pilbeams ch 6 Flashcards
The primary goal of volume controlled CMV
is to achieve a Ve that matches the patient’s metabolic needs
Metabolic rate is directly related to
body mass and surface area in humans
Male Ve=
4 x BSA
Female Ve=
3.5 x BSA
Ve must be adjusted for abnormal conditions such as
hypo/hyperthermia, hyper-metabolism, and metabolic acidosis.
Lung disorders that increase physiological dead space
will also require an increase in Ve.
Normal spontaneous Vt for a healthy adult is about
5 to 7ml/kg with a spontaneous rate of 12-20 bpm
Vt for ventilated patients ADULTS
6-8ml/kg IBW
Vt for ventilated patients CHILDREN
4-8 ml/kg IBW
Lower Vt’s such as 4ml/kg IBW
have been successfully used with ARDS (minimize damage)
RR=
Ve/Vt
RT’s set the following in VC
Vt, RR, FiO2, PEEP, flow
RT’s set the following in PC
IP(PiP), RR, FiO2, PEEP, Ti(inspiratory time)
Ve=
(f)XVt
TCT
total cycled time
Ti
inspiratory time
Te
expiratory time
TCT=
Ti+Te
Te=
TCT-Ti
Ti=
Vt/flow/60sec
I/E=
Te/Ti 1:? 1 is contant
Vt=
IBW(10)
To estimate metabolic rate
we use an individual’s gender, height and weight, body surface area(BSA).
Ve (minute ventilation) can be estimated using
a patient’s BSA. Box 6-1
Vt’s vary based on lung pathology
Normal lungs
6-8ml/kg, RR 10-20bpm
Vt’s vary based on lung pathology
COPD/Asthma
6-8ml/kg, RR 8-12bpm
Vt’s vary based on lung pathology
Restrictive disease
4-6ml/kg, RR15-25bpm
Vt should be adjusted to maintain
Pplat less than 30cmh20 and rates adjusted to minimize auto-peep
When setting Vt and rate, the goal is not to focus so much on the exact Vt and rate, but to focus on using settings that do not harm the patient
Maintaining plateau pressure lower than 30cmh20 is VERY important.
In some cases it may even be necessary to let
PaC02 rise and pH fall outside the patient’s normal values to avoid lung injury.
Tubing Compliance
As pressure builds in the ventilator circuit during inspiration, circuit expands along with the patients lungs, therefore the total volume that goes to the circuit never reaches the patient.-COMPRESSIBLE VOLUME
Current ICU ventilators measure and correct this
Can be calculated, Box 6-4
Inspiratory Flowand Flow Patterns VC-CMV
Goal is to set the shortest possible Ti
I:E of 1:2 or less, usually 1:4
Initial peak flow rate of 60L/min
Range 40-60L/min
Flow Patterns
Constant flow-most common *square
Ascending ramp
Sine flow *libra sign
Descending ramp-most common
Constant flow-
most familiar to clinicians or only one on the ventilator in use. Provides the shortest Ti available flow pattern with an equivilent peak flow rate setting.
Descending-
Descending-The amount of gas flow at the beginning of inspiration is always the highest. Descending pattern flow is greatest at the beginning. This occurs naturally with pressure ventilation.
Ascending ramp-
not used. Progressive increase in flow.
Sine-
Produces tapered flow at the end of inspiratory phase. Suggested that it can provide a more even distribution; it is not used.
Inspiratory Pauseduring Volume Ventilation
Is used to:
Obtain measurements of Pplateau
Improve distribution of air throughout the lungs
Use with care or not at all in COPD and flow limitation
Not commonly used in clinic
Setting baseline pressure—PEEP
Determining VT in pressure ventilation
Measure Pplateau and baseline pressure after initial volume-targeted breath.
Check VT and adjust after initiating pressure ventilation at low pressure(10-15cmh20)
PEEP increases
FRC, FRC decreases when the pt. is intubated or placed in the supine position. Minimum levels of 3-5cm.h20.
Raw =
(PIP – Pplateau)/flow
PSV =
(PIP – Pplateau)
Goals of adjusting PSV are
To help increase VT (4-8 mL/kg)
To decrease respiratory rate (to <30 breaths/min)
To decrease work of breathing (WOB) associated with breathing through an artificial airway
PC-CMV
can improve oxygenation and gas exchange, increase Paw and facilitate lung healing.Initial values of 10-15cmH20 with volume measurement
the Ti required for the ventilator to reach the set pressure at the beginning of inspiration(PSV)
PRVC
Closed loop pressure breaths and targets the pressure to achieve the set Vt.
Pressure limited, time cycled, Vt is feedback control
Important to set the upper pressure limit
Adaptive pressure support, PRVC,Vc+, Autoflow
Ti instead of flow
Volume Support
Spontaneous mode
Operator sets sensitivy, Vt, and upper pressure limit
Advantage is that spontaneously breathing pt.’s can establish their own RR and Vt
The set Vt is the minimum
VS,SPN-CPAP/VS,VS
