Neonatal Anesthesia Flashcards
Children < 1 year have higher incidence of complications than older children often related to
Ooxygenation, ventilation, airway management, and response to anesthetic agents and medications
The transition from fetal to neonatal physiology takes place during the first __-__ hours of life
24-72.
First 72 hrs the most important for cardiac, pulmonary, and renal systems.
A premature infant is born less than ___ weeks gestation
37
A postmature infant is born over ___ weeks gestation
42
Growth and development is massive in the first year of life. Body weight alone will increase by a factor of
3
Importance of catecholamines at birth
- Helps them prepare for birth, adapt to extrauterine life, and cope with hypoxia
- Animals deprived of a catecholamine surge at birth less likely to survive hypoxia
- Catecholamines aid in the clearance of liquid from the lungs, which improves lung compliance after birth
- Are important for the release of surface-active material from alveolar type II cells
- During asphyxia, catecholamines maintain cardiac output and redistribute blood flow from the periphery to the heart, brain, and adrenal glands
- They also increase arterial blood pressure and slow the heart rate, which reduces myocardial oxygen consumption
- Infants delivered by cesarean section without maternal labor have lower blood glucose concentrations and less blood flow to peripheral organs than after vaginal delivery and is related to plasma catecholamine concentrations
- Neonates with elevated catecholamine concentrations have higher Apgar scores than those who have low concentrations
- Catecholamines help to redistribute CO. Causes preferential redistribution to brain, heart, etc.
Immediate physiologic changes at birth
- Cessation of umbilical circulation
- Initiation of ventilation/lung expansion
- Stress and associated catecholamines
Fetal circulation
Fetal Circulation:
Oxygenated blood comes from placenta through the umbilical vein to IVC to Right Atrium
In RA, about 40% of this oxygenated blood mixes with desaturated blood returning from the upper body/head via the SVC. Then goes through the Right Ventricle and into the PA. Only 5-10% of this goes to the fetal lungs since PVR is HIGH. The rest is shunted through the DUCTUS ARTERIOSUS to the descending aorta
The remaining 60% of oxygenated blood that came from the placenta is shunted through the FORAMEN OVALE to the LA the LV and the ascending Aorta
Based on this, overall 60% of oxygenated blood goes to the upper body and 40% goes to the lower body.
Why is the pressure so high in the fetal pulmonary circulation?
1) Low pH promotes vasoconstriction
2) Low PaO2 promotes vasoconstriction
3) The alveoli are full of fluid, which compresses the blood vessels
The ductus arteriosus is dilated by
Low O2.
This is why it is open during fetal life, and closes once the lungs start functioning and the newborn experiences higher O2 concentrations.
Permanent closure of the foramen ovale occurs
after a few months.
However, 10-20% of the population will never have a truly anatomically closed FO.
True fibrotic closure of the ductus arteriosus doesn’t occur until
2-3 weeks of age
It can take longer if the child was born premature
What causes the ductus venosus to close?
Drop in portal pressure due to removal of the placenta
PVR decreases dramatically at birth due to
lung expansion, breathing, increased pH, and the increase in alveolar oxygen tension that occurs at birth
These factors can increase PVR
Hypoxia, acidosis, hypovolemia, hypoventilation, atelectasis, and cold increase PVR
Fetal circulation can be re-established if these factors occur during the first 2 weeks of life
Hypoxia, hypothermia, or acidosis
Why is hydration important in keeping normal circulation?
Because dehydration would drop the SVR and re-establish fetal circulation
Closure of the ductus arteriosus
Functional closure: within 1-2 days after birth.
–> O2(most important), catecholamines, and PSNS activation all encourage functional closure.
Anatomical closure: In 10-14 days in healthy neonate (up to several months in premature infants) the ductus arteriosus is replaced by connective tissue and is known as the ligamentum arteriosum.
How can we prevent the patient from reverting to fetal circulation?
Keep the patient warm, hydrated, normal PaO2, PaCO2, minimize myocardial depression related to anesthetic agents, maintain SVR*****
Myocardial depression will also cause BP to drop.
A baby’s first breath requires
40-60 cmH2O negative intrathoracic pressure.
Thus, if we have to ventilate, it’s a better idea to do so by intubating than mask ventilating
Surfactant production in the fetus and its importance in the newborn
Surface active material important for normal lung function. By 20 weeks’ gestation it is present within the alveolar lining cells,and by 28-32 weeks gestation, is present within airway lumens. Significant amounts don’t appear in terminal airways until 34-38 weeks gestation, unless SAM production and release stimulated by stress or steroids.
