Test 5 Flashcards
What is the goal of mechanical ventilation?
Reduce 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 ________ modes in order to protect the newbornโs lungs from barotrauma.
pressure-limiting
In pressure-limited modes, a mechanical positive pressure breath will be terminated once a ______ has been reached.
preset peak inspiratory pressure (PIP)
A limit variable that will not allow the delivered breath to result in a pressure greater than the set PIP.
PIP
A positive pressure maintained in the patientโs airway and throughout the closed ventilator circuit during the expiratory phase of ventilation.
Positive End-Expiratory Pressure (PEEP)
A suggested starting point for PIP is between _____.
16 and 20 cm H2O.
The tidal volume achieved in pressure-limited ventilation is variable, depending on what?
Lung compliance and airway resistance.
Patients with poor lung compliance require higher _____ than those with good compliance to achieve the same tidal volume.
PIP levels
If the ventilator is unable to reach the set PIP before the breath is cycled into exhalation, it may be due to things like what?
A leak, such as an endotracheal tube cuff leak or a ventilator circuit leak.
If PIP is reached too soon, limiting the resulting tidal volume, it may be due to what?
An airway obstruction, a kink in the endotracheal tube, bronchospasm, or decreased lung compliance.
Endotracheal tube resistance can be reduced by:
Shortening the tube
In the presence of which of the following scenarios could shorter inspiratory times and faster rates be used without the risk of air trapping?
RDS
Which is the main factor that determines airway resistance?
Airway radius
As volume is extracted from the thorax at its unstressed volume, the ribs:
Recoil outward
What best describes wasted ventilation?
The ratio of physiologic deadspace to tidal volume
Normal lung compliance in a newborn is:
2.5 to 5 ml/cm H2O
It can decrease to as low as 0.5 mL/cm H2O/kg with RDS
The normal airway resistance in a spontaneously breathing neonate is:
20 to 30 cmH2O/L/sec
The maximum pressure exerted against the patientโs airway during inspiration
Peak inspiratory pressure
PEEP is considered a _______, which means at the end of exhalation the airway pressure will return to this level prior to the trigger of the next breath.
baseline variable
Higher levels of PEEP may
lead to ______________.
increased mean airway pressure, resulting increased intrathroacic pressure and the possible reduction of cardiac output.
If PEEP is increased in pressure-limited modes, the resulting tidal volume will be __________________.
a. Increased
b. Reduced
b. Reduced
What type of variable is frequency (rate)?
Trigger variable determined by the cycle time of each breath.
The number of inspirations that occur in 1 minute
The frequency of ventilation or rate
Modern conventional neonatal ventilators have the capacity of providing rates of up to _____.
150 bpm.
___________ is set by the operator and is a cycle variable that will cycle the breath into exhalation once the preset IT is achieved.
Inspiratory time (IT)
The average pressure exerted on the airway and lungs from the beginning of inspiration until the beginning of the next inspiration.
Mean Airway Pressure (MAP)
What is MAP affected by?
PIP, PEEP, IT, and rate.
MAP levels above____________ have been shown to contribute to barotrauma.
12 cm H2O
Minute ventilation is equal to the ________.
tidal volume multiplied by the respiratory rate.
Any gas that does not participate in gas exchange.
Deadspace
Deadspace is divided into two categories:
anatomic deadspace and alveolar deadspace.
The volume of tidal gas that fills the airways at the end of inspiration.
Anatomic deadspace
Anatomic deadspace comprises the airways beginning at the _____.
nose and ending at the terminal bronchioles.
Anatomic deadspace in a neonate is roughly __________ mL/kg.
2 to 2.2 mL/kg
Which type of deadspace is impossible to determine and can vary tremendously from hour to hour in the same patient?
Alveolar deadspace
The total of anatomic and alveolar deadspace is called what?
physiologic deadspace (VD).
The portion of tidal gas actually participating in gas exchange.
Alveolar ventilation
The difference between the baseline pressure, or PEEP (if the baseline is above 0 cm H2O), and the PIP.
Driving pressure
The amount of gas remaining in the lungs at the end of a passive exhalation.
FRC - Functional Residual Capacity
The amount of gas inhaled in a single breath is called the _________.
Tidal volume (VT)
During mechanical ventilation, the tidal volume is the volume of gas that enters the patientโs lungs during which respiratory phase?
Inspiratory phase
The two ventilator parameters that most directly affect tidal volume in pressure control ventilation are _____ and _________.
PIP and PEEP
There are several factors that determine the level of flow through a tube. They are:
1) the difference between the inlet and the outlet pressures, which is the driving
pressure
2) the radius of the tube
3) the length of the tube
4) the viscosity of the gas
FACTORS THAT INCREASE AIRWAY RESISTANCE
- Bronchospasm
- Airway secretions
- Edema of the airway walls
- Inflammation
- Artificial airway
a. Endotracheal tube
b. Tracheostomy tube
The direction of thoracic recoil depends on the ______.
volume in the thorax.
The amount of pressure required to increase the volume in the lungs is directly related to the number of ___.
elastic elements that are present in the lung tissue.
Compliance measured during an active breath is called _____.
Dynamic compliance
When is static compliance measured?
It is measured when there is no airflow through the lung at the end of inhalation through an inspiratory hold maneuver.
What are the determinants to delivered tidal volume?
- PIP
PEEP levels are usually kept between _____ cmH2O
4 and 6
If PEEP is increased in pressure-limited modes, the resulting tidal volume will be reduced. In order to maintain the same minute ventilation in this instance, it is necessary to _______________.
either increase PIP to maintain the same tidal volume or increase respiratory rate to maintain the same minute ventilation.
