1 PEDIATRIC ANESTHESIA MANUAL A.Matveevskii, S.White Second edition 2007 2 Introduction The purpose of the pediatric anesthesia rotation is to provide an initial exposure to a variety of pediatric cases. The length of this rotation, 4 weeks, is enough to allow participation in the care of about 100 patients. Residents on this rotation should be able to develop skills for setting up OR’s for pediatric patients of different ages and should master skills in mask ventilation and intubation of pediatric patients including neonates. Topics for discussion should include neonatal emergencies, pediatric airways, ENT cases, general surgical cases, and questions from written and oral boards. One of the goals of this rotation is to prepare residents for routine “bread and butter” cases, to be safe with pediatric patients, and to be able to identify situations in which he or she might need help. Content OR set up for pediatric cases Preoperative evaluation Prematurity Premedication Equipment, monitoring and set up Fluids, electrolytes and transfusion therapy Emergence and recovery Newborn physiology and development Anesthesia for otolaryngology surgery Anesthesia for ophthalmic surgery Anesthesia for children with musculoskeletal disorders Anesthesia for children with congenital heart disease Anesthetic management children with hematologic and oncologic disorder Delivery room resuscitation PALS Anesthesia and sedation outside of OR (new) Anesthesia for ambulatory surgery in children (new) Pediatric pain management (new) Written exam questions Oral exam questions 3 OR set up for pediatric cases/Shands Hospital/ For pediatric cases, the OR should be warmed, as high as 85 F for neonates and especially premature patients. Warming lights, a circulating water warming blanket on the OR table, and an infant forced air warming blanket (“Bair Hugger”) may be helpful. The anesthesia machine should be preset for ventilation of small patients. Pressure controlled ventilation may be the best choice- since it will deliver whatever volume will generate the set pressure (such as 20 mm Hg). Be SURE the ventilator is NOT set to deliver an adult volume (which could cause pneumothorax in an infant). Monitors should be changed appropriately, to neonatal or pediatric, with alarms adjusted. All tools for intubation should be appropriate size including blades (Miller or WH), masks and ETT. ETT size should be 4 + (age in years/4). You can confirm that the ETT size is appropriate by comparing the tube to the external nare or the diameter of the little finger. Normal newborns can accommodate a 3.5 ETT. {The marking that should appear at the lips should be 12 plus [age in years/2]. For tiny infants the distance should be 6 plus the weight in kg.} You should have a stylet in the ETT you plan to use, and have available two other ET tubes, one size larger and one size smaller. You will need a selection of different size airways and a tongue blade. The wrong size artificial airway can obstruct the child’s airway. An oral airway that is too small can indent the tongue and push it back into the hypopharynx, effectively preventing air exchange. An oral airway that is too long can touch the tip of the epiglottis and cause laryngospasm. When measuring the oral airway on the outside of the jaw, make sure that the tip will not extend past the angle of the mandible. A pulse oximeter should be the first monitor placed on the child, followed by a precordial stethoscope. The pulse oximeter will count the heart rate and also confirmation that each beat generates a pulse. When left to right shunting may occur (as in all infants), two oximeters (one on the right arm or right ear) and another on one of the other three extremities will reflect the amount of shunting occurring. The precordial stethoscope will tell you that air is moving in the trachea, the patient is not having laryngospasm (hopefully!), and the heart tones are not muffled. (Cases of previously unsuspected cardiomyopathy have been diagnosed by alert residents using precordial stethoscopes!) Also- the precordial stethoscope is an excellent monitor for transporting the patient to the Recovery Room when the pulse oximeter must be disconnected, unless clinical conditions necessitate a portable transport monitor. ECG leads should be appropriately positioned considering the location of the surgery as well as patient position. Suction should be checked and working. Suction tubing should be connected to a suction catheter of appropriate size. Be careful not to have a suction catheter that is too small. On the anesthesia cart you should have succinylcholine, atropine, and a syringe with a mixture of succinylcholine and atropine. If you put 4 cc of succinylcholine (80 mg) with 1 cc atropine (0.4 mg) in a 5 cc syringe you will have the intramuscular dose for a 20 kg child. Half the syringe (2.5 cc) will be the dose for a 10 kg child (usually about a one year old), and ¼ of the syringe (1.25 cc) will be the dose for a 5 kg child. Use of this syringe will be necessary extremely rarely- in the instance where a child develops laryngospasm during inhalation induction before intravenous access has been achieved. However- if it is needed, it will be needed emergently. Succinylcholine is only given in the most life-threatening circumstances in children because some children may have an undiagnosed muscular disorder that could result in hyperkalemic cardiac arrest, or MH. Propofol and paralyzing agent should also be available. Pediatric patients are more likely than adults to require dextrose in their intravenous fluids. Almost all adults will react to the stress of surgery with a rise in their serum glucose. Unfortunately, at least 15% of toddlers will react to the stress of surgery with a FALL in their serum glucose. 