During cesarean delivery, factors such as placental removal, uterine exteriorization, and uterine incision increase the risk of air embolism. The uterine sinuses, particularly in cases of placenta previa, are vulnerable to air entry and create a direct route for air to reach the central venous system. Due to ventilation-perfusion mismatch, air bubbles trapped in the pulmonary vasculature result in gas exchange abnormalities, including hypoxemia and hypercapnia. In severe cases, this can lead to pulmonary hypertension, right ventricular overload, and eventual cardiac arrest.
Risk Factors of Air Embolism During Cesarean Section
- Surgical positioning: The Trendelenburg position increases the pressure gradient between the uterus and the right atrium and allows air entry.
- Placental complications: Abruptio placentae and placenta previa heighten the risk by increasing venous exposure to air during placental removal.
- Uterine exteriorization and manual removal of the placenta are also key risk factors.
- Maternal conditions: Hypovolemia, preeclampsia, and severe antepartum hemorrhage further exacerbate the risk by lowering venous pressure, making it easier for air to be entrained.
Clinical Presentation of Air Embolism During Cesarean Section
Conscious patients may experience chest tightness, dyspnea, or a sudden drop in oxygen saturation. In patients under general anesthesia, a sharp decrease in end-tidal CO₂ is the first sign of venous air embolism. Hypotension and oxygen desaturation also occur but are late signs. Severe cases present with acute right ventricular dysfunction or cardiac arrest, especially in patients with significant air entrapment in the pulmonary circulation.
Prevention and Management of Air Embolism During Cesarean Section
- Positioning: Avoid the Trendelenburg position during a cesarean section because it increases the pressure gradient between the right atrium and uterine incision. Instead, a reverse Trendelenburg position of 5° to 10° reduces the risk of venous air embolism.
- Flooding the surgical field: Ensuring the surgical field is flooded with saline during uterine incision and placental removal helps minimize air entry into venous channels.
- Positive end-expiratory pressure (PEEP): Although PEEP can prevent air entry and increase venous pressure, it must be used cautiously, as it may lower cardiac output and increase pulmonary vascular resistance, especially in the supine position.
- Discontinuing nitrous oxide: Nitrous oxide should be immediately stopped if venous air embolism is suspected, as it can expand air bubbles in the pulmonary vasculature, worsening the condition.
- Air aspiration: Up to 50% of entrained air can be aspirated by a central venous catheter or a multi-orifice catheter technique.
- Pharmacological support: Inotropic agents such as norepinephrine may improve right ventricular function. Milrinone or dobutamine can provide inotropic support and reduce right ventricular afterload.
