Case Study
An otherwise healthy nulliparous 26-year-old woman at 40 weeks’ gestation presented to the labor and delivery unit. She was scheduled for induction of labor and was not experiencing uterine contractions at that time. On vaginal examination, her cervix was closed and not effaced.
She requested labor analgesia prior to the start of labor induction. An epidural catheter was placed by the anesthesiologist using the loss of resistance to air technique without complications. The catheter was threaded 5 cm into the epidural space. Patient-controlled epidural analgesia was started with a 15-ml bolus of bupivacaine 0.0625% and fentanyl 2 µg/ml and then maintained with a 10 ml/h basal infusion of the same solution.
Four hours later, the patient complained of numbness on her left side and increasing discomfort on her right side. On physical examination, she was unable to move her left leg but had complete range of motion of her right leg.
The patient was positioned laterally with her right (painful) side in the dependent position, and a bolus of 5 ml of bupivacaine 0.25% was administered through the epidural catheter. Over the next 15 minutes, her pain was reassessed, and no difference was observed. The epidural catheter was pulled back 1 cm, and a dose of 10 ml of lidocaine 2% was given. After an additional 10 minutes, the patient felt some relief on the right side but was still visibly uncomfortable.
The decision was made to replace her epidural catheter using the combined spinal epidural technique. She received 25 µg of intrathecal fentanyl prior to insertion of an epidural catheter. The maintenance infusion of bupivacaine and fentanyl was restarted. She remained comfortable until delivery 5 hours later.
Key Points
This patient experienced inadequate labor analgesia, specifically a unilateral or patchy block.
Multiple interventions were used to correct her incomplete analgesia without success.
Ultimately, the procedure was repeated employing the combined spinal-epidural technique.
Discussion
Neuraxial analgesia is commonly used to mitigate the pain associated with labor. Its popularity has increased secondary to both its efficacy and its safety. From the anesthesiologist’s perspective, the epidural catheter provides a means not only of labor analgesia but also of surgical anesthesia if an operative procedure such as cesarean delivery is required. During progressive stages of labor, the volume and/or concentration of local anesthetic administered through the epidural catheter can be altered to maintain adequate analgesia. Also, an adjunct, such as an opioid, can be added to the local anesthetic to minimize side effects (e.g., hypotension and motor block). The catheter is used to maintain a low dermatomal level of analgesia for labor; T10–L1 for the first stage of labor and additionally S2–S4 for the second stage. If necessary, the dermatomal level can be raised to T4 for cesarean delivery.
Although epidural analgesia is considered the “gold standard” for labor analgesia, inadequate analgesia can occur in up to 15 percent of epidural catheter placements.1 Pan et al.2 reviewed approximately 19,259 deliveries, of which 12,590 had neuraxial analgesia. The overall failure rate was 12 percent, with a 14 percent failure rate with epidural techniques and 10 percent with the combined spinal epidural (CSE) technique. Even when adequate analgesia was established initially, 6.8 percent still required epidural catheter replacement due to the development of inadequate analgesia as labor progressed. During cesarean delivery, 7 percent of the epidural catheters placed failed. In another study, Eappen et al.3 found that 13.1 percent of all epidural catheters required replacement. Inadequate labor analgesia not only leads to a dissatisfied patient but can also be more serious if an urgent cesarean delivery is required and an adequate level of anesthesia cannot be readily achieved. It may also lead to legal action.4
Risk Factors
Many patient factors can influence the rate of inadequate labor epidural analgesia (Table 3.1). These include advanced age,3 morbid obesity, scoliosis (whether corrected or not), and a history of spinal disc surgery. Additionally, multiparity, history of a previous failure of epidural analgesia, and cervical dilatation greater than 7 cm at insertion are associated with inadequate epidural analgesia.5
Tonidandel et al.6 retrospectively examined the differences in obstetric and anesthetic outcomes, including failed epidural rate, between 230 morbidly obese parturients (weight > 136 kg) and their matched controls (weight < 113 kg). The rate of repeat procedures due to inadequate pain control or failure to achieve bilateral dermatomal sensory levels was significantly greater in the morbidly obese group (17 versus 3 percent).
In a literature review of neuraxial procedures in parturients with scoliosis, Ko and Leffert7 found that patchy, asymmetric or unilateral blocks were seen in 8% of patients without surgical correction. Failed placement or multiple attempts at placement occurred 4% of the time. Patients who had undergone surgical scoliosis correction had greater rates of neuraxial anesthesia complications than those without correction, including failed placement (22 percent) and multiple placement attempts (13 percent).
Patients are often concerned that their history of lumbar spine surgery, unrelated to scoliosis, will preclude them from receiving labor neuraxial analgesia. Bauchat et al.8 found no difference in time to epidural placement or local anesthetic consumption in patients with a history of lumbar discectomy compared with control individuals. However, the number of interspaces attempted prior to successful placement was greater in the discectomy group (more than one interspace attempted, 17 versus 2 percent).
Preventing or Avoiding Inadequate Analgesia
It is best if one can avoid or reduce the occurrence of inadequate analgesia in the first place, and this requires attention to detail during placement of the block and an understanding of the anatomy of the neuraxis.
Placement Techniques
The key to successful placement of an epidural or combined spinal epidural (CSE) is finding the midline. This is accomplished by palpating the spinous processes and rolling the fingers in both medial-to-lateral and cephalad-to-caudad directions. At times, the spinous processes cannot be felt, and an approximation of the midline can be achieved by drawing a line from the seventh cervical vertebral (C7) spinous process, which is generally prominent even in the morbidly obese, and the gluteal cleft.
Some clinicians also use ultrasound to assist in finding the midline. In a randomized trial, Grau et al.9 found fewer insertion attempts were required when using spinal ultrasound prior to epidural placement than with palpation alone (2.6 ± 1.4 attempts in the ultrasound group versus 1.5 ± 0.9 attempts in the palpation group). However, Arzola et al.10 found no difference in the number of attempts or median epidural insertion time in a study that randomized patients with easily palpated landmarks to either pre-epidural spinal ultrasound or palpation only. For a complete discussion of the role of ultrasound in obstetric anesthesia, see Chapter 6.
After the midline is found and the skin is adequately anesthetized, the epidural needle is advanced into the space using a loss of resistance to air or saline technique. In a randomized study, Beilin et al.11 found that the saline technique was superior to the air technique with regard to the ultimate success of the block as well as fewer complications. However, others have questioned this finding, particularly if it requires the practitioner to use a technique he or she may not otherwise use.12 In a meta-analysis of seven studies involving over 800 patients undergoing epidural placement, Antibas et al.13 found that there was no difference in identification of the epidural space or reduction of complications when using either an air or saline loss-of-resistance technique.
The distance the catheter is threaded is important to increase the likelihood that the catheter will remain in the midline within the epidural space. Beilin et al.14 found that threading a multiorifice catheter 5 cm into the epidural space, compared with 3 or 7 cm, is associated with a greater analgesic success rate. The use of multiorifice catheters is associated with a more even distribution of local anesthetic and a lower incidence of a “patchy” block – requiring less manipulation than single-orifice catheters.15 Additionally, wire-reinforced flexible catheters demonstrate a lower incidence of intravascular cannulation, paresthesia, and inadequate analgesia than stiffer catheters.16
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