News Letter Nov 2014 Ultrasound Guided Caudal Epidural Block

Ultrasound Guided Caudal epidural block

Abstract: Intractable lower back pain is increasingly adding to the morbidity of general population. Conservative therapy failure and refusal for operative procedures has led to the use of regional pain options in form of caudal epidural blocks. Increasingly popular with the anaesthetists in cases of patients for lower abdominal surgeries, caudal epidural block has transgressed that boundary from the operating theatres to the OPD and orthopaedic practice for pain relief with steroid injections. Blind procedures till not so long ago had been making rounds in the OPD’s with sometimes failed ( 5-25%)and sometimes good results. With the advent of sate of art MSK dedicated ultrasound machines, such procedures when performed under USG guidance have taken an enormous leap in the pain management mainly because of less complications rate, accurate needle placement in the sacral hiatus and less percentage of failed blocks.

Key words: Ultrasonography, caudal epidural, pain relief, sacral hiatus, needle placement
Source of support: Waldman SD
Conflict of interest: nil

INTRODUCTION

In Medicine there are multitudes of ways devised for effective pain relief and we are moving towards more and more sophisticated procedures, making them safer under guidance of investigative modalities such as ultrasound.

The term interventional Ultrasound refers to a wide and heterogeneous range of invasive procedures performed percutaneously using ultrasound guidance.This article is about the basic technique adopted at our centre to localize the needle under US guidance to accurately give caudal epidural steroid injection for effective , non-messy, longest duration of pain relief so that the entire exercise to the patient is as pleasant as the end result should be.

Indications for a Caudal Epidural Block

1.PAIN RELIEF ACUTE
2. CHRONIC PAIN.
3.POST OPERATIVE – FAILUE OF PAIN RELIEF.
4. Radiculopathies
5.Gluteal claudication

Surface markings of caudal region (posterior view)

ANATOMIC LANDMARKS :

The triangular sacrum consists of the five fused sacral vertebrae, which are dorsally convex. The sacrum inserts in a wedge like manner between the two iliac bones, articulating superiorly with the fifth lumbar vertebra and caudad with the coccyx. The vestigial remnants of the inferior articular processes project downward on each side of the sacral hiatus. These bony projections are called the sacral cornua and represent important clinical landmarks when performing caudal epidural block.

Although there are gender and race determined differences in the shape of the sacrum, they are of little importance relative to the ultimate ability to successfully perform caudal epidural block on a given patient. The triangular coccyx is made up of three to five rudimental vertebrae. Its superior surface articulates with the inferior articular surface of the sacrum. The tip of the coccyx is / was considered an important clinical landmark when performing caudal epidural nerve block (BLIND PROCEDURE).However, when performing the procedure under USG guidance sacral cornu and saccral hiatus are important.

The sacral hiatus is formed by the incomplete midline fusion of the posterior elements of the lower portion of the S4 and the entire S5 vertebrae. This U-shaped space is covered posteriorly by the sacrococcygeal ligament, which is also an important clinical landmark when performing caudal epidural block. Penetration of sacrococcygeal ligament provides direct access to the epidural space of the sacral canal.

IMAGE SOURCE

SONOANATOMY

In prone position the scanning is initiated from midline in transverse probe alignment from the median crest of the sacrum which is seen as an echogenic bony prominence .As we proceed caudad from this level we encounter in para-sagittal region bilaterally two convex echogenic shadows with a hypo echoic 2-3mm band running between the two. These are the saccral cornua with saccral hiatus in between . Superior to this configuration, is a hypoechoic band of saccrococcygeal ligament and posteriorly a dense echogenic line of posterior surface of the sacral bone.

In the longitudinal view, sacral hiatus is seen as a darkish hypoechoic beak like structure which is enclosed between the sacrococcygeal ligament superiorly and sacral bone inferiorly.

Sonograhic Long. View sacral hiatus Tr. View sacral hiatus with sacral cornu

The CONTRAINDICATIONS for caudal epidural steroid block

Coagulation disorders
Infection: Caudal epidural block should not be used if there is an active infection at the site of injection either at the skin surface or below. This includes active cellulitis, pilonidal/ perirectal abscess, and meningitis.
Unstable blood pressure and/or heart rate
Congenital anatomic anomalies of the spinal cord or vertebral bodies - in cases of Spina Bifida, caudal epidural block should not be attempted as the spinal cord may be tethered within the spinal canal.
Scoliosis is not an absolute contraindication to caudal epidural block though scoliosis may make caudal epidural steroid injection technically more difficult to achieve.
The dose of local anaesthetic agent must be carefully controlled in patients with decreased cardiac function, as is often the case of patients with muscular dystrophy.

NOTE: No absolute contraindications except local skin infections ,coagulopathies and lignocaine allergy.Relative contraindications- DM, HT, glaucoma.

