Regional Anesthesia for Inguinal Herniorrhaphy in the Ex-Premie
Introduction: Initially, interest in neuraxial block (NB) anesthesia for hernia repair in the ex-premie was stimulated by the desire to avoid postanesthesia apnea. The procedure has now matured to the point where it is a viable option for the primary anesthetic. The technical skills required are familiar to all pediatric anesthesiologists and the procedure is safe when performed by experienced clinicians.
NB is not indicated for all infants. If the infant is beyond the age range for risk of postoperative apnea1 (e.g. 52-60 weeks post-conceptual age and not on an apnea monitor or methylxanthine drug), less advantage is conferred by regional anesthesia. Similarly, not all hernia repairs are simple. If the surgeon feels the hernia(s) may be technically challenging to repair, he may be uncomfortable with time constraints imposed by NB. Similarly, the awake patient may move, strain or sneeze, all of which may make repair more difficult. Some surgeons are uncomfortable without the absolute stillness conferred by intubation and paralysis.
The main advantages for regional anesthesia are respiratory. Avoidance of instrumentation of an already compromised respiratory tract (BPD) can help prevent complications such as hypoxemia, laryngospasm, bronchospasm, post-intubation stridor, and the potential for prolonged ventilation. Also, neuraxial block greatly decreases the incidence of postoperative apnea.
Literature Review: Several articles demonstrate the utility and safety of both subarachnoid block (SAB) and caudal block (CB)2-5. The largest series published was by Frumiento et al, from the University of Vermont6. They reviewed 269 cases of inguinal hernia repair in which successful spinal anesthesia was achieved in 262 (95% percent on the first attempt). The mean gestational and postconceptual (PCA) ages were 32 and 44 weeks, respectively. After subtracting 4 cases in which supplemental GA was administered, the final apnea rate was 4.2%. A "high" spinal was noted in 8 patients; none required intubation. In the discussion section of the article the authors give a spirited argument against routine overnight apnea monitoring of outpatients.
There are, however, several reported cases of apnea after both caudal and spinal block. In the majority of these cases a supplemental CNS depressant (e.g. midazolam, ketamine, codeine) was given in the perioperative period. The apnea can be life-threatening. In high-risk neonates, Bailey et al7 reported apnea in 4/61 and Sukhani et al8 reported tactile stimulation for a SpO2 <90 % in 4/99. Moss and Hatch9 reported apnea in 0/63 infants under 2 months of age although the percentage who were born prematurely was not specified. Veverka et al10 observed no apnea after SAB in 62 ex-premies. They discharged outpatients home after an average observation period of 5.6 hours for those with a history of apnea and 3.5 hours for those without. Sartorelli et al11 reported no episodes of apnea in 140 high-risk neonates after SAB and monitored their patients overnight. Although the exact incidence of apnea in high-risk ex-premies receiving GA has not been published, it certainly exceeds that of the above studies and may be as high as 30%3.
Krane et al12 studied 18 ex-premies undergoing GA or SAB. All patients had 12-hour impedance pneumocardiograms performed pre- and postoperatively. Although the number of central apnea episodes lasting >15 seconds were not different between groups, a significant reduction in postoperative O2 desaturations and bradycardias were noted in the spinal group. In addition to infrequent apnea and occassional high spinal, some authors have noted technical difficulty obtaining CSF7,13. The literature demonstrates greater technical success rates with increased patient numbers6,11.
The generally recommended dose of bupivacaine or tetracaine for spinal anesthesia ranges from 0.3-1.0 mg/kg with approximately 5-10 mcg epi/kg. Rice, et. al14 found a surgical duration of 90 minutes after 0.4 mg/kg tetracaine with epi, 60 minutes without. The higher dose requirement and shorter duration compared to adults are related to a larger relative CSF volume, which is also reflected by a higher length-to-weight ratio.
