Respiratory Failure Flashcards
What is respiratory failure?
- inability to maintain gas exchange
In respiratory failure type 1, what happens to PaO2 and PaCO2?
- hypoxaemia (low O2 in blood)
- <8.0kPA or <60mmHg
- normal CO2
What is hypoxaemia?
- blood oxygen is low
What is hypoxia?
- low O2 supply to tissue
What is hypocapnia?
- low CO2 - <4.5kPA or <33.8mmHg
What is hypercapnia?
- high CO2
- >6.0kPA or >45mmHg
Why does CO2 remain normal in type 1 respiratory failre?
- damaged lungs are sufficient to expire CO2
What is the main problem with the lungs in type 1 respiratory failure?
- damage to lung tissue
- lungs unable to facilitate gas exchange
What is ventilation/perfusion in the lungs?
- ratio between ventilation and perfusion across alveoli and capillaries
In type 1 respiratory failure, why is there ventilation/perfusion mismatch?
- ventilation is sufficient
- perfusion is low causing ⬇️ O2
Is blood flow to the lungs affected in type 1 respiratory failure?
- generally no
In respiratory failure type 2 what happens to PaO2 and PaCO2?
1 - hypoxaemia
- PaO2 = <8.0kPA or <60mmHg
2 - hypercapnia
- PaCO2 = >6.0kPA or 45mmHg
What is the main problem in the lungs causing type 2 respiratory failure?
- ⬇️ ventilation, generally affects whole lung
- inability to overcome ⬆️ resistance to ventilation
- generally caused by ⬇️ compliance and/or ⬆️ elasticity
- CO2 cannot be removed from blood
- O2 cannot reach the blood for gas exchange
What happens to patients breathing in type 2 respiratory failure?
- hypoventilation with short shallow breathes
- insufficient for normal function
- low O2 enters and CO2 not removed effectively
In acute type 2 respiratory failure, is renal function able to maintain homeostasis?
- no
- kidneys are slow to react
- retention of HCO3- is too slow to buffer ⬆️ CO2
What generally happens to pH in acute and chronic 2 respiratory failure?
- pH ⬇️
- ⬆️ CO2 = ⬆️ carbonic acid and ⬆️ H+
- HCO3- is insufficient to ⬆️ pH
How quickly can acute type 2 respiratory failure commence?
- minutes to hours
In chronic type 2 respiratory failure, is renal function able to maintain homeostasis?
- partially
- kidneys excrete carbonic acid H2CO3
- kidneys retain HCO3-
What generally happens to pH in chronic type 2 respiratory failure?
- HCO3- retention ⬆️ pH slightly
- not to normal pH though
What is a restrictive lung disease?
- compliance is ⬇️
- elasticity is ⬆️
- lungs struggle to inflate and ventilation is ⬇️
What is a obstructive lung disease?
- compliance is ⬆️
- elasticity is ⬇️
- lungs are able to inflate but not recoil
- CO2 is ⬆️ and O2 is ⬇️
What is stagnant hypoxia?
- blood flow is slow
- ⬇️ blood supply to tissues
- O2 levels in the blood are normal
What is histotoxic/cytotoxic hypoxia?
- ⬇️ or no O2 absorbed from blood
- caused by tissue poisoning
- ⬇️ blood supply to tissues
- O2 levels in the blood are normal
What is anaemic hypoxia?
- ⬇️ haemoglobulin binding to blood
- ⬇️ O2 delivered to tissue
- CO could cause this, inhibiting O2 binding
What is hypoxaemia?
- low level of O2 in arterial blood
What are the 5 mechanisms that can hypoxaemia?
1 - hypoventilation
2 - ⬇️ fraction of O2 (FiO2) in the air
3 - diffusion impairment
4 - shunt
5 - V/Q mismatch
What is hypoventilation?
- slow and shallow breathing
- ⬇️ ventilation and perfusion = low O2
- insufficient O2 arterial blood
Following hypoventilation, what happens to oxyhemoglobin saturation, measured by pulse oximetry?
- ⬇️ oxyhemoglobin or ⬇️ SaO2
During hypoventilation what happens to CO2 levels?
- CO2 can ⬆️
- CO2 cannot be removed from lungs sufficiently
What is the Alveolar/arterial gradient (A-a)?
- measure of arterial (A) and alveolar blood concentration of O2
What does the big and little a mean in Alveolar/arterial gradient?
- A = alveolar 2 concentration - a = arterial concentration
In the Alveolar/arterial gradient (A-a), what should the difference be between O2 in the alveolar and arterial blood flow?
- ideally the same same as O2 defuses from alveolar to arteries
- normal difference is 5-15mmHg
What does FiO2 mean?
