Week 6 - Neonatal Anesthesia Flashcards
What are the classifications of Premature Infants?
Premature Infant = born before 37 weeks gestation
Moderate-Late Prematurity = 32-37 weeks
Very Premature = 28-<32 weeks
Extremely Premature = <28 weeks
Define:
- Gestational Age
- Chronological Age
- Postmenstrual Age
- Corrected Age
- Post Conceptual Age
-Gestational Age: weeks between 1st day of LMP, and
day of delivery
-Chronological Age: Time since birth
-Postmenstrual Age: Gestational Age + Chronological Age
-Corrected Age: Chronological Age reduced by the number of weeks born before 40 weeks gestation
-Post Conceptual Age: Time between conception and delivery (incorrect, should not be used)
Describe Fetal Circulation
– Relies on placenta for O2 and CO2 transport
– High pulmonary vascular resistance (deflated atelectatic lungs, hypoxic vasoconstriction)
– Low systemic circulatory resistance (high flow, low impedance of placental vessels)
– Extracardiac Shunts: Ductus Arteriosus (DA), Ductus Venosus (DV)
– Intracardiac Shunt: Foramen Ovale (FO)
Explain the transitional circulation of blood from from fetal to adult
- End of placental blood flow = Increase in aortic pressure
- Clamping umbilical vein = Doubles SVR
- Lungs Expand = Decrease PVR
- Increase in partial pressure of arterial O2 = Decrease in PVR
- Decrease in RA pressure + Increase in LA pressure = functional closure of the FO
- DA closes due to increase in SVR & decrease in PVR (kept open by prostaglandins)
- DV closure mechanism unknown
What factors maintain fetal circulation?
Anything that increases PVR: hypoxia, hypercarbia, acidosis, hypothermia
- May cause circulation to revert back to deoxygenated blood being shunted from right to left via PFO or PDA
- This explains why some babies are hypoxic despite adequate ventilation with 100% FiO2
How does the neonatal CV system differ from an adult?
- Fewer muscle cells, more connective tissue, fewer and unorganized myofibrils
- Immature contractile components (sarcoplasmic reticulum and T-tubule network)
- Neonate myocardium relies on free calcium for contractility — decreasing extracellular ionized calcium (citrate in PRBC, and albumin) decreases contractility!! (replace calcium frequently)
What is persistent pulmonary hypertension in neonates? What is its causes and treatment?
Failure of PVR to decrease at birth
-results in maintained right to left flow via PFO or PDA
Possible Causes: meconium aspiration, sepsis, asphyxia, increased muscularization of PA vessels, impaired endothelial nitric oxide release
Treatment: PEEP, exogenous serfactant, iNO, phosphodiesterase-5 inhibitor, inhaled prostaglandin-I2, endothelium receptor antagonists
What is the airway anatomy of a neonate?
Cephalad larynx at C3-4 (adults are C4-5)
Hyoid bone at C2-3
Base of tongue more superior to larynx = more acute angle between tongue and glottic opening
Epiglottis is narrow, omega shaped
**makes airway visualization more difficult
Immature lungs predispose neonates to what?
Alveolar Collapse and Hypoxia
- type II pneumocytes produce surfactant at 22-26 weeks and peaks at 35-36 weeks
- high risk of mechanical lung injury – nasal CPAP, high flow, ETT all common in NICU setting
What can apnea in the neonate lead to?
Bradycardia – heart rate 80 bpm or below
*usually at beginning of apnea spell –> then SpO2 falls (can be big trouble)
What is Bronchopulmonary Dysplasia?
Need for oxygen 28 postnatal days
- alveolarization begins at 36 weeks – prematurity interrupts this process = few, but large alveoli
- low surface area for gas exchange
- can lead to pulmonary hypertension, RV hypertrophy
- anesthetic goals: low FiO2, small TV, SpO2 90-94%
How can you help prevent intraventricular hemorrhage in neonates?
Avoid hypercarbia, hypoglycemia, hypothermia, rapid increases in BP
What is the renal function and considerations in neonates?
Full-term infants on have 30% of normal GFR
- renal excretion of antibiotics and NMBD is prolonged = increased duration of action, high blood concentrations
- interval between doses of antibiotics should be increased
- hyponatremia: neonates are obligate sodium excreters, very prone to hyponatremia
What are some liver function considerations in the neonate?
-Fetal liver can synthesize glycogen (98% of it is
used during first 48 hours) — Neonates at high risk of hypoglycemia
-Albumin levels are low = less ability to bind drugs to plasma proteins = increase in free drug
-Liver enzyme production low = low metabolism
-Hyperbilirubinemia common in term infants (Physiologic vs. Pathologic)
-7 days for clotting factors to reach adult levels (Vitamin K commonly given at birth)
What are GI considerations with the neonate?
