Acid Base Disturbances Flashcards
What is the primary defect and effect on pH during respiratory acidosis?
Alveolar hypoventilation (increased paCO2) Decreased pH
What is the compensatory response for respiratory acidosis?
Increase renal HCO3 reabsorption to increase plasma [HCO3]
What is the primary defect and effect on pH of respiratory alkalosis?
Alveolar hyperventilation (decreased PaCO2) Increased pH
What is the compensatory response for respiratory alkalosis?
Decreased renal HCO3 reabsorption (to decrease [HCO3]
What is the primary defect in metabolic acidosis?
Loss of HCO3 or gain of H
Decreased pH
What is the compensatory response for metabolic acidosis?
Alveolar hyperventilation to increase pulmonary CO2 excretion (decrease PaCO2)
What is the primary defect during metabolic alkalosis?
Gain of HCO3 or loss of H
Increased ph
What is the compensatory response during metabolic alkalosis?
Alveolar hypoventilation to decrease pulmonary CO2 excretion (increase PaCO2)
What are the causes for acute respiratory acidosis?
CNS depression, airway obstruction, neuromuscular disorders, severe pneumonia embolism and edema
CANS
What are the causes of chronic respiratory acidosis?
COPD
Anything chronic that leads to impaired ventilation
For every 10mmHg increase in PaCO2 during acute chronic respiratory acidosis the HCO3 should increase by how much?
1 mEq/L
For every 10mmHg increase in PaCO2 during chronic respiratory acidosis the HCO3 should increase by how much?
3.5 mEq/L
For every 10mmHg decrease in PaCO2 during acute respiratory alkalosis, the HCO3 should decrease by how much?
2 mEq/L
For every 10mmHg decrease in PaCO2 in chronic respiratory alkalosis, there should be a decrease in HCO3 by how much?
5 mEq/L
What are the causes for respiratory alkalosis?
CNS disease —> hyperventilation Hypoxia Anxiety Mechanical ventilators Progesterone (stimulates respiratory center during pregnancy) Salicylates (aspirin)/sepsis CHMAPS
What are some causes for high anion gap metabolic acidosis (HAGMA)?
Glycols (ethylene or propylene) Oxoproline (pyroglutamic acid) - intermediate of acetaminophen toxicity L-lactate D-lactate (unusual, e.g. when short bowel resection —> overproduction by lactobacilli after a carbohydrate load) Methanol Aspirin Renal failure Ketoacidosis GOLDMARK
What are some causes for non anion gap metabolic acidosis (NAGMA)?
Hyperalimentation (high Cl in TPN)
Acetazolamide
Renal tubular acidosis (1, 2 and 4) (main cause)
Diarrhea (main cause)
Ureterosigmoid fistula (colon wastes HCO3)
Posthypocapnia or pancreatic fistula (wastes HCO3)
Spironolactone
HARDUPS
What are other causes for high anion gap metabolic acidosis (MUDPILERS)?
Methanol Uremia DKA/alcoholic KA Paraldehyde (obsolete sedative hypnotic) Isoniazid (used to tx tuberculosis) Lactic acidosis EtOH/ethylene glycol Rhabdo/renal failure Salicylates
What is Winter’s formula?
PaCO2 = (1.5 x [HCO3]) + 8 +/- 2
Used during metabolic acidosis
If there is hypokalemia and urine Cl is >20 mEq/L, what is indicated?
Chloride resistant metabolic alkalosis caused by hyperaldosteronism, K+ losing diuretics, etc
What does it mean when anion gap is high?
Means other solutes in plasma (alcohols, lactic acidosis, ketoacidosis)
How is anion gap calculated?
[Na+] - [Cl-] + [HCO3-]
Normal range between 8-16
What is the delta gap?
Calculated anion gap - normal anion gap
What is the delta [HCO3]?
Normal HCO3 - delta gap
If measured [HCO3] is equal to the delta HCO3 then what disorder is present?
Simple acid base disorder
If measured [HCO3] is greater than delta [HCO3] then what disorder is present?
Metabolic alkalosis + HAGMA
If measured [HCO3] is less than delta [HCO3] then what disorder is present?H
Non gap metabolic acidosis + HAGMA
If the delta AG/delta HCO3 ratio is 1:1, what is occurring?
Simple HAGMA
If the delta delta ratio is <1 what is occurring?
