Respiratory Flash Cards
How does CPAP affect Laplace’s law?
P=2(surface tension)/radius
CPAP increases the radius and decreases the pressure needed to keep alveoli open
What are the 3 effects of CPAP in respiratory system?
- Increases transpulmonary pressure
- Reduced apnea by activating stretch receptors and preventing airway collapse
- Reduces collapsing alveoli by increasing FRC, larger TV, reduced VQ mismatch and improved compliance
What are the air dispersion mechanisms for HFOV?
- Convection: Bulk flow for proximal airways (convection)
- Convection and diffusion: Turbulent flow and Taylor dispersion (asymmetric flow velocities->mixing of inspiratory and expiratory flows)
- Diffusion: Penduluft & collateral ventilation (gas flows from alveoli with short time constant to alveoli with longer time constants)
Differences between HFOV and HFJV
- is exhalation passive or active?
- is I:E fixed?
- is Vt dependent on frequency?
HFOV CPAP system with piston displacement of gas Exhalation active Rate is Hz I:E fixed TV dependent of frequency (Hz)
HFJV Jet pushes bursts of gas on top of conventional ventilator Exhalation passive Rate is breaths/min IT is variable TV independent of frequency/rate
What type of air flow does sigh breaths deliver on HFJV?
Bulk flow
conventional breath used to increase lung recruitment via augmenting bulk flow
How can mean airway pressure be adjusted on ventilator?
By adjusting PIP PEEP and insp times
Paw=(Ti x PIP) + (Te x PEEP)/ Ttot
Minute ventilation calculation
Minute ventilation=TVxRR
What are some of the issues when you set flow rate on the ventilator too low or high?
Usually 6-10 L/min
Low flow rates
- might not allow to reach targeted pressures or volume
- increases dead space ventilation
- can cause air hunger
High flow rates
- too rapid achievement of targeted P or V
- increased turbulence->inc resistance and inadvertent PEEP
Time constant equation
How many time constants are needed to empty lungs?
Time constant=Resistance x compliance
3 time constants=95% empty
How does time constant differ between RDS and BPD?
Time constant is shorter in RDS because the compliance is much lower
Time constant is longer in BPD because of increased resistance
What are the reported advantages of volume targeted ventilation?
- Decrease in BPD
- Decreased rate of pneumothorax
- Less hypocarbia
- Decreased risk of IVH
- Decreased risk of PVL
- Shorter duration of MV
What is difference between volume control vs volume targeted?
Volume control constant preset Vt with pressure rising passively and cycles off after reaching peak volume. Doesn’t measure Vt reaching patient lungs.
Volume targeted is modification of PC ventilation delivering target Vt by adjusting pressure over time. Exhaled Vt more closely resembles flow reaching pt lungs
How does pulse oximetry detect arterial saturation sP02?
Looks at the differences in frequencies of light absorbed through light source and photo sensor during pulsation. Oxygenated Hgb absorbs infrared light and deoxygenated Hgb absorbs red light. Photosensor detects red light and therefore % is extrapolated to give SpO2.
Can have false readings w poor perfusion position difficulties and presence of other hemoglobin species
How does NIRS work?
Assesses regional tissue oxygenation through light of varying frequencies passing from source through tissue and to near-infrared detector sensors
For every 1mmHg change in PaCO2 we expect inverse change in pH of?
0.006
Anion gap calculation
Na -(Cl+Hco3)
Normal AG: 6-12
Elevated AG: lactate or ketones
Normal AG: renal losses GI, losses
Winters formula
Expected PaCO2= [1.5x(serum HCO3)] +(8+/-2)
Used in the case of primary metabolic disturbance to assess degree of resp compensation
What does Poiseuille’s law refer to?
Resistive pressure is relative to air viscosity and length of tube and inversely related to radius to power 4
R=8nL/pi r^4
What are the limitations (3) of ventilator graphics to asses pulmonary function?
