Respiratory AP and Vent Modes

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Questions and Answers

What is the name of the last structure that is perfused by the bronchial circulation that represents an end of anatomic dead space/conducting airways?

Respiratory bronchioles

Alveolar ducts

Terminal bronchioles (correct)

Pulmonary capillaries

What is the approximate number of generations prior to reaching the alveoli?

30-35

10-15

20-25 (correct)

40-45

What is the term for the lung volume at which small airways close?

Functional residual capacity

Closing capacity

Closing volume (correct)

Residual volume

What is the term for the pressure-volume relationship when air is not moving?

Static effective compliance Signup and view all the answers

What is the definition of lung compliance?

The change in volume per unit pressure Signup and view all the answers

What is the name of the space that is perfused by the pulmonary circulation?

Alveolar dead space Signup and view all the answers

What is the term for the combination of closing volume and residual volume?

Closing capacity Signup and view all the answers

What is the term for the lung's tendency to return to its original shape after it has been stretched or compressed?

Elastic recoil Signup and view all the answers

What is the relationship between pressure and volume according to Boyle's Law?

Inversely proportional Signup and view all the answers

What is the term for the difference in pressures across the entire lung and pleura?

Transpulmonary pressure Signup and view all the answers

What is the purpose of surfactant in the lungs?

To decrease the surface tension of the alveoli Signup and view all the answers

What is the characteristic of turbulent flow in airways?

More resistance to ventilation Signup and view all the answers

What is the definition of dead space in the context of ventilation?

Ventilated but not perfused Signup and view all the answers

What is the characteristic of pulmonary blood flow?

Low pressure system very sensitive to small changes Signup and view all the answers

What is the term for the diversion of blood flow from hypoxic or atelectic alveoli to an area of better ventilation or diffusion?

Hypoxic Pulmonary Vasoconstriction Signup and view all the answers

What is the term for the amount of CO2 in arterial blood compared to that in exhaled gas, which is used to describe the amount of physiologic dead space in a person's lungs?

Bohr equation Signup and view all the answers

What is the normal Ventilation/Perfusion ratio?

4L/5L Signup and view all the answers

What is the term for the pressure in the lungs?

Intrapulmonary pressure Signup and view all the answers

What is the term for the pressure inside the alveoli at the end of inspiration where there is no airflow that reflects lung compliance?

Pplat Signup and view all the answers

What is the result of high O2 tension and hypocapnia on pulmonary vessels?

Vasodilation Signup and view all the answers

What is the definition of the conducting zone in the airway?

All parts of the airway prior to the respiratory bronchioles, i.e. from the nose to the terminal bronchioles Signup and view all the answers

What does the respiratory zone consist of?

Respiratory bronchioles, alveolar ducts, and alveoli Signup and view all the answers

What type of airways are responsible for gas exchange after the terminal airways?

Respiratory bronchioles, alveolar ducts, alveoli Signup and view all the answers

What is the main structural difference between terminal bronchioles and other bronchioles?

Terminal bronchioles are tented by connective tissue, not cartilage Signup and view all the answers

During respiration, what happens to terminal bronchioles?

They are more susceptible to compression Signup and view all the answers

Closing volume is similar to atelectasis in what ways?

Both are forms of airway collapse with closing volume occurring in small airways and atelectasis occurring to alveoli Signup and view all the answers

What is a characteristic of closing volume?

It is dynamic and depends on disease state and position of patient Signup and view all the answers

What happens to static effective compliance in situations where it's harder to inflate the lung, such as in fibrosis, ARDS, or obesity?

It decreases Signup and view all the answers

What happens to static effective compliance in cases of emphysema?

It increases Signup and view all the answers

What is dynamic compliance in relation to lung function?

The compliance of the lung when air is moving (Vt/PIP-PEEP) Signup and view all the answers

Why do lungs exhibit less compliance at high and low volumes?

At high volumes, lungs are less compliant because there is less change in volume per unit of pressure, and at low volumes, lungs are less compliant because it takes more pressure to fill. Signup and view all the answers

What forces influence elastic recoil and therefore dynamic compliance in the lung?