_________ is the most powerful influence on oxygenation.
Mean Airway Pressure (MAP)
High levels of MAP lead to _______________.
- decreased cardiac output
- pulmonary hypoperfusion
- increased risk of barotrauma
What is the best indicator of balance between adequate ventilation and excessive pressures?
MAP
The delivered tidal volume is directly related to the what?
vertical distance from the baseline pressure to the PIP level.
The portion of the tidal gas that fills unperfused alveoli.
Alveolar deadspace
When physiologic deadspace (VD) is compared to tidal volume (VT), the ratio (VD:VT) reflects the portion of the tidal breath that _________ participating in gas exchange.
is not participating in gas exchange.
Opening pressure and alveolar recruitment can be assessed when crackles are heard in the lungs during _______.
inspiration
How are crackles heard?
As the wet alveoli are opened, the pulling apart of the alveolar walls creates the crackles. Heard on end-inspiration.
In theory, when mechanically ventilating a neonate, the driving pressure must be equal to the ____ to open and ventilate the alveoli.
opening pressure
Clinically, in addition to assisting with oxygenation, PEEP is used to what?
stabilize the alveoli and reduce the surface tension.
The surface tension in the alveoli is reduced as FRC deceases/increases, resulting in less pressure being required to open the alveoli during inspiration.
increases
Alveolar ventilation is also affected by the length of time that the gas is in contact with the alveoli, or _______.
the diffusion time
The diffusion time is controlled by the ______and ___.
inspiratory time and peak flow
Increasing or decreasing peak flow changes what?
the speed at which the gas enters the alveoli.
The flow rate used determines the _____.
wave pattern of the ventilator breath.
True or false: Any change in ventilator parameters will change another parameter to some degree.
True!
The exception to this is the FiO2.
An __________ has the ability to resist deformation when a force is exerted against it, and thus produces a recoil force.
Elastic structure
According to ______, when an elastic substance is stretched, tension develops that is proportional to the degree of deformation that is produced.
Hookeโs law
This relationship between a given change in volume and the pressure difference required to achieve that volume change is called ___________ and directly reflects the ability of the lungs to stretch.
compliance
A plateau pressure is measured during the _________.
0.5 second inspiratory hold.
Which type of compliance only reflects the elastic properties of the lungs?
Static compliance
Compliance measured during an active breath is called ______.
Dynamic compliance
Static compliance equation
VT/(Pplat-PEEP) or VT/Driving pressure
Dynamic compliance equation
VT/(PIP-PEEP)
__________ compliance better reflects the elastic recoil of the lungs
Dynamic
The two main determinants of lung compliance are ______.
alveolar surface forces and elastic elements in the lung tissue.
Does the lung recoil inward or outward?
Inward
When the pressure inside the thorax is the same as outside the thorax, this is referred to
as the _______.
Unstressed volume.
_______ is determined when the inward pull of the lungs is balanced with the outward pull of the thorax and the unstressed volume in the chest is reached.
FRC
High pressure also further decreases cardiac output by _____________.
decreasing venous return to the right heart
The pressure difference between the inlet and the outlet determines the rate of flow, with a greater pressure difference resulting in a greater flow and vice versa.
Poiseuilleโs law
When dealing with the airways, the length of the airway and the viscosity of the gas remain relatively constant, so the only factor that changes resistance to airflow is a change
in the _______.
radius of the airway
____ is measured as the ratio between the driving pressure, measured in cmH2O, and the amount of flow in liters per second.
Resistance
The basic definition of airway resistance is the _________________________.
driving pressure needed to move gases through the airways at a constant flow rate.
In the lung, the driving pressure is the difference between _____ and________.
the pressure at the mouth (inlet pressure) and the alveoli (outlet pressure).
There are other factors that may lead to increased airway resistance that are not associated with the normal anatomy of the airway. Neonates have an increased level of_______, which reduces the radius of the airway.
interstitial fluid in the lungs
Turbulent flow is present in a 2.5 mm ETT at flow rates exceeding _____________.
3 Lpm and at flows exceeding 7.5 Lpm in a 3.0 ETT.
Of all the factors that affect resistance in the airway, by far the most powerful influence is a change in the __________.
radius of the airway.
According to Poiseuilleโs law, for every decrease in the radius, resistance increases to the______.
fourth power
Driving pressure equation
Vt/Cstat
Airway resistance that exists due to the placement of an endotracheal tube can be reduced by doing what?
Shortening the tube and only allowing 4 cm of the tube extends beyond the lips.
_______ reflect the amount of time required for alveolar and proximal airway pressures to equilibrate.
Time constants
In other words, time constants are the amount of time required for the lungs to inhale or exhale.
What are the two forces that determine the time required for exhalation?
- The elastic recoil of the lung
- Chest wall (compliance) and the opposition to airflow (resistance).
One time constant equals the time required for the alveoli to discharge ___ of the tidal volume.
63%
Three time constants are required before ____ of the tidal volume is emptied.
95%
What is the immediate indication for mechanical ventilation?
Respiratory failure
Mixed respiratory failure is manifested by both ________ and ________.
Hypoxemia and hypercapnia.
What is the end result of hypercapnic respiratory failure?
Hypoxic-ischemic encephalopathy
Define hypoxemic respiratory failure
- PaO2 โค50 mmHg on a FiO2 of โฅ60% (PaO2/FiO2 ratio < 300 observed in acute lung injury) despite the use of continuous positive airway pressure (CPAP)
- decreasing PaO2 (or SpO2)
Frequently, they present with hypocapnia and respiratory alkalemia.