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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.51 no.6 Campinas Dec. 2001
Spinal anesthesia in children*
Anestesia subaracnóidea en niños
Norma Sueli Pinheiro Módolo, M.D.I; Yara Marcondes Machado Castiglia, M.D.II
IProfessora Assistente Doutora do
Departamento de Anestesiologia da FMB - UNESP; Presidente do Comitê de
Sub-Especialidade em Pediatria da Sociedade Brasileira de Anestesiologia
IIProfessora Titular do Departamento de Anestesiologia da FMB - UNESP
BACKGROUND AND OBJECTIVES: Pediatric spinal
anesthesia has gained popularity mainly as an alternative to general anesthesia
in pre-term neonates at risk for developing neonatal apnea. This study aimed
at evaluating anatomic, physiologic and pharmacological differences of the technique
CONTENTS: Spinal anesthesia in children is being used since the early 20th century, but was overlooked for many years due to the introduction of inhalational anesthetics and neuromuscular blockers. It regained popularity in 1979. Its positive effects in pediatric anesthesia are cardiovascular stability in children up to 8 years of age, satisfactory analgesia and muscle relaxation. Most popular pediatric anesthetics are tetracaine and bupivacaine in doses adjusted to body weight, but this technique is limited by a relatively short duration of anesthesia. Surgical procedures cannot last more than 90 min and there is no satisfactory postoperative pain control. Complications are the same for adult patients and include post-dural puncture headache and transient radicular irritation. Indications are: lower abdomen, genitalia, perineal region, lower limbs and, in some cases, even thoracic surgeries. It is particularly attractive for pre-term neonates at higher risk for postoperative apnea after general anesthesia.
CONCLUSIONS: Spinal anesthesia in children is a relatively safe technique with few complications and may be considered an alternative for general anesthesia, especially for pre-term neonates at risk for postoperative respiratory complications.
Key Words: ANESTHESIA, Pediatric; ANESTHETIC TECHNIQUES, Regional: spinal block
JUSTIFICATIVA Y OBJETIVOS: Ha aumentado
mucho el empleo de la anestesia subaracnóidea en niños, principalmente
neonatos con riesgo de desarrollar apnea neonatal. El objetivo de este trabajo
fue rever las diferencias anatómicas, fisiológicas y farmacológicas
de esta técnica en niños.
CONTENIDO: La anestesia subaracnóidea en niños, a pesar de haber sido técnica empleada desde el inicio del siglo XX, tuvo su popularidad diminuida con el adviento de los anestésicos inhalatorios y bloqueadores neuromusculares, para ser nuevamente rescatada en 1979. Las características favorables de esta técnica en pediatría son relativas a la estabilidad cardiovascular, en niños de hasta 8 anos de edad, a la analgesia satisfactoria y al relajamiento muscular. Los anestésicos mas utilizados en niños son la tetracaína y la bupivacaína, cuyas dosis son ajustadas tomándose por base el peso corporal. Esta técnica es limitada por la duración relativamente corta, debiendo ser utilizada para procedimientos quirúrgicos que no ultrapasen 90 minutos, también por su analgesia al llegar y al pós-operatorio. Las complicaciones son as mismas encontradas en el paciente adulto, incluyendo cefalea por punción dural e irritación radicular transitoria. Las indicaciones son varias: en cirugías de abdomen inferior, genitales, miembros inferiores, región perineal y, en algunos casos, incluso en cirugías torácicas. Su empleo tiene particular interés en los recién-nacidos prematuros, por causa del riesgo de presentar la apnea de la prematuridad.
CONCLUSIONES: La anestesia subaracnóidea en niños es técnica relativamente segura, con pocas complicaciones y puede ser considerada como opción para anestesia general, principalmente en los recién-nacidos prematuros con riesgo de presentar complicaciones respiratorias en el pós-operatorio.
The first report on pediatric spinal anesthesia was published by August Bier in 18991, when the technique was performed with cocaine in an 11-year old boy submitted to ischium abscess drainage.