Elastic fibers and surface tension from surfactant Signup and view all the answers

What is true about intrapleural/intrathoracic pressure? (select 2)

It is always negative to keep lungs inflated Signup and view all the answers

Which spinal nerves provide the motor innervation for the diaphragm?

Phrenic nerve Signup and view all the answers

What happens to the diaphragm and intercostal muscles during inspiration?

They contract/diaphragm flattens and move downward to increase lung volume Signup and view all the answers

What happens to the diaphragm and intercostals during exhalation?

They relax and move upward to decrease lung volume Signup and view all the answers

What type of innervation does the vagus nerve supply to the lungs?

Sensory and parasympathetic Signup and view all the answers

What is the approximate distance from the incisors to the carina in normal-sized adults?

26cm Signup and view all the answers

Pressure is directly proportional to tension and inversely proportional to radius according to what law?

Laplace's law P = 2T/R Signup and view all the answers

Why are smaller alveoli more likely to collapse?

They have higher pressures Signup and view all the answers

What are the factors that contribute to turbulent flow?

All of the above Signup and view all the answers

According to Poiseuille's law, why do pulmonary vessels have decreased resistance compared to systemic vessels?

They are shorter and have a smaller diameter Signup and view all the answers

What are some causes of dead space that block perfusion?

Pulmonary embolism (PE) Signup and view all the answers

What are some causes of shunt that can block ventilation?

All of the above Signup and view all the answers

What is the relationship between the volume of conducting airways and anatomic dead space?

The volume of conducting airways is equal to anatomic dead space, which is 2mL/kg Signup and view all the answers

What does the term 'shunt' refer to in the context of airway zones?

Perfused but not ventilated Signup and view all the answers

What does Pplat, or plateau pressure, measure and what is the goal pressure?

Static lung compliance; <35cmH2O Signup and view all the answers

What does PIP measure?

Airway resistance and compliance by measuring the highest pressure generated at the end of the inspiratory phase Signup and view all the answers

What is the significance of a PIP target of less than 30 cmH2O?

It is the ideal pressure for a ventilated patient Signup and view all the answers

What is the normal I:E ratio, and how can it change in obstructive disease?

1:2, increases to 1:4 Signup and view all the answers

What is the significance of static vs dynamic lung compliance?

Static lung compliance is a measure of lung elasticity, while dynamic lung compliance is affected by airway resistance. Signup and view all the answers

What is true about Pressure-Controlled Ventilation (PCV)?

There is a pressure limit but no volume limit in PCV Signup and view all the answers

What is a key benefit of PCV-VG in airway management?

Delivering a set volume at the lowest possible pressure using a decelerating flow Signup and view all the answers

What type of ventilation is SIMV?

Synchronized intermittent mandatory ventilation where ventilator breaths are synchronized with patient's inspiratory effort with added pressure support Signup and view all the answers

What is the guaranteed Vt in a trigger window in SIMV?

Only the Vt within the trigger window, whether pt triggered or ventilator triggered Signup and view all the answers

What is a requirement for SIMV mode?

It must be used with PCV, VCV, or PCV-VG Signup and view all the answers

In SIMV-VCV, what type of breaths does the ventilator deliver , and what type of support do additional breaths receive?

Synchronized breaths at a set volume and rate, pressure supported Signup and view all the answers

In SIMV-PCV, how does the vent deliver breaths?

At set inspiratory pressure and RR with additional breath being pressure supported Signup and view all the answers

What is the main function of the vent in SIMV-PCV-VG mode?

Delivers synchronized breaths at the lowest possible inspiratory pressure to achieve a set volume based on set RR with additional breaths being pressure supported Signup and view all the answers

What is the significance of setting the flow trigger to the lowest level of 0.2?

Independent respiratory effort correlates to a flow trigger of 0.2 Signup and view all the answers

What is the effect of lowering the flow trigger on impedance?

Decreases impedance - it's hard to breathe through a straw Signup and view all the answers

What is the difference in the effect of PIP/driving pressure and PEEP on alveoli?

PIP/driving pressure recruit alveoli, while PEEP maintain openness of alveoli Signup and view all the answers

What ventilator modes are used for spontaneously breathing patients?