Post Procedure side effects to watch out for:

Temporary worsening of local symptoms- can be because of use of steroids, needle trauma, microcrystalline synovitis Side effects of steroid injection- flushing, patches of de-pigmentation, local fat resorption. The volume of the sacral canal with all of its contents removed averages approximately 34 mL in dried bone specimen. It should be emphasized that much smaller volumes of local anaesthetic are used in day-to-day pain management practice. The use of large volumes of local anaesthetic, will result in an unacceptable level of local anaesthetic-induced side effects, such as incontinence and urinary retention, and should be avoided.

The sacral canal also contains the epidural venous plexus, which generally ends at S4 but may continue inferiorly. Most of these vessels are concentrated in the anterior portion of canal. Both the dural sac and epidural vessels are susceptible to trauma by advancing needles or catheters cephalad into the sacral canal. The remainder of the sacral canal is filled with fat, which is subject to an age-related increase in its density. Some investigators believe this change is responsible for the increased incidence of “spotty”caudal epidural nerve blocks in adults

Diagrammatic representation of Caudal epidural anatomy( Lat. View): Grant Atlas of Anatomy

POSITIONING

Caudal epidural block can be performed in prone or lateral position. In USG guided caudal epidural block, prone position is preferred to optimize patient as well as consultant comfort level for probe manoeuvrability. The patient’s head is placed on a pillow and turned away from the pain management physician. The legs and heels are abducted to prevent tightening of gluteal muscles, which can make identification of the sacral hiatus more difficult.

Preparation of a wide area of skin with antiseptic solution is then carried out so that all of the landmarks can be palpated aseptically. A fenestrated sterile drape is paced to avoid contamination by the operating hand.

Just as with the starting of any interventional procedure an accurate ultrasound examination of the affected part should be performed to confirm and correlate with the clinical findings and also to identify the most appropriate path of approach. Utmost efforts should be made to find an appropriate and comfortable position for the patient and the examiner as well. A folded sheet or a pillow under the patient in prone position to eliminate the lordotic curve usually helps to define the landmarks accurately. In obese and old patients the prone position should be maintained for shortest interval of time for the risk of precipitating hypotension or compromise respiratory system.

Separating the gluteal folds either with the help of double sided tapes or with the help of an assistant increases the accuracy of injection placement particularly in obese patients. Information to the patient as to why and how the procedure will be conducted should be given verbally as well as in a written form .Possibility of complications which , under normal circumstances are negligible , should be touched upon gently without alarming the patient too much. Once the position has been achieved , all routine precautions in order to maintain highest levels of sterilization of the ROI and instruments used, should be observed before the needle placement.

PROCEDURE:

Ultrasound probe with frequency range between 12-7 MHz is placed transversely at the level of the sacral dip in midline for the location of the sacral hiatus. Sacral cornu are sonographically important landmarks and the space of few millimeters between the two, seen transversely as hypoechoic region, is the sacral hiatus.

At this level the transducer is then rotated longitudinally and the relatively echogenic band superior to the is hiatus is the sacrococcygeal ligament and the inferior echogenic line is formed by the posterior cortical surface of the sacral bone.

After locating the sacral hiatus, a 25-gauge, 1 ½- inch needle is inserted through the anesthetized area at a 45-degree angle into the sacrococcygeal ligament. The use of longer needles will increase the incidence of complications, including intravascular injection and inadvertent dural puncture, yet add nothing to the overall success of this technique.

As the sacrococcygeal ligament is penetrated, a “pop” should be felt, even when performing the procedure under USG guidance . As soon as the needle enters the hiatus , the part within the hiatus cannot be appreciated as the bone overlying it obscures the vision. On transverse view of the hiatus , it can be seen as a an echogenic pin head and the tissue movement under USG guidance can further confirm the accurate placement.

An air acceptance test, when the procedure used to be performed blindly, still holds some value under USG guidance for the novices and can be performed by injecting of 1 mL of air. There should be no bulging or crepitus of the tissues overlying the sacrum. The force required for injection should not exceed that necessary to overcome the resistance of the needle. If there is initial resistance to injection, the needle should be rotated 180 degrees in case the needle is correctly placed in the canal but the needle bevel is occluded by the internal wall of the sacral canal. Any significant pain or sudden increase in resistance during injection suggest incorrect needle placement, and the pain management physician should stop injecting immediately and reassess the position of the needle.

When the needle is satisfactorily positioned, a syringe containing 5 ml of 1.0% preservative-free lignocaine with 40 mg Tricort and 80 mg of Depomederol is combined and reconstituted to 20cc in normal saline. For post operated patients for back surgeries, 5 ml of hylase is added to the drugs which helps in cases with fibrotic reaction in the ROI.

