Acid-base balance Flashcards
Acids and bases are
An acid is a compound that will donate a H+ ion to a solution
A base is a compound that will bind to H+ ions
Acidosis is when an animals blood pH is below the normal range
Alkalosis is when an animals blood pH is above the normal range
What is buffering
Balancing acids and bases
The body’s ability to maintain pH between 7.35-7.45
It is critical to maintain pH within the normal range to ensure the function of cells and enzymes within the body
3 ways the body buffers itself
Chemical buffering
Excretion of hydrogen and bicarbonate ions in urine
Adjustment of the resp rate
When would you get an arterial sample
Elevate lung function
When would you get venous samples
Metabolic function
Why is pH important
Changes in pH affect enzyme and cell function → affect tissue and organ function including the brain and heart
May lead to death of patient
Presence of a change in body pH may also help us to determine the type of pathology that is occurring
Severe acidosis in a diabetic patient may indicate diabetic ketoacidosis
Lactic acidosis occurs with poor tissue perfusion
Physiological buffering system
Carbonic acid is not stable and rapidly breaks down into bicarbonate and hydrogen ions
Summary: the amount of CO2 in the body varies a lot based on the resp rate. During cellular respiration, CO2 is produced and is rapidly converted to carbonic acid, which is rapidly converted to bicarbonate and hydrogen ions
How is the carbonic acid equilibrium equation be affected
The body tries to regulate its own pH by adjusting the amount of CO2 in the body. This determines how much H+ is being produced. The concentration of H+ determines pH. The change in bicarbonate levels don’t have as significant of an effect on the body’s pH.
Take away message
The higher the level of CO2, the lower the bodys pH
4 types of acid bace disturbances
Metabolic acidosis
Respiratory acidosis
Metabolic alkalosis
Respiratory alkalosis
Metabolic acidosis is and causes
Blood pH is low <7.3
2 causes
Loss of bicarbonate (usually as diarrhea)
Normal ~25 mmol/L
Gain of organic acids
Ketoacids- diabetes mellitus
Uremic acids- severe kidney failure
Lactic acid- insufficient oxygen delivery to tissues
Organic acid toxicity- antifreeze poisoning, aspirin toxicity, alcohol poisoning
What is base excess
Base excess (BE) is a measure of metabolic acidosis
Reported in mmol/L or mEq/L
It is the amount of a strong acid that would be required to bring the body’s pH of 1 L to 7.4
BE increases with a metabolic alkalosis and decreases with a metabolic acidosis
If the value is zero (+/-5), there is no metabolic acidosis
When value for base excess is less then -5 it is sometimes called a base deficit
Metabolic acidosis and potassium is
In acidosis
Extracellular H+ is high
H+ can be exchanged for intracellular K+
This exchange may result in hyperkalemia
Cause bradycardia and death if severe enough
Correcting acidosis is an important component of treating hyperkalemia
Metabolic acidosis and potassium clinical signs
Depression
Weakness
Recumbency
Alterations of cardio system
Death (pH<7)
Metabolic acidosis and potassium treatment mild to moderate
Mild to moderate, pH 7.35-7.2
May rely on general therapy
Correct underlying problems
Fluids to improve tissue function
Allow body’s homeostatic mechanisms to correct pHMild or moderate cases may be treated with:
Oral electrolyte solutions
Polyionic IV electrolyte solutions
Solutions contain sodium bicarbonate OR sodium acetate, Lactate or propionate as alkalizing agents
Metabolic acidosis and potassium treatment moderate to severe
Moderate to severe, pH <7.2
Generally corrected
Direct benefits
May promote excretion of toxic acids
Severe metabolic acidosis is treated by
metabolic acidosis
Sodium bicarbonate IV
Na+ HCO3-
Bicarbonate requirement is calculated based on the severity of the acidosis
Respiratory acidosis is and underlying causes
Low pH
Caused by accumulation of CO2
High CO2 drives production of carbonic acid
Underlying causes
Lung disease (asthma, pulmonary edema, lung neoplasia)
Too much anaesthetic gas
Changes in pCO2 indicate ventilation problems
Anaesthetic problems
Lung disease
High pCO2 is called hypercapnia
Respiratory acidosis treatment
Anesthesia: what should you do if pCO2 is high
Check anaesthetic depth
Increased ventilation rate
Bagging patient
Reduce dead space
Ensure the mask/tube and bag size is appropriate for the patient
Diseased lung → improve lung function
Bronchodilators (asthma)
Diuretics (pulmonary edema)
Antibiotics
Anti inflammatories
May take time to resolve
Metabolic alkalosis causes and treatment
High pH >7.45
High bicarbonate
Most common causes are:
Vomiting
Loss of HCl in the vomit
Upper GI obstruction
Pooling of HCl in the stomach
Iatrogenic
Treatment
Large volumes of 0.9% saline
Dilutes blood bicarbonate
As blood flows through the kidneys Cl- is reabsorbed from the urine and exchanged for bicarbonate which is secreted into the urine
Respiratory alkalosis is and causes
High pH >7.45
Low pCO2
Caused by hyperventilation
Stress, anxiety
Excess manual ventilation during anaesthesia
How to interpret blood gas analysis
Look at the pH first
-Acidotic or alkalotic
Look at the pCO2
-Increased → resp acidosis
-Decreased → resp alkalosis
Look at bicarbonate
-Decreased → metabolic acidosis
-Increased → metabolic alkalosis
Problem may be mixed for compensation
Normal pH range
7.35-7.45
