Acid Base Balance

Question 1

What metabolic processes produce acids?

Answer 1

Protein/ phospholipid metabolism, CO2 from carbohydrate metabolism

Question 2

What is acid buffered by?

Answer 2

HCO3-, haemoglobin, plasma proteins

Question 3

How is acid excreted?

Answer 3

Lungs & kidney

Question 4

Why is acid-base such a big deal?

Answer 4

Most enzyme systems in the body will function optimally within a narrow range of pH (7.4- homeostasis- optimal)

Question 5

When does an acid-base imbalance occur?

Answer 5

When there is a change in the production or excretion of a specific acid or base. e.g. lack of insulin in diabetic animals can lead to being unable to use glucose for energy. Instead they use fatty acids. These acids can build up and lead to a drop in the serum pH of the patient. This is diabetic ketoacidosis

Question 6

What happens in chronic renal failure to cause an imbalance?

Answer 6

Kidney is no longer able to retain bicarbonate, which is a base, increased loss of bicarbonate in the urine causes an acidosis in the body

Question 7

What is an acid?

Answer 7

Simply a molecule that can donate a proton; H+ is the most basic acid itself

Question 8

What significantly impacts H+’s concentration?

Answer 8

Na+, K+, Ca++ (cation concentrations), etc.

Question 9

What significantly impacts HCO3-‘s concentration?

Answer 9

Cl-, phosphates, sufates, etc. (anions)

Question 10

The body must always remain electroneutral. Therefore, electroneutrality takes precedence over what?

Answer 10

Acid-base balance

Question 11

What is the chain reaction when a patient vomits gastric fluid?

Answer 11

Lose HCl- –> H+ and Cl- and H2O–> loss of H+ creates mild alkalotic environment–> Na+ is retained to help water retention–> Na+ or K+ is retained in place of lost H+ –> Less Cl- now availalble, HCO3- is retained in order to maintain electroneutrality–> Increase in bicarbonate will cause the alkalosis to become much more severe

Question 12

What is the first strategy for balancing acid-base?

Answer 12

Buffering

Question 13

What are buffers?

Answer 13

Proteins or ions that can take up or release H+ as needed. HCO3-, lactate, albumin (in the blood stream) and Hb, phosphates, proteins (in the cells)

Question 14

What percentage of acute acid load can be buffered by bone?

Answer 14

40%

Question 15

What does acidosis cause in regards to bone?

Answer 15

Calcium release

Question 16

Where is the Calcium excreted

Answer 16

Through urine

Question 17

What can chronic acidosis lead to in regards to bone (2)?

Answer 17

Fragile bones & pathological fractures, alkalosis causes carbonate to be laid down in bone

Question 18

What happens if there is a change in the metabolic acid base balance?

Answer 18

Respiratory acid base system will compensate and vice versa

Question 19

What happens in metabolic acidosis?

Answer 19

Increased production of acid (cellular hypoxia- anaerobi metabolism, ketoacidosis, lactic acidosis), decreased excretion of acid (hypoadrenocorticism, renal tubular acidosis, uraemia), increased acid intake (ethylene glycol toxicity, salicylate toxicity, metaldehyde toxicity), increased excretion of base (chronic renal failure, severe small intestinal diarrhoea)

Question 20

In severe acidosis (<7.2) what are the clinical effects?

Answer 20

Cardiac arrhythmias, decreased cardiac contractility, arterial vasodilation (low blood pressure), decreased blood flow to liver and kidney, shift of oxygen-haemoglobin dissociation curve to the right (increased off loading of oxygen in tissues), insulin resistance, increased intracranial pressure, alterations in K+ and Ca++

Question 21

What are some clinical causes of metabolic alkalosis?

Answer 21

Increased retention of bases, increased base intake, increased loss of acid (endocrine disease), most common cause is low Cl- concentration (vomiting of gastric contents, increased urinary excretion of Cl-)

Question 22

What are the clinical effects of metabolic alkalosis?

