Induction of Anesthesia

The method of inducing anesthesia is determined by a number of factors: the medical condition of the patient, the surgical procedure, the level of anxiety of the child, the ability to cooperate and communicate (because of age, developmental delay, language barrier), the presence or absence of a full stomach, and other factors.^[238]

Infants

Mask induction is generally used in infants younger than 10 to 12 months because this age group readily separates from their parents. Induction by mask is accomplished most easily by holding the end of the anesthesia circuit in a cupped hand over the infant's face or with the mask held just off the surface of the face; the other hand can adjust the concentration of anesthetic. Allowing neonates and small infants to suck on a rubber nipple or a gloved finger generally prevents crying during induction. As the infant loses consciousness, the anesthesia mask is adjusted to improve delivery and decrease operating room pollution. This phase of induction is the most dangerous time because it is very easy to misjudge the depth of anesthesia and depress the heart. Once anesthesia has been induced, it is critical to rapidly reduce the inspired concentration of halothane (down to 1.0% to 1.5%) or sevoflurane (down to 2% to 2.5%) and keep it at this level or less until an intravenous line is in place. After the intravenous line is inserted, one may either deepen the plane of anesthesia or add a muscle relaxant. It is dangerous to proceed directly to a deep plane of anesthesia without having an intravenous line in place; without this precaution, resuscitation would be difficult.

The second most dangerous point occurs immediately after endotracheal intubation. If the vaporizer has not been closed before laryngoscopy, it is easy to forget that a relatively high inspired concentration is being delivered and, while checking for breath sounds, to perhaps give an overdose of inhaled anesthetics. Therefore, a prudent individual will discontinue all anesthetics until laryngoscopy and endotracheal intubation have been completed. With a Mapleson D circuit, a high concentration of anesthetic can be delivered more easily because the anesthetic enters directly at the airway. In contrast, changes made at the vaporizer of a circle system take longer to achieve equilibration with the circuit; therefore, the inspired concentration of anesthetic rises (or decreases) more gradually unless high fresh gas flow is being used. Particular caution should be used when changing from sevoflurane to halothane or isoflurane because the myocardial depressant effects of these drugs are additive.

Older Pediatric Patients

Successful, psychologically atraumatic induction of anesthesia by mask in an older pediatric patient requires that the patient understand and cooperate. Premedication is particularly helpful in the 1- to 4-year-old age group. Several different techniques may be used. One method is to play a game. For example, a smaller child may be asked to "blow up a balloon." A slightly older child (4 years and older) may be receptive to hypnotic suggestions during induction. A young child may be susceptible to a suggestion that the anesthesia mask is an "airplane pilot's mask" and that the smell of halothane or sevoflurane is "oxygen" or "aviation fuel." Stating that the "faster and higher the plane goes, the stronger the aviation fuel smells" is one means of distracting the child. During this type of induction, the operating room must be free of distractions, and the anesthesiologist must be able to communicate with the child. The use of constant conversation and incremental increases in the inspired concentration of anesthetic every third or fourth breath usually produces a smooth transition to general anesthesia. Often, the patient will breath-hold. If so, one should not attempt to assist respirations because that action often elicits coughing or laryngospasm. The anesthesiologist must be certain that airway obstruction and laryngospasm can be differentiated from breath-holding. Observing the chest wall and abdomen helps identify airway obstruction, which creates a rocking-type movement of the chest and

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A third method of induction uses flavored masks. A variety of flavored scents (Loran Oils, Inc., Lansing, MI) are available to reduce the noxious smell of the anesthetics; the child can select a favorite scent.

A fourth method, the single-breath technique, requires a very cooperative patient who can follow instructions. Using an unattached anesthesia mask, the anesthesiologist should demonstrate the procedure to the child, who then rehearses the following steps: (1) take a big breath in and hold at full inspiration; (2) exhale completely, hold at full expiration, and place the mask on the child's face at exactly the end of expiration; (3) take another full inspiration held as long as possible; (4) and then resume normal breathing. Before induction, the anesthesia circuit is filled with either 5% halothane or 8% sevoflurane in 60% nitrous oxide. The circuit bag must be emptied and filled several times so that the entire circuit is filled with 5% halothane or 8% sevoflurane. Steps 1 to 4 are then repeated with the mask attached to the Y-piece of the anesthesia circuit. When placing the facemask, care should be taken to not direct the gas toward the eyes because this can frighten the child. If the patient fully cooperates, loss of the eyelid reflex generally occurs in less than 1 minute. Occasionally, a patient does not take a full breath or becomes frightened. If the child is partially anesthetized, induction takes slightly longer, but the child does not usually remember the induction. If the child panics before inhalation of the anesthetic, induction should not be forced, and an alternative plan should be undertaken.