Patient age affects the approach to induction, need for preanesthetic medication, and anesthetic risk. Children less than 1 year of age have an increased risk of complications, especially children in the first 2 months of life [20]. If possible, procedures that are entirely elective should be postponed until after 6 months of age. The weight of the child affects the dose of medications administered and reflects the child’s general state of health. Significant medical problems often result in growth failure. A determination of BMI and ideal body weight are essential for dosing in overweight/obese patients. Heart rate, blood pressure, and temperature should be determined prior to induction of anesthesia. Pulse oximetry (SpO2) is measured prior to transfer to the operating room in order to rule out unanticipated lower respiratory tract system or cardiac pathology.

The examination of the airway focuses on mask fit, mouth opening, neck mobility, tongue size, thyromental distance, and mandibular size. Patients who are less than a year old, weigh less than 10 kg, have short thyromental distance, and have preexisting airway or craniofacial abnormalities are at risk for difficult intubation [21–24]. Examination of mouth opening in the uncooperative infant may be facilitated by removing and inserting a pacifier and observing the extent of opening. The modified Mallampati grading system for mouth opening divides patients into four groups: Class 1: the soft palate, uvula, fauces, and pillars can all be visualized; Class 2: the soft palate, uvula, and fauces are visible; Class 3: the soft palate and base of uvula are visible; and Class 4: only the hard palate is visible [25, 26]. If the Mallampati score can be obtained, higher incidences of difficult laryngoscopy are seen in patients with Mallampati scores 3 and 4 [23].

Protruding or loose teeth (especially in children aged 5–9 years) should be noted to assess whether in the former case they may interfere with laryngoscopy or whether in the latter case they should be removed to minimize pulmonary aspiration risk. Adequate neck mobility is important in the alignment of the oropharyngeal and tracheal axis for the best laryngoscopic view.

The chest examination should include observations on the symmetry of chest excursion, ease of respiratory effort, and auscultatory findings. Elective procedures should be postponed if rhonchi are heard, indicating active bronchitis or pneumonia. Mild to moderate wheezing may be treated with a bronchodilator in advance of induction to see if it improves and to prepare the airway for the stimulus of intubation. The cardiac examination should note the color of the extremities and the quality of peripheral pulses. Heart murmurs are most commonly innocent functional murmurs, but can be indicative of serious undiagnosed pathology. Functional murmurs are soft systolic murmurs that are best heard along the left sternal border, change with respiratory cycle and patient position, and have no diastolic component or clicks. If the child’s pediatrician has noted the murmur on previous examinations and believes it to be innocent, no additional workup is generally needed. Cardiology is consulted if the patient is symptomatic or if there is any doubt about murmur type.

Although anesthesia is generally considered very safe for healthy children, the preoperative meeting with the family should still include a discussion on the potential risks and complications of anesthesia. Some common adverse reactions to anesthesia include postoperative nausea and vomiting (6%) and sore throat. Less common complications include respiratory complications such as airway obstruction (1.1%), laryngospasm (1.7%), bronchospasm (0.2%), aspiration (0.04%), and allergic reactions (0.01–0.1%) [29–32]. Severe complications, such as cardiac arrests that are attributed to anesthesia, are rare (0.65–1.4:10,000 procedures) [33, 34]. The incidence of both respiratory complications and cardiac arrest are much higher in children under 1 year old and especially children under 1 month old.

