flow controller and the effects of compliance and Raw

in a flow-controlled ventilator, what variables remain constant despite changes in compliance

flow, volume, and Ti remain constant

which variables are affected by changes in compliance

Pm and PA

does the Pmi change with compliance

no, because volume = 0

what is the relationship between Cs and PA

inverse relationship

how does decreased compliance affect PA and Ppeak/PIP

when compliance decreases, alveolar pressure increases and the mouth pressure increases

how does increased compliance affect PA and Ppeak/PIP

when compliance increases, alveolar pressure decreases and the mouth pressure decreases

in a flow-controlled ventilator, which variables are unaffected by changes in Raw

flow, Vt and Ti remain constant

which variable is affected by changes in Raw

Pm from the beginning to the end of inspiration

does PA change with Raw

no

how does increasing flowrate affect airway resistance and mouth pressure

as flowrate increases, airway resistance increases, which causes Pm to increase

what factors affect resistance to flow through the airways

gas viscosity, gas density, length and diameter of the airway, and flow rate through the airway

what is deltaP during inspiration

deltaP is the pressure difference between Pm and PA, representing the pressure generated in the airway

how is Paw calculated from deltaP

Paw = Pm − PA or Paw = flow × Raw

what does a change in deltaP over time indicate if flow is constant

it indicates a change in airway resistance

how does a square flow pattern affect deltaP

it remains constant

how does a decreasing flow pattern affect deltaP

it changes during inspiration, end-of-inspiration pressures are used to calculate deltaP

how do changes in Raw affect deltaP

changes in Raw change Paw, so deltaP changes and PA is not affected

how do changes in Cs affect deltaP

changes in Cs affect PA and Pm, but deltaP remains constant

how can deltaP be used clinically

analysis of deltaP and Ppeak can help determine whether changes in pressure are due to Raw or Cs

what is the effect of a decreasing flow pattern on Ppeak

Ppeak is lower because it occurs at the lowest flowrate or lowest alveolar pressure

how does a decreasing flow pattern affect mean airway pressure (Paw)

mean airway pressure is higher because a longer Ti is required to deliver the tidal volume

what is mean airway pressure (Paw)

the average pressure above baseline during a total respiratory cycle

why is increasing mean airway pressure significant

it increases mean alveolar pressure, encourages alveolar recruitment, improves alveolar ventilation, increases PaO2, and can decrease PaCO2

what are the disadvantages of increased mean airway pressure

higher pressures in the thoracic cavity for longer can reduce cardiac output and blood pressure, which may decrease oxygen transport, especially in patients with cardiac or hypotensive issues

how does decreasing flow help when airway resistance (Raw) increases

tidal volume can still be delivered at a lower peak pressure because flow is lowest when the set tidal volume is delivered, unlike square flow where Ppeak rises more with increased Raw