Respiratory failure Flashcards
What is respiratory failure?
Syndrome of inadequate gas exchange due to dysfunction of one or more components of the respiratory system
Describe the process of oxygen loading in the lungs
- Blood flows through the alveolar capillary (lining the alveolar)
- Oxygenation occurs through the alveolar- capillary membrane barrier (v. thin)
- Oxygen is taken up by the erythrocytes (RBCs)
- CO2 also will flow from a higher conc in your blood across into the alveolous to be excreted (down the conc gradient)
What is meant by “pulmonary transit time”?
“time taken for oxygenation to occur”
- in some disease (e..g lung infection)
- the barrier is wider;
- Diffusion is less efficient
- transit time increases
compare the “pulmonary transit time” with the “gas exchange time”
Gas exchange time is less (occurs faster);
- Exchange of CO2 happens much faster
- goes down much larger conc gradient
- CO2 excreted more rapidly
Describe the ventilation/ perfusion ratio at the top of the lungs
The apex (zone 1) of the lung has a higher V/Q ratio
- Very low perfusion (wasted ventilation)
= less ventilation (less perfusion than ventilation)
- GRAVITY:
- reduced blood flow to the apex
= wasted ventilation; not enough blood for gas exchange - ALVEOLI SIZE:
- Alveoli larger (but less compliant; don’t expand)
- less blood flow
- decreased pulmonary intravascular pressure
= less perfusion
- less ventilation
Describe the ventilation/ perfusion ratio at the base of the lungs?
The base (zone 3) of the lung has a lower V/Q ratio
- more ventilation
- much more perfusion (not enough air to match the O2 from the blood= wasted perfusion)
- GRAVITY:
- increased blood flow
- increased perfusion - ALVEOLI SIZE:
- smaller alveoli (more compliant; expand)
- increased blood flow
- higher intravascular pressure
= more perfusion
- more ventilation
describe the change in alveolar and arterial pressure in zones 1,2 and 3
Zone 1:
- PA>Pa>Pv
(pressure in the alveolar A is higher than the arterial pressure a)
- poor perfusion= poor ventilation
- if pulmonary pressure drops no gas exchange takes place= dead space
Zone 2:
Pa>PA>Pv
- ventilation and perfusion fairly well matched (both good)
Zone 3:
Pa>Pv>PA
-(pressure in the arterial is higher than the alveolar pressure)
- increased perfusion
What is meant by “tidal volume”?
Tidal volume is the amount of air breathed in with each normal breath
What is “inspiratory reserve volume”?
Inspiratory reserve volume is the maximum amount of ADDITIONAL air that can be taken into the lungs after a normal breath. (additional air; does not include tidal volume)
What is meant by “inspiratory capacity”?
The maximum volume of air that can be inspired after reaching the end of a normal, quiet expiration
(IC= IRV + TV)
usually= 3600 ml
What is meant by “Expiratory reserve volume”?
Expiratory reserve volume is the maximum amount of ADDITIONAL air that can be forced out of the lungs after a normal breath. (additional; does not include tidal volume)
What is meant by “residual volume”?
Residual volume is the amount of air that remains in a person’s lungs after fully exhaling.
- Lungs don’t completely empty
- that would cause them to collapse
What is meant by “vital capacity”?
Vital capacity (VC) refers to the maximal volume of air that can be expired following maximum inspiration
VC= IRV + TV + ERV
What is meant by “functional residual capacity”?
Functional residual capacity (FRC), is the volume remaining in the lungs after a normal, passive exhalation
FRC= ERV + RV
What is “total lung capacity”?
The total lung capacity (TLC) is the maximal volume of gas in the lungs after a maximal inhalation:
TLC= IRV + TV +ERV +RV
What is “minute ventilation”? how is it worked out?
“Gas entering and leaving the lungs”
Minute ventilation (L/min)=
Tidal volume (L) x breathing frequency (breaths/ min)
usually= 6L/min
What is “alveolar ventilation” how is it worked out?
“Gas entering and leaving the alveoli”
Alveolar ventilation (L/min)=
[Tidal volume (L) - Dead space (L)] x breathing frequency (breaths/ min)
usually= 4.2 L/ min
What is meant by dead space?
the volume of ventilated air that does not participate in gas exchange- just oscillating to keep the airway open
What is meant by “compliance”? how is it worked out?
“The tendency to distort under pressure”
Compliance= change in vol in airway/ change in pressure needed to do so
What is meant by “elastance”? how is it worked out?
“The tendency to recoil to its original volume”
Elastance= change in pressure/ change in vol
What is the difference between acute and chronic respiratory failure?
Acute respiratory failure is a short-term condition. It occurs suddenly and is typically treated as a medical emergency. Chronic respiratory failure is an ongoing condition. It develops gradually and requires long-term treatment
What are some example of acute respiratory failure?
- Pulmonary:
- Infection
- aspiration
- Pulmonary embolus
- Haemoptysis
- Primary graft dysfunction (Lung Tx) - Extra-pulmonary:
- Trauma
- New medications
- pancreatitis
- sepsis - Neuro-muscular:
- Myasthenia/GBS
What are some examples of chronic respiratory failure?
- Pulmonary/Airways:
- COPD
- Lung fibrosis
- CF
- lobectomy - Musculoskeletal:
- Muscular dystrophy
What is meant but acute-on-chronic respiratory failure?
Acute-on-chronic respiratory failure (ACRF) occurs when relatively minor, although often multiple, insults cause acute deterioration in a patient with chronic respiratory insufficiency
