Shoulder Dystocia

Introduction

 

 

Shoulder dystocia is defined as a delivery that requires additional obstetric manoeuvres to release the shoulders after gentle downward traction has failed. Shoulder dystocia occurs when either the anterior or, less commonly, the posterior fetal shoulder impacts on the maternal symphysis or sacral promontory.

There is a wide variation in the reported incidence of shoulder dystocia but unselected population studies in North America and the UK found a 0.6% incidence.2001-01 There can be a high perinatal mortality and morbidity associated with the condition, even when it is managed appropriately.1998-01 Maternal morbidity is also increased, particularly postpartum haemorrhage (11%) and fourth-degree perineal tears (3.8%), and their incidence remains unchanged by the manoeuvres required to effect delivery.1997-01 Brachial plexus injuries are one of the most important fetal complications of shoulder dystocia, complicating 4?16% of such deliveries.1997-01,1985-01 This appears to be independent of operator experience.2002-01 6, Most cases resolve without permanent disability, with fewer than 10% resulting in permanent brachial plexus dysfunction.1998-028 In the UK, the incidence of brachial plexus injuries is 1/2300 live births and has not changed over the last 40 years.2003-019 Neonatal brachial plexus injury is the single most common cause for litigation related to shoulder dystocia. Not all injuries are due to excess traction by the accoucheur2002-016 and there is now a significant body of evidence that maternal propulsive force may contribute to some of these injuries. Moreover, a substantial minority of brachial plexus injuries are not associated with clinically evident shoulder dystocia.2002-0210 Specifically, where there is Erb?s palsy, it is important to determine whether the affected shoulder was anterior or posterior at the time of delivery, because damage to the plexus of the posterior shoulder is considered not due to action by the accoucheur.

The Confidential Enquiries into Stillbirths and Deaths in Infancy?s (CESDI) 5th annual report recommended ?a high level of awareness and training for all birth attendants?. Annual skill drills, including shoulder dystocia, are recommended jointly by both the Royal College of Midwives (RCM) and the Royal College of Obstetricians andGynaecologists (RCOG).

Prediction, prevention and management of shoulder dystocia.

 

Owing to the emergency nature of the condition, most published series examining procedures for the management of shoulder dystocia are retrospective case series or case reports.

Can shoulder dystocia be predicted? Risk assessments for the prediction of shoulder dystocia are insufficiently predictive to allow prevention of the large majority of cases. A number of antenatal and intrapartum characteristics have been reported to be associated with shoulder dystocia.

Risk factors before labour include previous shoulder dystocia, macrosomia, diabetes mellitus, maternal body mass index > 30 kg/m2 and, with labour, induction of labour, during labour, prolonged first stage of labour, secondary arrest, oxytocin augmentation, prolonged second stage of labour, assisted vaginal delivery.

There is a relationship between fetal size and shoulder dystocia1985-015 but it is not a good predictor. The large majority of infants with a birth weight of ≥4500 g do not develop shoulder dystocia1995-0117 and, equally importantly,48% of incidences of shoulder dystocia occur in infants with a birth weight less than 4000 g. Moreover, clinical fetal weight estimation is unreliable and third-trimester ultrasound scans have at least a 10% margin for error for actual birth weight and a sensitivity of just 60% for macrosomia (over 4.5 kg).1999-0119 Conventional risk factors predicted only 16% of shoulder dystocia that resulted in infant morbidity.1987-0121 The large majority of cases occur in the children of women with no risk factors. Shoulder dystocia is, therefore, a largely unpredictable and unpreventable event.1996-0122

Clinicians should be aware of existing risk factors but must always be alert to the possibility of shoulder dystocia with any delivery. 

 

Does induction of labour prevent shoulder dystocia?  

There There is no evidence to support induction of labour in women without diabetes at term where the fetus is thought to be macrosomic. There are a number of evidence-based reviews that have demonstrated that early induction of labour for women with suspected fetal macrosomia who do not have diabetes does not improve either maternal or fetal outcome.2000-0124 Induction of labour in women with diabetes mellitus does not reduce the maternal or neonatal morbidity of shoulder dystocia. A Cochrane review of elective delivery for women with diabetes concluded that induction of labour in women with diabetes treated with insulin reduces the risk of macrosomia.2004-0125 There was a small decrease in the number of deliveries complicated by shoulder dystocia in the induction group1993-0126 but the risk of maternal or neonatal morbidity was not modified.

 

Should elective caesarean section be recommended for suspected fetal macrosomia? 