In 1900, Bainbridge2 reported 40 surgical procedures under spinal anesthesia, including a patient under 3 months of age. In this case - strangulated inguinal hernia - the author noted that the child would not survive a general anesthesia. In fact, this was justified because by that time general anesthesia was induced with dripping chloroform3.
The British surgeon Tyrell Gray has published, in 19094, the results of a series of 300 pediatric spinal anesthesias for procedures below the diaphragm. The author was impressed with the low incidence of postoperative nausea and vomiting.
Several other reports on spinal anesthesia were published by Junkin (1933)5, Robson (1936)6 and Berkowithz et al. (1951)7.
Leigh et al.8, in 1948, have observed that all pediatric anesthesias in the Vancouver Hospital were spinal. There is even a report on spinal anesthesia for more complex surgical procedures, such as lobectomies and pneumectomies.
With the overall improvement of general anesthesia, the introduction of neuromuscular blockers (1944) and of modern inhalational anesthetics, starting with halothane in 1956, there was a decrease in the use of spinal anesthesia3.
Gouveia9, in 1970, has published his personal experience with this technique performed in 50 children between 3 months and 12 years of age. The author has observed no complications.
Pediatric spinal anesthesia was also considered safe by Cunto10 who, in 1975, has performed it in 84 children between 19 days and 13 years of age.
In 1984, Abajian et al.11 reported the use of spinal anesthesia in 78 children under one year of age, 36 being considered at high risk. These facts explain the rebirth of the technique.
Technological advances and better training of neonatal intensive care units staff have increased the survival rate of pre-term neonates often referred to anesthesiologists for inguinal hernia correction. Spinal anesthesia has been proposed as the single anesthetic technique with the aim of decreasing immediate postoperative apnea, which is high in this group of patients depending on the post-conceptual age.
There are important anatomic differences between children and adults, which are related to the child's development stage which should be considered at spinal blockade induction.
Neonates spinal cord extends at the level of the third lumbar vertebra (L3) and, at the end of the first year of life reaches the location seen in adults, at the first lumbar vertebra (L1)9,10,12-14.
Lumbar puncture in this age group must be performed below the 4th or 5th lumbar vertebrae (L4-L5 or L5-S1 interspace), for additional safety due to the risk of reaching the spinal cord with the needle3,9,15. In plotting an imaginary line between neonate's iliac crests, it will cross the spine at L4-L5 interspace, while in the adult it will cross the spine at L3-L4 interspace16.
The spinal cord of a neonate weighing 3 to 4 kg is approximately 20 cm long, while in the adult it is 60 to 75 cm long. So, the neonate spinal cord is, proportionally, 5 times longer as compared to its weight than that of the adult11,16,17.
Another important factor is CSF volume, which in the adult is 140 ml with 75 ml in the spinal space. In children, total volume varies from 40 to 60 ml with half of it in the spinal space. So, although a reduced total volume in children, the relative volume is higher (2 ml.kg-1 in adults and 4 ml.kg-1 in children)3,9,10,12-18.
Children's spinal cord is highly vascularized allowing for a fast local anesthetic clearance11,14.
Esther-type local anesthetics (procaine, tetracaine) are metabolized in the plasma by pseudocholinesterase. Neonates and children up to 6 months of age have 50% of such enzyme as compared to adults. Clearance may be decreased and local anesthetic effects may be prolonged, although without clinical relevance12,19.
Amide-type local anesthetics (prilocaine, lidocaine, bupivacaine, ropivacaine) are metabolized in the liver and show high protein binding capacity. Liver blood flow is lower in neonates and children under 3 months of age and metabolic mechanisms are immature. In addition, albumin and a1 acid glycoprotein concentrations are low, contributing to the increased concentration of free local anesthetics and increasing the odds for toxic effects12,19-21.
The large balanced distribution volume may give clinical protection by decreasing local anesthetics and other drugs plasma concentration12,21,22.
