Traction force during vacuum extraction: a prospective observational study

Abstract

Objective: To investigate the traction force employed during vacuum extractions.

Design: Observational cross-sectional study.

Setting: Obstetric Department, Karolinska University Hospital, Sweden, and the Swedish National Congress of Obstetrics and Gynaecology, 2013.

Population: Two hundred women with vacuum extraction at term and 130 obstetricians participating in a simulated setting.

Methods: In a normal clinical setting, we used a specially adapted device to measure and record the force used to undertake vacuum extraction. In a subsequent part of the study, the force employed for vacuum extraction by a group of obstetricians in a fictive setting was estimated and objectively measured.

Main outcome measures: Applied force during vacuum extraction in relation to the estimated level of difficulty in the delivery; perinatal diagnoses of asphyxia or head trauma; estimated force compared with objectively measured force employed in the fictive setting.

Results: The median (minimum-maximum) peak forces for minimum, average and excessive vacuum extraction in the clinical setting were 176 N (5-360 N), 225 N (115-436 N), and 241 N (164-452 N), respectively. In 34% of cases a force in excess of 216 N was employed. There was no correlation between the umbilical arterial pH at delivery and the traction force employed during extraction. Four cases of mild hypoxic ischaemic encephalopathy were observed, three of which were associated with a delivery whereby excessive traction force was employed during the vacuum extraction. In the fictive setting, the actual exerted force was twice the quantitative estimation. The measured forces in the clinical setting were four times higher than that estimated in the fictive setting.

Conclusions: Higher than expected levels of traction force were used for vacuum extraction delivery. As obstetricians tend to underestimate the force applied during vacuum extraction, objective measurement with instantaneous feedback may be valuable in raising awareness.

Keywords: Failed vacuum extraction; traction force; vacuum extraction.