- Fetal GI function develops late in gestation (intestinal motility increases 29-32 weeks)
- Prolonged gastric emptying, lower esophageal sphincters are incompetent
What is Necrotizing Enterocolitis?
Bowel necrosis due to harmful bacteria in a slow moving intestine that has little GI immune defenses
Early Signs are non-specific (temp instability, poor feeding, lethargy, apnea, bradycardia)
Late Signs = tachycardia, hypotension, metabolic acidosis, thrombocytopenia, peritonitis
What does anemia in a neonate increase the risk of?
Apnea
Intraparenchymal Brain Hemorrhage
Periventricular Leukomalacia
How are pharmacokinetics different in the neonate?
Cardiac output = 4x faster in neonate –> rapid IV drug onset, rapid metabolism (if liver/kidney function has matured)
Increased total body water and ECF –> water soluble drug dose is higher but can stay in CNS longer due to reduced redistribution
Decreased protein –> less binding sites = greater free drug
Decreased renal excretion due to decreased GFR and tubular function
Why is a neonates response to NDMRs unpredictable?
Neonates can be resistant to muscle relaxants: nAchR remains open longer after binding Ach
Neonates can also be sensitive to NDMRs due to
reduction in Ach release at NMJ
*Sugammadex use is controversial in neonates/small children
What inhalation anesthetics are use in neonates?
Sevoflurane and Isoflurane are most common
-Sevo = rapid induction and emergence
- Des is contraindicated due to being an airway irritant – not recommended for infants with BPD
- N2O not routinely used in neonates – reduces FiO2
Why are neonates very sensitive to the myocardial depression caused by inhalation anesthetics?
Because inhalational anesthetics block calcium channels and neonatal hearts depend on ionized calcium for contractility
**Induce Neonates SLOWLY
How does the MAC level change in the neonate?
Decreases in neonates <32 weeks gestation — Peaks at 30 days age — Then decreases again
What are the neonatal dosages for Fentanyl, Morphine, Remifentanil, Hydromorphone?
Fentanyl: 2-10 mcg/kg (half life prolonged, creates hemodynamic stability during surgery but increases risk of postop apnea)
Morphine (most popular): 0.05-0.2 mg/kg (prolonged half life – decreased renal function = risk of active metabolite)
Remifentanil: 0.05-0.1 mcg/kg/min (used in infants for its rapid clearance - NOT common choice)
Hydromorphone = not common to give to neonate population
What is the neonatal dose of ketamine?
0.25-3 mg/kg — VERY popular in pediatrics
- provides analgesia, amnesia, and unconsciousness
- causes increased secretions (use glycopyrrolate)
- minimal cardiac depressant
*can still depress ventilation and airway reflexes (apnea)
What are considerations of benzodiazepine use in neonates?
Increased duration due to liver immaturity
Respiratory depression and severe hypotension can occur after bolus administration
What are considerations of Propofol use in neonates?
- Used with caution in neonates, may cause significant hypotension, low cardiac output
- Delayed clearance and recovery in neonate
- Many providers avoid its use in very preterm infants (29-32 weeks due to hypotension)
- Reports exist of cardio respiratory collapse in neonates after single induction dose
- Not routinely used for prolonged infusions such as ICU setting (propofol infusion syndrome)
*Common to use in sedation of full-term infants for
diagnostic scans/procedures — 1-3 mg/kg
What are the neonatal dosages of Acetaminophen?
PO: 10-15 mg/kg (given preop – not common to give in neonate prior to anesthesia)
PR: 35-40 mg/kg for 1st dose 20mg/kg Q6H for 24 hours (give after induction)
IV (Ofirmev): dosing is based on child’s size
Max Dose = 75 mg/kg per day
What is Choanal Atresia?
Nasobuccal membrane blocks communication between nasal cavity and nasopharynx
Oral airway usually needed after induction
*associated with CHARGE syndrome
What conditions (diseases) cause laryngeal and upper tracheal obstruction in neonates?
Webs: membranes that partially or completely cover larynx or trachea
Subglottic Stenosis: most common need for neonatal tracheostomy
What is Subglottic Hemangioma?
most common vascular tumor in infants
- related to PHACES syndrome
- medical therapy attempted first (propranolol - bradycardia/hypotension)
- surgical therapy
What are anesthetic considerations in neonatal airway surgery?
