Acid-Base Disturbances Flashcards
What is an acid?
a molecule that can release a H+
What is a base?
an ion or molecule that can accept or combine with a H+
Why are acids continuously generated?
as by-products of metabolism
What is a volatile acid?
-H2CO3 is in equilibrium with CO2 (H2CO3 ⇌ CO2 + H2O)
-Ability of the lungs to exhale CO2 determines levels of H2CO3
What is a non-volatile or fixed acid?
-Buffered by body proteins or extracellular buffers (HCO3-) then excreted by the kidneys
How is CO2 dissolved in blood plasma for transport?
-Quantity dissolved in plasma can be determined by its PCO2
-Dissolved CO2 is converted to H2CO3 which contributes to blood pH
-H2CO3 ⇌ CO2 + H2O
How is CO2 transported as bicarbonate?
-Within the RBC, carbonic anhydrase catalyzes its conversion into H2CO3
-H2CO3 then dissociates into H+ and HCO3-
-H+ combines with hemoglobin (HHb) and HCO3- diffuses into plasma
-HCO3- now participates in acid- base regulation
How is CO2 transported as carbaminohemoglobin?
-Remaining CO2 in RBCs binds to Hb to form HbCO2
-Loose bond - so CO2 can easily be released in capillaries and can exhaled
What are the 3 major mechanisms pH of body fluids is regulated by?
-Chemical buffer systems (combine with excess acids or bases to prevent large changes in pH)
-Respiratory system (control the elimination or retention of CO2)
-Renal system (eliminates H+ and both reabsorbs and generates new HCO3-)
What do buffer systems do to regulate pH?
-Control minute-to-minute pH changes
-Respond temporarily to larger changes (1st line of defense)
What does the respiratory system do to regulate pH?
-Responds quickly and with fast results (2nd line of defense)
-Does not return to homeostasis
What does the renal system do to regulate pH?
-Main responsibility for return to homeostasis
-Slow to respond, slow to work (3rd line of defense)
What is acidosis?
increased concentration of H+ ions (pH < 7.35)
What is alkalosis?
decreased concentration of H+ ions (pH > 7.45)
What is normal pH in humans?
7.35-7.45
What is Respiratory Acidosis/Alkalosis?
altered PCO2 (35- 45mmHg)
What is Metabolic Acidosis/Alkalosis?
altered HCO3- (22-26mEq/L)
What is metabolic acidosis?
-Involves a decreased concentration of plasma HCO3- levels and decreased pH
-The body compensates for the acidosis with an increased respiratory rate in an attempt to lower PCO2 and therefore H2CO3
What conditions can cause metabolic acidosis?
-Uncontrolled diabetes mellitus ( + ketoacids)
-Starvation or severe carbohydrate reduced diet (+ ketoacids)
-Severe exercise (increase in lactic acid)
-Severe diarrhea (GI loss of HCO3)
-Renal failure (failure to excrete H+)
-Cardiac failure or arrest (increase in lactic acid)
-Acute alcohol intoxication (increase in fixed acids)
-Salicylate overdose (increased fixed acids)
-Shock (increase lactic acid)
How does lactic acidosis cause metabolic acidosis?
-Caused by the increased production or decreased removal of lactic acid
-Lactic acid is a byproduct of anaerobic metabolism of glucose
-Can occur when the metabolic tissue demands exceed the aerobic production of ATP
-Often caused by inadequate oxygen delivery or severe hypoxia
-Anemia, shock, cardiac arrest, hypotension, decreased CO Causes
How does ketoacidosis cause metabolic acidosis?
-Ketoacids are a source of fuel for many body tissues
-An overproduction of ketoacids occurs when carbohydrate stores are inadequate or the body can’t use available carbs (lack of insulin)
-Common causes include: Poorly controlled diabetes, Fasting or food deprivation
How does salicylate toxicity cause metabolic acidosis?
-Acetylsalicylic acid (Aspirin - ASA) is absorbed in the stomach and small bowel and then converted to salicylate acid
-An OD of ASA can produce a mixed disorder
-Cross the blood brain barrier and stimulate the respiratory centre to produce hyperventilation (respiratory alkalosis)
-Kidneys respond by excreting HCO3-, Na+ and K+ (metabolic acidosis)
How does decreased renal function cause metabolic acidosis?
-CKD (chronic kidney disease) is the most common cause of chronic metabolic acidosis
-Results in a loss of glomerular filtration and tubular reabsorption/secretion - retention of wastes and metabolic acids
How does increased bicarbonate loss cause metabolic acidosis?
-Loss of HCO3- rich fluids or with impaired renal conservation of HCO3-
-Intestinal secretions have a high HCO3- concentration, severe diarrhea
-Hyperchloremic Acidosis:
What is hyperchloremic acidosis?
-Occurs when Cl- levels are increased out of proportion to Na+
-Cl- and HCO3- are interchangeable anions, therefore, when plasma Cl- increases, plasma HCO3- decreases
-Can occur due to impaired renal reabsorption or treatment with chloride containing medication
What are the signs and symptoms of metabolic acidosis?
