APEX Unit 11: Neonatal Anatomy & Physiology

The neonatal period encompasses the first _____ days of life, and infant period lasts from _________.

28 days

29 days to one year

VS of newborn (SBP, DBP, HR, RR)

70/40

HR 140

RR: 40-60

VS 1 year old (SBP, DBP, HR, RR)

95/60

HR 120

RR=40

VS 3 year old (SBP, DBP, HR, RR)

100/65

HR 100

RR 30

VS 12 year old (SBP, DBP, HR, RR)

110/ 70

HR 80

RR 20

Neonates consume _____ as much O2 and produce twice as much carbon dioxide than the adult on a weight-adjusted basis

twice

It's metabolically more efficient to increase the ______ than it is to increase ______

respiratory rate

tidal volume

______ is the primary determinant of cardiac output and systolic pressure, while stroke volume is relatively fixed

heart rate

the non compliant left ventricle is sensitive to _________, so increasing _____ is the best way to support BP

increased afterload

HR

Hypotension in newborn is defined as:

< 60 mmHg

Hypotension in 1 year old is defined as:

< 70 mmHg

older than 1 year old hypotension is defined as:

< [ 70 + ( age in years x 2)] mmHg

Autonomic regulation of the heart is ______ at birth, with the _____ being less mature than the _____.

immature, SNS, PNS

Although the neonate has an immature SNS, _____ activates the SNS.

pain

The combination of hypertension, an immature cerebral autoregulatory response, and a fragile cerebral vasculature predispose the neonate to _______

intracranial hemorrhage

O2 consumption of a neonate

6-9 ml/kg/min

O2 consumption of an adult

3-5 ml/kg/min

Alveolar ventilation of neonate

130 ml/kg/min

Alveolar Ventilation of Adult

60 ml/kg/min

Respiratory rate of a neonate

35 bpm

Respiratory of adult

15 bpm

Tidal volume of neonate

6 ml/kg

Tidal volume of adult

6 ml/kg

breathing pattern of an adult

mouth or nose

breathing pattern of infant

preferential nose breather up to 5 months of age

_______ may require emergency airway management if the infant is unable to breath

bilateral choanal atresia

Tongue in adult vs infant

Adult: small relative to oral volume

Infant: large relative to oral volume

2 implications of infants having a large tongue

- tongue is closer to soft palate, which makes it more likely to obstruct the upper airways

- more difficult to displace during larngoscopy

Neck length in adult vs infant

adult: longer

Infant: shorter

1 implication of infant having a shorter neck

more acute angle required to visualize glottis

Epiglottis shape adult vs. infant

adult: leaf or C, floppier, shorter

Infant: U or omega, stiffer, longer

implication of infants having a stiffer epiglottis

makes it more difficult to displace during laryngoscopy

Vocal cord position in adult vs infant

Adult: perpendicular to trachea

Infant: anterior slant

3 implications of infant having more anterior/slanted vocal cords

- visualization and passage of ETT may be more difficult

- ETT may get stuck in anterior commissure

- nasal intubation is also more difficult

Laryngeal Position in Adult vs Infant

Adult: c5-c6

Infant: c3-c4

The only time the infants airway/larynx is more anterior is during ______

neck flexion

the larynx descends to C4 at _______ and achieves adult position at what age

1 yr

5-6 yr

What is the preferred blade in infants?

miller

the larynx is more ______ but NOT _____ in infants

superior/cephalad/rostral

NOT anterior

What anatomical feature allows infants to spontaneously ventilate while bottle feeding/nursing

a higher laryngeal position that places the epiglottis in contact with the soft palate

Narrowest point of airway in adults vs infants

Adult: glottis/vocal cords

Infant: cricoid or glottis

Subglottic airway shape in adults vs infants

Adult: cylinder

Infant: funnel

in neonates, resistance to ETT insertion beyond the vocal cords is likely at the ______

cricoid ring

right mainstem bronchus in adults vs infants

adult: more verticle (25 degree off of midline)

Infant: less verticle (55 degree take off of midline)

up to age ______, both bronchi take off at 55 degree off midline

3

in the adult, the right bronchus takes off at _____ and the left takes off at _____

25 degree - right

45 degree - left

intubation position in adults vs infants

adult: sniffing

Infant: head on bed with shoulder roll

Why do neonates desaturate faster than adults during anesthetic induction?

They have increased oxygen consumption, increased alveolar ventilation, and a smaller functional residual capacity (FRC), leading to faster depletion of oxygen reserves.

What is the ratio of alveolar ventilation to FRC in neonates compared to adults?

The ratio is 2-3 times higher in neonates, meaning they exchange gases in their FRC more quickly.

