Pediatric anesthesia

Pediatric Anesthesia:

Anatomic and physiologic differences among neonates, children and adults require differences in the administration of anesthesia compared to adults.

Preoperative Preparation:

The anesthesiologist first assesses the medical condition of the child and psychological status of the child and family while considering the surgical procedure. The anesthesia induction plan is made and explained to the family in order to alleviate fears the child and family may have. Chart review, physical examination is performed. Any medications to be used and equipment monitoring should be explained to patient. Informed consent should be obtained. Care should be taken to alleviate the anxiety of a child and parents, as anxiety felt by the parents my be transferred to the child. For the extremely anxious child that cannot be consoled by these methods heavy premedication is often used. Premedication combination is often midazolam,ketamine, and atropine.

Fasting: Infants and children have a higher metabolic rate and a larger body surface area:weight than adults. As such they become dehydrated more easily than adults. Studies have not found a difference in gastric residual volume and pH in children permitted unlimited clear liquids 2 to 3 hours prior to anesthesia induction anesthesia induction.

Current Fasting guidelines by the American Association of Anesthesiologists:

Ingested Material Minimum Fasting Period

Clear liquids 2 h

Breast milk 4 h

Infant formula 6 h

Nonhuman milk 6 h

Light meal 6 h

Premedication: Premedication is not often necessary for children 6 months and younger. Premedication is often used in the extremely fearful child or 10-12 month olds as this is the peak time a child has severe separation anxiety from parents. Oral midazolam is most commonly used .25-.33 mg/Kg in the US. Premedications may be administered orally, intravenously, intramuscularly, nasally, rectally and sublingually. Premedication in infants in children typically consists of midazolam, ketamine, and atropine. Except for atropine, anticholinergics are not commonly used in infants and children as they often do not reduce laryngeal reflexes during anesthesia induction. However, atropine in infants less than 6 months of age less than 45 minutes before induction reduces hypotension during induction with inhaled anesthetics. As such, it is included during premedication.

Pediatric Anesthesia Induction: There are different methods of induction of anesthesia in a pediatric patient: inhalation induction, intravenous induction, intramuscular induction, and rectal induction. The method of induction of anesthesia is chosen based on: the medical condition and surgical procedure of the child; the ability of the patient to cooperate and communicate; level of anxiety of the child often influencing their ability to cooperate; and whether or not the stomach is full.

Inhalation Induction of Anesthesia: Inhalation anesthesia with inhalation anesthetics and moderated to high dose opioids has been the standard of pediatric anesthesia.

Infants: Infants newborn to 12 months often require mask induction. Mask induction is performed by holding the masked end of the anesthesia air circuit off the face and with the other hand adjusting the concentration of anesthetic. In neonates and small infants, a rubber nipple or gloved finger is often provided for suckling in order to prevent crying during induction. As the infant loses consciousness, the mask is maneuvered to an appropriate location to improve delivery of the anesthetic and decrease anesthetic pollution in the operating room. After anesthesia is induced, a pediatric anesthesiologist reduces the inspired concentration of inhaled anesthetic, usually halothane or sevoflurane to an appropriate level while placing an intravenous line. Once the intravenous line is placed, the pediatric anesthesiologist has the option of increasing the depth of anesthesia or add a muscle relaxant. During this process endotracheal intubation occurs. Vaporizer of the laryngoscopy is closed. All anesthetics are discontinued until endotracheal intubation has been completed.

Children: Children 1-4 years of age often require premedication as it is difficult for them to understand and cooperate with mask anesthesia. Often games are used to distract the child to help the child cooperate. For example, telling the child he or she is an astronaut and they are breathing in their special astronaut mask. With the mask, every 3-4 breaths the inspired amount of anesthetic is increased. In pediatrics, flavored masks are often used to reduce the unpalatable smell of anesthetics. Occasionally, children will hold their breath. It is not accepted practice to attempt to assist with respiration when a child holds their breath as this typically elicits laryngospasm. However, before the pediatric anesthesiologist proceeds breath holding must be differentiated from laryngospasm or airway obstruction. When this is determined, the inspired concentration of anesthetic may be increased until the child loses consciousness.

If there is a laryngospasm or airway obstruction a few methods may be used to alleviate: 1) close the valve and set 10 cm H₂O of positive pressure and then let the child attempt to breath on his or her own; 2) administer positive pressure breaths, while preventing inflation of the stomach; 3) administer succinylcholine, a muscle relaxer to alleviate the laryngospasm.

Older Children: A single breath technique is also often used with older children as this requires a cooperative child that can follow instructions. Have the child follow the following steps: 1) take a full inspiration breath in and hold it with the mask above the face; 2) exhale the full expiration into the mask; 3) take another full expiration breath with the mask over the face; 4) then resume normal breathing into mask. During induction the Y-piece of the anesthesia circuit is attached to the mask and steps 1-4 are repeated until the child is fully anesthetized. Typically the anesthesia circuit is filled with either 8% sevoflurane or 5% halothane.

Intravenous Induction of Anesthesia: Total intravenous anesthesia induction is the most rapid and reliable method. This method is increasingly becoming available with the development of propofol, midazolam,and short acting opioids. Intravenous induction is often indicated when inhalation induction of anesthesia is contraindicated, such as a full stomach. The method varies with the age of the patient. For younger children, a common method is a utilization of a two needle with a butterfly catheter with a 25 gauge needle in order to access vein. Once anesthesia is induced, an intravenous catheter is placed. Older children will often permit the placement of the intravenous catheter after just local anesthestic and 50% nitrous oxide. However, many young children will cry or become hysterical when they see the intravenous catheter. Many pediatric anesthesiologists handle this by not permitting the child to see the intravenous catheter while being placed.

