Pressure-Volume & Flow-Volume Loops Flashcards
Why monitor spirometry?
Airway obstruction & bronchospasm have highest incidence of severe injury
Fresh gas decoupling
Fresh gas is diverted by a decoupling valve to the manual breathing bag, and is thus not added to the delivered tidal volume- manual breathing bag inflates during inspiration & deflates during expiration (contents empty into absorbant and move on toward patient)
D-lite sensor technology
Flow signal conducted as a pressure difference- allows continuous dynamic compliance using end-inspiratory plateau pressure
Tidal Volume
Volume of gas entering or leaving patient during inspiratory or expiratory phase time
Minute Ventilation
RR x TV (*with her x dosing narcotic)
Ppeak
Maximum airway pressure during inspiratory phase time in cmH2O
Pplat
End inspiratory pressure after inspiratory pause in cmH2O
Pmean
Mean inspiratory pressure in cmH2O
PEEP
Positive end-expiratory pressure (at end of exhalation) in cmH2O
I:E
Ratio of inspiratory and expiratory times
Raw
Dynamic airway resistance (cm H2O/L/second)
Compliance
Ratio of change in volume/change in pressure in mL/cmH2O – dynamic compliance– measurement of well lung-thoracic system can change its total volume as changing pressure is applied [exp TV/(pressure at end of inspiration - pressure at end of expiration)
What can Pplat be used for?
A pause at the end of inspiration may benefit alveolar gas distribution from compliant to less compliant while maintaining lower airway pressures - beneficial for restrictive disease
How is PEEP identified on pressure-volume curve?
Rightward shift on horizontal axis
How is PEEP identified on airway pressure waveform?
Elevation from baseline of zero
Calculating I:E of 1:2, RR 10/min
Have a 6 second breath (60 sec/10), and 3 parts (1:2 ~> 1+2), 6/3 = 2 sec for inspiration leaving 4 for expiration
Why would you increase inspiratory time length?
Increase mean airway pressure, allow redistribution of gas from more compliant to less
What are the disadvantages of longer inspiratory times?
Increase risk of gas trapping, intrinsic PEEP, barotrauma, less well tolerated, decrease peak pressure at expense of decrease inspiratory flow, dangerous for COPD because they need longer amount of time to exhale
Normal adult & pediatric compliance
Adult: 35-100 mL/cmH2O (usually about 60), Ped: About 15 mL/cmH2O
When would you see a decrease in compliance?
Inadequate muscle relaxation, laparoscopic case, pneumoperitoneum, tumor, air embolism, narcotics, bronchoconstriction
Elastitance
Change in pressure/change in volume
Increase in resistance from what?
Obstruction, bronchoconstriction, airway collapse, too small ETT
When would you see peak pressure increase?
Deep trendelenberg, one lung intubation
What is the difference between the dotted line & the solid line?
Addition of PEEP (shifts rightward on x axis)
What is this picture representing?
Decrease compliance, more pressure is required to fill the lungs at a given volume, slope moves towards horizontal
What does this picture represent?
Unintentional one lung intubation - peak pressure increases
What does this picture represent?
Endobronchial intubation (one-lung), not as much tidal volume and decreased expiratory flow
What does this picture represent?
Esophageal intubation, increased pressure needed for small volume
What does this picture represent?
Esophageal intubation (irregular inspiratory and expiratory parts)
What does this picture represent?
Decreased tidal volume from kink in ETT
What does this picture #1 to #2 represent?
Kink in ETT causes high peak pressure, low compiance, high resistance and decreased tidal volume (solid line)
What does this picture represent?
Cuff leak or leak between D-lite & patient – big difference in TV insp/exp, non-closing loop
What does this picture represent?
Leak between D-lite and anesthesia machine- both insp & exp have decreased
What does this picture represent?
Leak between D-lite & anesthesia machines, decrease in both insp/exp TVs
What does this picture represent?
Diaphragmatic movements, patient trying to take breath during exhalation
What does this picture represent?
Spontaneous ventilation, cessation of mechanical ventilation, will have negative inspiratory force = negative pressure
What does this picture represent?
Patient breathing against machine– may cause uneven emptying of alveoli and interfere with surgery
What does this picture represent?
Bronchospasm- increased pressures, decreased compliance, right shift of PV loop
What does this picture represent?
Bowing configuration of expiratory part of FV loop is characteristic of obstruction/bronchospasm
What does this picture represent?
Severe emphysema & chronic bronchitis– increase in lung compliance, decreased ease of expiratory flow
What does this picture represent?
Reduced lung volume for higher peak pressures, increased elastic work & decreased comlpliance – obesity increases abdominal pressure
What does this picture represent?
