🫀🫁Cardio & Resp🫀🫁 - Respiratory Failure Flashcards
What is the definition of respiratory failure?
Syndrome of inadequate gas exchange due to dysfunction of one or more components of the respiratory system
What are the 3 categories of causes for respiratory failure?
Nervous system
Respiratory muscle
Pulmonary causes
What are the sites of nervous system based respiratory failure?
CNS/brainstem
Peripheral nervous system
Neuro-muscular junction
What are the sites of respiratory muscle based respiratory failure?
Diaphragm and thoracic muscles
Extra-thoracic muscles
What are the pulmonary causes of respiratory failure?
Airway disease
Alveolar-capillary diseases
Circulation disruption
In which context is NMJ related respiratory failure usually seen?
Chronic respiratory failure
More severe end
What can affect the respiratory muscles, leading to respiratory failure?
Trauma
What are some examples of airway disease?
COPD
Asthma
What are some alveolar-capillary causes of respiratory failure?
Leak of alveolar fluid
Interstitial disease of the tissue itself - pulmonary fibrosis - autoimmune or secondary to infection
What is a circulation-based cause of respiratory failure?
Impeding of blood flow
e.g. embolic disease in the lung
What is a key epidemiological statistic of respiratory failure in men compared to women?
Women disproportionately more affected
“cook and clean” ideology - exposed to cooking and gases
Outline the key epidemiological points for chronic respiratory failure?
3rd leading cause of death:
-males: smoking biggest risk factor
-women: household air pollution from solid fuels
Huge social and financial costs:
-EU spends €380million annually
-Accounts for: inpatient care, lost productivity
What is meant by cooperative binding, in the context of oxygen transport?
The bonds of oxygen to Hb become stronger the more oxygen is bound
Why must lungs be specially adapted immunologically compared to other organs of the body?
Lungs receive entire blood flow every minute - exposed to anything in circulation + outside world
What is the average RBC pulmonary transit time?
0.75s
What is the average gas exchange time?
0.25s - oxygenation time
Shorter for CO2 removal - less CO2 to remove
Overall time - 0.25s
How is ventilation spread across the lung?
How is perfusion spread across the lung?
What is ventilation-perfusion matching?
Matching blood flow to the areas that are more heavily ventilated
What is the difference between a volume and capacity in lung mechanics?
Volume is a discrete section or movement (e.g. tidal volume, residual volume etc…)
Capacity is the sum of 2+ volumes
What is the tidal volume?
Volume inhaled/exhaled in a normal, relaxed breath
What is the inspiratory reserve volume?
Volume of air that can be inhaled past tidal volume on a total, forced inhalation
What is the expiratory reserve volume?
Volume of air that can be exhaled past tidal volume on a total, forced exhalation
What is the residual volume?
The volume of air left in the lungs after a forced exhalation
What is the inspiratory capacity?
Tidal volume + inspiratory reserve volume
What is the functional residual capacity?
Air remaining in lungs after tidal breaths
Expiratory reserve volume + residual volume
What is vital capacity?
Total amount of air that can be moved in and out of the lungs
Inspiratory reserve volume + tidal volume + expiratory reserve volume
Total lung capacity - residual volume
Multiple ways of calculating
What is total lung capacity?
The total volume of air able to be held in the lungs upon maximum inhalation
Vital capacity + residual volume
Sum of all volumes
Function residual capacity + inspiratory capacity
What is the clinical significance of vital capacity?
Monitor conditions of patients with neuromuscular disease
Falls below 1.5L means support is required (e.g. ventilation, breathing tuve, tracheostomy etc…)
What is minute ventilation?
Gas entering and leaving the lungs
What is alveolar ventilation?
Gas entering and leaving the alveoli
What is meant by “dead space”?
Areas/surfaces that do not participate in gas exchange
e.g. trachea, nose, mouth
What is the difference between minute ventilation and alveolar ventilation
Minute ventilation is just air entering the lungs while alveolar ventilation is air entering the alveoli specifically
Alveolar accounts for dead space, so effectively measures the volume of air that can participate in gas exchange
What is compliance?
The tendency to distort under pressure
Compliance = ∆V/∆P
A condom is very compliant, so if you blow it up, there will be an increase in volume with a subsequent relatively small increase in pressure from the condom trying to revert to its original shape, giving a high compliance value
What is elastance?
The tendency to recoil to its original volume/shape
Elastance = ∆P/∆V
A condom is not very elastic, so if you blow it up, there will be a small increase in pressure due to it trying to return to its original shape, but a large volume change, giving a small elastance value
What are the acute causes of respiratory failure?
Pulmonary: Infection, aspiration, Primary graft dysfunction (Lung Tx)
Extra-pulmonary
Trauma
Pancreatitis
Sepsis
Neuro-muscular: Myasthenia/GBS
What are the chronic causes of respiratory failure?
