Respiratory Flashcards
Developmental stages of lung development
Embyronic, pseudoglandular, canalicular, terminal sac (saccular), aveolar and vasculature
Embyronic stage: GA development, structural devo, developmental abnormalities
0-5 weeks
ventral lung bud forms, asymmetric bronchi, 5 lobes, pulm vascular devo
problems: laryngeal cleft, tracheal stenosis, TEF, bronchogenic cysts
Pseudoglandular stage: GA development, structural devo, developmental abnormalities
5-16 weeks
branching up to terminal bronchi, broncho-pulm epithelium produces fluid, vasculature of aa & vv, separation of thorax & peritoneal cavity
problems: branching abn, CDH, congenital lobar emphysema, CPAM, pulm lymphangiectasia
Canalicular stage: GA development, structural devo, developmental abnormalities
16-25 weeks
respiratory bronchioles, prelim gas exchange unites, T2 pneumocytes -> T1
problems: pulm hypoplasia, surf deficiency, alveolar capillary dysplasia
Saccular stage: GA development, structural devo, developmental abnormalities
25-36 weeks
alveolar ducts, gas exchange via alveolar capillary membrane
problems: pulm hypoplasia, surf deficiency
Alveolar & vasculature stage: GA development, structural devo, developmental abnormalities
36+ weeks
alveoli increase in diameter, microvascular growth & vessel maturation
problems: surf deficiency, congenital lobar emphysema, pulm HTN
O2 content =
O2 content = O2 bound + O2 unbound
= [(1.34 x Hb) x O2 sat] + [(0.003) x paO2]
A-a gradient =
A-a gradient = pAO2 - paO2
= [FiO2 x (pB - H2O)] - paCO2/R - paO2
O2 delivery =
O2 delivery = CO x O2 content
O2 consumption =
O2 consumption = (blood flow x O2 content in arterial blood) - (blood flow x O2 content in venous blood)
= CO x (1.34 x Hb) x (arterial O2 sat - venous O2 sat)
SP A
Expressed early 3rd trimester
Tubular myelin and host defense
Sp B
Expressed at end of 1st trimester
Surfactant function
Tubular myelin
Surface adsorption of phospholipids
Surfactant administration in the setting of Sp B deficiency is ineffective
Sp C
Expressed at end of 1st trimester
Surfactant function
Surface adsorption of phospholipids
Sp D
Expressed last, after early 3rd trimester
Host defense
Anti oxidant
Surfactant lipid homeostasis
Laplace’s law
P = 2T / r
P is distending pressure or pressure needed to resist alveolar collapse
Boyle’s Law
P1V1 = P2V2
Hering Breuer inflationary reflex
Lung overdistention -> inspiration arrest
Hering Breuer deflation reflex
^RR with abrupt deflation of lungs
Chemoreceptors that sense CO2 changes
In the medulla, and actually more sensitive to H changes
Chemoreceptors sensitive to O2 changes
Carotid and aortic bodies (peripheral)
These are less sensitive in preterm infants and so they, instead of having initial hyperpnea and then decreased ventilation in term infants, preterm infants respond to hypoxemia with respiratory depression
Alveolar ventilation equation
VA = (TV - dead space) x RR
Bohr equation of physiologic dead space
Dead space V = TV x ((alveolar CO2 - expires CO2) / alveolar CO2)
In patients without significant venous-to-arterial shunts then arterial pCO2 represents the pCO2 of perfused alveoli
Physiologic dead space = TV x ((arterial CO2 - expires CO2) / arterial CO2)
Resistance equation
R = change in P (cm H2O) / change in flow (L/sec)
Normal is 40-55
Due to chest wall (1/4), airway (1/2), lung tissue (1/4)
Resistance relationships in laminar flow
Increased radius decreases resistance
Increased length increase resistance
Laminar flow unaffected my density of gas
R = (length x viscosity) / radius^4
Poiseuille law for laminar flow
Flow = (change in P x pie x radius^4) / (8 x length x viscosity)
Turbulent flow and resistance relationships
Inc length -> inc R
Inc radius -> Dec R
Inc density of gas -> inc R
R proportional to (length x density) / radius^5
Elastance equation
Elastance = change in P / change in volume
Compliance equation
Compliance = change in V / change in P
Work of breathing equation
Work of breathing = pressure (or force) x volume (or displacement)
Power equation
Power = work x frequency
Time constant equation
Time constant = resistance x compliance
Time = (P/flow) x (V/P)
Time constant healthy newborn
Healthy teen time constant = 0.09-0.15 and it takes 3-5 time constants for inspiration and expiration = 0.45 second
Time constant in RDS
Smaller time constant (0.05) because compliance is very even though resistance is higher
Time constant in CLD
Time constant is high (>0.15) (because of very high resistance even though compliance is low)
Alveolar gas equation
pAO2 = pIO2 - (paCO2/R) + f
F is a correction factor (usually 2mmHg)
pIO2 = FiO2 x (pB - pH2O)
What increases oxygen consumption?