CPAP-PSV Signup and view all the answers

What is the main feature of the PSV Pro mode in mechanical ventilation?

Pressure control. Pt triggers RR, Vt, and timing. Backup to SIMV-PCV if apneic Signup and view all the answers

What are the characteristics of CPAP PSV mode? (select 2)

Set pressure and minimum RR, patient triggers RR, Vt, and timing Signup and view all the answers

What is atelectrauma?

Shearing forces through constant collapse and opening of alveoli Signup and view all the answers

What is Biotrauma?

Trauma from infection Signup and view all the answers

Study Notes

Airway Zones

Conducting zone: all parts of the airway prior to respiratory bronchioles (nose to terminal bronchioles), also known as anatomic dead space
Respiratory zone: everything after respiratory bronchioles, consisting of respiratory bronchioles, alveolar ducts, and alveoli
20-25 generations prior to reaching alveoli
7th generation and beyond: small airways

Terminal Bronchioles

Last structure perfused by bronchial circulation
End of conducting airways (anatomic dead space)
Cellular structure changes from moving air to gas exchange after terminal airways
Tent-like structure, not supported by cartilage, prone to closure from compression of pulmonary tissue during respiration
Closing volume: lung volume at which small airways close, dependent on disease state and patient position
Closing capacity: closing volume + residual volume

Compliance

Definition: change in volume/pressure
Compliant lungs have a greater change in volume than less compliant ones
Static effective compliance: describes pressure-volume relationship when air is not moving (Vt/Plateau pressure – PEEP)
Dynamic compliance: compliance of the lung when air is moving (Vt/PIP-PEEP)
Compliance is volume-dependent: at extremely high and low volumes, lungs are less compliant

Elastic Recoil

Lung's tendency to return to its original shape after stretching/compression, responsible for emptying the lung during exhalation
Forces influencing elastic recoil (e.g., elastic fibers and surface tension from surfactant) are responsible for emptying the lung during exhalation and influence compliance

Pulmonary Pressures

Intrapulmonary pressure: pressure in the lungs
Intrapleural/intrathoracic pressure: pressure between 2 layers of the pleura, always negative to keep lungs inflated, becomes more negative during inspiration
Transpulmonary pressure: difference in pressures across the entire lung and pleura
Diaphragm innervated by phrenic nerve branch
Normal breathing is negative pressure breathing

Laplace Law

P = 2T/R, pressure is directly proportional to tension and inversely proportional to radius
Smaller alveoli have higher pressures and are more likely to collapse, surfactant prevents this by reducing tension

Flow

Both laminar and turbulent flows are present in airways
Turbulent flow: more resistance to ventilation, factors contributing to turbulent flow include >25-degree bend in tube, high flows, corrugated tubing, ETT tube (smaller tubes are more turbulent)

Pulmonary Blood Flow

Pulmonary vessels are shorter than systemic vessels, decreasing resistance – Poiseuille's law
Bronchial arteries: feed the lungs, 2% of CO, do not participate in gas exchange
Pulmonary arteries: transport unoxygenated blood to the lungs for oxygenation, low-pressure system, sensitive to small changes

V/Q Basics

Normal Ventilation/Perfusion: 4L/5L
Dead space: ventilated but not perfused, 2mL/kg anatomic dead space
Shunt: perfused but not ventilated
Bohr equation: describes physiologic dead space by comparing arterial CO2 to exhaled gas
High V/Q: high O2 and low CO2
Low V/Q: low O2 and high CO2

Hypoxic Pulmonary Vasoconstriction

HPV: diversion of blood flow from hypoxic or atelectic alveoli to areas of better ventilation or diffusion
Increase blood flow to lungs to improve gas exchange
High O2 tension and hypocapnia vasodilate pulmonary vessels, hypercarbia and acidosis cause vasoconstriction

Ventilator Modes

Pplat: reflection of pressure inside alveoli at the end of inspiration, correlates with lung compliance
Restrictive lung disease: reduced compliance, PIP and Pplat elevated, require higher PIP and PEEP
Obstructive lung disease: increased compliance, PIP elevated, Pplat normal or elevated, require higher PIP and potentially lower PEEP

