Regional anesthesia has become a routine part of the practice of anesthesiology in infants and children. Local anesthetic toxicity is extremely rare in infants and children; however, seizures, dysrhythmias, cardiovascular collapse, and transient neuropathic symptoms have been reported. Infants and children may be at increased risk from local anesthetics compared with adults. Larger volumes of local anesthetics are used for epidural anesthesia in infants and children than in adults. Metabolism and elimination of local anesthetics can be delayed in neonates, who also have decreased plasma concentrations of α1-acid glycoprotein, leading to increased concentrations of unbound bupivacaine. Most regional anesthetic procedures in infants and children are performed with the patient heavily sedated or anesthetized; because of this, and because a test dose is not a particularly sensitive marker of intravenous injection in the anesthetized patient, detection of intravascular local anesthetic injection is extremely difficult. The same local anesthetics used in adult anesthetic practice are also used in infants and children. Because of its extremely short duration of action, chloroprocaine has been used primarily for continuous epidural techniques in infants and children. The use of tetracaine has generally been limited to spinal and topical anesthesia. Lidocaine (lignocaine) has been used extensively in infants and children for topical, regional, plexus, epidural and spinal anesthesia. The association between prilocaine and methemoglobinemia has generally restricted prilocaine use in infants and children to the eutectic mixture of local anesthetics (EMLA). Because of its greater degree of motor block compared with other long-acting local anesthetics, etidocaine has generally been limited to plexus blocks in infants and children. Mepivacaine has been used for both plexus and epidural anesthesia in infants and children. Because postoperative analgesia is often the primary justification for regional anesthesia in infants and children, bupivacaine, a long-acting local anesthetic, is the most commonly reported local anesthetic for pediatric regional anesthesia. Given the lower toxic threshold of bupivacaine compared with other local anesthetics, the risk-benefit ratio of bupivacaine may be greater than that of other local anesthetics. Two new enantiomerically pure local anesthetics, ropivacaine and levobupivacaine, offer clinical profiles comparable to that of bupivacaine but without its lower toxic threshold. The extreme rarity of major toxicity from local anesthetics suggests that widespread replacement of bupivacaine with ropivacaine or levobupivacaine is probably not necessary. However, there are clinical situations, including prolonged local anesthetic infusions, use in neonates, impaired hepatic metabolic function, and anesthetic techniques requiring a large mass of local anesthetic, where replacement of bupivacaine with ropivacaine, levobupivacaine or (for continuous techniques) chloroprocaine appears prudent.

Benefit and risks of local anesthetics in infants and children.

Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field It is of paramount importance that the anesthesiologist shares this understanding Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes

https://journals.sagepub.com/doi/pdf/10.1177/0271678X18789273

Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection:

Caudal anesthesia is the single most important pediatric regional anesthetic technique. The technique is relatively easy to learn (1), has a remarkable safety record (2), and can be used for a large variety of procedures. The technique has been reviewed in the English (3) and French (4) literature, as well as in German guidelines (5) and in pediatric anesthesia textbooks (6).

Caudal blocks: Caudal blocks

Single-shot "kiddie caudal" with bupivacaine alone is losing popularity because of its duration of 4-8 h. In a prospective randomized double-blind clinical study, we assessed and compared the efficacy of ketamine, midazolam, and neostigmine coadministered with bupivacaine in a caudal epidural to provide intraoperative and postoperative pain relief. Eighty children (ASA status I) aged 5-10 yr undergoing unilateral inguinal herniotomy were allocated randomly in equal numbers (n = 20) into 4 groups to receive a caudal injection of 0.25% bupivacaine (1 mL/kg) with or without ketamine (0.5 mg/kg), midazolam (50 microg/kg), and neostig-mine (2 microg/kg), after the induction of standardized general anesthesia without premedication. Monitoring for pain, sedation, postoperative nausea/vomiting, dizziness, and pruritus was performed by anesthesiologists blinded to the study allocation. The time to first analgesic administration (paracetamol syrup) was longer (P < 0.05) in the bupivacaine-neostigmine group and the bupivacaine-midazolam group than in the other groups. Undesirable effects, such as emesis, pruritus, and dizziness, were comparable in all groups. However, the incidence of hallucination was more frequent in the bupivacaine-ketamine group compared with the other groups. This study shows that single-shot caudal coadministration of bupivacaine-neostigmine and bupivacaine-midazolam was associated with an extended duration of postoperative pain relief.

