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Management of General Anesthesia
There are many features of the administration of general anesthesia that differ between children and adults. In this chapter, we discuss those differences, with an emphasis on anesthetic medications and ventilation strategies. We also review the importance of racial disparities in pediatric anesthesia, surgical site infection prophylaxis, and the possibility of neurotoxicity of anesthetics to the developing brain.
In the United States, most children that require general anesthesia undergo inhalational induction by face mask with intravenous (IV) catheter placement after loss of consciousness ( Fig. 19.1 ). Most hospitals have taken pride in their “ouch-less” environment, and thus, parents expect that their children will not undergo any painful injections while awake. This strategy is entirely optional, as some children prefer IV insertion while awake instead of the uncomfortable feeling of having a noxious mask over their face.
Infant mask induction. This beats adults any day!
Not all (healthy) children that are administered sevoflurane require IV access during general anesthesia. Two common examples are myringotomy for ear tube insertion and computed tomography (CT) scan, mainly because they are very brief procedures.
For difficult IV placement in anesthetized children, it has become standard practice to use ultrasound guidance. The use of ultrasound has higher first attempt success rates and greater overall success of cannulation than without ultrasound. The short axis out-of-plane technique together with dynamic needle position, where the needle tip is followed as the ultrasound probe is moved proximally, may further increase the success rate of peripheral IV placement in small children.
Sevoflurane
Sevoflurane is the anesthetic agent of choice for inhalational induction of general anesthesia in children because of its relatively low pungency and its lower blood-gas solubility coefficient (0.63) that speeds loss of consciousness.
The minimum alveolar concentration (MAC) of sevoflurane is 3.2% in neonates and infants up to 6 months of age; the MAC of sevoflurane peaks at 3 months of age. In school-aged children, MAC is 2.5%; the concentration that prevents 95% of children from moving in response to a surgical stimulus (ED95) is 2.9%. When 60% nitrous oxide (N 2 O) is added to sevoflurane, the MAC is lowered to 2.0%. Summary graphs of MAC according to age have been published.
Induction of general anesthesia with sevoflurane may be accomplished in several different ways. In some cases, the vaporizer is set to the maximal 8% setting from the start. Whether or not this is combined with N 2 O, most children will lose consciousness within 5 to 10 breaths.
Most children develop tachycardia during inhalational induction with sevoflurane. Twenty percent of children will develop a nodal rhythm and infants less than 6 months of age may demonstrate lengthening of the QT interval that continues into the postoperative period. These changes, however, do not result in adverse clinical manifestations. Sevoflurane may cause a dose-dependent bradycardia and hypotension in some children, especially those with trisomy 21; pretreatment with IV glycopyrrolate or oral/intramuscular (IM) atropine may be considered in this population.
During the early stages of sevoflurane induction, a peculiar type of agitation may be observed, mainly in teenagers. It consists of muscular rigidity and generalized tonic-clonic or myoclonic movements, and can worry some practitioners that it is the onset of malignant hyperthermia (it is not). It may be caused by electrical seizure activity , especially when concentrations exceed 4.5%. This effect is accentuated with hyperventilation, and is suppressed by N 2 O and opioids. These stimulatory effects of the central nervous system are not associated with postoperative sequelae.
Single-Breath Induction Technique
The single-breath induction technique ( ) will considerably speed the loss of consciousness in older, cooperative children. It is performed by priming the anesthesia circuit and ventilation bag with 70% N 2 O and 8% sevoflurane. The distal end of the breathing circuit is sealed off to prevent leakage of sevoflurane into the operating room (OR) environment. The child is instructed to first blow all the air out of their lungs (it is helpful to practice this technique with the child before entering the OR). At the very end of the child’s exhalation, the facemask is placed over the child’s mouth and nose, and the child is instructed to take “the biggest breath of their life.” This technique invariably results in loss of consciousness soon after the vital capacity breath.
