title: Traction force during vacuum extraction: a prospective observational study.
abstract: OBJECTIVE
  To investigate the traction force employed during vacuum extractions.
  
  
  METHODS
  Observational cross-sectional study.
  
  
  METHODS
  Obstetric Department, Karolinska University Hospital, Sweden, and the Swedish National Congress of Obstetrics and Gynaecology, 2013.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
authors.affiliation: Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Pettersson
authors.affiliation: Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Ajne
authors.affiliation: Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Yousaf
authors.affiliation: KTH Royal Institute of Technology, School of Technology and Health, Stockholm, Sweden.
authors.forename: D
authors.initials: D
authors.lastname: Sturm
authors.affiliation: Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Westgren
authors.affiliation: Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Ajne
mesh_terms: D000328:Adult; D001720:Birth Injuries / Q000209:etiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D020925:Hypoxia-Ischemia, Brain / Q000209:etiology; D055595:Mechanical Phenomena; D011247:Pregnancy; D011446:Prospective Studies; D013548:Sweden; D014620:Vacuum Extraction, Obstetrical / Q000009:adverse effects / Q000379:methods*
keywords: Failed vacuum extraction; traction force; vacuum extraction