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57 Cards in this Set

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What parts of the lung are developing during weeks 6-17?

Conducting zones (1-17)


-entire air collecting bronchial tree


-terminal bronchioles


-(pseudoglandular period)

What parts of the lung are developing during weeks 17-24?

Respiratory zone (17-23)


-respiratory bronchioles


-capillaries adjacent to respiratory bronchioles


-lung becomes more vascular


-(canalicular period)

At _____ weeks, _____ pneumocytes begin to produce surfactant.

24 weeks


Type II pneumocytesproduce surfactant

What occurs during the period from 24 weeks to term?

Alveoli form


-type II pneumocytes produce surfactant


-rapid proliferation of capillaries around alveoli


-alveoli develop from sacules (week 32-36)


-alveolar (terminal sac) period

During the post-natal period alveoli increase in number until _____ years of age




Alveoli grow in size until when?

Alveoli increase in number until 8 years of age




Alveoli increase in size until chest wall growth ceases (adolescence)

Full term newborns have _______ alveoli




Adults have _________ alveoli

Newborns = 25 million alveoli




Adults = 300 million alveoli

How do airways (bronchioles and bronchi) grow during childhood.

Increase in length and diameter

How much do fluid do fetal lungs produce?



What is this fluid called?

50-150 mL/kg/day




Ultrafiltrate

What is the purpose of the alveolar fluid?

Expands airways and helps stimulate lung growth.




Expelled from lungs making up 1/3 of amniotic fluid

At any given time the fetal lung contains how much fluid?

30 mL/kg




(up to 2/3 expelled during birthing process)

What triggers initial neonatal breaths?

-touch, temperature, environment


-respiratory/metabolic acidosis

How is fluid expelled from lungs



-2/3 expelled during vaginal birth


-initial breaths generate negative pressures (-40 to -60 cm H2O)


-overcomes high surface tension


-air fills lungs/fluid expelled from upper airways


-residual fluid absorbed by pulmonary lymphatics

Delayed removal of residual fluid in lungs can lead to ________-

transient tachypnea of the newborn


(24-72 hours)

_______________ initiates rhythmic breathing

clamping of umbilical cord



____________ during air breathing augments continual rhythmic breathing?




What is the consequences of this?

Relative "hyperoxia" maintains breathing.




Therefore, hypoxia depresses/abolishes continual breathing

How does neonatal CO2 compare to that of older children/adults?

Lower - usually around 28 mmHg.




-Due to poor buffering capacity in neonates


-Compensates for metabolic acidosis at birth

An adequate amount of _________ is necessary for smooth transition to air breathing

Surfactant

What is the consequence of inadequate surfactant levels?

-collapse of alveoli


-maldistribution of ventilation


-impaired gas exchange


-poor lung compliance


-increased work of breathing


-Infant Respiratry Distress Syndrome (IRDS)

The infant chest wall is highly ____________




Why?


What are the consequences of this?

Highly Compliant


-ribs extend horizontally/provide minimal assistance in chest wall expansion


-floppy chest wall




Consequences


-limited ability to increase tidal volumes


-collapse inward during inspiration (paridoxical breathing)

When is paridoxical breathing seen in?


-Premature neonates


-Term neonates


-Infants/children

Preemies = always




Term = during REM sleep




Infants/children = during exertion

What role do the intercostal muscles play in neonatal respiration?

Play an active role due to highly compliant chest wall.

Describe the composition in neonatal and infant intercostal muscles

Deficient in TYPE I muscle fibers


-until 2 months of age


-prone to ventilatory failure during inc. WOB


-intercostal muscles depressed under GA


(leads to paradoxical breathing)

________________ is the primary ventilatory muscle during infancy

The diaphragm

Compare the neonatal diaphragm to the adult diaphragm

Sits high in thorax


Deficient in TYPE I muscle fiber


-prone to fatigue

Where are the central chemoreceptors located?

Ventrolateral medulla

Describe how the central chemoreceptors function.