How does a high alveolar ventilation/FRC ratio affect anesthetic induction in neonates?

It causes faster uptake of inhaled anesthetics and quicker changes in alveolar and brain partial pressures.

Why do neonates reach anesthetic steady state faster than adults?

Their smaller FRC means fewer alveoli need to be filled to reach equilibrium, speeding up anesthetic uptake.

The risk of apnea is _____ related to gestational and post conceptial age

inversely

Neonates are at risk of _____ following surgery and anesthesia

apne

Since neonates are at risk of apnea following surgery and anesthesia.... Patients less than _____ weeks post conceptual age ashould be admitted for ______ observation with an ______.

60 weeks

24 hours

apnea monitor

The _______ the child, the greater the risk of postoperative apnea

younger

Prophylactic _______ is the treatment of choice for apnea following surgery. ____ can also be used, however its associated with higher risk of toxicity

caffeine (10 mg/kg IV)

Theophyline

FRC in neonate vs Adult

Neonate: 30

Adult: 34

VC in neonate vs adult

Neonate: 35

Adult: 70

TLC in neonate vs adult

Neonate: 63

Adult: 86

RV in neonate vs adult

Neonate: 23

Adult: 16

CC in neonate vs adult

Neonate: 35

Adult: 23

VT in neonate vs adult

Neonate: no change- 6 ml/kg

Adult: 6 ml/kg

What is the primary muscle of inspiration?

The diaphragm is the primary muscle of inspiration.

How do the intercostal muscles contribute to neonatal ventilation?

They are inadequately developed and contribute little to ventilation; the ribs are more horizontal, so they can't significantly augment thoracic volume.

What are the two types of muscle fibers in the diaphragm and intercostal muscles?

Type I (slow-twitch, endurance, fatigue-resistant) and Type II (fast-twitch, short-burst, fatigue-prone)

Which fibers are built for short bursts of work and fatigue easily

type II fast twitch fibers

What type of muscle fibers are built for endurance and resistant to fatigue?

Type I slow twitch fibers

How does the neonatal diaphragm differ from an adult diaphragm in Type I fibers?

Neonatal diaphragms have only 25% Type I fibers (adults have 55%); preterm infants may have only 10%

What does a lower percentage of Type I fibers mean for neonates?

It decreases their ventilatory reserve and increases their risk of respiratory fatigue and failure

Why are neonates at greater risk for respiratory fatigue and failure?

They have fewer Type I slow-twitch endurance fibers in the diaphragm, which makes their respiratory muscles tire quickly

Respiratory does not mature until _______ post conceptial age

42-44 weeks

before respiratory maturation: ______ decreases ventilation

hypoxemia

after respiratory maturation: ______ stimulates ventilation

hypoxemia

How does lung compliance in neonates compare to adults?

Neonates have decreased lung compliance due to fewer alveoli.

Why is the neonatal chest wall more compliant than in adults?

bc of the cartilaginous rib cage, which makes the chest wall stiffer

How does the neonate regulate FRC

by dynamically increasing FRC to reduce V/Q mismatch through sustained inspiratory muscle activity,, glottic narrowing, and shortened expiratory time with faster RR

What happens when closing capacity overlaps with tidal volume in neonates?

It creates V/Q mismatch and increases the A-a gradient, predisposing the neonate to hypoxemia

What are the three main processes that support FRC in neonates?

- sustained tonic activity of inspiratory muscles

- narrowing of the glottis during expiration

- shorter expiratory time and faster RR creating end expiratory pressureq

What can abolish the mechanisms that support neonatal FRC?

GA and/or muscle relxation

How does airway resistance differ in neonates?

Airway resistance is higher, especially in small airways; even small decreases in diameter (from edema or secretions) greatly increase work of breathing

Why is airway resistance in neonates so significant?

Because resistance is inversely proportional to the radius⁴, so minor airway narrowing causes large increases in resistance.

: What two forces must neonates overcome when inspiring?

airflow resistance and the elastic recoil of the chest wall and lungs

What stimulates a newborn's first breath after birth?

Clamping of the umbilical cord causes a rise in PaO₂, stimulating rhythmic breathing

What causes apnea in neonates?

hypoxemia

What happens to the newborn's lungs immediately after birth?

The lungs are filled with fluid, and the newborn takes deep breaths to replace it with air, generating a normal FRC within about 20 minutes

WHy does the newborn experience hyperventilation after birth

Due to poor buffering capacity and limited compensation for nonvolatile acids, leading to temporary respiratory alkalosis

What happens to pH and PaCO₂ after the first few minutes of life?

both stabilize as the newborn established regular ventilation

What happens to PaO₂ in the weeks after birth?

It continues to rise toward adult values over the next several weeks