Pathophysiology of Acid Base

Question 1

What’s the biggest source of acid in the body

Answer 1

1- carbonic acid produced from cell respiration that is excreted from lungs as gas
2- non-carbonic involatile acid form cell metabolism that is excreted by kidneys

Question 2

What is the PH calculation

Answer 2

PH= 6.1 + log { HCO3- / (0.224xPCO2 ) }

Question 3

What can cause an acidosis ( think chemicals )

Answer 3

Increase in PCO2 ( respiratory) or decrease in bicarbonate ( metabolic )

Question 4

What results in increase or decrease of PCO2

Answer 4

Increase : respiratory acidosis

decrease: respiratory alkalosis

Question 5

Why would you see some increase in bicarbonate during acute respiratory acidosis

Answer 5

Other buffers ( ex: haemoglobin ) buffering Hydrogen ions but there isn’t much of an increase

Question 6

How is respiratory acidosis compensated

Answer 6

With time kidneys compensates for lungs inability to expel CO2 by :
1- Excreting more hydrogen ions
2- Retain bicarbonate ions to act as an alkali to neutralize acidosis

Question 7

How long does it take till renal compensation develops

Answer 7

A few days - week

Question 8

What if there is an increase of H+ concentration but the PCO2 did not change , explain what that means

Answer 8

That indicates that there is something wrong with the respiratory system, and it hasn’t compensated for the metabolic acidosis , meaning this is a mixed respiratory and metabolic acidosis

Question 9

What happens when there is an increase or decrease in PH

Answer 9

increase: alkalosis
decrease: acidosis

Question 10

What type of acidosis is it if PaCO2 increases , what if HCO3 decreases ?

Answer 10

PaCO2: respiratory

HCO3 “ metabolic

Question 11

How to differentiate between acute or chronic respiratory acidosis

Answer 11

Acute : less or no change in bicarbonate

Chronic : increase in bicarbonate

Question 12

What happens if there is metabolic acidosis and bicarbonate decreases

Answer 12

There is a decrease in PaCO2

Question 13

What is the anion gap

Answer 13

Shows if metabolic acidosis is due to carbonic acid only or other acid as well. Gap is anions that haven’t been measured, shows if it is high or normal .

Question 14

What happens if there is respiratory alkalosis , what about metabolic alkalosis

Answer 14

Respiratory : Decrease in PaCO2

Metabolic : Increase in HCO3

Question 15

How to differentiate between acute or chronic respiratory alkalosis

Answer 15

acute : same or increase in HCO3

chronic : decrease in HCO3

Question 16

What follow metabolic acidosis increase in HCO3

Answer 16

Increase in PaCO2

Question 17

Does acute asthma cause respiratory alkalosis or acidosis and explain how

Answer 17

Acute asthma causes irregular bronchoconstriction that causes a mismatch in ventilation and perfusion. This causes hypoxia and hypocapnia which results in respiratory alkalosis .

Question 18

Does deteriorating asthma cause respiratory alkalosis or acidosis and explain how

Answer 18

Deterioration causes fatigue that respiration muscles are unable to keep up and results in hypoventilation. Hypoventilation increases PaCO2 , causes hypoxia and acute respiratory acidosis

Question 19

What is the treatment of acute asthma , what is it for deteriorating asthma

Answer 19

Acute: bronchodilators

Deteriorating : assisted ventilation

Question 20

How Hyperventilation leads to Respiratory alkalosis

Answer 20

1- Anxiety increases ventilation which causes hypocapnia and increases respiratory exchange ratio. Can cause tetany. This all leads to acute respiratory alkalosis
2- if chronic there will be renal compensation and it will be chronic respiratory alkalosis

Question 21

What is tetany

Answer 21

Reduced free ionized calcium in body fluids by increased binding of calcium onto plasma proteins due to the being less occupied by hydrogen ions.

Question 22

How to treat hyperventilation

Answer 22

Reassure and explain , treat cause or underlying disease

Question 23

How COPD can result in Respiratory alkalosis or acidosis and is it acute or chronic ( Hint: 2 ways )

Answer 23

1- ventilation is impaired and there is a ventilation perfusion mismatch . Causes Hypoxia and hypercapnia. Result: chronic respiratory acidosis
2- If there is exacerbations then it will result in further hypoventilation , more hypercapnia and thus an acute on chronic respiratory acidosis

Question 24

What complications can come from COPD treatment

Answer 24

Assisted ventilation can result in too high FIO2 which will result in hypercapnia.