- fraction of O2 in inspired air
What is normal partial pressure of atmospheric air at sea level?
- 760mmHg - written as Patm
What does Ph2O mean in the Alveolar/arterial gradient (A-a) formula?
- partial pressure lost to water in upper respiratory tract - water dilutes gases
At normally body temperature, what is the partial pressure of air lost to water vapour in the upper respiratory tract?
- 47mmHg
What does R mean in the Alveolar/arterial gradient (A-a) formula?
- respiratory quotient - respiratory exchange ratio - ratio between O2 and CO2 of expired air
The R in the Alveolar/arterial gradient (A-a) relates to the ratio between O2 and CO2 in expired air, why is this useful?
- provides information about metabolism - <1 = carbohydrates - 0.9 = proteins - 0.7 = fats
What is the normal value in the western world used for R in the Alveolar/arterial gradient (A-a) formula?
- 0.8
What is the Alveolar/arterial gradient (A-a) formula?
- PAO2 = FiO2 x (Patm-Ph20) - (PaCO2/R) - PaO2 - PAO2
- standard values = 0.21 x (760-47) - (PaCO2/0.8) - PaO2
- standard values can be affected by disease, altitude etc…
How do you acquire PaO2 for the Alveolar/arterial gradient (A-a)?
- value is taken from arterial blood gas
Why does partial pressure of gas decrease at altitude?
- gas molecules spread out
- Boyles law = ⬆️ volume = ⬇️ pressure
- Boyles law = ⬇️ volume = ⬆️ pressure
If at high altitude where pressure is lower, what can happen to the Alveolar/arterial gradient (A-a)?
- it will not balance
If at high altitude where pressure is lower, and the Alveolar/arterial gradient (A-a) is offset, patients suffer with altitude sickness, such as nausea, headaches, tiredness, loss of appetite etc…, how would you treat this immediately?
- give patients 80% gas
What is impaired diffusion?
- inability to facilitate gas exchange at alveolar/capillaries
What is the most common cause of impaired diffusion?
- blockage of interstitial space (0.5um)
- space between alveolar and capillaries
Why could exercise cause impaired diffusion?
- speed of blood is ⬆️ due to increased cardiac output
- ⬇️ time allowed for diffusion
Why could pulmonary fibrosis cause impaired diffusion?
- fibrosis causes thickening of alveoli
- thickening of alveoli ⬇️ surface area ⬇️ perfusion
- fibrosis may block the alveoli all together due a ⬇️ in parenchyme tissue
In patients with impaired diffusion, is high flowing O2 (80-90%) able to help?
- yes
- forces O2 in alveoli and ⬆️ perfusion
What is a continuous positive airway pressure (CPAP) machine?
- machine that applies continuous pressure with ⬆️ O2
- ensures respiratory tract remains open
- ⬆️ diffusion
What is shunting?
- blood may not reach alveoli and be oxygenated
- capillaries may reach alveoli but and low O2 perfusion occurs
- capillaries do not reach alveoli and no O2 saturation
- essentially O2 and CO2 rich blood can mix, causing a reduction in SaO2
What happens to O2 saturation where shunting has occured?
- SaO2 ⬇️
- oxygenated blood mixes with non oxygenated blood
What is airspace shunting?
- pressure in part of lung is high meaning O2 will not move down the partial pressure gradient
- can occur in pneumothorax
What is an example of airspace shunting?
- pneumothorax
- increased pressure on part of the lung
What is vasculature shunting?
- blood vessels do not reach the alveoli
- blood is not oxygenated
What is heart shunting?
- blood crosses from right to left side of the heart
- oxygenation of blood is ⬇️
Can shunting be treated with ⬆️ O2 gases?
- generally no
- helps confirm diagnosis as a form of shunting
What is ventilation/perfusion (V/Q) mismatch?
- mismatch between ventilation (V) and perfusion (Q)
- most common cause of hypoxia
Is ventilation/perfusion equal throughout the lungs?
- no
- gravity contributes
Where is ventilation highest in the lungs?
- at the apex
- lowest at the base
Where is perfusion highest in the lungs?
- base of the lungs - lowest at apex
What is dead space in the respiratory tract?
- air in lungs that does not take part in perfusion
What are some common diseases that can cause ventilation/perfusion (V/Q) mismatch?
- pulmonary embolism - COPD - pneumonia
Will air help patients with a high ventilation/perfusion (V/Q) mismatch?
- yes
- ⬆️ in perfusion
How do we quantify ventilation?
- amount of air inhaled that reaches the alveoli during 1 minute
- measured in L/min
How do we calculate ventilation?
