Ventilator Waveform Interpretation. Corona Flashcards
What are the different types of ventilator patient dyssynchrony?
- trigger dyssynchrony
- flow dyssynchrony
- cycle dyssynchrony
- expiratory dyssynchrony
What determines the inspiratory time in MV?
- flow rate and tidal volume
TI (inspiratory time) = VT / flow rate
can use set inspiratory time and flow rate to determine VT –> VT = flow rate x inspiratory time
What determines the cycle time in MV?
cycle time (Tc) = inspiratory time (Ti) + expiratory time (TE)
how can you approximate pleural pressure?
by measuring esophageal pressure
Explain the pressure changes in the pleural space (Ppl) and alveoli (PA) during spontaneous breathing
at the end of inspiration or expiration PA is equal atmospheric (0 cm H2O), i.e., no air flow
Ppl is about - 5 cm H2O at end of expiration and - 10 cm H2O at end of inspiration
during inspiration PA is about -3 to -5 cm H2O –> air flow in
during expriation PA is about + 5 cm H2O –> air flow out
What can you assess with the plateau pressure?
- approximation of the PA (alveolar pressure)
- assess airway resistance
- assess static respiratory system compliance
What are risk factors for Auto-PEEP?
- short expiratory times
- high minute ventilation
- inreased airway resistance leading to collapse of small airways before expiration is complete (bronchospasms, increased secretions, mucosal edema)
- small endothracheal tube
Describe the respiratory compliance
ease at which the lungs distend, i.e., elastic forses that oppose lung inflation
change in volume for a given change in pressure –> C = volume change/ pressure change
sum of the lung compliance and compliances of surrounding thoracic structures (influences by lungs, pleural space, chest wall, intra-abdominal structures)
Describe respiratory elastance
elastic properties arising from the lungs and thorax
elastic forces together with frictional forces oppose lung inflation
elastance describes the tendency of the lungs and chest wall to return to their origninal form after being distended (recoil)
What does the resistance to airflow through conductive airways depend on?
viscosity and density of the gas
flow rate of the gas
length and diameter of the conductive airways
Describe the equation of motion during mechanical or spontaneous ventilation
The pressure applied to the respiratory system that must work against the compliance and resistance of the respiratory system
ventilator pressure + muscle pressure = elastic recoil pressure + flow resistance
elastic recoil pressue = elastance x volume
flow resistance = resistance x flow
so … ventilator pressure + muscle pressure = (elastance x volume0 + (resistance x flow)
What are the two ways a patient can trigger a breath in assist-control mode?
- change in pressure (e.g., - 2 cm H2O)
- change in flow (e.g., 2 L/min)
What is the rise time?
determines how quickly the ventilator achieves the set target pressure
What are your differentials for a patient where the volume does not reach 0 by the end of expiration of the volume/time scalar?
- air leak
- bronchopulmonary fistula
- gas trapping (auto-PEEP)
What are your differentials for a patient where the volume goes below 0 at the end of expiration of the volume/time scalar?
active exhalation by the patient
flow transducer malfunction
What determines the expiratory flow limb on the flow/time scalar?
- airway resistance
- resistance of the artificial airways
- elastic recoil
what directions do volume/pressure loops move in spontaneous versus PPV?
clockwise in spontaneous breath as whith volume increase negative pressure is needed (inspiratory limb on the left of the y axis, and expiratory on the right/positive side)
counter-clockwise in PPV, pressure increases with volume increase during inspiration. both inspiration and expiration are on the right side of the y axis
What does this volume pressure loop indicate?
Volume doesn’t return to 0 –> doesn’t expire all air that is given, e.g., bronchopulmonary fistula, air leak
What does a left/up or down/right shift of the pressure/volume loop indicate?
up/left - increased compliance
down/right decreaed compliance
What does a widening of the pressure/volume loop indicate?
increased resistance
Explain what the upper and lower inflection points indicate and how you can use these values to improve ventilation strategies.
Lower inflection point (LIP) indicates pressure at which large number of alveoli are recruited
upper inflection point (UIP) indicates pressure at which alveoli become overdistended (“beaking”)
ideally ventilate patient between LIP and UIP - i.e., set PEEP above LIP and set VT below UIP
what is this flow-volume loop change indicative of?
- airway obstruction, i.e., increased resistance
- “scooping”
What is this change in the flow-volume loop indicative of?
- “saw tooth” sign
- commonly from increased airway secretions
What is this change in the flow-volume loop indicative of?
- gap between the expiration and the beginning of inspiration
- indicative of an air leak (volume does not return to baseline
