Anesthesia Effects on Respiratory System Flashcards
The supine position decreases FRC by ___
30%
The induction of GA decreases FRC by ___. Why?
15-20%
Loss of inspiratory muscle tone
Increased expiratory muscle tone
Diaphragm moves cephalad 4 cm
Chest wall rigidity changes
Decrease the transpulmonary pressure
Promotes alveolar collapse
Obesity and FRC
Decreases it due to:
decreased chest wall compliance &
increased airway collapsibility
Pregnancy and FRC
Decreases it due to:
Diaphragm shifts cephalad as a result of the gravid uterus
Decreased chest wall compliance
Neonates and FRC
Less alveoli leads to decreased lung compliance
Cartilaginous ribcage that is prone to collapse
Advanced age and FRC
Decreased elastic lung tissue leads to air trapping which results in increased residual volume and thus INCREASED FRC
Which positions increase FRC?
Prone, sitting, lateral
Paralysis and FRC
Decreases due to diaphragm moving cephalad which decreases lung volumes
Inadequate anesthesia and FRC
Straining leads to forceful expirations which decreases lung volumes
Excessive IV fluids and FRC
Decreases it
Fluid accumulation in dependent lung favors zone 3
High FiO2 and FRC
Decreases it
Absorption atelectasis, conversion of low V/Q unit, shunt unit
Reduced Pulmonary Compliance and FRC
Decreases it
Conditions like acute lung injury, pulmonary edema, pulmonary fibrosis, atelectasis, pleural effusion
Obstructive Lung Disease and FRC
Increases it
Air trapping increases residual volume which increases FRC
PEEP and FRC
Increases it
Recruits collapsed alveoli
Partially overcomes effects of GA
decreases venous admixture which increases PaO2
Sigh breaths and FRC
Increases it
Recruits collapsed alveoli
Prevention of Atelectasis happens through _____.
Recruitment Maneuvers
1)PEEP
2) Sigh breaths
How do you figure out PEEP values for different patients?
BMI below 25 = 6 cm H2O
BMI up to 30 = 8 cm H2O
10 cm H2O consistently reopens collapsed lung tissue
What are components of a sigh breath?
Doubling of Vt (tidal volume)
Sustained inflation of lungs to 30 cm H2O
To open all collapsed lung tissue 40 cm H2O is required
BMI > 45 will require more
The closing capacity is the sum of ___.
the closing volume and the residual volume
Closing capacity is normally well below ____.
FRC, but it rises steadily with age.
What is closing capacity?
The volume at which small airways begin to close in the dependent parts of the lungs.
Intrapulmonary shunting of deoxygenated blood promotes _____.
hypoxemia
Factors that Increase Closing volume
“CLOSE-P”
- COPD
- LV failure
- Obesity
- Extremes of age
- Pregnancy
General facts about V/Q Ratio
V/Q = alveolar ventilation/cardiac output
V/Q = (4 L/min)/(5 L/min)
V/Q are perfectly matched where the lines intersect
V > Q towards the apex
V < Q towards the base
Zone 1
Dead Space: PA > Pa > Pv
V/Q = ∞
Zone 2
Waterfall: Pa > PA > Pv
V/Q = 1
Zone 3
Shunt: Pa > Pv > PA
V/Q = 0
West Lung Zones
During anesthesia, arterial oxygenation is impaired in which patient populations?
Elderly – obese – smokers