Caudal Block

 

 

Indications for a Caudal Block 

Surgery below the umbilicus

    Hernia repair

    Lower limb surgery

    Skin grafting

    GU procedures

    Procedures on the anus and rectum

    Orthopedic surgery on the pelvic girdle

 

Obstetric Analgesia

    2nd stage or instrumental deliveries

    Not as common today as in the past

    CAREFUL… Fetal head lies close to the site of injection

 

Caudal blocks are not common in adults

 

 Reasons

    Lumbar and thoracic epidural space is easier to access in the adult than is the caudal space.

    Sacral Hiatus is more difficult to identify and the caudal space is more difficult to enter with increasing age as the sacral bones begin to fuse.

    Increased risk of injecting local anesthetic into the fetus with a caudal block due to the level of  fetus and the level of needle insertion site.

 

Sacral anatomy

 

The sacrum is a triangular bone that consists of the five fused sacral vertebrae (S1- S5). It articulates with the fifth lumbar vertebra and the coccyx.

 

 

 

 

The caudal epidural space is the lowest portion of the epidural system and is entered through the sacral hiatus.

 

 

Contents of sacral canal

The terminal part of the dural sac, ending between S1 and S3.

 

The five sacral nerves and coccygeal nerves making up the cauda equina. The sacral epidural veins generally end at S4, but may extend throughout the canal. They are at risk from catheter or needle puncture.

 

The filum terminale - the final part of the spinal cord which does not contain nerves. This exits through the sacral hiatus and is attached to the back of the coccyx.

 

Epidural fat, the character of which changes from a loose texture in children to a more fibrous close-meshed texture in adults. It is this difference that gives rise to the predictability of caudal local anesthetic spread in children and its unpredictability in adults

 

 

Pediatric anatomic considerations

 

The sacrum is cartilaginous in infants and children which can allow for inadvertent intra-osseous injection.

 

The spinal cord reaches L3-4 in the neonate and the dural sac can be found at S3-4.  Adult levels of L1 and S1 are usually reached by 1 year of age.

 

 

Note the proliferation of vascular and intra-osseous spaces to avoid, and remember the close proximity of the bowel.

 

Drugs

Most commonly used drugs include Lidocaine 1% and Bupivacaine 0.25%.

Bupivacaine has a longer duration of action than Lidocaine and is used more often.

Drugs used for Caudal injection should come from single use ampoules and be preservative free.

 

Drug Dosage

Armitage Formula:

0.5 ml/kg for a lumbosacral block

1 ml/kg for a thoraco-lumbar block

1.25 ml/kg for a midthoracic block

0.25% Bupivacaine up to a maximum of 20ml

 

Drug Dosage

Scott’s Calculation:

Calculates the dose based on the child’s age and/or weight (See table below).

If the child is of average weight for his or her height, both figures will be the same.

If the child is overweight, use the figure based on age to avoid the possibility of overdose.

  

Drug doses for Caudal Anesthesia 

 

 

Adult Dosage

Bupivacaine 0.25%

20-30 ml for a block of the lower abdomen

15-20 ml for a block of lower limb and perineum

 

Maximum Dose

Bupivacaine- 3 mg/kg

Lidocaine- 5 mg/kg

Lidocaine with Epi- 7 mg/kg

 

Adjuvants to local anesthetics

Fentanyl 1-2 ug/kg

Morphine (Duramorph) 30-70 ug/kg

Lower doses for surgery below the umbilicus

Higher doses for abdominal or thoracic procedures

Epi 1:200,000 (with Lidocaine)

 

Patient positioning – Adult

 

Adults can be positioned either lateral or prone.  Lateral is more common; however, the prone position is often easiest in the adult, as fat tends to move away from the mid-line and landmarks are easier to find.

 

 

Position (a) causes contraction of the gluteal muscles.

Position (b) allows relaxation of gluteal muscles

 

 

Landmarks

 

 

In an adult, the distance from the tip of the coccyx to the sacral hiatus is approximately the same as the distance from the tip of the index finger to the proximal inter- phalangeal joint.

