Table 1: Indications for spinal anesthesia
Understanding of the anatomic differences between adults and infants are crucial in order to safely, and in a technically proficient fashion administer spinal anesthesia in children. (Table 2)
Table 2: Anatomic differences in Spinal canal
The spinal cord terminates at a much more caudad level in neonates and in infants compared to adults, Figure 1. The conus medullaris ends at approximately L1 in adults and at the L2 or L3 level in neonates and infants. In order to avoid potential injury to the spinal cord, dural puncture should be performed below the level of the spinal cord, i.e. below L2-L3 in neonates and infants. In adults, spinal anesthesia is often administered at the interspace that is nearest an imaginary line that stretches across the top of both iliac crests, the intercristal or Truffier’s line; corresponding to the L3-4 interspace. However, neonates and infants have a proportionately smaller pelvis than adults and the sacrum is located more cephalad relative to the iliac crests. Therefore, Truffier’s line crosses the midline of the vertebral column at the L4-5 or L5-S1 interspace, well below the termination of the spinal cord making this landmark applicable in all pediatric patients14-16 The dural sac in neonates and infants also terminates in a more caudad location compared to adults, usually at about the level of S3 compared to the adult level of S1. The more caudad termination of the dural sac makes it more likely to have an inadvertent dural puncture during performance of a single-shot caudal block if the caudal needle is advanced too far into the caudal epidural space.15
Figure 1. The spinal cord terminates at a much more caudad level in neonates and in infants compared to adults. The conus medullaris ends at approximately L1 in adults and at the L2 or L3 level in neonates and infants.
Cerebrospinal fluid (CSF) volume is larger on a mL/kg basis in infants and neonates (4mL/kg) compared to their adult counterparts (2mL/kg). This may, in part, account for the higher local anesthetic dose requirements and shorter duration of action of spinal anesthesia in this population.
Technique of Spinal Anesthesia in Children
A plan should be made regarding the concomitant use of intravenous sedation or general anesthesia. The approach should be dictated by the medical condition and age of the patient, the comfort level of the anesthesia provider and the nature and anticipated length of the surgical procedure. In former preterm infants undergoing lower abdominal procedures of less than 90 minutes duration, it is common practice to perform spinal anesthesia without adjuvant sedation and to conduct the anesthetic without supplemental intravenous or general anesthesia. In fact it has been shown that the use of concomitant sedation may predispose these infants to apnea and bradycardia.17 Older children may require supplemental sedation or light general anesthesia prior to performing the block. In some cases, spinal anesthesia may be combined with caudal or epidural anesthesia.
Spinal anesthesia is customarily administered in the lateral (Figure 2) or sitting position in children, Figure 3. Hypobaric solutions are not commonly utilized in infants. If the sitting position is preferred, special attention must be paid in infants to insure that the neck is not flexed which may result in airway obstruction Figure 3. Neck flexion is not necessary as it does not facilitate performance of the block.18 (Fig-1) In older children, an assistant should be present to maintain good positioning and to reassure and distract the child while the block is being performed. It is essential to monitor the oxygen saturation of the infant while performing the spinal to ensure the adequacy and patency of the airway.
Figure 2. Spinal anesthesia in the neonate; shown is the lateral position.
Figure 3. Spinal anesthesia in the neonate in the sitting position; head flexion must be avoided to prevent respiratory obstruction.
In infants, the L4-5 or L5-S1 interspace should be identified; the L3-4 interspace may be used in older children. The area should be cleared and draped in a sterile fashion. If EMLA or LMX were not applied preoperatively, local anesthesia should be administered prior to the block in awake or sedated children, Figure 4. The desired dose of local anesthetic should be calculated and be prepared in a syringe prior to dural puncture to insure that the correct dose is administered. A short 22- or 25-gauge spinal needle is often used. A midline approach is usually recommended over a paramedian approach. The ligamentum flavum is very soft in children and a distinctive “pop” may not be perceived when the dura is penetrated. Once clear CSF is seen exiting the needle, drug(s) should be injected slowly. The barbotage method is not recommended as this may result in unacceptable high levels of motor blockade and potential for a total spinal blockade. The caudal end of the patient should not be elevated for placement of the electro-cautery return electrode as a total spinal can result from spread of local anesthetic solution to a higher spinal level. One of the techniques we have resorted to in our teaching institution to prolong the duration of surgical analgesia is the use of spinal anesthesia using 0.8 mg/kg of bupivacaine followed immediately by a caudal block using 0.1% bupivacaine. We turn the patient to the side that has the largest hernia at the time of performance of the block. This prolongs the duration of anesthesia and analgesia. Alternatively, hypobaric solution of local anesthetic can be injected in the lateral position with the operative side up, Figure 5 and Figure 6.
Figure 4. Equipment for spinal anesthesia in the neonate. Shown are the disinfectant, hypodermic needle for local infiltration and the spinal needle.
Figure 5. Spinal anesthesia in the neonate; needle insertion.
Figure 6. Spinal anesthesia in the neonate; injection of the local anesthetic.
Assessing the block
Assessing the level of blockade may prove difficult in infants and young children, particularly if the patients have received sedation or those in whom the block is being performed under general anesthesia. In infants, pin prick or their response to cold stimuli (e.g., an alcohol swab) may be used as well as observation of their rate and pattern of ventilation. In children older than 2 years we use the Bromage scale. Care should be taken to avoid placing the patient in the Trendelenburg position following the block as this will result in an extremely high or total spinal, as may occur when placing a electrocautery grounding pad on an infant’s back by lifting the lower extremities. In the event of a rapidly rising level of blockade, the patient may be placed in reverse Trendelenburg.