- alveolar ventilation rate (AVR) x respiratory rate (RR)
- AVR = tidal volume - alveolar dead space
- ventilation = (AVR - dead space) x RR
What are the normal values for tidal volume, respiratory rate and dead space at rest?
- tidal volume = 500ml
- deadspace = 150ml
- respiratory rate = 12 breaths/minute
Using the values below, what would ventilation be at rest? - tidal volume = 500ml - deadspace = 150ml - respiratory rate = 12 breaths/minute
- ventilation (V) = (AVR - dead space) x RR - V = (500-150) x 12 = 4200ml/min
- this can ⬆️ significantly during exercise
What is perfusion and what can we use to calculate it?
- perfusion is the amount of blood reaching the capillaries at a given time
- cardiac output is used to determine this
What is a normal cardiac output at rest?
- 5000ml/min or 5L - 5000 ml of blood reaches the capillaries/minute
If we know a ventilation at rest is approx 4200ml and a cardiac output is 5000ml, what is the ventilation/perfusion?
- ventilation/perfusion - 4200 / 5000 = 0.84 - normal V/Q is 0.8
What are the 3 things that drive ventilation and perfusion of the lungs?
1 - gravity 2 - pleural pressure 3 - compliance and elasticity
Clinically what does ventilation/perfusion mismatch lead to in the blood?
- ⬇️ O2 saturation
Generally, pneumonia (an infection) will reduce surface area of alveoli and destroy the alveoli altogether. Will this mainly affect ventilation or perfusion?
- pneumonia infection causes damage throughout the lungs
- this can reduce ventilation
- ⬇️ surface area due to damaged alveoli
- pus can block alveoli altogether
A pulmonary embolism (blood clot) can block blood flow to part of the lungs, is this likely to affect ventilation of perfusion?
- perfusion as no blood is available to perfuse with
- ventilation continues as normal
Where is the largest proportion of dead space in the respiratory tract?
- upper respiratory tract
- conducting zone
- mouth, pharynx, larynx and bronchi
In dead space there is high ventilation, but is any perfusion able to occur?
- no
- wasted air
In type 1 respiratory failure, is the cause generally due to damaged lung tissue or V/Q mismatch?
- damage to lung tissue
- damage to alveoli means air arrives but cannot perfuse
- which can lead to V/Q mismatch
What is the definition, according to O2 levels of type 1 respiratory failure?
- O2 <8kPA or 60mmHg
- hypoxaemia
In type 1 respiratory failure, what are the 2 things that can happen to CO2 levels?
- CO2 can ⬆️ - CO2 can remain normal
In type 2 respiratory failure, is the cause generally due to damaged lung tissue or V/Q mismatch?
- V/Q mismatch - ⬇️ removal of CO2 from blood
In type 2 respiratory failure, why can CO2 not diffuse across the capillary/alveoli efficiently?
- ⬇️ ventilation effort - ⬆️ resistance to ventilation so CO2 cannot leave lungs due to partial pressure gradients
What is the definition, according to CO2 and O2 levels of type 2 respiratory failure?
- CO2 >6.5kPA or 50mmHg = hypercapnia
- O2 <8kPA or 60mmHg (can be normal as well) = hypoxaemia
Asthma is a form of type 1 respiratory failure, what is an effective way to treat this?
- provide a bronchodilator - ⬆️ ventilation
Asthma is a form of type 1 respiratory failure, what is the aim when treating this?
- return SaO2 to normal levels - normal SaO2 = 94 - 98%
COPD is a form of type 2 respiratory failure, what is the aim when treating this?
- return SaO2 to good levels - CANNOT CURE
- normal SaO2 = 88 - 92%
- these SaO2 levels are likely to be normal for them
What is an example of non-invasive ventilation?
- nasal cannula or simple mask - both provide ⬆️ O2
In patients who are extremely hypoxic, will basic masks or nasal cannulas be sufficient to treat these patients?
- generally no - use continuous positive airway pressure (CPAP)
If masks and CPAP are insufficient in patients with type 2 respiratory failure, what else can be used in really hypoxic patients?
- intubation and ventilation
What is intubation?
- tube is inserted into patients throat
- acts as patients respiratory tract
- commonly called tracheal intubation
What is assisted ventilation?
- patients are attached to a respiratory machine
- essentially breathes for the patient
What is physiological and pathological dead space in the lungs?
- physiological = normal parts of lungs where gas exchange does not take place
- pathological = part of lung normally involved in gas exchange is damaged and unable to be involved in gas exchange
What is a portal blood system?
- blood flows from one capillary bed into another
- blood flows between veins and not straight back to heart
- characteristic of blood is de-oxygenated