Pulmonary Physiology

Factors influencing lung compliance:
- Emphysema (increased compliance)
- Fibrosis, ARDS, obesity (decreased compliance)
Compliance is volume-dependent:
- Lungs are less compliant at extremely high and low volumes
- At high volumes, it's harder to fill the lungs (less change in volume per pressure)
- At low volumes, it takes more pressure to fill the lungs
Elastic recoil:
- Tendency of the lung to return to its original shape after stretching/compression
- Responsible for emptying the lung during exhalation
- Forces influencing elastic recoil (e.g., elastic fibers, surface tension from surfactant) affect compliance

Pulmonary Pressures

Boyle's Law: pressure and volume are inversely related
Intrapulmonary pressure: pressure inside the lungs
Intrapleural/intrathoracic pressure: pressure between the two layers of the pleura (always negative to keep lungs inflated, becomes more negative during inspiration)
Transpulmonary pressure: difference in pressures across the entire lung and pleura
Diaphragm: innervated by the phrenic nerve, contracts/flattens/moves downward during inspiration, relaxes/moves upward during exhalation

Laplace Law

P = 2T/R: pressure is directly proportional to tension and inversely proportional to radius
Smaller alveoli have higher pressures and are more likely to collapse (surfactant reduces tension to prevent this)

Airflow and Resistance

Both laminar and turbulent flow are present in airways
Turbulent flow contributes to resistance to ventilation
Factors contributing to turbulent flow: >25 degrees bend in tube, high flows, corrugated tubing, ETT tube (smaller tubes are more turbulent)

Pulmonary Blood Flow

Pulmonary vessels: shorter than systemic vessels, with decreased resistance (Poiseuille's Law)
Bronchial arteries:
- Like coronary arteries in the heart
- Feed the lungs (2% of CO)
- Do not participate in gas exchange
Pulmonary arteries:
- Transport unoxygenated blood to the lungs for oxygenation
- Low-pressure system with low PVR, sensitive to small changes
- Changes in circulation are locally mediated by changes in O2 and CO2

V/Q Basics

Normal Ventilation/Perfusion: 4L/5L
Dead space: PE, cardiogenic shock
Shunt (i.e., Airway Zones): conducting zone (anatomic dead space) and respiratory zone (alveoli)
Terminal bronchioles:
- Last structure perfused by bronchial circulation
- End of conducting airways (anatomic dead space)
- Cellular structure changes to facilitate gas exchange
- Tented by connective tissue, prone to closure during respiration
- Closing volume: lung volume at which small airways close (dependent on disease state, patient position)

Compliance and Ventilator Management

Compliance definition: change in volume per pressure
Compliant lungs have a greater change in volume than less compliant ones
Static effective compliance describes the pressure-volume relationship when air is not moving (Vt/Plateau pressure - PEEP)
Decreased compliance in situations where it's harder to inflate the lung (e.g., shunt, pneumonia, atelectasis, airway obstruction)

Dead Space and Shunt

Dead space: ventilated but not perfused
Alveolar dead space: perfused by pulmonary circulation
Physiologic dead space: anatomic dead space + alveolar dead space
Shunt: perfused but not ventilated
Bohr equation: describes the amount of physiologic dead space in a person's lungs by comparing CO2 in arterial blood to that in exhaled gas

Hypoxic Pulmonary Vasoconstriction

Diversion of blood flow from hypoxic or atelectic alveoli to areas of better ventilation or diffusion
Increases blood flow to lungs to improve gas exchange
High O2 tension and hypocapnia vasodilate pulmonary vessels, while hypercarbia and acidosis cause vasoconstriction

Ventilator Modes

Pplat: reflection of the pressure inside the alveoli at the end of inspiration, correlates with lung compliance
Restrictive lung disease: reduced compliance, increased resistance, elevated PIP and Pplat
Obstructive lung disease: increased compliance due to air trapping, increased airway resistance, elevated PIP, normal or elevated Pplat

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Description

Learn about the different airway zones, including the conducting zone and respiratory zone, their structures, and functions in the respiratory system.