Pathophysiology of Acid Base Flashcards
What’s the biggest source of acid in the body
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
What is the PH calculation
PH= 6.1 + log { HCO3- / (0.224xPCO2 ) }
What can cause an acidosis ( think chemicals )
Increase in PCO2 ( respiratory) or decrease in bicarbonate ( metabolic )
What results in increase or decrease of PCO2
Increase : respiratory acidosis
decrease: respiratory alkalosis
Why would you see some increase in bicarbonate during acute respiratory acidosis
Other buffers ( ex: haemoglobin ) buffering Hydrogen ions but there isn’t much of an increase
How is respiratory acidosis compensated
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
How long does it take till renal compensation develops
A few days - week
What if there is an increase of H+ concentration but the PCO2 did not change , explain what that means
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
What happens when there is an increase or decrease in PH
increase: alkalosis
decrease: acidosis
What type of acidosis is it if PaCO2 increases , what if HCO3 decreases ?
PaCO2: respiratory
HCO3 “ metabolic
How to differentiate between acute or chronic respiratory acidosis
Acute : less or no change in bicarbonate
Chronic : increase in bicarbonate
What happens if there is metabolic acidosis and bicarbonate decreases
There is a decrease in PaCO2
What is the anion gap
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 .
What happens if there is respiratory alkalosis , what about metabolic alkalosis
Respiratory : Decrease in PaCO2
Metabolic : Increase in HCO3
How to differentiate between acute or chronic respiratory alkalosis
acute : same or increase in HCO3
chronic : decrease in HCO3
What follow metabolic acidosis increase in HCO3
Increase in PaCO2
Does acute asthma cause respiratory alkalosis or acidosis and explain how
Acute asthma causes irregular bronchoconstriction that causes a mismatch in ventilation and perfusion. This causes hypoxia and hypocapnia which results in respiratory alkalosis .
Does deteriorating asthma cause respiratory alkalosis or acidosis and explain how
Deterioration causes fatigue that respiration muscles are unable to keep up and results in hypoventilation. Hypoventilation increases PaCO2 , causes hypoxia and acute respiratory acidosis
What is the treatment of acute asthma , what is it for deteriorating asthma
Acute: bronchodilators
Deteriorating : assisted ventilation
How Hyperventilation leads to Respiratory alkalosis
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
What is tetany
Reduced free ionized calcium in body fluids by increased binding of calcium onto plasma proteins due to the being less occupied by hydrogen ions.
How to treat hyperventilation
Reassure and explain , treat cause or underlying disease
How COPD can result in Respiratory alkalosis or acidosis and is it acute or chronic ( Hint: 2 ways )
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
What complications can come from COPD treatment
Assisted ventilation can result in too high FIO2 which will result in hypercapnia.
What happens if through assisted ventilation you lower CO2 while renal compensation of rise in bicarbonate still exists
Can result inputs hypercapnic metabolic alkalosis
How Chronic Kidney disease can result in acidosis or alkalosis ( 2 ways )
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
How Renal tubular acidosis Type 1 causes metabolic acidosis
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
How Renal tubular acidosis Type 2 causes metabolic acidosis
Failure to reabsorb bicarbonate in proximal tubule results in normal anion gap metabolic acidosis
How to treat renal tubular acidosis
Type 1 & 2 : bicarbonate
What could happen when renal tubular acidosis is treated with bicarbonate
Increased potassium secretion resulting in hypokalaemia. Unusual situation where potassium levels are going down and hydrogen concentration is going up
How Diarrhoea can cause acidosis or alkalosis
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
What can cause the unusual combination of acidosis and hypokalaemia
1- Diarrhoea
2- Renal tubular acidosis
3- diabetic keto acidosis
How is diarrhoea acidosis treated
Fluids and electrolytes
How Vomiting can lead to alkalosis or acidosis
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
How does Aldosterone ( hyperaldosteronism ) cause metabolic alkalosis
Stimulates sodium bicarbonate pumps in DCT which assists hydrogen ion secretion and thus metabolic alkalosis usually to make up for hypovolaemia
In the case of hypovolaemia causing metabolic alkalosis what can result in prolongation of alkalosis and how can it be treated
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
What does hypoaldesteronism cause , acidosis or alkalosis
Metabolic acidosis since there is a decrease in hydrogen ion secretion
How Diabetic Ketoacidosis leads to metabolic acidosis
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
How does Diabetic Ketoacidosis cause hypokalaemia
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
How does Hepatocellular dysfunction lead to Acidosis or alkalosis
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
How can Salicylate ingestion cause acidosis or alkalosis
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
How do you treat salicylate ingestion causing acidosis or alkalosis
Forced Alkaline diuresis that transforms salicylate into ionized form that will be excreted
How can IV saline result in metabolic acidosis
Excess isotonic saline ( PH 7. ) dilutes bicarbonate which can result in hyperchloraemia that results in metabolic acidosis
How can IV saline result in metabolic acidosis
Excess isotonic ( sodium chloride ) saline ( PH 7. ) dilutes bicarbonate which can result in hyperchloraemia that results in metabolic acidosis
List diseases that can cause respiratory alkalosis ( Hint: 7 )
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
List diseases that can cause respiratory acidosis ( Hint : 3 )
1- Hypoventilation
2- asthma
3- respiratory depressants ( morphine )
List diseases that can cause metabolic alkalosis ( Hint : 8 )
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
List diseases that can cause metabolic acidosis ( Hint: 9 )
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
What happens in lactic acidosis
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
Normal arterial blood PH
7.4 ( 7.35-7.45)
Normal Arterial blood PaCO2
5.3 ( 4.6-6.4)
Normal arterial blood HCO3
24 ( 22-30)
Normal Total CO2
26 ( 23-31 )
Normal arterial blood base excess
0 ( -2 - +2)
Normal venous blood PH
0.05 less than arterial ( 7.35)
Normal venous PaCO2 and HCO3
1 above arterial blood PaCO2 and HCO3 ( 6.3 & 25 )
What would a normal anion gap be
Less than 12mmol/L
65 year old women with 5 day of progressive confusion.
PH: 7.43
PCO2: 3.7
Bicarbonate: 18
Chronic respiratory alkalosis
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
High anion gap metabolic acidosis probably due to aspirin for her arthritis
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
High anion gap metabolic acidosis but PaCO2 is not showing any compensation so she has Mixed high anionic metabolic and respiratory acidosis
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
V/Q mismatch leads to hypoventilation which results in respiratory acidosis
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
Increased ventilation resulting in post hypercapnic metabolic alkalosis