Obesity - reduced lung volume for higher peak pressures, decreased compliance
What does this picture represent?
Incorrect prone position @ #1 line– decrease compliance & slightly increase inspiratory pressures
What do these pictures represent?
Top - supine position, bottom trendelenburg position
What does this picture represent?
Lateral decub positioning obstructing left upper lobe
What does this picture represent?
During one-lung ventilation, inspiratory pressures increased and compliance decreased - obstruction of left upper lobe
What does this picture represent?
Loss of chest wall elasticity
What do these pictures represent?
Left- PV curve shifted to right with increased inspiratory pressure - compression of R lung via abdominal pressure.. Right - exhalation not complete at beginning of new inspiratory phase.
What does this picture represent?
Manual ventilation with positive pressure applied at the wrong time– decreased inspiratory volume
What does this picture represent?
CO2 insufflation during laparoscapy causing decreased compliance and increased airway resistance
What does increasing PEEP do to compliance?
It may improve compliance, noted by pressure-volume loop curving toward the vertical axis.. look mostly at tidal volumes - are they improving?
What is intrinsic PEEP?
Air trapping- if expiratory time is too short to enable complete emptying of the lungs (COPD, inverse I:E)
What are pressure-volume loops used for?
Providing information on dynamic trends of respiratory COMPLIANCE.. detects lung overdistention
When can pressure-volume loops be generated?
Under static (no flow), low flow or dynamic conditions
What are flow-volume loops used for?
Providing information on dynamic rends of respiratory RESISTANCE..
Static Compliance
Mirrors elastic features of respiratory system
Dynamic compliance
Provides information on both elastic and resistive (flow-dependent) components of the airways & ETT– affected by variations in volume, compliance, secretions, bronchospasm
What is seen on the monitor when there is overdistension in volume controlled ventilation?
Bird beak, will have it past the upper inflection point (small volume increase produces large pressure increase)
From left to right, what do these pictures indicate?
Normal, early small airway obstruction, COPD, fixed large airway obstruction, variable EXTRATHORACIC large airway obstruction, restrictive disease
What does peak expiratory flow rate show?
Allows assessment of expiratory muscle strength, large airway patency, (asthmatic may have normal or decreased values)
What does this picture represent?
Patient with asthma– obstruction to intrapulmonary airflow, inspiratory limb relatively unaffected
What does this picture represent?
Elderly subject - small airway obstruction possible
What does this picture represent?
COPD- early collapse of large airway, inspiratory limb unaffected
Upper airway lesion and what will show on FV loop
Plateaus in Insp/Exp cycles, diminished PIFR & PEFR, FEV1 diminished as rAW increases, FVC remains unchanged
At what plateau pressure will there be shear lung damage?
>35 cm H2O
What does this picture represent?
Intrathoracic central airway obstrcution
What does this picture represent?
Extrathoracic airway obstruction, collapse of trachea during inspiration opssibly due to goiter
What will you see on the flow diagram of peak inspiratory & plateau pressures if there is obstruction or kink/bronchospasm
Increased PIP with no change in plateau
What will you see on the flow diagrams in PIP & plateau pressures if problem is with decreased distensibility of lungs & chest wall (pneumo, pulmonary edema)
Increased PIP & plateau pressure
Decreased compliance & alveolar transmural pressure
Transmural pressure increases - compresses capillaries, decreases preload to left heart
Prophylactic PEEP
1-5 cm H2O to increase FRC, prevent atalectesis, decrease shunting
Conventional PEEP
6-20 cm H2O if PaO2 is <60 mmHg with FiO2 > 50%
High PEEP
>20 cm H2O applied if extreme hypoxia & no response to conventional PEEP
Max PEEP
50 cm H2O
Advantages of PEEP
Improved PaO2, Reduces right to left intrapulmonary shunting, increases FRC through max alveolar recruitment, prevents airway & alveolar closure at end-expiration
Disadvantages of PEEP
Excessive distention of alveoli may cause compression of pulmonary vasculature = decrease preload (decreased SV, CO, BP, SVo2), increased CVP, risk for barotrauma, redistribution of blood flow, promotion of pulmonary edema
“Best” PEEP defined
Level of PEEP that produces max PaO2 with FiO2 <50% with least decrement in CO & overdistention of alveoli (look for biggest TV that will arise with same peak airway pressure)
“Best” PEEP by Pressure-Volume Loop
If there is a marked lower inflection point PEEP benefits but keep it from having an upper inflection point that is too great (bird-beak)
What can the lower inflection point tell us?
If it is marked - it indicates the pressure at which many collapsed alveoli are opening at the same time (PEEP will benefit), if it absent- there may be diffferent alveolar threshold opening pressures (no benefit of PEEP)
