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Objective: To characterize the performance of vacuum equipment used in operative vaginal deliveries., Study Method: We measured wall suction in eight Cleveland area labor-and-delivery units. Additionally, we tested samples of hand-operated and electric vacuum pumps. For each apparatus we recorded vacuum in millimeters of mercury using a calibrated, diaphragm-type gauge. We calculated mean maximal vacuum. Work required to produce 500 mm Hg of vacuum was determined for the hand-operated pumps. At increments of vacuum, we compared the vacuum displayed by the gauge head included with the device to our standard., Results: Mean wall suction was 494 mm Hg (range, 248-655). As compared to the Mity-vac, the CMI hand-operated pump needed significantly more work to generate 500 mm Hg of vacuum. Electric pumps produced a reliable and consistent vacuum. Gauges included with the pump had an average error of 4% over 400-600 mm Hg., Conclusion: Wall suction was an unreliable source of vacuum. The two hand-operated pumps tested required significantly different amounts of work to achieve an adequate vacuum. Addition of a fluid trap does not affect the vacuum, and head gauges supplied with vacuum pumps are accurate.

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.

Objective: Our objective was to describe the effect of off-axis traction on the performance of modern vacuum extractors., Study Design: Eight vacuum extractors were examined in the laboratory with a force indicator and fetal cephalic model. Devices evaluated included the 6 cm Malmstrom, Mity-Vac, M-Type, O'Neil, Posterior, Silc, Tender-Touch, and silicone elastomer. Maximal tractive force (pop-off) was measured for each device at 10-degrees increments from the vertical., Results: Multivariate regression analysis described the best model as follows: Maximal tractive force = Constant + Angle + Vacuum (p < 0.05). The partial regression coefficients for angle were negative in all devices except the Posterior cup. At increasing angles of off-axis traction, maximal tractive force decreased in the following order: Silc, silicone elastomer, Tender-Touch, M-Type, Mity-Vac, O'Neill, Malmstrom, and Posterior., Conclusions: Application of oblique traction resulted in a linear decline in maximal tractive force. An understanding of in vitro performance may allow tailoring of cup selection to the clinical situation.