Cardiac Arrest in Pregnancy: Key Differences and Algorithm

Cardiac arrest in pregnancy is one of the most dramatic emergency situations you can encounter in your clinical career. Although the event is rare – with an incidence of approximately 1:12,000 to 1:30,000 pregnancies – the consequences always affect two patients simultaneously: mother and child. The physiological changes of pregnancy render standard resuscitation according to the usual ACLS algorithm insufficient. You need to know the key differences in order to act quickly and purposefully in this extreme situation. The current AHA guidelines therefore emphasize specific modifications that must be consistently implemented in every resuscitation of a pregnant patient.

Physiological Changes as the Basis for Modified Resuscitation

To understand the modifications to the resuscitation algorithm, you need to have internalized the profound physiological changes of pregnancy. They affect virtually every organ system and influence both the etiology of cardiac arrest and the effectiveness of resuscitation measures.

Cardiovascular Changes

• Cardiac output: Increases by 30–50% compared to pre-pregnancy baseline
• Blood volume: Increases by 40–50%, with plasma volume rising disproportionately (relative dilutional anemia)
• Heart rate: Increases by 15–20 beats per minute
• Systemic vascular resistance: Decreases by approximately 20%, leading to physiologically lower blood pressure values
• Aortocaval compression: From approximately 20 weeks of gestation, the gravid uterus in the supine position can compress the inferior vena cava and the aorta – reducing venous return by up to 30–40%

Respiratory Changes

• Functional residual capacity (FRC): Reduced by approximately 20% due to diaphragmatic elevation
• Oxygen consumption: Increases by 20–30%
• Minute ventilation: Increases by approximately 50% (primarily through tidal volume)
• Compensatory respiratory alkalosis: PaCO₂ of 28–32 mmHg as the normal value in pregnancy

This combination of increased O₂ consumption and reduced FRC means that pregnant patients desaturate significantly faster during apnea than non-pregnant patients. You have less time for airway management.

Gastrointestinal Changes

Increased intra-abdominal pressure, hormone-induced relaxation of the lower esophageal sphincter, and delayed gastric emptying make pregnant patients high-risk for aspiration. This fact must critically influence your airway management.

Aortocaval Compression: The Central Problem

Aortocaval compression by the gravid uterus is the decisive factor that distinguishes resuscitation in pregnant patients from standard resuscitation. In the supine position, the uterus compresses the large retroperitoneal vessels from approximately 20 weeks of gestation. The consequences are severe:

• Reduction of venous return to the right heart by up to 40%
• Decreased cardiac output despite preserved cardiac function
• Ineffective chest compressions, since even correctly performed CPR generates only approximately 25–30% of normal cardiac output – further reduction due to aortocaval compression can lower the already minimal output below the critical threshold for coronary perfusion and cerebral blood flow

Manual Left Uterine Displacement

The current AHA guidelines recommend manual left uterine displacement (LUD) as the primary intervention, rather than the previously advocated left lateral tilt on a wedge.

Technique:

• A second helper stands on the patient's left side
• Grasps the uterus with both hands above the umbilicus
• Continuously displaces the uterus to the left and cephalad, away from the inferior vena cava
• Alternatively: standing on the right side and pushing the uterus to the left

Why no longer the wedge? The previous recommendation of a 15–30° left lateral tilt (e.g., using a Cardiff wedge or rolled blankets) has proven problematic: chest compressions on a tilted surface are demonstrably less effective. Compression depth decreases and force distribution becomes unfavorable. Manual uterine displacement, on the other hand, allows resuscitation on a hard, flat surface while simultaneously relieving the vena cava.

Key point: Manual uterine displacement must be established immediately at the start of resuscitation and maintained continuously until either ROSC is achieved or perimortem cesarean delivery is performed.

The Modified Resuscitation Algorithm in Pregnant Patients

The basic structure of the ACLS algorithm remains intact. The modifications are additive and do not replace any step of the standard algorithm.

