Respiratory Faliure Flashcards
what does hypoventilation mean
under breathing
what can hypoventilation cause
type 1 and 2 RF
what is hypoventilation caused by
inadequate alveolar ventilation resulting in low alveolar pO2 (and high pCO2)
when does hypoventilation occur
when the respiratory drive is impared
what does low FIO2 result in
low alveolar PO2
how do you manage low FIO2
supplemental o2
what does disease or damage to the basement membrane
a reduction in the amount of oxygen that diffuses across the interstitium and this results in Hypoxaemia
what are the oxygen values like for diffusion impairment
Normal PAO2 but reduced PaO2
what does TLCO measure
difusion capacity
how do you calculate TLCO
small amount of CO
what is the alveolar- arterial gradient used for
if theres a problem in diffusion capacity
what factors affect diffusion of gasses
surface area
thickness
diffusion coefficient
partial pressure
how do you manage diffusion impairment
- Treatment of underlying condition if possible
Supplemental oxygen
what are the types of shunt
physiological
anatomical
cardiac
pulmonary
what is an anatomical shunt
blood that goes from the right side to the left side of the heart without traversing pulmonary capillaries
What is the main difference between anatomical and physiological shunts
Anatomic shunts cause a ventilation-perfusion ratio of zero, and physiologic shunts cause a low ventilation-perfusion ratio, contributing to the lowering of partial pressure of oxygen (PaO2)
what does anatomical shunts result in
mixing of venous and arterial blood
how does anatomical shunts result in the mixing of venous and arterial blood
- Deoxygenated blood from bronchial circulation → pulmonary veins
- Deoxygenated blood from coronary circulation → Thebesian vein → left ventricle
what is a cardiac shunt
A cardiac shunt is a pattern of blood flow in the heart that deviates from the normal circuit of the circulatory system. It may be described as right-left, left-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemi
how can cardiac shunts arise
either congenital or acquired
what is a pulmonary shunt
passage of deoxygenated blood from the right side of the heart to the left side without participating in gas exchange in the pulmonary capillaries
what is a physiological shunt
when nonventilated alveoli remain perfused, thus functioning as a shunt even though there is not an anatomic anomaly
what are reasons for physiological shunts forming
consolidation e.g. pneumonia
atriovenous malformation
hypoxaemia
what is ventilation (v)
flow of oxygen into the alveoli
what is perfusion (Q)
the flow of blood of alveolar capillaries
what is a normal V/Q value
0.8 ratio
how do you calculate ventilation
alevolar ventilation rate x resp rate
how do you calculate alveolar ventilation rate
tidal volume- alveolar dead space
what is perfusion equal to
cardiac output
where is ventilation lowest in the lung
apex
why is ventilation lowest at the apex of the lung
Because more negative pleural pressure means higher transpulmonary pressure- more distending pressure on the alveoli
alveoli at functional residual capacity have lower compliance at this higher volume
less airflow during inspiration
what happens to ventilation as you move down the lung
increases
where is ventilation highest
lung base
when is ventilation higher than perfusion
lung apex
when is ventilation equal to perfusion
middle of the lung
when is ventilation lower than perfusion
lung base
what area is relativley over ventilated
lung apices
what area is relativley over perfused
lung bases
In healthy lungs, how is VQ mismatch minimised
Hypoxic Vasoconstriction which directs blood away from poorly ventilated areas
what is anatomical dead space
the upper respiratory tract up to the terminal bronchioles
do not take part in gas exchange
what is the function of anatomical dead space
warming, filtering and humidifcation of inspired air
what is alveolar dead space
alveoli that have lost blood supply do not participate in gas exchange
what is physiological dead space
Anatomical dead space + Alveolar dead space
in healthy lungs what is the ratio of physiological dead space to anatomical dead space
they are equal
what is hypoxic pulmonary vasoconstrictuon
constriction of pulmonary arteries in the presence of alveolar hypoxia to re-direct blood flow from areas that are poorly ventilated to areas that are well ventilated and more oxygen rich
where are ABG’s taken from
A sample of blood is taken from an artery, usually the radial artery as that is the most accessible artery (or brachial artery or femoral artery)
what is the difference between type 1 and type 2 resp faliure
type 1 has normal co2 levels
what is acute resp faliure
sudden deterioration
what is chronic resp faliure
gradual and usually permanent change
what is acute on chronic resp faliure
worsening of existing abnormalities
what is mechanism of resp faliure
Lung Failure → Gas Exchange Failure → Hypoxaemia Pump Failure → Ventilatory Failure → Hypercapnoea
why does type 1 resp failure (hypoxaemic) occur
Due to disease of the lungs which prevents adequate oxygenation of the blood
are the lungs able to excrete CO2 during type 1 resp failure
yes
what are the oxygen and carbon levels like in type 1 respiratory failure
This results in ↓ O2 but normal or ↓ CO2 levels
what are the 5 mechanisms of type 1 RF
Hypoventilation
Low inspired oxygen (FIO2)
Diffusion impairment
Shunt
Ventilation/perfusion (VQ) mismatch
why does type 2 RF occur
Occurs due to failure of ventilation, resulting in alveolar hypoventilation
what are the o2 levels and co2 levels like in type 2 rf
Hypoxaemia (pO2 < 8.0 KPa) and Hypercapnoea (pCO2 > 6.5 kPa)
what is acute tyoe 2 Rf like
can develop within minutes to hours, renal buffering does not have time to act, so HCO3- remains normal and pH ↓↓ (= Acidosis)
what is chronic type 2 RF like
can develop over several days to weeks, to months. The kidneys excrete H2CO3, reabsorb HCO3-, increasing its levels and slightly ↓ pH (Compensation)
what are the causes of type II respiratory failure
chronic lung disease
chest wall deformity
Neuromuscular and peripheral nerve disorders
Neuro-muscular lung disorders
disorders of the respiratory centre
how do you manage type 1 RF: hypoxaemia
- Treatment of underlying condition
- Correct hypoxaemia by giving oxygen and maintaining O2 saturation between 94- 98%
- Intubation and ventilation
what is the management of Type II RF: hypoxaemia and hypercapnoea
- Treatment of underlying condition if possible eg COPD
- Administering controlled O2 aiming to keep saturation between 88-92%
- Non-invasive ventilation (NIV)
- Intubation and ventilation
what is cytotoxic or histotoxic hypoxia
(Cyanide poisoning impairs mitochondrial cytochrome oxidase): Reduced ability to utilise O2
what is circulatory or stagnant hypoxia
(heart failure): Reduced ability to deliver O2
what is anaemic hypoxia
(CO poisoning): Reduced ability to deliver O2
what is Hypoxaemic or hypoxic hypoxia
(PaO2): Reduced ability to deliver O2
