics. This is best accomplished by manual left uterine displacement rather than patient tilt, as tilting the patient may impair the quality of chest compressions, defibrillation pad placement, and airway interventions. It is also unknown how patient tilt may change the intrathoracic position of the heart and subsequent hand placement for compressions. Optimally, one responder should be assigned exclusively to LUD, however this may be infeasible in small teams and thus necessitate lateral tilt with a firm wedge backing. Regarding airway interventions, intubation may also be more difficult due to the edematous glottis in pregnant individuals that occurs due to fluid shifts of pregnancy. In such cases, a slightly smaller ET tube selection (6.0-7.0) may facilitate easier first-attempt placement. Finally, in patients who have received magnesium sulfate in the peri-arrest period, administration of calcium will help reverse any respiratory or circulatory effects caused by magnesium toxicity. Treating the underlying cause of arrest is also key, but extensive discussion of the possible causes of maternal cardiac arrest is beyond the scope of this review. Common causes of out-of-hospital maternal arrest include pulmonary embolism, cardiac causes, and trauma and would mostly benefit from previously described strategies regarding optimization of hemodynamics and oxygenation.
Resuscitative Hysterotomy
The greatest change from routine cardiac arrest care comes from the consideration of resuscitative hysterotomy, formerly termed “perimortem c-section”. This procedure is indicated in order to relieve aortocaval compression in the case that initial attempts at resuscitation are unsuccessful and should be attempted in patients at a gestational age of 20-24 weeks or greater as compression is sufficient to potentially compromise hemodynamics. In the absence of clear gestational dating, the uterine fundus at the level of the umbilicus indicates approximate gestational age greater than or equal to 20 weeks. Hysterotomy should be performed in any type of arrest, including traumatic or medical, in patients for whom initial resuscitative measures are not successful. The procedure should be initiated at minute four of cardiac arrest in order to perform successful fetal extraction by minute five. This is based on the increased likelihood of permanent maternal neurologic injury occurring beyond 5 minutes of ischemic time. Because of the short interval between arrest and initiation of resuscitative hysterotomy, the procedure should be performed at the site of arrest when possible. It should be performed by a physician but may occur in the prehospital setting if an EMS physician is present during the arrest. Otherwise, patients should be taken to the nearest appropriate facility. While a facility with obstetric coverage is ideal, if hysterotomy cannot occur at the site of arrest or en route, then transport should proceed to the nearest facility capable of resuscitative hysterotomy, which may simply be the nearest physician-staffed ED. If multiple centers are nearby, transport should not be prolonged more than 10 minutes to seek a facility capable of providing a higher level of care (e.g. obstetric support, neonatal ICU). In the case that arrest occurs shortly after initiating transfer of a critically ill, gravid patient, this may necessitate returning to the original emergency department.
Once in the emergency department, the procedure should be performed at the bedside, as transport to the OR has been associated with decreased resuscitation quality and delays in delivery. Skin preparation is not necessary and may delay delivery but can be considered at the start of arrest in order to serve as a visual cue for the team that hysterotomy is impending (at minute 0 of arrest, for example). For the procedure itself, a scalpel is the only necessary instrument, but other materials may be helpful. These materials include a surgical gown and other standard sterile attire, blunt scissors (such as Mayo or bandage scissors), cord clamps or hemostats, retractors, sponges, suction, towels or other packing material, and sutures.
To begin the hysterotomy, an incision should be made through the skin, abdominal wall and fascia and into the peritoneum. Most commonly, a midline vertical incision that runs from pubic symphysis to the uterine fundus is recommended. However, sources generally agree that the best approach is the fastest approach, so a Pfannensteil or low transverse incision is acceptable if preferred by the performing provider. Given the low likelihood that EM providers will be familiar with this entry, a midline vertical skin incision is likely the most reasonable recommendation as the linea nigra can be used as a clear landmark. This approach is also thought to be faster and allow for better visualization of the uterus for most practitioners. As the incision extends to the pubic symphysis, proceed carefully to avoid injury to the bladder, if possible. Once in the peritoneal cavity with the uterus in view, hysterotomy is performed by first making a small incision in the lower uterine segment, then cutting from the lower segment to the fundus using blunt scissors. When extending the incision vertically towards the uterine fundus, the physician’s non-dominant hand should be placed between the fetus and anterior uterine wall to avoid fetal injury. If blunt scissors are unavailable, the incision can also be made with a scalpel.
Next, gently deliver the infant , clamp the umbilical cord twice, cutting the cord between the clamps, and hand the infant to whomever will be performing the neonatal resuscitation. Given the poor circulation and subsequent hypoxia that occurs during maternal cardiac arrest, it is common for neonates to need additional support. At this point, pressure on the aortocaval system will be relieved and maternal hemodynamic status may begin to improve. The final step is to deliver the placenta with gentle traction on the umbilical cord and manual blunt dissection, when necessary. Using a dry laparotomy sponge or clean towel, wipe the uterine cavity in order to remove any potential retained products of conception. This will reduce risk of postpartum bleeding in the event of sustained ROSC.
With delivery of the fetus, the most significant component of the procedure is complete and subsequent steps are less important to resuscitative measures . Closure of the uterus and incision is optional, with some sources recommending packing the uterus and abdomen with towels and leaving closure until the patient is more stable, while other sources recommend more immediate closure of the uterus and abdomen. However, if ROSC occurs, surgical closure can likely be completed by obstetric or surgical services at the nearest trauma center.
While the initial procedure is expected to be relatively bloodless due to the lack of a perfusing cardiac rhythm, if ROSC is achieved after hysterotomy, there may be significant post-procedural bleeding. While in the case of ordinary postpartum bleeding, oxytocin may be used as a first-line agent to treat presumed uterine atony, caution should be utilized in choosing this medication after maternal arrest as oxytocin may cause hypotension and increase the risk for re-arrest. Additional uterotonic agents, tranexamic acid, and blood products can be considered to treat hemorrhage if available. Antibiotics for surgical prophylaxis should be administered perioperatively due to the low-sterility environment in which the surgery likely occurred.
Conclusion
Returning to the first case described at the start of this review, management guidelines recommend that the ambulance crew should begin CPR with LUD, administer IV calcium, and notify the nearest Emergency Department of the need for possible hysterotomy. In the second case of traumatic arrest, CPR should begin while the physician prepares for field hysterotomy if ROSC is not obtained by minute four of arrest. Subsequently, mother and baby can be transported to the closest appropriate receiving facilities. While outcomes are generally poor, there are documented cases of preserved neurologic function in mothers and newborns even at longer durations of arrest (>25 min). As such, while it’s recommended that initial resuscitation be aimed at controlling hemorrhage, airway issues, and other reversible causes of arrest (e.g. pneumothorax), hysterotomy should not be withheld exclusively due to missing the 4-minute time window. It is important to note that while cases of maternal arrest can seem overwhelming, few changes are made to typical ACLS algorithms, with the notable exception of resuscitative hysterotomy. Other small considerations such as those mentioned here may slightly improve the quality of resuscitation and hopefully increase the likelihood of survival. By remembering three key resuscitative measures: to displace the uterus, aggressively correct hypoxia, and proceed with hysterotomy at four minutes of arrest, you will be prepared to take on this challenging scenario.
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