Acid-base abnormality Flashcards
What is metabolic acidosis?
Metabolic acidosis is commonly classified according to the anion gap.
What characterizes normal anion gap metabolic acidosis?
Normal anion gap (hyperchloraemic metabolic acidosis) can be due to gastrointestinal bicarbonate loss, renal tubular acidosis, certain drugs, and Addison’s disease.
What are some causes of gastrointestinal bicarbonate loss?
Diarrhoea, ureterosigmoidostomy, and fistula.
What drugs can cause normal anion gap metabolic acidosis?
Acetazolamide and ammonium chloride injection.
What conditions lead to raised anion gap metabolic acidosis?
Lactate (shock, hypoxia), ketones (diabetic ketoacidosis, alcohol), urate (renal failure), and acid poisoning (salicylates, methanol).
What is metabolic alkalosis?
Metabolic alkalosis may be caused by a loss of hydrogen ions or a gain of bicarbonate, mainly due to kidney or gastrointestinal tract problems.
What are some causes of metabolic alkalosis?
Vomiting/aspiration, diuretics, liquorice, hypokalaemia, primary hyperaldosteronism, Cushing’s syndrome, Bartter’s syndrome, and congenital adrenal hyperplasia.
What conditions can cause respiratory acidosis?
COPD, decompensation in respiratory conditions (e.g. life-threatening asthma, pulmonary oedema), and sedative drugs (benzodiazepines, opiate overdose).
What are common causes of respiratory alkalosis?
Anxiety leading to hyperventilation, pulmonary embolism, salicylate poisoning, CNS disorders (stroke, subarachnoid haemorrhage, encephalitis), altitude, and pregnancy.
What is the formula to calculate the anion gap?
(sodium + potassium) - (bicarbonate + chloride)
What is a normal anion gap range?
8-14 mmol/L
In which condition is the anion gap particularly useful?
It is useful to consider in patients with a metabolic acidosis.
What are the causes of a normal anion gap or hyperchloraemic metabolic acidosis?
- Gastrointestinal bicarbonate loss: diarrhoea, ureterosigmoidostomy, fistula
- Renal tubular acidosis
- Drugs: e.g. acetazolamide
- Ammonium chloride injection
- Addison’s disease
What are the causes of a raised anion gap metabolic acidosis?
- Lactate: shock, hypoxia
- Ketones: diabetic ketoacidosis, alcohol
- Urate: renal failure
- Acid poisoning: salicylates, methanol
- 5-oxoproline: chronic paracetamol use
What is the first step in arterial blood gas interpretation?
How is the patient?
What indicates hypoxaemia in arterial blood gas interpretation?
The PaO2 on air should be >10 kPa.
What pH values indicate acidaemia or alkalaemia?
pH < 7.35 indicates acidaemia; pH > 7.45 indicates alkalaemia.
What does a PaCO2 > 6.0 kPa suggest?
It suggests a respiratory acidosis (or respiratory compensation for a metabolic alkalosis).
What does a PaCO2 < 4.7 kPa suggest?
It suggests a respiratory alkalosis (or respiratory compensation for a metabolic acidosis).
What bicarbonate levels suggest metabolic acidosis?
Bicarbonate < 22 mmol/l (or a base excess < -2 mmol/l) suggests metabolic acidosis (or renal compensation for a respiratory alkalosis).
What bicarbonate levels suggest metabolic alkalosis?
Bicarbonate > 26 mmol/l (or a base excess > +2 mmol/l) suggests metabolic alkalosis (or renal compensation for a respiratory acidosis).
What does ROME stand for in arterial blood gas interpretation?
Respiratory = Opposite; Metabolic = Equal.
What does low pH + high PaCO2 indicate?
It indicates acidosis.
What does high pH + low PaCO2 indicate?
It indicates alkalosis.
What does low pH + low bicarbonate indicate?
It indicates acidosis.
What does high pH + high bicarbonate indicate?
It indicates alkalosis.
Arterial blood gas interpretation - ROME
What is metabolic acidosis commonly classified according to?
