Gregs lecture part 1: development and pharmacology/volatiles
What happens in the first, second, and third trimesters (Developmental)?
1st: Organogenesis – within first 8 weeks of conception.
2nd: Organ function develops
3rd: Infant gains weight via fat and muscle
What types of stressors are there during pregnancy?
drugs, infections, poor nutrition.
Define pre and post maturity
Prematurity: defined as an infant born before 37 weeks gestation.
Postmaturity: Postmature infant is born after 42 weeks gestation
Any infant less than _____g is considered low birth weight.
What equation did greg give us to figure out the weight based on age of the patient?
2 x age (years) + 9 = weight in kilograms
What are the average heights of newborn to 12 year old?
Newborn: 50 cm
1 to 6 mos: 54cm
1-2 years: 75 cm
2-3 years: 86 cm
7 years: 95-110 cm
12 years: 132 –149 cm
What are the average weights of a newborn to 12yr old?
Newborn: 3.5 kg
1 to 6 mos: 4 kg
1-2 year: 10 kg
2-3 year: 13 kg
7 years: 25 kg
12 years: 40 kg
Why do the shunts at birth close?
Baby takes breath, lungs expand, iNO is being released so PVR is decreasing so now blood is going to lungs.
Systolic pressure is higher (vasoconstriction) than pulmonary pressure and mechanically closes the PDA and PFO.
What is transitional circulation?
Transitional Circulation: Stress can lead to return to fetal circulation from adult.
Hypoxia, hypercarbia, anesthesia induced changes in the vascular tone. A rapid downhill spiral may occur and result in severe hypoxemia. Hypoxic events can be prolonged in these infants despite adequate pulmonary ventilation with oxygen.
What are risk factors for resorting to transitional circulation?
pulmonary disease resulting in hypercarbia or hypoxemia
aspiration of meconium hypothermia
congenital heart disease
What is different (besides the shunts) in the pediatric heart?
Less contractile mass & less compliant ventricles
Poor tolerance of increased afterload
Cardiac output dependent on heart rate (Fixed stroke volume so only HR can increase CO)
HR is faster and BP lower
Reduced endogenous calcium stores (our volatiles have ca channel blocking activity)
Underdeveloped compensatory mechanisms
Hypotension without tachycardia
Increases metabolic rate
What is the oxygen consumption in infants, kids, and adults?
5-8 cc/kg/min in newborn
4-6 cc/kg/min in children
3-5 cc/kg/min in adults
What is the oxygen delivery???
CO x arterial O2 content
4-5 times the VO2 regardless patient size
What are the anatomic differences of the pulmonary circulation in peds?
Increased resistance to airflow.
Highly compliant airways.
Poorly supported surrounding structures.
Highly compliant chest wall.Ribs provide little support for lungs.
What is important to remember about the pulmonary system in preemies?
Poorly developed hypoxic and hypercapnic ventilatory drives.
What are the FOUR airway differences in pediatrics vs that of adults
Tongue disproportionately larger in mouth
Larynx is higher in neck (C3/C4)
Narrowest portion is at the cricoid ring
Composition of diaphragm and intercostal muscles changes during the first ________ of life.
The # of type 1 muscle fibers is inversely related to age. Why is this important?
May account in part the ease of inducing respiratory fatigue as WOB increases.
Babies are going to fatigue quicker, esp. at a younger age than older pediatric patients and adults.
What is different about the kidney function in neonates?
Diminished on neonates and preterm infants
Neonates with limited ability to conserve Sodium and concentrate/dilute urine.
Normal GFR after ___year and normal tubular function after ___ years
What does less kidney function put neonates at risk for?
Neonates at risk for hyponatremia, hypocalcemia, and hypoglycemia
Risk for large evaporative water losses
Although functional maturity of infant is incomplete.Infant’s ability to metabolize drugs increases due to...(two things)
(1) increased hepatic blood flow.
(2) the enzyme systems develop and are induced.
The cytochrome P450 system reaches ___% of adult function at birth.
50%; reaches adult level by 1st year
Phase II reactions (conjugation) are impaired in neonates: Why is this important to us as CRNAs?
prolonged drug half lives for morphine and benzodiazepines.
What is the liver function of a preemie?
low glycogen stores
unable to handle large protein loads
tendency toward hypoglycemia, acidemia, and failure to gain weight, with high protein loads.
Prone to coagulopathy
Increased levels of free drug with hypoalbuminemia.
CYP450 is responsible for phase ___ metabolism of lipophilic compounds, but this generalization doesn’t hold true for all lipophilic medications.
The ability of the neonate to metabolize specific drugs is dependent on drug specific cytochromes and enzymes subfamilies.
