Amnioinfusion refers to the instillation of fluid into the amniotic cavity. This procedure is typically performed during labor through an intrauterine pressure catheter introduced transcervically after rupture of the fetal membranes. Alternatively, fluid can be infused through a needle transabdominally, the reverse process of amniocentesis.
The rationale for amnioinfusion is that augmenting amniotic fluid volume may decrease or eliminate problems associated with a severe reduction or absence of amniotic fluid, such as severe variable decelerations during labor.
In the absence of other indications for antibiotic use, we do not administer antibiotics during amnioinfusion. A randomized trial showed that prophylactic use of cefazolin in the infusate (1 g/1000 mL of normal saline) did not significantly reduce rates of maternal or neonatal infection .
The transcervical approach is preferred for women in labor because it does not require ultrasound guidance and the catheter can be used for repeated fluid instillation. After rupture of the fetal membranes, an intrauterine pressure catheter is inserted using standard technique and attached to intravenous extension tubing; a pediatric nasogastric feeding tube can be used if an intrauterine pressure catheter is not available . The catheter is used to infuse Lactated Ringers solution without dextrose into the amniotic cavity. We prefer Lactated Ringers to normal (0.9 percent) saline because the latter may cause small changes in the concentration of fetal electrolytes ; however, the electrolyte concentrations remain in the physiologic range so normal saline is an acceptable alternative [4,5].
Protocols vary across institutions and no one protocol has been proven to be superior. A survey of obstetrical units revealed that they used the following methods in decreasing order of frequency: (1) a fluid bolus (50 to 1000 mL) followed by a constant infusion, (2) serial boluses (200 to 1000 mL administered every 20 minutes to four hours), and (3) constant infusion (15 to 2250 mL/hour) . A randomized trial found that continuous and intermittent infusions were similarly effective .