CMV Flashcards
ventilation
normal movement of gases into and out of the lung
external respiration
gas exchange b/w the lung and the blood stream
internal respiration
gas exchange b/w the blood and the cells - cellular level
on inhalation describe what happens in the thoracic cavity
diaphragm descends and enlarges the vertical size of the thoracic cavity, the external intercostals contract and raise the ribs slightly increasing thorax
on exhalation describe what happens in the thoracic cavity
exhalation is passive and diaphragm returns to normal position
what must you have to have flow
must have pressure gradient to have flow
what causes a volume change
gas flow
when is there no gas flow
at end of inhalation and end or exhalation
what pressure do you measure vent pressure in
cmH2O
what reference is equal to 760 mmhg for vents
zero reference
proximal pressure is often called what
Pawo or Pm
unless pressure is applied the upper airway Pawo is what
zero
what is intrapleural pressure (Ppl)
pressure in the potential space b/w the parietal and visceral pleura
Nml intrapleural pressure is what at the end of expiration and what at the end of inspiration
-5 and -10
what changes as intrapleural pressure changes
alveolar pressure (intrapulmonary pressure) Pa
what are the four basic pressure gradients
transairway pressure, transthoracic pressure, transpulmonary pressure, transrespiratory pressure
transpulmonary pressure
alveolar pressure - pleural pressure
transthoracic pressure
alveolar pressure - body surface pressure
transairway pressure
airway pressure - alveolar pressure
transrespiratory pressure
airway pressure - body surface pressure
where do you measure pressure
very close to the mouth or inside ventilator
baseline pressure
usually pressure at end expiration before next breath
what raises baseline pressure
PEEP
peak pressure
highest pressure recorded at the end of inspiration
plateau pressure
breath hold / inspiratory pause - elastic recoil of lung is still exerting a pressure
when is plateau pressure taken
after breath has been delivered but before exhalation is allowed to occur
compliance
volume change per unit of pressure change
dynamic compliance
reflects elastic recoil of lung (stiffness) and airway resistance to flow
static compliance
pressure is measured at static or no-flow conditions and eliminates airway resistance
resistance
obstruction to air flow
what is EEP
end expiratory pressure or baseline pressure
what is normal compliance value
0.05 to 0.17 L/cm H2O or 50 to 170 mL / cm H2O
what is the normal compliance value of intubated patients
males: C = 40 - 50 mL/cmh2o up to 100 mL/cmH2O
females: C = 35 -45 mL/cmH2O up t 100 mL/cmH2O
normal resistance values
0.6 to 2.4 cmH2O/L/sec at 0.5 L/sec flow
resistance values for intubated patients
approx. 6 cm H2O/L/sec or higher
when does the RAW increase for intubated patients
increases as the endotracheal tube size decreases
clinical conditions that increase RAW - COPD
emphysema, chronic bronchitis, asthma, bronchiectasis
clinical conditions that increase RAW - mechanical obstruction
post intu obs, FB obs, endotracheal tube, condensation in tubing
clinical conditions that increase RAW - infection
croup, epiglottitis, bronchiolitis
what is the time constant
the product of R and C which has units of time
why is the time constant called constant
for any value of R and C equals the time necessary for the lungs to empty 63% of volume
2-time constants
86%
3-time constants
95%
4-time constants
98%
5-time constants
100%
one time constant = what
C x RAW
what does the C and RAW stand for
c = compliance of the unit and RAW is resistance of the unit
time constant formula
time constant = C x R
types of mechanical ventilation
negative pressure, positive pressure, high-frequency
who uses high - frequency ventilation
infants IRS, adults with air leaks, ARDS
what is high - frequency ventilation
high rates and low volumes
HFPPV
60-100 breaths/min
HFJV
100-600 breaths/min
HFO
up to 4000 breaths/min