Administration of SAM decreases the incidence of hyaline membrane disease and the incidence of serious cardiopulmonary complications. Giving SAM at birth reduces the inflammatory response to mechanical ventilation and improves lung function.
Stimulation for breathing immediately after birth
. Stimulation of the respiratory centers by mild acidosis, hypercarbia, hypoxia, pain, cold, touch, noise, and clamping of the umbilical cord initiates and sustains rhythmic respiration. Severe acidosis, hypoxia, CNS damage, and maternal drugs (e.g., narcotics, barbiturates, local anesthetics, magnesium, alcohol) depress breathing. A few minutes after birth, the respiratory rate is 30 to 60 bpm - removes the increased CO2 produced by the high oxygen consumption of the neonate (about 6 mL/kg/min) and helps maintain a normal FRC by not allowing sufficient time for the FRC to be expired.
Normal FRC and ABG values are obtained within __ minutes after birth
10-20 minutes
Normal TV and MV are established within __ minutes after birth
5-10 minutes
Immediately after birth, it is normal to see sats in the ____
and PaO2 in the _____
Sats 20s-30s%
PaO2 40s-50s
How do babies establish their FRC?
By not fully exhaling. They breath in more than they exhale. This helps to establish FRC. Also their rapid RR doesn’t allow enough time for full exhalation, resulting in the buildup of FRC.
RBF and GFR in the fetus
Minimal d/t
1) Low SVR
2) High renal vascular resistance
3) Lower permeability of capillaries in the glomerulus
4) The glomeruli present are few and small
GFR will double in the first 2 weeks of life and reaches adult values in 2 years.
At 1 month of age, the kidneys are __% mature
60%
Be careful giving drugs that rely on renal excretion for termination of effect
Is fetal urine output important for removing waste?
No, the placenta does this
Proper laryngoscopy of the newborn
Head neutral- “sniffing” position during bag-&-mask ventilation & intubation. Extension can cause the airway to be very anterior.
Laryngoscope held with thumb and index finger & chin grasped with ring and middle fingers of left hand. This allows the head and hand to become a single unit, reducing the likelihood of lacerations if the neonate moves.
Pressure applied over hyoid bone with small finger of the left hand (moves the larynx posteriorly and exposes the VC).
ETT tip of the tube placed 1- 2 cm below the VC and 1-2 cm above carina.
Remember that babies have STRONG vagal presence. Atropine often given prophylactically before DVL to prevent bradydysrhythmias.
EtCO2 monitoring in neonates
Often difficult because proper readings require large TVs.
The combination of low TVs and low pulmonary blood flow in some infants at birth can make EtCO2 readings inaccurate.
LMA size in neonates
Size 1 for 1- 5 kg
Size 1.5 for 5-10kg
Masking vs. intubating neonates
Masking is rare. Large pressures needed, and can cause insufflation of stomach. Usually place ETT with RSI
When do we extubate neonates?
Awake! This helps avoid laryngospasm.
Awake enough when eyes are open, attempts to cry, and grasps at tube.
If a fiberoptic scope is to be used, the ETT must be AT LEAST this size
3.5
Generic NeonatalVentilator Parameters for Neonates
Vt 10ml/kg
RR 20-25 bpm
PIP ~ 20 cmH2O
PEEP 3-5 cmH20
Fluid distribution of neonates vs. infants and young children
Fetus and neonate ECF ~ 40% TBW; ICF ~20% TBW
Infant & young child ICF ~40% TBW, ECF ~20% TBW
The high ECF means they have large fluid shifts and less buffer against dehydration. The ICF usually serves as a reserve to draw on.
These will increase insensible water loss
radiant warmers and phototherapy (jaundice lights)
These will decrease insensible water loss
heated humidifiers and warm air mattresses preserve body heat and reduce insensible water loss
Why do immature babies have more insensible water losses?
The more physically immature the patient, the higher the skin permeability, the ratio of BSA:weight, and the metabolic demand
Daily fluid requirements for the term neonate in the first few days of birth
day 1, 70 mL/kg/24 hours
day 3, 80 mL/kg/24 hours
day 5, 90 mL/kg/24 hours
day 7, 120 mL/kg/24 hours
Slightly higher for a premature infant d/t even thinner skin, BSA ratio, higher ECF%, etc.
Newborns have a lot of extra ECF when born, and it takes a few days for their kidneys to get rid of it. Therefore, they have a smaller fluid requirement during their first week of life.
ECF is comprised of
Plasma volume and interstitial fluid
Newborns are usually started on this type of fluid
10% glucose. This is continued for several days until glucose values are stable.