Increased caloric intake
Decreased body temperature
Neonate»_space; adult
Term > preterm
AGA > SGA
Altitude calculations
(pB - H2O) x FiO2 = (pB - H2O) x FiO2
Total CO2 equation
Total CO2 = dissolved CO2 + HCO3- + carbamino compounds
Bohr effect
Changes in O2 bound to Hb based on response to pCO2 in lungs vs body because of shifts of the oxyhemoglobin dissociation curve with CO2/pH changes
Haldane effect
Changes in CO2 binding to Hb based on amount of O2
So when O2 is removed in the tissues, CO2 can bind
But when O2 binds in lungs, CO2 unloaded
This effects co2 content rather than pCO2
Henderson Hasselbach equation
[Hydrogen] = (24 x pCO2) / [bicarb]
MAP equation (mean airway pressure)
MAP = k(PIP-PEEP) x [itime / (itime + etime)] + PEEP
K is a constant
Ventilator triggers, limits and cycles
Triggers: time, pressure, flow, or chest impedance/abdominal movement
Limits: pressure or volume
Cycle: time, volume, or flow (assist/control, pressure support)
Units for Hertz
Hz = 1 cycle / second
So 11 hz = (11 cycles / second) x 60 seconds/min = 660 breaths per minute
Etiology of apnea
Prematurity (typically starts after 24 HOL)
Infection
Metabolic abnormalities
Arrhythmia
Hypoxemia
Anemia
Hypothermia
Hyperthermia
Medications (I.e, PGE)
Maternal meds (narcotics, mag, beta blocker)
Upper airway malformation leading to increases secretions or anatomical blockage
CNS disorder (IVH, congenital anomaly)
Intrapulmonary shunt equation
Qs/Qtotal = %shunt = (O2 content pulm cap - O2 content systemic artery)/(O2 content pulm cap - O2 content mixed venous)
Lung compliance in a healthy newborn vs RDS vs CLD
Healthy newborn: 3-5 mL/cm H2O
RDS: 0.5-1 mL/cm H2O
CLD: <1 mL/cm H2O
Resistance in healthy newborn vs RDS vs CLD
Healthy newborn: 20-40 cm H2O/L/sec
RDS: >40 cm H2O/L/sec
CLD: >150 cm H2O/L/sec
Time constant for healthy newborn vs RDS vs CLD
Healthy newborn: 0.09-0.15
RDS: 0.05
CLD: >0.15
Base deficit correction
Give enough to correct half the base
Bicarb to be administered = BD x kg x 0.3
Causes of neonatal pneumonia
Early: GBS, E. coli, klebsiella, listeria
Late: above plus S aureus, pseudomonas, fungal, chlamydia, ureaplasma, CMV, herpes, RSV, enterovirus, rubella, syphilis
Pulmonary interstitial emphysema causes within lung?
Decreased lung compliance
V/Q mismatch
Increased dead space
CDH LHR mortality
LHR < 1.0 is poor prognosis
LHR > 1.4 is good prognosis
If liver and LHR <0.8 then high mortality
