Vaginal delivery may be facilitated by the use of forceps or a suction cup (ventouse). Which instrument is used depends on the clinical situation and the operator’s skill. The Royal College of Obstetricians and Gynaecologists (RCOG) classification of instrumental deliveries is given in Table 32.1. Low- and mid-cavity positions may be further subdivided into a rotational delivery if the fetal head is more than 45 degrees from the occipito-anterior position.
In the UK, 10-13% of deliveries are performed with forceps or ventouse, but the figure varies considerably from one unit to another and is greatly affected by individual policies with respect to the maximum allowable duration of the second stage, the use of oxytocin to augment contractions, and criteria for caesarean section.
In general, instrumental delivery can be indicated by maternal factors (exhaustion, failure to descend, illness precluding Valsalva manoeuvre) or fetal factors (fetal distress, prematurity). The commonest indication is prolongation of the second stage, often defined as longer than 2 hours for a primigravida (3 hours with an effective epidural) or 1 hour for a multigravida (2 hours with an epidural).
An instrumental delivery may be associated with maternal and fetal trauma. Measures to reduce its incidence, such as continuous maternal support and delayed pushing for women with epidurals, are therefore recommended.
Table 32.1 Classification of instrumental delivery
|
Classification |
Description |
|
Outlet |
Fetal head has reached labia or pelvic floor |
|
Low |
Fetal head is 2 cm below the ischial spines but has not reached the pelvic floor |
|
Mid-cavity |
Fetal head is 1/5 palpable from the abdomen, and below the ischial spines |
|
High |
Fetal head is 2/5 palpable and above the ischial spines (instrumental delivery not recommended; caesarean section advised) |
Adapted with permission from RoyalCollege of Obstetricians and Gynaecologists. Operative Vaginal Delivery. Green-top Guideline 26. London: RcOG, 2011.
Problems and special considerations
Instrumental delivery and regional analgesia
There is no doubt that, in most centres, there is a higher rate of instrumental delivery in mothers who opt for regional analgesia. Although it is very difficult to exclude potential confounders (e.g. it is likely that women who need epidural analgesia are those with other factors that predispose to instrumental delivery, such as slow progress, malpresentation, multiple gestation, relative cephalopelvic disproportion), and most randomised trials of epidural analgesia have been complicated by considerable crossover between groups (mostly from non-epidural to epidural), meta-analysis suggests an increased likelihood of instrumental delivery with epidural techniques (relative risk ~1.4). This must be weighed against the improved quality of analgesia compared with alternatives, the beneficial effect of epidural analgesia on fetal acid-base balance, and the ability to avoid general anaesthesia in many cases should caesarean section be required.
Analgesia
Analgesia produced by low-dose epidural solutions may be adequate for low-outlet (‘lift- out’) forceps or ventouse delivery, but mid-cavity forceps delivery requires dense surgical anaesthesia. A good pelvic block is essential, and the perineum should be tested before inserting the instrument. For anything other than an outlet forceps or ventouse, the sensory block should extend up to T10, and a block suitable for caesarean section should be considered, depending on the likelihood of failure and the speed at which progression to surgery is likely to be required (see below). It is advisable for the anaesthetist to be present when anything other than the most straightforward instrumental delivery is being performed, in order to assess the existing block, consider the options, and give (and monitor the effects of) an appropriate top-up.
'Trial' of forceps
When it is anticipated that instrumental delivery may be difficult, this should be considered as a ‘trial’ of instrumental delivery, and provision should be made for immediate conversion to caesarean section. A systematic review has suggested a failure rate of 9% with attempted forceps delivery and 14% with vacuum devices, though a failed forceps delivery is more likely to result in a caesarean section. The procedure should be carried out in the operating theatre, and regional anaesthesia should be adequate for rapid operative delivery. Attempted instrumental delivery is more likely to fail if the mother’s body mass index (BMI) exceeds 30 kg/m2, if the baby is large, or if the head is in the occipito-posterior position or mid-cavity or above. A trial of instrumental delivery should be abandoned if there is no evidence of descent with traction during each contraction, or if delivery is not imminent following three effective attempts by an experienced obstetrician.
Management options
For deliveries other than outlet forceps and ventouse, with a functioning epidural in situ, it is usually an easy matter to intensify the block by administering 10-20 ml of 0.5% levobupivacaine, 0.75% ropivacaine or 2% lidocaine with adrenaline (± bicarbonate), depending on the anticipated difficulty with delivery and the urgency, and local protocols.
Pelvic spread may be encouraged by sitting the mother up, and it is therefore important to establish the block before putting the legs into stirrups. Maternal pushing may be compromised by sensory and motor blockade, so effective coaching by the midwife and partner is often required.
When no epidural is in place, spinal anaesthesia is most appropriate, using ~1.5 ml of hyperbaric 0.5% bupivacaine in the sitting position, ± 10-15 µg fentanyl. However, if caesarean section is anticipated, a spinal or a combined spinal-epidural technique, using the same dose as required for surgical anaesthesia, may be more appropriate.
Pudendal block may be performed by the obstetrician if there is no anaesthetist available, although it has a high failure rate and needs at least 10-20 minutes to become effective. Pudendal block may also be used to supplement an existing epidural with sacral sparing, and infiltration of the perineum with local anaesthetic is a useful adjunctive technique before performing an episiotomy.
In all cases, care must be taken to ensure that aortocaval compression is avoided, for example by tilting the mother’s pelvis with a wedge.
Aftercare
It should be remembered that the extensive episiotomy that usually accompanies instrumental delivery, coupled with the inevitable tissue trauma, often results in significant pain in the immediate postpartum period. Non-steroidal anti-inflammatory drugs (NSAIDs) should be used prophylactically if there are no contraindications, and epidural opioids are often required. At present there is insufficient evidence to support routine antibiotic prophylaxis, though local policy should be followed. Significant postpartum haemorrhage can result from cervical or vaginal tears, and this may exceed that at a caesarean section, and so vigilance regarding blood loss is essential. The need for thromboprophylaxis must be reassessed after an operative vaginal delivery.
Key points
• A good pelvic block is essential for operative vaginal delivery, and should be confirmed by testing.
• Conversion to caesarean section may be required.
• Anaesthesia should be established before elevating the legs.
Further reading
Anim-Somuah M, Smyth RM, Cyna AM, Cuthbert A. Epidural versus non-epidural or no analgesia for pain management in labour. Cochrane Database Syst Rev 2018; (5): CD000331.
Liu EH, Sia AT. Rates of caesarean section and instrumental vaginal delivery in nulliparous women after low concentration epidural infusions or opioid analgesia: systematic review. BMJ 2004; 328: 1410.
Royal College of Obstetricians and Gynaecologists. Operative Vaginal Delivery. Green-top Guideline 26. London: RCOG, 2011. www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg26 (accessed December 2018).