4 NICU patients may have almost no glucose stores, and generally should receive dextrose in maintenance infusions. Other patients with increased glucose requirements are children with FTT (failure to thrive- weights lower than expected on the basis of age), liver failure, or sepsis. A normal newborn should weigh about 3 kg. They should double their birthweight by 3 months of age, and triple it by one year. A normal 4 year old should be 40 pounds and 40 inches. For a simple procedure like hernia repair, simply adding 40 cc of D5LR to the buretrol (and adding an equal amount of LR from the hanging bag to create 80 cc of D2.5 LR) should be adequate. Never use dextrose containing solutions for fluid boluses or to replace third space or intravascular volume losses. If there is any concern about procuring the airway, dextrose administration should be deferred until this has been accomplished as dextrose infusions have been associated with worsening the outcomes of hypoxic episodes. Preoperative evaluation Meeting pediatric patients and parents prior to induction is very important. The preoperative interview should meet the following objectives: 1. to obtain essential details of the child’s present illness and medical history 2. to assess potential anesthetic risk factors and discuss their likelihood and treatment with the patient and family 3. to initiate an anesthetic plan that is acceptable to the patient and family 4. to discuss recovery, postoperative analgesia and discharge planning 5. to allay anxiety and to establish trust and confidence with the patient and family 6. to find topics of interest to the child (pets, sports, games, TV shows) 7. to offer play therapy and tours of operating, induction and recovery rooms (if you are having the luxury of seeing the patients prior to the day of surgery) Prematurity Infants are considered premature if they are born before 38 weeks of gestation or weigh less than 2500 g at birth. Age definitions: the term newly born is used to describe the infant in the first minutes to hours after birth; the term neonate describes infants in the first 28 days/first month/ of life; the term infant includes the neonatal period and up to 12 months. Chronic respiratory dysfunction with risk of apnea is the most common sequela of prematurity. Controversy persists regarding at what age former premature infants are no longer at risk for postoperative apnea, with ages ranging from 44 weeks PCA to 60 weeks PCA. Common problems of prematurity: Respiratory distress syndrome/RSD/ Meconium aspiration syndrome Apnea Bronchopulmonary dysplasia/BPD/ Persistent pulmonary hypertension Patent ductus arteriosus Congenital heart disease Necrotizing enterocolitis/NEC/ 5 Gastroesophageal reflux Jaundice Anemia Hypoglycemia Hypocalcemia Congenital infections/STORCH/ Group B streptococcal infection Intraventricular hemorrhage Neonatal seizures Retinopathy of prematurity Common problems of prematurity. Respiratory distress syndrome – absence or deficiency of surfactant; characterized by hypercarbia and hypoxia with resultant acidosis; may be complicated by pneumothorax, pneumomediastinum, and pulmonary interstitial emphysema. Meconium aspiration syndrome – characterized by respiratory insufficiency, pneumonia, and asphyxia. Apnea – absence of breathing for 15 to 30 sec, often accompanied by bradycardia and cyanosis. Bronchopulmonary dysplasia – chronic obstructive lung disease of neonates exposed to barotraumas and high inspired oxygen concentration; characterized by persistent respiratory difficulty and radiographic evidence of diffuse linear densities and radiolucent areas. Persistent pulmonary hypertension – pulmonary hypertension and vascular hyperreactivity with resultant right to left shunting and cyanosis; associated with cardiac anomalies, respiratory distress syndrome, meconium aspiration syndrome, diaphragmatic hernia, and group B streptococcal sepsis. Treatment: oxygen, mechanical ventilation, high-frequency oscillatory ventilation, vasodilator drugs such as tolazoline, nitric oxide, and ECMO/extracorporeal membrane oxygenation/. Patent ductus arteriosus/PDA/ - left-to-right shunt from the aorta to the pulmonary artery through the ductal remnant of fetal circulation; commonly found in premature infants with RDS; the shunt can result in congestive heart failure and apnea. Necrotizing enterocolitis /NEC/ - ischemic injury to intestinal mucosa, often complicated by bowel necrosis and perforation, causing abdominal distention, bloody diarrhea, apnea, acidosis, and septic shock. Gastroesophageal reflux – involuntary movement of stomach contents into the esophagus; physiologic reflux is found in all newborns; pathologic reflux can result in failure to thrive, recurrent respiratory problems/aspiration, bronchospasm, and apnea, irritability, esophagitis, ulceration and gastrointestinal bleeding. Jaundice – hyperbilirubinemia from increased bilirubin load and poor hepatic conjugation/unconjugated, physiologic/ or abnormalities of bilirubin production, metabolism, or excretion/non-physiologic/. Hypoglycemia – blood sugar less than 40 mg/100ml, characterized by lethargy, hypotonia, tremors, apnea, and seizures. Hypocalcemia – total serum calcium concentration less than 7 mg/100ml or ionized calcium less than 3.0 to 3.5 mg/dl; characterized by irritability, jitterness, hypotonia, and seizures. 6 Intraventricular hemorrhage/IVH/ - periventricular-intraventricular hemorrhage associated with immaturity and hypoxemia. Characterized by bradycardia, respiratory irregularity, apnea, seizures, and hypotonia. Treatment – shunting and supportive care. Retinopathy of prematurity /ROP/ - vasoproliferative retinopathy seen in premature infants exposed to high concentrations of oxygen for prolonged periods. Treatment – cryotherapy or laser to the avascular retina. Premedication The primary goals of premedication in children are to facilitate a smooth separation from the parents and to ease the induction of anesthesia. Other effects that may be achieved by premedication include: Amnesia Anxiolysis Prevention of physiologic stress Reduction of total anesthetic requirements Decreased probability of aspiration Vagolysis Decreased salivation and secretions Antiemesis Analgesia Children greater than 10 months usually receive midazolam 0.5 mg/kg/max10-15 mg/. These medications should be given about 15-20 min prior to entering the OR. Dose: midazolam 0.5 mg/kg PO 0.3 mg.kg intranasal 0.08 to 0.5 mg/kg IM 0.2 mg/kg OT 1 mg/kg PR Midazolam is commonly administered in Ibuprofen, 10 mg/kg to provide postoperative pain relief. Barbiturates: pentobarbital or secobarbital. Opioids: morphine or meperidine, fentanyl; sufentanyl. Dose: morphine 0.1 to 0.2 mg/kg IM Meperidine 1 to 2 mg/kg IM Fentanyl 10 to 15 mcg/kg OT Sufentanyl 1.5 to 3 mcg/kg IN Clonidine is an alpha-2 agonist that given in combination with atropine produces satisfactory preoperative sedation, easy separation from parents and mask acceptance within 30-60 min. Dose: clonidine 4 mcg/kg PO Atropine 0.03 mg/kg PO administered together Hypnotics: Chloral hydrate 25 to 75 mg/kg and triclofos 70 mg/kg PO. Anticholinergics: atropine 0.02 mg/kg IM, PO scopolamine 0.02 mg/kg IM glycopyrrolate 0.01 mg/kg IV, IM 7 Antihistamine : hydroxyzine 0.5 to 1 mg/kg PO, IM Premedication/induction: methohexital 1%-10% solution to 20-30 mg/kg PR Thiopental 1 to 2 mg/kg IV Propofol 2-4 mg/kg IV (over 1 year) Ketamine 2 to 5 mg/kg IM 6 mg/kg PO 3 mg/kg IN 8 to 10 mg/kg PR Equipment and monitoring Airway equipment Circuits commonly used for children under 12 to 15 kg include Mapleson D, Bain, Jackson-Rees modification of Ayre’s T-piece and pediatric circle. The circuits used for pediatrics were traditionally designed specifically to decrease the resistance to breathing by eliminating valves; decrease the amount of dead space in the circuit; and in the case of the Bain circuit, decrease the amount of heat loss by having a coaxial circuit with warm exhaled gas surrounding and warming the fresh gas flow. The reservoir bag should contain a volume similar to that of the child’s vital capacity. Airways: To determine whether an oral airway is the proper size, hold the airway beside the patient’s face with the top of the airway beside the mouth. The bottom of the airway should end just before the angle of the mandible. If the airway is too long, it may touch the epiglottis and trigger laryngospasm. If the airway is too short- it can indent the tongue and push the posterior portion of the tongue into the hypopharynx, CAUSING (rather than alleviating) upper airway obstruction. Laryngoscopes: The use of small pediatric handle is recommended. It is less bulky, allowing laryngoscopy to be performed while cricoid pressure is applied with the fifth finger of the same hand. In general straight blades/Miller/ are used in infants to facilitate picking up the elongated epiglottis and exposing the vocal cords.The wider-phlanged Wis- Hippel or Robert-Shaw blades are sometimes preferred for ease of exposure. The oxyscope has a separate port to which oxygen tubing can be attached. The light wand facilitates blind intubation of the trachea . The Bullard laryngoscope consists of a rigid blade with a fixed fiberoptic bundle. The Shikani optical stylet is a combination of a lightwand, stylet and fiberoptic scope. Endotracheal tubes: small-diameter endotracheal tubes increase airway resistance and work of breathing. The anesthesiologist should calculate ideal tube size and have available one size larger and one size smaller. Age/yr/+16/4 or wt/kg/+35/10 Cuffed tubes are generally not used for patients under age 8. Ultimately the proper tube size is confirmed by the ability to generate positive pressure greater than 30 cm H2O and by the presence of a leak at less than 20 cm H2O. A stylet should be placed in the ET or be readily available to facilitate tracheal intubation. 