Random + Biochemistry Flashcards
Give definitions for the following: FiO2 PaO2 SpO2 SaO2
FiO2 = fraction of inspired oxygen – the concentration of inspired oxygen PaO2 = partial pressure of O2 in arterial blood, measured in kPa. PaO2 measures oxygen in blood SpO2 = peripheral capillary oxygen saturation SaO2 = percentage of oxygen saturation of arterial blood
What are the four types of tissue hypoxia?
- Circulatory
- Anaemic
- Toxic
- Hypoxaemic
Describe circulatory hypoxia
In this form of hypoxia the lungs are working just fine and the blood can carry sufficient oxygen. However, the tissue is not receiving sufficient oxygen because the heart cannot pump the blood to the tissue (or the arteries leading to the tissue have been blocked by clots etc). Sickle cell anaemia can lead to circulatory hypoxia as the cells sickle in the blood vessels and block them (it also produces an anaemic hypoxia as the sickled blood cells are removed from circulation)
Describe anaemic hypoxia.
In this form of hypoxia, the lungs are in perfect working condition, but the oxygen carrying capacity of the blood has been reduced. As the name implies, anaemia is a very effective way of producing anaemic hypoxia. Carbon Monoxide produces anaemic hypoxia - because it binds to the Hb with such high affinity, preventing oxygen from binding, it reduces the oxygen carrying-capacity of the blood. The tissues do not get sufficient oxygen to maintain their metabolic needs because the blood is not carrying it.
Describe toxic hypoxia
Toxic hypoxia - in this form of hypoxia, there is no problem getting the oxygen to the tissue - the lungs, blood and circulatory system are all working just fine. However, the tissue is unable to use the oxygen. Cyanide leads to histotoxic hypoxia by poisoning the systems that utilize oxygen to create energy and preventing them from using the oxygen. Even though there is plenty of oxygen there, the cells experience a lack of oxygen and are affected as if there was too little/no oxygen available.
Describe hypoxaemic hypoxia
Hypoxaemic hypoxia - in this form of hypoxia, the PaO2 is below normal because either the alveolar PO2 is reduced or the blood is unable to equilibrate fully with the alveolar air. Possible causes:
- Low inspired O2 conc
- Alveolar hyperventilation
- Impaired diffusion
- Shunt
- Deadspace
What are the four things you should prescribe oxygen for?
- MI
- Major trauma
- Anaphylaxis
- Septic shock
Define these biochemical terms:
Accuracy
Precision
Accuracy is how close the result is to the true value. Precision is a different kind of concept that requires repeated measurement of something – it gives you an idea of how predictable your test result will be.
Look back over the examples in lecture 1
Look back over the examples in lecture 1
Define sensitivity
The % of people with MI who have a high CK
Define specificity
The % of people without MI who have a normal CL
Define positive predictive value
The % of people with a high CK who have MI
Define negative predictive value
The % of people with normal CK who don’t have MI
Define prevalence
% of people tested who have MI
Define acidaemia
Increased [H+]
