Intrapartum care
DOI: 10.1111/1471-0528.13222 www.bjog.org
Traction force during vacuum extraction: a prospective observational study K Pettersson,a J Ajne,a K Yousaf,a D Sturm,b M Westgren,a G Ajnea a Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden b KTH Royal Institute of Technology, School of Technology and Health, Stockholm, Sweden Correspondence: G Ajne, Department of Obstetrics and Gynaecology, Karolinska University Hospital, K 57, Huddinge, S-14186 Stockholm, Sweden. Email [email protected]
Accepted 15 October 2014. Published Online 5 January 2015.
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.
Please cite this paper as: Pettersson K, Ajne J, Youssaf K, Sturm D, Westgren M, Ajne G. Traction force during vacuum extraction: a prospective observational study. BJOG 2015;122:1809–1816.
Introduction Vacuum extraction is often chosen as an alternative to obstetric forceps for expediting a vaginal delivery because it is easy to perform and is associated with less extensive maternal perineal damage.1,2 However, the prevalence of neonatal complications such as asphyxia, intracranial haemorrhage3–6 and seizures7 is higher compared with that observed with a spontaneous vaginal delivery.5 Whether this is caused by the actual application of the instrument or by the prolonged intrauterine forces exerted on the fetus preceding the operative assistance is still debatable because a similar increase rate is also observed with caesarean sections.5 Caesarean section also carries with it additional
ª 2015 Royal College of Obstetricians and Gynaecologists
potential maternal risks such as excessive haemorrhage, uterine tears8 and sepsis.9 Prolonged labour also increases the risk of postpartum haemorrhage.8 Failed vacuum extraction (i e when a sequential method of delivery is required) is associated with significantly higher risk of perinatal morbidity compared with spontaneous delivery or successful vacuum extraction.6,10,11 O’Mahony et al.12 suggested that this increase in adverse outcome of vacuum extraction can be largely explained by poor clinical judgement by the obstetrician. Safety measures recommended for vacuum extraction delivery include restricting the total time of the procedure and the number of traction pulls, employing vacuum extraction delivery for pregnancies beyond 34 weeks of
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gestation, and using the procedure only when the station of the fetal vertex is at or below the ischial spines.13 An additional piece of advice is to avoid excessive traction force. All of these measures for safe vacuum extraction deliveries can be achieved with training except for the amount of traction force employed; the difference between excessive, average or minimum traction forces employed during the vacuum extraction is usually determined subjectively by the obstetrician. There is little information regarding the traction force employed during vacuum extraction deliveries, but a few studies measuring this force using a rigid plastic device with an internal meter have been reported.14,15 The aims of the present study were to investigate the actual traction forces employed for vacuum extraction in a university hospital and to analyse the correlation between the applied force and clinical outcome. We also sought to determine whether the subjective assessment of the traction force (minimum, average or excessive) estimated by the obstetricians during a vacuum extraction in a fictive setting correlated with the objectively measured force.
Methods The first part of this study was undertaken from August 2012 to October 2013 at Karolinska University Hospital. A total of 438 vacuum extraction deliveries were performed during this period. This was 9% of all deliveries at the hospital, which is similar to the Swedish national rate.16 All singleton pregnancies resulting in a vacuum extraction delivery were eligible for inclusion into the study, including failed vacuum extraction, and the standards of the Royal College of Obstetricians and Gynaecologists in the UK were used to classify the extractions.13 All obstetricians were encouraged to use the Bird metal cup that is attached to the traction force measurement device described below. However, a large proportion of the outlet vacuum extraction procedures were excluded from the study because some obstetricians preferred to employ the plastic cups instead for such deliveries. The main outcome measures were the peak force and the total force related to three categories of vacuum extractions. These categories have been used in the Swedish maternity system since 1992 and represent the obstetrician’s subjective perception of the traction force employed: minimum, average or excessive. The forces used in successful and failed vacuum extractions were also compared. Secondary outcomes were the neonatal umbilical blood gases, Apgar scores and birthweight, and diagnoses at the neonatal intensive care unit (birth asphyxia with pH in the umbilical artery
DOI: 10.1111/1471-0528.13222 www.bjog.org
Traction force during vacuum extraction: a prospective observational study K Pettersson,a J Ajne,a K Yousaf,a D Sturm,b M Westgren,a G Ajnea a Department of Obstetrics and Gynaecology, The Karolinska Institute, Karolinska University Hospital, Stockholm, Sweden b KTH Royal Institute of Technology, School of Technology and Health, Stockholm, Sweden Correspondence: G Ajne, Department of Obstetrics and Gynaecology, Karolinska University Hospital, K 57, Huddinge, S-14186 Stockholm, Sweden. Email [email protected]
Accepted 15 October 2014. Published Online 5 January 2015.