- Not validated in ELBW infants
- Does not capture poor compliance in very distal airways
- Cannot accurately represent heterogenous lung disease
During inspiration what happens to cardiac output?
-How does systemic venous return and pulmonary venous capacitance affect this?
Cardiac output decreases
There is an increases venous return
Blood in R heart Increases displacing IV septum leading to increase RV stroke volume and decrease LV stroke volume
Pulmonary venous capacitance increases w negative intrathoracic pressure reducing return PV return to LA
What is the overall influence of respiration on cardiac output?
During inspiration there’s a transient BP decrease 2/2 decrease in CO that is physiologic and will equilibrate w increase in CO during expiration
What is pulsus paradoxus?
Exaggerated decrease in systolic pressure during inspiration
cardiac tamponade - there is R heart compression and decrease venous return during inspiration
Severe airway obstruction - more negative intrathoracic pressure—-> increase pulmonary capacitance and decrease left atrial return
How does alveolar vessel resistance and extraalveolar vessel resistance change with inflation and deflation?
Alveolar vessel resistance increases with inflation (decrease in radius and increase in length of vessels when alveolus is extended) while extraalveolar resistance decreases (intrapleural P decreases, transmural P increases->vessel dilated and R decreases
With deflation the opposite occurs
How does positive pressure ventilation affect pulmonary venous return and LV after load?
PPV increases alveolar pressure-> inc intrathoracic and intrapleural pressure
which in turn
-Decreases pulmonary venous capacitance lead to increased PV return
-Decreased aortic transmural pressure leads to decreased LV afterload
How does PPV affect the right heart vs left heart?
Increases intrathoracic P Decreases systemic venous return Decreases RV preload Decreases RV stroke volume Increases RV afterload
Left heart
Increases pulmonary venous return
Increases LV stroke volume
Decreases LV afterload
right heart effects predominates therefore PPV decreases overall cardiac output
What are the 4 mechanisms for pulmonary edema according to starlings equation?
- Increased vascular hydrostatic P (ie LV dysfunction, pulmonary venous hypertension, volume overload)
- Decreased interstitial hydrostatic P (ie post-obstructive pulmonary edema)
- Decreased transmural oncotic P (decreased proteins ie poor nutrition)
- Increased permeability (sepsis, aspiration)
What is the mechanism of Nitric oxide?
In endothelial cell l-arginine is converted to NO via eNOS.
NO goes into smooth muscle cell and stimulates guanylate cyclase enzyme.
Guanylate cyclase converts GTP to cGMP which causes vasodilation of smooth muscle.
There is no data to support iNO use in which 3 populations?
Premature infants
Congenital heart disease
CDH
OI index
OI=MAPxFiO2/paO2
When should iNO be initiated?
To optimize lung recruitment
OI>25 or paO2 <100 despite 100% FiO2
Why is rebound effect noted in rapid weaning of iNO?
Inhibition of endogenous nitric oxide synthase (eNOS)
Risks associated with use of iNO
Formation of peroxinitrite which can lead to vasoconstriction and lipid peroxidation affecting surfactant function
Can be oxidized into nitrogen dioxide->causes methHgb, hypoxemia, pulmonary edema
Inhibits platelet aggregation
Contraindications of iNO use
Structural heart defects depending on right to left shunting
- Critical AS
- interrupted aortic arch
- coarctation
- HLHS
Obstructive TAPVR
Factors that decrease RDS risk?
Antenatal corticosteroids
Chronic intrauterine stress
How does RDS appear histologically?
Appear as an eosinophilic membrane that lines airspaces
Antenatal corticosteroids have been found to decrease the incidence of which diseases?
RDS
IVH
NEC
Neonatal death
Too many doses can be associated w fetal growth restriction
Porcine or bovine surfactant contain which surfactant proteins?
Surfactant proteins B and C
Phospholipids
What is the pathophysiology of TTN?
