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When does organogenesis occur in the fetus?
first 8 weeks following conception
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When does the fetus develop organ function
2nd trimester
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Prematurity
Birth before 37 weeks gestation
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Postmaturity
Birth after 42 weeks gestation
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Low birth weight
< 2500 g
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T or F, infants that are premature, post mature, high BW, or low BW are more likely to have anesthesia issues
T
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Avg newborn body weight
3.5 kg
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Avg weight, 1 mo to 6 mo
4 kg
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Avg weight, 1-2 yrs
10 kg
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Formula to estimate child weight
Age (years) x 2 + 9= wt in kilos
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Pressure difference between pulmonary and systemic circulation in the fetus vs. the adult
- Adult- large pressure difference, avg PA pressure = 15, avg MAP= 100
- Fetus- not a large pressure difference as the pulmonary circuit pressure is high due to to HPV
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What factors cause the DA and FO to close when the infant is born and takes a breath?
Pressure difference, pulmonary vascular pressures decrease and the blood takes the path of least resistance.
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Describe the path of fetal circulation- well oxygenated blood
- Oxygenated blood leaves the placenta via the umbilical vein
- Half is shunted by the ductus venous and goes to the IVC
- Other half passes thru the liver
- Hence blood entering the IVC is mixed
- Well oxygenated IVC blood enters the RA
- Passes thru FA to LA
- To LV and pumped into ascending aorta
- This well oxygenated blood goes to: coronary arteries, upper body and brain (majority), and rest of fetal body
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Describe path of fetal circulation- poorly oxygenated blood
- Poorly oxygenated blood comes from the IVC (after going thru the hepatic circulation) and from the SVC
- Enters the RA, goes to RV, to PA
- Thru ductus arteriosus (low O2 tension of this blood increases PVR)
- Then to descending aorta
- This blood supplies the lower extremities
- Then goes to umbilical arteries back to placenta for gas exchange
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Risk factors for returning to pulmonary circulation in an infant
- Stress
- prematurity
- infection
- acidosis
- pulmonary dz- hypercarbia or hypoxemia
- Meconium aspiration
- Hypothermia
- CHD
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Why might hypoxia, hypercarbia, and anesthetic agents cause the infant to revert to fetal circulation
- All increase PVR
- PA may increase to systemic levels causing blood to be shunted thru DA and FO
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Why might hypoxic events be prolonged in infants? Does supplemental O2 help?
- Blood gets shunted via the fetal circulation
- No, because there's a shunt
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How does the normal pedi heart differ from the adult heart?
- Less contractile mass (not as strong)
- Less compliant ventricles (stiffer)
- Poor tolerance of increased after load (not that strong)
- HR dependent CO
- Underdeveloped compensatory mechanisms- can't compensate for hypotension with tachycardia
- Increased O2 consumption
- Lower BP
Fixed SV
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Normal O2 consumption in a newborn, child, adult
- Newborn 5-8 ml /kg/ min
- Child 4-6
- Adult 3-5
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Avg newborn and infant HR
- Newborn 133 bpm
- Infant (6-12 mo) 120 bpm
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Avg newborn and infant SBP
- Newborn- 80
- Infant- 6 mo- 90
- 12 mo- 96
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Avg HR 2 yo, 5 yo, 12 yo
- 2 yo 105 bpm (+ / - 25)
- 5 yo 90 bpm (+ / - 10)
- 12 yo 70 bpm (+ / - 17)
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Avg SBP 2 yo, 5 yo, 12 yo
- 2 yo 100 (+ / - 25)
- 5 yo 100 (+ / - 14)
- 12 yo 115 (+ / - 18)
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Describe the differences between the infant and adult pulmonary systems
- Smaller airways- more rx to airflow
- Poorly maintained negative intrathoracic pressure (can't take a large negative P breath)- higher closing capacity
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Infant RR and FRC compared to adults
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T or F, infants have well developed hypoxic and hypercapneic drives?
F, especially poorly developed in premies
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Pedi airway differences (4 major)
- Large occiput (causes neck flexion when supine)
- Large tongue size in relation to mouth size
- Larynx is higher in neck (C3-4 vs C4-5 in adults)
- Narrowest portion is at cricoid ring
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Narrowest point in the airway
-adult
-pedi
- Adult- glottis
- Pedi- cricoid
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What physiologic differences explains why infants experience respiratory fatigue faster than adults
- Decreased number of type 1 muscle fibers (don't normalize until 2 years)
- Underdeveloped intercostal muscles
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Why might an uncuffed ETT be preferable in peds < 6 yo?
- Narrowest point is below the vocal cords
- Risk of cuff inflation causing tracheomalacia
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Can a cuffed ETT be used in peds?
