Mechanism of dural puncture epidural effect. The dural puncture epidural (DPE) technique. Following the introduction of a 17 to 18 gauge epidural needle through the ligamentum flavum, a longer 25 to 26 gauge spinal needle is introduced through the epidural needle and punctures the dura (dural ligament or sac). The spinal needle is removed, and an epidural catheter is placed. Medication is dosed through the epidural catheter, which translocates though the spinal-needle-created passageway, into the subarachnoid space.
In comparison to the epidural technique, the DPE technique has a number of advantages, including a faster sacral blockade, greater bilateral coverage and a lower epidural catheter failure rate (Table 10.2). In addition, the epidural catheter is immediately tested with medications for correct placement; this is the principal advantage over the CSE technique, particularly for parturients with a difficult airway or a high probability of an instrumental or operative delivery.
As with any dural puncture technique, the risk for a PDPH and infection is present, but uncommon.
Preparing for a neuraxial technique
History, physical, testing and informed consent
Prior to proceeding with any neuraxial technique, a focused review of the obstetric, anaesthetic, medical and surgical history should be performed, accompanied by a brief physical examination with vital signs. Routine platelet count and blood typing with screening or cross-matching are not necessary; however, lab and additional testing (i.e. electrocardiogram or imaging) should be dictated by the current condition of the patient and anticipated likely outcomes. Communication with the multidisciplinary team is encouraged.
A discussion of the potential risks and consent for the procedure should be undertaken antenatally if possible, or at the earliest possible convenience when in labour. The presence of labour pain does not preclude an informed consent; however, care should be taken to query and document the comprehension of the information discussed.
Medications, equipment and monitors
As expected and unexpected physiologic sequelae may occur following neuraxial techniques, intravenous access should be established, with medications and equipment available to respond to common (e.g. hypotension) and less frequent side effects and complications (e.g. high spinal, local anaesthetic toxicity; see below). Medications to have readily available include ephedrine and phenylephrine, but also atropine, epinephrine, naloxone, calcium chloride and lipid emulsion. Emergency equipment, including a self-inflating bag and mask, an oxygen source, a cardiac resuscitation trolley and a difficult airway trolley should be immediately available in a known, accessible location.
The maternal blood pressure should be measured between contractions at baseline, and every 1 to 3 minutes after neuraxial technique placement for approximately 20 minutes, or until haemodynamic stability has been demonstrated. Subsequently, throughout labour, maternal blood pressure should be measured every 15 to 30 minutes, or in accordance with local guidelines. Continuous pulse oximetry is useful to monitor maternal heart rate and saturation, and should be considered throughout labour in selected patients (e.g. sleep apnoea, cardiac disease, etc.). Assessment of the sensory level and motor ability should occur regularly (Box 10.3).
Sensory evaluation
Cold, pinprick or touch sensation from caudad to cephalad orientation in the midaxillary line
Motor evaluation
Bromage scale (modified)-degree of blockade
| None: | Full flexion of knees and feet |
| Partial: | Partial ability to flex knees, able to move feet |
| Almost Complete: | Inability to flex knees, able to move feet |
| Complete: | Unable to move knees or feet |
Fetal heart rate (FHR) monitoring should occur before and after the administration of neuraxial analgesia; opioid administration within the subarachnoid versus epidural space is associated with a higher incidence of non-reassuring FHR patterns. Continuous external FHR monitoring is often used for the remainder of the labour; however, it may not be necessary or possible in every clinical setting. In some cases, particularly when external monitoring proves difficult (e.g. high BMI), a fetal scalp electrode may be indicated.
Hydration and position
Insertion of an intravenous catheter (>18 gauge) is an absolute requirement prior to the placement of a neuraxial technique, to allow for correction of hypovolaemia and treatment of the sympathectomy-induced hypotension with fluids or vasopressors (e.g. phenylephrine 40 µg, or ephedrine 10 mg). A fixed volume of fluid prior to the administration of a neuraxial technique is not necessary, and recent investigations with spinal anaesthesia-induced hypotension during caesarean delivery indicate that fluid administration at the time of neuraxial technique administration (co-loading), versus in advance (preloading), is more effective. A balanced crystalloid solution (e.g. lactated Ringers or Hartmann’s solution) without dextrose is the most commonly used fluid in labouring women; however, colloid solutions, which have a longer intravascular dwell time and consequently a more prolonged effect on preload and cardiac output, may be valuable, particularly when hypovolaemia is initially present or when the presence of even modest hypotension would be detrimental (e.g. aortic stenosis).
Although the sitting position is the most common position used for the initiation of neuraxial techniques, the lateral decubitus position may offer greater maternal comfort, less orthostatic hypotension, and improved ability to monitor FHR and maintain optimal maternal and fetal positioning. Moreover, the lateral position offers the option of providing a neuraxial technique in the setting of a presenting fetal part or cord prolapse. The sitting position may facilitate identification of the midline in high body mass index patients and improved respiratory mechanics in patients with respiratory issues. FHR monitoring during positioning may provide information on optimal positioning for fetal perfusion; aortocaval compression must be avoided at all times.
Insertion of a neuraxial technique
The timing of neuraxial technique insertion should be based on a conversation between the patient, the obstetric care team and the anaesthetist. The initiation of neuraxial analgesia early vs. late in labour does not affect the caesarean delivery rate. The choice of neuraxial technique, agents and dosages is based on a number of factors, including patient and provider preferences.
