Local anesthetics and their adjuncts

Evolving approaches in neonatal postoperative pain management

Neonates experience significant moderate and severe postoperative pain. Effective postoperative pain management in neonates is required to minimize acute and long-term effects of neonatal pain. Protecting the developing nervous system from persistent sensitization of pain pathways and developing primary hyperalgesia is essential. Opioids and acetaminophen are commonly analgesics used for pain control. Regional anesthesia provides adequate intraoperative and postoperative analgesia in neonates. It decreases exposure to opioids, reduces adverse drug effects, and facilitates early extubation. It suppresses the stress response and can prevent long-term behavioral responses to pain. The most common blocks performed in neonates are neuraxial blocks. Using ultrasound increased the number of peripheral nerve blocks performed in neonates. Recently, various peripheral nerve blocks (paravertebral, transverse abdominis plane, rectus sheath, quadratus lumborum, erector spinae plane blocks) were safely used. Many studies support analgesic efficacy but highlight neonates' unpredictability and variability of fascial blocks.

A Review of Regional Anesthesia in Infants

Regional anesthesia provides effective anesthesia and pain relief in infants with age-specific data attesting to safety and efficacy. Regional anesthesia decreases exposure to opioids and general anesthetic agents and associated adverse drug effects, suppresses the stress response, and provides better hemodynamic stability compared to general anesthesia. Regional anesthesia can prevent long-term behavioral responses to pain. As a result, the overall number and variety of nerve blocks being used in infants is increasing. While neuraxial blocks are the most common blocks performed in infants, the introduction of ultrasound imaging and a better safety profile has advanced the use of peripheral nerve blocks. Infant-specific pharmacokinetic and pharmacodynamic data of local anesthetic medications are reviewed including risk factors for the accumulation of high serum levels of unbound, pharmacologically active drug. Bupivacaine accumulates with continuous infusion and 2-chloroprocaine can be used as an alternative. Local anesthetic systemic toxicity has the highest incidence in infants less than 6 months of age and is associated with bolus dosing and penile nerve blocks. Local anesthetic toxicity is treated by securing the airway, suppression of seizure activity and implementation of cardiopulmonary resuscitation. Administration of intralipid (intravenous lipid emulsion) is initiated at the first sign of toxicity. A high level of expertise in regional anesthesia is needed when treating infants due to their unique development.

Newer nerve blocks in pediatric surgery

PURPOSE OF THE REVIEW

The purpose of this manuscript is to provide a brief discussion of the current direction in pediatric regional anesthesia, highlighting both newer nerve blocks and techniques and traditional nerve blocks.

RECENT FINDINGS

The number of nerve blocks performed in pediatric patients continues to increase. This growth is likely related in part to the recent focus on perioperative multimodal analgesia, in addition to growing data demonstrating safety and efficacy in this patient population. Multiple studies by the Pediatric Regional Anesthesia Network (PRAN) and the French-Language Society of Pediatric Anesthesiologists (ADARPEF) have demonstrated lack of major complications and general overall safety with pediatric nerve blocks. The growing prevalence of ultrasound-guided regional anesthesia has not only improved the safety profile, but also increased the efficacy of both peripheral nerve blocks and perineural catheters.

SUMMARY

As the push for multimodal analgesia increases and the breadth of pediatric regional anesthesia continues to expand, further large prospective studies will be needed to demonstrate continued efficacy and overall safety.

Recent trends in paediatric regional anaesthesia

Paediatric regional anaesthesia today is one of the fastest growing and exciting aspects of paediatric anaesthesia, which requires an ongoing fervour to learn. Application of paediatric regional anaesthesia in neonates, infants, toddlers and children is undertaken to treat perioperative pain without disturbing the physiological milieu with additional advantages elaborated in the review. The available choices, traditional methods and the most recently described methods are discussed with emphasis on their advantages and disadvantages. Clear pointers for selection of the blocks are also discussed. To present a holistic overview of this rapidly growing subject, a comprehensive literature search was performed in May 2019 in MEDLINE, PubMed and Google Scholar to retrieve articles pertaining to all the above topics. The keywords used in various combinations included 'Central neuraxial, blocks, Paediatric(s)', 'Peripheral Nerve blocks', 'Safety, controversies, regional, anaesthesia'.

A primer on nerve agents: what the emergency responder, anesthesiologist, and intensivist needs to know

PURPOSE

The purpose of this review article is to familiarize first responders, anesthesiologists, and intensivists with the medical management of patients exposed to nerve agents.

SOURCE

This review is based on the current medical literature available to the general medical community.

PRINCIPAL FINDINGS

Nerve agents are some of the deadliest substances known to humanity. Though they kill primarily via muscle paralysis, which leads to respiratory arrest, these agents affect virtually every organ system in the body. Their primary mechanism of action is the body-wide inhibition of cholinesterases. This inhibition leads to the accumulation of acetylcholine, stimulating both nicotinic and muscarinic receptors. After decontamination, the primary treatment is with atropine to control muscarinic symptoms and with oximes to reactivate the cholinesterases and treat the nicotinic symptoms. Atropine doses can be much higher than conventionally used. Seizures are generally best treated with benzodiazepines. Patients with substantial exposure may require ventilatory and intensive care unit support for prolonged periods of time.

CONCLUSION

While it is unlikely that most medical practitioners will ever encounter nerve agent poisoning, it is critical to be aware of the presenting symptoms and how best to treat patients exposed to these deadly agents. History has shown that rapid medical treatment can easily mean the difference between life and death for a patient in this situation.

