Respiratory Failure Flashcards
What is respiratory failure?
syndrome of inadequate gas exchange due to dysfunction of one or more components of the respiratory system
What failing parts of the nervous system that can cause respiratory failure?
1- The Nervous system- Central nervous system through disordered consciousness, peripheral nervous system e.g. the outflow of the cervical spinal cord, NMJ- e.g., Myasthenia gravis
2- The respiratory muscles- Injured or splinted, or weak
3- Pulmonary
The conducting airways and the tissue of the lung- Reactive airways disease, inspissation with secretions, pulmonary oedema, PEs
What are the failing respiratory muscles which can cause respiratory failure?
- Diaphragm & thoracic muscles
- Extra-thoracic muscles
What are the failing parts of the pulmonary system which can cause respiratory failure?
- airway disease
- alevolar-capillary
- circulation
How has the epidemiology of chronic respiratory failure changed since the 1990s?
More prevelant, rise in 40%
Disproportionate effect on women across Russia and North America which has not improved
What is the biggest risk factor of chronic respiratory failure for men?
smoking
What is the biggest risk factor of chronic respiratory failure for women?
household air pollution from solid fuels
What is the prevalence of acute respiratory failure?
- 6-700 people/year
- 30-40% mortality
What are the risk factors for chronic respiratory failure?
- COPD
- Pollution
- Recurrent pneumonia
- Cystic fibrosis
- Pulmonary fibrosis
- Neuro-muscular diseases
What are the risk factors for acute respiratory failure?
- viral or bacterial infection
- aspiration
- trauma
- pancreatitis
- transfusion
-aspiratioon
What factors can increase the mortality of acute respiratory failure?
- severity
- age
Which dieseases can be classified as acute respiratory failure?
- infection
- aspiration
- primary graft dysfunction
- trauma
- pancreatitis
- sepsis
- myasthenia/GBS
What possible diseases are classed as chronic respiratory failure?
- COPD
- Lung fibrosis
- CF
- lobectomy
- muscular dystrophy
What are examples of acute on chronic respiratory failure?
- Infective exacerbation (COPD, CF)
- Myasthenic crises
- Post-operative complications
Which area of the lung has greater ventilation and why?
- bottom of lung
- smaller transmural pressure
- alveoli are smaller and more compliant
Which part of the lung has greater perfusion and why?
- bottom of lung
- higher intravascular pressure
- more recruitment and less resistance
- higher flow rate
Where will the bulk of gas exchange occur in the lungs?
Middle and bottom
What is compliance?
The tendency to distort under pressure
Compliance is the volume per unit pressure- ease of stretching
Describe the pressure in each zone in ventilation perfusion matching
Zone 1- Alveolar pressure is higher than arterial and venous
2- arterial pressure is higher than alveolar and venous
3- arterial and venous are higher than alveolar
What is elastance?
The tendency to recoil to its original volume
Elastance is the amount of pressure required to distend by a volume- resistance to being stretched
-The elastic recoil of the chest and lung tissue
What are the equations for minute ventilation and alveolar ventilation?
Minute ventilation is gas entering and leaving the lungs
tidal volume x breathing frequency
Alveolar ventilation is gas entering and leaving the alveoli
(tidal volume - dead space) x breathing frequency
What happens in type 1 (hypoxemic) respiratory failure?
PaO2 < 60 failure of oxygen exchange - increased shunt fraction (QS/QT) - due to alveolar flooding - refractory to supplemental oxygen
What can cause type 1 respiratory failure?
- collapse
- aspiration
- pulmonary oedema
- fibrosis
- pulmonary embolism
- pulmonary hypertension
What happens in type 2 (hypercapnic) respiratory failure?
PaCO2 > 45
failure to exchange or remove carbon dioxide
- decreased alveolar minute ventilation
- dead space ventilation
What can cause type 2 respiratory failure?
- CNS/PNS
- muscle failure
- airway obstruction
- chest wall deformities
What happens in type 3 (perioperative) respiratory failure?
- increased atelectasis (airway collapse) due to low functional residual capacity
- abnormal abdominal wall mechanics (limiting chest movement)
- hypoxaemia OR hypercapnia
How do you prevent type 3 respiratory failure?
- anethetic or operative technique
- posture
- incentive spirometry
- analgesia
- efforts to lower intra-abdominal pressure
What happens in type 4 (shock) respiratory failure?
poor lung perfusion in patients that are intubated and ventilated during shock (septic, cardiogenic, nuerologic)
How do you prevent type 4 respiratory failure?
optimise ventilation to improve gas exchange and to unload the respiratory muscles, lowering oxygen consumption
What are the effects of ventilation on the heart?
reduced afterload (good for the LV) increased preload (bad for the RV)
What are the 5 main origins of shortness of breath?
- lower respiratory tract infections viral or bacterial
- aspiration
- trauma transfusion
- pulmonary vascular disease
- extrapulmonary: pancreatitis; new medications