Week 4 - Pediatric Physiology and Development Flashcards
What happens with the cardiovascular system at birth?
First breath –> decrease in pulmonary vascular resistance –> increases pulmonary blood flow –> increasing LV preload
Constriction of umbilical vessels increases SVR –> functional closure of the foramen ovale (increase in LA pressure greater than RA pressure closes flap over foramen ovale)
PaO2 increases –> decrease in prostaglandins –> constriction of Ductus Arteriosus
What will cause reversion back to fetal blood flow?
Conditions of stress (decrease PaO2, increase CO2, decrease pH, lung collapse, septic mediators (LT, TXA, PAF))
Causes contraction of smooth muscles of pulmonary vasculature –> increase in PVR –> right to left shunt via PDA, PFO bypassing the lungs –> desaturation
*must overcome R–>L shunt to reperfuse
How is cardiac output different in infants?
They have relatively fixed stroke volume so cardiac output is heart rate dependent
*Frank-Starling curve – lower ability to augment CO at any LVEDP
What is the effect of maturation of SNS innervation later than PSN innervation in infants?
PNS predominates while the SNS is still developing in infants
This imbalance can be seen as marked bradycardia or even asystole (during laryngoscopy, orogastric tube placement, tracheal suctioning)
What occurs with the pulmonary vasculature at birth?
Low number of thick media walled arterioles (causes high PVR) – 20:1 ratio of Alveoli to artery (adult ratio is 6:1)
Maturation to many thinner arterioles and continue to remodel as they age - lowering PVR
PVR reaches adult levels by 6 months under normal conditions (unless exposed to chronic stress conditions, ie. hypoxemia or volume overload)
What increases PVR in infants? **
- PEEP
- High airway pressures
- Atelectasis
- Low FiO2
- Respiratory and metabolic acidosis
- Increased hematocrit
- Sympathetic stimulation
- Direct surgical manipulation
- Vasoconstrictors (ie. phenylephrine)
What decreases PVR in infants? *****
- No PEEP
- Low airway pressures
- Lung expansion to FRC
- High FiO2
- Respiratory and metabolic alkalosis
- Low hematocrit
- Blunted stress response (deep anesthesia)
- Nitric oxide (vasodilates only pulmonary arterioles that are perfused)
- Vasodilators (ie. milrinone, prostacyclin, others)
What are vascular access options in neonates?
PIV, a-line, central line, IO – can be difficult
Cannulation of umbilical vessels (up to 20 days post partum) is relatively easy
-proper catheter position reduces serious complications such as arterial thrombosis w/ organ ischemia, vasospasm, portal vein thrombosis, pulmonary infarction
What is the proper placement of an umbilical vein catheter (UVC) and an umbilical artery catheter (UAC)?
UVC = tip at the IVC-right atrium junction
UAC = tip at either L3-5 or T7-9
What is the most common cause of neonatal bradycardia?
Hypoxia
How is the lung water removed during birth of the neonate?
Squeezing through birth canal
Lymphatics
Absorption into pulmonary vasculature
*high negative inspiratory pressure with first breaths – 1% pulmonary air leak
How is pediatric lung tissue and compliance different than an adult?
- Pliable rib cage due to lots of cartilage — intercostal indrawing
- Decreased compliance of lung parenchyma
- Abdominal breathing
- Horizontal ribs
- High diaphragm
- High chest wall compliance
- Low lung tissue compliance
Describe how the infant’s body shape affects their respiratory system
They have a large abdomen which causes cephalad displacement of the diaphragm
- the closing capacity of the alveoli is near the FRC
- overcome this by auto PEEP (airway resistance, partial closure of the vocal cords, inspiratory muscles during expiration)
Why are infants respiratory rates so high?
Their metabolic demands are so high
-O2 consumption in neonates is 2x that of an adult –> Minute ventilation is very high –> Minute ventilation is the product of RR and tidal volume –> tidal volume is equal between neonate and adult thus RR is the only factor that can be augmented
What respiratory parameters are increased in infants compared to adults? Which are decreased?
Increased:
- O2 consumption (I: 5-8; A: 2-3)
- Respiratory Rate (I: 40-60; A: 12)
- Minute Ventilation
Decreased:
- Total Lung Capacity (I: 53mL/kg; A: 85mL/kg)
- Airway Diameter (I: 5mm; A: 14-16mm)
- Trachea/Bronchus/Bronchiole
*Tidal Volume is equal (I: 6-8mL/kg/min; A: 7mL/kg/min)
Describe the anatomy of an infant airway
Nasal Breathing
Large Tongue
Epiglottis = large, floppy, Ω-shape
Cephalad Larynx (Level C3) – funnel shaped larynx
“Anterior” airway
Narrowest point is the cricoid level (up for debate)
