Strong Ion Approach to Acid-Base

Question 1

What are the two main goals of acid base analysis?

Answer 1

identify and quantify the magnitude of an acid-base disturbance
and to determine the mechanism for the acidbase
disturbance

Question 2

What are stewarts three independent varibales

Answer 2

CO2, SID, Atot (conc of weak buffers)

Question 3

What are ‘strong ions’

Answer 3

Ions that full dissociate at a physiologic pH

Strong ions are fully dissociated at physiologic
pH and therefore exert no buffering effect
they act as a collective positive unit of charge (SID).

Question 4

What are the important strong ions?

Answer 4

Na, K ,Ca2, Mg2, Cl, lactate, ß-hydroxybutyrate,
acetoacetate, and SO4
.

Question 5

What effect will an increase or decrease of SID have on pH

Answer 5

An increase in SID (by decreasing [Cl] or increasing [Na] will cause a strong ion (metabolic) alkalosis, whereas a decrease in SID (by decreasing [Na] or increasing [Cl], [SO4] or organic anions) will cause a strong ion(metabolic) acidosis.

Question 6

What effect will in increased or decreased Atot have on pH

Answer 6

Increase = acidosis, decrease = alkalosis

Question 7

What are the 6 derangements that may occur in the strong ion approach?

Answer 7

respiratory, strong ion, or Atot acidosis and alkalosis

Question 8

What may cause acidaemia in reference to the strong ion appropach

Answer 8

increase in PCO2, a decrease in SID or an increase in nonvolatile buffer concentrations (albumin, globulin, phosphate)

Question 9

What may cause alkalaemia in reference to the strong ion approach

Answer 9

a decrease in PCO2, an increase in SID or from a decrease in nonvolatile buffer
concentration.

Question 10

What are the three major contributors to Atot?

Answer 10

Alb, glob, phos

Question 11

What are the main causes of Atot acid-base abnormalities

Answer 11

Alkalosis (decrease atot) –> hypoalbuminaemia.
Acidosis (increase atot) –> hyperalbuminaemia, hyperphosphataemia (tumour lysis, rhabdo, renal disease)

Question 12

Disorders of SID

Question 13

WHat are the three general mechanisms with which SID can change?

Answer 13

(1) an increase in strong anions relative to strong cations
(2) a decrease in strong anions relative to strong cations;
(3) a change in the free water content of plasma
(change in extracellular fluid volume) with no change in strong anions relative to strong cations.

Question 14

What are potential causes of SID alkalosis

Answer 14

an increase in
[Na, a decrease in [Cl, or a decrease in plasma free
water,

Pure water loss, hypochloremic alkalosis, bicarb admin due to sodium,

Question 15

What are the three mechanisms that can cause SID to decrease, causing SID acidosis

Answer 15

(1) a decrease in Na
(2) an increase in [Cl]
(3) an increased concentration
of other strong anions (e.g., L-lactate in lactic
acidosis, ß-hydroxybutyrate in diabetic ketoacidosis, sulfate
in uremic acidosis)

Question 16

what may cause a hyperchloraemic acidosis (decreased SID)

Answer 16

chloride retention (e.g., early renal failure, renal tubular acidosis), excessive loss of sodium relative to chloride (e.g., diarrhea), or by administration of substances containing more chloride than sodium as compared with normal ECF composition (e.g., administration of 0.9% NaCl). Administration of 0.9% NaCl

Question 17

What is the strong ion gap?

Answer 17

The difference in charge between all unmeasured strong anions and all unmeasured strong cations

Question 18

What is the SIG equation

Answer 18

SIG = Na +K -Cl = UCstrong - UAstrong
SIG = [Atot] (conc weak base) - AG
Sigsimp = albumin as estimate of atot - AG