Mechanical Ventilation Flashcards
The two main factors that influence ventilation are
Respiratory rate, tidal volume
Lung compliance refers to
How distensible the lungs are
When lung compliance is decreased, work of breathing is
Increased
When functional residual capacity is decreased, there is
Less air in the lungs at the end of expiration
When PaC02 rises, chemoreceptors cause
An increase in ventilation
Diffusion of oxygen and carbon dioxide is influenced by the
Thickness of the alveolar capillary interface
Carbon dioxide levels are primarily determined by
Respiratory rate or tidal volume (ventilation)
Tidal volume is
The volume of air in one breath during normal relaxed breathing
During inspiration
Intrathoracic and interpulmonary pressures decrease
The diaphragm contracts
Intercostal muscles contract & thoracic cavity increases in size
In the upright person, the lower portions of the lung receive
More ventilation than the upper portions
In the upright person, the lower portions of the lung receive
More blood flow/perfusion than the upper portions
The right lung has
2 fissures and 3 lobes
Type 1 alveolar cells
Comprise 90% of the alveolar wall
Are the main structural cells of the alveolar wall
Are susceptible to injury
Exchange of respiratory gases does not occur in
Terminal bronchioles
Exchange of respiratory gases occurs in all of the following
Alveolar ducts
Alveoli
Respiratory bronchioles
DECREASES airway resistance
SNS stimulation
The most sensitive region in the respiratory tract for triggering the cough reflex is
Carina
Oxygen levels in the arterial blood are influenced by
Ventilation
Perfusion
Diffusion
Pulmonary surfactant:
Prevents alveolar collapse
Reduces alveolar surface tension
Increases lung compliance
Is secreted by Type II cells
Ventilation-perfusion mismatching affects which of the following primarily
Work of breathing
Ventilation
the movement of gases in and out of the lungs
Gas exchange
refers to the exchange of oxygen and carbon
dioxide across the alveolar-capillary level.
Normal ventilation
Muscular contraction causes the ribs to move outward and the diaphragm to move downward, resulting in an increase in the volume of the thoracic cage.
This increased volume / size results in a increased negative intrathoracic pressure (and intra-pulmonary pressure) - which, in turn, ‘sucks‘ the air into the lungs - and inhalation or inspiration occurs. It is key to note that inhalation is active - it requires muscular work for it to occur.
Exhalation or expiration of air is passive. The ventilatory
muscles relax and the diaphragm moves up. The simple
process of muscular relaxation results in the thoracic cage volume decreasing, as well as increased intrathoracic and intrapulmonary pressures - and air moves out of the lungs.
Physiologic effects of mechanical ventilation on hemodynamic
function
As intrathoracic pressure falls, the resistance for blood flow returning to the right side of the heart is less. Thus, the mechanics of normal breathing support venous return, adequate preload and cardiac output.
The increased intrathoracic pressure that occurs during inspiration for a mechanically ventilated patient can
make it more difficult for the blood to return to the heart,
inhibiting venous return and lowering the patient’s preload.
At the same time, the increased intrathoracic pressure can falsely increase a patient’s CVP value. the patient’s actual preload might have dropped too low to maintain adequate cardiac output and as a result, the patient becomes hypotensive. I
A/C
Assist control mode, respiratory rate and tidal volume are set on the ventilator. Patients can
initiate additional breaths above the set rate (commonly referred to as “assisting” or “triggering” the ventilator). When a patient assists above the set rate, they receive the set tidal volume. Other settings on A/C include PEEP and Fi02.
Absorption Atelectasis
When a patient is on high levels of oxygen 90-100% the oxygen washes out the nitrogen.
As the oxygen in the alveoli is absorbed into the blood stream, the alveoli collapse.
Nitrogen is important in supporting alveoli opening and is not absorbed into the blood
stream when at normal atmospheric pressures.
Acute respiratory failure
Acute respiratory failure is the primary indication for initiation of mechanical ventilation
(Clochesy et al., 1996). Acute respiratory failure can be broadly categorized into two types:
ventilatory failure or an issue related to ventilatory mechanics, and hypoxemic failure or
inadequate gas exchange across the alveolar-capillary membrane.
Alveolar hypoventilation
Occurs when the amount of oxygen brought into the alveoli does not meet the needs of the
body (Urden, Stacy and Lough, 2022). Common conditions that can cause alveolar
hypoventilation include narcotic overdoses or airway obstruction.