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.
Please cite this paper as: Pettersson K, Ajne J, Youssaf K, Sturm D, Westgren M, Ajne G. Traction force during vacuum extraction: a prospective observational study. BJOG 2015;122:1809–1816.
Introduction Vacuum extraction is often chosen as an alternative to obstetric forceps for expediting a vaginal delivery because it is easy to perform and is associated with less extensive maternal perineal damage.1,2 However, the prevalence of neonatal complications such as asphyxia, intracranial haemorrhage3–6 and seizures7 is higher compared with that observed with a spontaneous vaginal delivery.5 Whether this is caused by the actual application of the instrument or by the prolonged intrauterine forces exerted on the fetus preceding the operative assistance is still debatable because a similar increase rate is also observed with caesarean sections.5 Caesarean section also carries with it additional
ª 2015 Royal College of Obstetricians and Gynaecologists
potential maternal risks such as excessive haemorrhage, uterine tears8 and sepsis.9 Prolonged labour also increases the risk of postpartum haemorrhage.8 Failed vacuum extraction (i e when a sequential method of delivery is required) is associated with significantly higher risk of perinatal morbidity compared with spontaneous delivery or successful vacuum extraction.6,10,11 O’Mahony et al.12 suggested that this increase in adverse outcome of vacuum extraction can be largely explained by poor clinical judgement by the obstetrician. Safety measures recommended for vacuum extraction delivery include restricting the total time of the procedure and the number of traction pulls, employing vacuum extraction delivery for pregnancies beyond 34 weeks of
1809
Pettersson et al.
gestation, and using the procedure only when the station of the fetal vertex is at or below the ischial spines.13 An additional piece of advice is to avoid excessive traction force. All of these measures for safe vacuum extraction deliveries can be achieved with training except for the amount of traction force employed; the difference between excessive, average or minimum traction forces employed during the vacuum extraction is usually determined subjectively by the obstetrician. There is little information regarding the traction force employed during vacuum extraction deliveries, but a few studies measuring this force using a rigid plastic device with an internal meter have been reported.14,15 The aims of the present study were to investigate the actual traction forces employed for vacuum extraction in a university hospital and to analyse the correlation between the applied force and clinical outcome. We also sought to determine whether the subjective assessment of the traction force (minimum, average or excessive) estimated by the obstetricians during a vacuum extraction in a fictive setting correlated with the objectively measured force.
Methods The first part of this study was undertaken from August 2012 to October 2013 at Karolinska University Hospital. A total of 438 vacuum extraction deliveries were performed during this period. This was 9% of all deliveries at the hospital, which is similar to the Swedish national rate.16 All singleton pregnancies resulting in a vacuum extraction delivery were eligible for inclusion into the study, including failed vacuum extraction, and the standards of the Royal College of Obstetricians and Gynaecologists in the UK were used to classify the extractions.13 All obstetricians were encouraged to use the Bird metal cup that is attached to the traction force measurement device described below. However, a large proportion of the outlet vacuum extraction procedures were excluded from the study because some obstetricians preferred to employ the plastic cups instead for such deliveries. The main outcome measures were the peak force and the total force related to three categories of vacuum extractions. These categories have been used in the Swedish maternity system since 1992 and represent the obstetrician’s subjective perception of the traction force employed: minimum, average or excessive. The forces used in successful and failed vacuum extractions were also compared. Secondary outcomes were the neonatal umbilical blood gases, Apgar scores and birthweight, and diagnoses at the neonatal intensive care unit (birth asphyxia with pH in the umbilical artery