Yes, use a size smaller
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Differences in TBW composition in preterm, vs term infants, vs 1 yr, vs adult ?
What is the implication of this?
- Preterm 85%
- Term 80%
- 1 yr 60%
- Adult 50%
- Water soluble drugs have a larger Vd
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Differences in fat composition in term infants, vs 1 yr, vs boy puberty, vs girl puberty?
- Infant 12%
- 1 yr 30%
- Boy 10-15%
- Girl 20-30%
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Differences in kidney function in peds
- Kidney function is decreased in neonates and premies
- Neonates have limited ability to conserve sodium and dilute / concentrate urine
- Normal GFR after 1 year
- Normal tubular function after 3 years
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How do the endogenous Ca++ stores of the infant compare to that of the adult?
Decreased
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T or F, infants are at risk for large evaporative water losses, hyponatremia, hypoglycemia, and hypocalcemia?
T!
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T or F, the half life of renal excreted meds is unchanged in infants
F, it is prolonged
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Infant liver function
Functional maturity is incomplete
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Is the infant's ability to metabolize drugs increased or decreased? Why?
Increased, due to increased hepatic blood flow and ability to induce C450 enzyme system with introduction of drug
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Is the infant's ability to conjugate drugs (phase 2 reaction) increased or decreased? What is the implication of this?
- Decreased, may reach adult activity by 1 yr
- Increased drug half life of benzos and morphine
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T or F, the ability of the neonate to metabolize specific drugs is dependent on drug specific cytochromes and enzyme subfamilies?
T
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Infant glycogen stores compared to adult, what are the implications of this?
- Decreased glycogen stores
- Risk of hypoglycemia, acidemia, inability to handle a large protein load
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glycogen
Storage form of glucose
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T or F, GERD is uncommon in newborns and premies?
F, many infants on GI prophylaxis
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GI pH
1st day of life
2nd day of life
- 1st day- alkalotic
- 2nd day- normal adult pH
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When does coordination of swallowing and respiration occur?
4-5 mos
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Why are infants at risk for hypothermia?
- Large ratio of surface area to body weight
- Increased O2 consumption
- Inability to shiver well
- Increased metabolic rate for up to 12 hours post-op
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Non shivering thermogenesis
-anesthetic agent effect on
- Brown fat metabolism (premies have limited fat stores)
- Anesthetic agents can inhibit this
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Protein binding ____ as age increases
increases
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Premies have a ____ TBW content and a ____ fat content.
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MAC peaks at what age?
- 6 mo
- likely due to high fat content
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T or F, there is a narrow safety margin btw inadequate anesthesia and overdose in infants
T due to functional immaturity of cardiac muscle and rapid rise in anesthetic levels
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MAC multiple
amount of agent that can be delivered by the vaporizer divided by the MAC of the agent
increased MAC multiple associated with potential OD in neonates
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What age groups are most vulnerable to OD from volatile anesthetics? Why?
- Premies and neonates
- Due to immature cardiac muscle
- This population experiences the least increase in HR and the most decrease in SBP
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What volatile is most commonly used in pedi?
Sevo
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Profound myocardial depression seen in kids and infants with CHD is associated with what volatile agent?
Halothane, this agent should be avoided in this population
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What volatile agent is typically used for induction
sevo
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Iso is associated with ___ myocardial depression and preservation of ___. Unfortunately, it is also associated with a higher incidence of ______.
- less
- HR
- airway events (laryngospasm and bronchospasm)
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Why is des not used commonly in pedi?
- Higher incidence of emergence delirium due to rapid awakening
- 50% incidence of laryngospasm on induction!
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Why are propofol induction doses increased for pedi?
Due to higher fat content
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Propofol induction doses
< 2 yo
6-12 yo
- < 2 yo- 2.9 mg / kg
- 6-12 yo 2.2 mg / kg
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Only benzo approved for use in neonates
midaz
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Is midaz water or fat soluble?
water soluble
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Newborns have ___ clearance of morphine
- decreased
- A lower dose results in decreased plasma values, longer elimination half time
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Most commonly used long acting opiate in peds
morphine
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Succ is ___ soluble
water
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Infant succ dose
- 2 mg / kg
- dose increased due to high TBW content
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Succ must be given with ___
- atropine
- give atropine first due to risk of bradycardia or cardiac arrest
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Infants are generally ____ sensitive to NDMR
more
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Initial dosing of NDMR is ___ to that of adults, but the excretion is ___ and the effects are ____.
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T or F, the DOA of vec is similar to that of panc in newborns
T
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Neonate
1st 30 days of life
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Newborn
1st 24 hours of life
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When do the DA and FO permanently close?
within the first few months of life
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How long does it take for PVR to decrease to normal levels?