What is the normal development of the GI system?
Alkalotic ph at first day, normal adult ph by second day of life.
Coordination of swallowing and respiration by 4 to 5 mos
What GI illness is very common in newborns and preemies?
GERD common in newborns and premature infants
GI development problems will usually manifest __ to __ hours after birth.
What are the s/s of upper and lower intestinal problems??
Upper intestinal problems: vomiting, and regurgitation
Lower intestinal problems: failure to pass meconium and distention
Why are infants so prone to hypothermia.
Large ratio of body surface to weight and inability to cope with cold stress.
Increased oxygen consumption and metabolic acidosis.
Premature infants: thin skin and limited fat stores.
Shivering vs. non-shivering (cellular) thermogenesis.
Anesthesia blocks what important piece of thermoregulation in infants?
Anesthetic agents can alter many thermoregulatory mechanisms, particularly nonshivering thermogenesis in neonates (metabolism of brown fat)
Infants may have an increased metabolic rate (without protein catabolism) for up to ____ hours postoperatively
What are some warming methods we can use???
Warm mattress or warm OR (conduction).
Incubator covered with blankets (convection)
Use of double shelled isolette during transport (radiation)
Cover their heads
Warm disinfectant solutions, warm humidified air and inspired gases, plastic wrap around skin (evaporation)
What is different about body composition changing the pharmacology in pedi?
Body composition; total body water content, fat and muscle content increase with age
Infant, most CO is going to vessel rich organs, as you grow bigger more muscle that decreases.
A drug that is water soluble has a larger Vd and usually requires a larger initial dose to achieve the desired blood level. Versed, you can give a lot (relativley) because of the total body water content almost the same dose of the elderly, again, total body water.
What happens w/protein binding as kids age?
What happens w/drugs that are stored in fat or muscle when given to the neonate?
Longer clinical duration of action
Because neonates have less fat a drug that depends on redistribution into fat for termination of its action will have a longer duration of clinical effect. Think thiopental, it won’t redistribute into fat because it’s not there, stays in central compartment longer.
Drug that redistributes into muscle will have longer clinical effect, fentanyl.
What is different about the MAC in pediatrics?
See how MAC values tend to elevate 1st year of age, then decrease as you get older.
So 6M of age, MAC values are at their highest, probably something to do w/fat content.
MAC values are higher in young newborns, preemies than adults
What is the variation in MAC due to?
↑ respiratory rates, ↑ cardiac index, ↑ proportional distribution of CO to vessel rich organs
Other factors: state of hydration, type of circuit, and MAC multiples of vaporizer
What is important to know about the safety margin of the volatiles in peds?
Narrow safety margins between inadequate anesthesia and overdose. (functional immaturity of cardiac muscle and rapid rise in anesthetic levels).
Little tiny lungs that are vessel rich, receive a lot of CO and a heart that has poor endogenous Ca stores is prone to CV collapse from inhaled anesthetics
What is perhaps the most important factor in anesthetic overdose in neonates????
the # of MAC multiples that can be delivered by the vaporizer.MAC multiple is the amount of anesthetic that can be delivered by the vaporizer divided by MAC.
Sevo vs Halothane, which is more effective for inhalation induciton. Which one causes more bronchospasm and laryngospasm?
Effective as Halothane for inhalational induction but slightly more rapid.
No difference in incidence of bronchospasm and laryngospasm with Sevo vs. Halothane. (slighty less coughing)
What does Sevo and Halothane do to TV and RR?? What about HR and BP????
Sevo may produce dose related decrease in tidal volume and respiratory rate. (Halo may increase resp. rate).
Sevo: ↑ HR and ↓SBP (Halo. ↓ HR and ↓ SBP)
Which has higher levels of post-op delirium, sevo or halothane?
Apparently higher levels of postoperative delirium than halothane (difficult to measure, more often in children under 5 years of age)
What type of procedure might Halothane be better than Sevoflurane for?
Risk inadequate anesthesia for bronchoscopy compared to Halothane.
Why don't we use Halothane in pediatric patients w/heart defects?
Profound myocardial depressant effects on neonates and children with congenital heart disease.
What is good vs bad about isoflurane?
Good: Less myocardial depression, preservation of HR, Greater reduction in the cerebral metabolic rate for oxygen than Halothane. (good for maintenance)
Bad: Noxious smell unacceptable for induction. Higher incidence of airway events (laryngospasm and bronchospasm). Higher incidence of hypotension with rapid increase in inspired concentration.
What did greg tell us about desflurane in pediatrics?
~ 50% incidence of layngospasm on induction.
More rapid awakening. ( after Sevo or Halo induction)