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Spinal Anesthesia for Repair of Meningomyelocele in Neonates

Viscomi, Christopher M. MD; Abajian, J. Christian MD; Wald, Steven L. MD; Rathmell, James P. MD; Wilson, James T. MD

Pediatric Anesthesia
Free
SDC

The use of spinal anesthesia for meningomyelocele repair in neonates has received minimal attention.Spinal anesthesia may lessen the stress response to surgery and decrease postoperative respiratory complications. We therefore examined the efficacy of spinal anesthesia in 14 neonates requiring repair of lumbar or sacral meningomyelocele. All neonates were positioned prone with a small chest roll. Hyperbaric 0.5% tetracaine with epinephrine was injected into the caudal end of the meningomyelocele sac. If necessary, supplemental tetracaine was administered directly into the intrathecal space by the surgeon during the operation. Blood pressure, heart rate, and oxyhemoglobin saturation were measured throughout surgery. Neonates were monitored with transthoracic impedance apnea monitors, electrocardiogram (ECG), and pulse oximetry for 36 h after surgery. Spinal anesthesia was successful in all cases. Seven patients received one supplemental tetracaine injection; one patient received two supplemental injections. Arterial blood pressure decreased an average of 5 mm Hg with the largest decrease being 10 mm Hg. Two postoperative respiratory events occurred in the first 8 h after surgery. Both neonates had received intraoperative midazolam for sedation. Neurologic function was assessed pre- and postoperatively. Twelve patients had no change in neurologic function after surgery, while two infants demonstrated improved function. We conclude that spinal anesthesia can be safely used for meningomyelocele repair.

(Anesth Analg 1995;81:492-5)

Department of Anesthesiology (Viscomi, Abajian, Rathmell) and Division of Neurosurgery, Department of Surgery, University of Vermont College of Medicine, Burlington, Vermont (Wald, Wilson).

Section Editor: Paul R. Hickey.

Accepted for publication April 21, 1995.

Address correspondence and reprint requests to Christopher M. Viscomi, MD, Department of Anesthesiology, MCHV, Burlington, VT 05401.

Failure of neural tube formation and closure (dysraphism) may occur anywhere along the neural axis. Meningomyelocele occurs in 2-5/1000 births. The incidence varies with environmental and genetic factors [1,2]. In addition to the neural tube defect, several associated problems concern the anesthesiologist. Most infants develop hydrocephalus, usually associated with an Arnold-Chiari type II malformation (downward displacement of the cerebellum into the brainstem and cervical canal with medullary kinking). This may cause cervical cord compression, and cervical flexion during intubation may cause brainstem compression [2]. Airway management may be difficult in patients with significant hydrocephalus [2]. Most patients show a diminished response to hypoxia, and may be more susceptible to postoperative apneic episodes [3]. The effect of positioning the neonate for induction of general anesthesia must also be considered: no direct pressure should be applied to the exposed neural placode [2]. In combination, these factors led us to consider alternatives to general anesthesia for meningomyelocele repair. We therefore prospectively studied the safety and utility of spinal anesthesia for meningomyelocele repair in neonates.

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Methods

Institutional Review Board approval and parental consent were obtained. During our study, 18 neonates presented for meningomyelocele closure. We did not offer spinal anesthesia to the parents of four neonates because of thoracic lesion (one patient), congenital thrombocytopenia (one patient), and need for preoperative magnetic resonance imaging under general anesthesia (two patients). The remaining 14 neonates had lumbar or sacral meningomyeloceles and received spinal anesthesia for meningomyelocele closure Table 1. All neonates had intravenous (IV) catheters inserted shortly after birth, and received parenteral antibiotic therapy (ampicillin plus gentamicin) from the time of IV catheter insertion until the seventh postoperative day. Prior to spinal anesthesia, continuous electrocardiography, pulse oximetry, and noninvasive blood pressure monitors were applied to all neonates. Patients were positioned prone with facial padding and a small chest roll to elevate the thorax to a level slightly higher than the lumbar region. Dural puncture was performed in the most inferior (caudad) region of the meningomyelocele sac in an area devoid of neural elements. A 1-mL tuberculin syringe and a 26-gauge 10-mm needle were used for the spinal injection. Tetracaine 0.5% in dextrose 5% with 20 micro gram of epinephrine was used for all intrathecal injections.

Table 1

Table 1

If supplemental anesthesia was needed during the surgery, additional intrathecal tetracaine was administered by the surgeon. The technique for administering additional intrathecal tetracaine differed from the initial injection. The dura is open during surgery, and the nerve roots lie within a pool of cerebrospinal fluid (CSF). Supplemental tetracaine was distributed throughout the exposed intrathecal space using a tuberculin syringe and a 26-gauge 10-mm needle. Table 2 lists operative times and anesthetic variables. All data are presented as mean +/- SD.

Table 2

Table 2

Infants who cried or were "fussy" during the procedure were offered a pacifier dipped in sugar water. Crying related to surgical manipulations or accompanied by movement at or below the surgical site was treated with additional intrathecal tetracaine. IV midazolam was titrated if crying appeared unrelated to surgical stimulation and the pacifier was ineffective. "Blow-by" oxygen was administered if IV midazolam was given.

After surgery, all neonates were monitored by electrocardiogram, transthoracic impedence apnea monitoring, and pulse oximetry in an intensive care unit for at least 36 h postoperatively.

