Acid Base Balance Flashcards
Acid + example
substance that releases H+ when dissolved in water/body fluids
H+ = proton
Base + example
substance that accepts or binds to hydrogen ions
HCO3-
Acidosis
the process by which protons are produced in a large amount
increase in proton production
Alkalosis
the process by which there is a decrease in proton production/concentration (H+)
Buffer
can react as either acid or base, depending on pH of the solution
What are arterial blood gases
Provide valuable information on patient’s acid-base and oxygenation status
Reflect respiratory and metabolic functions
Constant byproduct of cellular metabolism: CO2 and water
What is pH and normal value?
7.35-7.45
* Concentration of hydrogen ions
* Hydrogen ions = acidic
What does PCO2 tell you and normal value?
35-45mmHg
Partial pressure of carbon dioxide
The amount of CO2 is directly proportional to:
the number of hydrogen ions; corresponds with acid
The more carbon dioxide in your blood the more _____ your blood is
Acidic
Carbon dioxide levels will be altered in ______
respiratory acidosis/alkalosis
Controlled by lungs
Bicarb normal value
22-28mmol/l
The more bicarbonate you have in your blood, the more ____ it is
basic
Bicarbonate levels will be altered in:
Metabolic acidosis/alkalosis
Normal PaO2 levels and when are decreases seen?
80-100mmHg
decreases above sea level and with increasing age
What does PaO2 give information on?
does not give information on whether patient is in respiratory/metabolic acidosis only hypoxemia
Normal base excess level
0 + 2.0mEq/L
4 Steps of ABG analysis
- Identify acidosis/alkalosis
- look at pH - Identify respiratory/metabolic
- look at CO2 (altered in resp)
- look at HCO3 (altered in metabolic) - Identify compensation
- other value normal = none
- other value outside = compensated
> normal pH = full
> abnormal pH = partial
Respiratory Alkalosis Values
high pH, low CO2, normal HCO3 (unless compensated)
Respiratory Acidosis Values
low pH, high CO2, normal HCO3 (unless compensated)
Metabolic Alkalosis Values
high pH, high HCO3, normal CO2 (unless compensated)
Metabolic Acidosis Values
low pH, low HCO3, normal CO2 (unless compensated)
What causes respiratory acidosis + 3 conditions
Retention of CO2
* CNS Depression
* Neuromuscular Disorder
* Obstructive Lung Disease
What causes respiratory alkalosis + 3 conditions
Excretion of CO2
* CNS Hyperactivity (anxiety, fever, pain)
* Hypoxemia - can stimulate hyperventilation
* Increased ICP
What 3 things cause metabolic acidosis?
Gain of Acid (DKA, lactic acidosis)
Loss of Base
Inability to excrete acid
What 3 things cause metabolic alkalosis?
Loss of Acid (vomiting, increased aldosterone, total volume loss, administration of NaHCO3)
gain of base
excessive renal loss
Effects of acidosis on the heart
- hypotension due to decreased contractility, decreasing CO and MAP
- hypotension due to increased vasodilation
- increased HR causing VT arrhythmias
- resistance to vasopressors
Effects of alkalosis on the heart
- increases vasoconstriction
- increases HR leading to VT arrhythmias, vfib, SVT arrhythmias
Effects of acidosis on the lungs
increases RR - increased WOB - fatigue
Effects of alkalosis on the lungs
decreases RR - hypoxemia
Effects of acidosis on metabolism
- high proton concentration causes extra to intracellular fluid shift, increasing potassium ARRHYTHMIA RISK
- high proton concentration alters insulins effect, promoting resistance INCREASING BG
Effects of alkalosis on metabolism
Decreases potassium and magnesium (to a lesser extent)
Effects of acidosis on CNS
Altered mental status – coma
Effects of alkalosis on CNS
Altered mental status – coma
Seizures/tetany
Volatile Acids
Can be converted to gas for excretion by lungs
carbonic acid to carbon dioxide
Example of volatile acid
Carbonic acid
Nonvolatile acids
Metabolic acids
Cannot be converted to gas; must be excreted by kidneys
Can only do a small amount each day - slow process
Nonvolatile acid examples and how they are formed
- Sulfuric acid: formed by protein breakdown
- Fatty acids & ketoacids: formed by fat breakdown
- Lactic acid: when cells metabolize under anaerobic (no oxygen) conditions
How does the body acutely respond to acid base imbalances?
The bicarb/carbonic acid buffer system
What occurs in the buffer system when there is a low pH?
Bicarbonate can bind to free H+ when too many are present, or release them when not enough are present, forming carbonic acid
Carbonic acid can then be excreted through lungs
What occurs in the buffer system when there is a high pH?
If there are too few H+ ions, carbonic acid will disassociate into a hydrogen ion and bicarbonate
What does the carbonic anhydrase equation show
This reaction (driven by carbonic anhydrase enzyme) shows how H+ and CO2 levels are directly related. An increase in one causes an equal increase in the other
Describe the carbonic anhydrase equation?
carbon dioxide + water <> carbonic acid <> hydrogen + bicarbonate
What are the 3 buffering systems in the body?
- Bicarbonate - acute/not highly effective
- respiratory - fast system based on chemoreceptors of CO2 concentration
- renal - slower regulates HCO3
How do the lungs compensate/act as an acid-base buffer system?
Control carbon dioxide and thus carbonic acid excretion
Ventilation based on CO2 levels via chemoreceptors
How do the lungs compensate in acidosis?
Increased Rate and depth of ventilation = attempt to rid body of CO2
* Low pH stimulates chemoreceptors in CNS stimulates an increase in RR (in attempt to breathe off CO2)
How do the lungs compensate in alkalosis?
Decreased Rate and depth of ventilation = retention of CO2
* High pH inhibits chemoreceptors in CNS lower RR retention of CO2
How do the kidneys compensate/act as an acid-base buffer?
Takes hours to days/longer
* Regulate HCO3- level (excretion and reabsorption) in the renal tubules
How do the kidneys compensate in acidosis?
kidneys excrete H+ and conserve HCO3-
How do the kidneys compensate in alkalosis?
kidneys retain H+ and excrete (/decrease resabsorption) HCO3-
Uncompensated ABG values
- Abnormal pH
- One abnormal and one normal value (other system has not been compensated)
Partially compensated ABG values
- Abnormal pH
- Two abnormal values (opposite system has attempted to compensate)
Fully compensated ABG values
- Normal pH
- Two abnormal values (opposite system has compensated enough to move pH into normal range)