A 29-yr-old, 1.54 m tall, 79 kg, nulliparous female, presented to the obstetric unit in active labour with 4 cm cervical dilation. Epidural analgesia was requested and informed consent was obtained. In the sitting position, with aseptic technique, an 18-G Tuohy needle was introduced on first pass into the epidural space using the loss of resistance to air technique at the L3–L4 interspace. The distance from the skin to the epidural space was 4.5 cm. No blood or cerebrospinal fluid was observed. A multi-holed catheter was threaded 4 cm into the epidural space without eliciting paraesthesia. After a negative aspiration, 10 mL of a solution containing 0.16% ropivacaine and 10 μg of sufentanil was administered as a bolus in incremental doses. No labour pain relief was observed over the following 30 min. After re-checking that the composition of local anaesthetic solution was correct and presuming catheter misplacement, another catheter was placed at the L2–L3 interspace using the same technique. The epidural space was found at the same distance from the skin. A catheter was easily passed 4 cm into it. An 8 mL bolus of 0.2% ropivacaine was then administered, but no analgesic effect was recorded in the following 20 min. Assuming that the epidural space was correctly identified the catheter was pulled back 1 cm, negative aspiration was re-confirmed and another 8 mL bolus of 0.2% ropivacaine was administered. Shortly after, the parturient complained of paraesthesia followed by anaesthesia of the anterior and lateral aspects of the right thigh. Motor function was preserved. No other anomalies were identified in the neurological examination. She had no labour pain relief.
The patient was closely observed with the catheter in place. Labour proceeded until complete cervical dilation. At the beginning of the second stage, due to acute fetal distress associated with fetopelvic incompatibility, an emergency Caesarean section was performed uneventfully under general anaesthesia.
Two hours after general anaesthesia and 4 h after the last administration of local anaesthetic, the right thigh sensory alterations were no longer present. Complete neurological examination was normal. At this time written informed consent was obtained and a Computed Tomography scan with contrast administration through the epidural catheter was performed (Fig. 1). The catheter was then removed. No events were recorded during the ensuing hospital stay. The patient was observed 1 and 6 months later and demonstrated a normal clinical examination.
Incomplete or failed epidural analgesia or anaesthesia has been reported with variable incidences, apparently reflecting variability in definitions, authors’ clinical judgement and perception, practice parameters or hospital settings [1–3]. It is one of the major concerns of anaesthetists performing this technique in the setting of obstetric care.
The aetiology and mechanisms of failed or incomplete epidural analgesia in obstetrics are complex, multifactorial and not entirely understood. The potential causes and contributing factors have been grouped in the literature into four major categories: anatomic factors; technique, methodology and equipment; patient-related factors; technical skills or performance factors. In this case, technical difficulties or equipment problems were not found. The epidural space was easily identified in both attempts. Transforaminal catheter migration as seen in Figure 1, is clearly the cause of epidural failure in this case. In our opinion this could have occurred due to anatomic factors. The existence of a connective tissue structure in the epidural space could have worked as a barrier preventing cephalic progression, directing and facilitating catheter extrusion through the intervertebral foramen. In fact, several authors, using autopsy, imaging and endoscopy studies, have shown the presence of epidural midline structures that can interfere with epidural performance [4–7].
Another contributing factor could be a ‘disproportionate’ insertion – ‘too much catheter’ – in this short stature patient. Even though 3 or 4 cm insertion into the epidural space is correct, we could speculate that effective analgesia would be obtained if the catheter had been pulled back leaving only 1 or 2 cm in place.
The sensory alterations the patient had in the right thigh can be explained by the accumulation of local anaesthetic in the proximity of the lumbar plexus nerves responsible for the innervation of that area.
Optimizing the loss of resistance technique does not preclude having challenging problems when performing epidurals or trying to find a cause for failure. Also, in this particularly demanding setting, alternatives are significantly less effective and often less safe.
Imaging methods applied to the epidural technique could be the definitive answer to some of our well-founded concerns when performing this modality of anaesthesia/analgesia.
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