Intramuscular Induction of Anesthesia: Intramuscular induction of anesthesia is obtained by a shot to the muscle. In pediatric patients, methohexital, ketamine, midazolam, atropine or midazolam are often given intramuscularly. This method is not as common as inhalation or intravenous. This method is very reliable.

Rectal Induction of Anesthesia: This approach is mainly used in children that are still in diapers. The advantage of this approach is that it permits a very young child to fall asleep from anesthesia in a parent's arms. Many medications may be administered in this fashion: methohexital, ketamine, midazolam, thiopental and midazolam. The disadvantage of this technique is that medication absorption is not uniformly absorbed.

Parents in the Operating Room: Many institutions permit parents in the operating room. Most institutions limit this to one parent. Parental presence is to reduce the child's anxiety. Often parental presence reduces the child's anxiety enough to reduce the amount of premedication or eliminate premedication altogether. If the child will not benefit from a parent's presence or a physician is uncomfortable with having a parent in the room, many institutions will not have a parent present. Each physician and institution should decide what is best for the child and situation. If a parent is present, it is important to explain that as the child falls asleep the child's eyes rolls forward and to not worry. It is also important to let the parent know that as a child falls asleep he or she may make noises via the throat and to not be alarmed. Most physicians explain to the parents that during anesthesia induction, the neurons get excitable as a person is going to sleep. As such, it is common for a child to move or writhe their arms and legs prior to becoming fully anesthetized. Most anesthesiologists make sure the parent knows that as soon as it is time for a parent to leave, they must leave. This is to ensure that the anesthesiologist and surgeon may completely focus on the health and well being of their child.

Anesthesia Monitoring:

Minimal Monitoring: Typical minimal monitoring equipment include a stethoscope, a blood pressure cuff, EKG, temperature probe, pulse-oximeter, end-tidal carbon dioxide monitor, and an anesthestic concentration analyzer. An automated blood pressure cuff permits frequent blood pressure readings while the anesthesiologist is attending to other matters. The end-tidal carbon dioxide monitor, pulse oximeter, and blood pressure cuffs give information that permit an early warning of decompensation of the circulatory system before clinical signs become apparent. Late signs of circulatory system decompensation are cyanosis, bradycardia, hypotension, and absence of breath sounds.

Pediatric Airway Management: Vital component of general anesthesia in a pediatric patient is opening and maintaining a patent airway usually via intubation. In order to intubate and obtain an airway in an infant or child, it is important to choose the appropriate size endotracheal tube and larynogoscope blade. Even though technology continues to evolve, currently, there are two types of endotracheal tubes utilized to obtain an airway in a pediatric patient: uncuffed and cuffed endotracheal tubes. Many of the equipment adjustments are to suit a patient that is smaller and anatomically different an adult. Uncuffed endotracheal tubes are typically used for patients 6 years old and younger. The age is just a guideline. The ultimate decision is made based on patient anatomy, clinical condition, and surgical procedure. The procedure for utilizing an uncuffed endotracheal tube is somewhat different than a cuffed endotracheal tube. A small gas leak should be apparent while the peak inflation pressure is set at 20 to 30 cm H₂O. If at a higher pressure such as 40 cm H₂O there is no leak, try a smaller endotracheal tube. For cuffed endotracheal tubes, the cuff pressure is adjusted to make sure there is a leak with a peak inflation pressure of 20 to 30 cm H₂O. In this case the cuff pressure is adjusted. Straight laryngoscope blades are typically used for children 4 and under. Depending on clinical necessity, straight or curved laryngoscope blades are used in older children.

Miller Anesthesiology recommendations on Endotracheal Tube and Laryngoscope Blades in Pediatric Patients

Miller Anesthesiology Recommendations on Endotracheal Tube and Laryngoscope Blades in Pediatric Patients

Age of Patient	Endotracheal Tube Diameter (mm)	Laryngoscope Blade Size	Distance of Insertion (cm)
<1250 g	2.5	0	6-7
Full-term Infant	3.0	0-1	8-10
Full-term infant - 1 yr old	4.0	1	11
1 yr old-2 yr old	5.0	1-1.5	12
2 yr old-6 yr old	5.5	1.5-2	15
6 yr old-10 yr old	6.5	2-3	17
10 yr old-18 yr old	7-8	3	19

Capnography is the traditional method for assessment of successful intonation. CO₂ waveform shape or magnitude patterns can show if there is a kinked endotracheal tube, bronchospasm, endobronchial intubation, or poor pulmonary blood flow. A common problem with capnography that occurs with children when utilizing rebreathing circuits is that the measurements can be inaccurate. Hence, a pediatric anesthesiologist should sample and measure expired gases. As a reference, the CO₂ measured should be 2-3 mm Hg of CO₂measurements of arterial blood. In certain disease states, such as pulmonary disease or atelectisis, the difference between expired CO₂ measured and of arterial CO_{2</sub may be quite large, reflecting the level of shunting}

Emergent surgeries: Often in emergent surgeries a child has a full stomach. This provides a challenge in obtaining an airway due to aspiration risk. Rapid Sequence Induction of anesthesia is indicated and cricoid pressure applied. While administering oxygen to the child, atropine is often administered to prevent succinylcholine induced bradycardia.

Anesthesia for Pediatric Patients on a Ventilator: For infants on a ventilator, midazolam and fetanyl are used to maintain an anesthetized state on the ventilator. In infants not older children, clonidine is often added to reduce the doses of midazolam and fetanyl while maintaining deep sedation.

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