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NURS601 Week 1
Concept 3: Acid-base balance (too much/too little acid)
Blood pH levels
Dependent on H+ concentration |
Normal pH: 7.35-7.45 |
Alkalosis: 7.45-7.8 |
Acidosis: 7-7.35 |
Anything >7.8 or <7 is deadly |
Buffers
Buffering is the primary regulator of acid-base balance. |
Buffers act chemically to change strong acids into weaker ones, or bind them to neutralise them |
Different buffer systems assume dominant roles in different parts of the body: |
Extracellular Fluid (ECF) |
Major buffer: Bicarbonate buffer system |
| |
Minor buffers: Intracellular problems, Phosphate buffer system |
Blood |
Major buffers: Bicarb buffer system, Hemoglobin |
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Minor buffers: Plasma proteins, Phosphate buffer system |
Intracellular fluid (ICF) |
Major buffers: Proteins, Phosphate |
| |
Minor buffers: None |
Urine |
Major buffers: Ammonia, Phosphate |
| |
Minor buffers: None |
Renal
Secretes free hydrogen ions into renal tubules |
Excretes weak acid |
Excretes HCO3 (if there is metabolic acidosis) |
Reading arterial blood gases (ABG)
Respiratory Acidosis |
Decreased pH, increased PaCO2, normal HCO3 |
Respiratory Alkalosis |
Increased pH, decreased PaCO2, normal HCO3 |
Metabolic Acidosis |
Decreased pH, normal PaCO3, decreased HCO3 |
Metabolic Alkalosis |
Increased pH, normal PaCO2, increased HCO3 |
Normal ABG figures |
pH |
7.35-7.45 |
PO2 |
80-100 |
PCO2 |
35-45 |
HCO3 |
22-28 |
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Acid-base homeostasis
How is it maintained? |
Buffers |
Bicarbonate (HCO3) - reacts rapidly, less than an second. Chemically change strong aicds to weaker acids or bind to neutralise effect |
Resipratory system |
Reacts rapidly - seconds to minutes |
Renal system |
Reacts slowly - hours |
Respiration
CO2 formed and excreted in lungs |
Lungs excrete CO2 + H2O as by-products of cellular metabolism |
CO2 is regarded as an acid |
Homeostasis cycle of CO2 in the body: |
During exercise or other activity, cell metabolism increases and produces more CO2, then: |
More CO2 dissolves in blood, forming carbonic acid which lowers blood pH slightly, then: |
Receptors in the brain sense the drop in pH and send nerve signals to increase breathing rate, then: |
Increased breathing rate quickly removes more CO2 from blood. Blood pH rises slightly, returning to normal - cycle starts again |
Continuous mixing of body fluids/gases
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