ANESTHESIA


•  Infant chest wall deforms easily → because of cartilaginous structure


• Accessory muscles provide limited support (poor anatomic rib configuration)


• Infantile diaphragm contains 20–25% of fatigue-resistant type I muscle fibers → paradoxical chest wall movement when there is ↑ inspiratory effort


• ↑ work of breathing → deterioration into resp failure, esp in premature infant


•  FRC similar in both infants & adults per kg


• Owing to limited elastic recoil, infant closing capacity may near/exceed FRC:


Leads to air trapping → when small airways close at end-expiration


Cause of age-related changes in PaO2


•  ↑ tracheal compliance in infants; can lead to dynamic tracheal collapse


•  Changes in PaO2, PaCO2, & pH control ventilation → act on chemoreceptors


• Degree of response directly related to gestational & postnatal age


• Hypoxia stimulates newborn resp effort; high conc of O2 may depress it


• Nonspecific factors (blood glucose, Hct, temp) also affect infant breathing


Cardiovascular


•  Infant/neonatal myocardium contains less contractile tissue than adult heart


• Neonatal ventricle less compliant during diastole & generates less tension


• Infant ventricle cannot adequately ↑ stroke volume when metabolic needs ↑


• Cardiac output proportional to changes in heart rate


• Bradycardia → ↓ cardiac output; factors contributing to bradycardia (hypoxia, hypercarbia, surgical manipulation) should be corrected


•  Consider empiric anticholinergic admin (atropine) to offset laryngoscopy-induced bradycardia


Renal


•  Kidneys very active in utero & produce copious amounts of urine (contribute to maintenance of amniotic fluid volume)


•  At birth GFR = 15–20% of adult levels; reaches 50% within 2 wks & 100% by 1 yr (low GFR means infants cannot excrete excessive fluid loads/renal cleared drugs)


•  Ability to excrete organic acids poorly developed in neonates (causes observed “physiologic acidemia” of newborn)


•  Concentrating ability poor & newborns can conc urine only to 600–800 mOsm/kg


Hepatic


•  Gluconeogenesis & protein synthesis begin at 12 wks’ gestation (liver structure near term similar to adults; functional development lags)


•  Preterm & small for gestational age infants usually have diminished glycogen stores


→ Prone to hypoglycemic episodes after delivery


→ Treat hypoglycemia promptly (D10 at 4 mL/kg/hr)


•  Albumin levels in preterm infants are often low and affect drug binding & availability


•  Physiologic jaundice: Due to RBC breakdown & ↑ enterohepatic circ of bilirubin


→ As opposed to pathologic jaundice (encephalopathy from kernicterus)


Gastrointestinal


•  Esophageal tone ↓ in many newborns; reaches adult level ≈6 wks


→ Projectile vomiting after feeding = classic sign of pyloric stenosis


•  Meconium (water, pancreatic secretions + intestinal epithelial cells)


• Usually passed a few hours following delivery


• Premature infants often have delayed evacuation


• May also indicate GI dz (meconium ileus/intestinal atresia)


Hematopoietic


•  Neonatal estimated blood volume = 85–90 mL/kg at term, gradually ↓ with age


•  HbF: Most prevalent after birth, greater O2 affinity than HbA (adult)


• “Physiologic anemia of infancy” due to HbF (replaced with HbA by 3 mos)


• Hg levels rise to 12–13 g/dL by age 2; in adults, they reach 14 for females & 15.5 for males


•  Vit K–dependent coag factors ≈40% adult levels (2° to immature liver synthesis)


• Prolonged PT normally seen in both preterm & full-term infants


Neurologic


•  Brain growth phases: (1) Neuronal cell division (15–20 wks’ gestation) & (2) glial cell division (25 wks–2 yrs); myelination continues into 3rd yr


•  Malnutrition, disruption of blood–brain barrier, & trauma may affect development


•  Developmental milestones represent average rate of neurologic maturation


• Deviations from norm do not necessarily indicate significant problems


• Premature infant’s developmental delay may be considered normal (depending on degree of prematurity)


Temperature Regulation


•  Infants lose heat rapidly 2° to: ↑ surface area:wt ratio, lack of adipose/SQ tissues


• Infants rely on nonshivering thermogenesis


• Cathecholamine-mediated increase in brown fat metabolic activity


→ Catecholamines also cause: Pulm & peripheral vasoconstriction, ↑ O2 use, hypoxia, acidemia


•  Effective methods for limiting heat loss include


• ↑ ambient room temp, cover infant with thermal insulator, use of heat lamp


PHARMACOLOGY


Body Fluid Composition


•  TBW in infants ≈85%, ≈60% by 1 yr of age; extracellular water (ECW) dec faster than intracellular water (ICW)