3-4 days
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Persistent pulmonary HTN patho
- Hypoxia, acidosis, and inflammatory mediators increase PA pressure, increased PVR occurs
- Right to left shunt thru the DA and FO occurs
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Potential causes of persistent pulm Htn
meconium aspiration, sepsis, PNA, respiratory distress, CDH
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Treatment of persistent pulmonary HTN
- goal directed
- surfactant
- ventilation
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Enlarged ___ ventricle may occur with persistent pulmonary HTN
right
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Bronchopulmonary dysplagia
- Inflammation and scarring of lung parenchyma and small airways
- Can result from long term ventilation
- Occurs in LBW and premie infants
- Increased airway reactivity
- Decreased lung compliance
- V/Q mismatch
- Hypoxia
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Management of bronchopulmonary dysplagia
Managed like asthma
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RDS
- Impaired gas exchange at alveolar level due to deficient levels of surfactant
- R to L shunting, metabolic acidosis, hypoxia
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Mature levels of surfactant are not present until __ weeks of age
35
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Why does R to L shunting occur in RDS
Due to increased PVR (no surfactant)
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S/sx RDS
Tachypnea, IC and substernal retractions, nasal flaring, cyanosis
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RDS treatment
- mechanical ventilation if PaO2 < 50 on 70-100% FiO2
- maintain Hct at 40%
- careful hydration (use albumin)
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Apnea
cessation of breathing that lasts longer than 20 seconds or is accompanied by cyanosis or bradycardia
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Types of apnea
- obstructive (neck flexion, pharyngeal instability)
- central (immature control of respiratory function)
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Hct < __ is a risk for ___ regardless of gestational age
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Infants < ____ weeks post conceptual age are most at risk for apnea
60
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Non essential surgeries should be postponed in infants < ___ weeks post conceptual age
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Risk of apnea is ___ proportional to gestational age and post-conceptual age
inversely
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Anesthetics (inhaled and IV) affect control of breathing for ___ post surgery
up to 12 hours
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T or F, a 2 yo who was born premature with a h/o apnea is suitable to have outpatient surgery
F!
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Examples of L to R shunts
ASD, VSD, PDA, Eisenmenger's syndrome, endocardial cushion defect (trisomy 21)
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Examples of R to L shunts
TOF, pulmonary atresia, tricuspid atresia, Ebstein's anomoly
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Anesthesia management of CHD
- Avoid drops in SVR to prevent L to R shunt
- Maintain IV volume
- BB to control HR
- R to L shunting may slow uptake of inhalation agents
- Avoid acidosis
- Maintain normal airway pressures
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What occurs in L to R shunts
- SVR > PVR causes pulmonary blood flow to increase
- Pulmonary congestion and CHF may result
- Increased susceptibility to respiratory tract infection
- Long standing shunt can lead to P HTN
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What occurs in R to L shunts
- defect btw R and L heart
- Resistance to pulmonary blood flow
- Hypoxia and cyanosis result
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PDA beyond the ___ day of life is abnormal
4th
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PDA can lead to __ to __ shunt
L to R
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PDA medical treatment
indocin (COX 2 inhibitor)
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Anesthesia considerations for PDA
- Abx to prevent endocarditis
- PPV is well tolerated
- Consider nipride post-op if SVR is elevated
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Risks associated with surgical repair of PDA
- IC hemorrhage
- recurrent laryngeal nerve paralysis (in infants born < 28 weeks)
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Necrotizing enterocolitis
- ulceration and necrosis of small bowel and colon
- unknown cause
- prematurity is a risk factor
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S/sx necrotizing enterocolitis
feeding intolerance, abd distention, bloody stools
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Necrotizing enterocolitis tx
NG decompression, holding oral feedings, IV, HD support, abx, possible surgical exploration
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Anesthesia implications of necrotizing enterocolitis
- Pts are hypovolemic and have metabolic acidosis
- Fluid and lyte deficiencies
- IVF / blood products
- Careful induction or awake intubation
- Caution with agents that depress myocardial function due to potential sepsis
- Mechanical ventilation post-op
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Hypertrophic pyloric stenosis
- Interferes with emptying of gastric contents
- High aspiration risk
- Avoid use of LR (lactate gets metabolized to bicarb, these pts have metabolic alkalosis)
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Kernicterus
Neuro d/o caused by toxic effects of unconjugated bilirubin in the brain stem nuclei and basal ganglia
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Anesthesia implications of kernicterus
Avoid vec (contains benzyl alcohol- associated with IC hemorrhage)
