Week 3 - Moonshine Flashcards
What are the three immediate compensatory mechanisms for changes in serum pH?
Bicarbonate-carbonic acid buffering system
Intracellular protein buffers
Phosphate buffers
What is the normal pH range?
7.35 - 7.45
How long does the renal mechanism take to work?
6 hours
How does the renal system work?
Kidneys excrete H+ into the urine and retain HCO3- in acidosis
Kidneys excrete HCO3- and retain H+ in alkalosis
How does bone have the potential to be a buffering system?
- Contains a large reservoir of bicarbonate and phosphate
- can buffer a significant acute acid load
- patients who have low albumin levels and bone density due to malnutrition or chronic disease and anaemic patients have an ineffective buffering capacity
What acid-base imbalance does Amir have? PH of 7.32 PCO2 36mmHg PO2 137 mmHg Serum bicarbonate was 18 mmol/L The anion gap 20 mmol/L
Metabolic acidosis
Amir’s anion gap starts at 4.7 mmol/L and goes to 20 mmol/L
Why is this?
Delayed effects of methanol poisoning
When he first arrives he is in Phase I
What is the normal range of an anion gap?
8-16 mmol/L
Name some common reasons for an elevated anion gap
Methanol, metformin Ethylene glycol Toluene Alcoholic ketoacidosis Lactic acidosis Aminoglycosides, other uraemia agents Cyanide, carbon monoxide Isoniazid, iron Diabetic ketoacidosis Generalised seizure-producing toxins ASA or other salicylate Paraldehyde, phenoformin
Briefly describe respiratory acidosis
PH less than 7.35
PaCO2 is above 45mmHg
Hypercapnia
Alveolar hyperventilation is the only mechanism for pCO2 to be higher than the upper limit
Balance between pCO2 and HCO3- in the serum, minimal changes
Over a period of 1-3 days, renal conservation of HCO3- results in an increase in pH
Chronic secondary respiratory acidosis can occur secondary to a chronic reduction in alveolar ventilation (COPD and other chronic lung diseases)
Briefly describe respiratory alkalosis
Common in critical care
PCO2 is reduced
Causing an increase in pH above 7.45
Most common cause of respiratory alkalosis is increased alveolar ventilation e.g. hyperventilation, pregnancy or septicaemia
In chronic respiratory alkalosis, the compensatory mechanisms result in mild reduction in plasma HCO3- to maintain a near normal pH
Treatment of respiratory alkalosis is directed at discovering the underlying aetiology (e.g. if anxiety hyperventilation then breathe into a paper bag to breathe in their CO2, if ventilator check and monitor so doesn’t go into respiratory acidosis)
Briefly describe metabolic acidosis
Increase in amount of absolute body acid or excessive loss of bicarbonate, sodium and potassium
Causes of metabolic acidosis include: lactic acidosis, diabetic ketoacidosis, loss of bicarbonate wasting through the kidneys or GI tract
