APPENDIX A Amnioinfusion

Amnioinfusion is the administration of room temperature isotonic solution such as normal saline or Ringer’s lactate via a double-lumen intrauterine pressure catheter (IUPC) by either a gravity flow or an infusion pump to restore amniotic fluid volume. The procedure is intended to relieve intermittent umbilical cord compression that results in variable fetal heart rate decelerations and transient fetal hypoxemia. This procedure has no known impact on late decelerations, and is no longer recommended for dilution of meconium.

An amnioinfusion generally begins by administering a bolus of fluid (250 to 500 ml) over 20 to 30 minutes. The maintenance dose is infused at a rate of 2 to 3 ml/min (maximum of 180 ml/hr), during which time it is imperative that the amount of fluid returning is approximated and documented to avoid overdistention of the uterus. Assessment of the output can be accomplished by weighing the absorbent pads underneath the woman (1 ml = 1 g) and counting the number of pads changed.

Assessment of uterine resting tone is also an important aspect of surveillance during the procedure, and it should not exceed 40 mm Hg. It is unlikely that more than 1000 ml of fluid need to be administered, and if variable decelerations persist even after this amount of fluid has been instilled into the uterus, other therapies should be used as treatment. Iatrogenic polyhydramnios may cause a placental abruption or pressure on the maternal diaphragm causing shortness of breath, tachycardia, and a change in maternal blood pressure. A rapid release or “gush” of fluid predisposes the woman to a prolapsed umbilical cord. The preterm fetus may benefit from a warmed solution, thus avoiding bradycardia. A blood warmer is the safest method for administering warmed fluid. The fluid should not be heated in a microwave or blanket warmer. Warmed fluid is also suggested if the rate of the amnioinfusion exceeds 15 ml/min.

There are a variety of ways to perform an amnioinfusion. It is important that the institution has a policy and procedure in place and they are followed.

Indications for amnioinfusion

1. Laboring preterm women with premature rupture of the membranes (prophylactic)

2. Variable decelerations uncorrectable with conventional interventions

3. Significant oligohydramnios (amniotic fluid index ≤5) at term when labor is being induced

Equipment and supplies

Normal saline or Ringer’s lactate solution, 1000 ml at room temperature

Intrauterine catheter equipment, preferably with a double lumen and amnioport (if using single-lumen water-filled IUPC, intravenous [IV] extension tubing with twin sites or arterial line [12 inches] and a three-way stopcock are needed)

Volumetric infusion pump and tubing, or IV pole for gravity flow

Blood warmer or blood/fluid warming set (optional)

Procedure

Amnioinfusion should be initiated after insertion of the intrauterine catheter. Before the procedure, the intrauterine resting tone should be noted with the woman in the right and left lateral and supine positions for later comparison. Various procedures have been discussed in the literature, and each institution determines its own obstetric policies and procedures. A sample procedure follows:

1. Connect the 1000-ml bottle of amnioinfusion solution to the IV tubing.

2. Flush the tubing with the solution.

3. Connect the tubing to the woman’s IUPC via the amnioport or double-lumen IUPC, or via a three-way stopcock, depending on the type of IUPC used.

4. Initiate the flow of amnioinfusion and instill the initial bolus, usually 250 to 500 ml over a 20- to 30-minute period (10 to 15 ml/min) using either an infusion pump or gravity flow. If gravity flow is used, the solution must be hung about 3 to 4 feet above the level of the tip of the IUPC. If fluid will not run by gravity, check the position/placement of the IUPC.

5. When variable decelerations resolve, continue the infusion at a slower rate, usually about 2 to 3 ml/min (120 to 180 ml/hr), as ordered by the care provider. If variable decelerations are not relieved after infusing 800 to 1000 ml of solution, discontinue the procedure and perform an alternative intervention.

6. Observe and evaluate for amount and character of vaginal drainage. Vaginal output is assessed and documented to demonstrate that the volume infused is also coming back out and not causing overdistension of the uterus. Be vigilant for sudden “gushes” of fluid and assess for cord prolapse.

NOTE: Intrauterine resting tone will appear higher than normal, from 25 to 40 mm Hg, because of resistance to outflow through the tiny holes in the tip of the catheter. The true resting tone can be checked by temporarily discontinuing the flow of infusion.

Patient care

Care of the woman undergoing amnioinfusion includes the following:

1. Stop the infusion periodically, approximately every 30 to 60 minutes, to note the baseline uterine pressure. If the resting tone of the uterus exceeds 40 mm Hg, discontinue the infusion and notify the physician.

2. Change the underpads frequently to ensure the woman’s comfort.

3. Note the color and amount of fluid on the underpads. The underpads may be weighed. Amounts of fluid returned should be determined (1 ml = 1 g).

4. Monitor for signs and symptoms of infection.

5. Monitor for signs and symptoms of cardiac or respiratory compromise secondary to an overexpanded uterus (maternal shortness of breath, hypotension, or tachycardia).

6. Monitor fetal heart rate patterns on the electronic fetal monitoring strip.