8 The tube should be secured so that the second mark at the tip just passes through the cords. Extending the neck decreases tube depth (“EX”tension tends to “EX”tubate); flexing the neck deepens the tube position within the trachea. Laryngospasm is defined as approximation of true vocal cords or both true and false cords. It is caused most often by inadequate depth of anesthesia with sensory stimulation /secretions, manipulation of airway, surgical stimulation/. Treatment includes removal of stimulus, 100% oxygen, continuous positive pressure by mask, and muscle relaxants. Usually laryngospasm will break under positive pressure but on the rare occasion that this fails, only a very small dose of succinylcholine is required for relaxation of the vocal cords, which are quite sensitive to muscle relaxation. While 1-2 mg/kg maybe required for complete relaxation, only one tenth of this will generally relax the vocal cords. Laryngeal mask airway/LMA/ consists of a silicone tube fused to a spoon-shaped mask with an inflatable cuff. It is manufactured now in following sizes: 1. 11/2, 2. 21/2, 3. LMA is indicated in patients who are candidates for inhalation anesthesia who do not require intubation; LMA is useful in children with possibility of difficult intubation; for neonatal resuscitation; for anesthesia outside OR. Elective LMA placement may not be recommended for children under 2 years; LMA may increase dead space. ProSeal LMA available now in pediatric sizes starting from 1 ½. ECG: the T waves in infants are much larger, because the electrodes are situated much closer to the heart; the most prominent P wave in infants is seen in lead 3, because of R axis shift. Blood pressure monitoring: Cuff size can be determined using the following criteria: cuff bladder width should be approximately 40% of the arm circumference; bladder length should be 90 to 100% of the arm circumference. Placement of two BP cuffs on upper and lower extremities may be recommended when there is no arterial line. Invasive monitoring ( intraarterial catheters); Smaller catheters provide greater accuracy in monitoring, but larger are more practical for blood sampling. Generally neonates and infants will need 24G. Temperature monitoring. The consequences of thermal stress include cerebral and cardiac depression, increased oxygen demand, acidosis, hypoxia, and intracardiac shunt reversal. Oximetry. Use of the oximeter is particularly important in pediatrics because of the greater tendency of the infant to develop rapid desaturation and hypoxemia. The goal of neonatal oxygen monitoring is to maintain saturation in the low 90s to minimize risks of oxygen toxicity. In infants, two probes/preductal (right ear or right arm) and postductal (left arm or either leg) will reflect the amount of right to left shunting occurring. Gas monitoring. The ASA lists capnometry as a monitoring standard. Indeed it may be THE most important monitor, especially in patients being sedated, particularly if supplemental oxygen is being administered. Extra oxygen will be stored in the FRC, meaning that a patient can be apneic for a while before there will be a drop in oxygen saturation. Constant monitoring of ETCO2 will guarantee that apnea is 9 identified promptly. Also, while a patient may become noticeably cyanotic when the sat drops below 90%, there is no level of hypercarbia that is reliably clinically evident. In the recovery area, hypercarbia itself acts as a sedative and will contribute to delayed emergence. Patient pathophysiology may contribute to an increased gradient between end-tidal and arterial CO2 measurements, usually by increasing shunt and increasing dead space. ETCO2 will not accurately reflect arterial CO2 if something is interfering with delivery of CO2 to the lungs, such as pulmonary embolism (clot or air). Decreased cardiac output of any etiology will decrease CO2 deliver to the lungs. ETCO2 shows adequacy of cardiopulmonary resuscitation. Factors that increase West’s Zone I of the lungs (where alveolar pressure surpasses arterial pressure) will increase gradient. Such factors include hypovolemia (decreasing arterial pressure) and increased mean airway pressure (increasing alveolar pressure). In children with cyanotic heart disease, end-tidal underestimates arterial CO2. Neuromuscular blockade. Infants will not display head lift or respond to commands, even with full return of neuromuscular function. Lifting both legs may indicate that the patient can generate adequate negative inspiratory force. Nerve stimulation is recommended at the superficial ulnar nerve and posterior tibial nerve. The facial nerve is not recommended