- Patients may be slowly induced with Sevofluane if no IV present, but always kept spontaneously breathing (IV placed prior to induction if airway compromise expected)
- Prior to surgical intervention – anesthetic transitioned to TIVA with possible agents: propofol, dexmedetomidine, ketamine, remifentanil
- Glycopyrrolate usually given early in anesthetic
- Specific combination of anesthetic very provider dependent – NARROW margin of error in keeping patient spontaneously breathing, adequately anesthetized, yet NOT apneic
What are preoperative anesthetic considerations for Tracheoesophageal Fistula/Esophageal Atresia surgery in neonates?
-Usually babies can be optimized: IV access, labs
(including type and screen), correct anemia and electrolyte imbalances, evaluate for congenital anomalies, echo (?!)
-Know what type of defect exists!! – Preop imaging, rigid bronchoscopy while spontaneous breathing immediately prior to surgical correction to view fistula
-Special Equipment: Fiberoptic scope at appropriate size, CMAC with appropriate blade
-In-depth discussion of anesthetic plan with all members of care team may be necessary
What are intraoperative anesthetic considerations for Tracheoesophageal Fistula/Esophageal Atresia surgery in neonates?
- Mostly done via thoracoscopy, with lung isolation not necessary – tip of ETT placed above carina, but distal to the fistula. (Purposely right-main stem, then withdraw ETT until bilateral breath sounds heard) - Verify with fiber optic
- Usually baby kept spontaneously breathing until fistula is isolated & ligated – if stomach becomes inflated, surgeon may have to needle decompress
- Gastrostomy may be performed – allow for Fogarty catheter to be placed through stomach to occlude fistula from below
What are anesthetic considerations for congenital diaphragmatic hernia repair in a neonate?
Neonates are stabilized prior to surgical intervention: including jet ventilation, measures to reduce PVR, iNO, and ECMO
NG should always be in place
Small TV (high RR), limited peak inspiration pressures, NO, N2O, may need 1 lung ventilation
What are anesthetic considerations for congenital bronchogenic and pulmonary cysts in neonates?
- Anesthetic planned around location of cyst
- May require spontaneous respiration during intubation or bronchial blocker in case of cyst rupture (so contents don’t fall into lung tissue)
*rupture may cause hemorrhage or bronchopulmonary fistula formation
What are anesthetic considerations for congenital lobar emphysema in neonates?
- No N2O
- If positive pressure is needed, low peak airway pressures/IVs
- Single lung ventilation may be needed
- Epidural catheter threaded up from caudal space may be useful for pain control
What are anesthetic considerations for hypertrophic pyloric stenosis in neonates?
Considered FULL STOMACH – empty the stomach with OG placed in various positions prior while awake, then modified RSI
No opioid used - only LA and acetaminophen
What are anesthetic considerations for omphalocele and gastroschisis?
Continue volume resuscitation
Prevent hypothermia
What are anesthetic considerations for NEC?
Huge volume losses: need large IV access – hopefully time for CVC
-albumin 5%, massive transfusion
Hyperkalemia and renal failure common
Inotropic support usually needed (epi, dopamine, milrinone)
What are anesthetic considerations for myelomeningocele in neonates?
- Usually patient can be induced supine with donut padding around defect – (may have to be lateral if very large defect)
- Prepare for transfusion, may not be needed
- Large IV access critical (anticipate possibility of large blood loss)
- Usually extubate to ICU afterward
- Treat as latex allergy as increased sensitivity has been reported with this diagnosis
- +/- muscle relaxants: discuss with surgical team prior to administration
What do you need to set up airway supplies for neonates?
- ETT sizes 2.0 to 3.5 (size 2.0 and 2.5 are uncuffed, micropremie)
- Miller 0 (nice to have CMAC)
- Neonatal circuit with neonatal HME
- Size 1 or 2 mask
- Shoulder roll
- Percordial or Esophageal stethoscope
How do you calculate minimal allowable blood loss (MABL) in neonates?
EBV x (Child’s Hct - Minimum acceptable Hct) / Child’s Hct
How do you calculate the volume of PRBCs in a neonate?
(Desired Hct - Present Hct) x EBV (70mL/kg x 10kg) / Hct of PRBCs
What is the blood volume of a preterm infant, term infant, and 3 months to 1 year old?
Preterm = 90-100 mL/kg
Term = 80-90 mL/kg
3 months - 1 year = 70-80 mL/kg
*preterm neonates can be up to 90% water – term neonate 75%
What questions should you ask during preop exam for a neonate?
- Gestational Age
- Any known prenatal concerns (including no prenatal care)
- Any maternal factors that would influence baby (gestational diabetes, hypertension, drug abuse)
- Any suspected syndromes or anomalies
- Is patient being fed (NPO guidelines still apply) – If not, how are they receiving glucose (and other nutrients)
- Any apnea/brady (sometimes documented as “spells” by NICU)
- Airway and Oxygen use
- Any existing IV access – Labs!
- Consent can be tricky and time consuming
