Anesthesia and Pain Management

Fasting Prior to Anesthesia and Surgery

Pulmonary aspiration of gastric contents has long been recognized as a cause of morbidity and mortality in patients of all ages undergoing anesthesia and surgery. The incidence of this complication in pediatric anesthesia is reported as 0.02% in one series (Tan and Lee 2016). Of the various preventative measures that have been advocated to reduce the incidence of this complication, the preoperative fast has long since achieved universal acceptance with the result that patients are required to abstain from food and drink prior to induction of anesthesia. Excessive fasting leads to dehydration and hypoglycemia, however, and may accentuate the risk of hypotension at induction of anesthesia. Furthermore, fasting leads to infants and children becoming hungry, thirsty, and fractious. Point-of-care ultrasound examination of the stomach may be useful in demonstrating residual gastric volumes (Van de Putte and Perlas 2014). Current recommendations for infants are a 2-h fast from clear fluids, 4 h for breast milk, and 6 h for formula milk, milk, and solids. Infants and children at particular risk of regurgitation, e.g., pyloric stenosis, intussusception, or perforated appendix, must fast from all oral or nasogastric intake for 6 h (Brady et al. 2005).

Breathing System

An appropriate anesthetic circuit for use in infants and children needs to be light, has minimal resistance and dead space, allows for warming and humidifying of inspired gases, and be adaptable to spontaneous, assisted, or controlled ventilation. The most widely used system is the circle system, which allows inspiration and expiration via a dual-limbed length of tubing. Connectors and tubes should also offer minimal flow resistance and dead space. Knowledge of the probable diameter and length of the endotracheal tube appropriate for any given infant is essential. The use of an endotracheal tube (ETT) of too large a diameter may result in tracheal wall damage, while excess length leads to endobronchial intubation. Cuffed ET tubes are now used as standard for managing the neonatal airway and ventilation of the lungs during major surgery (Spitzer and Sims 2016). Facemasks may be used for short surgeries but are limited in use by the neonatal propensity to develop apnea and the need for a tight seal on the face. Laryngeal mask airways (LMAs) are used widely in pediatric anesthesia but less in small infants due to their unreliability in maintaining an adequate and safe airway during surgery and due to their inherent inability to prevent aspiration of gastric contents (Bradley et al. 2013).

Laryngoscopes

Because of the anatomical differences in the infant airway, most anesthetists prefer to use a laryngoscope with a straight blade, lifting the epiglottis up directly to expose the vocal cords. Curved blades are also used, especially in bigger children. The video laryngoscope is increasingly employed in the management of pediatric airways, and it is anticipated that video laryngoscopy will become established as a key tool in achieving intubation efficiently and safely (Lingappan et al. 2015). There should be a “difficult airway trolley” available in every operating department (Calder et al. 2012).

Ventilators

Most children can be ventilated using standard adult ventilators provided the ventilator is of low internal compliance and equipped with pediatric breathing tubes. The ventilator should be capable of delivering small tidal volumes and rapid respiratory rates and have an adjustable inspiratory flow rate and inspiratory to expiratory ratio so that peak airway pressure is kept as low as possible. Pressure-controlled ventilation is frequently used to minimize the risk of pulmonary barotrauma. A suitable temperature-controlled humidifier should be incorporated in the inspiratory limb of the ventilator circuit. The ability to deliver air and oxygen mixtures through the ventilator or the anesthetic circuit should be available.

Monitoring

The clinical condition of the anesthetized infant can deteriorate more rapidly and with less warning than that of patients of an older age group. It follows that continuous and careful monitoring is required. The monitoring is employed and interpreted by a meticulous and experienced pediatric anesthetist. The incidence of perioperative pediatric cardiac arrest has been linked inversely to the training and experience of the anesthetist in a number of retrospective studies (Zgleszewski et al. 2016).

Cardiovascular Monitoring

Respiratory Monitoring

Temperature

Monitoring temperature is important in pediatrics because of the increased risk of both hypo- and hyperthermia. Common sites for perioperative temperature probes include the nasopharynx, esophagus, bladder, and rectum.

Neuromuscular Blockade

Monitoring neuromuscular blockade using a peripheral nerve stimulator is routine practice when non-depolarizing muscle relaxants have been administered.

Recovery

Following completion of surgery, the child is transported, fully monitored, to the recovery room. Intubated patients are nursed one to one by trained pediatric recovery nurses. Monitoring of vital signs, adequacy of protective airway reflexes, and correct positioning to prevent airway obstruction, regurgitation, and aspiration are key priorities. The recovery room nurse also monitors the wound site for bleeding, checks the security of the dressings, and administers prescribed pain relief. When infants and children are awake, they may be offered clear fluids or milk to drink. Comfort may be provided by breastfeeding in the recovery room. Exceptions to early feeding should be made following some dental or oral procedures, and when local anesthesia has been applied topically to the vocal cords. In addition to post-discharge instructions provided by the surgical team, parents or guardians need to be given verbal and written instructions regarding postoperative pain relief and what to do if problems arise.

