(cardioresp) 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 is the predominant feature of respiratory failure?
shortness of breath
which two systems can be involved in respiratory failure?
nervous system, respiratory system (respiratory muscles)
which parts of the nervous system can be involved in respiratory failure?
brainstem/CNS, peripheral nervous system, neuromuscular junction
which parts of the musculoskeletal system can be involved in respiratory failure?
diaphragm, thoracic muscles, extra-thoracic muscles
which parts of the pulmonary system can be involved in respiratory failure?
airways, alveolar capillaries
what is the epidemiology of chronic respiratory failure?
the 3rd leading cause of death around the world
what is the biggest risk factor for chronic respiratory failure in men?
smoking
what is the biggest risk factor for chronic respiratory failure in women?
household air pollution from solid fuels (i.e. from cooking)
what are some possible causes for a decrease in mortality from respiratory failure?
patients living longer
treatments working/getting better
patients dying of other diseases
what is the acute type of respiratory failure?
acute respiratory distress syndrome
what is ARDS?
life-threatening condition wherein the lungs become severely inflamed and fluid builds up within the lungs impairing oxygen transport, significantly and dangerously lowering blood oxygen levels
what is the prevalence of ARDS in the UK?
6-7 per 100,000
how do people with ARDS present usually?
heterogenous disease presentation (i.e. can present w different conditions - infective exacerbation of COPD, worsening of pulmonary hypertension, pneumonia)
how is ARDS classified?
using the ARDS Berlin definition
what four aspects are there to the ARDS Berlin definition?
timing, chest imaging, origin of oedema and oxygenation
Two Can Out One
what is the ARDS Berlin definition in terms of timing?
should be within 1 week of known clinical insult or new/worsening respiratory symptoms
what is the ARDS Berlin definition in terms of chest imaging?
bilateral opacities present (not caused by pleural effusion, lung collapse or nodules)
what is the ARDS Berlin definition in terms of origin of oedema?
oedema should not be caused by cardiac conditions
what is the ARDS Berlin definition in terms of oxygenation?
different levels of oxygenation - mild, moderate and severe
what are the three classifications of respiratory failure?
acute
chronic
acute on chronic
what are the three causes of acute respiratory failure?
pulmonary (infection, aspiration, primary graft dysfunction)
extra-pulmonary (trauma, pancreatitis, sepsis)
neuromuscular (myasthenia, GBS)
what are the pulmonary causes of acute respiratory failure?
infection, aspiration, primary graft dysfunction
what are the extra-pulmonary causes of acute respiratory failure?
trauma, pancreatitis, sepsis
what are the neuromuscular causes of acute respiratory failure?
myasthenia gravis, GBS (Guillain-Barre syndrome)
what are the causes of chronic respiratory failure?
pulmonary (COPD, lung fibrosis, cystic fibrosis, lobectomy)
musculoskeletal (muscular dystrophy)
what are the pulmonary causes of chronic respiratory failure?
COPD, cystic fibrosis, lung fibrosis, lobectomy
what are the neuromuscular causes of chronic respiratory failure?
muscular dystrophy
what are the possible causes of acute on chronic respiratory failure?
infective exacerbation of COPD/CF
myasthenia crises
post operative
what are the two types of respiratory failure?
type I respiratory failure (hypoxemic)
type II respiratory failure (hypercapnic)
what is type I respiratory failure also known as?
hypoxemic respiratory failure
what is type II respiratory failure also known as?
hypercapnic respiratory failure
how does type I respiratory failure occur?
failure of oxygen exchange due to damage to lung tissue
= damaged tissue is insufficient for efficient oxygenation of the blood BUT is enough to enable carbon dioxide to be excreted
how does type II respiratory failure occur?
failure to exchange or remove carbon dioxide
= when alveolar ventilation is insufficient to allow efficient carbon dioxide excretion
what are the expected blood oxygen and blood CO2 levels in hypoxemic RF?
low oxygen
normal/low CO2
what are the expected blood oxygen and blood CO2 levels in hypercapnic RF?
low oxygen
high CO2
what are the causes of type I respiratory failure?
lung collapse
aspiration
pulmonary oedema
lung fibrosis
pulmonary embolism
pulmonary hypertension
what are the causes of type II respiratory failure?
neuromuscular causes
muscle failure
airway obstruction
chest wall deformity
nervous system impairment
what PaO2 is expected in hypoxemic RF?