 

Elective caesarean section is not recommended to reduce the potential morbidity for pregnancies complicated by suspected fetal macrosomia without maternal diabetes mellitus. Elective caesarean section is not recommended for suspected fetal macrosomia (estimated fetal weight over 4.5 kg) without diabetes. Estimation of fetal weight is unreliable and the large majority of macrosomic infants do not experience shoulder dystocia.1995-0117 In the USA, a decision analysis model estimated that an additional 2345 caesarean deliveries would be required, at a cost of US$4.9 million, to prevent one permanent injury from shoulder dystocia.1999-0119 There is some difficulty in grouping all fetuses with an expected weight of over 4.5 kg together: some fetuses will be much larger than this.  Elective caesarean section should be considered to reduce the potential morbidity for pregnancies complicated by suspected fetal macrosomia associated with maternal diabetes mellitus. Planned caesarean section should be considered for the small group of women with diabetes and suspected fetal macrosomia (estimated fetal weight greater than 4.5 kg).1999-0119

 

What is the appropriate mode of delivery after a previous episode of shoulder dystocia?

 

Either caesarean section or vaginal delivery is appropriate after a previous shoulder dystocia. The decision should be made by the woman and her carers. There is a reported recurrence rate of shoulder dystocia of between 1% and 16%.1996-0122,1995-0229 However, this may be an underestimate owing to selection bias, as caesarean section may have been advocated for pregnancies after severe shoulder dystocia, particularly with a poor outcome. There is, therefore, no requirement to advise elective caesarean section routinely but factors such as the severity of any previous neonatal or maternal injury, fetal size and maternal choice should all be considered when offering recommendations for the next delivery.

 

What measures should be taken when shoulder dystocia is anticipated?

 

If shoulder dystocia is anticipated then some pre-emptive preparation may help. An experienced obstetrician, that is one on the second tier of an on-call rota, should be available on the labour ward for the second stage of labour when shoulder dystocia is anticipated. However, it is recognised that not all cases can be anticipated and therefore all birth attendants should be conversant with the techniques required to facilitate delivery complicated by shoulder dystocia.

 

How is shoulder dystocia diagnosed?

 

 

Routine traction in an axial direction may be employed to diagnose shoulder dystocia. Routine traction is defined as ?that traction required for delivery of the shoulders in a normal vaginal delivery where there is no difficulty with the shoulders?. Evidence from cadaver studies suggests that lateral and downward traction is more likely to cause nerve avulsion and therefore this should be avoided in the management of shoulder dystocia. Timely management of shoulder dystocia requires prompt recognition. The attendant health-carer should routinely observe for:

● difficulty with delivery of the face and chin

● the head remaining tightly applied to the vulva or even retracting

● failure of restitution of the fetal head

● failure of the shoulders to descend.

The use of the McRoberts? manoeuvre compared with the lithotomy position before clinical diagnosis of shoulder dystocia does not appear to reduce the traction force on the fetal head during vaginal delivery in multiparous women. Therefore its use cannot be recommended to prevent shoulder dystocia.2004-0234 

 

How should shoulder dystocia be managed?

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Shoulder dystocia should be managed systematically. It is important to manage the problem as efficiently as possible but also carefully: efficiently so as to avoid hypoxia acidosis, carefully so as to avoid unnecessary trauma. Immediately after recognition of shoulder dystocia, extra help should be called immediately. In a hospital setting, this should include further midwifery assistance, an obstetrician, a paediatric resuscitation team and an anaesthetist.1998-0335 Maternal pushing should be discouraged, as this may lead to further impaction of the shoulders, thereby exacerbating the situation.2003-0236 The woman should be manoeuvred to bring the buttocks to the edge of the bed. Fundal pressure should not be employed. Fundal pressure should not be used for the treatment of shoulder dystocia. It is associated with an unacceptably high neonatal complication rate and may result in uterine rupture.1987-0121

Episiotomy is not necessary for all cases. Some authors have advocated that episiotomy is an essential part of the management in all cases but others suggest that it does not affect the outcome of shoulder dystocia.1993-0238 The authors of one study have concluded that episiotomy does not decrease the risk of brachial plexus injury with shoulder dystocia.2004-0339 An episiotomy should therefore be considered but it is not mandatory. McRoberts? manoeuvre is the single most effective intervention and should be performed first.

  • The woman's legs should be maximally flexed on her abdomen
  • Apply additional mild downward traction on the fetal head with the aim to deliver the impacted anterior shoulder
  • McRoberts manoeuvre results in a straightening of the lumbar spine with consequent cephalic rotation of the symphysis pubis
  • This manoeuvre is successful in more than 40 % of cases (over 50 % when combined with supra- pubic pressure)

The McRoberts? manoeuvre is flexion and abduction of the maternal hips, positioning the maternal thighs on her abdomen.42 It straightens the lumbo-sacral angle, rotates the maternal pelvis cephalad4 and is associated with an increase in uterine pressure and amplitude of contractions. The McRoberts? manoeuvre is the single most effective intervention, with reported success rates as high as 90%.1997-014,1996-0244?46 It has a low rate of complication and therefore should be employed first.

