The effect of artificial caput on performance of vacuum extractors.

OBJECTIVE

To isolate and describe the effect of chignon formation (vacuum-induced caput) on the performance of six vacuum extractors.

METHODS

Six vacuum extractors were examined in the laboratory: the 6-cm Malmstrom, Mityvac, M-Type, Silc, Silastic, and Tender-Touch. The devices were tested in two model systems that duplicated the fetal scalp with and without chignon. A fetal cephalic model mimicked the head without chignon. The second model used the hind quarters of anesthetized dogs. Chignon was formed by slowly increasing vacuum until the target vacuum was reached. At increments of vacuum, traction was applied in the axis of the cup and maximal tractive force (pop-off) was measured.

RESULTS

A statistically unique regression line described each device. There was no significant difference in the regression lines for the Malmstrom and M-Type cups with or without chignon. At equal vacuum, there was a significant decrease (P < .05) in maximal tractive force with chignon formation in the bell-shaped cups.

CONCLUSIONS

There is a demonstrable deterioration in the performance of bell-shaped cups with the formation of chignon. These data suggest that when using a bell-shaped extractor, efforts should be directed toward minimizing chignon formation by applying vacuum only with traction.