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Spinal anaesthesia in children

INTRODUCTION:- Spinal anaesthesia (SA) in infants and children (Pediatric spinal anaesthesia) is safer than the SA in adults and it has many advantages over general anesthesia as well. It is time tested, strongly recommended for abdominal and lower limb operations as it gives good muscle relaxation and true pain free fields. In thoracic surgery it can be combined with SSS (short, safe, sleep).

 ANATOMICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN ADULTS AND NEONATES:- The spinal cord ends at L3 level at birth and reaches L1 by first year. The dural sac is at S4 level at birth and reaches S2 by the end of the first year of life. So it is common sense to use low approach (L5 or L4) to avoid damage to spinal cord in newborn.

The line joining the two superior iliac crests (inter-cristal line) crosses at L5-S1 inter-space at time of birth, L5 vertebra in young children and L4-5 inter-space in adults, a landmark for puncture site.

Another feature which is unique in infants is that there is only one anterior concave curvature of the vertebral column at birth. The cervical lordosis begins in the first 3 months of life when the child starts holding the head upright. The lumbar lordosis starts as the child begins to walk at the age of 9 months. Therefore, the spread of local anesthetic is different in infants as compared to adults.

The volume of cerebrospinal fluid CSF is 4 ml/kg which is doubles the adult volume, moreover in infants half of this volume is in the spinal space whereas adults have only one-fourth of it. This significantly affects the pharmacokinetics of intrathecal drugs.

Newborns have a narrow subarachnoid space (6-8 mm) and low CSF pressure, necessitating greater precision and avoidance of lateral deviation. Further laminae are cartilaginous, hence paramedian approach should be avoided too.

Hemodynamic suppression following SA is less in children due to a smaller peripheral blood pool, immature sympathetic autonomic system and compensatory reduction in vagal efferent activity. Still preloading before SA should be routine in children.

Infants respond to high thoracic spinal anesthesia by reflex withdrawal of vagal parasympathetic tone to the heart. It is one of the reasons why spinal anesthesia has been the technique of choice in critically ill and moribund neonates who present for surgery in grave hemodynamic instability.

High levels (T2-4) of block reduce outward motion of lower ribcage, decrease intercostal muscle activity and may lead to paradoxical respiratory movement in children. However, diaphragm compensates for loss of ribcage contribution in most cases.

 PHARMACOLOGY:- The most important concern with the use of in­trathecal local anesthetics in infants and young children is the risk of toxicity of medicine. A relatively higher cardiac output, highly vascular piamater, and regional blood flow in infants lead to rapid re-absorption of LA and shorter duration of block. Children also require higher dose of local anesthetic drug due to higher total CSF (neonates 10 ml/kg, infants 4 ml/kg and adults 2 ml/kg) and spinal CSF volumes (50% in children vs. 33% in adults).

Various anesthetics have been used for pediatric spinal anesthesia but bupivacaine spinal remain the drug of choice.

 INDICATIONS:- Abdominal and lower limbs operations can be done under spinal anaesthesia. Examples are umbilical hernias, inguinal hernias, orchidopexy, circumcision, hypospadias, cystoscopy, gut surgery, colostomy for imperforate anus, rectal and perineal pathologies; lower extremity orthopedic and reconstructive surgeries, meningomyelocele.

Preterm infants and with other co-morbidities who are prone to postoperative complications of general anesthesia are also its candidates. Neonates with respiratory diseases like bronchop­ulmonary dysplasias, hyaline membrane disease, children with history of or at high risk for malignant hyperthermia, acute respiratory conditions, and chronic disease of the airways like asthma or cystic fibrosis.

 CONTRAINDICATIONS:- The contraindication of spinal block in children is similar to those of adults. Examples are progressive neurological disease, uncontrolled convulsions, infection of the skin or subcutaneous tissue locally at puncture site, coagulation defects, true allergy to local anesthetics and severe hypovolemia.

NPO:- The standard practice are preoperative fasting for elective spinal anesthesia, 2-3 hrs fasting for clear fluids, 4 hrs for other fluids and 6 hrs for solids but our observations are it does not matter the patient is NPO or not.

PREMEDICATION:- Children are apprehensive from the thought of parental separation, pain of surgery, and use of needles. Performing spinal puncture in a struggling, agitated child is difficult and should be avoided. Adequate premeditation can smooth these factors and facilitate spinal anaesthesia. Various drugs (ketamine, midazolam, thiopentone, propofol, halothane, sevoflurane, or nitrous oxide), via different routes may be used to achieve a well sedative child who allows venous puncture, placement of monitors and even a lumbar puncture. Ketamine 4-6 mg/kg, midazolam 0.4 mg/kg and atropine 0.03 mg/kg is quite effective and safe in most cases.  Whatever may be the drug and the route of administration, it is important that it is customized for each type of patient and surgery involved and also safe during the entire preoperative period.

