Mechanism of Amnioinfusion
Amnioinfusion works by infusing normal saline solution into the uterine cavity to increase amniotic fluid volume, which relieves umbilical cord compression and dilutes meconium when present. 1
Primary Mechanisms of Action
- Amnioinfusion relieves umbilical cord compression by increasing the amniotic fluid volume, thereby creating more space around the umbilical cord and reducing the risk of compression during contractions 1, 2
- It dilutes meconium when present in the amniotic fluid, potentially reducing the risk of meconium aspiration syndrome 3, 4
- It improves the intrauterine environment by correcting oligohydramnios, which is often associated with variable decelerations in fetal heart rate 5, 4
Clinical Applications
During Labor
- Amnioinfusion is indicated for recurrent, moderate to severe variable decelerations in fetal heart rate during labor 1
- The procedure involves infusing room temperature normal saline (0.9%) through an intrauterine pressure catheter 5
- Typically performed as either:
- A bolus infusion followed by continuous slow infusion, or
- Repeated bolus infusions to maintain adequate amniotic fluid volume 6
For Meconium-Stained Amniotic Fluid
- Amnioinfusion dilutes thick meconium, potentially reducing the risk of meconium aspiration syndrome 3
- Under standard perinatal surveillance, amnioinfusion has been shown to reduce:
- Heavy meconium staining of amniotic fluid
- Variable fetal heart rate decelerations
- Cesarean section rates 3
For Previable PPROM (Preterm Prelabor Rupture of Membranes)
- Serial amnioinfusions have been investigated for previable PPROM (16-24 weeks)
- However, randomized trials found no significant reduction in perinatal morbidity compared to expectant management 1
- Current guidelines consider serial amnioinfusions for previable PPROM investigational and recommend they be used only in clinical trial settings 1
Procedural Considerations
- For intrapartum use, normal saline is typically infused through an intrauterine catheter, preferably one with a catheter-tip pressure transducer 6
- The goal is to achieve and maintain adequate amniotic fluid volume throughout labor 6
- Monitoring is essential to prevent complications such as uterine overdistention 5
Efficacy and Outcomes
- In cases of variable decelerations during labor, amnioinfusion has been associated with:
- For meconium-stained fluid, benefits include:
- Reduced meconium below the vocal cords
- Decreased incidence of meconium aspiration syndrome
- Reduced need for neonatal ventilation 6
Potential Complications
- Umbilical cord prolapse
- Uterine overdistention
- Fetal bradycardia
- Rare reports of amniotic fluid embolism 5
Amnioinfusion represents an important tool in modern obstetric practice, particularly for managing variable decelerations and meconium-stained amniotic fluid during labor, though its use for previable PPROM remains investigational.