Indirect response to CO2


-respond to increase H+ in CSF


-increase Vt and RR


-response directly related to age

Describe how the peripheral chemoreceptors in infants function.

React rapidly to changes in PaO2 and pH

-most responsive to PaO2 < 60 mmHg


-will lead to significant increase in ventilation



Where are the peripheral chemoreceptors located?

Carotid bodies and aortic arch

Describe the neonatal response to hypoxia

Transient increase in ventilation (short)


-Quickly causes sustained ventillatory depression




*automatic ventilatory depression in response to hypoxia for premature infants



Describe the effects of hypothermia, acidosis, and hypercarbia on the response of a premature infant to hypoxia.

Immediate and profound respiratory depression

Describe the Hering-Breuer reflex in neonates

A protective reflex that induces apnea in response to significant lung inflation.


-stretch receptors on bronchial smooth muscle


-reflex inhibition of respiration


-Strong/physiologically relevant in neonates

What is periodic breathing?

Recurrent pauses (apneic spells) lasting 5-10 seconds (without desaturation/cyanosis)

What is the incidence of periodic breathing in infants?

93% of premature neonates


78% of full-term neonates

What is central (clinical) apnea of infancy?

Unexplained apnea lasting > 15 seconds


-or-


Any apnea with


-bradycardia (HR < 100)


-cyanosis


-pallor


-loss of muscle tone

What is the incidence of central clincal apnea?

Rare in term neonates




Up to 55% of premies

Treatment for central clinical apnea of infancy

Terminated by tactile stimulation/BVM


-Theophylline


-Caffiene


-PEEP

Major risk factors for post-operative apnea

Prematurity (< 55 weeks post-conception)




Previous history of central clinical apnea

Patients at risk for post-operative apnea should be monitored for __________ hours

24 hours


Neonates are obligate ________ breathers

Nasal (until 3-5 months)

Describe five features of the neonatal airway

Large tongue (obstructs)


Stiff/U shaped epiglottis


Laryx = cephalad, anterior


Large arytenoids


Slanted vocal cords



What is the distance from cords to carina for:


-neonates


-1 year old

3-5 cm


5-9 cm

The narrowest portion of the airway is ________________

The cricoid ring

Diameter of newborn trachea

4 cm

Compare neonatal and adult alveolar ventilation

Neonate = 130 mL/kg/min




Adult = 60 mL/kg/min

Compare neonatal and adult respiratory rate

Neonate = 35/min




Adult = 15/min

Compare neonatal and adult tidal volume

The same (about 6 mL/kg/min)

Compare oxygen consumption for:


-premies


-infants


-adults

9 mL/kg/min


6 mL/kg/min


3 mL/kg/mg

What is the clinical implication of neonates consuming TWICE as much oxygen/kg/min as an adult?

Rapid desaturation during periods of apnea

Neonates increase alveolar ventilation by increasing ____________

respiratory rate

Respiratory rates


-neonate


-infant


-toddler


-preschooler


-school age


-adolescent

Neonate = 30-50


Infant = 20-40


Toddler = 20-35


Preschooler = 20-30


School age = 16-25


Adolescent = 14-20

Functional Residual Capacity (Adults vs Infant)




* what are the consequences of this?

Infant = 30 mL/kg


Adult = 34 mL/kg




*More rapid inhalation induction/emergence


** more rapid de-saturation

Compare TLC (Adults vs infant)

Infant - 63 mL/kg


Adult - 82 mL/kg




*diaphragm & inspiratory muscles under-developed

Closing volumes infants vs. adults

Infants = falls within normal tidal volume



*Airway closure occurs during normal tidal breathing leads to V/Q mismatch




-neonates prone to atelectasis/hypoxia

P50 for HbF

17 mmHg




(HbA = 26 mmHg)

HbF releases O2 less readily at the tissues. What adaptations does a neonate have that allow for adequate oxygenation?

Hbg = 17-18 mg/dL at birth

Fetal hemoglobin is shifted ________

left

What is the Hb composition at birth?

80% HbF


20% HbA