Week 3 - H - Physiology 8 - Arterial blood gases (acidosis&alkalosis) Flashcards
What is a person’s normal plasma pH? When is it acidic and when is it alkali?
pH - 7.35 to 7.45 Acidic - below 7.35 and lkali is above 7.45
What is the normal bicarbonate and CO2 range for a patient?
Bicarbonate (HCO3-) - 23 to 27 mmol/l CO2 - 35-45 mmol/l
If normal acid-base balance is disrupted, the first priority is to restore pH to 7.4 as soon as possible What is this known as?
This is known as compensation
What is the correction of the acid base disturbance then?
This is the stage of returning the HCO3-, CO2 and pH levels to normal Compensation is the restoration of pH irrespective of what happens to [HCO3-]p and PCO2
When an acidosis occurs, what happens to the CO2 levels and pH levles?
CO2 levels increase causing a fall in pH in acidotic conditions (CO2 becomes an acid in solution)
What is the main buffer system in the human body?
The bicarbonate buffer system

If there is a riise in H+ ion concentration therefore causing a decrease in pH, what in the blood quickly binds to the increase [H+] to buffer the blood? What regenerates this ion?
HCO3- binds to the increased hydrogen ions The kidney then works to regenerate the bicarbonate used
How is the bicarbonate used to monitor the H+ levels reasborbed?
Once it binds to H+ it becomes H2CO3 (carbonic acid) filtered into the tubular lumen, this then dissociates to become CO2 and HCO3- and reenters the tubualr cells/interstitial fluid
What is the Henderson Hasselbach equation?
pH = pK + log [A-/HA]
In the henderson hasselbach equation, if regarding the bicarbonate and CO2 levels, what is the pH proportional to?
pH is proportional to the HCO3- levels and inversely proportional to the levels of CO2 in the blood

A blood-gas analyser can measure pH and PCO2 [HCO3-] can be calculated What type of diagram can these variables be plotted on?
Can be plotted on a Davenport diagram
What type of arterial blood gas does the green circle represent?

Represents the normal value
What are some cause of CO2 retention in the body?
Type II repsiratory failure - chronic bronhcitis, emphsyema Respiratory depression
What is the sydnrome characterised by obesity and hypoventialtion which drives a person into hypercapnia?
This is Pickwickian Syndrome
An increase in carbon dioxide levels drives the equilibirum in which direction?
Drives the equilibrium to the right therefore accounting for the increased hydrogen ions
When there is a rise in CO2 this causes an increase in both HCO3- and H+ ions Why is it that the pH will fall? The pH is proportional to HCO3- and inversely to pCO2, what does this mean for respiratory acidosis?
There are many many times more bicarb ions than there is hydrogen. You see a bigger overall increase in hydrogen than bicarb because there was so many bicarb ions to start off with. This means that when the carbon dioxide levels rise, the pH falls
What does the purple dot represent?

A low pH - since HCO3- is high then cannot be metabolic acidosis SO respiratory acidosis

What organ needs to compensate for the respiratory acidosis? Recall that blood PCO2 drives H+ secretion by this organ
The kidneys compensate as the increased pCO2 will increase H+ secretion by the kidneys
H+ secretion is stimulated All filtered HCO3- is reabsorbed (i.e. no HCO3- excretion) What does the increased secretion of H+ generate in the urine (previous lecture)?
The increased H+ secretion stimulates the production of titratable acid (H2PO4) and NH4+ [HCO3-]p rises; (a) as a result of the disorder & (b) as a result of the renal compensation
How are the normal pressures of carbon dioxide brought back in the process of correction?
Correction requires lowering PCO2 by restoration of normal ventilation

What is respiratory alkalosis known as?
Excessive removal of CO2 from the body resulting in a rise in the pH
Give examples of when a respiratory alkalosis may occur?
During hyperventialation Hypoxia causing a subsequent hyperventilation: pulmonary embolism, high altitude During hysterical overbreathing
What does the blue circle represent?

This represents the respiratory alkalosis -seen by the high pH with a low HCO3 showing this is not the cause
Since the respiratory system is the cause of the disturbance the renal system must compensate Recall that it is blood PCO2 that drives H+ secretion by the kidney Excessive removal of CO2 reduces H+ secretion into the tubule What does the renal system do to compensate for the respiratory alkalosis? What does this do to [HCO3-]p and what does it do to urine pH?
Compensates by lowering [HCO3-] plasma (bicarbonate plasma concentration) This causes an increase in pH of the urine








