Failed Epidural Block

Introduction:

➧ Failure of epidural anesthesia and analgesia occurs in up to 30% of clinical practices.

➧ Some technical factors can help to increase the primary and secondary success rates.

A) Technical factors influencing block success:

1-Patient Position:

➧ Patient positioning potentially affects needle placement by changing the relationship between osseous and soft tissues.

a) Sitting Position

➧ Results in shorter insertion times and higher accuracy at the first attempt than in the lateral position.

➧ Causes more vagal reflexes than lateral position.

➧ This leads to epidural venous plexus distension, which may theoretically increase the risk of vascular puncture, especially in parturients.

b) Lateral Position

➧ Increases the distance from the skin to the epidural space.

➧ Results in more technical difficulties compared with the sitting position.

2-Puncture Site:

➧ Inaccurate dermatomal block-level or anatomical landmarks of neuraxial puncture are not suitable for the type of surgery.

3-Approach:

a) Midline Approach

➧ Results in a higher incidence of paresthesia than the paramedian approach.

➧ Results in a bloody puncture in non-pregnant adults than paramedian approach.

➧ The ligamentum flavum is not continuous in all patients, and the presence of midline gaps may make the loss of resistance (LoR) to needle advancement and injection of air/saline less perceptible when the midline approach is used.

b) Paramedian Approach

➧ Results in faster catheter insertion times, and less dependent upon spine flexion.

➧ Paramedian catheters cause less epidural tenting, and pass cephalad more reliably than midline catheters.

4-Identification of the Epidural Space:

➧ Correct placement obviously requires correct identification of the epidural space. The LoR using saline has become the most widely used method, while LoR to air and the hanging drop technique is less widely used with no difference in the success rate or adverse events, other than a 1.5% reduction in post-dural puncture headache [1] when using saline.

➧ In obstetric epidurals, using saline for LoR results in fewer attempts than using air, but with comparable final success rates.

➧ The use of the ‘preferred technique’ (i.e. the technique used by anesthetists 70% of the time) results in significantly fewer attempts, a lower incidence of paresthesia, and fewer dural punctures, irrespective of whether saline or air is used for LoR.

➧ The hanging drop technique depends on negative pressure within the epidural space and is useful only in the sitting position.

➧ Identification of the epidural space was reported at 2 mm deeper for the hanging drop when compared with LoR, possibly indicating an increased risk of dural puncture.

➧ Ultrasound pre-assessment of lumbar epidural space depth has been shown to correlate well with actual puncture depth in obese parturients.

➧ The use of ultrasound led to less bony contact, a shorter time to block success, and decreased supplemental opioid requirements.

5-Epidural Catheter Location:

➧ Epidural catheters may primarily be placed incorrectly, or become dislodged during operation.

➧ Primary misplacement of epidural catheters in the paravertebral space, in the pleural cavity, or intravascularly.

➧ Transforaminal migration of the catheter tip and asymmetric spread during epidural analgesia.

➧ During normal patient movement, epidural catheters may be displaced by centimeters.

➧ Changes in epidural pressure and cerebrospinal fluid (CSF) oscillations can contribute to the displacement of epidural catheters.

➧ Midline fat pedicles may form a barrier to the spread of local anesthetics (LA).

6-Catheter Insertion and Fixation:

➧ The catheter should be inserted at least 4 cm into the epidural space.

➧ Suturing of the epidural catheter is associated with less migration, but at the cost of increased inflammation at the puncture site.

➧ Tunneling the epidural catheter for 5 cm is associated with less movement of the catheter and decreases catheter migration but it will not maintain the original position.

➧ Tunneling caudal epidural catheter in children reduces the risk of bacterial colonization to levels comparable to untunneled lumbar catheters because tunneling places the catheter entry point above the diaper in babies and toddlers.

➧ For lumbar and epidural catheters, the advantages of tunneling are less obvious and the need to prevent dislodgement must be weighed against the increased incidence of erythema at the puncture site, potentially linked to increased risk of bacterial colonization.

➧ Catheter fixation devices are available which may significantly reduce migration percentage and reduce rates of analgesic failure.

7-Test Dose:

➧ A test dose is given with two main objectives of detecting intrathecal or intravascular catheter placement.

➧ A test dose of lidocaine (to detect intrathecal placement) and epinephrine (to detect intravascular placement) is recommended in patients without contraindications to epinephrine.

➧ Specific regimens to detect intravascular catheter position:

-Fixed epinephrine test dose for non-pregnant adult patients.

-Fentanyl test dose for parturients.

-Weight-adjusted epinephrine test dose for children.

➧ Patients sensitive to intravascular epinephrine (parturients, patients with cardiac or vascular disease) may experience undesirable side effects if the test is positive. However, this risk is outweighed by the systemic toxic effects of LA if the intravascular placement was not detected.

8-Equipments:

➧ The orifice of the catheter can lie laterally or anteriorly in the epidural space putting the LA more to one side and producing a unilateral block. In general, multi-orifice catheters are considered better than single-orifice catheters.

➧ Manufacturing errors, such as faulty markings on the epidural catheter, can lead to a wrong depth of placement.

➧ Debris in the catheter or disconnection can cause epidural failure.

➧ Obstruction of the epidural infusion system by an airlock, as little as 0.3–0.7 ml of air, in the bacterial filter.

➧ The knotting of the catheter internally or externally can cause obstruction.

➧ Removal of a presumed knotted catheter can be attempted after sensation has returned to monitor neurological symptoms during catheter removal. When radicular symptoms or pain occur during the removal of a catheter, this should be immediately stopped. It has been found that removal is easiest if the patient is in the same position as at insertion. Surgical removal of a broken catheter is not compulsory if the patient remains asymptomatic.

References:

1. Shaat AM, Abdalgaleil MM. Is theophylline more effective than sumatriptan in the treatment of post-dural puncture headache? A randomized clinical trial. Egyptian Journal of Anaesthesia 2021; 37(1): 310-316. https://doi.org/10.1080/11101849.2021.1949195.

Anesthesia Morbidity and Mortality

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