Gentle aspiration is carried out to identify cerebrospinal fluid or blood. Although rare, inadvertent dural puncture can occur, and careful observation for spinal fluid must be carried out. Aspiration of blood occurs more commonly. This can be due either to damage to veins during insertion of the needle into the caudle canal or, less commonly, to intravenous placement of the needle.

Should the aspiration test be positive for either spinal fluid or blood, the needle is repositioned and the aspiration test repeated. If the test is negative, subsequent injection of 0.5-mL increments of local anaesthetic steroid are undertaken. Careful observation for signs of local anaesthetic steroid toxicity or subarachnoid spread of local anaesthetic steroid during the injection and after the procedure is indicated.

There are two ways of directing the needle under USG guidance :

a.Indirect technique – where USG is used to establish the puncture site and the depth of the target, but not to guide advancement of the needle.

b.Real time technique- probe is placed close to the puncture site and the needle is advanced under USG guidance. This approach can be lateral or co-axial to the USG probe. In the lateral approach, we can see the entire length of the needle and the degree of visualization is dependent upon the gauge of the needle and also the angle of incidence Thicker the needle and greater the angle , better is the needle localization in the soft tissues.

With co-axial approach, only the needle tip is visualized and confirmation can be achieved by little lignocaine or air instillation.

Biopsy guide attachment can be utilized by the professionals who are not ambidextrous. However use of such equipment makes the procedure less flexible as compared to free hand technique.

Whatever the technique used, it is important to accurately examine the soft tissues structures along the needle path in order to avoid incidental damage to the nerves, tendons or vessels.

Pearls: Shortest path is the most adequate and patient not complaining of the pain is the best parameter that the technique employed has been correct and successful.

Caudal space volume is approximately 34cc.Anaesthetic agent gives instantaneous pain relief and stays for 24-36 hours before the steroids’ anti-inflammatory action takes over for longer interval of pain relief. Also the dose of steroid reduces when combined with lignocaine.

It’s important to note that the amount and type of drugs injected, along with the accuracy of injection in caudal epidural space is directly proportional to the efficacy of treatment.

USG allows precise needle placement within the small space with millimetre accuracy thus reducing injuries to the adjacent structure and side effects related to the extra-articular instillation of the drugs .

Although Flouroscopy, CT or MR imaging can be used as alternatives to US , these techniques are time consuming, less handy and involve radiation exposure or require special loss of resistance needles in order to achieve the same purpose. Cost benefit ratio cannot be over-stated

COMPLICATIONS

The complications for caudal epidural block can be classified as:

Failed or incomplete block.Between 5- 25 % of caudal epidural blocks can be considered "failed or incomplete", this includes a number of different problems .The dural sac can extend to the level of third or fourth sacral vertebrae in the newborn and therefore care must be taken to avoid an inadvertent intrathecal injection. The sacrococcygeal ligament binds the sacral hiatus posteriorly, superiorly by the sacral cornu and the fused arch of the sacrum. There is considerable variation in the anatomy of the sacral hiatus, which may account for the small percentage of caudal epidural block failures

The Consultant may not be able to identify the anatomic landmarks and are therefore unable to insert the caudal needle into the epidural space.

Unilateral block:less common than with lumbar epidural because the sacral/ caudal epidural space is bigger and requires more volume to fill. Patchy and one-sided blocks are rare with caudal epidural block but can result from too rapid injection of local anaesthesia dose. Injection of drugs should be injected slowly over 2 minutes after test dose. It is not infrequent though to have too low a block. This is a result of insufficient local anaesthetic volume. Remember that the volume of the dose is often limited by total mg/kg dose of the local anaesthetic that is chosen and must remain less than the toxic dose for that drug. One solution to this problem is to give a more dilute solution.

Local anaesthetic toxicity

Intravascular injection:Even though most local anaesthetics have close to 100% bio-availability from the epidural space, they are absorbed over time. Intravascular injection allows immediate bioavailability of the total dose of the local anaesthetic with consequent systemic toxicity if the peak plasma concentrations are with the toxic range. Peak concentration is lower if drugs are injected slowly. As the extra-dural veins have no valves, local anaesthetic can enter the cerebral circulation by retrograde flow, producing convulsion at doses lower than recommended maximum safe doses. If large volumes of local anaesthetic are given (>10mls) the consultant should aspirate again in the middle of the injection as the expansion of the potential epidural space can displace the tip of the needle. The consultant should be aware of potential intravascular injection throughout the injection.

Dural puncture (intra-thecal injection).The spinal cord typically ends at the first lumbar vertebra in the adult .There is considerable variation in the level of termination of the spinal cord. If unintentional dural puncture is performed, a large dose of local drug is injected intra-thecaly. This will produce a ’total spinal block’, characterized by sudden apnoea, unconsciousness and dilated pupils. There is usually little in the way of hemodynamic disturbance in young children and babies.

Intra-osseous injection.An intra-osseous injection is equivalent to an intravenous injection.

Penetration of the sacrum