Ventilator Waveform Interpretation. Corona

Question 1

What are the different types of ventilator patient dyssynchrony?

Answer 1

• trigger dyssynchrony
• flow dyssynchrony
• cycle dyssynchrony
• expiratory dyssynchrony

Question 2

What determines the inspiratory time in MV?

Answer 2

• 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

Question 3

What determines the cycle time in MV?

Answer 3

cycle time (Tc) = inspiratory time (Ti) + expiratory time (TE)

Question 4

how can you approximate pleural pressure?

Answer 4

by measuring esophageal pressure

Question 5

Explain the pressure changes in the pleural space (Ppl) and alveoli (PA) during spontaneous breathing

Answer 5

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

Question 6

What can you assess with the plateau pressure?

Answer 6

• approximation of the PA (alveolar pressure)
• assess airway resistance
• assess static respiratory system compliance

Question 7

What are risk factors for Auto-PEEP?

Answer 7

• 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

Question 8

Describe the respiratory compliance

Answer 8

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)

Question 9

Describe respiratory elastance

Answer 9

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)

Question 10

What does the resistance to airflow through conductive airways depend on?

Answer 10

viscosity and density of the gas
flow rate of the gas
length and diameter of the conductive airways

Question 11

Describe the equation of motion during mechanical or spontaneous ventilation

Answer 11

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)

Question 12

What are the two ways a patient can trigger a breath in assist-control mode?

Answer 12

• change in pressure (e.g., - 2 cm H2O)
• change in flow (e.g., 2 L/min)

Question 13

What is the rise time?

Answer 13

determines how quickly the ventilator achieves the set target pressure

Question 14

What are your differentials for a patient where the volume does not reach 0 by the end of expiration of the volume/time scalar?

Answer 14

• air leak
• bronchopulmonary fistula
• gas trapping (auto-PEEP)

Question 15

What are your differentials for a patient where the volume goes below 0 at the end of expiration of the volume/time scalar?

Answer 15

active exhalation by the patient
flow transducer malfunction

Question 16

What determines the expiratory flow limb on the flow/time scalar?

Answer 16

• airway resistance
• resistance of the artificial airays
• elastic recoil

Question 17

what directions do volume/pressure loops move in spontaneous versus PPV?

Answer 17

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

Question 18

What does this volume pressure loop indicate?

Answer 18

Volume doesn’t return to 0 –> doesn’t expire all air that is given, e.g., bronchopulmonary fistula, air leak

Question 19

What does a left/up or down/right shift of the pressure/volume loop indicate?

Answer 19

up/left - increased compliance
down/right decreaed compliance

Question 20

What does a widening of the pressure/volume loop indicate?

Answer 20

increased resistance

Question 21

Explain what the upper and lower inflection points indicate and how you can use these values to improve ventilation strategies.

Answer 21

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

Question 22

what is this flow-volume loop change indicative of?

Answer 22

• airway obstruction, i.e., increased resistance
• “scooping”

Question 23

What is this change in the flow-volume loop indicative of?

Answer 23

• “saw tooth” sign
• commonly from increased airway secretions

Question 24

What is this change in the flow-volume loop indicative of?

Answer 24

• gap between the expiration and the beginning of inspiration
• indicative of an air leak (volume does not return to baseline