Lecture 7 - Acid Base Balance 2 Flashcards
What is pH homeostasis?
Is a balance between acid production and acid excretion
What causes a low pH?
Metabolic acidosis (decrease in bicarbonate) and increase in respiratory acidosis (increase in PCO2)
What causes a high pH?
Metabolic alkalosis (increase in bicarbonate) and respiratory alkalosis (decrease in PCO2)
How do you compensate for metabolic acidosis?
Increased ventilation with a decrease pCO2 and H+
How do you compensate for respiratory acidosis?
Increased H+ secretion and excretion, all filtered bicarbonate reabsorbed, increased ammonia excretion
How do you compensate for metabolic alkalosis?
Decreased ventilation and increased PCO2
How do you compensate for respiratory alkalosis?
decreased HCO3- and decreased H+ secretion
What is compensation?
To try and correct the fault
What causes respiratory acidosis?
Obstructive airway disease and drugs which depress respiration
What is the primary defect for respiratory acidosis?
Increase in PCO2
What causes respiratory alkalosis?
Hyperventilation e.g. panic attacks, asthma and mechanical ventilation (salicylate overdose)
What is the primary defect for respiratory alkalosis?
Decrease in PCO2
What is a salicylate overdose?
Aspirin overdose
What is the primary defect for metabolic acidosis?
Decrease in bicarbonate
What are the causes for metabolic acidosis?
Gain of nonvolatile acid e.g. lactic acid, ketoacidosis and solvent abuse, lose of bicarbonate and decreased renal secretion
What is the primary defect for metabolic alkalosis?
Increase in bicarbonate
What are the causes of metabolic alkalosis?
Increased GI loss of protons - vomiting, increased renal loss of protons, administration of bicarbonate IV and liquorice
What can too much liquorice cause?
Pseudohyperaldosteronism
Why do people need bicarbonate IVs?
People who get acid reflux
What is the first line of defence of acid base disturbance?
To minimise the changes in pH - although it does not correct the underlying disorder
What is the multi step process for recovery from an acid-base disturbance process?
Acid base disturbance, buffering, respiratory compensation, renal compensation and correction of defect
What is the immediate response for acid base disturbance?
Immediate/minutes
What is the several hours response in acid base disturbance?
Respiratory compensation
What is the longer (hours-day) response for acid base disturbance?
Renal compensation
What is Pendrin?
It is a chloride bicarbonate antiporter
What are beta intercalacted cells also know as?
Bicarbonate intercalating cells
How do protons go back into the blood stream? - in the beta-intercalated cells of the distal tubule
By the V-ATPase
When is the activity of the bicarbonate intercalated cells increased?
It is increased during metabolic alkalosis
What helps with Cl- exchange?
The chloride transporter
What diagram is used for acid-base disturbances?
The davenport diagram (it is not used clinically)
What mmHg of CO2 is acidosis?
60mmHg
What mmHg of CO2 is alkalosis?
20mmHg
What is considered the buffer line in the davenport diagram?
40mmHg - this is where all the equivalences join together
What does high bicarbonate acidosis = (in the davenport diagram)
Respiratory acidosis
What condition is it where you have a low bicarbonate acidosis?
A metabolic acidosis
What condition is it called if there is a high Bicarboante alkalosis?
Metabolic alkalosis
What condition is it if you compensate with low bicarbonate alkalosis?
Respiratory alkalosis
Acidosis with decrease pCO2 =
Metabolic acidosis
Acidosis with increased bicarbonate =
Respiratory acidosis
Alkalosis with increased PCO2 =
respiratory alkalosis
Alkalosis with decreased bicarbonate =
Respiratory alkalosis
Example Q - what is the condition, 7.28pH 26mmHg of PCO2, 14mEq of bicarbonate?
Bicarbonate = disorder and there is a decreased PCO2 therefore it is metabolic acidosis
What is renal tubular acidosis?
To results from impaired H+ excretion by the kidneys
What is type 1 renal tubular acidosis?
Distant renal tubular acidosis
What is type 2 renal tubular acidosis?
Proximal renal tubular acidosis
What are examples of Type 1 renal tubular acidosis?
Distal nephron dysfunction, increased H+ permeability and Sjogen syndrome
How can type 2 - proximal tubular (RTA) be caused?
Usually due to a general dysfunction rather than specific transporter defect
What does impaired H+ secretion in PT lead to?
Decreased in bicarbonate reabsorption
What is the anion gap?
It is the difference in concentration of major ECF cations and anions
What is the normal value for the anion gap?
8-16mEq
What happens to the anion gap when there is acidosis from acid loading?
It increased to 17 and bicarbonate is reduced
What happens to the anion gap when acidosis results from Bicarboante loss?
It decreased to 10 - it is within the normal range
What is the equation for the anion gap with Na+, bicarbonate and Cl?
([Na+] - ([Cl-] + [HCO3-])
Increased acid retention =
Decreased pH and increased RAAS production
What causes decreased acid retention
Increased acid excretion and increased ammonia
What does angiotensin II contribute to?
It contributes to tubular injury and fibrosis in chronic kidney disease
What does ammonia genesis in chronic kidney disease result in?
It activates complement and exacerbates tissue damage - leads to an alternative compliment cascade