Prior to commencing the technique, the patient should be asked to confirm her identity and understanding of the anticipated technique, and the anaesthetist should verbally review aloud the relevant medical, obstetric and anaesthetic issues; these steps serve to improve patient safety.
The epidural space should be identified with a loss of resistance to intermittent or continuous pressure with either air, saline or their combination. Midline and paramedian approaches have been used. A specific epidural approach, method or medium used for loss of resistance has not been uniformly found to be better in ensuring successful placement, improving analgesia or minimizing risks.
If the epidural loss of resistance is equivocal, or the intent is to perform a CSE or DPE technique, a longer spinal needle (10 to 15 mm longer than the epidural needle when completely inserted) can be advanced as a ‘finder needle’ through the shaft of the epidural needle (needle-through-needle method) into the dural sac with cerebrospinal fluid (CSF) confirmed. If CSF is not obtained, the epidural needle may be of insufficient depth (thereby not allowing the spinal needle to reach the dural sac) or off the midline (allowing the spinal needle to miss the dural sac). If CSF is not confirmed, but the epidural catheter is threaded and dosed, a higher failure rate of the resulting analgesia or anaesthesia has been observed.
If during the epidural needle placement an inadvertent dural puncture (i.e. ‘wet tap’) occurs, an epidural catheter can be inserted into the subarachnoid space and used as a continuous spinal catheter technique. The patient, as well as the catheter itself and patient’s chart, should be marked to clearly indicate the presence of a spinal catheter. Safety with the continuous spinal technique is reliant on all practitioners having familiarity and comfort in managing such a catheter; if accidentally dosed as an epidural catheter, a high spinal is likely.
Epidural catheters should be inserted 5 cm into the epidural space; catheter insertion less or greater than this amount may result in a greater incidence of failed block (due to movement out of the epidural space) or a one-sided block (due to the catheter residing towards one side), respectively. The spinal catheter insertion depth has not been well studied; however, most clinicians insert the catheter 3 to 5 cm into the subarachnoid space.
Test dose
Neuraxial techniques may be complicated by the inadvertent placement of the needle or catheter into intravenous, subdural or subarachnoid spaces. This typically occurs during the insertion process, although catheter migration may occur, perhaps through a defect created during the placement. To date, there is not an ideal test that can reliably distinguish the location of the needle or catheter.
A commonly used test dose is composed of 3 mL of 1.5% lidocaine with epinephrine (1:200,000 solution = 15 µg/3 mL). When given intravascularly, the lidocaine component may provide limited symptoms (e.g. tinnitus, palpitations, light-headedness, dizziness), but the epinephrine should increase heart rate. However, the heart rate may increase by only 10 beats per minute (bpm) within 45 seconds, instead of 20 bpm in non-pregnant individuals; a transient decrease in FHR from uterine artery constriction may be observed as well. A test dose should be avoided during uterine contractions, when pain may also increase the heart rate. When a test dose enters the subarachnoid space, the lidocaine dose will provide a quick onset (within 3 minutes) sensory and motor blockade and an anaesthetic block within 10 minutes; this contrasts with a slower onset of less dense analgesia if the test dose is within the epidural space. Subarachnoid epinephrine will have minimal effects.
The best ‘test’ for an incorrectly placed needle or catheter is an astute clinician, who can critically assess haemodynamic and neuraxial blockade responses, as well as the often subtle symptoms parturients may experience. Good practice dictates that every clinician-administered bolus through any neuraxial catheter begins with aspiration, inspection of any aspirate, fractionation of the desired dose into smaller increments (0.5 mL spinal, 3 mL epidural), and evaluation of the effects.
Labour analgesia agent selection
Agents used to create labour analgesia include lipid-soluble opioids and long-acting local anaesthetic agents (Table 10.3). Opioids alone can provide sufficient analgesia for early first stage of labour in the intrathecal space only. A combination of opioids with local anaesthetics is necessary during this stage in the epidural space, as well as for later stages of labour in both the subarachnoid and epidural spaces. The combination of agents allows for smaller doses of both agents to be used, thereby minimizing undesirable side effects (e.g. opioid-induced pruritus, local anaesthetic-induced motor blockade), and provides faster onset.
| Drug | Epidural analgesia | Spinal analgesia |
|---|---|---|
| Local Anaestheticsa | ||
| Initiation/Maintenance | ||
| Bupivacaine | 0.0625%–0.125% | 1.25–2.5 mg |
| L-Bupivacaine | 0.0625%–0.125% | 1.25–2.5 mg |
| Ropivacaine | 0.08%–0.2% | 2.5–4.5 mg |
| Breakthrough/Delivery | ||
| Bupivacaine | 0.125%–0.25% | NA |
| L-Bupivacaine | 0.125%–0.25% | NA |
| Ropivacaine | 0.2%–0.4% | NA |
| Lidocaineb | 0.75%–1.0% | NA |
| Opioids | ||
| Initiation/Maintenance/Breakthrough | ||
| Fentanyl | 50–100 µg | 15–25 µg |
| Sufentanil | 5–10 µg | 1.5–5 µg |
| Morphine | NA | 0.125–0.25 mg |
NA = not applicable.
a The volume used to initiate an epidural labour analgesic is 10–20 mL of local anaesthetic solution.
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