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Results

Spinal anesthesia was successful in all cases. We confirmed adequacy of spinal anesthesia by having the surgeon perform skin pinches with forceps immediately cephalad to the meningomyelocele. No neonate lost upper extremity tone. Beyond these two extremes, the exact level of the sensory blockade was not determined. Seven patients required a supplemental intrathecal tetracaine injection during the surgery, averaging 93 +/- 14 min after the initial injection. One patient, whose surgical time was 200 min (the longest in our series), received two supplemental tetracaine injections. No neonates developed intraoperative respiratory distress, or oxyhemoglobin desaturation (<or=to92%). Systolic blood pressure decreased an average of 5 mm Hg from 70 to 65 mm Hg (range [+]2 to [-]10 mm Hg).

Two postoperative respiratory events occurred: one transient apnea/bradycardia episode 5 h after surgery in a neonate with a history of preoperative apnea/bradycardia, and a brief decrease in oxyhemoglobin saturation (80%) accompanied by bradycardia 8 h after surgery after an IV morphine injection. These two patients had received the largest amount of intraoperative midazolam (0.28 mg/kg and 0.16 mg/kg, respectively) among the nine neonates who received midazolam sedation. A Kruskal Wallis rank sum analysis of midazolam dose and occurrence of postoperative respiratory event revealed a significant correlation (P = 0.038).

Preoperative and postoperative neurologic examinations were conducted Table 3. All patients have had continued followup in our institution's multidisciplinary spina bifida clinic. In 12 patients, postoperative neurologic examinations were identical to preoperative status. In two patients, neurologic function improved after spinal anesthesia and surgery.

Table 3

Table 3

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Discussion

Spinal anesthesia is a safe and effective technique for anesthetizing high-risk infants having infra-umbilical surgery. A major impetus for providing regional anesthesia in these patients is an attempt to decrease postoperative respiratory complications and minimize the stress response to surgery [4-10]. Only one previous report of spinal anesthesia for repair of meningomyelocele exists. Calvert [11] reported a series of 26 neonates with spina bifida who received intrathecal lidocaine via a trocar and angled Eynards connector. Although no complications were reported, routine monitoring was limited to a rectal thermometer. This report (1966) also antedated neonatal apnea monitors, and did not provide pre- and postoperative neurologic examination information.

A drawback of spinal anesthesia is its limited duration. Attempts to increase anesthetic duration may involve choosing high doses of local anesthetic, with the attendant risk of excessive cephalad block. We administered hyperbaric local anesthetic in our patients. The presence of a chest roll caused the thorax to be slightly higher than the lumbar region. Initial local injection was made at the inferior (caudad) region of the meningomyelocele sac. We thought this position made hyperbaric local anesthetic solutions the safest choice to avoid a high spinal injection. The prone position and ready accessibility to the subarachnoid space during surgery allow a conservative initial dose of local anesthetic, with supplemental intrathecal injections provided intraoperatively as needed. The surgical site allowed what is, in effect, a "continuous" subarachnoid technique.

We noted two postoperative respiratory events in our series. Both occurred in neonates who received intraoperative midazolam. One patient had preoperative apnea/bradycardia episodes, while the second had recently received IV morphine. Previous reports have suggested that unsedated spinal anesthesia is less likely to produce postoperative apneic episodes than general anesthesia or spinal anesthesia with sedation [12-14]. Some groups have recommended ketamine as the safest intraoperative sedative [5]; others have noted a high incidence of postoperative apnea associated with its use [14,15]. Ketamine increases intracranial pressure [16], which may adversely impact patients with hydrocephalus [17]. Five of our patients received no sedatives. In the remaining nine patients we chose to titrate midazolam, in part because of its purportedly mild respiratory effects [18,19] and ability to decrease intracranial pressure [20]. We noted a statistically significant correlation between dose of midazolam and occurrence of postoperative adverse respiratory events. This has caused us to be more judicious in the use of sedatives in neonates.

A significant concern with providing spinal anesthesia to neonates with spinal cord pathology is that postoperative neurologic impairment might be attributed to the anesthetic technique [21,22]. Lambert et al. [23] recently reported that bathing desheathed frog sciatic nerves in 0.5% tetracaine produced permanent conduction impairment. However, there are important differences between clinical spinal anesthesia and bathing isolated nerves in local anesthetic solution. The initial local anesthetic we inject (approximately 0.4 mL) is rapidly diluted in CSF contained in the meningomyelocele sac. However, significant intraoperative loss of CSF occurs during the dissection of the meningomyelocele. A concern might be that supplemental local anesthetic doses are not well diluted, given the diminished quantity of CSF. However, during surgery, the meninges are open, and supplemental local anesthetic injections were administered in multiple locations in the pool of CSF bathing the nerve roots. We believe this technique may prevent potentially neurotoxic concentrations of local anesthetic that may occur if a single point of injection were chosen. Although our series is limited, we did not find any evidence of anesthetic-induced neurologic damage. Other groups [4-7,12,14,24] have administered intrathecal tetracaine (0.5%-1.0%) to infants without any adverse neurologic events. In 12 of our patients, the postoperative neurologic deficits we observed were identical to preoperative deficits Table 3. Two patients demonstrated improved function after spinal anesthesia and surgery.

In summary, the use of spinal anesthesia was a safe and effective technique in our series of neonates requiring meningomyelocele closure. Postoperative respiratory monitoring remains essential, particularly if intraoperative sedatives are administered. Conservative initial tetracaine doses can be chosen, since additional subarachnoid injections can be performed intraoperatively if necessary. Studies comparing respiratory and neurologic outcomes between neonates receiving spinal or general anesthesia for meningomyelocele closure appear to be warranted.

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