Pulmonary Hypertension in Pregnancy

Background

• Patients with pHTN may present with varying degrees of disease severity. Severe cases can carry exceptionally high mortality, typically secondary to cardiac events (reported range of 25-56%).¹
• Due to high mortality risk, pregnancy has been considered contraindicated in patients with pHTN, with termination historically recommended.
• PHTN is 4 times more common among women, with roughly 80% being of childbearing age. Despite the high risk and recommendations to terminate pregnancy, many patients carry their pregnancy through to delivery.²
• Decompensated pHTN and RV failure can occur at any time during pregnancy, with the highest risks being in the second trimester through the postpartum period, when cardiovascular changes are most pronounced.³

Definition, Presentation, and Diagnosis

• PHTN is defined as a mean pulmonary artery pressure (mPAP) ≥ 25mmHg on resting right heart catheterization (RHC).
• The World Health Organization categorizes pHTN into five groups based on etiology (Table 1).⁴

• Patients may present with various symptoms, including:
  • Dyspnea
  • Fatigue
  • Palpitations
  • Syncope (typically secondary to decreased cardiac output)
  • Angina/Chest pain
  • Lower extremity edema
  • Hepatomegaly
• RV dilation, a proxy for pHTN, is a frequent incidental finding detected via workup for other pathologies (e.g., pulmonary embolism, trauma, etc)
  • CT scan
  • CXR
  • Point-of-care ultrasound
• Alternatively, pHTN can be suspected via initial screening with a transthoracic echocardiogram, which demonstrates several qualitative and quantitative findings (Table 2).

• The diagnosis of pHTN can be confirmed via RHC, as mentioned above (mPAP ≥ 25 mmHg).

Pathophysiology

Pulmonary Vascular System

• Primarily increased pulmonary vascular resistance (PVR) to flow, as a result of:
  • Increased thromboxane A2, endothelin-1 activity —> Endothelial and media smooth muscle hypertrophy, hyperplasia
  • Reduced prostacyclin and nitric oxide production
• Additionally, increased pulmonary venous pressure can be seen.
• A negative feedback loop ensues, as endothelial hyperplasia can trigger an inflammatory and coagulation cascade, worsening pHTN.²
• Additional capillary bed injury and alveolar injury ultimately lead to decreased diffusion capacity of lung for carbon monoxide, worsening oxygenation, hypoxic pulmonary vasoconstriction, and worsening oxygenation, which reproduces a negative feedback loop with increased PVR.

Right Ventricle

• Increased pulmonary arterial resistance increases vascular pressure load on the thin-walled RV, initially leading to adaptive concentric wall hypertrophy and increased muscle contractility, often referred to as coupling.²
• To maintain cardiac output, the RV dilates and the heart rate increases, thereby increasing wall stress and oxygen consumption.
• Increased oxygen consumption leads to RV ischemia, further worsening RV failure.

Additional Pregnancy and Postpartum-Specific Considerations

• Reduced O₂-carrying capacity due to dilutional anemia worsens hypoxemia.
• Increased O₂ consumption (Fetal Hb extraction) also worsens hypoxemia.⁶
• While elevated estradiol, testosterone, and progesterone normally cause pulmonary arterial dilation during pregnancy, these hormonal changes are decreased or absent in parturients with pHTN.

Treatment Considerations

Anesthetic Approach and Monitoring with Delivery

Mode of Delivery

• Vaginal or assisted second-stage delivery may carry less risk than cesarean delivery.
• Mortality has been reported to be higher with cesarean (18%) versus vaginal deliveries (5%).¹⁰

Monitoring

• Standard American Society of Anesthesiologists monitors (noninvasive blood pressure, 5-lead EKG, continuous pulse oximetry)
• Arterial line
• Central line +/- pulmonary artery catheter may be considered if benefits are thought to outweigh risks.
• If under GA, transesophageal echocardiography can be utilized to assess volume status and RV function.
• Pulse pressure variation can also be used to guide volume assessment.
• Caution with intravenous fluid use – targeting euvolemic state is recommended

Medications

Postdelivery

• Mortality risk remains high AFTER delivery.
• During the postpartum period, drastic hormonal and physiologic changes occur in the immediate period, taking up to six weeks post-delivery to return to prepregnancy baselines.
• Normalization of blood volume, placental autotransfusion, increased hemorrhage, and thrombotic risk all present a high risk for postpartum pHTN crisis and RV decompensation.
• Admission to intensive care immediately postpartum to monitor for a decline in cardiovascular function and/or concerning arrhythmias should be highly considered.
• Care must be given to continued management and follow-up/monitoring of patients for weeks to months after delivery.