Lecture 13 10/22/24 Flashcards
What are the general principles of electrolytes and acid/base?
-blood pH should be maintained in a narrow range
-electrolytes are closely linked to acid/base balance
-electroneutrality must always be maintained
What are the categories of acid/base disturbances?
-metabolic acidosis/ low HCO3-
-metabolic alkalosis/ high HCO3-
-respiratory acidosis/ high pCO2
-respiratory alkalosis/ low pCO2
What is a primary acid/base disturbance?
pathophysiologic state causing alkalosis or acidosis
What is a compensatory acid/base disturbance?
-body’s response to a primary acid/base disturbance
-goal is to keep pH as close to normal as possible
-usually the opposite of the primary disturbance
What is a mixed acid/base disturbance?
more than one primary disturbance at the same time
What are the compensatory mechanisms for each acid/base disturbance?
-metabolic acidosis <-> respiratory alkalosis
-metabolic alkalosis <-> respiratory acidosis
What are the characteristics of respiratory compensation?
-in response to primary metabolic disturbance
-change in resp. rate or volume results in change in pCO2
-starts within minutes
What are the characteristics of metabolic compensation?
-in response to primary respiratory disturbance
-kidney adjusts H+ and HCO3- secretion/resorption
-may take several days
What are the key points about compensation?
-does not bring pH back to completely normal
-aims to return blood pH as close to normal as possible during mixed disturbances
What are the cations of importance?
-sodium
-potassium
What are the anions of importance?
chloride
-bicarb.
What are the characteristics of neutrality?
-cations must equal anions
-gain of a cation requires either gain of an anion or loss of a different cation
Which hormones impact sodium conc.?
-ADH
-aldosterone
What are the effects of aldosterone?
-resorption of 3Na+ and 1Cl- in exchange for the secretion of 2K+
-overall increase in Na+ concentration
What are the effects of ADH?
-resorption of water
-overall decrease in Na+ conc. due to dilution
How are changes in sodium conc. interpreted?
in conjunction with body water
What can lead to hypernatremia?
-decreased water intake (dehydration)
-loss of water that is greater than loss of sodium (ADH issue)
What can lead to hyponatremia?
-increased total body water (edema)
-loss of sodium that is greater than loss of water (hypoadrenocorticism)
What are the characteristics of Cl- changes in response to Na+ changes?
-Cl- moves with Na+ to maintain neutrality
-change in Cl- is proportional to Na+
What are the characteristics of Cl- changes in response to acid-base status?
-Cl- can exchange for HCO3- to maintain electroneutrality
-change in Cl- is NOT proportional to Na+
What are the causes of hyperchloremia?
-processes that lead to increased Na+ (inc. Cl- and Na+)
-metabolic acidosis (inc. Cl-, dec. HCO3-)
What are the causes of hypochloremia?
-processes that lead to decreased Na+ (dec. Cl- and Na+)
-metabolic alkalosis (inc. HCO3-, dec. Cl-)
What are the factors affecting blood levels of K+?
-degree of renal excretion
-translocation
-GI losses
-intake
What can cause hyperkalemia?
-decreased renal excretion
–dec. urine production
–hypoadrenocorticism
-ICF to ECF
–metabolic acidosis
-artifact in large animals
What can cause hypokalemia?
-increased renal loss
–polyuria
-ECF to ICF
–metabolic alkalosis
-increased GI loss
–diarrhea
-decreased intake
What are the characteristics of bicarbonate?
-major body buffer
-produced by cells with carbonic anhydrase
-total CO2 is about equal to HCO3- conc.
What is the equation for bicarb. formation?
H2O + CO2 <> H2CO3 <> H+ + HCO3-
What are the unmeasured cations included in anion gap?
-H+
-calcium
-magnesium
-immunoglobulins
What are the unmeasured anions included in anion gap?
-albumin
-lactate
-phosphates and sulfates
-ketones
-ethylene glycol metabolites
What are the two equations for anion gap?
-AG = UA - UC: how AG is interpreted
-AG = (Na+ + K+) - (Cl- + HCO3-): how AG is calculated
What causes increased anion gap?
-increased unmeasured anions
-decreased unmeasured cations
What causes decreased anion gap?
-decreased unmeasured anions
-increased unmeasured cations
What is the most common cause of an abnormal anion gap?
increased unmeasured anions
What are the differentials for increased unmeasured anions and thus increased anion gap?
-lactic acidosis
-renal acidosis
-ketoacidosis
-ethylene glycol toxicosis
What are the analytes for blood gas analysis?
-blood pH
-pCO2
-HCO3-
-base excess
-pO2
What are the characteristics of blood gas sample collection?
-stringent
-need special heparinized syringe
-protect sample from air
-analyze promptly
What are the characteristics of pH?
-tightly regulated
-buffer systems include carbonic anhydrase and hemoglobin
What are the characteristics of acidemia?
-blood pH below ref. interval
-at least one primary acidosis is present
-every acidosis in the patient is primary
What is acidosis?
process promoting acidemia
What are the characteristics of alkalemia?
-blood pH above ref. interval
-at least one primary alkalosis is present
-every alkalosis in the patient is primary
What is alkalosis?
process promoting alkalemia
What are the characteristics of pCO2?
-proportional to dissolved CO2 in blood
-acts as a respiratory acid
-measurement on blood gas is the only way we can evaluate the resp. component of acid/base