Flip-Flop Phenomenon in Epidural Sufentanil Pharmacokinetics: A Population Study in Children and Infants

The aims of this study were to develop a population pharmacokinetic model of sufentanil coadministered with 0.2% ropivacaine as an epidural infusion in infants and describe the sufentanil absorption profile from epidural space. Data from 2 previously published studies were merged for analysis-20 infants aged 3-36 months receiving sufentanil as an epidural infusion and 41 children 0-17 years old receiving sufentanil as a long-term intravenous infusion. A population nonlinear mixed-effects model was built in NONMEM. Sufentanil pharmacokinetics were described by a 2-compartment model with first-order absorption. The effect of body size on all volume and clearance parameters was included in the model according to allometric scaling with theoretical exponents. The maturation process of metabolic clearance was described by the Hill model. During the model-building process the population was divided into 2 fractions with different typical values of metabolic clearance (CL1 and CL2). The typical values of systemic clearance scaled to a 70-kg patient for the 2 subpopulations were CL1 = 52.6 L/h and CL2 = 158 L/h. The parameters of the Hill function were 54.9 weeks for the postmenstrual age of 50% clearance maturation and 0.802 for the Hill coefficient. The typical values of distribution clearance and volumes of the central and peripheral compartments for a patient with a weight of 70 kg were Q = 40.5 L/h, VC = 7.63 L, and VT = 473 L, respectively. The value of the absorption rate constant from the epidural space was 0.0459/h, which suggests flip-flop pharmacokinetics of sufentanil after epidural administration.

Pharmacokinetics of 400 mg ropivacaine after periarticular local infiltration analgesia for total knee arthroplasty

BACKGROUND

Although considered safe, no pharmacokinetic data of high dose, high volume local infiltration analgesia (LIA) with ropivacaine without the use of a surgical drain or intra-articular catheter have been described. The purpose of this study is to describe the maximum total and unbound ropivacaine concentrations (C_max , C_{u max} ) and corresponding maximum times (T_max , T_{u max} ) of a single-shot ropivacaine (200 ml 0.2%) and 0.75 mg epinephrine (1000 μg/ml) when used for LIA in patients for total knee arthroplasty.

METHODS

In this prospective cohort study, 20 patients were treated with LIA of the knee for primary total knee arthroplasty. Plasma samples were taken at 20, 40, 60, 90, 120, 240, 360 min and at 24 h after tourniquet release, in which total and unbound ropivacaine concentrations were determined.

RESULTS

Results are given as median [IQR]. Highest ropivacaine concentration (C_max ) was 1.06 μg/ml [0.34]; highest unbound ropivacaine concentration (C_{u max} ) was 0.09 μg/ml [0.05]. The corresponding time to reach the maximum concentration for total ropivacaine was 312 min [120] after tourniquet release, and for the unbound fraction 265 [110] min after tourniquet release.

CONCLUSION

Although great inter-individual variability was found between the maximum ropivacaine concentrations, both maximum total and unbound serum concentrations of ropivacaine remained well below the assumed systemic toxic thresholds of 4.3 and 0.56 μg/ml.

Adjuvants in pediatric regional anesthesia

SUMMARY Local anesthetics have a limited duration of action. Adjuvants are used to prolong the duration of action and to augment analgesia allowing lower concentrations of local anesthetic to be used. Adjuvants have been used more extensively with neuraxial blocks, particularly caudal epidural blocks, but more recently to supplement peripheral nerve blocks. Intrathecal adjuvants are not covered in this review since spinal anesthesia is not widely used in children except in ex-premature infants. Morphine is the historical gold-standard with which other adjuvants are compared. Clonidine is most useful and is becoming increasingly popular, while the side-effect profile of other agents reduces their utility. Concerns with regard to the neurotoxicity of ketamine in animal models has led to its withdrawal in some countries.

Applications of regional anaesthesia in paediatrics

Advances in the field of paediatric regional anaesthesia have specific applications to both acute and chronic pain management. This review summarizes data regarding the safety of paediatric regional anaesthetic techniques. Current guidelines are provided for performing paediatric regional techniques, with a focus on applications for postoperative pain management. Brief descriptions of relevant anatomy followed by indications for commonly performed blocks are highlighted along with the potential of adverse side-effects.

The pain-free ward: myth or reality

Over the last 25 years, pediatric care has changed dramatically with increased survival after premature birth, more complex care, better outcomes, and reduced mortality. There is a better understanding of how pain pathways and receptor systems develop and also how to assess pain at different stages of development. The myth that children do not feel pain has been comprehensively dispelled. Safe analgesic dose regimens for neonates, infants, and children have been developed based upon a better understanding of developmental pharmacokinetics and pharmacodynamics. It is a myth that pain in children cannot be prevented or treated safely and effectively because of the risks of adverse effects and addiction. Large-scale prospective audits have clarified the safety profile and risk-benefit balance for different techniques. There is now a substantial evidence base supporting many techniques of postoperative and procedural pain management for all age-groups of children. Guidelines based upon systematic review of this evidence have been published and updated, but the real challenge is in implementation of accurate pain assessment and safe, effective pain management comprehensively to all children whatever the procedure, clinical setting, developmental stage of the child, or comorbidities. In developed countries, these are core topics in the education of all doctors and nurses who care for children, and they are integrated into clinical practice by acute pediatric pain teams for most hospitals. However, it is disappointing that many country's healthcare systems do not give pediatric pain management a priority and in many parts of the world there are no analgesics available. So pain-free healthcare is sadly lacking in many hospitals. My hope is that the current knowledge can be used more effectively to relieve the unnecessary suffering of children in the 21st century.