-Weakness, fatigue, general malaise, vomiting, and abdominal pain
-Depression of neuronal excitability leads to drowsiness, altered LOC, stupor and coma
-Sympathetic tone of blood vessels decreases (hypotension, warm, flushed skin)
-Decreased cardiac contractility and responsiveness to catecholamines cause hypotension, tissue hypoxia and lethal arrhythmias
What are changes in function happen in the body systems due to metabolic acidosis?
GI:
anorexia, nausea, vomiting, abdominal pain
Neural Function:
weakness, lethargy, malaise, confusion, stupid, coma, depression of VS
Cardiovascular Function:
peripheral vasodilation (hypotension), bradycardia, cardiac arrhythmias
Skin:
Warm, flushed. Skeletal - bone disease (chronic acidosis)
Compensation:
hyperkalemia, acid urine, increased RR and depth
What compensation occurs due to metabolic acidosis?
Primary Disturbance:
⬇pH
⬇HCO3-
Respiratory Compensation:
⬆RR
⬇PCO2
Renal Compensation:
⬆H+ excretion
⬆HCO3- reabsorption
What is metabolic alkalosis?
-A systemic disorder caused by an increase in plasma pH due to a primary excess in HCO3-
-Can result from a variety of situations including: Ingestion of antacids, vomiting and renal loss of H+
What are the causes of metabolic alkalosis?
Excess Base Loading, Loss of Fixed Acid, Post-Hypercapneic Metabolic Alkalosis,
What conditions can cause metabolic alkalosis?
-Excess administration of sodium bicarbonate when treating cardiac arrest (increased HCO3-)
-Prolonged volume depletion (excessive diuretic use)
-Prolonged vomiting (gastric loss of H+)
-Gastric suctioning (gastric loss of H+)
-Hyperaldosteronism (i.e. Cushing’s disease, renal loss of H+)
How does excess base loading cause metabolic alkalosis?
-Rarely a cause of metabolic alkalosis due to the efficiency of healthy kidneys
-Excessive ingestion of HCO3- containing antacids, or IV sodium bicarb (NaHCO3)
-Calcium carbonate, sodium bicarbonate
-Gaviscon, Alia-Seltzer, Rolaids, Zantac, Tums
How does loss of fixed acids cause metabolic alkalosis?
-Occurs mainly through loss of stomach acid (excess vomiting) and loss of Cl- in the urine - can also occur due to excessive gastric suctioning
-Gastric secretions contain HCl (hydrochloric acid)
-When Cl- is secreted into the stomach (from the blood) it is replaced with HCO3-
-Resultant volume depletion, hypochloremia and hypokalemia further worsen the alkalosis
-Increased HCO3- reabsorption in the kidneys
What is Post-Hypercapnic Metabolic Alkalosis?
-Patients with chronic respiratory acidosis tend to have compensatory HCO3- retention along with H+ and Cl- loss in the urine
-Mechanical ventilation in attempt to correct the respiratory acidosis (lower the high levels of CO2) can lead to metabolic alkalosis
-PCO2 drops rapidly, but HCO3- levels remain elevate
What conditions that accompany metabolic alkalosis can further worsen the problem?
Volume depletion, hypochloremia, hypokalemia, increased HCO3- reabsorption in the kidneys
What are the clinical manifestations of metabolic alkalosis?
-Often asymptomatic or has signs related to volume depletion or hypokalemia
-Neurological S&S occur less frequently than with other acid-base disorders
-Confusion, hyperactive reflexes, tetany, carpopedal spasm
-Compensatory hypoventilation can occur which can lead to hypoxemia and respiratory acidosis
-Severe rise in pH can lead to respiratory failure, arrhythmias, seizure, coma
What compensation occurs due to metabolic alkalosis?
Primary Disturbance:
⬆pH
⬆HCO3-
Respiratory Compensation:
⬇RR
⬆PCO2
Renal Compensation:
⬇H+ excretion
⬇HCO3- reabsorption
What is respiratory acidosis?
-Results from conditions that impair alveolar ventilation and cause an increase in plasma PCO2 (hypercapnea) and a decrease in pH
-Can be acute or chronic but is often due to decreased ventilation
-Decreased respiratory drive, lung disease, disorders of chest wall and respiratory muscles. Rarely can occur from excess CO2 production
What is acute respiratory acidosis?
hypoventilation causes rapid rise in PCO2, minimal increase in plasma HCO3-, and a large decrease in pH
What is chronic respiratory acidosis?
sustained increase in PCO2 resulting in renal compensation (increased plasma HCO3- and slight decrease in pH)
What are the causes of respiratory acidosis?
Acute Disorders of Ventilation, Chronic Disorders of Ventilation, Increased CO2 Production,
What conditions can cause respiratory acidosis?
-Lung disease (i.e. COPD and pneumonia, causes impaired gas exchange, retention of CO2)
-Barbiturate or narcotic overdose (depression of respiratory center, retention of CO2)
-Head injury (brain damage, depression of respiratory center, retention of CO2)
-Any condition causing hypoventilation
How does increased CO2 production cause respiratory acidosis?