Suprapubic pressure is useful. Suprapubic pressure can be employed together with McRoberts? manoeuvre to improve success rates.1997-014 Suprapubic pressure reduces the bisacromial diameter and rotates the anterior shoulder into the oblique pelvic diameter. The shoulder is then free to slip underneath the symphysis pubis with the aid of routine traction.1994-0145 Suprapubic pressure is applied in a downward and lateral direction to push the posterior aspect of the anterior shoulder towards the fetal chest. It is advised that this is applied for 30 seconds. There is no clear difference in efficacy between continuous pressure or ?rocking? movement. Advanced manoeuvres should be used if the McRoberts? manoeuvre and suprapubic pressure fail. If these simple measures (the McRoberts? manoeuvre and suprapubic pressure) fail, then there is a choice to be made between the all-fours-position and internal manipulation. Traditionally, internal manipulations are used at this point but the-all-fours position has been described, with an 83% success rate in one case series.1998-0447

The individual circumstances should guide the accoucheur. For a slim mobile woman without epidural anaesthesia and with a single midwifery attendant, the allfours- position is probably the most appropriate. For a less mobile woman with epidural anaesthesia in place and a senior obstetrician in attendance, internal manoeuvres are more appropriate. There is no advantage between delivery of the posterior arm and internal rotation manoeuvres and therefore clinical judgement and experience can be used to decide their order. Delivery of the fetal shoulders may be facilitated by rotation into an oblique diameter or by a full 180-degree rotation of the fetal trunk.2004-0449 Delivery may also be facilitated by delivery of the posterior arm. The fetal trunk will either follow directly or the arm can be used to rotate the fetal trunk to facilitate delivery. Delivery of the posterior arm has a high complication rate: 12% humeral fractures in one series, but the neonatal trauma may be a reflection of the refractory nature of the case, rather than the procedure itself.1996-0244 Some authors favour delivery of the posterior arm, particularly where the mother is large.2003-0351 There are no comparative studies available and therefore the accoucheur should base their decision on their training and clinical experience and the prevailing circumstances.

 

What measures should be taken if first- and second-line manoeuvres fail?

 

Third-line manoeuvres require careful consideration to avoid unnecessary maternal morbidity and mortality. It is difficult to recommend a time limit for the management of shoulder dystocia, as there are no conclusive data available. Several third-line methods have been described for those cases resistant to all simple measures. These include cleidotomy (bending the clavicle with a finger or surgical division), symphysiotomy (dividing the symphyseal ligament) and the Zavanelli manoeuvre. It is rare that these are required.

Cephalic replacement of the head, or the Zavanelli manoeuvre, and delivery by caesarean section has been described1985-0252 but there can be poor outcome.1995-0353 Similarly, symphysiotomy has been suggested as a potentially useful procedure. However, there is a high incidence of serious maternal morbidity and poor neonatal outcome.1997-0257 Consideration should be given to these facts, particularly if training has not been received. After delivery, the birth attendants should be alert to the possibility of postpartum haemorrhage and third- and fourth-degree perineal tears.

 

What measures can be taken to ensure optimal management of shoulder dystocia?

 

Training for all birth attendants in the management of shoulder dystocia is recommended by the Royal College of Midwives and RCOG. The optimal frequency of rehearsals is not known. More recently,Deering demonstrated that training with a simulation-training scenario improved resident performance in the management of shoulder dystocia.60 Moreover, training with a mannequin which provides force feedback may reduce the peak force used by the accoucheur during simulated delivery. Rehearsal can often be accommodated locally in delivery rooms62 using mannequins or the ubiquitous doll and pelvis. It is probably useful to demonstrate the manoeuvres in direct view, as they are complex and difficult to understand by description alone.

The HELPERR mnemonic H Call for help E Evaluate for episiotomy L Legs (the McRoberts? manoeuvre) P Suprapubic pressure E Enter manoeuvres (internal rotation) R Remove the posterior arm R Roll the patient.

 

How can successful litigation be avoided when shoulder dystocia occurs?

 

Accurate documentation of a difficult and potentially traumatic delivery is essential. It may be helpful to use a structured pro forma to aid accurate record keeping.

It is important to record:

● the time of delivery of the head

● the direction the head is facing after restitution

● the manoeuvres performed, their timing and sequence

● the time of delivery of the body ● the staff in attendance and the time they arrived

● the condition of the baby (Apgar score) ● umbilical cord blood acid-base measurements.

It is particularly important to document the position of the fetal head at delivery as this permits identification of the anterior and posterior shoulders during the delivery.


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