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FHgb vs adult Hgb
- FHgb more likely to hold onto O2 (left shift)
- FHgb is 2,3 DPG resistant (left shift)
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Premature infants < 55 weeks post conceptual age need a Hgb of at least ___ for elective surgery
10
-
-
-
-
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> 5 -10 years Hgb value
14 g/ dl
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Retinopathy of prematurity
- Associated with hyperoxia
- Associated with premature infants < 1000 g
- Retinal detachment and blindness may occur
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Anesthesia considerations to prevent ROP
- PaO2 50-80
- normocarbia
- O2 sat 89-94%
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Infants undergoing peripheral retinal ablation have increased risk of both ___ and ___ 1-3 days post -op
apnea and bradycardia
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IC hemorrhage
- Inversely proportional to gestational age or birth weight
- intraventricular hemorrhage is of the most significance
- major complication of prematurity
- due to incomplete auto regulation of blood flow and immaturity of cerebral capillary beds
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Anesthesia considerations to prevent IC hemorrhage
- Avoid large swings in BP, esp. HTN
- Slow volume expansion
- normal BP is at low end of auto regulation limit
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Most common metabolic issue in newborns
- hypoglycemia, due to inadequate glycogen stores and deficient gluconeogenesis
- Highest in SGA infants
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Hypocalcemia
- Infants have decreased levels of endogenous Ca stores
- LBW infants, premies, and infants born to IDDM mothers are at risk
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Most common cause of neonatal seizures
Hypocalcemia
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Pyloric stenosis
- Palpable "olive" in RUQ
- Hypertrophy of esophageal sphincter
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S/sx of pyloric stenosis
- projectile vomiting
- met alkalosis progressing to met acidosis
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Anesthesia management of pyloric stenosis
- Awake intubation and IV induction, NO inhalation induction
- NGT to sx prior to induction
- Extubate fully awake
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Most common type of tracheal esophageal fistula
- type C (90%)
- upper esophagus ends in blind pouch, lower esophagus connects to trachea
breathing causes gastric distention, feeding leads to aspiration PNA and choking
-
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vertebral defects, anal atresia, TEF, radial dysplagia
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Anesthesia considerations of TEF
- Avoid PPV
- Awake intubation
- Keep spontaneously breathing with min assist until fistula is ligated
- Ensure ETT is btw carina and fistula (visualize with FO scope)
- Often dehydrated and malnourished (can't feed)
- Frequent suctioning (copious secretions)
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CDH
- Gut herniates into thorax during fetal development
- Left sided is most common
- Associated with pulmonary HTN
- Pulmonary hypoplasia
-
Anesthesia implications of congenital diaphragmatic heria
- NGT
- Avoid high ventilation pressures (< 30 cm H20)
- Awake intubation often without muscle relaxants
- Caution with expansion of the ipsilateral lung
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Trisomy 21
- Down's syndrome
- short neck and large tongue= difficult airway
- may be associated with CDH, VSD, subglottic stenosis, TEF, sz, chronic pulmonary infections
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Anesthesia considerations for trisomy 21
- Possible difficult airway, esp during infancy
- Use smaller ETT
- Resp issues are common (stridor and apnea)
- Neck flexion may result in A/O dislocation
- Caution air in IV due to possibility of R to L shunts
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Diseases associated with micrognathia
- Pierre Robin syndrome
- Treacher collins syndrome
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Klippel feil syndrome
- short neck
- restricted c-spine mobility
- fusion of C2-3 is common
- prone to neuro damage
- awake FOI!!
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Tetralogy of Fallot
- 1) RV outflow obstruction (pulmonary stenosis)
- 2) RV enlargement
- 3) overriding aorta
- 4) VSD
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Why is prostaglandin used in TOF
- To keep PDA open
- Neonate may decompensate with closure of PDA
- Prevent severe L to R shunt
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Acute epiglottis
- SUPRAglottic edema
- a pre-emergency
- bacterial infection
-
S/sx acute epiglottis
- Drooling
- Difficulty swallowing
- Usually seen in kids ages 2-8
-
Anesthesia considerations for acute epiglottitis
- No MR
- Intubate in OR (ER if emergent)
- ENT should be aware (possible need for a trach)
- Half to 2x smaller ETT
- Extubate when cuff leak demonstrated
- Keep pt with mom, avoid stressing them
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Croup
- laryngotracheobronchitis
- SUBglottic edema that develops slowly over time in kids with a URI
- rarely requires intubation
- barking cough
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Kids at risk for OSA
- craniofacial abn
- neuromuscular d/o
- obesity
- adenotonsillar hypertrophy
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OSA anesthesia considerations
- Higher sensitivity to respiratory depressant effects of narcotics (unregulated Mu receptors)
- Narrowed upper airway
- Propensity to upper airway collapse
- Non narcotics or short acting narcotics
- Steroids
- regional or LA for post-op pain
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