Metabolic acidosis is commonly classified according to the anion gap.
How is the anion gap calculated?
The anion gap is calculated by: (Na+ + K+) - (Cl- + HCO-3).
What is the normal range for the anion gap?
The normal range for the anion gap is 10-18 mmol/L.
What is normal anion gap metabolic acidosis also known as?
Normal anion gap is also known as hyperchloraemic metabolic acidosis.
What are some causes of normal anion gap metabolic acidosis?
Causes include gastrointestinal bicarbonate loss, prolonged diarrhoea, ureterosigmoidostomy, fistula, renal tubular acidosis, drugs like acetazolamide, ammonium chloride injection, and Addison’s disease.
What are the causes of raised anion gap metabolic acidosis?
Causes include lactate (shock, sepsis, hypoxia), ketones (diabetic ketoacidosis, alcohol), urate (renal failure), and acid poisoning (salicylates, methanol).
What are the two types of lactic acidosis?
Lactic acidosis is subdivided into type A (sepsis, shock, hypoxia, burns) and type B (metformin).
What is metabolic alkalosis?
Metabolic alkalosis may be caused by a loss of hydrogen ions or a gain of bicarbonate. It is due mainly to problems of the kidney or gastrointestinal tract.
What are the causes of metabolic alkalosis?
Causes include vomiting/aspiration, diuretics, liquorice, carbenoxolone, hypokalaemia, primary hyperaldosteronism, Cushing’s syndrome, and Bartter’s syndrome.
How does vomiting contribute to metabolic alkalosis?
Vomiting may lead to hypokalaemia and is associated with conditions like peptic ulcer leading to pyloric stenosis and nasogastric suction.
What role does the renin-angiotensin II-aldosterone (RAA) system play in metabolic alkalosis?
Activation of the RAA system is a key factor; aldosterone causes reabsorption of Na+ in exchange for H+ in the distal convoluted tubule.
What happens during ECF depletion in metabolic alkalosis?
ECF depletion (vomiting, diuretics) leads to Na+ and Cl- loss, activating the RAA system and raising aldosterone levels.
How does hypokalaemia contribute to metabolic alkalosis?
In hypokalaemia, K+ shifts from cells to ECF, causing alkalosis due to the shift of H+ into cells to maintain neutrality.
What is respiratory acidosis?
Respiratory acidosis is a condition characterized by an increase in carbon dioxide in the blood due to inadequate ventilation.
What are some causes of respiratory acidosis?
Respiratory acidosis may be caused by a number of conditions: COPD, decompensation in other respiratory conditions (e.g., life-threatening asthma, pulmonary oedema), neuromuscular disease, obesity hypoventilation syndrome, and sedative drugs (e.g., benzodiazepines, opiate overdose).
What is COPD?
COPD stands for Chronic Obstructive Pulmonary Disease, a progressive lung disease that obstructs airflow.
What is neuromuscular disease?
Neuromuscular disease refers to a group of disorders that affect the muscles and the nerves that control them.
What is obesity hypoventilation syndrome?
Obesity hypoventilation syndrome is a condition in which severely overweight individuals fail to breathe deeply, leading to low oxygen levels and high carbon dioxide levels.
How can sedative drugs cause respiratory acidosis?
Sedative drugs, such as benzodiazepines and opiates, can depress the respiratory system, leading to inadequate ventilation and increased carbon dioxide levels.
What is respiratory alkalosis?
A condition characterized by a decrease in carbon dioxide levels in the blood due to hyperventilation.
What are common causes of respiratory alkalosis?
- Anxiety leading to hyperventilation
- Pulmonary embolism
- Salicylate poisoning
- CNS disorders: stroke, subarachnoid haemorrhage, encephalitis
- Altitude
- Pregnancy
What is the effect of salicylate poisoning on respiratory alkalosis?
Salicylate overdose leads to a mixed respiratory alkalosis and metabolic acidosis. Early stimulation of the respiratory centre leads to a respiratory alkalosis whilst later the direct acid effects of salicylates (combined with acute renal failure) may lead to an acidosis.