A caveat must be done as to the use of prilocaine in neonates. Its metabolism produces oxidants which may lead to methemoglobinemia. Pre-term babies and neonates are more susceptible to such complication for having, in different degrees, fetal hemoglobin (HbF) which, only at 6 months of age is totally replaced by adult hemoglobin (HbA), more easily oxidized, and low levels of methemoglobin redutase19,23. Local eutectic anesthetic mixtures (LEAM) for venous or even spinal puncture in neonates should be very carefully used.
Local anesthetic doses for children, especially neonates, are higher than the corresponding doses for adults14,17.
Several anatomic aspects have already been studied and may explain higher doses. As examples:
1. Higher CSF volumes (4 ml.kg-1) could dilute injected local anesthetics14-16;
2. Spine and spinal cord are longer than in the adult as compared to body weight and the spine/body weight ratio in children is five times that of the adult14,17.
The literature reports different local anesthetics used for spinal anesthesia in children and tetracaine (0.2 to 0.6 mg.kg-1) is the most popular.
There are two local anesthetic drugs commercially available in Brazil for this aim: lidocaine and bupivacaine9,10,12.
Table I shows local anesthetics and their doses for pediatric spinal anesthesia.
Two anesthesiologists are needed for this technique: one performing the puncture and the other positioning the child and maintaining free airways. Most of the times there will be the need for sedation or even anesthesia to perform the puncture, which may be done in the lateral or sitting position. Head extension, especially in sedated or anesthetized children, is mandatory due to the risk for hypoxemia14,15,18,30.
In the sitting position, reference points are more easily identified and CSF will more easily flow due to higher hydrostatic pressure18,19.
Puncture shall be performed between L4-L5 or L5-S1 to avoid spinal cord damage. Structures crossed by the needle are more difficult to identify12,16. Most common needles are 24, 25 and 26G Quincke. The use of a mandrel prevents epidermal cells to be carried to the neural axis, which may cause epidermoid tumors11-13,15,16.
Spinal puncture in children is more difficult than in adults. For better mastering such technique, training should be performed first in adults, then in children and eventually in the neonate. This way, the risk for complications is decreased.
Several authors have evaluated spinal puncture difficulties in children and classified them as:
puncture, varying from 51%31 to 100%32;
· lumbar puncture difficulty, varying from 21.3%31 to 9.5%33;
· lumbar puncture failure, varying from 10.2%11 to 4.8%33.
After puncture success confirmation by CSF flow through the needle, local anesthesia is induced. It should be prepared in syringes used for insulin with the exact dose to be injected11-13.
Distance from skin to dura must be observed to prevent unnecessarily introducing the needle thus increasing the odds for complications. Several reports have attempted to define this distance. In practice, it is around 0.5 to 1 cm from the skin in the neonate and increases with the development of the child10-12.
Local anesthetic injections have received several recommendations. CSF aspiration before and after drug injection to assure the correct positioning of the needle is recommended by some16 and not advised by others11. When CSF aspiration is the choice, one must have in mind that the local anesthetic dose to be injected is low and this procedure may dilute the agent in the CSF.
The administration of extra 0.04 ml of local anesthetics to compensate needle dead space is preconized by some authors11,14.
Abajian et al.11 recommend that the needle should not be removed immediately after local anesthetic injection; it should be removed 5 to 10 seconds after injection to prevent local anesthetic return through the puncture hole.
After needle removal, patient is placed in the supine position. Motor block is installed in 1 to 2 minutes and peak of analgesia is reached after 20 minutes32. Children should not be manipulated soon after being placed in the supine position because some authors have observed very high blockades caused by leg rising to position the electrocautery plate3,9-11.