BLS Measures

1. Call for help: Immediate activation of the resuscitation team and the obstetric team (including neonatology)
2. Hard surface: Position the patient supine on a hard surface
3. Manual left uterine displacement: Immediately by a dedicated person
4. Chest compressions: Standard – 100–120/min, depth 5–6 cm, full recoil. Hand position may need to be placed slightly more cephalad as the diaphragm is elevated by the gravid uterus
5. Ventilation: Prefer early intubation (aspiration risk!), typically choose a tube one size smaller (6.0–7.0 mm ID), be aware of increased risk of difficult airway due to mucosal edema
6. Defibrillation: Standard energies, standard pad positions. Defibrillation is not harmful to the fetus. No delay!

ACLS Measures

• Epinephrine: 1 mg IV every 3–5 minutes – no dose modification
• Amiodarone: 300 mg IV bolus for refractory VF/pVT, followed by 150 mg – no dose modification
• Defibrillation: Biphasic 120–200 J (manufacturer-dependent) or 360 J monophasic – standard energies
• Intravenous access: If possible above the diaphragm (upper extremity, external jugular vein), since access in the lower extremity may show delayed and diminished drug delivery to the heart due to aortocaval compression
• Intraosseous access: Proximal humerus as the preferred site

Airway Management – Special Challenges

Airway management in the pregnant patient in cardiac arrest deserves special attention:

• Difficult airway: Hormone-induced mucosal swelling in the pharynx and larynx, enlarged breasts (impeding laryngoscope handle), and increased aspiration risk make endotracheal intubation more challenging
• Video laryngoscopy: Should be considered as the first-line method
• Tube size: 6.0–7.0 mm internal diameter recommended (instead of 7.0–8.0 in non-pregnant patients)
• Rapid Sequence Induction (RSI): Not classically relevant during cardiac arrest, but should be considered during the perimortem phase or during resuscitation with residual perfusion
• Cricoid pressure: No longer routinely recommended according to current evidence, as it may impede intubation
• Capnography: Mandatory – both for tube placement confirmation and as a marker of CPR quality (target EtCO₂ > 10 mmHg during CPR, ideally > 20 mmHg)

Reversible Causes: The Expanded "H's and T's"

In addition to the classic reversible causes of cardiac arrest (4 H's and 4 T's), there are pregnancy-specific etiologies that you must actively search for and treat. The use of an expanded mnemonic has proven valuable – the supplement "A BEAU-CHOPS" is frequently used:

Letter	Cause	Intervention
A	Anesthetic complications (spinal anesthesia-induced hypotension, local anesthetic systemic toxicity)	Lipid rescue therapy for LA toxicity: Intralipid 20% – 1.5 ml/kg IV bolus, then 0.25 ml/kg/min
B	Bleeding (atony, placenta previa, uterine rupture, placental abruption)	Massive transfusion, uterotonics, surgical hemostasis
E	Embolism (pulmonary embolism, amniotic fluid embolism)	Consider systemic thrombolysis for PE; supportive therapy for amniotic fluid embolism
A	Aortocaval compression	Manual uterine displacement
U	Uterine atony / rupture	Surgical intervention
C	Cardiac (peripartum cardiomyopathy, myocardial infarction, aortic dissection)	Cause-specific therapy, PCI if indicated
H	Hypertension / preeclampsia / eclampsia	Magnesium sulfate 4–6 g IV over 15–20 min, blood pressure management
O	Other (standard H's and T's)	Hypoxia, hypovolemia, hypothermia, hypo-/hyperkalemia, tamponade, thrombosis, tension pneumothorax, toxins
P	Placental pathology (abruption, previa, accreta)	Surgical intervention, massive transfusion
S	Sepsis	Broad-spectrum antibiotics, volume resuscitation, source control

Special Attention: Magnesium Sulfate Overdose

Many pregnant patients receive magnesium sulfate for eclampsia prophylaxis or tocolysis. An overdose can itself lead to cardiac arrest. Clinical signs of magnesium toxicity:

• Loss of patellar reflexes (> 4 mmol/L)
• Respiratory depression (> 5 mmol/L)
• Cardiac arrest (> 12.5 mmol/L)

Antidote: Calcium gluconate 10% – 30 ml (3 g) IV over 2–5 minutes, repeat if necessary.