•  Fat, muscle, organ wt are age dependent, affect pharmacodynamics/kinetics


•  Infants have greater ECW than adults → volume of distribution for drugs is expanded


• Drugs with limited tissue uptake may require higher wt-based dosing


Organ System Maturity


•  Enzyme systems involved in biotransformation relatively immature


• Drugs may have prolonged elimination half-lives


Protein Binding


•  Often only unbound drug is clinically active (many drugs are protein bound)


• Albumin is the major binding protein for acidic drugs (benzos & barbiturates)


• Neonatal albumin quantitatively & qualitatively deficient → dec binding capacity


Receptors


•  Age-related variations in response to drugs may be 2° to receptor sensitivities


PREOPERATIVE EVALUATION


Psychological Assessment


•  Use clear, simple language to discuss potential risks (avoid disclosing info in a child’s presence that may ↑ anxiety)


•  Psychological goals of the preoperative interview


• Identify specific causes of anxiety & evaluate potential benefit of preop sedation


• Address potential risks pertinent to procedure


• Describe reasonable expectations for postop discomfort, side effects


• Reassure both parents & patient


•  Child-life specialists can facilitate pt education & relieve anxiety


• Comfort objects may accompany pt into OR


• Parental presence may be useful; perceived legal risks are largely exaggerated







OR EQUIPMENT AND SETUP


•  Oral ETT size ≈ (age/4) + 4; depth ≈ (ETT internal diameter × 3)




Intravenous Fluids


•  Fluid replacement: Based on NPO deficit, ongoing maintenance requirement, blood loss, & potential for surgically induced fluid shifts (3rd spacing)


•  Lactated Ringer’s often appropriate


•  Normal saline advised for pts with renal dysfx, mitochondrial myopathy, or neurosurgical procedures


•  Dextrose soln for neonates (limited glycogen stores) & diabetes who got hypoglycemic meds


•  “Buretrol” or other metered device often used for children <6 mos


• Allows careful control of fluid admin


• Older children may receive IV fluids through a 60 drop/mL gravity infusion set


Remove all air bubbles (risk of PFO) from IV tubing & injection ports


Emergency Drugs


•  All emergency drugs should have 1.5 in. 22 gauge needle for emergency IM injection



ANESTHESIA TECHNIQUES


Induction



Maintenance


•  Volatile agents or TIVA-based techniques can be used


• Drug selection guided by coexistent dz & surgery duration


•  “4–2–1 rule” can guide fluid replacement


• Neonates & infants require additional care to avoid fluid overload (metered devices) & provide glucose supplementation (D5NS)


• EBV should always be calculated to guide fluid when surgery has high EBL


• While children tolerate lower Hcts, they also have ↑ metabolic rates & O2 needs




CLINICAL CONDITIONS


Respiratory


Apnea of Prematurity


•  Newborns <34 wks’ gestational age → inc risk for perioperative resp complications


• Immature response to hypoxia & hypercarbia → central apnea


•  GA may exacerbate; regional may ↓ incidence of postop spells (does not eliminate); other contributing factors include hypoglycemia, hypothermia, anemia


•  Therapies: Positioning (avoid mechanical airway obstruction), resp stimulants (methylxanthine/caffeine 10 mg/kg) in high-risk pts, appropriate monitoring


•  Usually premature newborns <60 wks’ postconception → need continuous cardiorespiratory monitoring for 24 hrs postop (no outpatient procedures)


Prematurity—Perioperative Concerns


•  ↑ risk of hypothermia


•  Unable to regulate glucose control


•  ↑ risk of postop apnea (esp if <50 wks’ postconceptual age)


•  Retinopathy of prematurity (esp if. <44 wks’ postconceptual age)


•  Pulmonary dysfunction


Meconium Aspiration


•  Presence of thick, meconium-stained amniotic fluid during concerning aspiration → may result in profound resp distress & hypoxemia


•  Suction nares & oral cavity immediately after delivery


• Transfer newborn to a radiant warmer & intubate


• Apply suction & withdraw ETT; repeated until only trace meconium seen


•  PPV should not be used initially


• Can spread meconium distally into bronchial tree


• If bradycardia/cyanosis develop → gentle PPV with 100% O2 pressure


Bronchopulmonary Dysplasia (BPD)


•  Lung dz of newborn; problematic to accurately define as presentation has varied


•  Initially described lung injury from aggressive mech ventilation & high FiO2


• Develop smooth muscle hypertrophy, airway inflammation, pulm HTN


• Exogenous surfactant, steroids, & gentler vent modes → improved survival (overall dz incidence has not decreased)


•  Babies <30 wks’ gestational age →


• Present with immature lung parenchyma & dysfunctional alveoli


•  Pulm dysfx will be persistent to varying degrees (may affect later management)


