hepatic, renal, and respiratory systems in the child mean that large differences in drug effects, drug metabolism, and cardiac and respiratory compensations exist. Some of these differences are predictable, whereas others are not. In general, the interpatient variability in the pediatric patient can be far greater than that in an adult, necessitating more caution in the provision of anesthesia and complicating the titration of common anesthetic drugs.
Since children are smaller and weigh less than adults, the total doses of anesthetic drugs that may be safely given will be less. Due to the immaturity of the hepatic liver enzymes at birth, infants do not metabolize drugs as effectively as adults, and the clearance of many drugs can be prolonged significantly, with most individuals attaining full liver microsomal function at about one year of age [16]. Other physiological systems take longer to reach maturity, particularly the cardiovascular and respiratory systems.
The pediatric airway is characterized by a more cephalad position of the larynx, a thicker epiglottis, and angulation of the true vocal folds, which can make direct visualization more challenging (see Figure 1.1) [20]. In addition, the narrowest part of the pediatric airway occurs at the level of the cricoid cartilages just below the vocal folds; in contrast, the narrowest portion of the adult airway is typically the glottis itself. The chest wall and upper airway of the infant and young child are more compliant such that collapse of the airway occurs more easily and leads to airway obstruction [20]. Not only are children more prone to airway obstruction, but their increased oxygen and metabolic demand makes them more sensitive to hypoxia. Respiratory arrest can quickly lead to cardiac arrest if not promptly addressed.
Fig. 1.1. Compared to an adult airway, the pediatric airway demonstrates more cephalad position of the vocal folds, a wider and angled epiglottis, a relatively larger tongue and lymphoid tissue (including lingual tonsil), and a narrower funnel‐shaped cricoid cartilage.
The pediatric cardiovascular system is different from that of adults as well. In children, cardiac output is maintained primarily through heart rate rather than systemic vascular resistance. A sudden or sustained decrease in heart rate can precipitate a severe drop in blood pressure and cardiac output in a child due to the relative lack of compensation via increase in peripheral vascular resistance. In practice, this means that most cardiac arrests in children are preceded by bradycardia.
Children also have an increased body surface area relative to their mass and are more susceptible than adults to hypothermia and insensible fluid losses. They may be more prone to hypoglycemia and dehydration and less able to tolerate prolonged preoperative fasting.
Children are frequently less able to communicate effectively, less cooperative, and more prone to anxiety and emotional outbursts. The increased emotional lability of some children can make these patients challenging to manage preoperatively and can complicate and prolong the postoperative recovery period. The age and anticipated level of cooperation of a given child patient often dictate the anesthetic plan, with pediatric patients sometimes requiring oral premedication prior to the planned procedure.
The range of complications that can occur in pediatric patients during ambulatory anesthesia is the same as for adults, though not all complications occur with similar frequency. In children, respiratory complications are among the most frequently reported serious adverse effects. The overall rate of adverse events is higher in children than in adults, ranging from 1.45% to as high as 6% in different studies [15, 23, 24].
Pediatric Respiratory Complications
Respiratory complications in the pediatric population are the most frequently observed adverse event and are typically mild in nature, responding well to supplemental oxygen or head repositioning. The most common complication in children is respiratory depression and oxygen desaturation and ranges from less than 1–11% of subjects, depending on the study [24]. More frequent respiratory depression and desaturation are observed with combinations of IV medications, particularly combinations of narcotics and benzodiazepines or narcotics and propofol [24]. In a recently published report from the Pediatric Sedation Research Consortium on the use of propofol sedation/anesthesia for outpatient procedures, the number of respiratory complications outnumbered other complications significantly and included the following specific events in decreasing order of frequency: desaturation less than 90% for greater than 30 seconds; airway obstruction; cough; excessive secretions; apnea; and laryngospasm [23]. The authors of the study identified 1 in 65 anesthetics as being complicated by adverse respiratory events, and 1 in 70 anesthetics required airway interventions, including placement of an oral or nasal airway, positive pressure ventilation, or endotracheal intubation [23]. A study by Kakavouli et al. reports an overall incidence rate of intraoperative respiratory complications of 1.9% with laryngospasm and bronchospasm identified as the most common adverse events [22]. Two separate studies on perioperative cardiac arrest in children list respiratory events [7] and airway‐related causes [2] as the main causes of cardiac arrest attributable to anesthesia. Cravero et al. report two cases of cardiac arrest in children, one of which occurred secondary to laryngospasm and profound hypoxia, and the second that resulted after an apneic episode and bradycardia [23]. These cases underscore the fact that cardiac arrest in children is frequently preceded by respiratory arrest, whereas adults more frequently experience cardiac arrest secondary to MI or arrhythmia.
Pediatric Cardiovascular Complications
Children typically do not suffer from systemic hypertension, coronary artery disease, or congestive heart failure as in adult patients. Though there is always the possibility of undiagnosed congenital heart disease, most children who present for ambulatory anesthesia will be free of cardiac disease. Notwithstanding this, cardiac complications do occur in the pediatric population though at a much lower rate. In the study by Kakavouli et al., cardiac complications accounted for 8.6% of all observed complications [22]. Cravero et al. reported a rate of cardiac complications (defined as a change of more than 30% in heart rate, blood pressure, or respiratory rate) of 60.8 events per 10 000 anesthetic cases [23]. Cardiac arrest, though rare, does occur in children who undergo anesthesia and has a reported incidence rate of between 4.95 per 10 000 [2] and 22.9 per 10 000 [7]. The majority of anesthetic‐related cardiac arrests are cardiac, mainly due to hypovolemia from surgical blood loss. Respiratory compromise leading to cardiac arrest is the second most common, the majority of which arise from respiratory obstruction such as from laryngospasm. Medication‐related cardiac arrest is third most common, and has become significantly less common as sevoflurane has replaced halothane [25].
Other Pediatric Complications
In many other regards, the anesthetic complications that may occur in children are similar to those that occur in adults. The rate of aspiration (between 1 and 4 per 10 000 cases) is similar in adults and children as is the rate of PONV, though children may experience more emesis with certain medications such as ketamine. Children may experience a paradoxical reaction and become stimulated or excited when given certain sedative‐hypnotic drugs. In addition, children may be more prone to agitation, delirium, or hallucinations upon emerging from anesthesia. Research studies have estimated the incidence of post‐procedure agitation, nightmares, and/or behavioral problems in children given ketamine to be between 4% and 17% [24]. Ketamine is also associated with higher rates of PONV (6–12%) [24]. The combination of midazolam and ketamine appears to reduce the incidence of emesis but not the incidence of postoperative agitation [24]. Allergic reactions, including anaphylaxis, are rare but have been associated with midazolam, ketamine, methohexital, and morphine. Of these, the majority are related to methohexital. Allergy to propofol has been reported; however, most severe cases also included treatment with other anesthetic drugs. The association of propofol allergy with egg, soy, and peanut allergy has been disproven [26].
PREVENTION