as the orbicularis oculi muscle is more resistant to blockade and if one successfully blocks this muscle, the patient’s neuromuscular blockade may be unreversible. Also, direct muscle stimulation in this area may result in the administration of excessive amounts of relaxant. Intravenous equipment. Small-gauge catheters are available for venous cannulation: 24G, 22G; a 25 or 27-gauge for very small premature infants. Use of a T-piece connector with stop-cock is recommended in children. It speeds delivery of medication by limiting tubing dead space. Most infants are going to have a patent foramen ovale. Because of the possibility of an intracardiac shunt, all IV’s should have air bubbles scrupulously removed. Tubing with built-in stopcocks is notorious for trapping air. It will be much easier to administer medications and remove air from the intravenous system by using a separate stopcock and attaching it to a plain piece of extension tubing. In children who weigh less than 10kg a burette/150cc/ should be used for fluid administration. For children weighing over ~15kg minidrop /60gtt/ml/ is useful. Extensions for intravenous systems are particularly advisable as intravenous access is sometimes obtained in lower extremities. Fluids, electrolytes and transfusion therapy Preterm and small infants have a relatively high percentage of total body water/85% in a preterm and 75% in a full-term infant/.The minimum amount of water required to meet ongoing insensible losses is 60 to 100 ml/kg/day. Preoperative assessment of the child’s fluid status is important to determine intraoperative needs. Dehydration is classified by its tonicity according to the concentration of serum sodium. Replacement of fluid deficits: ”easy- to- use” formula – 4-2-1; 4ml for first 10kg. 2ml for second 10kg and 1ml for the rest per hour. Generally either lactated Ringer’s or normal saline is used for routine intraoperative fluid administration. 10 When acute intravascular volume loss has occurred, the rapid administration of 10 to 20 ml/kg of lactated Ringer’s or normal saline may be warranted. Glycogen stores in the neonatal liver are limited and are rapidly depleted within the first few hours of life. Preterm infants may be hypoglycemic without demonstrable symptoms, necessitating close monitoring of blood glucose levels. Full-term neonates undergo a metabolic adjustment after birth with regard to glucose. Hypoglycemia is defined in full-term infants as a serum glucose concentration less than 30mg/100ml in the first day of life or less than 40 mg/100ml in the second day of life. The routine intravenous replacement solution for normal neonates contains 5- 10% dextrose. Transfusion of blood components is indicated to increase oxygen-carrying capacity or to improve coagulation. Fresh whole blood may also be chosen for trauma patients, transplant patient, or infants needing exchange transfusion or having open heart surgery. Transfusion reactions: Acute hemolytic reactions are usually the result of clinical errors. Extravascular hemolysis is usually seen when antibodies other than ABO are present. Nonimmune hemolysis is caused by mechanical or osmotic factors. Febrile reactions occur when antibodies against leuckocytes or platelets are transfused. Anaphylaxis is seen in patients with IgA deficiency who have anti- IgA antibodies as a result of previous transfusion. Emergence and recovery The primary goal of the postanesthesia care unit/PACU/ is to provide a safe environment, where patients can return to their preanesthetic homeostasis. The most important aspect of awakening is the return of cardiorespiratory reflexes: the ability to gag and cough to protect the airway, the return of baroreceptor reflexes to support perfusion, and the return of chemoreceptor responses to hypercapnia and hypoxia. Ventilation: Upon the patient’s arrival in the recovery room, attention should be focused on patency of the airway and adequacy of ventilation. Oxygenation: Children recovering from general anesthesia are at greater risk for hypoxia; continuous administration of oxygen during monitoring of SpO2 has been advocated for children. It may be necessary to administer oxygen and monitor SpO2 in the transfer from OR to PACU. Normothermia: Both hypothermia and hyperthermia are common intraoperative problems, particularly in infants. Neuromuscular Blockade: Reversal of neuromuscular blockade in toddlers and school-age children can be assessed by the same clinical indices as in adults: full train-of-four and sustained tetany on NMB monitor, inspiratory force greater than –20 cm H2O and a vital capacity of at least 15 ml/kg. Brisk flexion of the hips and knees is an indication of return of adequate peripheral muscle strength in infants. Leg lift in children may be an equivalent of head lift in adults. Analgesia: Preverbal children cannot convey their perception of pain. Prompt treatment of pain is urged. Crying is not always an indicator of pain but may represent anxiety, hunger, thirst or nausea. Intravenous opiates are used most commonly to treat moderate to severe pain.