Acidosis/Alkalosis Flashcards
The acidity or alkalinity depends on the concentration of this ion.
H+
normal pH
7.35-7.45
What is an ABG?
a measurement of the partial pressure of O2, CO2, pH, and HCO3 in arterial blood
Who normally draws this bloodwork? Where is it drawn from?
Respiratory therapists commonly draw from the radial, brachial, and femoral arteries.
What is acidosis?
It is characterized by an abundance of H+ ions in the arterial blood, with a pH of less than 7.35.
What are the acids?
H+, CO2, and H2CO3 (carbonic acid)
How are acids produced?
They are produced during metabolic processes.
How are acids excreted from the body?
Some exit via the lungs; others are buffered and excreted via kidneys.
What is alkalosis?
It is characterized by a decrease of H+ ions in the arterial blood, with a pH of more than 7.45.
What are the bases?
HCO3 (bicarbonate)
What is a buffer?
A chemical substance that reduces changes in systemic pH by either releasing or binding H+ ions. It is considered to be a moment by moment regulation.
Why is CO2 considered a “potential acid”?
Because it forms carbonic acid when combined with H2O.
What are compensatory mechanisms?
Mechanisms that try to prevent large changes in pH and/or attempt to correct alterations in acid-base balance; compensatory mechanisms ALWAYS alter the pH towards a normal level.
Give 2 examples of compensatory mechanisms.
lungs and the kidneys
What is partial pressure?
Pressure exerted by a single gas.
What is the goal in the regulation of pH?
To maintain or restore body pH to a normal level - either through buffers or compensatory mechanisms.
What are some examples of buffers?
proteins, carbonic acid - bicarbonate, phosphate
How do the lungs function as a compensatory mechanism?
By expiration, in which CO2 is eliminated from the body, thereby reducing the amount of acids. (note that the lungs cannot eliminate H+ ions)
normal range of PaCO2
35-45mmHg
normal range of HCO3 (bicarbonate)
22-26 mEq/L
normal range of PO2
80-100 mmhg
What does a low PO2 indicate and what is the potential (respiratory) result?
A low PO2 indicated hypoxia and can result in hyperventilation.
ABG Interpretation : What does the relationship between pH and PCO2 indicate?
A respiratory problem
ABG Interpretation : What does the relationship between pH and PHCO3 indicate?
a metabolic problem
What type of compensation is indicated if either pH and PCO2 or pH and PHCO3 are out of range (i.e. only 2 components)?
uncompensated compensation
What type of compensation is idicated if pH, PCO2, and PHCO3 are all out of range?
partially compensated
What type of compensation is indicated if the pH is WNL and PCO2 and PHCO3 are out of range?
Fully compensated compensation (note : need to determine whether pH is closer to acidosis or alkalosis to determine respiratory vs. metabolic)
How does the brain respond to retained CO2 in the body?
the blood vessels dilate, resulting in confusion
What are the characteristic values of respiratory acidosis?
low pH; high PCO2 (lungs to not rid the body of CO2, the excess of which binds to H2O to form H2CO3)
What is the cause of respiratory acidosis? What can lead to this condition?
CAUSE = HYPOVENTILATION
factors leading to this include :
trauma, disease, meds, CNS depression from narcotics, slower breathing
trauma that results in impaired respiratory function
What are some manifestations of respiratory acidosis?
tachycardia confusion (due to dilation of cerebral vessels) weakness tremors/paralysis stupor - coma warm/flushed skin
What is the respiratory compensation for respiratory acidosis?
an increase in respiration rate (unless CNS depression)
What are the renal compensations for respiratory acidosis?
excretion of H+ ions, and production and retention of HCO3
What are the characteristic values for respiratory alkalosis?
high pH; low PCO2
What is the cause of respiratory alkalosis and what is this secondary to?
CAUSE = HYPERVENTILATION secondary to
pain
anxiety/fear
fever/sepsis
CNS lesions
What are some manifestations of respiratory alkalosis?
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CONSTRICTION of cerebral vessels
CARDIAC DYSRHYTHMIAS rapid, deep breathing dizziness/light-headedness tetany numbness/tingling of fingers/toes panic seizures
What is the renal compensation for respiratory alkalosis?
a decrease in production of HCO3 (at around 24 hours)
Is metabolic acidosis or metabolic alkalosis seen more often in a clinical setting?
metabolic acidosis
What are the characteristic values of metabolic acidosis?
low pH; low PHCO3
note : this is usually secondary to significant health problems such as DKA and CKD
What are some causes of metabolic acidosis?
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- renal failure (decreased production of HCO3 as well as decreased excretion of H+ ions)
- severe diarrhea (increased loss of HCO3)
- lactic acidosis (increased production of acids)
- asprin toxicity (AKA : ASA Toxicity)
- starvation
- anaerobic metabolism secondary to hypoxia (remember cell injury leads to lactic acid production and accumulation)
What are some manifestations of metabolic acidosis?
EXPECT HYPERKALEMIA
abdominal pain
cardiac dysrhythmias
bone disease
What are the respiratory compensations for metabolic acidosis?
an increase in respiration rate & depth (Kussmauls respirations = deep, rapid resp. pattern to blow off CO2 - this is very characteristic)
What are the characteristic values for metabolic alkalosis?
high pH; high PHCO3
What are some causes of metabolic alkalosis?
- increased renal production of HCO3
- excess ingestion of alkali (antacids/baking soda)
- GI suctioning/vomiting/bulimia/diuretic therapy (all involve a loss of acids)
What are some manifestations of metabolic alkalosis?
EXPECT HYPOKALEMIA
hyperactive reflexes/tetany
hypotension
cardiac dysrhythmias
What is the respiratory compensation for metabolic alkalosis?
decreased respiration rate
excess CO2 retention
respiratory acidosis
excess CO2 excretion
respiratory alkalosis
HCO3 loss- acid retention
metabolic acidosis
HCO3 retention- acid loss
Metabolic alkalosis
deficiency in the amount of oxygen reaching the tissues.
hypoxia
oxygen deficiency in arterial blood
hypoxemia
what is very characteristic of metabolic acidosis?
Kussmaul’s respirations
” to blow off CO2” compensation for what?
metabolic acidosis
What are Kassmauls respirations?
deep, rapid resp. pattern to blow off CO2
In respiratory acidosis, how do the kidneys compensate for the acid-base imbalance?
the kidneys would increase the rate of tubular secretion of hydrogen ions into the renal tubules. This has two purposes:
(A) It allows all of the filtered bicarbonate ion to be converted to carbon dioxide in the tubular lumen and absorbed into the tubular lining cells. Here the carbon dioxide can be reconverted to bicarbonate ion and added to the bloodstream to prevent the blood pH from decreasing even further.
(B) The excess hydrogen ion remaining in the nephron tubule after all of the bicarbonate ion has been converted to CO2 can bind to ammonia (NH3) to produce ammonium ion (NH4+) and to monohydrogen phosphate (HPO4-2) to produce dihydrogen phosphate (H2PO4-). These compounds do not get reabsorbed and thus provide a vehicle for the excretion of excess H+ ions from the body.
Why might excessive vomiting cause acid-base disturbance in someone experiencing metabolic alkalosis?
The gastric secretions in the stomach are very acidic. If vomiting several times a day, there is a net loss of H+ ions from the stomach lumen and ultimately from the bloodstream. This raises arterial blood pH and causes a metabolic alkalosis