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Neonatal Considerations Principles-II Juan E. Gonzalez, CRNA, MS, ARNP Clinical Assistant Professor based on prior lecture by: John P. McDonough, CRNA, Ed.D., ARNP Professor & Director Anesthesiology Nursing Classifications Neonate Less than 30 days of age Infant 1-12 months of age

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Neonatal ConsiderationsPrinciples-IIJuan E. Gonzalez, CRNA, MS, ARNPClinical Assistant Professorbased on prior lecture by:

John P. McDonough, CRNA, Ed.D., ARNP

Professor & Director

Anesthesiology Nursing

classifications
Classifications
  • Neonate
    • Less than 30 days of age
  • Infant
    • 1-12 months of age
  • Children
    • 1-12 yrs of age
what makes them different
What makes them different?
  • Physiologic (compared to adults)
  • CO is heart rate dependent (CO=SVxHR), ↑ HR, ↓ BP, ↑ RR, ↓ lung compliance, ↑chest wall compliance, ↑BSA/wt ratio, ↑ total body water content
    • Fetus 90%Body Water
    • Preterm 80% Body Water
    • Full-term 70% Body Water
    • 6-12 mo 60% Body Water (similar to adults)
    • ↑ECF
      • At birth 45% of body wt is ECF
      • At 2mo 30% of body wt is ECF
      • At 6 y/o 20% of body wt is ECF
      • Adults: 16-18% of body wt is ECF
what makes them different4
What makes them different?
  • Anatomic:
  • ↓ LV compliance, residual fetal circulation, difficult A&V cannulation, large head & tongue, narrow nasal passages, anterior & cephalad larynx, long epiglottis, short trachea & neck (obligate nasal breathers until 5 months of age)
  • prominent adenoids & tonsils, ↑ resistance to airflow
what makes them different5
What makes them different?
  • Pharmacologic:
    • Immature hepatic biotransformation
    • Immature renal function
    • ↓protein binding (higher free drug in plama-> reduced drug metabolism/delayed elimination)
    • ↑Vd for (H2O soluble drugs) -> higher loading dose required to achieve desired clinical response
    • Immature NMJ (infants less than 6mo have ½ pseudocholinesterase activity than older kids. However redistribution of SUX from small muscle mass to ↑ ECF volume appears to terminate SUX quickly).
      • require ↑ SUX (pedi IV dose is 2mg/kg)
    • smaller proportion of fat & muscle stores
cardiovascular
Cardiovascular
  • Bradycardia →↓ CO (↓ B/P, death)
    • Parasympathetic activation, anesthetic overdose, hypoxia
  • Sympathetic NS & baroreceptors not fully developed
  • ↓ catecholamine stores
  • ↓ circulating volume → ↓ B/P w/o ↓ HR
  • Problems with B/P monitoring
fetal circulation
Fetal Circulation
  • Ductus arteriosus
    • Rt radial artery for monitoring
  • Foramen ovale
  • Ductus venosus
fetal circulation8
Fetal Circulation
  • Placenta (gets ½ CO) does resp gas

exchange

Lungs get low blood flow (pulm &

Syst circulations are parallel)

2 cardiac shunts:

-Foramen ovale

-Ductus Arteriosus

fetal circulation in motion
Fetal Circulation in Motion
  • Well O2-blood from placenta (80% O2 sat) mixes with venous blood returning from lower body (25% O2 sat) & flow via IVC into RA
  • RA anatomy preferentially directs blood from IVC (67% O2 sat) thru FO into LA (right-to-left shunt)
  • LA blood goes to LV & it is pumped to upper body (mainly heart/brain)
  • Poor O2-blood from upper body returns via SVC to RA
fetal circulation in motion10
Fetal Circulation in Motion
  • RA anatomy preferentially directs flow from SVC into RV
  • RV blood is pumped into PA
  • Because of high PVR, 95% of blood ejected from RV (60% O2 sat) is shunted across the Ductus Arteriosus into the descending Aorta and back to the placenta & lower body
fetal circulation in motion11
Fetal Circulation in Motion
  • Parallel circulation results in unequal ventricular flows
    • RV ejects 2/3 of combined ventricular outputs
    • LV ejects only 1/3
  • ½ of Well O2-blood in the umbilical vein can pass directly to the heart via the Ductus Venosus, bypassing the Liver
  • The remainder of of blood from placenta mixes with blood from the Portal vein and goes to the liver first (important in allowing rapid hepatic degradation of drugs/toxins from maternal circulation)
transition to normal circulation
Transition to Normal Circulation
  • At term, fetal lungs are developed but contain 90mL of plasma ultrafiltrate
  • This fluid is squeezed out during birth by forces of pelvic muscles and the vagina
  • Remaining fluid absorbed by pulm capillaries & lymphatics
  • Small (preterm) neonates & fullterms via C/S do not benefit from the vaginal squeeze & may have Transient Tachypnea of the Newborn
transition to normal circulation14
Transition to Normal Circulation
  • Mild hypoxia, acidosis and sensory stimulation (cord clamping, pain, touch, noise) help initiate & sustain respirations
  • Outward recoil of of the chest at delivery aids in filling the lungs with air
  • Lung expansion increases PAO2 & PaO2 & decrease PVR
  • ↑PaO2  PA vasodilation↑Pulm blood flow ↑blood to Left heart ↑press LAfunctional closure FO (may take months)
  • ↑PaO2  Closure DA (other chemical mediators Ach, bradykinin, prostaglandins) (not closed until 2-3 wks)
  • Overall result  elimination of right-to-left shunt
  • First few days of life, hypoxia or acidosis can prevent or reverse these changes  persistence of (or return to) fetal circulation
  • Positive feedback (more of the same thing) vicious cycle is established  R-to-L shunt promotes hypoxemia & acidosis  more R-to-L shunt (via FO, DA or both). If cycle is not broken soon  fetal demise
respiratory
Respiratory
  • Vt (6-8mL/kg), and dead space/Vt (0.3mL/kg) are same as adults
  • Small/limited number of alveoli (↓lung compliance)
  • Cartilaginous rib cage (↑chest wall compliance) Chest wall collapse during inspiration & low residual lung volume @ expiration (diaphragmatic breathing) ↓FRC (↓O2 reserve during apnea & predisposition to atelectasis/hypoxemia)
  • Hypoxic & hypercapnic drives not well developed
  • High Alveolar Ventilation & Low FRC ↑VE/FRC & high blood flow to VRG organs  rapid rise in alveolar anesthetic concentration (rapid induction & recovery from GA) rapid rise in FA/FI (fractional [alveolar]/fractional [inspired])
  • MAC is higher in infants than in neonates for VAA
respiratory con t
Respiratory (con’t)
  • During spontaneous breathing resistance is an issue
    • Unidirectional valves, tubes, absorber
    • Some use Mapleson-D or Bain system
    • Semi-closed circle OK if ventilation is controlled
  • Circuit pressure monitoring required
  • End-tidal CO2 monitoring required
  • Use ventilators with caution
  • Circuit (length & compliance) can be an issue
respiratory system
Respiratory System
  • Head & tongue problems
  • Obligate nasal breathers
  • Larynx at C-4 level
  • Cricoid cartilage narrowest point
    • small amount of edema = big problems
  • Right size ETT indicated by easy passage and gas leak at 10-25 cm H2O pressure

(age/4)+4 = ETT size in mm

ett placement

pre-term to 1 year:

range 2.5-4.0 uncuffed

Over 1 year:

age/4 + 4 is tube size. Have +/- 1/2 size ready. Depth = 3x tube size

123-789 rule: 

