Test 5 Ch. 17 Concepts of MV Flashcards
What is the goal of MV ?
To reduce the WOB by providing adequate alveolar gas exchange with minimal damage to lung tissue (barotrauma) and/or interference with the circulatory system
Most common conventional neonatal ventilators use _____________- limited modes in order to protrct the newborn’s lungs from _______________.
pressure;
barotrauma
In pressure-limited modes, a mechanical positive pressure breath will be terminated once a
preset peak inspiratory pressure (PIP) has been reached
PIP is a ________ variable that will not allow the delivered breath to result in a pressure greater than the set PIP
limit
Pts with poor lung complaince require
higher PIP levels than those with good compliance to achieve the same tidal volume
PEEP levels are usually kept between
3 to 5 cm H20
Higher PEEP leads to…
increased Pmean which results in increased intrathoracic pressure and possible reduction of cardiac output
Frequency or rate is considered a trigger variable determined by the cycle time of each breath
**
The initial breath rate varies but should be started at ___ to ___ bpm
20 to 40
Preterm neonates may require rates as high as
60 bpm
inspiratory time (itime) is set by the operator and is a cycle variable that will
cycle the breath into exhalation once the preset IT is achieved
Mean airway pressure (MAP) is the average pressure exerted on the airway and lungs from the beginning of inspiration until the beginning of the next inspiration
**
MAP is the most powerful influence on oxygenation and must be carefully monitored because high levels of MAP lead to (3)
decreased cardiac output, pulmonary hypoperfusion, and increased risk of barotrauma
MAP levels above ___ have been associated with barotrauma
12 cm H20
The amount of gas inhaled in a single breath is called the
tidal volume
What are the 2 ventilator parameters that most directly affect the tidal volume in pressure control ventilation are
PIP and PEEP
Minute ventilation (VE) is tidal volume x RR
**
What vent changes can alter VE? (3)
- PIP
- PEEP (alters Vt)
- RR
VE is broken down into alveolar ventilation, the portion participating in gas exchange and dead space ventilation, the portion not participating in gas exchange
**
Deadspace is any gas that does not particpate in
gas exchange
Deadspace is divided into two categories:
anatomic and alveolar deadspace
Anatomic deadspace is the
volume of tidal gas that fills the airways at the end of inspiration
Anatomic deadspace in a neonate is roughly (range)
2 to 2.2 mL/kg
Alveolar deadspace is that portion of tidal gas that
fills unperfused alveoli and is impossible to determine
The total of anatomic and alveolar deadspace is called
physiological deadspace (Vd)
What is driving pressure?
The difference between the PEEP and the PIP
In theory, when mechanically ventilating a neonate, the driving pressure must be equal to the opening pressure to open and ventilate the alveoli.
**
For example, if the opening pressure is determined to be 20 cm H2O and we desire a PEEP of 4 cm H2O, a PIP of 24 cm H2O would have to be used to achieve a driving pressure that is equal to opening pressure.
**
FRC is the amount of gas remaining in the lungs at the
end of a passive exhalation
Alveolar ventilation is also affected by the length of time that the gas is in contact with the alveoli, or the diffusion time.
**
The ______ rate determines the wave pattern of the ventilator breath
flow
PEEP may impact the FRC, which can alter ____________.
compliance
A change in compliance might require altering
PIP, resulting in possible alterations of time constants, expiratory time, and the I:E ratio
Changes in Fio2 does not change other parameters
**
A change in PIP will change both compression pressure and ______ _________ leading to a change in VE and an alteration of alveolar ventilation
tidal volume
The alteration of alveolar ventilation leads to changes in ________ which changes pH
PaCO2
A change in PEEP level also changes
driving pressure and Vt leading to the same alterations mentioned with PIP changes
According to Hooke’s law of elasticity, when an elastic substance is stretched, tension develops that is proportional to the degree of deformation that is produced. Thus, the more it is stretched, the more force it produces to recoil to its original size and shape.
**
recoil is measured by applying a known pressure to the lung and the change in volume that occurs is measured. This relationship between a given change in volume and the pressure difference required to achieve that volume change is called
compliance
Define static compliance
The change in volume for any given applied pressure
How is static compliance measured? (Pplat)
When there is no airflow through the lungs at the end of inhalation through an inspiratory hold maneuver
Compliance measured during an active breath is called (PIP)
dynamic compliance
Dynamic compliance better reflects the
elastic recoil in the lungs
What is normal compliance in a neonate
2.5 to 5 mL/cm H2O
What are the 2 determinants of lung compliance?
- alveolar surface forces
- elastic elements in the lung tissues
The thorax, like the lungs, is an elastic structure. It differs from the lung in that it recoils inward or outward, whereas the lung only recoils inward. The direction of thoracic recoil depends on the volume in the thorax.
**
Diseases that increase surface forces in the alveoli (RDS) decrease compliance and increase the amount of pressure required to ventilate the lungs. As the alveoli shrink in size, the FRC is reduced. Higher pressure is now needed to inflate the alveoli.
**
Define airway resistance (Raw)
The driving pressure needed to move gases through the airways at a constant flow rate
For every decrease in the radius, resistance increases to the fourth power. Who’s law is that?
Poiseuille’s
What is normal airway resistance in a spontaneous neonatal?
20-30 cm H2O