Fluid Balance

Healthy children undergoing minor operations can reasonably be expected to tolerate oral fluids a short time after completion of surgery and do not require intraoperative intravenous fluids. The goal of intraoperative fluid management in those who are dehydrated preoperatively or those who are undergoing major surgery is to sustain homeostasis by providing the appropriate amount of parenteral fluid to maintain adequate intravascular volume, cardiac output, and ultimately, oxygen delivery to tissues at a time when normal physiologic functions are altered by surgical stress and anesthetic agents. The composition of the fluid will vary according to the maturity of the child and the preoperative electrolyte and glucose levels. All infants should have their blood sugar checked following induction of anesthesia and a bolus of 2 ml/kg 50% dextrose administered if the blood sugar is less than 2 mmol/L (R). Surgical stress, opiates, and anesthetic medications stimulate increased release of antidiuretic hormone (ADH), which causes the retention of free water at the renal glomerulus. This may lead to the development of hyponatremia if hypotonic solutions such as 0.45% normal saline are used as intraoperative maintenance fluid. Normal saline 0.9% or lactated Ringer’s solution is now used as standard, with the addition of 5–10% dextrose as necessary (Choong et al. 2006).

Pain Assessment

To optimize pain management in the surgical patient, treatment is titrated to their degree of discomfort. The American Academy of Pediatrics has issued the following statement on pain treatment: “To treat pain adequately, ongoing assessment of the presence and severity of the pain and the child’s response to the treatment is essential” (Chou et al. 2016). Self-report remains the “gold standard” for pain assessment. However, as newborns are nonverbal, they require a different method of assessing their pain, usually focusing on posture, cry, and consolability. As they are less able to communicate pain, they may be vulnerable to distress, anxiety, and poor pain management. Pain assessment can be incorporated into routine monitoring as a vital signs measurement so that pain assessment becomes standard practice. A range of validated pain assessment tools for nonverbal children is available (American Academy of Pediatrics Committee on Psychosocial Aspects of Child and Family Health and Task Force on Pain in Infants, Children, and Adolescents 2001). Postoperative pain experienced by the infant is assessed using a variety of validated pain assessment tools, including the FLACC, and the COMFORT-behavior scale (Crellin et al. 2015; Boerlage et al. 2015).

Early recognition is important as it facilitates prompt and adequate management. It may also prevent long-term sequelae (Taddio and Katz 2005). Stress hormone levels have been studied in premature neonates who underwent surgery without perioperative analgesia; levels of cortisol, aldosterone, and other corticosteroids were markedly increased indicating significant stress (Anand et al. 1990; Bouwmeester et al. 2001). In the recovery room and intensive care unit (ICU) setting, stress and agitation resulting from pain and anxiety can lead children to accidentally remove medical devices endangering the child’s safety.

Analgesia

After assessment of pain, the treatment of pain is the next step, and standard treatment is a balanced, multimodal combination, which frequently includes opioids. Treatment with opioids means balancing between effective dosages and preventing oversedation, seeing that opioids have sedative properties as well. Oversedation may lead to longer duration of mechanical ventilation and ICU admission. Inadequate dosages may cause a wide range of endocrine, metabolic, and inflammatory reactions leading to increased sympathetic activity. Besides inadequate pain relief, this may result in prolonged recovery times after procedures, complications, and longer admission duration. Finally, inadequately treated postoperative pain poses a risk for the development of chronic pain.

Current literature lacks systematic data on acute perioperative pain management in neonates and mainly focuses only on procedural pain management. The usual stress response to surgery through hormone release and metabolic modulation is altered in the newborn, which has implications for cardiovascular monitoring , support, and sedation and analgesia. Intravenous opioids such as morphine or fentanyl as either intermittent bolus or continuous infusion remain the most common modality for the treatment of perioperative pain. Intravenous infusions are administered using the nurse-controlled analgesia system, where small doses of opiate are given following pain assessment and sedation assessment (Czarnecki et al. 2014). Patient-controlled analgesia infusions may be used in older children. Continuous infusions are used only in a high dependency or intensive care environment. Paracetamol has a promising role in decreasing opioid requirement (Padda et al. 1997). Among infants undergoing major surgery, postoperative use of intermittent intravenous paracetamol compared with tramadol resulted in a better recovery profile (Uyasal et al. 2011). Routine use of ketorolac or other nonsteroidal anti-inflammatory drugs (NSAIDs) is not usually recommended in the newborn, but NSAIDs are frequently used to augment analgesia in older children with normal renal function.