Answer 22

Muscle twitching, seizures, cardiac arrhythmias, shift in oxygen haemoglobin dissociation curve to teh left (Hb binds more tightly to oxygen), hypokalaemia, hypocalcemia

Question 23

With respiratory acid base, what is the main player? What does it act like?

Answer 23

CO2, acts like an ACID (increase in ventilatory rate will blow off more CO2, causing a respiratory alkalosis/ decrease in ventilatory rate will increase CO2, causing a respiratory acidosis)

Question 24

What are some causes of respiratory acidosis?

Answer 24

Any disease or process or injury that causes hypoventilation (decreased rate or depth of breathing), traumatic brain injury/ brain disease, anaesthesia, upper airway obstruction, end stage resp. disease, resp. muscle weakness/paralysis (snake venom, tick paralysis, myasthenia gravis, phrenic nerve injury)

Question 25

What are some causes of respiratory alkalosis?

Answer 25

Any disease process of injury that causes hyperventilation, stress, pain, catecholamine release, pulmonary disease or injury, pleural space disease, intracranial disease

Question 26

How does a clinical tell when things have gone wrong?

Answer 26

Venous blood gas analysis can be performed- important values: pH, pCO2, SBE (standard base excess)

Question 27

What is SBE?

Answer 27

Standard base excess. Measure of all the non-volatile acids and bases in the bloodstream. Does not include CO2 (which is volatile), includes organic molecules as well as ions

Question 28

What are the normal values in a venous blood gas analysis?

Answer 28

pH 7.4 (7.35-7.45), pCO2 40 mm Hg (35-45), SBE: 0 (-4, +4)

pCO2= respiratory component, SBE= metabolic component

Question 29

What does an increase pCO2 mean?

Answer 29

Respiratory acidosis

Question 30

What does an increase in pCO2 mean?

Answer 30

respiratory alkalosis

Question 31

What does a decrease in SBE mean?

Answer 31

Metabolic acidosis

Question 32

What does an increase in SBE mean?

Answer 32

Metabolic alkalosis

Question 33

Can have a mixed acid-base disorders.

Answer 33

Two primary disorders

Question 34

Example
7.1 pH
60 pCO2
+5 SBE

Answer 34

acidosis
resp. acidosis
metabolic alkalosis
Primary resp. acidosis with compensatory metabolic alkalosis

Question 35

Example
7.2
31 pCO2
11 SBE

Answer 35

acidosis
resp. alkalosis
metabolic acidosis
Primary metabolic acidosis with compensatory rep. alkalosis

Question 36

How can you tell if there is a mixed acid base disorder?

Answer 36

Overall acidosis (low pH) and a high CO2 (resp. acidosis) and low SBE (metabolic acidosis)- mixed acidosis
OR
high pH, low CO2, high SBE (mixed alkalosis)
OR
There is a resp. alkalosis and metabolic acidosis with a close to normal pH (mixed acid base disorder)

Question 37

What will resolve 90% of metabolic acid base disorders?

Answer 37

Fluid therapy (improve tissue perfusion, improve renal perfusion- facilitating excretion of acid or alkali load, normalize electrolytes, provide buffers)

Question 38

What is an important point to remember about body compensation with pH?

Answer 38

The body cannot compensate back to a normal pH. Must direct therapy towards the primary problem

Question 39

What is the most common cause of metabolic acidosis?

Answer 39

Anaerobic metabolism (produces H+ and lactate molecules)

Question 40

What is the most common reason for patients to have anaerobic metabolism?

Answer 40

Hypoperfusion. So most metabolic acidoses will resolve with appropriate fluid therapy.

Question 41

Why don’t we just give bicarbonate for metabolic acidosis?

Answer 41

The acidosis is an indication that there is decreased oxygen supply to the cells, if the cells are deprived of oxygen for too long, they will die. We will not stop cells dying by giving bicarbonate (and there are side effects to bicarb admin)

Question 42

What other therapies are used other than fluids?

Answer 42

e.g. patients with diabetic ketoacidosis need insulin so they can use glucose as fuel rather than ketones