• Airway hyperreactivity & resp infections common


• Supportive care in the OR → gentle ventilation, limit barotrauma, β2-agonists


• Consider need for postop ICU admission


Congenital Diaphragmatic Hernia (CDH)


•  Diaphragmatic defect → presents at birth with cyanosis, resp distress, scaphoid abd


• Get herniation of abd contents → result in lung & pulm vessel hypoplasia


Not simply lung compression & atelectasis


•  Surgical correction → postponed several days to optimize pt cardiopulmonary status


• Severe defects often require more support (ECMO or nitric oxide)


•  Anesthetic management


• Intubation (awake, inhalation, or RSI) should minimize gastric distention


• Maintenance usually volatile + narcotic (avoid N2O → risk of pneumothorax)


• A-line + CVP for blood sampling/fluid resuscitation; temp maintenance important


• Maintain low pulm vascular resistance → avoid hypoxia & hypercarbia


•  Contralateral pneumothorax → sudden cardiovascular collapse & ↓ lung compliance


•  Postop: Transfer to NICU intubated & paralyzed


Asthma


•  Triad of airway inflammation, reversible flow defects, airway hyperreactivity


•  Signs & symptoms: Wheezing, dyspnea, chest tightness, coughing


•  Preop interview: Freq of episodes, current meds, hospital admissions, steroid use


•  Severe bronchospasm → can restrict airflow so much that wheezing disappears


•  Anesthetic management: Supplemental O2, bronchodilators, anticholinergics


• Epinephrine may be required to treat severe episodes of bronchospasm


•  Avoid ETT use (may precipitate bronchospasm) for noninvasive procedures





Upper Respiratory Tract Infections (URIs)


•  Children have ≈6–8 URIs/yr; most caused by rhinovirus


• Croup, influenza, strep pharyngitis & allergic rhinitis → may mimic URIs


•  URIs ↑ airway reactivity for 4–6 wks following onset of symptoms


• Potential complications from GA → laryngospasm, bronchospasm, & desat


•  Risk factors for resp events: Hx of prematurity, coexistent reactive airway dz, 2nd-hand smoke exposure, ETT, nasal congestion/secretions, airway surgery


•  Not practical to cancel all children with recent URI; reschedule elective surgery if:


• Purulent nasal discharge, productive cough, fever >100°F


• No change in functional status (appetite, activity), likely to tolerate brief proc


•  LMA acceptable technique to avoid unnecessary airway manipulation


• Consider deep extubations (spontaneously breathing under ≥2 MAC of sevo) to minimize airway irritation during emergence


Secondary Smoke Exposure


•  2nd-hand smoke leads to inc risk of adverse resp events under GA → laryngo-/bronchospasm, breath holding, airway obstruction, ↑ oral secretions


Cardiac


Patent Foramen Ovale (PFO)


•  Intracardiac shunt → permits fetal circulation in utero (interatrial communication)


• Usually closes during delivery, soon after infant’s 1st breath


• Pulm vascular resistance falls & L atrial pressures exceed R → closes flap


•  Conditions which ↑ R-sided atrial pressures may reopen this conduit → hypoxia


•  Paradoxical air embolism: Can occur in pts with PFO → if precautions are not taken


Atrial & Ventricular Septal Defects (ASD/VSD)


•  ASD & VSD → result left-to-right shunts, do not present with systemic hypoxemia unless defects large & volume overload severe


•  Small defects usually asymptomatic & hemodynamically stable


• Over time, shunt flow may → lead to R-heart volume overload & CHF


• Corrective procedures usually timed according to disease severity


•  Anesthetic management


• Avoid hypoxia & hypercarbia (increased pulm vascular resistance)


• Conditions which ↑ R-sided heart pressure above L-side may provoke shunt reversal & critical hypoxemia


Neurologic


Duchenne Muscular Dystrophy


Associated with malignant hyperthermia, trigger-free anesthetic techniques should be employed


Metabolic


Mitochondrial Disease (MD)


•  Diverse group of enzyme complex defects that adversely affect energy metabolism


• Incidence 1:5,000 with variable age of onset & presentation


•  Abnl ATP production affects brain, heart, & muscle; can lead to:


Seizures, spasticity & developmental delay, hypotonia, cardiomyopathy, arrhythmias, chronic GI dysmotility, delayed growth


•  No proven assoc between MD & malignant hyperthermia


• Pts may be sensitive to propofol, but no clear guidelines regarding its use


• Be aware of potential for metabolic acidosis


•  Normal saline generally recommended for maintenance fluids


• Lactate admin may cause worsening of symptoms


• Fluid requirements may be elevated


• Children may also require glucose supplementation & serial monitoring


Gastrointestinal


Pyloric Stenosis


•  Obstruction of pyloric lumen usually age 5 wks → persistent, bile-free projectile vomiting


