Effect of angular traction on the performance of modern vacuum extractors.
OBJECTIVE
Our objective was to describe the effect of off-axis traction on the performance of modern vacuum extractors.


METHODS
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.
Muise
K L
KL
Department of Obstetrics and Gynecology, University MacDonald Womens Hospital, Cleveland, OH.
Duchon
M A
MA
Brown
R H
RH
D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D008962:Models, Theoretical; D011247:Pregnancy; D012044:Regression Analysis; D014143:Traction; D014620:Vacuum Extraction, Obstetrical / Q000592:standards*