Perimortem Cesarean Delivery (Resuscitative Hysterotomy)

Perimortem cesarean delivery is not an optional measure – it is an integral component of maternal resuscitation. The primary goal of this intervention is to make maternal resuscitation more effective by definitively eliminating aortocaval compression. The benefit to the child is an important but secondary consideration.

Time Frame: The 4-Minute Rule

The AHA guidelines emphasize the following time-critical sequence:

• Minute 0: Cardiac arrest – start CPR and activate the obstetric/neonatal team
• Minute 4: If ROSC is not achieved → begin perimortem cesarean delivery
• Minute 5: Target time for delivery of the infant

This time frame is ambitious and requires that the decision for cesarean delivery is made no later than minute 4 – not merely discussed at that point. Preparation (positioning, disinfection if possible, scalpel ready) should occur in parallel with ongoing resuscitation.

Indications

• Pregnancy ≥ 20 weeks (fundal height at or above the umbilicus) and failure to achieve ROSC under adequate CPR
• In cases of obviously non-survivable maternal injury (e.g., trauma with non-survivable injuries): immediate cesarean delivery for the benefit of the child

Critical Points

• Chest compressions are NOT interrupted during the cesarean delivery
• No anesthesia required (the patient has no circulation)
• Minimal skin disinfection – time is the decisive factor
• Midline laparotomy as the fastest approach
• The cesarean delivery takes place at the site of resuscitation – no transport to the operating room
• After delivery of the infant: continued resuscitation of the mother, often with significantly improved hemodynamics

Who May Perform a Perimortem Cesarean Delivery?

Any physician with basic surgical competency can and must perform a resuscitative hysterotomy in an emergency if no obstetrician is available within the time window. The technique of midline laparotomy with hysterotomy is surgically less complex than often assumed – missing the time window poses a greater danger than a technically imperfect procedure.

Post-ROSC Management

After successful resuscitation, the standard post-ROSC measures apply with the following pregnancy-specific additions:

• Targeted temperature management (TTM): May be considered, although data for pregnant patients are limited. Moderate hypothermia (32–36 °C) appears to be tolerable for the fetus; continuous fetal monitoring is mandatory
• Left lateral positioning: After ROSC, consistent 15–30° left lateral tilt or continued manual uterine displacement
• Hemodynamic monitoring: Invasive blood pressure monitoring, central venous catheter, frequent blood gas analyses
• Fetal monitoring: Continuous CTG, obstetric assessment of delivery indication
• Workup of underlying cause: Echocardiography, CT angiography (if PE is suspected), laboratory tests including coagulation studies, magnesium levels, troponin

Team Management and Resources

Resuscitation of a pregnant patient requires significantly more personnel than a standard resuscitation. The following roles must be filled:

• Team leader (resuscitation lead)
• Chest compressions (at least 2 people rotating)
• Airway management
• Manual uterine displacement (dedicated person)
• Drug administration and documentation
• Obstetrician (for potential perimortem cesarean delivery)
• Neonatal team (for initial care of the newborn)

That is a minimum of 7–8 people. Clear communication, pre-established institutional protocols, and regular interprofessional training are critical for outcomes.

Summary of Key Interventions

1. Standard ACLS algorithm retained as the framework
2. Manual left uterine displacement immediately and continuously
3. IV access above the diaphragm
4. Early intubation due to aspiration risk, reduce tube size
5. Pregnancy-specific causes actively sought and treated (A BEAU-CHOPS)
6. Perimortem cesarean delivery from minute 4 if ROSC is not achieved and pregnancy is ≥ 20 weeks
7. No dose modification for epinephrine, amiodarone, or defibrillation energy
8. Multidisciplinary team activated early (obstetrics, neonatology, anesthesiology)

Practical Training

Cardiac arrest in pregnancy is a rare but highly complex emergency situation in which theoretical knowledge alone is not sufficient. Coordinating a large team, performing simultaneous uterine displacement during chest compressions, making the decision for perimortem cesarean delivery under time pressure – all of this can only be internalized through practical, simulation-based training. In the ACLS courses offered by Simulation Tirol, you train these and other critical advanced resuscitation scenarios in realistic simulation environments, including structured debriefing and team communication. This is how you gain the confidence and competence you need in real-life situations.