PaO2 < 60
what PaCO2 is expected in hypercapnic RF?
PaCO2 > 45
how can pulmonary oedema cause respiratory failure and which type?
build-up of fluid around the lung increases diffusion distance, impairing the efficient oxygenation of blood = type I (hypoxemic) respiratory failure
how can muscle failure cause respiratory failure and which type?
muscle failure/weakness results in an inability to drive adequate tidal volumes and a sufficiently high respiratory rate = inability to remove CO2 well = type II respiratory failure
which type of respiratory failure is associated with decreased alveolar minute ventilation?
type II respiratory failure (hypercapnic)
which type of respiratory failure is associated with an increased shunt fraction?
type I respiratory failure (hypoxemic)
what is the shunt fraction?
the percentage of blood put out by the heart that is not completely oxygenated (increased in hypoxemic respiratory failure)
what is alveolar minute ventilation?
the volume of gas inhaled and exhaled from a person’s lungs per minute (decreased in hypercapnic respiratory failure)
what is type III respiratory failure?
(hypoxemic and hypercapnic) respiratory failure seen in patients around the time of surgery (perioperative respiratory failure)
low functional residual capacity + abnormal abdominal wall mechanics = airways cannot stay open = increased atelectasis (collapse of lungs)
what is type IV respiratory failure?
respiratory failure resulting from shock (septic/cardiogenic/neurologic)
= patients intubated/ventilated
wherein the body cannot provide oxygen adequately or maintain blood pressure for sufficient levels of pulmonary perfusion
define atelectasis
complete or partial collapse of the entire lung or lobe of lung
occurs when the alveoli within the lung become deflated or possibly filled with alveolar fluid
how can type III respiratory failure be prevented?
analgesia, posture, correct anaesthetic or operative technique
what is functional residual capacity and why is it physiologically important?
the volume in the lungs at the end of passive expiration
physiologically important as it is responsible for keeping the small airways open and prevent complete emptying of the lung during each respiratory cycle
why does atelectasis occur?
reduced functional residual capacity + abnormal abdominal wall mechanics
what is type IV respiratory failure usually secondary to?
cardiac instability
explain how cardiac instability leads to type IV respiratory failure
pressure in chest raised
pressure difference bw LV and thorax is less = less afterload = better for LV
pressure diff bw RV and thorax in increased = increased preload - worse for RV as it is harder to fill w blood and contractiliy reduced
= reduced perfusion of the lungs + peripheral pooling of the blood + reduce central return of blood to pulmonary vasculature SO type IV respiratory failure
what is the usual state of patients in type IV respiratory failure?
intubated/ventilated during shock (sepsis, cardiogenic, neurogenic)
what are the risk factors for acute respiratory failure?
infection (viral, bacterial)
aspiration
trauma
pancreatitis
transfusion
what are the risk factors for chronic respiratory failure?
pollution, COPD, recurrent pneumonia, cystic fibrosis, pulmonary fibrosis, neuromuscular diseases
(genetics = alpha-1-antitrypsin deficiency)
what are the pulmonary causes of ARDS?
infection -
trauma -
surgery -
drug toxicity -
burns (inhalation) -
aspiration
what are the extra-pulmonary causes of ARDS?
infection -
trauma -
surgery -
drug toxicity -
burns (inhalation) -
pancreatitis
transfusion
bone marrow transplant
define pulmonary causes (in terms of ARDS)
from airways down to alveoli
define extra-pulmonary causes (in terms of ARDS)
systemic disease, anything that activates neutrophils/macrophages/cytokine release
define extra-pulmonary causes (in terms of ARDS)
systemic disease, anything that activates neutrophils/macrophages/cytokine release
what are the three components of acute lung injury?
