Acid-Base Balance and Disturbances

Question 1

Steps to determining Acid-Base status:

Answer 1

1) from value of pH determine whether the patient is acidotic or alkalotic
2) From values of PaCO2 and HCO3-, determine primary disturbance, whether resp (it is resp if change in PaCO2 is compatible with change in pH) or metabolic (if the change in HCO3- is compatible with the change in pH)
3) From the values of PaCO2 and HCO3-, determine of a compensatory response has occurred
4) normal pH is 7.35-7.45, normal HCO3- is 22-27mEq/L, normal PaCO2 is 35-45 mmHg

Question 2

pH is determined by the ratio of _____ to _____.

Answer 2

HCO3- to PaCO2

Question 3

Name two acid base disturbances that can be COMPLETELY compensated.

Answer 3

1) respiratory acidosis

2) respiratory alkalosis

Question 4

Can complete compensation be achieved if there is metabolic acidosis or metabolic alkalosis?

Answer 4

No

Question 5

If an acid base disturbance is completely compensated, it is a _______ disturbance.

Answer 5

respiratory disturbance

Question 6

________ disturbances are a decrease/increase in blood H+ concentration caused by the addition of bases or acids to/from body fluids.

Answer 6

metabolic

Question 7

________ disturbances are an increase or decrease of blood H+ concentration caused by hypoventilation or hyperventilation leading to either CO2 retention or loss.

Answer 7

respiratory

Question 8

pH= 7.48, HCO3-=38, PaCO2=53

Answer 8

partially compensated metabolic alkalosis

Question 9

pH= 7.37, HCO3-=36, PaCO2=65

Answer 9

compensated respiratory acidosis

Question 10

pH= 7.32, HCO3-=32, PaCO2=65

Answer 10

partially compensated respiratory acidosis

Question 11

What is the underlying mechanism of bicarbonate ion reabsorption?

Answer 11

Na-H+ exchange

Question 12

_______ is a diuretic that works by inhibiting carbonic anhydrase, that ultimately inhibits reabsorption of Na and bicarbonate.

Answer 12

acetazolamide (diamox)

Question 13

______% of the filtered HCO3- is reabsorbed in the proximal tubule.

Answer 13

90%; the 10% that escapes reabsorption in the proximal tubule gets reabsorbed in later segments; HCO3- is not normally excreted

Question 14

____ is actively secreted into the lumen of the proximal tubule in exchange for _____, which enters the cell passively.

Answer 14

H+; Na+

Question 15

The kidneys produce _____ by excreting acids.

Answer 15

HCO3-; the H+-Na+ exchange is the key step in this process

Question 16

______ and _______ are the acids excreted by the kidneys.

Answer 16

titratable acids and ammonia (NH3)
*NH3 enters tubular lumen and reacts with H+ to form ammonium NH4–> very poorly penetrates cell membranes–> remains trapped in tubular lumen and is excreted–> process is called diffusion trapping

Question 17

What is the formula for Anion gap?

Answer 17

Na-Cl+HCO3=anion gap
can also be manipulated;
ex) HCO3= Na-Cl-anion gap

With potassium
The anion gap is calculated by subtracting the serum concentrations of chloride and bicarbonate (anions) from the concentrations of sodium and potassium (cations):

= ([Na+] + [K+]) − ([Cl−] + [HCO3−])

Without potassium (daily practice)
Omission of potassium has become widely accepted, as potassium concentrations, being very low, usually have little effect on the calculated gap. This leaves the following equation:

= [Na+] − ([Cl-] + [HCO3−]) =16 meq/lit

Question 18

What is the normal anion gap range?

Answer 18

~8-16mEq/L; sweat book says 10-12

Question 19

What is the utility of the anion gap?

Answer 19

the measurement of unmeasured anions= the “gap” (HPO4, SO4, etc); useful for the differential diagnosis of metabolic acidosis

Question 20

With an anion gap of 20-29, the diagnosis is ________ 67% of the time.

Answer 20

metabolic acidosis

Question 21

What is urine volume and osmolality when ADH release is inhibited?

Answer 21

osmolality low; Volume Large–> it gets inhibited because the bodys volume is TOO dilute and large…. needs to get rid of it by diuresis

Question 22

How does aldosterone affect sodium and potassium excretion?

Answer 22

Sodium excretion DECREASED and potassium excretion INCREASED

Question 23

What diuretic works by inhibiting the Na-K-Cl symporter?

Answer 23

furosemide (lasix)

Question 24

Spironolactone primarily works on what part of the renal tubule?

Answer 24

collecting duct

Question 25

The chronic renal failure patient has a tendency for increased bleeding, in part because of the production of defective _______.

Answer 25

von Willebrand’s factor

Question 26

Blood pressure in the individual at rest is controlled primarily by _______.

Answer 26

renin

Question 27

Which combination of acute electrolyte abnormalities will most stabilize nerve, skeletal muscle, and cardiac ventricular cells?

Answer 27

hypokalemia and hypercalcemia

Question 28

A clinically appropriate K+ concentration for cardioplegia solution is ______mEq/L.

Answer 28

30

Question 29

Which of the following is an important stimulus for aldosterone release from the adrenal cortex?

1) high serum Na
2) high serum K+
3) low levels of ADH
4) low serum K+

Answer 29

2) high serum K+–> aldosterone secretes more K+ to be excreted

Question 30

What hormone controls ECF VOLUME, and what hormone controls ECF sodium concentration?

Answer 30

VOLUME=aldosterone
Na CONCENTRATION= ADH
Answer from Scott: The answers hinge on a couple of key words in each question … ADH
(vasopressin) adjusts sodium concentration by altering water reabsorption in the kidney. Recall that concentration is Amount/Volume, so by adjusting body water volume via AHD at the kidneys, the ADH ultimately
adjusts sodium concentration.

Aldosterone, by altering the amount of sodium ind the body, adjusts TBW via osmosis—“where sodium goes, water follows.”

In “real life” both hormones are working simultaneously to constantly adjust sodium concentration and sodium amount, but when questions on which hormone most effects concentration versus volume, go with the
relationships above.