**3.7 Immune response**

The immune response is stimulated by LA. It is well known that trauma and surgery favor susceptibility to infection due to immune suppression. Opioids


also stimulate T lymphocyte activity, cell mediation, and antitumor immunity. Therefore, SA favors the immune response, allowing better possibilities of maintaining an adequate immune response to possible perioperative infections (**Table 1**) [12].

#### **4. Anatomy**

It is important to remember that the level of termination of the spinal cord depends on the age of the child. In the newborn, the spinal cord ends at L3, lower than in the adult. Therefore, it is prudent to do the lumbar puncture in the disc space between L4-L5 or L5-S1, below the termination of the spinal cord. Using the L4–5 or L5-S1 disc space is safe at this age. The intercrestal line or Tuffier's line can be used to determine the level of puncture since this line passes through these spaces.

During the first year of life, the dural sac regresses at the level of the adult and we find it at S1 and the spinal cord at the level of L1, which is the adult level. At this level, the depth to reach the subarachnoid space is 1 to 1.5 cm from the skin and 10 to 12 mm at one year of age. The volume of spinal fluid is 4 mL/kg, that is, twice that in adults [13]. The flexibility of the spinal column in children and the ease of touching and locating the intervertebral spaces facilitate spinal puncture [13].

Insufficient myelination and a weak layer of the endoneurium in the nerve tracts produce a weak and ineffective barrier for the diffusion of LA, which translates into a rapid onset of action. There are two other important factors to consider; a high cardiac output and a relatively wide vascularization, which help to maintain a short duration of action of SA [14].

#### **5. Spinal anesthesia technique**

The most common way to perform SA is to have the child seated with the back flexed. The assistant is responsible for firmly maintaining the sitting position and with the neck extended because flexion of the neck in very young children can cause moderate hypoxia. The child can also be placed in the slightly flexed lateral position. Avoid extreme flexion of the neck as it can also cause airway obstruction and cause hypoxia. A second assistant may be administering oxygen with a face mask. A 45-degree head tilt can help maintain increased CSF pressure, especially in children under one year of age. The depth of insertion of the needle is variable and was described in the anatomy section.

Ultrasound can help decide the puncture site, needle path, and needle depth. Today there are a variety and types of needles for spinal application; however, the most common is the pencil-point needle. The stylet of the needles is necessary to avoid the remote possibility of an epidermoid tumor. Needles 26 and 27 with a pencil point, for pediatric use with a length of no more than 50 mm, produce a low incidence of post-puncture headache [15]. The reflux of the CSF through the needle indicates that the placement of the needle is correct, and the LA should be injected within 20 seconds. Once the needle is withdrawn, the lower extremities should not be elevated because it can result in a high spinal block [14].

#### **6. Clinical monitoring of spinal block**

The clinical evaluation of the spinal block is practical during the entire surgical procedure, but especially during the first 10 to 20 minutes of its application, to

#### *Spinal Anesthesia in Pediatrics DOI: http://dx.doi.org/10.5772/intechopen.100590*

detect possible complications associated with the technique or the LA used. Most of the immediate complications are due to errors in the dose of LA, generally higher than required. The unwanted effects of LA can be masked by the simultaneous combination of GA. In which case it will be more difficult to notice possible reactions to LA. If the child remains conscious, the side effects of SA can be detected quickly.

Verification of sensory block usually consists of loss of skin sensitivity to cold, gentle pinching or touch. The motor block is also installed progressively and immediately, depending on the type of LA applied. Bupivacaine produces a total motor block. While ropivacaine and levobupivacaine produce a motor block of less intensity. The level of motor block can be verified by gentle puncture of the extremities, hips, and upper abdomen or thorax, being better evaluated using the modified Bromage scale. In sedated children, electrical stimulation is better and a more reproducible method, however, it is not always possible to do [16].