Pulmonary/Airways
COPD
Fibrotic lung disease
Cystic fibrosis
Lobectomy
Musculoskeletal
Muscular dystrophy
What are the acute on chronic causes of respiratory failure?
Infective exacerbation
COPD, CF
Myasthenic crises
Post operative
What is meant by “acute on chronic” in the context of respiratory failure?
Someone with chronic respiratory failure having a sudden, acute worsening (similar to an exacerbation, episode or crisis)
What is type 1 respiratory failure?
Hypoxemic (PaO2 <60 at sea level)
Failure of oxygen exchange
In clinic usually a pulmonary oedema - presents very acutely with very wet lungs
Fine crackles and pitting oedema
What is type 2 respiratory failure?
Hypercapnic (PaCO2 >45)
Failure to exchange/remove CO2
COPD/chest wall deformity, even neuromuscular disease
Basically anything that decreases alveolar minute ventilation
Patients present with tiring out very quickly
What is type 3 respiratory failure?
Perioperative respiratory failure
Increased atelectasis (collapse/lack of inflation of lung tissue) due to low functional residual capacity
(FRC) with abnormal abdominal wall mechanics
Hypoxaemia or hypercapnia
Can be prevented with proper anaesthetic/operative technique, posture, incentive spirometry, attempts to lower intra-abdominal pressure
What is type 4 respiratory failure?
Shock
Shock leads to inadequate perfusion of the lungs
Needs intubation
What are the risk factors for acute respiratory failure?
Infection
-Viral
-Bacterial
Aspiration
Trauma
Pancreatitis
Transfusion
How can transfusion lead to acute respiratory failure?
Transfusion-associated circulatory overload (TACO) is a fairly common transfusion reaction due to a too large circulating volume following a transfusion
Can result in acute respiratory distress and pulmonary oedema
What are the risk factors for chronic respiratory failure?
COPD
Pollution
Recurrent pneumonia
Cystic fibrosis
Pulmonary fibrosis
Neuro-muscular diseases
What are the pulmonary causes of acute respiratory distress syndrome (ARDS)?
Aspiration
Trauma
Burns: Inhalation
Surgery
Drug Toxicity
Infection
What are the extra-pulmonary causes of acute respiratory distress syndrome (ARDS)?
Trauma
Pancreatitis
Burns
Transfusion
Surgery
BM transplant
Drug Toxicity
Infection
What is the mechanism behind acute lung injury?
Infection triggers macrophage response
Macrophages crossing alveolar capillary barrier weakens it, leading to secondary chemotaxis and leaking of fluid and cytokines, also DAMPS
Loss of efficiency of gas exchange
Leads to secondary immune response - production of IL-8, TNF, IL-6, IFN-gamma
What is the underlying biological process in ARDS?
Vascular endothelialitis - endothelial cells by the lungs get gunged up and damaged
Lots of blood clots/clotting
Poor perfusion of lung
Briefly summarise the mechanism of ARDS
Alveolar macrophages release cytokines/cytokines present in blood from elsewhere in body
Attracts neutrophils
Neutrophils migrate into alveoli - secrete proteases that damage alveolar walls
Releases cytokines which stimulate inflammatory response
Release molecules that stimulates blood clotting
Makes vascular endothelial cells more permeable, leading to oedema and collapse of alveoli
OVERALL RESULT: inability for alveoli to ventilate or conduct gas exchange
What are the 3 aspects of therapeutic intervention for respiratory failure?
Treat underlying disease
Respiratory support
Multiple organ support
How is the underlying disease treated in respiratory failure?
Inhaled therapies
-Bronchodilators
-Pulmonary vasodilators
Steroids
Antibiotics
Anti-virals
Drugs
-Pyridostigmine
-Plasma exchange
-IViG
-Rituximab
What constitutes respiratory support in the context of respiratory failure?
Physiotherapy
Oxygen
Nebulisers
High flow oxygen
Non invasive ventilation
Mechanical ventilation
Extra-corporeal support
Which organs may need to be supported in respiratory failure?
Cardiovascular support
Renal support
Immune therapies
How is cardiovascular support given?
Fluids
Vasopressors
Inotropes
Pulmonary vasodilators
How is renal support given?
Haemofiltration
Haemodialysis
What immune therapies can be given in respiratory failure?
Plasma exchange
Convalescent plasma
How do plasma exchange and convalescent plasma help with respiratory failure?
Plasma exchange removes the plasma with high inflammatory mediators from the patient
Convalescent plasma containing antibodies from individuals who have recovered from an infection can be used to treat an underlying infection
What respiratory support should be given with ARDS of increasing severity
Bottom right is prone
Bottom left is ecmo
neuromuscular - paralysed so can control that ventilation
What is the Murray score?
A score that measures lung injury
What are measured in the Murray score?
PaO2
Compliance
Chest X-ray
Positive end-expiratory pressure
What Murray score suggests severe respiratory failure?
> 3.0