Spinal anesthesia duration in children depends on the local anesthetics and its association with a vasoconstrictor. However, literature and clinical practice have shown that this duration is of approximately 90 minutes, which limits its use for longer surgeries16,18. Tobias16 warns about practical criteria adopted by different studies evaluating spinal anesthesia duration. Some define surgical anesthesia duration as the end of anesthesia (surgical procedure's dermatome sensory block duration), while others define it as motor function recovery. Some studies have evaluated the addition of epinephrine to the spinal solution to increase anesthetic blockade duration.
Gouveia9, in 1970, has used 5% lidocaine in children from 3 months to 12 years of age and recommended higher doses (2 mg.kg-1) in children up to 3 years of age and lower doses (1 mg.kg-1) in older children. Mean blockade duration was 45 minutes and the association of a vasoconstrictor has not increased anesthesia duration. However, Cunto10, in 1975, has used the same anesthetics (5% lidocaine) in doses of 2, 3 and 4 mg.kg-1, with a maximum dose of 100 mg. The increased dose and the association of a vasoconstrictor were directly related to the increase in blockade duration.
Abajian et al.11 have shown a longer spinal anesthesia duration in neonates in whom 0.22 to 0.32 mg.kg-1 tetracaine was used; duration went from 84 ± 7.2 min to 109 ± 5.3 min, when epinephrine was associated.
Rice et al.32 have noticed a longer tetracaine action from 86 ± 4 min to 128 ± 3.3 min after epinephrine association to the spinal solution. Fosel et al.31 have also reported longer surgical anesthesia duration with bupivacaine associated to epinephrine, from 50 to 90 minutes. This short local anesthetic duration is explained by the increased absorption by a higher spinal cord vascularization present in this age group11.
EFFECTS OF SPINAL ANESTHESIA IN CHILDREN
The major advantage of spinal anesthesia in children is the relative post-blockade cardiovascular stability. Differently from adults, children have little or no heart rate and blood pressure changes4,10-12,15,35-37. Some authors predict this stability until 5 years of age while others predict it until 8 years of age11,12,23.
Dohi et al.36 have shown hemodynamic stability in children up to 5 years of age submitted to spinal anesthesia with high sensory block (T2, T3) without previous hydration or vasoactive drugs. Above 6 years of age there has been a mild decrease in blood pressure and between 8 and 15 years of age there has been a more marked blood pressure change.
Spinal blocks reaching the cervical segment have been induced for ductus arteriosus patency correction in neonates without previous hydration and with minor blood pressure changes35. Several authors have found similar hemodynamic stability in neonates or infants up to one year of age9-11,18,35-37.
Factors involved in this extraordinary hemodynamic stability are still not totally defined. One theory is that the relative immaturity of the sympathetic nervous system would make children's vasomotor tone less dependent on this system and that capacitance veins in lower extremities are small and send little blood flow for this region3,9-15,18,35-37.
Oberlander et al.37 have prospectively observed autonomic changes in a group of neonates submitted to spinal anesthesia with a high sensory block level. There has been hemodynamic stability and the authors concluded that spinal anesthesia would decrease heart vagal tone, thus compensating any sympathetic block-induced effect and maintaining cardiovascular stability.
Pascuci et al.38 have investigated the effects of spinal anesthesia with high thoracic sensory block in chest wall displacements of seven pre-term neonates submitted to inguinal herniorrhaphy. The inspiratory movement of the costal grid was decreased in 6 children and 4 of them presented paradoxical rib movements. However, there have been no heart rate or oxygen peripheral saturation changes.
On the other hand, other authors have reported respiratory failure or apnea when sensory and motor block levels were above the first thoracic dermatome (T1), with the need for ventilatory assistance until blockade regression12,39-41.
O'Higashi et al.42 have induced spinal block in 8 children with progressive muscular dystrophy and 2 patients presented with respiratory failure and bronchospasm due to the high level of the blockade. In adults, bronchospasms due to high spinal block are still controversial. It has been suggested that airways reactivity may increase due to the decrease in circulating catecholamines as a consequence of this anesthetic technique19,43,44.
