Dural puncture usually refers to puncture of the dura and the underlying arachnoid mater. It may be deliberate during subarachnoid anaesthesia or accidental during epidural analgesia. The incidence in the latter case is traditionally said to be around 1% in teaching centres, but many authorities consider this to be unacceptably high, with an incidence of 0.5-1% being a realistic target and < 0.5% attainable in experienced hands. Most would routinely include dural puncture in their discussion with patients of the risks associated with regional analgesia.
Most accidental dural punctures are caused by the epidural needle, although it is possible for an epidural catheter to migrate through the dura. In-vitro studies suggest that this can only occur if there has been prior (unrecognised) dural puncture or partial tear of the dura by the needle. While there is a lack of randomised controlled trials that evaluate the efficacy of different techniques for location of the epidural space, the use of continuous loss of resistance to saline has, in animal models, shown superiority over the intermittent technique and is associated with a reduced risk of pneumocephalus compared with loss of resistance to air. Rotating the Tuohy needle once its tip is within the epidural space has been implicated in dural puncture and is now generally considered undesirable.
Problems and special considerations
Diagnosis
Dural puncture is usually heralded by a ‘give’ as the needle passes through the dura, and passage of cerebrospinal fluid (CSF) through the needle. For subarachnoid block, these two signs may be influenced by the design of the needle. In a combined spinal-epidural technique, it is usually easier to identify the dura by feel, especially in less experienced hands, since the starting position of the spinal needle in relation to the dura is more precisely known.
When a 16-18 G Tuohy needle is accidentally passed into the subarachnoid space, there is usually free flow of CSF, which poses no diagnostic difficulty. However, studies during deliberate dural puncture when placing lumbar drains before neurosurgery have revealed that occasionally free flow is not obtained. Thus, the appearance of slowly dripping clear fluid at the hub of the needle may represent CSF from a dural puncture or backflow of saline injected into the epidural space during a loss-of-resistance technique and may cause confusion, especially during a difficult procedure. In this situation, testing for temperature, glucose and protein content and pH (the last three by using urinary testing strips) will reliably distinguish CSF from saline (even saline that has been injected into the epidural space).
Occasionally, typical postdural puncture headache (PDPH) may be the first evidence that dural puncture has occurred, although this may reflect either inexperience on the part of the operator in not recognising accidental dural puncture or the operator not wishing to ‘own up’ in the hope that PDPH will not occur.
Adverse consequences
Adverse consequences of dural puncture are PDPH (which occurs in 60-90% of cases of accidental dural puncture in parturients) and its sequelae such as cranial nerve palsies, convulsions, subdural or intracranial haemorrhage, and chronic headache (see Chapter 45, Postdural puncture headache).
Management options
The aims of management of accidental dural puncture during establishment of epidural analgesia should include provision of adequate analgesia, safety of the patient and, if possible, reduction of risk from the adverse consequences of the dural puncture.
Traditional immediate management of accidental dural puncture comprises removing the needle and placing an epidural catheter at the adjacent (cranial) interspace, although this carries an additional risk of another unintentional dural puncture. Most units advocate that all subsequent top-ups during labour should be administered by an anaesthetist. The woman, her partner and the attending midwives and/or obstetricians should be informed that accidental dural puncture has occurred.
Other management options include converting the initial block to subarachnoid, which may include inserting the catheter into the subarachnoid space for a continuous subarachnoid block, for example by using 1-2 ml of standard low-dose epidural solution as top-ups or 1-2 ml/hour by infusion. Some observational studies suggest that inserting the catheter has been associated with a reduced incidence of PDPH, and it has been suggested that a possible mechanism is via initiating an inflammatory reaction around the catheter. However, other studies have not found this to be the case. If the catheter is placed intrathecally, it must be clearly labelled and the whole team informed, since there is a risk that it might be mistaken for an epidural catheter.
Studies of the association between pushing during the second stage of labour and an increased incidence of PDPH have yielded conflicting results. Traditionally, women who have had an accidental dural puncture have been advised to accept instrumental delivery to avoid pushing, but this is now generally considered unnecessary.
The performance of prophylactic epidural blood patch (see Chapter 46) is not routinely recommended. Likewise, epidural infusion of crystalloid after delivery (e.g. 1 litre of saline over 24 hours) has not been found to reduce the incidence of PDPH.
The use of epidural or spinal opioids has also been claimed to reduce the incidence of PDPH, although most of the evidence for this is weak apart from one randomised controlled study that has shown a reduction in the incidence of PDPH with epidural morphine. The evidence on the usefulness of drugs such as sumatriptan, pregabalin, ACTH or cosyntropin is inconclusive.
After delivery, there is no benefit in restricting the mother to bed, since this does not prevent PDPH. Similarly, although dehydration can exacerbate PDPH there is no evidence that overhydration has any beneficial effect. The mother should be visited regularly and given full support, and if PDPH occurs she should be offered the various management options available (see Chapter 45, Postdural puncture headache). She should also be informed about the possible serious sequelae of dural puncture, but reassured that they are rare.
It is equally important that the anaesthetist is honest with his/her colleagues, since attempting to conceal accidental dural puncture may only serve to delay appropriate management. Each unit should have a clear protocol for managing accidental dural puncture, and there should be a system in place for recording and monitoring such cases, usually involving a senior anaesthetist. Postpartum follow-up at 6-10 weeks is recommended in order to check that symptoms have resolved and to advise about future pregnancies.
Key points
• The incidence of accidental dural puncture should be less than 1%.
• Immediate management includes re-siting the epidural or inserting the catheter into the subarachnoid space.
• All top-ups should be administered by an anaesthetist.
• The mother should be allowed to mobilise freely and advised to avoid dehydration.
• Mothers should be followed up regularly and any headache managed promptly.
Further reading
Apfel CC, Saxena A, Cakmakkaya OS, et al. Prevention of postdural puncture headache after accidental dural puncture: a quantitative systematic review. Br J Anaesth 2010; 105: 255-63.
Basurto Ona X, Osario D, Bonfill Cosp X. Drug therapy for treating post-dural puncture headache.
Cochrane Database Syst Rev 2015; (7): CD007887.
Peralta F, Devroe S. Any news on the postdural puncture headache front? Best Pract Res Clin Anaesthesiol 2017; 31: 35-47.