Adverse effects from Spinal Anesthesia
Adverse effects from spinal anesthesia commonly seen in adults are less common in children. These include hypotension, bradycardia, postdural puncture and transient radicular symptoms.
Hypotension and bradycardia are very rare occurrences when performing spinal anesthesia in children, in spite of high levels of blockade and the absence of routine fluid loading prior to blockade (10 mL/kg).19 We however do recommend that a venous access be obtained prior to performing spinal anesthesia in neonates or in infants. Puncah et al recently reported their experience with 1132 consecutive spinal anesthetics. Only 27/1132 received supplemental analgesia. All spinal blocks were performed with sedation. Hypotension was rarely reported. Mild decrease in blood pressure was reported in 9/942 patients who were
Postdural puncture headache
The incidence of PDPH is less in children compared to adults. Large series have been reported after frequent lumbar punctures for spinal tap in children with lower incidence of postdural puncture headaches.20 An incidence of 8% was noted in this subgroup of oncology patients with dural puncture. The use of different types of needles for spinal tap has been studied. They were divided into two groups either using a Quincke needle or a pencil point Whitacre needle. There was no difference in the incidence of headaches between to two needle groups (15% Quincke; 9% Whitacre; p=0.43)21 Moreover, the incidence of headaches was not different in different age groups with 8/11 PDPH occurring in children under 10 years of age with the youngest reported in a 23 month old baby. Transient radicular symptoms have been reported in children following spinal anesthesia with no long term adverse effects.22 Postdural puncture headaches have been treated with epidural blood patch (0.3mL/kg of blood) with very good results. 23 Bed rest and caffeine are initiated followed by blood patch if the headaches do not resolve.24 In our own practice we tend to place a prophylactic blood patch if a suspicion of PDPH is entertained.
Local Anesthesic Choices and Doses
Special consideration should be given to the child with a known difficult airway when considering a spinal anesthetic. While spinal anesthesia may be a reasonable choice in these patients, the first consideration should be the ability of the practitioner to manage the airway. Obviously the nature of the surgical procedure will dictate the use of regional techniques. Spinal anesthesia has been used for myelomeningocele repair, exploratory laparotomy and other invasive abdominal procedures in infants. The surgical site, anticipated length of the procedure and the surgical position (supine, lateral, prone) are important factors. A third consideration is the age of the child. Spinal anesthesia can be administered in infants while awake but preschool and school-age children may require intravenous sedation which poses its own set of risks in pediatric patients with a difficult airway.
Cote et al.9 performed a meta-analysis of eight studies investigating postoperative apnea in former preterm infants following general anesthesia comprising 255 patients. Overall, the risk of apnea was independently related to both gestational age and conceptual age. Additional risk factors for postoperative apnea were a hematocrit
The use of regional anesthesia may decrease but not eliminate the incidence of postoperative apnea. The concomitant use of ketamine may increase the incidence of postoperative apnea above that reported in control patients17;29 Unfortunately, very little information is available regarding the potential benefits of spinal anesthesia over general anesthesia in this particular population. A small randomized study of former preterm infants who received spinal anesthesia showed a decrease in the incidence of postoperative desaturation and bradycardia compared with those who received general anesthesia for inguinal herniorraphy.30 They observed no significant difference in the incidence of postoperative apnea between the two groups. An observational study of over 250 former preterm infants found a 4.9% incidence of postoperative apnea after spinal anesthesia for inguinal herniorraphy.11 A prospective study from France reported no incidence of postoperative apnea in a subset of 30 former preterm infants who received spinal anesthesia. Craven et al. reviewed several randomized controlled studies and found only borderline statistical advantage of a spinal anesthetic over a general anesthetic31
Spinal anesthesia for procedures other than herniorrhaphy
Spinal anesthesia has been successfully used for a variety of surgical procedures in children.12;13 Most of the reported series in the literature involve infants. The early report by Abajian et al.11 not only included infants undergoing herniorrhaphy but also those undergoing a variety of general, urologic and orthopedic procedures. Interestingly, the study population included infants with medical conditions the authors felt increased the risk of general anesthesia. These conditions included laryngomalacia, macroglossia, micrognathia, congenital heart disease, Down’s syndrome, adrenogenital syndrome, failure to thrive, arthrogryposis and Gordon’s syndrome.
Blaise et al. reported 30 patients aged 7 weeks to 13 years who underwent spinal anesthesia for a variety of surgical procedures.12 Kokki et al. reported satisfactory anesthesia in 92 of 93 children aged 1-17 yrs undergoing ropivacaine spinal anesthesia for lower abdominal or lower extremity procedures.26;32 Spinal anesthesia has been used in infants for various other procedures including meningomyelocele repair.33, and major abdominal surgery.
Spinal Anesthesia for cardiac surgery
Regional techniques have been used in cardiac surgery to facilitate early extubation.34 The largest series of use of spinal anesthesia for cardiac surgery comes from a prospective randomized analysis from Stanford University.35 The group that received spinal anesthesia for postoperative pain relief had less opioid requirement in the postoperative period in children undergoing elective cardiac surgery with early extubation in the operating room.
In summary, spinal anesthesia in pediatrics is most commonly used in the preterm infant undergoing anesthesia for hernia repair. Spinal anesthesia can also be used effectively in children for postoperative pain relief especially if opioids are used. Finally, in some clinical settings, spinal anesthesia may be may be the only anesthetic option available.