Paediatric caudal anaesthesia: Difference between revisions

The usual contraindications to regional anaesthesia such as coagulation disorders, local or general infection, progressive neurological disorders and patient or parental refusal apply to CA. Furthermore, cutaneous anomalies (angioma, hair tuft, naevus or a dimple) near the puncture point require radiological examination (ultrasound, CT or MRI), in order to rule out underlying spinal cord malformation such as a tethered cord.23 A Mongolian spot is not a contraindication to CA.  

The dural sac (i.e. the subarachnoid space) ends at the level of S3 in infants and at S2 in adults and children. It is possible to puncture the dural sac accidentally during CA, leading to extensive spinal anaesthesia. Therefore the needle or cannula must be cautiously advanced into the sacral canal, after crossing the sacro-coccygeal ligament. The distance between the sacral hiatus and the dural sac is approximately 10mm in neonates. It increases progressively with age (>30mm at 18 years), but there is significant inter-individual variability in children.1 The contents of sacral canal are similar to those of lumbar epidural space, predominantly fat and epidural veins. In children, epidural fatty tissue is looser and more fluid than in adults, favoring LA diffusion.  

 

According to the child’s size, needle diameter and length are respectively between 21G and 25G, and 25mm and 40mm. A short bevel improves the feeling of sacrococcygeal ligament penetration and decreases risk of vascular puncture or sacral perforation.2 Use of a needle with a stylet avoids risk of cutaneous tissue coring, and the (theoretical) risk of epidural cutaneous cell graft. If a styletted needle is not available, a cutaneous ‘pre-hole’ can be made with a different needle prior to puncture with the caudal needle. Another solution is to puncture with an IV catheter, the hollow needle of which is removed before injection through the sheath.  

After defining the bony landmarks of the sacral triangle, the two sacral cornuae are identified by moving your fingertips from side to side. The gluteal cleft is not a reliable mark of the midline. The puncture is performed between the two sacral cornuae. The needle is oriented 60° in relation to back plane, 90° to skin surface. The needle bevel is oriented ventrally, or parallel to the fibers of the sacro-coccygeal ligament.  

After verifying absence of spontaneous reflux of blood or cerebrospinal fluid (more sensitive than an aspiration test), injection of LA should be possible be without resistance. Inject slowly (over about one minute). Where available this may be preceded with an epinephrine test dose under ECG and blood pressure monitoring, in order to detect intravascular placement. Subcutaneous bulging at the injection site suggests needle misplacement. Blood reflux necessitates repeating the puncture, however in case of cerebrospinal fluid reflux caudal anaesthesia should be abandoned, in order to avoid the risk of extensive spinal anaesthesia. Aspiration tests should be repeated several times during injection. In skilled hands, the success rate of CA is about 95%, however a variety of misplacements of the needle are possible (Figure 6). The moment of surgical incision is the true test of block success, but various techniques have been suggested to authenticate the puncture success, such as injection site auscultation (the ‘swoosh test’), or searching for anal sphincter contraction in response to electrical nerve stimulation on the puncture needle. No clear benefit of these techniques against simple clinical assessment have been shown.3,4 More recently, ultrasound has been suggested to help sacro-coccygeal hiatus location and to visualize isotonic serum or LA injection into sacral epidural space (Figures 7 and 8).5,6 These authors have also outlined the interest in ultrasound control within the context of learning the technique, rather than for use in standard practice.5,7

Although CA was initially described as a single shot technique, some authors have described use of a caudal catheter to prolong analgesic administration in postoperative period. In addition advancement of the catheter in the epidural space up to lumbar or even thoracic levels can achieve analgesia of high abdominal or thoracic areas.8 However, two pitfalls restrict extension of this technique; a high risk of catheter bacterial colonization, particularly in infants and a high risk of catheter misplacement.9,10 Subcutaneous tunnelling at a distance from the anal orifice, or occlusive dressings decrease bacterial colonization.11 Electrical nerve stimulation or ECG recording on the catheter, or itsechographic visualization have been suggested to guide its advancement in epidural space.12,13 However, most anaesthetists presently prefer a direct epidural approach at the desired level that is appropriate to the surgical intervention.14,15

Early neurosensory warning symptoms of LA systemic toxicity are concealed by general anaesthesia. Halogenated anaesthetic agents worsen LA systemic toxicity and can also blunt the cardiovascular signs of an intravenous epinephrine test dose injection. Aspiration tests to elicit blood reflux are not very sensitive, particularly in infants. A test dose of epinephrine 0.5mcg.kg-1 (administered as 0.1ml.kg-1 lidocaine with epinephrine 1 in 200 000) allows detection of intravenous injection with sensitivity and specificity close to 100%, under halogenated anaesthesia. Warning symptoms are cardiac frequency modification (an increase or decrease by 10 beats per minute), increased in blood pressure (up to 15mmHg), or T-wave amplitude change in the 60 to 90 second period after injection (Figure 9).16,17 Slow injection of the whole LA dose under haemodynamic and ECG monitoring remains essential for patient safety.

{| class="wikitable"

|+Table 1. Spread of block as a function of caudally injected local anaesthetic volume18

LA choice prioritizes long lasting effects with the weakest motor block possible, since motor block is poorly tolerated in awake children. Bupivacaine meets these criteria. More recently available, ropivacaine and L-bupivacaine have less cardiac toxicity than bupivacaïne at equivalent analgesic effectiveness. They may also confer a more favorable differential block (less motor block for the same analgesic power) and the 2.5mg.ml-1 (0.25%) concentration is optimal for these agents. Four to six hours analgesia is usually achieved with minimal motor block.19,20

Several drugs have been demonstrated to prolong duration of analgesia by a few hours after single shot caudal injection of LA. Among them, most popular are opioids (fentanyl 1 µg.kg-1), clonidine (1-2 µg.kg-1) and preservative free ketamine (not the IV form) (0.5 mg.kg-1).21 Recent reports of spinal cord toxicity of intrathecal ketamine in neonatal rats leads us to discourage its use by caudal route in neonates and infants.22 Morphine and clonidine do not provoke such spinal cord toxicity in neonatal rats, but their dose requirements are decreased in younger pups.23 Principal adverse effects are: pruritus and nausea and vomiting for opioids, light sedation for clonidine, and hallucinations for ketamine. Theoretical risk of respiratory depression with opioids mandates adequate postoperative monitoring. Some cases of respiratory depression have been reported with caudal clonidine in neonates.24

Complications of CA are uncommon (0.7 per 1000 cases), are more likely if inadequate equipment is used and are more frequent in infants.16 If the technique fails it should be abandoned to avoid occurrence of potentially serious complications. Significant complications, in order of decreasing frequency, are:  

* '''Sacral osteomyelitis''' is rare (one case report).25