Hypercapnia & Hypoxia Flashcards
Define hypoxia
reduced O2 in tissues
Define hypoxaemia
reduced O2 in the blood
List the mechanisms behind hypoxia and hypoxaemia
reduced oxygen inspiration
cannot get 02 to lungs
cannot get 02 inot blood
reduced systemic O2
cannot bind to Hb
Provide a list of causes relating to reduced oxygen inspiration
Equipment related
Anatomy
Altitude
Hypoventilation
URT Obstruction
Pneumothorax
Provide a list of causes relating to inability to get oxygen into the lungs
Equipment
URT Obstruction
Pneumothorax
Provide a list of causes relating to reduced systemic O2
Anaemia (see pulse oximetry slide later)
Heart disease (e.g. resulting in output failure)
Hypovolaemia
-Periphery shuts down as preferential shunting to vital organs occur
Extreme vasoconstriction
-In cold environment the periphery is shut down for preferential shunts to vital organs
Sepsis (discussed more in later lectures)
Provide a list of causes relating to oxygen being unable to bind to Hb and/or cannot get off of Hb
Haemoglobinopathy
Methemoglobinemia
Provide a list of causes relating not being able to get oxygen into the blood
VQ mismatch
Intrapulmonary Shunts
Diffuse alveolar/interstitial disease
Explain how equipment reduces oxygen inspiration and reduces the amount of O2 getting into the lungs
Kinked/obstructed ET (endotracheal) tube.
If you have the luxury of a Capnograph, this will be spotted quickly (the wave form will look a bit like a sharks fin).
Obstructed due to a build up of mucous or it could be something physiological such as bronchoconstriction.
Rarely, it could be a kinked or damaged tube on the breathing system. These tubes are normally pretty robust so it wouldn’t be a common problem.
Breathing system may not be working properly due to leak (leak tests down prior to anaethesia)
Issue with oxygen supply
Resolution:
Unkink tube or re-intubate with a new tube.
If it is physiological, treat the root cause.
Explain how anatomy reduces oxygen inspiration
BOAS (brachycephalic obstructive airway syndrome)
-narrowed airways mean inspiration of reduced amounts of O2
-doesnt always lead to hypoxia but means higher risk
-airways can become easily obstructed
Resolution:
Short term intubate
Some may require surgery in the long term
Explain how altitude reduces oxygen inspiration
Lower atmospheric pressure which means decreased partial pressure of oxygen
Hyperventilation due to low atmospheric pressure
Leads to hypocapnia
An example of the link between CO2 and O2 is how the body compensates for lower atmospheric pressures by hyperventilating.
Explain how hypoventilation reduces oxygen inspiration
Results in hypercapnia
Very common cause
Partial pressure of oxygen in the alveoli (PAO2) decreases
Partial pressure of carbon dioxide in the alveoli (PACO2) rises
Resulting in hypercapnia
Explain how URT obstruction reduces oxygen inspiration and reduced the amount of oxygen getting into the lungs
Loss of pharyngeal muscle tone
Regurgitation
Vomiting
Laryngospasm
Stick injury
Laryngeal oedema
Tracheal collapse
Foreign body
Depending on the severity of the obstruction there may either be reduced O2 inspired or complete inability to get O2 to the lungs
Explain how pneumothorax reduces oxygen inspiration and reduced the amount of oxygen getting into the lungs
Air has reached the lungs but it escapes into the space between lung and chest wall and cannot take part in efficient gas exchange
Explain how Haemoglobinopathy lead to the inability of oxygen binding to Hb
Carbon monoxide binds to haemoglobin with much greater affinity and prevents the carriage of oxygen.
Shifts the haemoglobin-oxygen dissociation curve to the left
Exposure to even small concentrations of CO (carbon monoxide) hinder the ability of Hb to deliver oxygen to the body, because carboxyhaemoglobin forms more readily than oxyhaemoglobin (HbO2) does.
Carbon monoxide is produced in normal metabolism and is a common chemical, but excessive exposure can lead to big problems.
Explain how Methemoglobinemia leads to the inability of Hb to remove oxygen
Elevated methaemoglobin in the blood, haemoglobin iron is in the oxidized or ferric state and cannot reversibly bind oxygen – paracetamol toxicity
Methaemoglobin is a type of haemoglobin which carries oxygen through the blood but doesn’t release it to the cells
When there is too much methaemoglobin produced, it starts to replace normal haemoglobin, and therefore oxygen is not released and doesn’t reach tissues