•  Condition = medical (not surgical) emergency


• Infant may be severely dehydrated & have concurrent electrolyte abnl


• Emesis is H+ ion rich, causes hypokalemic, hypochloremic metabolic alkalosis


• Must correct before surgical repair


•  ↑ risk for aspiration


• Need gastric decompression (NG) immediately before induction


• Rapid-sequence IV induction with succinylcholine or


• Awake, oral ETT intubation may require help to physically restrain infant


• Procedure = usually brief, long-acting muscle relaxation unnecessary


Tracheoesophageal Fistula (TEF)


•  Most common presentation (85%) = Type C (proximal esoph atresia w/distal fistula)


•  Symptoms: Coughing, excessive drooling, & cyanotic episodes


• Failure to pass soft-tipped suction catheter into stomach = diagnostic


• Presence of blind esophageal pouch confirmed by x-ray


•  Preop assessment: Focused on resp support, aspiration precautions, & identification of other congenital abnl (echo to rule out endocardial cushion defects)


•  Anesthesia management: A-line usually placed


• Position pt on 30° wedge to avoid passive aspiration of gastric fluid


• Induction techniques: Should minimize aspiration risk (awake intubation, RSI)


• Avoid PPV prior to intubation


• May cause significant gastric distention, diaphragmatic elevation, & hypoxia


• Prophylactic gastrostomy may prevent accumulation of gastric air


•  Deliberate R-sided mainstem intubation → limit transmission of air across fistula


• Pass ETT distal to fistula, then withdraw until bilateral breath sounds obtained


•  Lung isolation indirectly achieved by surgical compression of nondependent lung


• May be poorly tolerated (V./Q. mismatch); consider intermittent lung reinflation


• Hypotension may occur → mediastinal structures distortion & ↓ venous return


•  Extubate stable pts (with good pain control) to avoid pressure on tracheal suture line


• If pt remains intubated, only suction with a premeasured catheter that does not extend beyond distal tip of ETT


Gastroschisis & Omphalocele


•  Involve defects of anterior abdominal wall with herniation of visceral components



•  Cover exposed viscera to avoid evaporative heat loss & limit infection


• Large fluid shifts occur; fluids should be aggressively replaced


• Serial electrolyte & glucose monitoring important (place A-line/CVP)


•  Anesthetic technique


• Awake intubation or RSI; avoid N2O


•  Defect closure may → ↑ intra-abdominal pressures which may cause → ↑ peak airway press, ↓ venous return, hypotension, lower extremity ischemia


•  Postop: Usually require mech vent support


Necrotizing Enterocolitis


•  Etiology multifactorial: Pts usually present with bowel distention & bloody feces


• Preterm infants <2 wks’ gestational age → highest risk


•  Intestinal hypoperfusion & ischemia → weakened intestinal wall → may perforate


•  Anesthesia management: Place A-line & CVP


• Resuscitation should include crystalloid & blood products


• Monitor urine output, avoid N2O


• DIC, thrombocytopenia may occur


•  Pts often return for reexploration


Pediatric Congenital Syndromes






NEONATAL & PEDIATRIC RESUSCITATION


Figure 26-2. Neonatal resuscitation algorithm.



Neonatal Resuscitation Algorithm


Note: The following summary is not to be a substitute for completion of the Neonatal Resuscitation course as administered by a certified instructor.


•  ∼10% of newborns require direct assistance to achieve cardiopulmonary stability during transition to extrauterine life. <1% require extensive efforts


•  Term neonates with adequate breathing/crying and tone should be dried and kept warm. All others require rapid assessment and the following sequential interventions


•  Dry and keep warm, position, airway check, stimulate to breathe


•  Ambu-bag ventilation, oximetry monitoring, possible intubation


•  Chest compressions


•  Medications and volume expansion


New recommendations since 2010:


•  Initial evaluation now followed by simultaneous assessment of heart and respirations. Oximetry monitoring should be used early


•  For full-term babies, resuscitation should begin with air rather than 100% FiO2


•  Supplemental oxygen should be blended with air and delivered concentration guided by oximetry


•  Current evidence neither supports nor contradicts the routine endotracheal suctioning of infants born in the presence of meconium-stained amniotic fluid


•  Neonatal chest compression–ventilation ratio should remain 3:1, higher ratio to be applied if neonatal arrest due to cardiac etiology


•  Therapeutic hypothermia may be considered for term/near-term infants with evolving hypoxic-ischemic encephalopathy


•  It is appropriate to consider cessation of resuscitation efforts if no detectable heart rate for 10 min


•  Delay cord clamping for at least 1 min in babies NOT requiring resuscitation


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Aug 28, 2016 | Posted by in ANESTHESIA | Comments Off on ANESTHESIA

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