Steal Induction
When a child is asleep upon entering the OR, a “steal” induction may be performed. The anesthesia breathing circuit is primed with N 2 O and sevoflurane in a similar fashion as that done for the single-breath technique. The child is not touched or moved to the OR table and no monitors are applied. The face mask is moved progressively closer to the child’s face without touching it. Once consciousness is lost, the child is moved to the OR table and monitors are applied. Proponents of this technique favor its atraumatic nature and the child’s lack of awareness of the OR environment. Opponents of this technique fear that a child could suffer psychological harm if they awaken from a painful procedure without adequate psychological preparation.
Nitrous Oxide
N 2 O can be used as an adjunct to inhalational induction because of its ability to reduce the MAC of inhaled agents and to speed the onset of unconsciousness via the second gas effect. It is discontinued when the IV catheter is inserted.
N 2 O has been associated with myoclonic movements and even generalized seizures in some unusual cases. Because N 2 O decreases the activity of two vitamin B 12 enzymes, methionine synthetase and thymidylate synthetase, its use has been implicated in the exacerbation of vitamin B 12 deficiency with development of neurologic symptoms in susceptible patients. Therefore, N 2 O should be avoided in children with vitamin B 12 deficiency or a known homozygous MTHFR (methylenetetrahydrofolate reductase gene) mutation. It has also been implicated in causing increased plasma homocysteine concentrations , the clinical significance of which is unknown.
Because N 2 O is equally as flammable as oxygen, it should not be used during procedures that carry risk for airway fire, such as a tonsillectomy (especially when using an uncuffed endotracheal tube, which you should not do anyway; see Chapter 22 ) or laser bronchoscopy, in which the oxygen concentration is lowered as much as possibly safe. Because of these above-mentioned drawbacks of N 2 O, its use has markedly decreased in lieu of using higher concentrations of sevoflurane. Also, N 2 O will diffuse into the endotracheal tube cuff and may cause tracheal edema from overly high cuff pressures if not monitored.
Propofol
IV induction of general anesthesia is reserved for children with established IV access, those with susceptibility to malignant hyperthermia, and those that require a rapid sequence induction (RSI) technique.
Propofol causes immediate loss of consciousness after administration of 3 to 6 mg/kg. Children require larger induction doses than adults because of a larger volume of distribution. Obese children, however, require less than normal-weight children of the same weight and therefore should receive propofol dosed at ideal bodyweight. Maintenance doses are also larger in children because of greater elimination and clearance. Propofol is particularly well suited for use in asthmatics because it blunts airway responses within its clinical dosing range. Propofol usually causes central apnea when administered as a bolus for induction of general anesthesia. If given in titrated doses, however, apnea can be avoided. The apneic dose of propofol is usually less than the dose required to prevent movement in response to a surgical stimulus. Administration of propofol may cause cardiovascular depression in hypovolemic children or those with a preexisting cardiomyopathy and should therefore be avoided or used with extreme caution.
Propofol injection can cause pain at the injection site. Although different methods have been studied to eliminate this pain, the most reliable method is to administer a small volume of 1% or 2% lidocaine while holding pressure proximal to the vein (i.e., a Bier block technique with your hand). Pressure is held for 5 to 10 seconds to assure that the wall of the vein is anesthetized after which the propofol is administered. This method effectively blunts the pain in most children.
During nonpainful medical procedures that require immobility (e.g., radiologic procedures) propofol can be used in moderate infusion doses (150–250 mcg/kg/min) that preserve spontaneous ventilation. For painful procedures (e.g., bone marrow biopsy, lumbar puncture, burn dressing changes) and surgical procedures that require a total intravenous anesthesia (TIVA) technique (e.g., rigid bronchoscopy, malignant hyperthermia-susceptible patient), greater doses of propofol are required to ensure immobility. These larger doses are inevitably associated with central or obstructive apnea. Alternatively, propofol can be combined with an opioid to decrease the total required propofol dose, but assisted ventilation will almost always be required.
Propofol is manufactured from the lipid components of egg and soy. Although these components may contain trace amounts of the residual protein, there have been no documented allergic reactions. Therefore, our policy has been to administer propofol to children with allergy to soy or egg protein, except in the case of documented anaphylaxis to egg or soy, where we practice more conservatively. Over the course of many years doing this, we are not aware of any allergic reactions.
