Respiratory failure Flashcards
What is respiratory failure?
syndrome of inadequate gas exchange due to dysfunction of 1 or more components of the respiratory system
What are the components of the respiratory system?
Nervous system: - CNS/brainstem - peripheral nervous system - neuromuscular junction Respiratory muscle: - diaphragm+thoracic muscles - extra thoracic muscles Pulmonary: - airway - alveolar-capillary - circulation
What are causes of acute respiratory failure?
- pulmonary: infection, acid aspiration, or primary graft dysfunction after lung tx
- extra pulmonary: trauma, pancreatitis, sepsis
- neuromuscular: myasthenia gravis or GBS
What are causes of chronic respiratory failure?
- pulmonary/airway disease: COPD, lung fibrosis, CF, post-lobectomy
- musculoskeletal: muscular dystrophy
What are causes of acute on chronic respiratory failure?
- infective exacerbation of chronic diseases: COPD, CF
- post operative
- myasthenia crises
What is type I respiratory failure?
- acute hypoxemic respiratory failure
- PaO2 <60
- failure of oxygenation
- due to alveolar flooding
- due to collapse, aspiration, pulmonary oedema, fibrosis, pulmonary embolism, pulmonary hypertension
- shunt
- hypoxemia refractory to supplemental oxygen (unresponsive)
What is type 2 respiratory failure?
- hypercapnic PaCO2 > 45
- failure to remove CO2
- due to decreased alveolar minute ventilation (hypoventilation)
- or dead space ventilation
- due to nervous system disease, neuromuscular, muscle failure, airway obstruction e.g. COPD, chest wall deformity
What is type 3 respiratory failure?
- perioperative
- due to atelectasis/collapse of airways due to low functional residual capacity (abnormal abdominal wall mechanics limiting the chest wall opening up)
- hypoxaemia OR hypercapnoea
- prevention: good postural position when when extubating, analgesia so not tensing abdominals
What is type 4 respiratory failure?
- shock
- patients who are intubated and ventilated in the process of resuscitation for shock
- poor perfusion of lungs
- ventilator good for LV due to reduced after load, but bad for RV due to increased preload
Which criteria are used to classify ARDS?
Berlin definition of acute respiratory distress syndrome
- timing: within 1 week of known clinical insult or new/worsening respiratory symptoms
- chest imaging: bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules
- origin of oedema: respiratory failure not fully explained by cardiac failure or fluid overload
- oxygenation/PF ratio
What are the possible causes of shortness of breath/ARDS?
- lower respiratory tract infection: viral or bacterial
- aspiration of gastric contents
- trauma–> transfusion
- pulmonary vascular disease: pulmonary embolus, haemoptysis
- extrapulmonary: pancreatitis, new medications, surgery, bM transplant, burns
How does acute lung injury occur? (inflammation, infection, immune response)
- infection in alveolus or higher up in airway, or systemic infection w/ bacteraemia
- alveolar macrophages activated by infection or inflammation release further cytokines: IL-6, IL-8, TNF-alpha
- -> in response, protein-rich oedema fluid builds up in alveolus–> inactivated/degraded surfactant, so alveolus can’t expand as well
- when alveolus inflamed, leukocytes migrate out of blood vessels into interstitium and cause damage, secreting proteases and other inflammatory mediators
- -> more oedema, increasing distance between alveolus and blood vessel- less efficient gas exchange
- -> respiratory failure and/or potential dependence on respiratory support
How has TNF signalling been implicated in in vivo experiments?
reduction of alveolar lung injury by using knockouts of TNFR-1 or blocking TNFR-1 signalling pathway w/ domain antibodies
What are the commonest DAMPS in lung injury?
HMGB-1 and RAGE
What are the commonest cytokines released in lung injury?
IL-6, IL-8, IL-1beta, and IFN-y
What therapies have been tried in ARDS?
- steroids e.g. dexamethasone
- salbutamol
- surfactant
- N-acetylcysteine (reduces viscosity of secretions)
- neutrophil esterate inhibitors
- GM-CSF
- statins
How do we treat the underlying disease in ARDS?
- inhaled therapies: bronchodilators, pulmonary vasodilators (in right heart failure)
- steroids
- antibiotics
- anti-virals e.g. Tamiflu
- drugs: pyridostigmine (for myasthenia gravis), plasma exchange, IViG (antibodies), rituximab
What respiratory support may be given in ARDS?
- physiotherapy
- oxygen
- nebulisers
- high flow oxygen
- non invasive ventilation
- mechanical ventilation (requires intubation)
- extra-corporeal support (ECMO)
How do we provide multiple organ support in ARDS?
- cardiovascular support: fluids, vasopressors, inotropes, pulmonary vasodilators
- renal support: haemofiltration, haemodialysis
- immune therapy: plasma exchange, convalescent therapy
What are the pitfalls of ventilation?
patients who don’t completely exhale in normal life/ with tight airways (e.g. COPD, asthma) = difficult to manage, as you can get trapped air in lung
What is the Murray score?
- scoring system to guide escalation of therapy
- uses P/F ratio CXR, PEEP, and lung compliance
- inc. score = more severe
- proning might reduce score
What are the inclusion criteria for ECMO?
- severe respiratory failure w/ non-cardiac cause (Murray lung injury score 3 or above)
- positive pressure ventilation not appropriate e.g. significant tracheal injury
What are the exclusion criteria for ECMO?
- contraindication to continuation of active treatment (i.e. select those who have reversible disease process that is unlikely to lead to prolonged disability)
- significant comorbidity
- significant life limiting comorbidity
What are the issues with ECMO?
- time to access
- referral system- geographical inequity
- consideration of referral (differs)
- technical difficulties obtaining access
- clotting/bleeding
- harm-dynamics
- ££££
