Infants and children have a larger volume of distribution, smaller proportion of muscle and fat stores, altered protein binding, and immature renal and hepatic function.

Therefore, most medications will have altered pharmacokinetic properties as compared to adults. Any clinician caring for patients in this population must be aware of the age-related alterations in drug absorption, distribution, and elimination since these result in an increased risk of drug overdose and toxicity [1].

Neonates have increased brain permeability due to an immature blood–brain barrier as compared to adolescents and adults making them more sensitive to sedatives, hypnotics, and narcotics. In addition, incomplete myelination in infants may allow for drugs that are insoluble to cross the blood–brain barrier to cross at a greater rate [7].

Administration and absorption of various medications may be altered based on mode of delivery. Intravenous is often the best route of delivery. However, the limiting factor is often the ability to place an IV in this population. Intramuscular injection of medication is affected by variations in blood flow to the muscle. Compared to adults, neonates have a lower muscle mass which could lead to decreased absorption [8]. Topical administration is affected by skin thickness, which is similar in both neonates and adults; however, neonates have a much larger body surface area to body weight ratio, which could lead to a much greater amount of drug absorption [9]. Oral delivery is affected by a variety of factors such as gastric pH (initially alkaline, especially in premature infants), gastrointestinal enzyme activity, volume of gastric juices, gastric emptying rate, and intestinal surface area. Given these factors, it is thought that the rate of drug absorption is slower in neonates [4].

Metabolism of drugs dependent on the liver will be decreased in the neonate due to decreased activity of phase I and phase II liver enzymes [10, 11]. In addition, drug metabolism is affected by hepatic blood flow which changes with obliteration of umbilical blood supply as well as closure of the ductus arteriosus [12].

Renal function in preterm and term infants is also less efficient than in adults. Glomerular filtration and tubular function rapidly develops during the first few months of life, and is nearly mature by 20 weeks, and fully mature at two years. Drugs excreted through the kidney will have prolonged pharmacologic levels if kidney function contributes to their elimination [7].

The minimum alveolar concentration (MAC) of an inhalation anesthetic in pediatric patients varies with age. One MAC represents the percent or concentration of an inhaled anesthetic at 1 atm that renders 50 % of patients unresponsive to a surgical stimulus.

Studies have found that infants have a higher MAC than that noted in older children or adults for reasons not clearly understood. Sevoflurane is an inhalational anesthetic that offers an advantage for rapid induction and rapid awakening due to its lower blood solubility, particularly useful in the pediatric population, as it has a less pungent smell than other inhalational agents. In children with congenital cardiac disease, fewer hemodynamic changes have been noted when compared with isoflurane, and it has a greater effect on respiratory depression by decreasing minute ventilation and respiratory frequency as compared with halothane.

Isoflurane has a more pungent odor and does not allow its use for mask induction. This inhalational agent is noted to have less myocardial depression, preservation of the heart rate, and a greater reduction in the cerebral metabolic rate for oxygen.

Desflurane, also pungent in nature, has made it difficult to use it for induction of anesthesia. It has been found to cause an incidence of laryngospasm of 50 % during the gaseous induction of anesthesia in children [13].

Nitrous oxide is a colorless, odorless gas that possesses both analgesic and anxiolytic effects. The drug must be delivered with oxygen to avoid a hypoxic gas mixture and is often used to supplement other inhalation agents. It has low blood–gas partition coefficient resulting in rapid induction and awakening. Although its low potency does not allow for it to be used as a sole anesthetic, it is an extremely useful agent. It is not a trigger for malignant hyperthermia. It increases uptake of sevoflurane on induction via the second gas effect and it also allows easier mask induction due to its neutral odor.

The “steal” induction technique allows the patient to breathe the odorless gas allowing for relaxation while the more pungent inhalant – sevoflurane – is titrated up [14].

Relevant to inhalational anesthetics, as well as other IV anesthetic agents, is emergence delirium, a dissociated state of consciousness in which a child is inconsolable, irritable, uncompromising, or uncooperative with psychomotor agitation in the immediate postoperative period. The incidence of emergence delirium is 12–13 % in children. The incidence of emergence delirium following halothane, isoflurane, sevoflurane, or desflurane ranges from 2 to 55 % [15].

Propofol is a sedative-hypnotic anesthetic agent useful in the induction and maintenance of anesthesia. It is a lipid macroemulsion with egg yolk and soybean oil components. This highly lipophilic drug is painful upon IV injection. It is rapidly distributed into vessel-rich organs accounting for its quick onset, while termination is due to rapid redistribution and hepatic and extrahepatic (kidney and lung) clearance. The dose of propofol required for loss of the eyelash reflex generally increases with decreasing age. Propofol induction dose is 3–4 mg/kg for children younger than 2 years to 2.5–3 mg/kg for older children. Maintenance of general anesthesia requires 200–300 μg/kg/min [16, 17].