We strongly recommended that the child should not be over sedated during spinal anesthesia.

 SPINAL NEEDLES:- Various types of spinal needles have been described depending upon the length, gauge, tip design (cutting/ pencil point), bevel (long/short), and presence /absence of stylet. The length of spinal needle varies from 25-50 mm (25-30 mm for infants, 50 mm for small children). A 90 mm adult spinal needle has also been used in children. A shorter pediatric needle allows more precision in movement, will bend rather than break in case of movement, and has a smaller dead space. A short bevel allows better appreciation of tissue resistance and reduces the chance of incomplete injection of drug. IV catheters, hollow stylet and hypodermic needles have also been used. We routinely use 5cc or 10cc hypodermic needles in babies depending upon depth of spinal canal.

 TECHNIQUE/ PROCEDURE:- The basic procedure of performing a spinal anaesthesia in children is similar to that of adults. Conventionally SA is performed in a lateral decubitus position with patient curled up and flexed at hip joint not at neck (to avoid suffocation). Sitting position is also suitable in difficult cases or for saddle block effect.

Secure IV access, preload the baby according to weight. Oximeter probe and NIBP cuff are applied to the lower extremity to avoid disturbing infants during surgery.

After aseptic precautions; select the L5 or L4 spinal space. Ideally do not over sedate the child, if needed use low dose ketamine or a short acting drug like thiopental/propofol intravenously or inhalation anesthetics like oxygen ­nitrous oxide, sevoflurane or halothane. Intraoperatively do not sedate the child. Apply local to entry point with insulin syringe then already filled routine syringe with abocaine spinal dose is used with its hypodermic needle to approach the subarachnoid space. After aspiration and confirm coming CSF, inject the dose there and then (in one go action). Depth of insertion at L5-4 varies with age (newborn 10-15 mm, up to 5 years 15-25 mm, 5-8 years 30-40 mm). Routine spinal needle can be used and their correct placement is ascertained by free flow of CSF. Always midline approach should be used not the lateral approach which can damage the nerve roots.

The child may be kept in the dependent side for a few minutes for lateralization of the block. Caution should be taken not to elevate the lower extremities higher because of resultant high or “total” spinal anaesthesia. The neurological sequelae can be minimized using appropriate volume, baricity and concentration of drug, selection of puncture site, ensuring free flow of CSF before injecting the drug, position of patient as well and pre loading.

A successful block usually takes more than 5 minutes to be effective and during that time care should be taken regarding the position of patient as hyperbaric abocaine spinal can spread cephalic resulting in high spinal. The extent of the sensory block can be checked by pin prick, finger pinch, forceps and that of the motor block by paralysis of leg movements.  Higher block is indicated by restlessness of baby, slowdown of baby, weakness of weeping and struggling respiration (diaphragmatic breathing). Children very often fall asleep with the de­afferentation following the block or semi vasovagal shock.

Loose soft restraints may be applied to the wrists to prevent infant from reaching on to the sterile field. Intraoperative sedation may not be required if SA is successful because de-afferentiation itself produces sedation. Intraoperative fluids only include deficit and for maintenance. The hypotensive cardiovascular response to sympathectomy is minimal due to small lower limbs in children. However standard monitoring is mandatory and if needed oxygen by face mask or mask ventilation.

 INTRATHECAL DRUGS:- Among the various drugs approved by FDA for pediatric intrathecal use, 0.5% bupivacaine is common and popular. The doses used are institutional though the standard protocol that we have been practicing is 0.5% bupivacaine 0.1 ml/kg or 0.5 mg/kg for infants weighing 0-5 Kg; or 0.08 ml/Kg or 0.4 mg/kg for 5-15 Kg body weight and 0.06 ml/kg or 0.3 mg/kg for >15 Kg weight. Rough calculation is one fourth of adult dose in young children.

Baricity is one of the most significant factors to affect the distribution of the local anesthetic and hence success and spread of the blockade. Spinal anesthesia is equally effective in both lateral and sitting position but 0.2 ml more needed in sitting position.

Duration is an important and a limiting factor for pediatric spinal anesthesia especially in infants and younger children. Spinal anesthesia alone for this reason is therefore generally restricted to one hour duration surgeries only. The duration is longer with larger doses in infants and varies directly with the age of the child. It has been seen that the duration of long acting local anesthetics like bupivacaine is only about 45 min in neonates and 75-90 min in children up to five years.

ADVANTAGES:- Spinal anesthesia produces a reliable, profound and uniformly distributed sensory block with rapid onset and good muscle relaxation. It results in more complete control of cardiovascular and stress responses than epidural or opioid anesthesia. It is ideal for day-­case surgeries and is safe and cost-effective. There is no additional requirement of any special drug or equipment for the procedure. Because of these benefits, spinal anesthesia has gained acceptance for children undergoing surgeries. This can be practice by surgeon himself where anaesthetic is not available.