Ketamine
In some cases, ketamine can be used instead of propofol as an induction and maintenance general anesthetic agent. At clinically useful doses (1–2 mg/kg IV), ketamine usually preserves spontaneous ventilation, upper airway patency, and normal cardiovascular function while providing analgesia and amnesia during painful procedures. Ketamine stimulates the sympathetic nervous system, which may cause undesirable increases in blood pressure, intracranial pressure, and intraocular pressure. However, it is useful for induction of anesthesia in patients in which cardiovascular stability is required, such as in the case of trauma or cardiomyopathy. Ketamine is associated with psychomimetic side effects (e.g., hallucinations, nightmares), increased airway secretions, postoperative nausea and vomiting, and delayed awakening. For these reasons, it has largely been replaced by propofol except for brief sedation for painful procedures and intramuscularly (2–4 mg/kg) as a sedative for uncooperative and/or developmentally delayed children.
Etomidate
Etomidate is mainly used in adults with cardiovascular disease and limited cardiovascular reserve. In these patients, it provides a stable induction with limited cardiovascular perturbation. Like ketamine, it may be useful in the traumatized child who is hypovolemic or in a child with a cardiomyopathy and decreased cardiovascular function. The dose range (0.2–0.3 mg/kg) and side effects (e.g., pain on injection, myoclonus, vomiting) appear to be similar to those in adults, including the risk for delayed adrenal suppression. Because of this risk for adrenal suppression, it is rarely used in pediatrics.
Opioids
Opioids are one component of a balanced anesthesia technique, contribute to postoperative analgesia, and attenuate or prevent postoperative emergence delirium or agitation. The choice of opioid depends on the nature and length of the surgical procedure and the expected duration and intensity of postoperative pain. For example, intranasal or intramuscular fentanyl (1–2 μg/kg) is often administered to children undergoing myringotomy and tube placement. IV fentanyl is administered for neurosurgical procedures because of the intense analgesia required for scalp incision and placement of skull tongs, and relatively fewer analgesic requirements during the procedure and postoperatively. Morphine or hydromorphone are administered for urologic and abdominal procedures because of the requirement for a relatively longer duration and intensity of postoperative analgesia.
Opioids are commonly included as a component of a TIVA technique for painful surgical procedures. Fentanyl and its congeners (e.g., alfentanil, sufentanil, and remifentanil) are ideally suited for use in TIVA because of their relatively low context sensitive half-time. Remifentanil possesses the most favorable profile as its termination of action is directly related to its metabolism by tissue and nonspecific plasma esterases. Its effects usually dissipate within 5 to 10 minutes of discontinuing the infusion, regardless of the duration of the infusion.
Remifentanil bolus and infusion doses are higher in infants and young children than in adults, reflecting the larger volume of distribution and increased elimination clearance, respectively. Typically, a bolus dose of 1 to 2 μg/kg will be administered over several minutes, followed by an infusion dose of 0.2 to 1 μg/kg/min. This infusion dose is then titrated up or down to achieve the desired analgesic and hemodynamic effects. The use of intraoperative remifentanil has been associated with development of tolerance and increased postoperative pain.
Historically, pediatric anesthesiologists have had concerns about the increased toxicity profile of opioids in the neonatal population because it is possible that opioids (especially the less lipid-soluble drug morphine) are allowed greater access through the blood-brain barrier in neonates and may result in proportionately greater levels in the brain. Furthermore, neonates have been shown to possess increased pharmacodynamic sensitivity, decreased clearance, and a relatively greater depression of CO 2 response curves to opioids compared with older subjects. These maturational changes appear to be most pronounced for morphine in comparison with fentanyl and its analogs. Opioids, like all types of medications administered to neonates, possess substantial interindividual variation in their pharmacokinetic and pharmacodynamic properties; thus, they should be titrated to effect while carefully observing for efficacy and side effects.
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