Started on either 5% or 10% dextrose solutions
Neonates of diabetic mothers or mothers who were given large amounts of glucose right before delivery may be (more/less) prone to hypoglycemia.
More prone to hypoglycemia.
Why are neonates prone to hypoglycemia? What are some s/s of hypoglycemia in neonates?
Neonates have low stores of hepatic glucose and immature gluconeogenesis mechanisms, so they can develop hypoglycemia with fasting.
Symptoms include apnea, cyanosis, respiratory distress, seizures, high-pitch cry, lethargy, limpness, and sweating.
Neonates and IV fluid requirements during surgery
Maintenance 4:2:1 rule – essentially 4ml/kg/hr
Deficit – 50% 1st hr, 25% 2nd hr, 25% 3rd hr
3rd space – 1-15ml/kg/hr depending on procedure
Glucose containing fluids are controversial
A balanced salt solution (LR) for deficits and third-space losses
D5 in 0.45% NS for maintenance requirement (remember, maintenance fluid always has glucose!)
Use a buretrol filled 25-50ml at a time!
Blood product transfusion in neonates
Newborn major surgery, keep Hgb => 10 g/dl
Severe cardiac or pulmonary disease, keep Hgb= >13 g/dl
We want platelets >50,000
Make sure PRBCs are irradiated in the neonate – 6 mo old to prevent graft vs host disease
When ordering blood products for neonates, we order a certain volume, not a certain number of units
Some reasons why pharmacology is different in neonates
1) Body composition –> Body compartments (fat, muscle, water) change with age. Total-body water content is significantly higher in premature than term infants and in term infants than 2-year-olds. Fat and muscle content increases with age.
2) Protein binding – lower
3) Body temperature– fluctuates more and can influence drugs
4) Distribution of cardiac output – higher % going to brain, heart, and lungs
5) Functional maturity of the heart – impairs ability to compensate
6) Maturation of the blood-brain barrier – immature
7) Relative size/maturity of the liver and kidneys
8) Congenital malformations
9) Pre-maturity, Sepsis, CHF, increased intra-abdominal pressure, controlled ventilation, and poor nutrition
10) Larger Vd, causing delayed excretion
11) Immature hepatic and renal function
12) Neonates have a larger distribution of their cardiac output to vessel-rich tissues. Neonates often require a larger initial dose of medication and then have prolonged elimination times
Concerns regarding anesthetics and development
Concerns for anesthetics influencing development only theoretical and only shown in extreme cases in animal studies
Neonates and their larger Vd
TBW content is significantly ↑ in the neonate
1) H20 soluble drugs have larger Vd (sux); larger initial dose to achieve the desired blood level (e.g., most antibiotics, succinylcholine); delayed excretion occurs as well
2) A drug that depends on redistribution into fat for termination of its action will have a longer clinical effect (e.g., thiopental)
3) A drug that redistributes into muscle may have a longer clinical effect (e.g., fentanyl)
Neonates and a balanced technique
The CV system of a premature infant rarely tolerates the cardiovascular depressant effects of volatile anesthetics. Synthetic narcotics (e.g., fentanyl, sufentanil, alfentanil, remifentanil) are usually well tolerated by even critically ill infants. Must be carefully titrated to response – keeping in mind the possibility of narcotic-induced bradycardia and its consequences on cardiac output. Low concentrations of potent inhaled anesthetics can be used with narcotics to provide a way of controlling hemodynamic responses without significantly depressing the myocardium. The relative merits of one anesthetic technique over another are not clear, and the few studies examining this issue are poorly controlled. Narcotics and inhaled anesthetics suppress the hormonal responses to pain.
Preemies and inhalational agents
POORLY TOLERATED BY PREEMIES! Use with extreme caution, and consider a balanced technique (inhaled + opioid)
Term neonates and inhalational agents
With iso, des, and sevo, will see similar drop in SVR as in adults.
N2O –> does cause myocardial depression, but less than in adults. Remember risk of demyelination!
Why do neonates have a faster uptake of inhalational agent and have increased risk of overdose?
Reasons for faster uptake:
1) The ratio of alveolar ventilation to FRC is 5:1 VS 1.5:1 in adult
2) More cardiac output to vessel rich group of organs (heart and brain)
3) Greater CO/kg in general
4) Infant has a lower blood gas partition coefficient for volatile agents
Rapid rise plus immaturity of the heart places the neonate prone to OD
MAC for anesthetic agents in neonates
Sevoflurane: MAC = 3.3% for neonates- fewer hemodynamic changes compared with iso
Desflurane: MAC = 9.2% for neonates
Isoflurane: MAC = 1.6% for neonates – keep in mind need to decrease muscle relaxants when iso used.
