respiratory failure Flashcards
Define respiratory failure
Syndrome of inadequate gas exchange due to dysfunction of one or more components of the respiratory system
What are the three components of the respiratory system?
Nervous system, respiratory muscle, pulmonary
How does the nervous system contribute to the respiratory system?
CNS/ brainstem (ventro-lateral medulla) contains respiratory centres.
PNS and neuromuscular junction
What happens in terms of ventilation when the pressure in the pleura is more negative?
There is a greater transmural pressure gradient therefore the alveoli become larger and less compliant resulting in less ventilation
What happens in terms of ventilation when the pressure in the pleura is less negative?
Smaller transmural pressure gradient therefore the alveoli become smaller and more compliant so more ventilation
What happens in terms of lung perfusion when there is a lower intravascular pressure?
Less recruitment, greater resistance, lower flow rate
What happens in terms of lung perfusion when there is a higher intravascular pressure?
More recruitment, less resistance and higher flow rate
What are the three classifications of respiratory failure?
Acute, chronic, acute on chronic
What are some examples of acute respiratory failure?
Pulmonary: infection, aspiration, primary graft dysfunction. Extra-pulmonary: trauma, pancreatitis, sepsis. Neuromuscular: myasthenia/GBS
What are some examples of chronic respiratory failure?
Pulmonary: COPD, lung fibrosis, CF, lobectomy. Muscoskeletal: muscular dystrophy
What are some examples of acute on chronic respiratory failure?
Infective exacerbation of COPD or CF, myasthenic crises, post operative
What is the biggest risk factor in males for respiratory failure and what is the biggest risk factors in females?
Males = smoking. Females = household air pollution
What are the four different physiological classifications of respiratory failure?
Type 1 (hypoxemic). Type 2 (hypercapnic). Type 3. Type 4
What is meant by the term hypoxemic?
below-normal level of oxygen in your blood, specifically in the arteries
What is meant by the term hypercapnic
an elevation in the arterial carbon dioxide tension
What is type 1 respiratory failure?
Failure of oxygen exchange, pO2<60. Leads to increased shunt fraction due to alveolar flooding. Hypoxemia despite adequate levels of inspiration. Causes collapse, pulmonary oedema, fibrosis or embolism and hypertension
What is type 2 respiratory failure?
Failure to exchange or remove CO2, pCO2>45. Decreased alveolar minute ventilation, dead space ventilation. Seen in NM disease or COPD, obstructive airway disease
What is type 3 respiratory failure?
Perioperative respiratory failure. Increased atelactasis due to low functional residual capacity with abnormal abdominal wall mechanics. Results in hypoxemia or hypercapnia, can be prevented with good postural positioning
What is type 4 respiratory failure?
Shock. Poor perfusion of the lung, intubated and ventilated during shock. Ventilator effects on LV reducing afterload but has negative effect on RV as increases preload
Define minute ventilation?
Gas entering and leaving the lungs per minute
Define alveolar ventilation
Gas entering and leaving the alveoli per minute
How do we calculate minute ventilation?
Tidal volume (L) x breathing frequency
How do we calculate alveolar ventilation?
(Tidal volume (L) - dead space (L)) x breathing frequency
What are the risk factors associated with chronic respiratory failure?
COPD
Pollution
Recurrent pneumonia
CF
Pulmonary fibrosis
Neuro-muscular diseases
What are the risk factors associated with acute respiratory failure?
Infection – viral, bacterial
Aspiration
Trauma
Pancreatitis
Transfusion
What is commonly seen alongside acute respiratory failure?
Lower respiratory tract infections, aspiration of gastric contents, trauma, pulmonary vascular disease, pancreatitis
Why is aspiration of gastric contents often seen alongside acute respiratory failure?
Acid results in response in the lungs
Outline how vascular supply injury can lead to acute lung injury
Leads to damage of lung interstitium which is necessary for structural support
Outline how activation of alveolar macrophages leads to acute lung injury
When alveolar macrophages are activated by infection or inflammation release further cytokines.
IL-6 and TNF-alpha, (also TNFR1) well established in response to ARDs
In response to inflammatory setup, get alveolar fluid build-up/protein-rich oedema forming within lung.
Degradation of surfactant so lung less efficient at expanding
Migration of leukocytes out of blood vessels into interstitium where they can cause damage before getting to site of interest, due to chemokines
Secrete proteases + other inflammatory mediators causing damage and fluid build up.
Larger gap between alveoli and capillary so gas exchange less effective
What are the pulmonary causes of ARDS?
Aspiration, trauma, burns, surgery, drug toxicity, infection
What are the extra-pulmonary causes of ARDS?
Trauma, pancreatitis, burns, transfusion, surgery, BM transplant, drug toxicity, infection
What pharmacological therapies have been tried to treat ARDS?
Steroids like dexamethasone, salbutamol, surfactant, N-acetylcysteine, neutrophil esterase inhibitor, GM-CSF, statins
What pharmacological treatments are currently being trialled for ARDS?
Mysenchymal stem cells, keratinocyte growth factor, mircovesicles, extra corporeal removal of CO2 using ECMO light circuit
What are the underlying distinct biological processes in ARDS?
Pulmonary vascular, endothelial inflammatory response
Thrombosis -> micro emboli – vast areas of lung with poor perfusion
Angiogenesis -> radiological evidence of new blood vessel formation
What therapeutic interventions are offered to treat underlying disease of ARDS?
Inhaled therapies -> bronchodilators, pulmonary vasodilators (esp. if proven RH failure)
Steroids
Antibiotics
Anti-virals
Drugs -> pyridostigmine, plasma exchange, IViG, rituximab
What therapeutic intervention is offered to give respiratory support to those with ARDS?
Physiotherapy
Oxygen (COPD + type 2 chronic resp. failure need diff. oxygen management to normal)
Nebulisers salbutamol, ipratropium bromide, saline, NAC to reduce mucus.
High flow oxygen – nasal cannula, face masks
Non invasive ventilation – stent to open alveoli
Mechanical ventilation
Extra-corporeal support – membrane lung
What therapeutic intervention is given for multiple organ support to those with ARDS?
Cardiovascular support fluids, vasopressors, inotropes, pulmonary vasodilators
Renal support haemofiltration, haemodialysis
Immune therapies plasma exchange, convalescent plasma
What are the sequelae of ARDS?
Poor gas exchange, infection, inflammation, systemic effects
