test 2 Flashcards
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
Blind suctioning of the airways can cause damage to
-carina which causes secretions to build up and airway collapse
what is the most common lung complication after bypass?
-atelectasis (70% of cases)
preoperative contributions to atelectasis
-Smoking, chronic bronchitis
-Obesity
-Cardiogenic Pulmonary Edema
intraoperative contributions to atelectasis
-Passive ventilation
-Monotonous ventilator pattern
bypass contributions to atelectasis
-Surfactant inhibition
-Plasma, lung distension, lung ischemia
-Increased extravascular lung water (complement activation)
-Heart rests on left lobe
-Open pleural cavity – accumulation of blood and fluid
CLINICAL CONSEQUENCES OF ATELECTASIS
-functional residual capacity decreased can decrease by 40-50%
pump lung
-acute respiratory failure
-Lungs diffusely congested
-Intra=alveolar and instersitial edema
-Hemorrhagic atelectasis
-Vessel lumen full of neutrophils
-Diffuse swelling of endothelial cells
WHAT MIGHT CAUSE ACUTE LUNG INJURY?
- Embolic load
- Complement activation / inflammatory response
- Hypoxia of lung tissue
- Hemodilution
- Elevated pulmonary artery pressure (increase resistance)
acute lung failure
-microemboli overload
-Aggregated proteins, Platelet fragments, Damaged, neutrophils, Fibrin, Fat globules
-Introduction of arterial and cardiotomy filters greatly
reduced degenerative lesions in lungs
acute lung failure complement activation
- found where blood meets foreign surface
- Provides function for fighting invading organisms
opsonization
-coats an invader with antibodies which tags it and stops it from attacking our cells
complement and the ECC
- complement exposes neutrophils - become sticky
- neutrophils degranulate- break into small pieces and release O2 free radicals which damage endothelial cells (capillary leakage)
ACUTE LUNG FAILURE: HYPOXIA
- lung tissue still has metabolic activity
- bronchial circulation is still functional
- COMPLIMENT IS THE BIGGEST PROBLEM
- atelectasis leads to compliment
hemodilution to lung injury
- provide potential for lung injury
- does not impair surfactant
what is the biggest offender of acute lung failure
COMPLIMENT ACTIVATION
acute bronchospasm during CPB
- C5a triggers it
- very rare
MANAGEMENT OF BRONCHOSPASM
- Stay on bypass or go back on bypass
- Support patient while anesthesia treats
PREVENTION AND TREATMENT OF ACUTE LUNG INJURY
- ECC – attenuate immune response
- coat circuit for better biocompatability
- Hemofiltration
- filter inflammatory mediators
- leukocyte depletion
- mechanical ventilation (anesthesia)
- corticosteroids= decrease immune response to CPB
- inhaled Nitric Oxide- causes pulmonary vasodilation and decreases neutrophil adhesion
what is the most common complication after bypass
- Acute lung injury
- atelectasis
most common cause of acute lung injury
mechanical ventilation