Question 25

What happens if through assisted ventilation you lower CO2 while renal compensation of rise in bicarbonate still exists

Answer 25

Can result inputs hypercapnic metabolic alkalosis

Question 26

How Chronic Kidney disease can result in acidosis or alkalosis ( 2 ways )

Answer 26

1- Failure to excrete non-carbonic acids and failure to reabsorb bicarbonate will result in low bicarbonate levels but high anion gap. Result: high anion gap metabolic acidosis 2- failure to excrete potassium causes hyperkalaemia which result sin displacement of hydrogen ions from cells that results in metabolic acidosis

Question 27

How Renal tubular acidosis Type 1 causes metabolic acidosis

Answer 27

1- Failure to secrete hydrogen ions due to problem with distal tubular cells. Results in normal anion gap metabolic acidosis. 2- failure to secrete and excrete potassium ions will result in hyperkalaemia and further metabolic acidosis

Question 28

How Renal tubular acidosis Type 2 causes metabolic acidosis

Answer 28

Failure to reabsorb bicarbonate in proximal tubule results in normal anion gap metabolic acidosis

Question 29

How to treat renal tubular acidosis

Answer 29

Type 1 & 2 : bicarbonate

Question 30

What could happen when renal tubular acidosis is treated with bicarbonate

Answer 30

Increased potassium secretion resulting in hypokalaemia. Unusual situation where potassium levels are going down and hydrogen concentration is going up

Question 31

How Diarrhoea can cause acidosis or alkalosis

Answer 31

1- Loss of fluids means loss of bicarbonate so there will be a normal anion gap metabolic acidosis 2- if there is loss of potassium then there will be acidosis with hypokalaemia

Question 32

What can cause the unusual combination of acidosis and hypokalaemia

Answer 32

1- Diarrhoea 2- Renal tubular acidosis 3- diabetic keto acidosis

Question 33

How is diarrhoea acidosis treated

Answer 33

Fluids and electrolytes

Question 34

How Vomiting can lead to alkalosis or acidosis

Answer 34

1- loss of gastric acid = metabolic alkalosis 2- loss of potassium results in hypokalaemia and thus further alkalosis 2- loss of fluids results in hypovolaemia which leads to hyperaldosteronism and thus further metabolic alkalosis

Question 35

How does Aldosterone ( hyperaldosteronism ) cause metabolic alkalosis

Answer 35

Stimulates sodium bicarbonate pumps in DCT which assists hydrogen ion secretion and thus metabolic alkalosis usually to make up for hypovolaemia

Question 36

In the case of hypovolaemia causing metabolic alkalosis what can result in prolongation of alkalosis and how can it be treated

Answer 36

Aldosterone drives sodium bicarbonate reabsorption to try and increase blood volume results in Kidneys unable to excrete excess bicarbonate and thus alkalosis is prolonged. Fluids need to be given

Question 37

What does hypoaldesteronism cause , acidosis or alkalosis

Answer 37

Metabolic acidosis since there is a decrease in hydrogen ion secretion

Question 38

How Diabetic Ketoacidosis leads to metabolic acidosis

Answer 38

Low cell glucose results in shift to fat metabolism which overwhelms the mitochondria. Leads to ketone bodies forming and thus a high anion gap metabolic acidosis

Question 39

How does Diabetic Ketoacidosis cause hypokalaemia

Answer 39

Ketoacidosis results in potassium coming out of cell which results in hyperkalaemia but once it is treated with insulin potassium could fall , needs to be monitored

Question 40

How does Hepatocellular dysfunction lead to Acidosis or alkalosis

Answer 40

1- Abnormal levels of toxins and hormones stimulate respiratory centre which can results in chronic respiratory alkalosis 2- Loss of ability to manufacture albumin ( an acid ) can result in hypoaalbuminaemia leads to metabolic alkalosis 3- abnormal amino acids and other acids can lead to metabolic acidosis

Question 41

How can Salicylate ingestion cause acidosis or alkalosis

Answer 41

1- Non-carbonic acid can result in high anion gap metabolic acidosis 2- Stimulate ventilation which leads to hyperventilation that leads to respiratory alkalosis 3- Can be a mix of 1 and 2

Question 42

How do you treat salicylate ingestion causing acidosis or alkalosis

Answer 42

Forced Alkaline diuresis that transforms salicylate into ionized form that will be excreted

Question 43

How can IV saline result in metabolic acidosis

Answer 43

Excess isotonic saline ( PH 7. ) dilutes bicarbonate which can result in hyperchloraemia that results in metabolic acidosis