The majority of preterm neonates are capable of glucuronidating morphine, but birth weight and gestational and postnatal age influence the glucuronidation capability. Term neonates, infants, and children are able to produce morphine glucuronides. Pharmacokinetic studies have demonstrated that drug half-life and clearance were found to be related to age, but volume of distribution was unchanged. Half-life was estimated to be 9.0 +/− 3.4 h in preterm neonates, 6.5 +/− 2.8 h in term neonates aged 0–57 days, and 2.0 +/− 1.8 h for infants and children aged 11 days to 15 years (Kearns et al. 2003). Longer half-lives mean smaller doses per kilogram are necessary to produce analgesic effects. The rate of morphine infusions need to be reduced in the neonatal and newborn period, particularly if the neonate is jaundiced. There is a large variability associated with infusion rates, which means that infusion rates may need to be adjusted, depending on feedback from pain scores, adjuvant medications, and adverse effects. If the child is feeding, oral morphine may be used instead of intravenous. Combining opiate administration with regular sedation and pain assessment and apnea and oxygen saturation monitoring is recommended.

Regional Anesthesia

With the advent of ultrasound and improvements in equipment, the applications of regional anesthesia in the pediatric population have continued to expand. Although frequently used for postoperative analgesia or as a means of avoiding general anesthesia in patients with comorbid conditions, the adjunctive use of regional anesthesia during general anesthesia may effectively decrease the intraoperative requirements for intravenous and volatile agents, thereby providing a more rapid awakening and earlier tracheal extubation and enhanced pain scores (Hamill et al. 2016). More recently, the limitation of the requirements for volatile and other anesthetic agents may be desirable, given concerns regarding the potential impact of these agents on neurocognitive outcome in neonates and infants (Johnson et al. 2008). Several authors have demonstrated the potential utility of combining a neuraxial technique (spinal or epidural anesthesia) with general anesthesia in neonates and infants undergoing intraabdominal procedures (Goeller et al. 2014; Adler et al. 2015).

Regional anesthesia techniques are often combined with light general anesthesia in infants and children. Regional blocks provide prolonged and predictable postoperative pain relief, using local anesthetics. These local anesthesia-based blocks avoid the side effects associated with opiates (e.g., respiratory depression, nausea, vomiting, ileus) and reduce the hormonal stress response to surgery (Abu Elvazed et al. 2016). The regional block usually produces a mixed sensory and motor blockade and may be suitable for use as the sole anesthesia mode, e.g., for inguinal herniotomy (Mueller et al. 2016). There is a greater potential for local anesthetic toxicity in infants as reduced protein binding with alpha(Smithers et al. 2016) acid-glycoprotein means a greater free fraction of the active drug in the bloodstream (Gunter 2002).

Monitoring and secure intravenous access must be in place before performing the local anesthetic block. The skin requires cleaning with 0.5% alcohol containing solution before commencing. Higher concentrations of alcohol in the cleaning solution may result in burns to the fragile neonatal skin or absorption of alcohol into the bloodstream (Sathiyamurthy et al. 2016). Nerves and nerve plexuses are frequently visualized using ultrasound, before specialized needles inject the local anesthetic, or introduce a catheter to administer medication over a longer period of time. The catheter is secured in position on the skin with adhesive tape. The other end of the catheter is attached to a filter to prevent entry of glass particles or bacteria. Dilute concentrations of levobupivacaine are infused continuously over a period of hours to days, depending on individual patient requirements. The rate of infusion of levobupivacaine should be reduced over a period of days to prevent accumulation and a rise in plasma levels (Lerman et al. 2003). Adjunct medications such as clonidine may be added to increase the effectiveness and duration of the regional block (Lak et al. 2012).

Subarachnoid anesthesia is utilized in awake babies for short surgeries on the lower abdomen or perineum, e.g., circumcision and orchidopexy, especially in ex-premature infants (Jones et al. 2015). Avoiding general anesthesia in ex-premature infants is preferable due to their higher incidence of chronic lung disease, oxygen dependency, and apnea. The risk of postoperative apnea with regional anesthesia is decreased but not eliminated (Davidson et al. 2015b).