Delayed activation of fetal lung fluid clearance through
- abnormal functioning Na/K atpase and eNac
- lack of proceeding labor results in lack of trigger switch from secretory to resorptive processes in type II epithelial cells
Risk factors for TTN
Male <38 weeks gestation LBW Macrosomia Maternal diabetes or asthma
How to prevent TTN?
Avoid elective c/s prior to 39 weeks
What is the difference between congenital, early onset or late onset Pneumonia?
Congenital -intrauterine aspiration of infected amniotic fluid or trans placental transmission
Early onset-aspiration during or after birth of vaginal organisms or infected amniotic fluid (1st week)
Late onset-environmental, inhalation or nosocomial (>1 week)
What are the 2 signaling pathways that lead to vasodilation and decrease in PVR at birth in neonate?
Nitric oxide generation from l-arginine via eNOS which converts to GTP to cGMP via guanylate cyclase.
Prostacyclin signaling from arachidonic acid via COX 1 prostacyclin synthase which coverts ATP to cAMp via adenylate cyclase.
PPHN is characterized by 3 types
Maladaptation (MAS, pneumonia)
Maldevelopment (ACD)
Underdevelopment (hypoplastic)
Hypoplastic vasculature
CDH has hypoplastic and excessive muscularization
What is a normal A-a gradient in RA?
How about in 100% FiO2?
RA is 10-15
100% FiO2 is 80-100
An A-a gradient > what number is strongly suggestive of patient needing ECMO?
> 600
Sildenafil acts in which pathway?
It’s acts in the nitric oxide pathway
It inhibits PDE5 and therefore blocks the conversion of cGMP to its inactive form GMP
What is the pathophysiology of PIE?
Air dissects and gets trapped in the perivascular connective issue. In preterm infants this connective tissue is more abundant and less dissectible trapping air.
Does collateral ventilation occur in the alveolus in newborns?
No. Develops ~3-4 years and likely reason why more likely to get pneumothoraces with proximal obstruction or atelectasis
- Intraalveolar through the pores of kohn. (Not developed in newborns)
- Bronchioalveolar through the channels of Lambert
- Interbronchial through the channels of Martin
How does nitrogen washout theoretically help in pneumothoraces?
100% O2 decreases partial pressure of nitrogen in alveolus compared to the pleural space leading to diffusion of nitrogen out of pleural space.
Name the proven preventative management strategies for BPD?
Vitamin A
Caffeine
Less invasive surfactant administration (1 retrospective review)
What value is considered abnormal for a sweat chloride test to diagnose cystic fibrosis?
> 60meq/L of chloride
Name the early marker for pancreatic exocrine insufficiency in CF?
Low fecal elastase 1
Describe the complete spectrum for a patient with CF?
Pancreatic insufficiency (80-90%) > fat malabsorption and FTT
Chronic obstructive airway disease (90%)> bacterial overgrowth
Bilateral genesis of vas deferens (90%)>male sterility (not female)
Other: meconium ileus in newborn (in 15% of newborns w CF),
polyposis, mucocele, sinusitis, gastrointestinal cancer,
CF related diabetes if pancreatic fibrosis, osteoporosis
CFTR-related disorder = CFTR gene mutation
e.g., recurrent pancreatitis isolated bilatera
Which is the most common vascular ring type?
Double aortic arch (40%)
Right aortic arch w ligamentum arteriosum/PDA (30%)
Name the 3 types of incomplete vascular rings
Aberrant R subclavian artery (20%)
Anomalous origin of the innominate artery (10%)
Aberrant left pulmonary artery (rare)
CDH
Most common side for defect?
%associated anomalies
Name associated anomalies
Left 85%
40% associated anomalies
CHD, undescended tested, meckels diverticulum, unilateral kidney
Assoc’d with
Fryns Syndrome (AR, CDH, limb abnormalities, abnormal facies)
Aneuploidies - Turners (XO), T13, T18