Question 44

How can IV saline result in metabolic acidosis

Answer 44

Excess isotonic ( sodium chloride ) saline ( PH 7. ) dilutes bicarbonate which can result in hyperchloraemia that results in metabolic acidosis

Question 45

List diseases that can cause respiratory alkalosis ( Hint: 7 )

Answer 45

1- Hyperventilation 2- Hypoxia ( reduces PaCO2) 3- Asthma : ventilation perfusion mismatch 4- Pulmonary vascular disease: ventilation perfusion mismatch 5- Liver disease 6- Heart failure : reflex increase in ventilation due to venous congestion 7- Respiratory stimulants : aspirin

Question 46

List diseases that can cause respiratory acidosis ( Hint : 3 )

Answer 46

1- Hypoventilation 2- asthma 3- respiratory depressants ( morphine )

Question 47

List diseases that can cause metabolic alkalosis ( Hint : 8 )

Answer 47

``` 1- Gastric secretion lost : vomiting 2- hyperaldosteronism 3- Hypovolaemia 4- hypercapnia 5- Alkali ingestion : antacids, bicarbonate 6- Diuretics : aldosterone response causes alkalosis 7- Seat loss in cystic fibrosis 8- Hypokalaemia ```

Question 48

List diseases that can cause metabolic acidosis ( Hint: 9 )

Answer 48

``` Normal anion cap 1- renal tubular acidosis 2- chronic renal disease 3- diarrhoea 4- ingestion ``` ``` Increases anion gap 1- chronic renal disease 2- lactic acidosis 3- ketoacidosis 4- liver disease 5- ingestion of acids : aspiring, methanol , ethylene glycol ```

Question 49

What happens in lactic acidosis

Answer 49

If oxygen supply to cells is diminished then pyruvate accumulates from glycolysis and can't undergo Krebs due to lack of oxygen. Pyruvate converts to lactic acids which is a non-measured anion. Happens in exercise and disease

Question 50

Normal arterial blood PH

Answer 50

7.4 ( 7.35-7.45)

Question 51

Normal Arterial blood PaCO2

Answer 51

5.3 ( 4.6-6.4)

Question 52

Normal arterial blood HCO3

Answer 52

24 ( 22-30)

Question 53

Normal Total CO2

Answer 53

26 ( 23-31 )

Question 54

Normal arterial blood base excess

Answer 54

0 ( -2 - +2)

Question 55

Normal venous blood PH

Answer 55

0.05 less than arterial ( 7.35)

Question 56

Normal venous PaCO2 and HCO3

Answer 56

1 above arterial blood PaCO2 and HCO3 ( 6.3 & 25 )

Question 57

What would a normal anion gap be

Answer 57

Less than 12mmol/L

Question 58

65 year old women with 5 day of progressive confusion. PH: 7.43 PCO2: 3.7 Bicarbonate: 18

Answer 58

Chronic respiratory alkalosis

Question 59

``` 65 year old women with 5 day of progressive confusion. Also has painful arthritis PH: 7.33 PaCO2 : 3.7 Bicarbonate : 14 Anion gap : 18 ```

Answer 59

High anion gap metabolic acidosis probably due to aspirin for her arthritis

Question 60

65 woman being treated for UTI develops high fever , shivering and hypotension. ``` PH: 7.1 PaCO2 : 5.3 HCO3: 12 Base excess: -16 Albumin: 15 Sodium : 140 Potassium : 5 Chloride : 115 Anion gap : 13 ```

Answer 60

High anion gap metabolic acidosis but PaCO2 is not showing any compensation so she has Mixed high anionic metabolic and respiratory acidosis

Question 61

31 man has severe breathlessness, can't complete sentence , pulse 120 bpm. Widespread wheeze, oxygen saturation 92%. Gets salbutamol by nebulizer and oxygen ``` At presentation: PH: 7.45 PCO2: 4.7 HCO3: 24 Base excess: + 1 ``` ``` 30 minutes later looks exhausted: PH: 7.35 PCO2: 6 HCO3: 24 base excess: - 1.2 ```

Answer 61

V/Q mismatch leads to hypoventilation which results in respiratory acidosis

Question 62

Patient on ventilator in ICU . ``` On admission: pH: 7.21 paCO2: 10.7 HCO3: 31 BE: +1 ``` ``` 24 hours later : PH: 7.48 PaCO2: 5.6 HCO3: 30 BE: + 6.6 ``` What has happened

Answer 62

Increased ventilation resulting in post hypercapnic metabolic alkalosis