Rice et al.45 have investigated transcutaneous CO2 and oxygen peripheral saturation and have observed no changes in such parameters in 15 high risk neonates submitted to spinal anesthesia with sensory block in T4.
Complications in children are lower than in adults46.
Several authors have referred a relative cardiovascular stability, even with blockades at T4. In children above 8 years of age, there is a decrease in blood pressure and bradycardia, as in adults.
Some respiratory failures were described with the need for ventilatory assistance, especially in spinal blocks close to T1 41,42.
Giaufré et al.46, in 1996, have published a study on regional anesthesia epidemiology and morbidity in children and spinal anesthesia had a very low morbidity rate. From 502 patients, there was only one complication caused by intravascular injection and without clinical effects.
Post-dural puncture headache may be present in children. Kokki et al.47 have shown that this adverse effect would be detected in younger children, although being rare in children under 10 years of age. These authors have reported post-dural puncture headache and symptoms such as nausea, vertigo and photophobia in 12% of children under 10 years of age, and in 13% of children above this age. No child needed epidural blood patch. The incidence of post-dural puncture headache was not changed with the use of Quincke or Whitacre needles and was 15% and 9%, respectively48.
In this same study, authors have shown that the risk for developing such complication was not age-dependent. Eight out of eleven patients with post-dural puncture headache were below 10 years of age and the youngest patient with such complication was 23 months old48.
Other complaints, such as lumbar pain and transient radicular irritation were also found within this age bracket47,48.
INDICATIONS AND COUNTERINDICATIONS
There is in the literature a broad indication of spinal anesthesia for surgeries going from lower limbs up to ductus arteriosus correction and pneumectomy.
Other applications of this technique are limited by anesthesia duration, which averages 90 minutes. However, the technique seems to be especially attractive for neonates with history of prematutiry apnea and pulmonary bronchodysplasia, due to the risk of developing postoperative respiratory complications and/or apnea.
Neonatal apnea is more frequent in pre-term neonates with post-conceptual age under 44 weeks, although the absence of such event does not rule out its postoperative incidence in this group of patients49. Surgical procedures in this group at risk for neonatal apnea are very frequent, especially inguinal herniorrhaphies. The observation that general anesthesia or sedation would increase the incidence of postoperative apnea has paved the way for the search for other anesthetic techniques. Some authors have shown the absence of postoperative apnea in pre-term neonates submitted to spinal anesthesia without simultaneous sedation11. However, Tobias et al.26 have described bradycardia and apnea in two pre-term babies who received spinal anesthesia alone without sedation or anesthetic supplementation. The exact mechanism of such events was not detected, but these side-effects were reverted at the end of the spinal block.
So, this group of children should not be submitted to outpatient anesthesia because they should be followed up for 24 hours after any anesthetic procedure, regardless of the technique.
Absolute counterindications are the same as for adults and include patients or relatives refusal, major and non corrected hypovolemia, blood coagulation abnormalities, needle insertion site infection, sepsis and changes in intracranial compliance with the increase in intracranial pressure13.
Spinal anesthesia in children has gained a new breath. In some cases it may be an alternative for general anesthesia. It is less expensive as compared to general anesthesia, promotes good muscle relaxation and postoperative analgesia if associated to other drugs and the incidence of adverse effects seems to be low.
However, it must be highlighted that the risk/benefit ratio of any anesthetic technique should be the major guide for the choice.
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Correspondence to Submitted for publication March 14, 2001 * Received
from Hospital de Clínicas da Faculdade de Medicina de Botucatu - UNESP
Dra. Norma Sueli Pinheiro Módolo
Address: Departamento de Anestesiologia da FMB - UNESP
Distrito de Rubião Jr s/nº - Caixa Postal 530
ZIP: 18618-970 City: Botucatu, Brazil
Accepted for publication May 11, 2001
Submitted for publication March 14, 2001
* Received from Hospital de Clínicas da Faculdade de Medicina de Botucatu - UNESP