Recent investigations have raised concern about the potential harm of anesthetic exposure to a developing child’s brain. Animal studies, including several in nonhuman primates, demonstrate that many general anesthetic agents used in human clinical practice can be neurotoxic to the developing brain. The issue was brought to scientific attention in 1999 when Ikonomidou et al. showed that blockade of N-methyl-D-aspartate (NMDA) glutamate receptors for only a few hours during late fetal or early neonatal life triggered widespread apoptotic neurodegeneration in the developing rat brain [35]. Early exposure to ethanol, which blocks NMDA glutamate receptors and activates gamma-aminobutyric acid (GABAA) receptors , results in similar pathology [36]. Neonatal rats exposed to a combination of midazolam (GABA-agonist), isoflurane (combined GABA-agonist and NMDA-antagonist), and nitrous oxide (NMDA-antagonist) maintained at a surgical depth of anesthesia experienced both immediate brain cell loss and impaired long-term neurocognitive function [37]. A variety of neurotoxic effects, including acute neuronal cell loss, altered dendritic architecture, reduced synaptic density, decreased levels of neurotrophic factors, mitochondrial degeneration, destabilization of the cytoskeleton, and cell cycle abnormalities, have been described following exposure to standard anesthetics and sedatives in a broad range of immature animal species [38].

Whether these findings translate to human risk remains unclear. There is no accepted unified mechanistic theory to explain the neurotoxic effects, and the pathologies themselves vary across animal species. Many of the animal studies utilize anesthetic agents in doses and durations that far exceed clinical equivalents for humans [39]. Furthermore, anesthetic management is less controlled in experimental neonatal animal models than in humans; the neonatal animal’s small size precludes continuous hemodynamic monitoring, assessment of acid-base status, and glucose levels, all of which normally dictate changes in anesthetic management of a human neonate [38]. Unrecognized hypotension, hypercarbia, metabolic acidosis, and hypoglycemia associated with anesthesia in a neonatal rodent could lead to pathology and neurologic deficits without direct biochemical neurotoxicity [38–42].

Several large retrospective human cohort studies evaluating behavioral and cognitive effects of anesthetic exposure in the developing brain have been completed. Researchers from the Mayo Clinic compared standardized aptitude test score in 5357 students, out of which 593 had general anesthesia before age 4 with their unexposed peers. In a follow-up study, 350 children who were exposed to anesthesia before age 2 were matched to 700 unexposed controls. Both studies showed there were no differences in test scores between children who were unexposed and children who had had a single anesthetic exposure. However, in both studies, children who had multiple anesthetic exposures did incrementally worse than their peers who received none [43, 44]. A study consisting of 2689 Danish children who had surgery in infancy were age-matched to a control group of 14,575 children who did not. Academic tests scores at ninth grade showed no differences between these groups [45]. Using the Western Australian Pregnancy Cohort Study data, consisting of 2608 children with 321 of them exposed to anesthesia before 3 years old, Ing et al. found some associations between anesthetic exposure and language, cognitive function, motor skills, and behavior outcomes at age 10 y [46]. However, the results were neither consistent within nor across modalities: one language test, the Clinical Evaluation of Language Fundamentals, showed clear differences in receptive language ability, whereas no differences were seen in the Peabody Picture Vocabulary assessment and no differences in visual tracking and attention (Symbol Digit Modality Test), fine and gross motor function (McCarron Assessment of Neuromuscular Development), or behavior (Child Behavior Checklist) related to exposure status.

Although the results of these retrospective cohort studies have not been conclusive, in aggregate they suggest that a brief, single anesthetic exposure is not associated with future learning disability and/or lower test scores. For outcome differences that are suggested in these nonrandomized studies, the child’s underlying pathology or surgery itself may confound effects otherwise attributable to anesthesia [38].

Researchers conducting the large multinational prospective trial, General Anesthesia versus Spinal (GAS Study), sought to more definitively answer the neurotoxicity question. The study design minimized the confounding effects of surgery by comparing only infants who had a single surgery – inguinal hernia repair. Subjects were randomized to general or regional anesthesia, the latter generally acknowledged being non-neurotoxic. Cognitive development at 2 y of age using the Bayley Scales of Infant Development III test were no different between the two groups when <1 hr of sevoflurane anesthesia was administered [47]. A 5-year follow-up intelligence test is planned.

