Acid-base Regulation Flashcards
What measurements could you expect to find in an arterial blood gas test
pO2 + pCO2 pH HCO3 Base excess Hb Haematocrit FHbO2 + FHbCO SaO2 FMetHb (Hb in the ferric methaemoglobin state)
What is base excess
Concentration of bases (bicarbonate) compared with the expected concentration assuming no renal or metabolic disturbance (due to CO2)
What is the importance of pH regulation
Proteins (ion channels, enzymes, hormones, receptors) can be altered by changes in pH
Impaired function and processes
Drug metabolism and clotting affected
What is a strong acid
Fully ionised/dissociated
What is a base
Anionic molecule capable of reversibly binding to protons
Describe the dynamic equilibrium of acids
Acids exist as either a complete molecule or a dissociated proton and anion
In standard conditions the preferred direction of the dynamic equilibrium is denoted by k
Give an example of acid dynamic equilibrium in the body
H2CO3 - H+ + HCO3-
What is the pH of the fluid intracellularly, extracellularly, in the arteries, veins and stomach
intra - 7.0 extra - 7.4 arterial blood - 7.4 venous blood - 7.36 stomach - 2.4
Where are the following acids produced: carbonic acid, HCl, Ketoacids, Phosphoric acids, lactic acids, pyruvic acid
Carbonic - CO2 in respiration Hydrochloric - stomach Keto - Fatty acid metabolism Phosphoric - incomplete phospholipid oxidation Lactic - energy production Pyruvic - energy production
Which acid is most important in evaluating acid-base status
Carbonic acid
Due to the rate of its production in cellular respiration
CO2 = respiratory acid (while lactic acid is metabolic)
What does acidemia and alkalaemia refer to compared to acidosis and alkalosis
acidaemia/alkalaemia = pH in the blood acidosis/alkalosis = circumstances that affect pH balance
What is the ratio of respiratory acids to metabolic acids
100:1
How is pH calculated
pH = -log [H+] (Sorensen)
What is the Henderson equation
Calculates dissociation constant
K = [H+][HCO3-] / [CO2][H2O]
What is the Henderson-Hasselbach equation
Combines Sorensen and Henderson
pH = pK + log10 [HCO3-] / [CO2]
What is the principal organ responsible for acid clearance
Lungs
Changes in ventilation can stimulate a rapid compensatory response to change CO2 elimination to alter pH
Which organs reuse or clear the acid
Liver or kidneys
Changes in HCO3 and H+ retention can stimulate a slow compensatory response to alter pH
How can hyper/hypoventilation affect acid-base balance
Increasing or decreasing the amount of CO2 eliminated in the lungs
What is the effect of non-hypercapnic hyperventilation
Voluntary or panic attack
Reduced PCO2
May cause alkalosis
Describe the buffers in the blood
Bicarbonate, phosphate and protein chains act s a buffers. The N- and C- terminals have the potential to liberate or gain
What is the normal base excess range
-2 to +2
What us the significance of base excess
Changes in bicarbonate that are due to pCO2 changes are eliminated
Any changes are therefore due to either metabolic acid base disturbance or change in renal excretion
What is the cause and effect of a rise in base excess
Due to an increase in renal excretion of acid, ingestion, or administration of base
May be due to acid loss from vomiting
Causes metabolic alkalosis
What is the cause and effect of a decrease in base excess
Overproduction of metabolic acids (E.g. lactic) or ingestion of acid
May be due to reduction in/ failure of acid excretion by the kidneys or excessive loss of alkali from the intestine with diarrhoea
Causes metabolic acidosis
What is the reporting procedure for acid-base disturbance
DACO Disturbance (acidosis or alkalosis) Aetiology (resp or met) Compensation (un-, partially, fully) Oxygenation
Name is in the order CADO e.g. uncompensated respiratory alkalosis with moderate hyoxaemia
How do you distinguish between metabolic and respiratory aetiology
Acidosis
PCO2 high = respiratory
PCO2 normal/low = Metabolic
Alkalosis
PCO2 high/normal = metabolic
PCO2 low = respiratory
What is suggested if both paCO2 and BE are low (abnormal pH)
Partially compensated metabolic acidosis
Partially compensated respiratory alkalosis
What is suggested if both paCO2 and BE are high (abnormal pH)
Partially compensated respiratory acidosis
Partially compensated metabolic alkalosis
What are the suggested conditions with acidosis, a high paCO2 and varying levels of BE
low BE = uncompensated mixed acidosis
normal BE = uncompensated respiratory acidosis
high BE = partially compensated respiratory acidosis
What are the suggested conditions with acidosis, a low paCO2 and low BE
partially compensated metabolic acidosis
What are the suggested conditions with alkalosis, a high paCO2 and high BE
high BE = partially compensated metabolic alkalosis
What are the suggested conditions with alkalosis, a low paCO2 and varying levels of BE
Low BE = Partially compensated respiratory alkalosis
normal BE = Uncompensated respiratory alkalosis
High BE = uncompensated mixed alkalosis
What is the general rule for identifying mixed acidosis/alkalosis
Abnormal CO2 and BE in opposite directions
What is the general rule for identifying a fully compensated distubance
CO2 and BE are abnormal in the same direction
Which disturbances can coexist
Respiratory acidosis and respiratory alkalosis cannot coexist
Metabolic acidosis and respiratory alkalosis can coexist
