The frequency of extramembranous placement of intrauterine pressure catheters.

Objective: To determine, and confirm, the frequency of extramembranous placement of intrauterine pressure catheters.Methods: It is estimated that 15% of all deliveries in the United States (600,000 deliveries/year) receive intrauterine pressure catheters (IUPCs). This study quantifies the frequency of inadvertently placing IUPCs between the chorioamnionic membranes and the myometrium. An attempt was made to aspirate amniotic fluid during placement. If amniotic fluid was obtained, the catheter was considered to be within the amniotic cavity. If amniotic fluid was not obtained but the catheter appeared to be clinically working (possibly extramembranous), normal clinical management was continued until just before the catheter was removed. At that time, 2 mL of indigo carmine was injected. The chorioamnionic membrane was examined to confirm the location of dye (intraamnionic vs extramembranous).Results: Approximately 40 Koala (Clinical Innovations, Inc.) and 40 Intran Plus catheters (Utah Medical Products, Inc.) were placed. In 70% of all first insertions, amniotic fluid was not obtained. When multiple attempts (2-5) were made, amniotic fluid was obtained. There was no statistically significant difference between IUPC brands. Dye confirmed extramembraneous placement.Conclusions: IUPCs are frequently (inadvertently) placed extramembraneous. Upon first insertion it is possible that as many as 30% of IUPCs do not go into the amniotic space. If fluid is not obtained upon placement, a different location should be tried since if amniotic fluid is visualized in the catheter the percentage of intraamnionic placement increases. Adverse results of artefactual waveforms, placental perforation, and abruption with or without amnioinfusion can occur when IUPCs are placed extramembraneous.