Acid-Base and Electrolytes Flashcards
How do you analyze arterial blood gas values?
- pH tells you acidosis or alkalosis as primary event
- Look at CO2
- Look at bicarbonate
True or false: The body does not compensate beyond a normal pH.
True. Overcorrection does NOT occur.
Common causes of respiratory acidosis?
COPD, asthma, drugs (e.g. opioids, benzos, barbs, alcohol, other respiratory depressants), chest wall problems (paralysis, pain), sleep apnea
Common causes of metabolic acidosis?
Ethanol, DKA, uremia, lactic acidosis (e.g. sepsis, shock, bowel ischemia), methanol/ethylene glycol, aspirin/salicylate overdose, diarrhea, carbonic anhydrase inhibitors
Common causes of respiratory alkalosis?
Anxiety/hyperventilation, aspirin/salicylate overdose
Common causes of metabolic alkalosis?
Diuretics (except carbonic anhydrase inhibitors), vomiting, volume contraction, antacid abuse/milk-alkali syndrome, hyperaldosteronism
What type of acid-base disturbance does aspirin overdose cause?
Respiratory alkalosis and metabolic acidosis (2 different primary disturbances). Look for tinnitus, hypoglycemia, vomiting, history of “swallowing several pills”. Alkalinization of urine (with bicarb) speeds excretion.
What happens to blood gas of patients with chronic lung conditions?
pH may be alkaline during the day because they breathe better when awake.
Just after episode of bronchitis or respiratory disorder, metabolic alkalosis (which usually compensates for respiratory acidosis) becomes primary disturbance (elevated pH and bicarb).
What type of heart failure can sleep apnea and other chronic lung diseases cause?
Right-sided heart failure (cor pulmonale)
Should you give bicarb to a patient with acidosis?
Almost never. First try IV fluids and correction of underlying disorder. If all other measures fail and pH remains <7.0, bicarb may be given.
Blood gas of a patient with asthma has changed from alkalotic to normal and patient seems to be sleeping. Is patient ready to go home?
Patient is probably crashing. pH is initially high in patients with asthma (eliminating CO2). If patient becomes tired and doesn’t breathe well, CO2 will rise and pH will normalize. Eventually patient becomes acidotic and requires intubation. Asthmatic patients are supposed to be slightly alkalotic during an asthma attack; if they are not, you should wonder why.
List the signs and symptoms of hyponatremia.
Lethargy, mental status changes/confusion, anorexia, seizures, cramps, coma
Causes of hypovolemic hyponatremia?
Dehydration, diuretics, diabetes, Addison’s disease/hypoaldosteronism (high potassium)
Causes of euvolemic hyponatremia?
SIADH, psychogenic polydipsia, oxytocin use
Causes of hypervolemic hyponatremia?
Heart failure, nephrotic syndrome, cirrhosis, toxemia, renal failure
How do you treat hypovolemic hyponatremia? Euvolemic? Hypervolemic?
Hypovolemic - normal saline
Euvolemic and hypervolemic - water/fluid restriction; may need diuretics for hypervolemic
What medication is used to treat SIADH if water restriction fails?
Demeclocycline (induces nephrogenic diabetes insipidus)
What happens if hyponatremia is corrected too quickly?
Central pontine myelinolysis. Hypertonic saline is used only when patient has seizures from severe hyponatremia, otherwise use normal saline.
What causes spurious (false) hyponatremia?
Lab value is low but total body sodium is normal. Do NOT give extra salt or saline.
- Hyperglycemia (when glucose is >200 mg/dL, sodium decreases by 1.6 mEq/L for each rise of 100 mg/dL in glucose)
- Hyperproteinemia
- Hyperlipidemia
What causes hyponatremia in postoperative patients?
Most common is a combination of pain and narcotics (causing SIADH) with overaggressive administration of IV fluids.
Rare cause may be adrenal insufficiency (potassium is high, BP is low).
What is the classic cause of hyponatremia in pregnant patients about to deliver?
Oxytocin, which has an ADH-like effect
What are the signs and symptoms of hypernatremia?
Basically same as hyponatremia: mental status changes/confusion, hyperreflexia, seizures, and/or coma
In chronic severe symptomatic hyponatremia, the rate of correction should not exceed what?
0.5 to 1 mEq/L/hour