Caudal Additives in Pediatrics: A Comparison Among Midazolam, Ketamine, and Neostigmine Coadministered with Bupivacaine

Background. Clonidine is used increasingly in paediatric anaesthetic practice to prolong the duration of action of caudal block with a local anaesthetic agent. Which route of administration of clonidine is the most beneficial remains unknown. We compared the effects of caudal and i.v. clonidine on postoperative analgesia produced by caudal bupivacaine after hypospadias repair. Methods. Forty-six children (ASA I or II) aged 24‐104 months received standardized premedication with midazolam, a general anaesthetic and a caudal block with bupivacaine 0.25%, 0.5 ml kg ‐1 . The children were randomized in a double-blind fashion to two groups: the i.v. group received clonidine 2 m gk g ‐1 i.v. and simultaneously the same volume of saline caudally. The caudal group received clonidine 2 m gk g ‐1 caudally and a similar volume of saline i.v. After surgery, all children received acetaminophen 20 mg kg ‐1 rectally or orally 6-hourly and were given a patient-controlled or nurse-controlled analgesia (PCA/NCA) pump with i.v. morphine (bolus of 25 m gk g ‐1 and an 8-min lockout period with no background infusion). Monitoring of scores for pain, sedation, motor block, and postoperative nausea and vomiting was performed by nurses blinded to the study allocations. Time to first activation of the PCA/NCA pump and 0‐24 h and 24‐48 h morphine consumption were also recorded. Results. Forty-four children completed the study. Age, weight and duration of anaesthesia and surgery were similar in the two groups. The median (range) time to first activation of the PCA/ NCA pump was similar in the two groups: 425 (150‐1440) min in the i.v. group and 450 (130‐ 1440) min in the caudal group. The number of children not requiring postoperative morphine was four and seven respectively. Morphine consumption during 0‐24 h and 24‐48 h was similar between groups. Conclusions. The analgesic effect of clonidine 2 m gk g ‐1 as an adjunct to caudal block with bupivacaine 0.25%, 0.5 ml kg ‐1 is similar whether administered i.v. or caudally. Br J Anaesth 2004; 92: 223‐7

Caudal bupivacaine supplemented with caudal or intravenous clonidine in children undergoing hypospadias repair: a double-blind study

Regional anaesthetic techniques are now widely used in children undergoing surgery. Despite a published history of nearly a century these techniques were restricted to small numbers of practitioners in few centres until relatively recently. The last 10–15 years have seen these techniques become commonplace in all types of hospital where children undergo surgery. This is particularly true of subarachnoid and epidural blocks. Advantages of these techniques include dense intra-operative analgesia, reduced requirements for volatile agents and opioids and analgesia continuing into the postoperative period. Central neuraxial analgesic techniques are not restricted to specialist anaesthetists in paediatric centres but also have a place in district general hospitals and specialist surgical centres where children undergo orthopaedic, plastic, urological and thoracic surgery. In the same period there has also been a large volume of material published on many aspects of central neuraxial blocks in children. This literature, when analysed critically, can be used to guide the use of these techniques in children in order to optimise the analgesia they provide, minimise the side-effects and improve safety.

Epidural and subarachnoid blockade in children.

The aim of this study was to determine the effect of nitrous oxide on cerebral blood flow velocity in children anaesthetised with desflurane. Eighteen healthy children scheduled for elective surgery were enrolled into the study. Anaesthesia was induced using sevoflurane, and a caudal block was performed following tracheal intubation. Anaesthesia was maintained with 1 age-adjusted MAC desflurane. A transcranial Doppler probe was used to measure middle cerebral artery blood flow velocity. Each patient was randomised to receive a sequence of either air/nitrous oxide/air or nitrous oxide/air/nitrous oxide in 30% oxygen. Fifteen minutes after each change in the nitrous oxide concentration, three measurements of cerebral blood flow velocity, blood pressure and heart rate were recorded. Neither the addition nor removal of nitrous oxide caused any significant changes in middle cerebral artery blood flow velocity, heart rate or blood pressure. This may be due to a more potent cerebral vasodilatory effect of desflurane in children.

https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2044.2004.03458.x

D. A. Rowney

Papers

Epidural and subarachnoid blockade in children.

The effect of nitrous oxide on cerebral blood flow velocity in children anaesthetised with sevoflurane.