Also losing HCO3 somewhere else (e.g. via diarrhea) or kidneys are rapidly eliminating anion (e.g. ketoacids, D-lactate)
If the delta delta ratio is >1 up to 2 what does this suggest?
Lactic acidosis
L-lactate is reabsorbed by the kidney, kidney function often compromised —> maintenance of lactate levels
Intracellular buffering of H+ means serum HCO3 doesnt fall as much
If delta delta ratio is close to or >2 what does this suggest?
Concurrent metabolic alkalosis or baseline HCO is elevated due to chronic respiratory acidosis
What is renal tubular acidosis?
Acidemia + normal anion gap + normal serum creatinine and no diarrhea
What is the primary defect occurring in type 1 RTA?
Impaired H secretion due to impaired function of alpha intercalated cells
“Classic distal”
Rare
What is the primary defect occurring in type 2 “proximal” RTA?
Impaired proximal HCO3 reabsorption
Very rare
What is the primary defect occurring in type 4 “Hyperkalemic” RTA?
Lack of aldosterone or failure of kidney to respond to it
High K and low NH3 synthesis by PT
Most common form
What is a secondary cause for type I RTA?
Autoimmune disorders
What are secondary causes for type 2 RTA?
Fanconi’s syndrome
In adults, multiple myeloma, various drugs
What are potassium levels during type 1 and 2 RTA?
Hypokalemia
What are the potassium levels during type 4 RTA?
Hyperkalemia
What are the causes of metabolic acidosis?
Contraction (e.g. selective loss of NaCl in urine, keeping HCO3) Licorice (if real, sweet glycyrrhizic acid blocks normal conversion of Aldo-agonist cortisol to cortisone in kidney so that it drive Na/K exchange) Endo (Conn, Cushing, Bartter) Vomiting (lose HCl) Excess alkali Refeeding alkalosis Post hypercapnia Diuretics (volume contraction + K loss)
What are the causes for chloride responsive metabolic alkalosis?
Vomiting, diuretics, nasogastric suction, diarrhea, villous adenoma
Describe Cl responsive metabolic alkalosis
Spot urine Cl should be less than 10 mEq/L (unless recent diuretic use) since the kidney should be conserving Cl
Tx with normal saline should fix the disturbance
What are the causes of Cl resistance metabolic alkalosis?
Distal exchange site stimulation by aldosterone resulting in increase H and K excretion in exchange for reabsorption of Na as NaHCO3, ongoing diuretic use/abuse
Describe Cl resistant metabolic alkalosis
Spot urine Cl >20 mEq/L despite fact kidney should be conserving Cl
Need to treat cause of H loss in order to treat the alkalosis
What are the sx for acute (or acutely worsening chronic) respiratory acidosis?
HA, confusion, anxiety, drowsiness, stupor tremors, convulsions, possible coma (CO2 narcosis)
What are the sx for slowly developing but stable (as in COPD) respiratory acidosis?
May be well tolerated
Pts have have memory loss, sleep disturbances, excessive daytime sleepiness and personality changes
Signs include gait disturbance, tremor, blunted DTRs, myoclonic jerks (brief involuntary twitching of muscle/muscle group), asterixis (flapping wrist) and papilledema
What are the sx of acute respiratory alkalosis?
Light headedness, confusion, peripheral and circumoral (around the lips) paresthesia, cramps and syncope
Thought to be due changes in cerebal blood flow and pH
Tachypnea or hyperpnea is often only sign
What can be seen with severe acute respiratory alkalosis?
Capopedal spasm due to decreased levels of hypocalcemia (Ca driven inside cells in exchange for H)
What are the sx for chronic respiratory alkalosis?
Usually asymptomatic
No distinctive signs
What are the sx for mild metabolic acidosis?
Usually asymptomatic
What are the sx for metabolic acidosis with a pH <7.10 (or higher change if developed rapidly)?
Nausea, vomiting, malaise
See long deep breaths at normal rate (respiratory compensation) without dyspnea
What are the signs and sx of mild metabolic alkalosis?
Signs and sx of underlying disorder
What are the sx for more severe metabolic alkalosis?
Increased binding of Ca leading to Hypocalcemia
HA, lethargy and neuromuscular excitability, sometimes with delirium, tetany and seizures
Lowered threshold for angina sx and arrhythmias
Possible weakness if also hypokalemia
