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.

Predictive value of traction force measurement in vacuum extraction: Development of a multivariate prognostic model

“…[26]. In our previous study[8], we observed a seven percent prevalence of (mild) hypoxic ischemic encephalopathy in strong category extraction. There is also some data suggesting that hypoxic encephalopathy and subgaleal hematoma might be comorbid conditions[29].…”

“…Two studies on plastic cup extractions suggest that the majority of deliveries require no more than the force equivalent to 11,5 kg (approximately 112 Newton)[6, 7]. Our research group found a different result in an observational study of 200 metal cup extractions, with average peak traction forces of 176, 225 and 241 N, depending on subjective category as easy, average or strong extraction respectively[8]. …”

“…As a result of risk group identification, we excluded outlet extractions, since our previous observational study on traction force levels showed no strong extractions within this group[8]. High extractions (vertex above the ischiatic spines) are not common practice in Swedish obstetrics.…”

“…To measure the traction force employed during vacuum extraction, we used an intelligent handle attached to the chain of a regular metal cup (Bird 50 mm, 80 kPa) as described in a previous study[8]. The handle contains a load cell, a well established type of force sensor[10].…”

Predictive factors for the success of McRoberts’ manoeuvre and suprapubic pressure in relieving shoulder dystocia: a cross-sectional study

“…Contrasting instrumental delivery where the head is pulled out by a stronger force in a relatively short period of time resulting in rapid descent of the fetal head and shoulders through the pelvis [20, 23]. It was estimated that during a vacuum extraction, the traction force on the fetus is up to 294 N [24], nine times higher than the usual force of spontaneous delivery [25]. This may result in the shoulders, especially the posterior shoulder, not descending along the curved sacral path synchronously with the pulled head.…”