For caudal anesthesia, 0.25% bupivacaine with epi 1:200,000 is used. A level of T6 is necessary to block pain associated with traction of the spermatic cord. Recommended doses range from 0.8-1.2 ml/kg (2.0-3.0 mg/kg). It is important that epi be included to slow the rate of systemic absorption. Surgical durations of at least 90 minutes again are found. Intravascular caudal injections are not uncommon, and safety measures must be taken to prevent catastrophic results. Initially, ¼ of the dose (0.25cc/kg) should be given with continuous observation of the ECG for 60-90 seconds. The most reliable finding of intravascular injection is T-wave elevation, typically occurring at 15-20 seconds15. Henderson et al16 reported a continuous catheter technique using 3% 2-chloroprocaine in former premies. No toxicity was noted with this rapidly metabolized drug.
Practical Considerations: Infants should be fed clear liquids 2 hours before the procedure so they are not agitated from hunger. For fussiness, a pacifier dipped in dextrose water may be given. Comfort is markedly improved if EMLA cream is applied over potential IV sites, midline back at L2-L5, and over the sacral hiatus 2 hours preop. It is my practice to place an IV before either block. Although one may be placed painlessly in a lower extremity after SAB, this practice "eats" into the surgical block time and takes away the anesthesiologist's attention just when close observation for a high spinal is imperative. I use a B-Dä clear-hubbed 1" 25g styletted neonatal spinal needle (to avoid the theoretical risk of later development of intraspinal epidermoid tumors) and do not aspirate CSF (dead space 0.04 ml). Holding infants in the sitting position causes less desaturation compared with being held rigidly in the flexed lateral position17. The depth to the subarachnoid space is usually just a few millimeters; beyond this a bloody tap is common. The OR table should be placed in 15° of reverse Trendelenberg position to decrease the risk of high spinal.
One ml each of 10% dextrose and 1% tetracaine are mixed yielding a final solution of D5 with 5 mg tetracaine per ml. To this, 75 mcg of epi is added. One mg/kg of tetracaine (0.2 ml/kg) is drawn into a tuberculin syringe and slowly injected over 30 seconds. After a properly placed SAB the legs cease movement immediately. When placing the dispersion pad it is important to horizontally levitate the baby and not lift up the legs. The key observation for high spinal is lack of chest or abdominal movement and rapid desaturation. Equipment for bag-and-mask ventilation and endotracheal intubation should be immediately available before placing the block. Following completion of surgery under SAB, a caudal may be painlessly placed using 1 ml/kg of 0.125% bupivicaine or ropivicaine with epi. In surgeries where a circumcision is also planned, the hernia repair should be done first.
For infants in which SAB cannot be achieved, consideration should be given for caudal block as the primary anesthetic. Often the thriving ex-premie has difficult to palpate cornu and/or laminar ridges comprising the inverted "V" of the sacral hiatus. The practitioner should perform firm palpation over the superior end of the intergluteal cleft by rolling the index finger in the lateral then cephaled-caudad directions. Injecting the solution through a 1" angiocatheter may help the block level reach T6. Infants with imperforate anus have grossly abnormal sacral hiatus anatomy and CB may be contraindicated.
In addition to a sweetened pacifier, I place blowby O2 near the face to help with oxygenation and venting of exhaled CO2 and tape a cut piece of gas sample tubing to the cheek so its tip lays near the nose to grossly monitor CO2. The blood pressure cuff should be placed on a lower extremity and the arms restrained. A precordial stethescope is used since apnea, although infrequent, can still occur.
The best time to discharge these patients is controversial. The most widely practiced and conservative measure is to admit all ex-premies less than 60 weeks PCA for overnight apnea monitoring, regardless of the anesthetic. Certainly this needs to be the case for infants on apnea monitors or methylxanthine drugs, or those who have received any form of a perioperative CNS-depressing medication. On the other hand, I consider "early" discharge for uncomplicated cases after 8 hours of apnea monitoring in those infants who do not have any of the above-listed conditions and who have demonstrated no apnea, bradycardia or desaturations during the surgery and for 8 hours postop.
Summary: There is a learning curve for regional anesthesia for herniorrhaphy in the ex-premie, but once mastered the practitioner will find the rewards are plentiful. The incidence of apnea is greatly reduced, instrumentation of the airway avoided, and pre-emptive analgesia obtained.
References
Samuel E. Golden, MD, FAAP
Loyola University, Chicago, IL
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