the lungs are covered with
-pleura
what covers the top of the diaphram
-parietal pleura
what is between the parietal pleura and visceral pleura
-serous fluid
what happens when our thoracic cage expands
-pulls the lungs
Inspiration (normal conditions)
- Diaphragm contracts (pulled down)
- Increases size of thoracic cavity
- Decreases pleural pressure (air comes in) (builds up - pressure) (goes from a place of higher pressure to lower pressure)
- Lifting up of the thoracic cage
- Lungs being stretched and pulled
Expiration (normal conditions)
- Diaphragm relaxes – domed position
- Lungs recoil
- Increases pleural pressure (force air out)
- Size of thoracic cavity decreased
PULMONARY PHYSIOLOGY
-Lungs are very elastic
-Want to collapse
-Surface tension very high
-Surfactant Decreases surface tenstion
Bronchial circulation
-High pressure, low-flow (small vessels)
-Arterial blood to the tissues of the respiratory system (1-2% of cardiac output)
-Branches off of thoracic aorta (Oxygenated blood)
-Returns venous blood to left
atrium
Pulmonary circulation
-Low pressure, high flow
-Venous blood to pulmonary
capillaries (Gas exchange)
-Returns arterial blood to left
atrium (Via Pulmonary veins)
What happens to the lungs when we go on bypass?
-Stop ventilating lungs (Lungs collapse)
-Resistance to blood flow increases (No pulmonary blood flow (Bypassing))
AND (Little bronchial flow (due to resistance))
Atelectasis
-Collapse of alveoli (Can be localized OR Can be entire lung)
what happens to the lungs post-CPB
-Some atelectasis remain
- Range in degree of severity
- can lasts for months after bypass
- acute respiratory distress syndrome (ARDS)
Degrees of severity of atelectasis
-Micro-atelectasis (Not detectable clinically)
-Complete collapse of entire lobe
-Intermediate degrees
Factors affecting pulmonary function
-Atelectasis
-Pleural disruption
-Impaired lung compliance
-SIRAB (systemic inflammatory response after bypass)
Atelectasis results from (2)
- Blockage of small bronchi with mucous
- Obstruction of a major bronchus (left side more likely to build up mucous)
What happens during atelectasis?
- air becomes trapped
- Air is absorbed into the pulmonary capillaries and creates negative pressure
- Alveoli collapse
If alveoli can’t collapse due to fibrosis
-Created negative pressure in alveoli
-Pulls fluid out of capillary into alveoli
-Massive collapse of entire lung
Why is atelectasis so common on bypass?
-anesthesia give neuromuscular blocker which relaxes the diaphram (moves up) which decreases space in thoracic cavity = pleural pressure increases and less likely to move air
Resorption atelectasis
- all air is sucked out
- low ventilation to perfusion ratios (mismatch) resulting in airway obstruction
residual atelectasis
- heart lies on lung
- lung lies on self so the back side of the lung effected
- retraction helps atelectasis
- venous cannula
what can we do to prevent atelectasis?
- not much
- must be aware of it!
- reduce chance of edema (not allowing it to go into the lungs)
- anesthesia has more control
Anesthesia’s role in atelectasis
-mechanical ventilation initiates atelectasis
Surfactant depletion
- surfactant lowers surface tension
- anesthesia lowers surfactant function
- there are huge stores of surfactant
atelectasis promotes produciton of pro-inflammatory cytokines which
-decrease surfactant synthesis which leads to lung collapse