 

 

 

Patient positioning - pediatric

 

 

 

The lateral position is often used in children, as the landmarks are easier to find than in adults. Care should be taken to avoid over flexing the hips, as this can make the landmarks more difficult to palpate.

 

 

 

 

 

 Landmarks

 

The sacral hiatus and the posterior superior iliac spines form an equilateral triangle pointing inferiorly.  The sacral hiatus can be located by first palpating the coccyx, then sliding the palpating finger cephalad until a depression in the skin is felt.  Always above intergluteal folds.

 

 

Preparation

 

Prep and drape

A bleb of local anesthetic is raised in the skin overlying the sacral hiatus, between the sacral cornua.

 

Note: The procedure must be carried out with a strict aseptic technique. The skin should be thoroughly prepared and sterile gloves worn. Any infection in the caudal space is extremely serious.

 

 

Technique

 

 

A 22 gauge short beveled cannula or needle is directed at about 45° to skin and inserted till a "click" is felt as the sacro-coccygeal ligament is pierced (position 1). The needle is then carefully directed in a cephalad direction at an angle approaching the long axis of the spinal canal (position 2).

 

 

Aspirate, looking for CSF or blood.

If the test is negative, this is followed by the injection of a 3ml test dose of local anesthetic, with a hand positioned over the sacrum to detect any tissue swelling resulting from malposition of the needle or catheter either subperiosteally or along the dorsal surface of the sacrum.

If CSF is aspirated or if blood continues to be aspirated after repositioning of the needle or catheter, the block should be abandoned.

Following a negative test dose and in the absence of pain on injection, the definitive dose may be injected slowly in small, repeated increments.

Single-shot needles or cannula are withdrawn following injection. Catheters are affixed to their connectors and filters and strapped in position.

 

 

Caudal Anesthesia

Procedure is technically easy in pediatric population.

Calcification of sacrococygeal ligament may make technique difficult or impossible in older adults.

Valuable for early tracheal extubation, post-op pain relief, early ambulation, early discharge.

Allows for decreased concentrations of volatile anesthetics, muscle relaxants and opioids.

Regular observation includes pain score, sedation, level of block, and continuous cardio respiratory monitoring.

Overall management should remain under the care of the anesthesiology department.

                                    

Anesthetic Technique

 

Few children accept regional anesthesia as the sole anesthetic regimen.

Most of those who accepted the block were psychologically unable to tolerate the surgical procedure.

Best results with GA & ETT.

 

 

LOCAL ANESTHETIC RISK FACTORS IN THE NEONATE

DEVELOPMENTAL DIFFERENCES

IMPLICATION

Diminished hepatic clearance

Drug accumulation with repeated administration

Diminished plasma protein binding 

Increased free drug concentrations

Diminished skin and mucosal barriers

More efficient dermal and mucosal absorption

Inability to speak

Absence of symptom reporting for premonitory CNS signs

 

 

Complications

 

Difficulty in Eliciting S&S of Toxicity in Peds

 

Aspiration  >>> veins may collapse >>> false negative response

Test dose >>> CNS toxicity confused with pain or agitation

HR response with epi after atropine and baseline high HR >>> negative response

Ectopy with higher dose of epinephrine

GA suppresses signs of toxicity

 

Intravascular or Intrathecal Injection – this may lead to grand mal seizures and/or cardiac arrest. Neonate presents with respiratory distress.

    Methods for Prevention of Intravascular Injection     

        *Slow Injection

        *Repeated Aspiration

        *Constant assessment of patient for clinical signs

 

Dural puncture – Extreme care must be taken to avoid this as a total spinal block will occur if the dose for a caudal block is injected into the subarachnoid space.  Unconsciousness, apnea and hypotension will rapidly result.  Manage with fluids, control the airway and breathing, and vasopressors.

 

Perforated rectum – contamination of the needle and spread of infection is extremely dangerous

 

Sepsis – can be avoided if strict aseptic technique is followed

 

Urinary retention – Not uncommon, temporary catheterization may be required

 

Subcutaneous injection

 

Hematoma

 

Absent or patchy block

 

Intraosseous injection

 

 

References

 

Questions