1 kg, depth is 7 cm, etc

ETT Placement
slide23

ADULT

PEDIATRIC

age related changes in vs range varies 25 50
Age related changes in VS(range varies 25-50%)
  • Neonate
    • RR=40, HR=140, B/P=65/40
  • 12 months
    • RR=30, HR=120, B/P=95/60
  • 3 years
    • RR=25, HR=100, B/P=100/70
  • 12 years
    • RR=20, HR=80, B/P=110/60
metabolism temp regulation
Metabolism & Temp Regulation
  • Metabolism & its associated parameters (O2 consumption, CO2 production, alveolar ventilation) correlate better with BSA rather than weight
  • Thin skin, low fat, ↑BSA = ↑heat loss (made worse with cold OR, wound exposure, IV fluids, dry anesthetic gases, & direct effect of anesthesia on temp regulation)
  • Hypothermia is a serious problem
    • delayed awakening, cardiac irritability, ↓ resp, ↑pulmonary VR, altered drug responses
  • Nonshivering thermogenesis (major mechanism of heat production)
    • metabolism of brown fat (VAA inhibits this!!)
temperature control
Temperature Control
  • Warm OR (> 25° C)
  • Warm and humidify inspired gases
  • Warming blanket/lights
  • Warming fluids
npo requirements
NPO Requirements
  • Healthy neonates w/o risk for delayed emptying or aspiration
  • Formula until 6-8 hrs preinduction
  • Clear liquids 2-3 hrs preinduction
renal function
Renal function
  • Healthy infants have normal renal function by age 6 months
  • NOT SO in premature neonates:
    • impaired Na+ retention, glucose excretion, HCO3 reabsorption & ↓ creatinine cl
    • glucose excretion problems often offset by hypoglycemia tendency
      • Hypoglycemia in neonates = < 30mg/dL
fluid requirements
Fluid Requirements
  • Neonate TBWC = 70-75% (adult=50-60%)
  • Maintenance (4,2,1 RULE)
    • 4mL/kg/hr for 1st 10 kg of wt, 2mL/kg/hr for 2nd 10kg of wt, 1mL/kg/hr for reminder kgs of wt
    • D5 ½ NS (with KCl 20 meq/L)
    • D5 ¼ NS may be better
  • Watch for:
    • prominent veins, flushed skin, ↓ Na+ , loss of eyelid folds
  • Deficits
    • Replace 50% of Deficit during1st hr, 25% 2nd hr, 25% 3rd hr
    • ½ NS or lactated Ringer’s
blood loss replacement
Blood Loss Replacement
  • Blood loss
    • blood volume: 100ml/kg in premmies, 80-90 ml/kg at full term, Hct 55% falling to 30% at 3 months, 76% HgbF at birth, 100 HgbA by 6 months
    • crystalloid 3:1 replacement
    • colloid 1:1 replacement
    • continue until lower limit reached
      • Sick neonates and premmies Hct ~ 40-50%
third space loss
Third Space Loss
  • 2 mL/kg/hr
    • atraumatic surgery
  • 6-10 mL/kg/hr
    • traumatic surgery
total fluid replacement
Total Fluid Replacement
  • Preoperative fluid deficit, plus
  • Maintenance fluid, plus
  • Blood loss, plus
  • Third space loss
  • ? other losses
recent uris
Recent URIs
  • “runny nose”
    • ? infectious process, ? allergic rhinitis
    • Viral infections within 2-4 weeks of GETA = ↑ risk wheezing, hypoxemia, atelectasis, laryngospasm
premeds
Premeds
  • Quick estimate of weight
    • 50th percentile wt (kg) = (agex2) + 9
  • Probably no sedation for neonates
    • except cardiac surgery where MS 0.1 mg/kg may be helpful
  • Versed (0.5-1.0mg/kg PO)
  • Chloral hydrate (Notec) 65-100mg/kg PO/PR
  • Ped PO cocktail
    • Versed 0.5mg/kg, Ketamine 5mg/kg, Glyco 0.02mg/kg for drying
  • Ped IM cocktail
    • Versed 0.01mg/kg, Ketamine 3mg/kg, Glyco 0.01mg/kg drying
nonvolatile anesthetics
Nonvolatile Anesthetics
  • Barbiturates & Opioids more potent in neonates than adults
    • Possible easier entry across BBB
    • Dec metabolic capability
    • Inc sensitivity of Resp Center
  • MSO4 should be used with caution (if at all) in neonates b/c hepatic conjugation is reduced & renal clearance of MSO4 metabolites is decreased
  • More resistance to ketamine
  • Cytochrome p-450 pathway is mature at 1 month
  • Propofol drip higher than adults
    • (150-250mcg/kg/min) high Vd & inc Clearance
induction
Induction
  • Inhalation
    • Sevoflurane often preferred
    • Start with 70% N2O & 30% O2
    • Begin VAA, ↑ by 0.5% q3-5 breaths
  • IV (do not attempt IV until pedi is well anesthetized via mask induction or  laryngospasm
    • thiopental 3 mg/kg (neonates)
    • Muscle relaxant if needed (more susceptible than adults to cardiac arrhythmias, hyperkalemia, rhabdomyolysis, masseter spasm & MH aftes SUX.) If cardiac arrest after SUX takes place, assume hyperkalemia and Tx as such
  • IM
    • ketamine 5-10 mg/kg
two interesting scenarios
Two Interesting Scenarios
  • Retinopathy of Prematurity (ROP) deserves special attention. ROP is a fibrovascular proliferation overlying the retina. O2 administration should be monitored with pulse Ox or transcutaneous O2 analysis (especially infants younger than 44wks postconception)
  • Scoliosis pt due to Muscular dystrophy are predisposed to MH, cardiac dysrhythmias, & untoward effects of SUX (↑K, myoglobinuria, sustained muscular contractures)
emergence
Emergence
  • Spontaneous ventilation, adequate Vt & rate
  • Reversal of residual muscle paralysis
  • Deep vs. awake extubation?? to avoid laryngospasm
  • “Purposeful movements” (eg. reaching for ETT) is key phrase for assessing readiness for extubation on pedi since they DO NOT FOLLOW COMMANDS!!
  • If Pedi/Neo ICU are far away, carry emergency intubation equipment for reintubation readiness
  • Postintubation croup (1-4yr) is associated with repeated intubation attempts, large ETT, prolonged Sx, head/neck Sx, excessive movement of ETT