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Caudal anesthesia is the most common technique of epidural anesthesia in children, especially in infants. It is performed through the sacral hiatus (see Chapter 44 ).
The sacral hiatus is a V-shaped orifice located just above the sacrococcygeal joint, corresponding to the lack of dorsal closure of the vertebral arches of the fifth and usually the fourth sacral vertebrae. It is limited by two easily palpable bony crests, the sacral cornua. It is covered by the sacrococcygeal membrane, which is the sacral continuation
In infants, the sacral canal is filled with fluid fat and loose areolar connective tissue, which allows easy spread of anesthetic solutions up to the age of 6 or 7 years, when the epidural fat becomes more densely packed, reducing anesthetic spread. The epidural fat is traversed by many veins that do not have valves. An inadvertent intravascular injection results in immediate systemic distribution of the local anesthetic accompanied by possible toxic effects. The sacral epidural space communicates freely with the perineural space surrounding the sacral and the lumbar roots (especially the lumbar-sacral trunk). Consequently, it is necessary to inject a comparatively large volume of local anesthetic to compensate for consistent leakage and to achieve an appropriate upper limit of sensory block.
Caudal anesthesia is recommended for most surgical procedures of the lower part of the body (mainly below the umbilicus), including herniorrhaphies; operations on the urinary tract, anus, and rectum; and orthopedic procedures on the pelvic girdle and lower extremities.[97] [98] [162] It is mainly used in ASA class 1 and 2 infants and young children, usually combined with light general anesthesia, but it can also be used as an alternative to spinal anesthesia in fully awake, ex-premature infants (infants born prior to the 37th week of gestation) younger than 50 to 60 weeks' post conceptual age.[163] [164] Because of the fluidity of the epidural fat in small infants, it is easy to introduce a catheter within the epidural space to provide long-lasting analgesia. This technique has gained much popularity in some countries, including the United States, whereas the proximity of the anal area in patients with no sphincter control and the subsequent danger of bacterial contamination make it unacceptable in others. The caudal approach can be used to introduce a catheter that can be threaded cranially to perform a lumbar or thoracic epidural anesthesia without approaching the epidural space through lumbar or thoracic intervertebral spaces.
Specific contraindications to caudal anesthesia include major malformations of the sacrum, myelomeningocele, and meningitis.
The patient is placed in the lateral position with the side to be operated lying lowermost, but the patient can also be placed in the prone position with a pillow slipped under the pelvis or, especially in awake ex-premature infants, the legs flexed in the frog position, which facilitates immobilizing the baby and improving his or her comfort.[164] The two sacral cornua are located by palpation of the spinal process line at the level of the sacrococcygeal joint. They delineate a triangle through which the block needle is introduced, close to upper summit. Several insertion routes have been described, but the most reliable consists of inserting the needle at right angles to the skin until it pierces the sacrococcygeal membrane ( Fig. 45-2 ). The needle is then redirected rostrally at a 20- to 30-degree angle to the skin and advanced for 2 to 3 mm into the sacral canal. When an intravenous cannula is to be used to allow intraoperative and postoperative injections for pain relief, it should be inserted at a 45-degree angle to the skin to avoid kinking of the device after removal of the introducer needle. The distance from skin to the sacral epidural space is hardly influenced by the age and weight of the patient ( Fig. 45-3 ). In virtually all cases, it is less than 20 mm from the skin.
When placement of a catheter is planned, an appropriate device must be used, and the length of catheter to be introduced should be evaluated before insertion by measuring the distance from the sacral hiatus to the desired vertebral level. The final position of the catheter tip must be verified radiologically before any injection because erratic placement occurs in one third of patients.[165] To improve the precision of catheter placement before performing a control radiograph, rather complicated techniques can be used, including analysis of electrocardiographic tracing by means of a metallic-wired catheter.[166] Tunneling of the caudal catheter[167] should decrease the risks of bacterial contamination but makes the technique more complicated.
Figure 45-2
Caudal block procedure. A,
Insertion of the needle at right angles to the skin in relation to the coccyx (1)
and the sacrococcygeal membrane (2). B, Cephalad
redirection of the needle after piercing the sacrococcygeal membrane.
Figure 45-3
Distance from the skin to the epidural and subarachnoidal
spaces at different intervertebral levels.
Determination of the optimal volume of local anesthetic has elicited many mathematical models and equations, the most dependable of which is that of Busoni and Andreucetti.[168] From a practical point of view, the prescription scheme of Armitage is easy to use.[169] It consists of injecting 0.5, 1.0, or 1.25 mL/kg of a local anesthetic, resulting in a high sacral, high lumbar, or midthoracic upper limit of the sensory block, respectively. Occasionally, the larger volume (1.25 mL/kg) can lead to excessive rostral spread (above T4).[121] [170] If more than 1 mL/kg (to a maximum of 20 mL) of local anesthetic needs to be administered, it is preferable to avoid the caudal route and use a higher epidural approach.
Complications are unusual, with about one case per 1000 procedures, [1] and usually minor. They result from misplacement of the needle into superficial soft tissues that causes failure of the block, intravascular or intraosseous injections that lead to systemic toxicity, and intrathecal penetrations with subsequent spinal anesthesia. Penetration into pelvic viscera and vessels has been reported. These complications are easily avoided by using appropriate devices with a proper technique and following the basic safety rules of injection. Although hemodynamic effects are clinically minimal, hypotension may occur in children older than 8 years, and significant changes may occur in regional blood flow distribution, such as increased pulmonary arterial resistance and descending aortic blood flow and decreased lower body vascular resistances.[171] [172] Postoperative voiding was occasionally delayed when preoperative fasting was excessive in children (especially infants), but true urinary retention is rare. Vomiting has been reported in up to 30% of patients, but the incidence is usually much less. Other complications include bacterial contamination (but true epidural abscesses are rare) and development of an inappropriate level of sensory block (i.e., excessive, lateralized, or too low). Complete failure of the block occurs in 3% to 5% of patients, especially in children older than 7 years, but even in younger patients, the failure rate can be relatively high.[125]
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