Respiratory - Lung Anatomy and Function Flashcards
Why do we apply PEEP when a patient is intubated?
During exhalation, vocal cords slightly adducted –> physiological PEEP ± 3-4 cmH2).
When a tube splints the vocal cords open this effect is lost. extrinsic PEEP at physiological levels of ± 5 cmH20 maintains FRC and prevents atalectasis following intubation.
What is the effect of PEEP on cardiac output and intracranial pressure
PEEP increases intrathoracic pressure –> increases venous pressure –> reduces venous return –> potential to decrease CO.
Increased intrathoracic pressure may hinder venous drainage from the cerebral venous sinuses –> increased ICP.
Describe the airway generations
CONDUCTING ZONE 0 Trachea 1 Main bronchi 2 Lobar bronchi 3 - 4 Segmental bronchi 5 - 11 Subsegmental bronchi 12 - 15 Bronchioles 16 Terminal bronchioles
RESPIRATORY ZONE (exponential increase in cross sectional area –> graph)
17 - 19 Respiratory bronchioles
20 - 22 Alveolar ducts
23 Alveolar sacs
How would increasing PEEP affect a tonsillectomy
Increased PEEP with increased venous pressure may increase bleeding at the tonsillar bed, obstructing the surgeons view of the operative field.
Under what circumstances are the filtration, warming and humidification functions of the upper airways bypassed. What does this caused and how does the anaesthetist get around this problem
Endotracheal intubation.
Absence of filters/humidification and warming leads to:
- Accumulation of mucus in the lower airways (dried)
- Increased risk of infection
- Increased heat loss
- Microatalectasis
HME used - artificial humidification and warming.
Where does the trachea start
C6 (Cricoid) - T5 (Carina)
Where is the trachealis muscle
In the posterior gap of the anterolateral cartilaginous rings of the trachea.
What is the function of the cartilaginous rings of the trachea
To prevent tracheal collapse during extreme inspiratory effort with associated high negative pressure.
Describe the lung lobes
Right has three lobes: Upper middle and lower
Left has two lobes and a lingula (latin ‘little tongue’) lobe.
Describe the bronchopulmonary segments
Right - there are 10
3 upper, 2 middle and 5 lower
Left - there are 9
5 upper, 4 lower
Describe the bifurcation of the main bronchi and the clinical relevance of this
Right main bronchus bifurcates 2 cm distal to the carina whilst the left main bronchus bifurcates 5 cm distal to the carina –> keep this in mind during the insertion of double lumen endotracheal tubes: DLETTs.
Left sided double lumen tubes are preferred to right sided double lumen tubes as right sided tubes risk the occlusion of the right upper lobe bronchus by the ETT cuff.
Describe the walls of the segmental and subsegmental bronchi compared to the bronchioles
Segmental and subsegmental have respiratory epithelium surrounded by smooth muscle containing plates of irregular shaped cartilage to prevent airway collapse
Bronchiloes contain only smooth muscle subject to bronchodilatation and bronchoconstriction
What proportion of gas exchange occurs in the respiratory bronchioles + alveolar ducts vs alveoli
Resp. bronchioles + Ducts 10%
Alveoli 90%
How many alveoli do we have and what is the surface area of this
300 million alveoli
surface area 70 meters squared
What are the cell types found in the alveolus and what are their attributes and functions
Type 1 pneumocytes
Thin, cover 90% alveolar surface area –> allow for efficient gas exchange
Type 2 pneumocytes
Make alveolar surfactant
Alveolar macrophages
Found within alveolar septa and the lung interstitium.
What is the alveolar capillary barrier, how thick is it
200nm thin
3 layers
- Type 1 pneumocytes
- Extracellular matrix
- pulmonary capillary endothelium
If the alveolar capillary barrier is so this, what gives it strength?
Type IV collagen in the extracellular matrix
What are the functions of the alveolar capillary barrier
- Allow gas exchange
- Prevent gas bubbles entering circulation
- Prevent blood from entering alveolus
- Limit transudation of water
Describe the muscle groups used in inspiration (rest and forced) and expiration (rest and forced)
Inspiration
- Diaphragm (rest)
- Ext. intercostals (forced)
Expiration
- Elastic recoil of lungs –> passive exp. (rest)
- Internal intercostals –> forced expiration
What are the accessory muscles of breathing and when are these used
When additional inspiratory (SCM, Scalene muscles) or expiratory (abdominal muscles) effort is required.
What is the normal intrapleural pressure at rest and why
-5cmH20 from the chest wall’s natural tendency to spring outwards.
What are the forces acting on the lung at rest
Intrapleural pressure Ppl = -5cmH20 (natural outward spring of chest wall on parietal pleura)
Inward elastic recoil Pel - stretched elastic fibres of the lung exert an inward force
How does lung compliance affect tidal volume achieved during breathing at rest with regard to Ppl and Pel
The volume inspired is much less in a patient with ARDS with the same change in intrapleural pressure as the lungs are less distensible.
Therefore greater negative pressure, energy expenditure and hence WOB is required to generate the same tidal volumes
Describe the pathophysiology of a traumatic pneumothorax
Resting Ppl is - 5cmH20. Communication between atm and pleural space means that PB now equals Ppl and the lung succumbs to its inward elastic recoil and collapses.
List the non-respiratory function of the lungs
IMMUNLOGICAL
- filtering inspired air
- Mucociliary escalator
- alveolar macrophages
- Secretion IgA
VASCULAR
- Filter debris (bubbles and clots) from blood.
METABOLIC AND ENDOCRINE
- Inactivation: NA, serotonin, PG, bradykinin, Ach
- Conversion: ANG 1 to ANG 2
- Synthesis: surfactant, NO, heparins
- Storage: Histamine, Endothelin, Platelet aggregating factor and adenosine
Which anaesthetic drugs undergo uptake and first pass metabolism in the lungs?
Lignocaine
Fentanyl
Noradrenalin