-CO2 is a product of the body’s metabolic process
-Increased CO2 production can occur during exercise, fever, sepsis and burns
-Increased CO2 production usually only causes acidosis in people lung disease (can’t eliminate the excess CO2
What are the clinical manifestations of respiratory acidosis?
-pH < 7.35, PCO2 > 45mmHg
-mixed with symptoms of hypoxemia (which usually present first)
-CO2 readily crosses the BBB, changing the pH of brain fluids
-Altered LOC from lethargy to coma develop as PCO2 rises
-CO2 causes vasodilation of cerebral blood vessels
-Headache, blurred vision, irritability, muscle twitching, psychological disturbances
-Mild acidosis can cause warm flushed skin, weakness and tachycardia
What are the system signs and symptoms of respiratory acidosis?
Neural Function:
-dilation of cerebral vessels and depression of neural function.
-Headache, weakness, behavior changes, confusion, depression, paranoia, hallucinations, tremors, paralysis, stupor, coma
Skin:
-warm and flushed
-Compensation - acidic urine
What is the treatment for respiratory acidosis?
Directed at improving ventilation and lowering PCO2
How does the body compensate for respiratory acidosis?
Primary Disturbance:
⬇pH
⬆PCO2
Respiratory Compensation:
None
Renal Compensation:
⬆H+ excretion
⬆HCO3- reabsorption
What is respiratory alkalosis?
A systemic disorder characterized by a primary decrease in plasma PCO2 (hypocapnea), which elevates pH and subsequently decreases HCO3-
What conditions can cause respiratory alkalosis?
-Salicylate overdose (stimulation of respiratory center, loss of CO2)
-High fever (stimulation of respiratory center, loss of CO2)
-Hysteria/voluntary over breathing (hyperventilation, loss of CO2)
-Central or peripheral stimulation of the medullary respiratory center: anxiety, pain, pregnancy, fever, sepsis, encephalitis, salicylate toxicity
-Any condition resulting in hyperventilation
How does a pulmonary embolism cause respiratory alkalosis?
dead space ventilation causes initial rise in PCO2. This is quickly detected by chemoreceptors and the RR compensates and quickly lowers the PCO2
levels to an alkaline level
What are the clinical manifestations of respiratory alkalosis?
-pH > 7.45, PCO2 < 35mmHg
-Hyperexcitability of the nervous system
-Transient hypocalcemia
-Decreased cerebral blood flow
-Decreased CO2 concentration causes cerebral vasoconstriction
-CO2 crosses the BBB quickly, so neuro symptoms are usually sudden
-Light-headedness, dizziness, tingling, numbness of the fingers and toes, sweating, palpitations, anxiety, dyspnea, carpopedal spasm
What are the system signs and symptoms of respiratory alkalosis?
Neural Function:
-constriction of cerebral blood vessels and increased neural excitability.
-Dizziness, panic, light-headedness. Tetany, numbness of fingers and toes, seizures,
carpopedal spasm
-Carpopedal Spasm - frequent, and painful, involuntary muscle contractions of the hands
and feet (mostly hands)
Cardiovascular Function:
-cardiac arrhythmias
How does the body compensate for respiratory alkalosis?
Primary Disturbance:
-⬆pH
-⬇PCO2
Respiratory Compensation:
-None
Renal Compensation:
-⬇H+ excretion
-⬇HCO3- reabsorption
What different levels would be seen in someone experiencing metabolic acidosis?
pH < 7.35
CO2 —> 35-45mmHg
HCO3- < 22mEq/L
What different levels would be seen in someone experiencing metabolic alkalosis?
pH > 7.45
CO2 —> 35-45mmHg
HCO3- > 26mEq/L
What different levels would be seen in someone experiencing respiratory acidosis?
pH < 7.35
CO2 > 45mmHg
HCO3- –> 22-26mEq/L
What different levels would be seen in someone experiencing respiratory alkalosis?
pH > 7.45
CO2 < 35mmHg
HCO3- –> 22-26mEq/L
How does crush syndrome cause metabolic acidosis?
-Anaerobic metabolism occurs due to disrupted tissue perfusion, lactic acid production
-Muscle cell necrosis causes rhabdomyolysis, destruction of muscle cells releasing their electrolytes and proteins
-When the crushing force is released, these harmful agents are released back into
systemic circulation
How does head/spine injury cause respiratory acidosis?
-Traumatic damage to the respiratory center in the medulla can cause respiratory depression and CO2 retention
-Spinal cord damage innervating the respiratory muscles can cause a decrease in their
function and impaired ventilation
-Decreased ventilatory efficiency leads to a buildup of CO2
How does chest trauma causes respiratory acidosis?
results in a decrease in lung inflation or a decrease
in the surface are for gas exchange (decreased exhalation of CO2
Ex. Pneumothorax, Pulmonary Edema, Pulmonary Contusion