infection, inflammation and immune response
explain the pathogenesis of acute lung injury
injury to the interstitium
macrophages activated either by infection or inflammation
release cytokines (IL6, IL8, TNFa)
protein-rich alveolar fluid oedema + degradation of surfactant = impairs expansion of alveoli
leukocyte migration to alveoli + secretion of proteases and inflammatory mediators = more damage to tissues + increased oedema
oedema = increased diffusion distance = inefficient gas exchange = respiratory failure
what are the three aspects to therapeutic intervention in ARDS?
treat underlying disease
respiratory support
multiple organ support
what pharmacological interventions are available to treat ARDS?
inhaled therapies (bronchodilators like salbutamol, pulmonary vasodilators)
steroids
antibiotics, antivirals
N-acetylcysteine
what respiratory support is available to treat ARDS?
physiotherapy
oxygen
nebulisers
high flow oxygen
non-invasive ventilation
mechanical ventilation
extra-corporeal support
what multiple organ support is available to treat ARDS?
cardiovascular = pulmonary vasodilators, fluids, ionotropes
renal = haemofiltration, haemodialysis
immune = convalescent plasma therapy, plasma exchange
what cardiovascular support is available for ARDS patients?
fluids, ionotropes, vasopressors, pulmonary vasodilators
what renal support is available for ARDS patients?
haemofiltration, haemodialysis
what immune support is available for ARDS patients?
convalescent plasma therapy, plasma exchange
how does poor pulmonary perfusion cause respiratory failure?
poor perfusion = poor gas exchange = poor oxygenation + hypercapnia = respiratory failure
what types of ventilation are available for ARDS patients?
volume controlled
pressure controlled
assisted breathing modes
advanced ventilatory modes
what is compliance (in lungs)?
a measure of lung expandability
what is the upper inflection point?
above this pressure any additional alveolar recruitment requires disproportionate increases in applied airway presssure
what is the lower inflection point?
the minimum baseline pressure needed for optimal alveolar recruitment
how does the compliance vary in a healthy lung vs an ARDS lung?
healthy lung has high compliance (as elasticity of alveoli maintained)
ARDS lung (tissue and surfactant damaged + oedema develop) has much lower compliance
how does the upper inflection point vary in a healthy lung vs an ARDS lung?
the UIP of the healthy lung is lower than that of an ARDS lung as lung is much stiffer
how does the lower inflection point vary in a healthy lung vs an ARDS lung?
the LIP of the healthy lung is lower than that of an ARDS lung as lung is much stiffer
which imaging modalities can be used to guide ARDS and respiratory failure management?
CXR, lung ultrasound, lung CT
how is ARDS severity graded?
Murray score = takes into account four factors (PaO2, CXR, PEEP, compliance)
what four factors are taken into account in a Murray score?
oxygen partial pressure (PaO2)
CXR
PEEP
compliance
(on christmas, people carol)
what does a Murray score determine?
ARDS severity and the need for ECMO
what does each Murray score mean?
0 = normal
1 - 2.5 = mild (proning treatment)
2.5 = severe (proning treatment)
3 = ECMO
what is the inclusion criteria for ECMO?
sever respiratory failure (w a non-cardiac cause)
Murray lung injury score greater than 3
where positive pressure ventilation is not appropriate (i.e. significant tracheal injury)
what is the exclusion criteria for ECMO?
contraindication to continuation of active treatment
significant co-morbidity
what are the two essential requirements for ECMO treatment?
must be a reversible disease process
+ must be unlikely to lead to prolonged disability
explain how ECMO occurs
pass very large cannula through femoral vein (GROIN)
slot it just below IVC below right atrium and then draw blood our of body through tubing
runs blood through pump that enables removal of CO2 and oxygenation of blood
pumped back into body
(can also do so via the jugular vein and down into the RA = jugular axis)
what are the advantages of ECMO?
improve oxygen delivery
improve carbon dioxide removal
rest lung and prevent ventilator associated lung injury
resolve respiratory acidosis
reduce multiple organ dysfunction arising from hypoxaemia and hypercapnia
what are the disadvantages of ECMO?
not universally available/inequity of provision of care
bleeding: intra-cerebral, venepuncture sites
infection
expensive
invasive