Esophageal Atresia

When the diagnosis of esophageal atresia is made (with or without a fistula to the trachea), the blind upper pouch should be continuously aspirated using a Replogle or similar tube. In general, the operation may be safely delayed pending further investigation – echocardiography is the most important – as there are frequently associated cardiac anomalies. Aspiration pneumonia should be treated, and surgery may then proceed when the infant is in good condition. Pre-thoracotomy fiber-optic bronchoscopy is ideal, as it assists in identifying the location of a fistula, if there is one, or indeed multiple fistulae (Atzori et al. 2006). Anesthesia is similar to that for other neonatal procedures, but special care must be taken to maintain spontaneous respiration until the endotracheal tip is placed below the level of any fistula. This prevents gastric distension, which may induce bradycardia. The fiberscope is useful in accurately positioning the ETT tip above the carina, but below any anomalous openings to the trachea. Surgical retraction during operative mobilization of the esophagus may compromise either respiratory or cardiac function, so that accurate monitoring is essential. Extubation may be planned shortly after completion of surgery if there has been no contamination of the mediastinum or if the anastomosis is not especially tight. A pleural drain is usually left in place until a contrast study has been performed a number of days later (Kinottenbelt and Skinner 2010). Regional anesthesia using an epidural or paravertebral catheter may assist in early weaning from mechanical ventilation and extubation (Bosenberg et al. 1992).

Congenital Diaphragmatic Hernia

The surgical repair of this condition is now planned for 5–10 days postdelivery, to allow adequate time to optimize the pulmonary pressures. Pulmonary hypertension related to lung hypoplasia and vasculopathy of the lungs, in addition to the normal relative pulmonary hypertension of the early neonatal period, may be challenging to manage. Sustained significant pulmonary hypertension causes dilatation and failure of the right ventricle, with resultant impairment of left ventricular function. If not aggressively managed with pulmonary vasodilators, this may lead to hypotension, renal impairment, and gut hypoperfusion. Preoperative admission to the PICU, ventilation, and hemodynamic support are required for all but the most minor defects. Inhaled nitric oxide, high frequency oscillation, intravenous sildenafil, and extracorporeal life support (ECLS) may be required to support the infant. Surgical repair may be performed on ECLS, but bleeding may be problematic as the infant is fully anticoagulated. Prior to intubation, positive pressure ventilation should be avoided to prevent expansion of the viscera contained within the hernia. Surfactant should not be administered as it may cause overdistension of the “good” lung, predisposing the infant to developing a pneumothorax. Anesthesia is conducted with the support of nitric oxide and inotropes, muscle relaxation, and fentanyl 2–5 mcg/kg. Volatile anesthetic agents are used cautiously. After surgery, the infant returns to the PICU for postoperative care.

Intestinal Obstruction

The various forms of neonatal intestinal obstruction account for approximately 35% of all surgical procedures in the newborn. The major anesthetic problems are those of fluid and electrolyte imbalance (which must be corrected preoperatively), abdominal distension (causing respiratory impairment by splinting diaphragmatic movement), and the risk of regurgitation and aspiration of gastric contents. Following four-quadrant decompression of the stomach, a modified rapid sequence incorporating a small dose of an intravenous induction agent and a muscle relaxant is performed. The lungs may be ventilated using low pressures (<10cmH2O) until the trachea is intubated. Many pediatric anesthetists do not use cricoid pressure in this context, as it may make intubation more difficult, leading to a need to mask ventilate at higher pressures, for longer, than if the ETT is placed in the trachea without undue delay. Anesthesia is then maintained in the usual fashion. Placement of paravertebral or rectus sheath blocks may facilitate a reduction in opiate needed for postoperative pain relief (Bosenberg 1998).

Exomphalos and Gastroschisis

Anesthetic concerns with large abdominal wall defects include heat and fluid loss from the exposed bowel, and the primary closure of the defect, which may impair respiration as the diaphragm, is pushed cephalad. Special care must be taken to keep heat loss to a minimum. Fluid requirements are much greater than in normal neonates, and there is an increased need for electrolyte replacement. Monitoring the changes in peak inspiratory pressures and central venous pressure during primary closure can be useful in advising the surgeon whether primary closure is feasible. A proportion of infants, especially after repair of gastroschisis, require postoperative mechanical ventilation. Large defects may be managed in a staged manner, by placing the external gut into a silo, which hangs above the patient’s abdomen. Gravity assists in the gradual return of the gut to the abdomen. Establishing enteral feed may be slow due to ongoing gut dysmotility, which may persist for a considerable length of time after closure.

Herniotomy for the ex-Premature Infant

Improved survival rates in premature and low birth-weight infants have led to increased numbers of them presenting for inguinal hernia repair. While the surgical procedure may be relatively straightforward, these babies represent a considerable challenge for the anesthetist. They must be managed by anesthetists and surgeons with adequate training and experience, in hospitals with appropriate facilities and personnel. Ex-premature infants up to 56 weeks postconceptual age are at risk of life-threatening apnea after anesthesia and surgery and should have apnea and oxygen saturation monitoring for at least 12 h postoperatively. They are not suitable for day-case surgery. Regional anesthesia techniques such as spinal and caudal anesthesia may be used to augment or replace general anesthesia, but they do not completely remove the risk of postoperative apnea (Davidson et al. 2015b).