COMPARISON WITH GENERAL ANaESTHESIA:- Spinal anaesthesia has many advantages over general anaesthesia for example; it is true pain blocker, safe, reliable, cost effective, less drugs used, less monitoring is required, less postoperative complications, early discharged as day-case, simple technique and can be practice by surgeon himself when anesthetist is not available.

General anaesthesia is associated with several life-threatening complications especially in preterm and those with comorbidities like sepsis, necrotizing enterocolitis, anemia, severe respiratory diseases like respiratory distress syndrome, bronchopulmonary dysplasias, cystic fibrosis etc. All these neonates are at much higher risk of apnea, bradycardia, desaturation, risk of postoperative respiratory depression and complications after general anesthesia. Intraoperative laryngo and bronchospasm are not uncommon even in healthy infants and children besides episodes of coughing, breath-holding, endotracheal tube obstruction and atelectasis.

Overall patient safety, feasibility and reliability are the key features of this technique which will only become better with greater use, experience and research.

 RECOVERY:- Before shifting the patient to recovery room, one must ensure stable vital signs, intact gag, swallowing and cough reflexes, and adequate respiration.

 DISCHARGE:- Criteria for discharge when the vital signs are stable for at least 1 hour, and there should not be intolerable pain, nausea/retching or vomiting, and patient is ambulatory (appropriate for age), orientation to time, place and person appropriate for child’s age, tolerating oral fluids as well. If residual sensory block is present, instructions to protect the child from hot, cold, or sharp objects should be given.

 SIDE-EFFECTS AND COMPLICATIONS:- The complications related to spinal anaesthesia are usually either due to the needle used to perform the procedure (backache, headache, nerve or vascular injury and infection) or the drugs injected (high or total spinal, drug toxicity). Complications of SA in children are usually minor and infrequent. There is no report in literature mentioning any fatal complication or permanent neurological sequelae following SA.

Some of the complications, which can occur include:

Commonly cry of baby slow down and may went into sleep with some time little difficult respiratory efforts. Just a little vigilance is needed with head side up.

Rarely oxygen drops and just oxygen support is needed.

Cardio-respiratory insufficiency: Hypotension and desaturation are rare in children, if at all then it is usually due to high block or use of over sedation.

Post-dural puncture headache: It is reality in children as well and do occur independent of age. Overall incidence of 4-5% (as in adults) has been reported in 2-15 years age group. Symptoms are generally mild in children and they recover faster without any specific treatment, except in few cases I/V fluid supplement on 2nd postoperative day may be needed.

Backache 5-10% in adults but it is not a common complaint in children.

High or total spinal anaesthesia can result if infant’s legs are lifted up just after injection of drug or with overdose resulting in apnea, requiring assisted ventilation. Limited thoracic kyphosis facilitates cephalad spread.

Intracranial migration of anesthetic drugs in SA is very rarely seen and may lead to complete senselessness and unconsciousness, but spontaneous respiration continues with cardiac activity and child definitely recovers within half an hour when the effects of drugs vein off. Extremely rare respiratory support is needed (oxygen support, mask ventilation or endotracheal intubation with positive pressure ventilation).

Transient neurological symptoms are described as new onset pain and dysesthesia originating in gluteal region and radiating to lower limbs. In most cases symptoms are mild and subside themself.

Infections only anecdotal reports of meningitis (aseptic and septic) are reported with SA in children, that too with no proven causal relationship. In case of post-spinal fever, prompt LP is indicated for quick diagnosis.

Failure: The failure rate of attempted spinal anesthesia is rare even when the subarachnoid space has reached and the local anesthetic injected, solution is to repeat it, may be in sitting position.

 LIMITATIONS:- Despite several specific indications and advantages, this technique has some limitations: Single shot technique provides mere 50 minutes of surgical anesthesia and shorter postoperative analgesia. This can be overcome with judicious use of additives. Need for sedation and GA in some children for performance of block. In fact there may be less risk of injury in an immobile child than in a child who is struggling during needle placement. However, sedation should be avoided in premature infants as far as possible.

 TECHNICAL DIFFICULTIES:- Lack of cooperation and their unique anatomical features make SA in children challenging. Bloody tap and difficulty in aspiration are associated with failure of SA. Technical difficulties and failure may thus be a matter of individual skill and experience.

 CONCLUSION:- Today, more than a century ahead since its inception, although firmly established as safe, SA still remains underutilized in children. Based upon extensive literature review and our own experience, we are convinced that SA is safe, cost-effective, and technically feasible technique. It has a remarkable safety record in pediatric population in the hands of an experienced anesthetist, proper patient selection, drugs, and dosages. As anaesthetists become more experienced, it may well become a preferred choice either alone or as a part of balanced technique in children undergoing elective surgeries, rather than just as an alternative in the high-risk pediatric patients.