Although these results were reassuring, there are still many important concerns and questions that cannot be answered by the GAS study. Brain function is very complex and cannot be fully measured with a single cognitive test. How does exposure to anesthetics affect the development of other functions such as memory, language, motor skills, and emotional development? Do these effects change when multiple anesthetic drugs are combined? Are the results the same for procedures other than hernia repair? Animal and epidemiological data suggest that the risk of anesthetics to the developing brain increases with longer duration exposure or multiple exposures. Is this true for children? Further research will be required to address these questions [48].

At present, however, healthcare providers may best be advised to follow and share the consensus statement released by SmartTots.​org, a partnership between the US Food and Drug Administration (FDA) and the International Anesthesia Research Society (IARS), which states the following [48, 49]:

…It is not yet possible to know whether anesthetic drugs are safe for children in a single short duration procedure…Concerns regarding the unknown risk of anesthetic exposure to the child’s brain development must be weighed against the potential harm associated with cancelling or delaying a needed procedure. Each child must be evaluated individually based on age, the type of procedure, level of urgency, and other health factors…

Clear liquids, including water, oral electrolyte solution (Pedialyte®), juices without pulp, carbohydrate drinks, and coffee or tea without milk, move rapidly out of the stomach; the 50% emptying time is 12 min [50]. Two hours after a clear liquid drink, most individuals’ gastric volume will be similar to someone who had completed an overnight fast [51–54]. Therefore, most pediatric anesthesiologists allow healthy children to drink clear liquids up to 2 hr prior to induction, which appear to be safe and has other benefits [55]. Children are less irritable, less thirsty and hungry, and tolerate the preoperative wait better if they are allowed to drink. They are also less likely to be hypoglycemic.

A minimum of a 4-hr fast is advisable after breast milk and 6 hr after nonhuman milk or infant formula [56–59]. Healthy infants <6 mo of age may be eligible for formula fasts relaxed to 4 hr [60]. Scheduling surgery early in the day helps minimize the waiting period and avoids some of the feeding problems for young infants.

Solid meals have linear gastric emptying patterns with the mean half-time of emptying of approximately 5 hr for a filling meal [55]. Based on current evidence, it is recommended to fast for 6 hr after a light meal and 8 hr after a full meal [61]. Chewing gum is considered equivalent to drinking clear liquids, as it generates saliva and stimulates gastric secretion. However, swallowing chewing gum would be considered as solid intake and delay the procedure for 6 hr [62].

Patient compliance is a potential problem for children, regardless of preoperative instructions. Explicit written instruction for patients and their families helps avoid feeding policy violations, and these instructions should be reinforced during preoperative visits or phone calls. On the day of surgery, the anesthesiologist should also verify the patient’s PO intake status.

Inhalation and intravenous induction are the most common techniques for the induction of general anesthesia. An inhalational induction is often chosen for fasted healthy children without preexisting intravenous lines. However, if a child requires an emergency procedure under general anesthesia and is not appropriately fasted, a rapid sequence intravenous induction is usually indicated. Children with complicated medical conditions such as a known or suspected difficult airway, cardiac disease, and severe gastroesophageal reflux require special induction strategies.

Basic monitoring for pediatric patients consists of pulse oximetry, electrocardiography, automated noninvasive blood pressure cuff, capnography, temperature monitoring, and agent-specific gas analysis. For brief procedures, such as nasolacrimal duct probing, an intravenous catheter may not be essential, but it may be beneficial for administration of intravenous fluids and medications to reduce the risk of nausea and vomiting, and management of pain and postoperative agitation.

Infants and children can rapidly cool in the operating room environment. The room temperature during induction and emergence should be appropriately warm; young infants should be kept warm with an underbody and overhead warmer. A warm blanket helps diminish heat loss during the procedure, as does a heat moisture exchanger in the anesthesia circuit [108]. For longer cases, the addition of a forced warm air blanket that covers or surrounds the child helps minimize the risks of either hypothermia or hyperthermia.

General anesthesia can be maintained either via face mask, laryngeal mask airway (LMA), or tracheal tube. The type of procedure, experience of the anesthesiologist, and age and comorbidities of the patient will determine the choice of appropriate airway.